Anthropogenic activities have led to environmental pollution by toxic heavy metals and dyes such as Congo red. Trimetallic nanoparticles can be used for enrichment heavy metals and photocatalytic degradation of Congo red from the environment. However, the processes used to synthesize nanoparticles can be hazardous to the environment. In the study, green synthesis of Phosphorous doped ZrO2CeO2ZnO nanoparticles were carried out using Flacourtia indica leaf aqueous extracts with phytochemicals as reducing agents. The nanoparticles were used as photocatalysts for degradation of Congo red dye and as sorbents for enrichment of selected toxic metals: lead, cadmium, arsenic and chromium. The influence of various parameters during the synthesis and solid phase extraction stages were investigated using Half, Full and Taguchi experimental designs. Interactions between factors were determined using ANOVA and response surface methodologies. The enrichment methods were validated by using spiked borehole, well, tap and effluent water samples. The P−ZrO2CeO2ZnO nanoparticles and P−ZrO2CeO2ZnO nanoparticles/alginate beads were characterized using Ultra Violet Visible spectrometry, Scanning Electron Microscope(SEM), Fourier Transform-Infra Red Spectroscopy, Transmitting Electron Microscopy (TEM), Brunauer Emmet Teller (BET) analysis, X-ray Photoelectron Spectroscopy (XPS) and X ray Diffraction (XRD). The most significant factors for P−ZrO2CeO2ZnO nanoparticle synthesis were pH, metal ion concentration and leaf extract concentration. The surface areas obtained under optimum synthesis conditions were 0.459 m2g−1 and 7.33 m2g−1for P−ZrO2CeO2ZnO nanoparticles and P−ZrO2CeO2ZnO nanoparticles/alginate beads respectively. The synthesized nanoparticles were crystalline and irregularly shaped The nanoparticles average size was 0.255 nm and the range of the size was from 0.1-4.51nm. Zn−O, Zr−O, C−O, O−H, functional groups were present in the nanoparticles from FTIR data. The optimum conditions for photocatalytic degradation of Congo red using P−ZrO2CeO2ZnO nanoparticles were 0.05 g/L catalyst dosage concentration, 10 mg/L Congo red concentration, 250 min irradiation time. The reaction followed pseudo first order kinetics with a rate constant of 0.069 min-1 and degradation efficiency of 85.85%.The reaction mechanism was explained by light, superoxide radicals and h+ holes. [...]
Table of contents
Abstract
Declarations
Approval Form
Dedications
Acknowdgements
List of Abbreviations and Symbols
Table of Contents
List of Figures
List of Tables
CHAPTER 1: : INTRODUCTION
1.1 Background to the study
1.2 Problem Statement
1.3 Aim
1.4 Objectives
1.5 Hypothesis
1.6 Structure of thesis
CHAPTER 2: : LITERATURE REVIEW
2.1 Background to Nanotechnology
2.1.1 Methods used to synthesize nanoparticles
2.1.2 Factors affecting nanoparticle synthesis
2.1.3 Mechanisms of Green Synthesis
2.1.4 Support material for nanoparticles
2.2 Photocatalysis
2.2.1 Introduction to photocatalysis
2.2.2 Photocatalysis of Congo Red
2.2.3 Factors affecting photocatalysis
2.2.4 Mechanism of Photocatalysis
2.2.5 Trimetallic nanoparticles as photocatalysts
2.2.6 Kinetic Models
2.3 Solid Phase Extraction
2.3.1 Background to Solid Phase Extraction
2.3.2 Methods used to enrich analytes
2.3.3 Factors affecting solid phase extraction of samples
2.3.4 Studies on enrichment of heavy metals using Solid Phase Extraction
2.3.5 Adsorption isotherms
CHAPTER 3: : PRELIMINARY STUDIES
3.1 Preparation of the aqueous leaf extract
3.2 Synthesis of P — ZrO2CeO2ZnO nanoparticles
3.3 Optimization of Synthetic Conditions
CHAPTER 4: METHODOLOGY
4.1 Chemicals and Materials
4.2 Equipment
4.3 Preparation of stock solutions
4.4 Synthesis of the P — ZrO2CeO2ZnO nanoparticles
4.5 Preparation of P — ZrO2CeO2ZnO nanoparticles/alginate beads
4.6 Characterization of the P — ZrO2CeO2ZnO nanoparticles
4.7 Determination of the metal’s concentration in P - ZrO2CeO2ZnO nanoparticles
4.8 Studies of kinetics and reaction mechanisms for photocatalytic degradation of Congo red using P — ZrO2CeO2ZnO nanoparticles photocatalyst
4.9 Enrichment of cadmium and lead
4.9.1 Adsorption Studies
4.10 Enrichment of Arsenic and Chromium by pipette tip solid phase extraction
CHAPTER 5: RESULTS AND DISCUSSION
5.1 Optimization of the method for the green synthesis of P-ZrO2CeO2ZnO nanoparticles using aqueous extracts from Flacourtia indica leaves
5.1.1 Optimization of Synthetic Conditions
5.1.2 Evaluation of interactions and significant factors for the synthesis of P - ZrO2CeO2ZnO using ANOVA
5.1.3 Main effects of variables on nanoparticle synthesis
5.1.4 Evaluation of interactions between influencing factors by response surface methodology for P — ZrO2CeO2ZnO nanoparticle synthesis
5.1.5 Possible reaction mechanism for P — ZrO2CeO2ZnO nanoparticles synthesis
5.1.6 Comparison with other studies
5.2 Characterization of surface composition
5.2.1 UV- Vis Spectroscopy Characterisation
5.2.2 Fourier Transform Infrared Spectroscopy (FT-IR)
5.2.3 Brunauer-Emmet-Teller (BET) analysis
5.2.4 Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy Characterisation
5.2.5 X-ray Diffraction Characterisation
5.2.6 X-ray photoelectron spectroscopy characterisation
5.2.7 Determination of Metal Composition by Inductively Coupled Plasma-Mass Spectrometry
5.3 Kinetics and reaction mechanisms for photocatalytic degradation of Congo red using P — ZrO2CeO2ZnO nanoparticles
5.3.1 Catalytic activity of the P — ZrO2CeO2ZnO
5.3.2 The effect of catalyst amount on the degradation of Congo Red... 103
5.3.3 The effect of changing Congo red concentration on its degradation
5.3.4 The effect of reaction time on the degradation of Congo Red 106
5.3.5 Reaction kinetics for the degradation of Congo red 107
5.3.6 Regeneration of the P — ZrO2CeO2ZnO nanoparticle catalyst ... 110
5.3.7 The reaction mechanism for the catalytic degradation of Congo red.
5.4 Enrichment of lead and cadmium from water using P — ZrO2CeO2ZnO Nanoparticles/Alginate Beads: Optimization and determination of significant factors and interactions using response surface methodologies
5.4.1 Adsorption Equilibrium Studies
5.4.2 Screening of significant factors for Cd and Pb extraction
5.4.3 Optimization of the significant extraction conditions for Cd and Pb using the Taguchi experimental design
5.4.4 Evaluation of significant factors and interactions using Analysis of Variance (ANOVA)
5.4.5 Main effects of sample volume, dosage and pH on the enrichment of Cd and Pb using P — ZrO2CeO2ZnO nanoparticles/alginate
5.4.6 Evaluation of the most significant factors and interactions using response surface methodology and interaction plots
5.4.7 Interference Studies
5.4.8 Desorption cycles for Cd and Pb recoveries
5.4.9 Acceptance Criteria
5.4.10 Analytical Applications
5.4.11 Comparison with other methods
5.5 Enrichment of Arsenic and Chromium by pipette tips loaded with P — ZrO2CeO2ZnO nanoparticles /alginate beads
5.5.1 Adsorption Experiments
5.5.2 Optimization of SPE Experiments
5.5.3 Full factorial designs and response surface methodology for optimization of the significant conditions for Cr and As enrichment
5.5.4 Effects of sample volume, pH and dosage on enrichment factors of As and Cr and the interactions between factors
5.5.5 The effect of main factors on As and Cr enrichment
5.5.6 Effect of organic interferences on As and Cr enrichment
5.5.7 Regeneration studies for As and Cr enrichment
5.5.8 Evaluation of the enrichment of As and Cr method performance
5.5.9 Application in real samples
5.5.10 Comparison with other methods
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
6.2 Recommendations for future work
CHAPTER 7: LIST OF PUBLICATIONS
CHAPTER 8: REFERENCES
CHAPTER 9: APPENDIX
9.1.1.1 Tauc plots data
9.1.1.2 Linear Model Analysis: Means versus pH, Dosage (g), metal concentration (M), volume ratio
9.1.1.3 Determination of hydrogen bonding active sites of the P — ZrO2CeO2ZnO nanoparticle using alcohols
9.1.1.4 Antiplagiarism Report
Abstract
Anthropogenic activities have led to environmental pollution by toxic heavy metals and dyes such as Congo red. Trimetallic nanoparticles can be used for enrichment heavy metals and photocatalytic degradation of Congo red from the environment. However, the processes used to synthesize nanoparticles can be hazardous to the environment. In the study, green synthesis of Phosphorous doped ZrO2CeO2ZnO nanoparticles were carried out using Flacourtia indica leaf aqueous extracts with phytochemicals as reducing agents. The nanoparticles were used as photocatalysts for degradation of Congo red dye and as sorbents for enrichment of selected toxic metals: lead, cadmium, arsenic and chromium. The influence of various parameters during the synthesis and solid phase extraction stages were investigated using Half, Full and Taguchi experimental designs. Interactions between factors were determined using ANOVA and response surface methodologies. The enrichment methods were validated by using spiked borehole, well, tap and effluent water samples. The P-ZrO2CeO2ZnO nanoparticles and P-ZrO2CeO2ZnO nanoparticles/alginate beads were characterized using Ultra Violet Visible spectrometry, Scanning Electron Microscope(SEM), Fourier Transform- Infra Red Spectroscopy, Transmitting Electron Microscopy (TEM), Brunauer Emmet Teller (BET) analysis, X- ray Photoelectron Spectroscopy (XPS) and X ray Diffraction (XRD). The most significant factors for P-ZrO2CeO2ZnO nanoparticle synthesis were pH, metal ion concentration and leaf extract concentration. The surface areas obtained under optimum synthesis conditions were 0.459 m[2]g-[1] and 7.33 m[2]g-[1]for P-ZrO2CeO2ZnO nanoparticles and P-ZrO2CeO2ZnO nanoparticles/alginate beads respectively. The synthesized nanoparticles were crystalline and irregularly shaped The nanoparticles average size was 0.255 nm and the range of the size was from 0.1-4.51nm. Zn-O, Zr-O, C-O, O-H, functional groups were present in the nanoparticles from FTIR data. The optimum conditions for photocatalytic degradation of Congo red using P-ZrO2CeO2ZnO nanoparticles were 0.05 g/L catalyst dosage concentration, 10 mg/L Congo red concentration, 250 min irradiation time. The reaction followed pseudo first order kinetics with a rate constant of 0.069 min-1 and degradation efficiency of 85.85%.The reaction mechanism was explained by light, superoxide radicals and h+ holes. The most significant variable for cadmium recovery using P-ZrO2CeO2ZnO nanoparticles / alginate beads was the sample volume and for chromium recoveries these were sample volume, eluent flow rate and sorbent dosage. Interactions between factors during enrichment occurred between sorbent dosage and pH, sample volume and sorbent dosage, sample volume and pH. The method recoveries were 33.12-116.5, 57.0 -147.70, 46.56-130.65 and 20.96-82.51% and, limits of detection were 0.1022, 0.0297 g/L 0.084 and 0.439 ng/L for lead, cadmium, chromium and arsenic respectively. The SEM, TEM and XRD results showed that P-ZrO2CeO2ZnO nanoparticles can be synthesized using F. indica leaves extracts and they can efficiently degrade Congo red dye. It was also demonstrated that P-ZrO2CeO2ZnO nanoparticles encapsulated in alginate beads enhanced the detection limit of selected heavy metals, which may find applications in toxic metal analysis.
Declaration
I, Nichodimus Hokonya declare that: Green Synthesis of Trimetallic Nanoparticles using Flacourtia Indica (Burm.F.) Merr: Characterization and Applications, is my work and that the sources used have been indicated by means of complete references .
Illustrations are not included in the reading sample
Approval form
The undersigned do hereby certify that they supervised, read and recommend to the Bindura University of Science Education for acceptance the dissertation entitled, “Green Synthesis of Trimetallic Nanoparticles Using Flacourtia Indica (Burm.F.) Merr.: Characterization and Applications”, submitted by Nichodimus Hokonya in partial fulfilment of the requirements for the Doctor of Philosophy in Chemistry
NHokonya 14./...09.../...2024
(Signature of student)
16./.. .09/.. .2024
(Signature of Main Supervisor)
(Signature of Co-supervisor)
17./ 09../.2024
(Signature of Co-Supervisor)
Dedications
The thesis is dedicated to the Almighty, my late father the “General” Moses Mutambiranwa Hokonya who will always be my source of inspiration and motivation, my mum Conelia Marovanidze, my wife Felisters, my son Kudzaishe Moses, my daughter Kunaishe, my brothers Washington, Maxwell Chiromo, Moses Thabani Mpofu, Simukai, my sisters Charity, Jubilant, Hazvineyi, Nothando my cousins Tinomuda Mkweva, Samantha Nokutenda Masvosva and Anotidaishe for their constant prayers and encouragement. It is by God’s grace that I managed to successfully pursue this DPhil degree.
Acknowledgements
I would like to pass my heartfelt gratitude to my main supervisor Prof C. Mahamadi, co-supervisors Dr N. Muchanyereyi and Prof T. Gutu for their patience and timely guidance. I would also like to thank Prof C. Zvinowanda for helping me with characterization and comments as well as suggestions on the photocatalysis paper. Special mention goes to the late Prof M. Mupa for his suggestions during presentations and making sure l had access to all the chemicals and equipment l needed during his tenure as Chairman; Dr C. Machingauta for his meaningful discussions on characterisation of nanoparticles, Prof P. Dzomba for his suggestions on solid phase extraction and Prof N, Chaukura for his suggestions on photocatalysis methodology. Mr T. Chayamiti and Mr V. Chibuku for their technical assistance with FT-IR and UV- Vis spectrometry as well as reagents.
List of Abbreviations and Symbols
ANOVA Analysis of Variance
BET Brunauer-Emmet-Teller analysis
FT-IR Fourier transform infrared spectrometry
GC-MS Gas Chromatography Mass Spectrometry
ICP-MS Inductively Coupled Plasma Mass Spectrometry
SEM Scanning Electron Microscopy
SPE Solid Phase Extraction
TEM Transmission Electron Microscopy
UV DRS Ultra Violet Diffractance spectrometry
WHO World Health Organization
P-XRD Powder X-ray Diffraction
List of Figures
Figure 2:1 A mechanism of biosynthesis of nanovalent ZnO
Figure 2:2: Structure of Sodium alginate
Figure 3:1 A: Flacourtia indica plant
Figure 3:2: F indica plant aqueous leaf extracts (A) and P — ZrO2CeO2ZnO nanoparticle solutions (B) at different pH
Figure 4:1: a) P — ZrO2CeO2ZnO nanoparticles/alginate beads being extruded from syringes and b) wet alginate beads in a petri dish
Figure 4:2. A) The LED warm white light coiled around the beaker photoreactor B) The complete photoreactor used during decolourization experiments consisting of LED light and the beaker wrapped with aluminium foil on a magnetic stirrer 60
Figure 4:3: (A) P — ZrO2CeO2ZnO nanoparticles/alginate beads loaded onto syringe tips and covered by glass wool (B) Sample reservoir, peristaltic pump and syringe setup used during solid phase experiments 62
Figure 4:4: Pipette tips loaded with P — ZrO2CeO2ZnO nanoparticles/alginate beads and glass wool 65
Figure 5:1 The main effects of change in (a) pH, (b) leaf extract concentration or dosage (c) metal ion precursor concentration and (d) metal ion to leaf extracts volume ratio on P — ZrO2CeO2ZnO nanoparticles synthesis 72
Figure 5:2: Response surface plot for the interaction of (a) volume ratio and metal concentration, (b) volume ratio and dosage, (c) metal concentration and dosage, (d) volume ratio and pH, (e) metal concentration and pH, (f) dosage and pH 76
Figure 5:3: UV-Vis spectrum of the P — ZrO2CeO2ZnO nanoparticles at a. 0.05M nanoparticles at pH 3, 5, 9 and 12, b. 0.1M nanoparticles at pH 3, 5, 9, and 12, c. 0.2M nanoparticles at pH 3, 5, 9 and 12 82
Figure 5:4 UV Vis spectrum of a) P — ZrO2CeO2ZnO nanoparticles and b) ZrO2CeO2ZnO nanoparticles and determination of band gap c)and e) for P — ZrO2CeO2ZnO nanoparticles at n=2 and n=1/2 respectively and d) and f) for ZrO2CeO2ZnO nanoparticles at n = 2 and n=1/2 respectively 85
Figure 5:5: FT-IR Spectrum of (a) raw plant (b) P — ZrO2CeO2ZnO nanoparticles
Figure 5:6: FT IR spectrum of a 1% P — ZrO2CeO2ZnO nanoparticles/alginate composite a) before and b) after adsorption
Figure 5:7: N2 adsorption-desorption curves of (a) raw plant and (b) P — ZrO2CeO2ZnO nanoparticles
Figure 5:8: Surface plots for alginate and 1% P — ZrO2CeO2ZnO nanoparticle/ alginate composite
Figure 5:9: Statistical thickness of a) alginate and b) 1% P — ZrO2CeO2ZnO NP alginate
Figure 5:10: (a) SEM image, (b) EDS spectrum, (c & d) TEM image, (e) Particle distribution (f) and (g) SAED images of P — ZrO2CeO2ZnO
Figure 5:11: EDX mapping images for a) oxygen, b) phosphorous, c) zinc, d) cerium, e) zirconium within the P — ZrO2CeO2ZnO nanoparticles
Figure 5:12: a), b), c) SEM image of P — ZrO2CeO2ZnO nanoparticles/alginate beads
Figure 5:13: XRD pattern of the P — ZrO2CeO2ZnO nanoparticles
Figure 5:14: XRD pattern of P — ZrO2CeO2ZnO nanoparticles/alginate beads
Figure 5:15 XPS showing the elements present in the P — ZrO2CeO2ZnO nanoparticles a) sodium, b) zinc, c) cerium, d) carbon, e) chlorine, f) zirconium, g) sulphur, h) phosphorous
Figure 5:16 The effect of 0.05, 1 and 2 g/L catalyst dosage on decolouration of 10 mg/L Congo red and insert colour changes with time after degradation. 105
Figure 5:17. The effect of changing congo red concentrations (10, 15 and 25 mg/L) on photodegradation by 1 g/L of P — ZrO2CeO2ZnO nanoparticles catalyst and insert colour changes as the reaction progressed 106
Figure 5:18. The effect of varying reaction time on the photocatalysis of 15 mg/L congo red by 1 g/L P — ZrO2CeO2ZnO nanoparticles
Figure 5:19. Kinetic modelling for the degradation of 10, 15 and 25 mg/L congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles a) Pseudo zero order, b) Pseudo first order, c) pseudo-second order
Figure 5:20. The recycling experiments for degradation of 20 mg/L congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles
Figure 5:21. Effect of different scavengers on degradation of 15 mg/L Congo red
Figure 5:22. a) Pseudo zero order, b) pseudo first order, c) pseudo second order kinetic modelling for the inhibition reactions of 15 mg/L congo red
Figure 5:23. The proposed mechanism of photocatalysis of Congo red using P — ZrO2CeO2ZnO nanoparticles
Figure 5:24: (a) Langmuir, (b) Temkin, (c) Freundlich and (d) Dubinin- Radushkevich plots for Cd adsorption
Figure 5:25: (a) Langmuir, (b) Freundlich, (c)Temkin and (d) Dubinin- Radushkevich plots for Pb adsorption
Figure 5:26: Normal plots for effects of flow, dosage, pH., sample volume, eluent flow rate and eluent concentration on extraction recovery
Figure 5:27: Pareto chart for the effects on flow, dosage, pH., sample volume, eluent flow rate and eluent concentration on extraction recovery of lead and cadmium
Figure 5:28: Residual plots for the enrichment of Cd and Pb
Figure 5:29: Main effect of sample volume, dosage and pH on enrichment factor of (A) Cd and (B) Pb
Figure 5:30 Distribution of lead hydroxide and cadmium hydroxide at various pH
Figure 5:31: Surface plots for sample volume, dosage and pH vs enrichment factor of Pb (A) and Cd (B)
Figure 5:32: Interaction plots for sample volume, dosage and pH vs enrichment factor for Pb and Cd
Figure 5:33: The effect of increasing the concentration of phenol and propanol on recoveries of Cd and Pb from water samples
Figure 5:34: Cd and Pbadsorption-desorption cycles
Figure 5:35: Pareto chart for optimization of the significant effect for solid phase extraction of a) As and b) Cr
Figure 5:36: Residual plots for the enrichment of a) Cr and b) As
Figure 5:37:Interaction plots for the effect of sample volume, dosage and pH on enrichment factors
Figure 5:38: Main effects plots for sample volume, dosage and pH on As and Crenrichment factor
Figure 5:39: Effect of a, b) methanol and c, d) ethanol on recovery of As and Cr
Figure 5:40 Extraction recovery cycles for As and Cr
Figure 9:1: Calibration curve for Cr and As SPE
Figure 9:2Calibration curve for Cr and As SPE
List of tables
Table 2:1: Studies on the synthesis of trimetallic nanoparticles
Table 2:2 Green synthesis of trimetallic nanoparticles
Table 2:3 Removal of pollutants using trimetallic photocatalysts
Table 2:4 Solid phase extraction of heavy metals using various sorbents
Table 3:1: The Taguchi design for the optimization of P — ZrO2CeO2ZnO nanoparticles synthesis
Table 5:1 Optimization of synthetic conditions of P — ZrO2CeO2ZnO nanoparticles
Table 5:2: ANOVA results for the determination of the most significant factors for synthesis of P — ZrO2CeO2ZnO nanoparticles
Table 5:3: A comparison of the current study for the synthesis of P — ZrO2CeO2ZnO nanoparticles with other studies
Table 5:4: BET Surface area analysis of alginate and P — ZrO2CeO2ZnO nanoparticle loaded beads
Table 5:5 XPS Chemical ID and Quantification
Table 5:6: Quantification of metal concentration in P — ZrO2CeO2ZnO nanoparticles and 1% P — ZrO2CeO2ZnO NP/alginate
Table 5:7. Parameters of kinetic study of the photocatalytic degradation of 10, and 25 mg/L congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles
Table 5:8. Kinetic parameters for the EDTA, t-butanol, and potassium dichromate inhibition reactions
Table 5:9. A comparison of photodegradation efficiency of catalysts using congo red as substrate
Table 5:10: Langmuir, Freundlich, D-R and Temkin isotherm parameters
Table 5:11: Multiple Response Prediction Parameters
Table 5:12: Results of the optimization of the most significant extraction conditions for Cd and Pb
Table 5:13: Taguchi model for optimization of enrichment of Pb
Table 5:14: Taguchi model for optimization of enrichment of cadmium from water samples
Table 5:15: Results of acceptance criteria for the analysis
Table 5:16 Recoveries for well water and borehole water
Table 5:17. Comparison of this study with some enrichment studies in the literature
Table 5:18: Langmuir, Freundlich, D-R and Temkin isotherm parameters
Table 5:19: Multiple Response Prediction Parameters
Table 5:20: Results for optimization of significant extraction conditions for As and Cr
Table 5:21: Results of the validation data for the analysis
Table 5:22: Recovery tests from well and effluent water samples
Table 5:23: Comparison of As and Cr enrichment and determination using other methods
Table 9:1 Tauc plots for undoped nanoparticles
Table 9:2 Tauc plots for dried doped P — ZrO2CeO2ZnO nanoparticles
Table 9:3 Estimated Model Coefficients for Means
Table 9:4: Fits and Diagnostics for Unusual Observations for P — ZrO2CeO2ZnO nanoparticle synthesis
Table 9:5: Adsorption equilibrium studies parameters
Table 9:6: Adsorption equilibrium studies parameters
Table 9:7Adsorption equilibrium parameters for Cd
Table 9:8: Adsorption equilibrium parameters for Pb
Table 9:9: Adsorption desorption cycles for Pb and Cd Solid phase extraction
Table 9:10: Effect of ethanol, methanol, propanol, phenol and mixture on bonds
CHAPTER 1 : INTRODUCTION
1.1 Background to the study
Dyes in wastewater.
Approximately 1-20 % of organic dyes are discharged into the environment after their use in dye-including industries and they pollute huge quantities of water (Nassar et al., 2016). Dyes find various applications in rubber, textile, plastic, cosmetic, leather, paper making and pharmaceutical industry (Ngulube et al., 2016). A large amount of dye material does not bind during the colouration process and is lost to wastewater and this may lead to serious contamination issues (Lima et al., 2018). Dye wastewater has the potential to be carcinogenic and mutagenic since it resists biodegradation and poses a threat to the adjacent environment when waste is disposed of without proper treatment. Hence there is a need to find treatment technologies that can reduce the toxic effects of dyes to within recommended water quality guidelines (Ngulube et al., 2016).
Various methods are used to remove organic pollutants such as dyes from aquatic systems such as biological treatment, advanced oxidation process, photocatalysis, adsorption and membrane bioreactors among others (Ahsan et al., 2018; Bouju et al., 2008; Martínez et al., 2011; Mohammadi & Veisi ., 2018). Metal oxide nanomaterials have attracted much attention as strong candidates for photocatalytic degradation of toxic pollutants (Pascariu et al., 2019). Visible light-induced photocatalysis is highly efficient in degrading dyes without any secondary contamination (Abdelwahab & Helaly, 2017). Photocatalytic degradation can be improved by lessening the band gap and extending the absorption range to the visible region leading to electron-hole separation by coupling semiconductor catalysts (Fazizadeh et al., 2017).
Various studies have shown that bimetallic and trimetallic nanophotocatalysts are more superior to their monometallic counterparts. Monometallic photocatalysts have limitations of fast electron-hole recombination and require a band gap of below 2.0 eV or below them for them to be activated. Bimetallic and trimetallic photocatalysts have a reduced band gap and their adsorption is shifted to the visible region thereby increasing their environmental applications. Both have comparable removal efficiencies. There is a need to combine different metals to study their effect on bandgap energy and hence their photocatalytic activity. The catalyst needs to be tested on various emerging contaminants to check their efficiencies and degradation products need to be identified to determine if they are toxic to the environment. Various ways for synthesizing catalysts have been used, but recently, green synthesis is of major importance since it uses environmentally friendly solvents and renewable materials.
Trace metals in the environment
Rapid growth of global industrialisation and extensive use of metals in manufacturing and mining has caused serious environmental issues in terms of pollution. Water pollution by trace metals has been a challenging problem for human health since some trace metals like arsenic, cadmium, mercury and lead are potentially carcinogenic, difficult to biodegrade and easily accumulate in living organisms even at low concentrations (Huang et al., 2018; Prasse et al., 2015).
Metalloids such as arsenic have maximum adverse effects on human health through drinking contaminated water. Arsenic exists in two oxidation forms namely: (III) and(V). Under anaerobic conditions in groundwater As (III) exists asH3AsO3, H2AsO3 andHAsO3-. As (V) dominates in surface water as H3AsO4, HAsO3-, H2AsO4 . Arsenic finds use in the production of pigments, semiconductors, herbicides, glass, transistors, pesticides, insecticides and paper. Long-term exposure to arsenic may result in the development of conjunctivitis, hyperkeratosis, hyperpigmentation, cardiovascular disease, skin cancer, gangrene of limps, and disorder of the central nervous system and peripheral vascular system (Martinez-Vargas et al., 2018; Masindi & Gitari, 2016; Nidheesh & Singh, 2017).
Chromium is widely used in the manufacture of products for corrosion protection, leather tanning, alloying, metal-ceramic, metal electroplating, manufacture of synthetic rubies, dye, wood preservation and paints. Chromium exists under the II, III and VI oxidation states. The less abundant chromium species is the divalent form because it is unstable. Chromium III has lower solubility, toxicity and mobility than the other forms. It plays an important role in lipid, glucose and protein metabolism making it an essential micronutrient for many living organisms. Chromium VI causes vomiting, liver damage, nausea, vertigo and fever when ingested orally because it is highly soluble, strongly oxidizing and mobile. The maximum permissible limit of chromium in drinking water according to WHO guidelines is 0.005 mg/L (Briffa et al., 2020; Sahayam et al., 2005).
Cadmium is a non-essential metal which is highly toxic at very low exposure levels. It is released into the environment through forest fires, volcanic eruptions and sea sprays. Human activities such as welding, mining, cigarette smoking, and refineries are also the greatest contributors to cadmium pollution (Kasa et al., 2019). The other contributors to cadmium contamination in drinking water are impurities in solders, galvanised pipes and metal fittings. It has a wide range of toxicities on respiratory, renal and nervous systems. Cadmium is also said to be carcinogenic in large doses (Hokonya & Mahamadi, 2017; Nunez et al., 2018). The maximum permissible limit for Cd in drinking water according to WHO guidelines is 0.003 mg/L.
Lead is highly toxic at low concentrations and long-term exposure to lead at low concentrations results in it being accumulated by the body due to its low rate of excretion. Lead accumulation in the body can cause blood and brain disorders as well as serious nervous system disorders (Fayazi et al., 2016).
Trace metal analysis is important for monitoring and identification of health problems. Various techniques have been used to determine the levels of trace metals including Flow Injection Analysis Atomic Adsorption Spectrometry (FIA-AAS), Electrothermal Atomic Absorption Spectrometry (ETAAS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Atomic Fluorescence Spectroscopy (AFS), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) (Akhtar et al., 2020;
Amran et al., 2020; Henríquez-Hernández et al., 2017; Magoda et al., 2016b). ICP- MS is the most powerful tool used to determine trace elements due to its wide dynamic linear range, rapid detection, low detection limit, multi-element/isotope analysis and very little interference. The application of ICP-MS for direct trace analysis of elements in complex systems sometimes suffers from problems of the concentration of the target elements being lower than the instrument limit of detection and matrix effects; hence there is a need for some form of appropriate sample pre-treatment for enrichment or removal of matrixes.
Trace metals have been enriched using solid phase extraction (Yavuz et al., 2016), liquid-liquid microextraction (Mandlate et al., 2017; Ozzeybek et al., 2020a), cloud point extraction (Blanchet-Chouinard & Lariviere, 2018; Smithies et al., 2008), coprecipitation (Arslan et al., 2018), reductive extraction (Jung & Baek, 2015) and electrodeposition (Najafi et al., 2009).
Solid phase extraction is used for the preconcentration of samples because the technique; has low cost, has low consumption of solvents, is simple, has high preconcentration factors and is rapid. The performance of solid phase extraction depends on the properties of the sorbent (Ahmad & Solimano, 2016; Calderilla et al., 2018; Molaei et al., 2017; Plotka-Wasylka et al., 2017). The challenge nowadays is on development of a sorbent with excellent enrichment properties. A wide variety of materials such as activated carbon (Dimpe et al., 2018) l-cysteine modified zeolites (S. Ahmad & Soleymanpour, 2016), carbon nanotubes (Li et al., 2009), nanoTiO2 (Yang et al., 2020) and ionic imprinted polymers (Barciela-Alonso et al., 2014) have been used as sorbents for solid phase extraction. Nanomaterials have gained popularity as solid-phase sorbents for trace elements due to their large surface area and chemical stability (He et al., 2017).
Sample preconcentration is influenced by the eluent volume, sorbent mass, time, eluent volume, pH, and sample volume. Screening of these factors one at a time is tedious, and expensive and fails to give information on synergism or antagonism simultaneous contribution to response (Alipanahpour Dil et al., 2018).
Response surface methodologies
Multivariate analysis or response surface methodologies allow optimization of procedures through fast, economic pathways as well as allow more than one variable to be optimized simultaneously. The analysis can also provide high-quality predictions in studying linear , quadratic and interaction effects, which influence a system whereas interactions are not observed in single-factor analysis (Asfaram et al., 2016).
Many studies have employed the one-factor at a time (OFAT) method to determine the sample sizes and testing procedures, regardless of the economic issues and the weakness of this method in examining the interaction effect of variables. The shortcomings of OFAT can be overcome by using Response surface methodology (RSM) which is comprised of statistical procedures applied to determine the optimum conditions for experimental conditions by considering the lowest numbers of experiments. The advantages of RSM are; a minimal number of experiments, fewer chemicals consumed and low cost. The RSM also generate mathematical models that permit the assessment of the relevant interaction effects and statistical significance of factors (Dimpe et al., 2018). The Taguchi experimental design is based on the application of orthogonal arrays which are employed to minimize the number of experiments to be performed and they are useful for identifying the effect and the importance of the factors on the response variable of the experimental design (Tovar- Gomez et al., 2015).
Green synthesis of nanoparticles
The study of nanocomposites is of great interest because they have a high surface area to mass ratio which enhances their absorbing and catalytic activity. This property enhances their effectiveness in pollutant removal from the environment. The properties of nanocomposites are enriched by alloying because it provides structural diversity and optimum composition synergic effect between the constituent metals. These enhanced properties have allowed trimetallic nanoalloys to be applied in various applications (Sharma et al., 2018; Wang et al., 2012). Physical techniques also require high vacuums, high temperatures and relatively expensive equipment. The drawback of chemical synthesis is some pollutants and toxic materials are created as products of chemical reactions (Gharagozlou et al., 2015), hence it is necessary to use environmentally friendly techniques like green synthesis. Based on the aforementioned, the following aims and objectives are highlighted.
1.2 Problem statement
1. Conventional methods used to treat wastewater contaminated with dyes can cause secondary contamination and are inefficient and expensive. Photocatalysis has attracted many researchers’ attention due to its high efficiency in degrading organic dyes and production of non-toxic products. Hence many efforts have been directed towards the synthesis of new catalysts (Li et al., 2019).
2. Direct determination of trace metals is a very difficult task since their concentration is close to or below most analytical instruments detection limit. Sample matrix can cause serious interference during the analysis of real samples. Hence there is a need for sample cleanup and preconcentration.
3. Nanoparticles are used as photocatalysts and adsorbents for the enrichment of toxic trace metals. Most physical and chemical methods used to synthesise nanoparticles suffer from several drawbacks such as the use of high pressure and temperature, long reaction time, toxic reagents, and requirements of external additives such as specific base, stabilizer and promoter during the reaction which limits the purity of the final product (Darroudi et al., 2014). There is a need to search for green and environmentally friendly methods.
1.3 Aim
To synthesize a trimetallic ( P — ZrO2CeO2ZnO) nanoparticles composite using Flacourtia indica (Governor’s plum) aqueous leaf extracts as the reducing agent and use the synthesized nanoparticles at the catalyst for photo-oxidation of toxic Congo red and also immobilize the P — ZrO2CeO2ZnO nanoparticles on alginate for the enrichment of selected toxic trace metals from environmental water solutions.
1.4 Objectives
1) To prepare phytochemical-rich aqueous extracts from F. indica leaves;
2) To study the effect of factors: pH, leaf extract dosage, metal ion concentration, metal ion concentration to leaf extract volume ratio and interactions between the factors on P — ZrO2CeO2ZnO nanoparticle synthesis;
3) To characterize the synthesised nanoparticles by Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction, X-Ray Photoelectron Spectroscopy, Uv- Vis Spectroscopy, Brunauer Emmet-Teller Analysis, Fourier Infrared Spectroscopy, Inductively Coupled Plasma Mass Spectrometry;
4) To determine the catalytic activity, kinetic models and mechanism for the photodegradation of Congo red using P — ZrO2CeO2ZnO nanoparticles;
5) To immobilize the P — ZrO2CeO2ZnO nanoparticles on alginate and characterize them using Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffraction and Inductively Coupled Plasma Mass Spectrometry; and,
6) To determine the significant factors and interactions which affect the enrichment of cadmium, lead, arsenic and chromium using P —ZrO2CeO2ZnO nanoparticles/alginate beads to detection using Inductively Coupled Plasma Mass Spectrometry and model the data using Half factorial, Full factorial and Taguchi designs.
1.5 Hypothesis
• P — ZrO2CeO2ZnO nanoparticles can be synthesised using F. indica as a reducing and stabilizing agent.
• P — ZrO2CeO2ZnO nanoparticles/alginate composite beads can be used for solid phase extraction for preconcentration of arsenic, cadmium, lead, and chromium and before ICP-MS analysis.
• P — ZrO2CeO2ZnO nanoparticles can act as an efficient catalyst for photodegradation of Congo red.
1.6 Structure of the thesis
Chapter 1 highlights the background of the study. Chapter 2 reviews the literature for green synthesis of trimetallic nanoparticles, solid phase extraction of cadmium, lead, chromium and arsenic and photocatalysis of Congo red. Chapter 3 highlights the preliminary studies carried out to optimize nanoparticle synthesis. Chapter 4 describes the methodologies applied during the thesis. Chapter 5 describes the (a) optimization of green synthesis of the —ZrO2eO2ZnO nanoparticles and effect of various factors on synthesis (b) reports on optimization of photodegradation of Congo red using P — ZrO2CeO2ZnO nanoparticles, (c) the use of P —ZrO2CeO2ZnO nanoparticles/alginate beads on recovery of lead and cadmium followed by ICP-MS analysis, (d) use of P — ZrO2CeO2ZnO nanoparticles immobilized on alginate loaded in pipette tips for the preconcentration of arsenic and chromium followed by detection using ICP-MS and effects of interactions on recovery. Chapter 6 summarises the research findings and highlights future work.
CHAPTER 2 : LITERATURE REVIEW
2.1 Background to Nanotechnology
Nanotechnology is the understanding and control of matter and processes typically at the nanoscale but not exclusively below 100 nm in one or more dimensions where the onset of size-dependent phenomenon usually enables novel applications. A Nanoobject has at least one spatial (Euclidean) dimension less than 100 nm. Nanofibers have two dimensions less than 100 nm and nanoparticles have all three dimensions less than 100 nm (Ramsden, 2018).
Nanotechnology has emerged as the most interesting area of research due to the unique properties of nanoparticles which are decided by crucial parameters such as shape, size and morphology (Sithara et al., 2017). Nanocomposites are enriched by alloying which provides structural diversity and optimum composition synergic effect between the constituent metals. (Sharma et al., 2018; Wang et al., 2012).
Nanoparticles have smart mechanical and physicochemical properties which are completely different from their bulk counterparts (Gnanamoorthi et al., 2015). The properties of nanoparticles are due to reduced dimension about the excitonic radius of the bulk material and high surface-to-volume ratio (Mohan et al., 2015). The physical and chemical properties of nanoparticles also depend on their morphological factors such as shape and size (Sathish & Balakumar, 2017). Metallic nanoparticles have higher surface Plasmon resonance whilst nanoparticles with different shapes and sizes have different scattering and adsorption properties (Martinez-Hurtado, 2011).
2.1.1 Methods used to synthesize nanoparticles
Nanoparticles are synthesised by chemical methods such as solvothermal (Arumugam et al., 2018), sonochemical (Muradov et al., 2018), chemical successive reduction (Suwannarat et al., 2018), biological chemical synthesis (Vaseghi et al., 2018a), microwave-mediated synthesis (Kuzmanoski et al., 2016), precipitation-precipitation and impregnation (Allaedini et al., 2015), wet chemical method (Singh & Khandpekar, 2016), catalytic chemical vapour deposition (CCVD) (Lobiak et al., 2015) and molten salt method (Wu et al., 2009). Physical methods used for nanoparticle synthesis include reverse microemulsion (Xu et al., 2018), co-impregnation (Bkour et al., 2017), water in oil (Fedorenko et al., 2017), solvent-induced (Pandey et al., 2017), practical hot injection method (Tang et al., 2016), sol-gel (Dubey et al., 2015), supercritical route (Zhao et al., 2015), ball milling and reduction (Sun et al., 2013), hydrothermal (Zahedifar et al., 2013), mechano-chemical processing (Sabri et al., 2012), solid-state reaction (Choudhary et al., 2010) and plasma arch discharge (Lee et al., 2010).
Physical and chemical methods are summarized in Table 2.1. Most physical and chemical methods used to synthesize nanoparticles suffer from several drawbacks such as the use of high pressure and temperature, long reaction time, toxic reagents, and requirements of external additives such as specific base, stabilizer and promoter during the reaction which limits the purity of the final product (Darroudi et al., 2014). Physical techniques also require high vacuums, high temperatures and relatively expensive equipment. Chemical synthesis has a drawback since some pollutants and toxic
materials are created as by-products of chemical reactions (Gharagozlou et al., 2015).
Thus, it is necessary to use environmentally friendly techniques called green synthesis.
Table 2:1: Studies on the synthesis of trimetallic nanoparticles
Illustrations are not included in the reading sample
Green synthesis of nanoparticles
The important issues in green synthesis methods of nanoparticles are utilization of non-toxic chemicals, environmental friendly solvents and renewable materials (Bozkurt, 2017). Biological synthesized nanoparticles exhibit greater specific surface area and catalytic activity compared to nanoparticles synthesized through chemical means (Nordmeier et al., 2017). Nanoparticles have been synthesized using coffee extract (Poggialini et al., 2018), leaf and bark extracts of Syzygiumjambos(L), Myrtaceae (Dutta et al., 2017), Rosa damascene, Thymus vulgaris, Urtiadioica (Fazlzadeh et al., 2017), leaf extracts of Azadirachta indica (Sharma et al., 2017b), Cucumis anguria leaf extracts (Muchanyereyi-Mukaratirwa et al., 2017), Solanum tuberosum (Ramezanpour et al., 2019), Aloe Vera (Ali et al., 2016b), Mangifera indica, Murraya Koenigii, Azadiracta indica, Magnolia champaca (Devatha et al., 2016), Moring orifera plant extracts (Ezhilarasi et al., 2016), Sapindus mukorosi (Jassal et al., 2016) Anthemis xylopoda flowers (Nasrollahzadeh et al., 2015), turmeric leaves (Mihir & Siddhivinayak, 2015), green tea extracts (Mystrioti et al., 2014) Sargassum muticum (brown seaweed) (Mahdavi et al., 2013), Magnolia Kobus and Diopyros kaki leaf extracts (Song et al., 2009). Green synthesis of trimetallic nanoparticles have been a subject to research on and some of the studies are summarised in Table 2.2
Table 2:2 Green synthesis of trimetallic nanoparticles
Illustrations are not included in the reading sample
Plant mediated synthesis of metal nanoparticles using whole or parts of plants is gaining extensive research focus due to its ease in scaling up for larger production, cost effectiveness and environmental friendliness (Devatha et al., 2016). The biomolecules in plants extracts act as electron shuttles in metal reduction whilst others act as capping agents, thereby controlling the aggregation of nanoparticles as well as post surface modification (Ali et al., 2016).
2.1.2 Factors affecting nanoparticle synthesis
The rate of production of nanoparticles, their quality and other characteristics are affected by the nature of plant extracts, concentration of metal salt, concentration of plant extract, the pH, contact time and temperature of the solution (Mittal et al., 2013).
Furthermore, concentration of the capping and reducing agent plays a vital role in green synthesis of nanoparticles since at very low concentration of capping agent, unstable nanoparticles can be formed and at high concentrations nanoparticles segregation can occur (Kumar & Upadhyay, 2016). Hence concentration is a major determinant for reduction and stabilization exerted by the biomolecules which may determine the shape and size of nanoparticles.
The synthesis of nanoparticles is only possible when the metal salt precursor’s concentration is within the appropriate range for nucleation. Nanoparticle synthesis by reduction of metals precursors is determined by the availability of capping and reducing agent. In a study by Kumar and Upadhyay, (2016) involving synthesis of copper nanoparticles using glucose and L-cysteine, they found out that at 0.1 M glucose/L-cysteine concentration no reduction occurred whereas reduction increased from 0.2 M to 1.0 M glucose/L-cysteine concentration and beyond 1.0 M no increase was observed. Zuo et al., (2014) synthesized ZnO using microcrystalline cellulose and they found out that the added amount of microcrystalline cellulose can tune the morphology of ZnO crystallites. When 0.5 g microcrystalline cellulose was added, ZnO nanoparticles slices existed as a cluster and when the amount of microcrystalline cellulose was increased from 1.0 to 3.0g the morphology of ZnO transformed into flower cluster.
The pH of the plant extract solution can influence the electrical charge of the phytochemicals thereby affecting growth of nanoparticles, the extract capping and stabilizing abilities. A particular pH range can be favourable for the formation of nanoparticles of certain shapes, hence achieving greater stability. Ali and other researchers synthesized ZnO nanoparticles and they found out that less adsorption by nanoparticles occurred at lower pH of 5.0-7.0. They suggested that it was probably due to aggregation rather than nucleation of ZnO nanoparticles to form larger particles. The maximum reduction of ZnSO4 occurred around pH 8.0 (Ali et al., 2016a).
Temperature control is critical during plant mediated nanoparticles synthesis since it may enhance the reaction rate and rapid formation of nuclei from metal ions. The metal ion concentration can also affect the size of the nanoparticles formed. In a study by Matinise et al., (2017), the equivalent diameter varied in a quadratic way with initial concentration i.e. it increases with increase in concentration.
2.1.3 Mechanisms of green synthesis
Three mandatory components are essential for plant mediated nanoparticles synthesis and they are the stabilizing agent, reducing agent and a solvent medium that can solubilise the metal of interest. The reactions which occur during the green synthesis are as follows (i) short induction period, (ii) growth phase (iii) termination period. The nanoparticles growth phase occurs at a slower rate than the reduction and nucleation phases of the metallic ions which leads to higher concentration of nanoparticles. Metallic ions interact with biomass through ionic binding with bioinorganic reducing agents such as terpenoids and flavonoids in the absence of another stronger ligand. The adsorption of bio-reducing agents on the surface of metallic nanoparticles is believed to be attributed to the presence of electrons and carbonyl groups in their molecular structure (Gan & Li, 2012).
Matinise and co-workers proposed a mechanism of biosynthesis of nanovalent ZnO nanoparticles (Figure 2.1). They suggested that three elemental reactions of the solvated zinc ions with phenolic acids, flavonoids and vitamin-based compounds. They suggested that L-ascorbic acid is oxidized to L-dehydro-ascorbic acid via a free radical reaction followed by electrostatic attraction between free radical and cation of the precursors (Matinise et al., 2017).
Illustrations are not included in the reading sample
Figure 2:1 A mechanism of biosynthesis of nanovalent ZnO
Source: Matinise et al. (2017)
In this study trimetallic nanoparticles were synthesised by combining three different metals and when used as catalysts their properties can be modified better than monometallic catalyst. The trimetallic catalysts’ surfaces are unstable and can be precipitated during the catalysis reactions. However they can be stabilized by block copolymers, organic ligands, surfactants and dendrimers (Sharma et al., 2017c). Doping is used to modify nanoparticles’ luminescence, optical and electrical properties of semiconductor nanoparticles by introducing traps and discrete energy states in the band gap of excited electrons (Muruganandam et al., 2017). Doping transition metals with phosphorous atom into the crystal structure has been widely studied recently. Trimetallic nanoparticles have been used as catalysts (Allaedini et al., 2015; Liang et al., 2018; Zhang et al., 2017), antimicrobials (Vaseghi et al., 2018a), adsorbents (Sharma et al., 2017a), immunosensors (Tian et al., 2016), sensors (Cheng et al., 2014) and charge storage elements for memory devices (Haik et al., 2014).
2.1.4 Support material for nanoparticles
Encapsulation of nanoparticles is necessary because it increases the adsorption properties of the material (Phiri, 2016) and agglomeration of nanoparticles is inevitable hence there is need for an ideal support to decrease nanomaterials agglomeration (Nasrollahzadeh et al., 2016). Support material for nanoparticles includes zeolites (Ghavaminejad et al., 2016) and cellulose nanofibers (Fu et al., 2015), polyvinyl alcohol/ sodium alginate beads (Lv et al., 2013). Alginate is a polymeric acid (Figure 2.2) which occurs naturally, and it is extracted from brown seaweeds namely Macrocystis, Laminaria, Fucus, Ascophyllum, Eklonia and Pelvetia. Microorganisms such as Pseudomonas and Azobacter vinelandi can also synthesize alginate. Alginate is composed of 1,4 linked fl -D- mannuronic acid (M) and a -L-glucuronic acid (G) of varying composition and sequence (Grassi et al., 2009; Qin et al., 2006). Alginates possess a high degree of physiochemical heterogeneity which influences their quality and determines their application potential. The physiochemical properties such as sol/gel transition, viscosity and water retention ability are influenced by its molecular weight, composition and distribution of M and G blocks (Szekalska et al., 2016). Alginate has been used for encapsulation of drugs (Joshy et al., 2018), encapsulation of vitamins (Ota et al., 2018), wound dressing (Taskin et al., 2013; Tong et al., 2017), preparation of hydrogels for sorption of organic compounds (Castilhos et al., 2017), nanoparticles synthesis (Oualid et al., 2017), adsorption of drugs (Fei et al., 2016), immobilization of enzymes (Anwar et al., 2009; Raghu & Rajeshwara, 2015), adsorption of ions (Zahid et al., 2015), adsorption of metals (Lv et al., 2013), drug release Abbaspour et al., 2013; Rajendran & Basu, 2009), thickening, gel forming and colloid stabilizing agent in food and beverages industries and binder in tablet formation (Mandal et al., 2010).
Illustrations are not included in the reading sample
Figure 2:2: Structure of Sodium alginate.
Source: Grassi et al., (2009)
2.2 Photocatalysis
2.2.1 Introduction to photocatalysis
Photocatalytic transformation of organic pollutants into non-toxic molecules is now widely used for their elimination from the environment due to its high mineralization efficiency, efficient degradation rate and low toxicity of some catalyst (Trandafilovic et al., 2017; Yu et al., 2017). Ideally chemical reactions are supposed to move to equilibrium quickly however some reactions are quite slow. Reactions, which do not reach equilibrium quickly often require harsh conditions like high pressure and temperature to reach equilibrium.
A catalyst is often used to enable reactions to reach equilibrium at acceptable costs, within a reasonable time frame and with economic yield. The catalyst is not consumed by the reactions but it lowers the activation energy required for the reaction to take place and also accelerates the rate at which equilibrium is reached. Catalysts are divided into two classes according to the relationship between the phases of the catalyst, reactants and products. Homogeneous catalysts are in the same phase as reactants and products and they have high activity and selectivity. The shortcomings for the aforementioned catalysis phase include; difficult to separate from raw materials and products.
Heterogeneous catalysis involves reactions in which catalysts are in different phases with reactants and products. The heterogeneous catalysts are stable and easy to separate from the reaction system after the reaction (Chen et al., 2018). Photocatalysts are metal oxide semiconductors which oxidises chemical processes by the aid of near Ultraviolet (UV) light (>385 nm) irradiation and results in the formation of hydroxyl radicals.
2.2.2 Photocatalysis of Congo red
Congo red dye is a non-biodegradable diazo compound which is fairly stable due to its complex aromatic structure. The dye can be difficult to remove from water due to its high solubility. It has carcinogenic properties, hence it has fatal consequences with effects on skin, eyes, reproductive and respiratory systems (Madan et al., 2019). Congo red is used in wool, silk, textile and food industries. It is also used in medicine as a biological stain for diagnosis of amyloidosis and an indicator in acidic medium (Sasmal et al., 2017).
Congo red has been removed from water using photocatalysts such as PANI nanoarrays anchored on 2D-BiOCl nanoplates (Namdarian et al., 2020), Ru nanoparticles supported on unfunctionalized single walled carbon nanotubes (HemrajBenny et al., 2018), copper(1) oxide (Zhang & Yan, 2018), MgZnCr-TiO2 (Ma et al., 2017), LaO8AO.TiO356(A=Ba, Sr, Ca) nanoperovskites (Bradha et al., 2015), TiO?/K (Nan et al., 2009).
ZnO is considered to be a promising photocatalyst however its optical absorption is limited in the UV region. However, it has been shown that doping with transition metals alters its photophysical properties and reduce the band gap energy as well as the rate of electron hole pair recombination, resulting in improved catalytic performance (Huerta-Aguilar et al., 2018).
2.2.3 Factors affecting photocatalysis
Photocatalysis is mainly affected by operational parameters such as initial substrate concentration, initial catalyst dosage, the pH of the aqueous solution.
The rate of a catalysed reaction increases with increasing catalyst loading up to a certain value and beyond that the rate reduces. The reduction is due to an increase in catalyst active sites that will be available for photocatalytic reactions and this occurs up to a point where all the particles of the catalyst are fully illuminated. A screening effect of excess particles occurs at higher concentration of catalyst and this musk the photosensitive surface partially. This masking hinders or reflects the penetrating light and a decrease or conversion to the plateau occurs due to loss of photons (Hapeshi et al., 2010). High concentration of catalyst provides more chance to produce hydroxyl radicals and improves the photocatalytic process whereas excess dosage may hinder the penetration of light (Zhang et al., 2017).
The pH of the solution affects the photocatalytic process by affecting the sorptiondesorption process on the surface of the catalyst electrostatic interactions between the surface of the catalyst, substrate molecules and charged radicals formed during the reaction process (Shet & Vidya, 2016).The conversion of substrate by a catalyst decrease with increasing initial substrate concentration because the increased substrate occupies most active sites of the catalyst, which inhibits generation of oxidants (Hapeshi et al., 2010).
2.2.4 Mechanism of photocatalysis
Photocatalysis involves ejecting electrons from valence band (VB) to conduction band (CB) of semiconducting materials creating an h+ holes in valence band. The process is facilitated by UV irradiation of the semiconductor with energy superior or equal to the band gap. An extremely reactive radical (e.g. OH) is formed at the semiconductor surface and direct oxidation of the pollutant adsorbed on the semiconductor occurs e.g. (TiO[2]). The equations for the whole photocatalysis process are shown from equations 2.1 to 2.6 (Zhang et al., 2007),
Illustrations are not included in the reading sample
The ejected electrons then react with electron acceptors like oxygen dissolved or adsorbed in water, (as shown in Equation 2.5);
Illustrations are not included in the reading sample
The electrons can also recombine without electron acceptor or donor (Equation 2.6);
Illustrations are not included in the reading sample
For the doped metallic nanoparticles, the mechanism of excitation is based on Localised Surface Plasmon Resonance (LSPR) in the visible light region. The localised surface plasmon resonance can exhibit a wide spectral range from near ultraviolet to visible to mid infra-red region depending on separation distance, dielectric environment, shape and size of the metal nanoparticles on the semiconductor. Collective oscillation of free electrons to form electron hole areas by surface plasmon of the dopant metal nanoparticles generates transient local electromagnetic fields. When the visible light irradiation is imposed as electromagnetic field the frequencies match and the surface plasmon is excited. An electron from dopant is directly transferred to the conduction band of the semiconductor due to the interband transitions between the semiconductor and plasmonic metal nanoparticles. The surface of the dopant on the semiconductor can act as electron trap and active reaction site (Krukowska et al., 2018).The efficiency of a catalyst is affected by its optical adsorption and charge separation efficiency properties as well as the number of catalytic sites (Shen et al., 2015). Doping of nanoparticles enhances photodegradation by trapping electron and holes, thus reducing electron -hole recombination (Mittal et al., 2014) . Addition of H2O2 and the pH value of the reaction solution plays an important role in the photocatalytic process (Liang et al., 2015).
The efficiency of single metal oxide photocatalysts have limitations of fast electron hole recombination and in order to activate the molecules in sunlight the band gap should be 2.0 eV or below. This presents a challenge when trying to activate the catalyst under visible light or natural sunlight. Doping or mixing reduces the band gap and shifts the adsorption to the visible region thereby increasing environmental application (Rani & Shanker, 2018).
Doping is used to modify nanoparticles’ luminescence, optical and electrical properties of semiconductor nanoparticles by introducing traps and discrete energy states in the band gap of excited electrons (Muruganandam et al., 2017). Doping of nanoparticles enhances photo degradation by trapping electron and holes, thus reducing electronhole recombination (Mittal et al., 2014). Addition of H2O2 and the pH value of the reaction solution plays an important role in the photocatalytic process (Liang et al., 2015).
The combination of two metals is a strategy used to prepare new materials with improved selectivity or new properties than monometallic ones. This is attributed to synergic effects. The band structure is modified due to decreased orbital overlap as the interatomic distance changes resulting in the density states of the d-band and its position in the Fermi level being affected. Hence the reactivity and adsorption properties of bimetallic nanoparticles are different from either metal considered separately (Rosseler et al., 2015).
2.2.5 Trimetallic nanoparticles as photocatalysts
Trimetallic nanoparticles have higher outstanding catalytic performance when compared with single or bimetallic nanoparticles. However, they can be stabilized by block copolymers, organic ligands, surfactants and dendrimers (Sharma et al., 2017c).
Trimetallic photocatalysts have been widely used to degrade organic pollutants (Table 2:3).
LaCuZr trimetallic nanoparticles have good charge recombination separation therefore making the catalyst a good candidate for photodegradation of organic pollutants (Sharma, et al., 2018). In the Co doped RGO-Bi-TiO2 nanotubes composite, Co doping helped to accomplish 1.5 and 3.8 times higher photocatalytic activity than single doping and undoped TiO2 nanotubes under the same conditions. Bi and RGO were favourable for separation of h+ and electron holes which reduces the recombination of charges and hence promotes the formation of OH radicals (Kim et al., 2017).
Deposition of AuPd nanoparticles on the surface of MoM3 nanowire enhanced the activity of the photocatalyst due to the synergic effect of Au and Pd which results in effective separation of electron and h+ holes as well as charge separation efficiency. The excellent photocatalytic activity can be attributed to the enlarged specific surface area and enhanced stability of the catalyst (Zhang & Park, 2018). CoFe2O4/BiO1 fibre exhibit strong magnetic response to external magnetic fields as well as excellent visible light photocatalytic performance towards the degradation of Rhodamine B regardless of preparatory method, in which h+ and O2- play the major roles (Chang et al., 2019). Ni/Pt doped TiO2 nanophotocatalysts were fabricated and exhibited large surface area as well as reduced band gap. The presence of dopants Ni and Pt did not compromise its porosity. Photocatalytic activity of the doped TiO2 outperformed the non-doped TiO2 (Pol et al., 2016).
Table 2:3 Removal of pollutants using trimetallic photocatalysts
Illustrations are not included in the reading sample
ZnO and TiO2 have been used as effective non-toxic and inexpensive photocatalyst for the effective degradation of a wide range of organic pollutants in recent years. ZnO has an advantage over TiO2 because it absorbs a larger fraction of the UV spectrum (Sacco et al., 2018). The optical absorption of zinc oxide which is a promising photocatalyst is limited to the UV region. However, it has been shown that doping with transition metals alters its photophysical properties and reduce the band gap energy as well as the rate of electron-hole pair recombination, resulting in improved catalytic performance (Huerta-Aguilar et al., 2018).
Cerium oxide (CeO2) has a band gap of 3.19 eV and it is a semiconducting material with a large exciton binding energy. CeO2 is used in pharmaceutical industry, catalysis, biosensors, electronics and drug delivery. It is an ideal for photocatalyst because of its strong light absorption. CeO2 materials have fast electron-hole pair regeneration under light illumination and a longer lifetime (Sharma et al., 2017b).
Zirconium dioxide ( ZrO2) absorbs a small fraction of light hitting its surface because it has a large band gap of 5.0 eV. ZrO2 has biological and environmental compatibility, high redox potentials of photogenerated e-and h+ pairs, good chemical and optical stability, which renders its suitability for photocatalytic reactions. ZrO2 has been modified with rare earth metals, transition metals and non-metals in order to achieve charge separation and photocatalytic reactions using lower electronic photons belonging to the visible light spectra (Dodson et al., 2011; Gionco et al., 2019). Inserting Zirconia into the ceria lattice can improve the lattice oxygen mobility resulting in a better redox quality (Pradeep et al., 2015).
The doping of transition metals with phosphorous atom into the crystal structure has been widely studied recently and studies show that phosphorous enhances the catalytic activity of the catalyst by drawing electrons from metal centres. The d-states at Fermi lever of the electronic structure of metal centre can be modified by the phosphorous atom with abundant valence electrons (Du et al., 2016)
2.2.6 Kinetic models
A catalyst increases the rate of a chemical reaction but does not appear in its stoichiometric equation. There are three classes of catalysis namely heterogeneous, homogeneous and enzyme catalysis. Enzyme catalysis is a special case of homogeneous catalysis and occurs in biological system. In heterogeneous catalysis the reaction occurs on the boundaries between two phases usually on the surface of the catalyst. Kinetic study is crucial because it describes the uptake of Congo red oxidation and controls the residual time of the process. Kinetic studies are represented by mathematical equations which describe how the concentration of reagents affect the rate of reaction. These equations include the pseudo zero order, pseudo second order and the Langmuir-Hinshelwood (L-H) kinetic model. The change in concentration is linear for reaction which follows pseudo zero order kinetics. The model is represented by equations 2.7 (Nan et al., 2009) .
Illustrations are not included in the reading sample
The Langmuir-Hinshelwood model describes catalysed reaction following pseudo first order kinetics at trivial initial concentration. The rate of change in concentration of reactants against reaction time is directly proportional to the remaining concentration of reactants in the system for pseudo first order kinetics because of the existence of a relatively small catalyst population relative to the number of degrading molecules. Equation 2.8 shows pseudo first order kinetics rate equation (Shoueir et al., 2018) and it was used to analyse the removal rate,
Illustrations are not included in the reading sample
and the integral form is shown in Equation 2.9 (Sravanthi et al., 2019).
Illustrations are not included in the reading sample
where C0 is the initial concentration, C is the concentration at time t, kapp is the apparent first order rate constant which is determined from the slope of the plot of ln Illustrations are not included in the reading sample vs t and it also gives the rate of photocatalytic degradation (min-[1]) and the higher the rate the faster the reaction (Mohanan et al., 2019). The half-life for the pseudo first order reaction is calculated using Equation 2.10.
Illustrations are not included in the reading sample
For a pseudo second order kinetic model the rate of concentration change is proportional to the square of the concentration at that particular instant, the differential equation for a second order photokinetic degradation is shown in Equation 2.11 (Wang, 2018).
Illustrations are not included in the reading sample
The pseudo second order model is represented by Equation 2.12 (Maldonado-Larios et al., 2020),
Illustrations are not included in the reading sample
where qt is the amount of dye adsorbed at time t per unit of catalyst (mg/g), k2is the pseudo-second order rate constant (g/mg/min), qe is the amount of dye adsorbed at equilibrium per unit of catalyst (mg/g). A plot of t/Qt vs t produces a straight line and the rate constant is calculated using the gradient of the slope.
Langmuir-Rideal kinetic mechanism (Equations 2.13-2.15) (Turolla et al., 2012) occurs when two substrates react with each other and only one reactant is adsorbed. This mechanism means that the other substrate in the fluid phase must collide with the adsorbed molecules without first being adsorbed
Illustrations are not included in the reading sample
The first order kinetics equation specifies that the rate of concentration decline is proportional to the concentration in the system. The time taken for a decrease in concentration by a certain percentage is constant and independent of the initial concentration of the one reactant or there is no significant reverse reaction. [C]o is the initial substrate concentration (mg/L), k lh (mg/L) is the Langmuir-Hinshelwood kinetic constant, k0 (mg/L/min) is the zero-order kinetic constant, Ka (L/mg) is the adsorption constant at equilibrium, K, (min) is the first order kinetic constant
2.3 Solid Phase Extraction
2.3.1 Background to solid phase extraction
Analytical laboratories are under pressure to carry out analysis at lower cost and short turnaround time. The rate determining step is sample preparation which is required to accommodate lower technical skills, provide cleaner extracts for the instrument measurement, provide more accurate and reproducible results, decrease the use of solvents and has a short turnaround time at less cost.
Sample preconcentration is the process of increasing an analyte concentration before analysis to enhance detection and quantification and it is used when complete recovery of analyte is desired and the analyte is transferred in such a manner that its concentration is increased. Separation techniques are used to preconcentrate analytes present in different sample matrix. Analytes and interferents can only be separated if there are significant differences in their chemical and physical properties.
2.3.2 Methods used to enrich analytes
Solid phase extraction (El-Sheikh et al., 2019; Yang et al., 2020), reverse phase dispersive liquid- liquid microextraction (Ozzeybek et al., 2020a), ultrasound-assisted surfactant enhanced emulsification microextraction (Yao et al., 2018), liquid phase microextraction (Karimi et al., 2015), mixed cloud point/solid phase extraction (Nekouei et al., 2016) have been used to enrich analytes.
Separation based on size includes filtration, dialysis, size exclusion chromatography and in these techniques, separation is achieved using a porous medium through which only the analyte or interferents passes through. Separation based on mass or density makes use of centrifugation to separate analytes.
Liquid-liquid extraction used to play a major role in sample clean-up and concentration in the past, however it has its shortcomings like being labour intensive and slow, recovery of sample components being incomplete and discharge of a large amount of solvent to the environment.
Solid phase extraction has shown to be a good replacement since it can be easily automated, is more efficient than liquid-liquid extraction, it is faster and less solvents are used. In solid phase extraction, the absorbing material is a suspension of solid particles in an aqueous sample. In order to have a rapid transfer of extracted solutes from one phase to another a large interfacial area is needed between the particles and sample solution. Column solid phase extraction where the liquid sample comes into intimate contact with the solid particles is more common than the batch mode. Solid phase extraction is the ideal method for sample preparation since it involves preconcentration, extraction and clean up procedures being performed in a single step. The advantages of micro solid phase extraction include low sample consumption, high concentration factors, excellent reproducibility, simplicity of operation and short extraction time (Ghorbani et al., 2020).
One of the most challenging parts of solid phase extraction is development of innovative micro-extraction materials which meets many requirements such as selectivity, stability, low costs, repeated use and versatility (Hakova et al., 2019).
2.3.3 Factors affecting solid phase extraction of samples
Solid phase extraction efficiency is affected by sample load volume, conditioning solvent, pH of solution, extraction time and elution solvent. The pH of solution influence the extraction forms of targets as well as surface binding sites of the adsorbent (Jia et al., 2017). Nano-adsorbents have a very high surface area to volume ratio and their short diffusion routes lead to a highly rapid adsorption process. Furthermore, equilibrium between sample solution and adsorbent surface is reached in a short contact time in comparison with other SPE sorbents (Parham & Saeed, 2014). Elution solvent volume determines the maximum achievable enrichment factor for the tested compounds and the volume should ideally be as low as possible while offering a reproducible and quantitative elution of the analytes. The choice of solvent depends on polarity of the substances to be eluted and the principle of solubility which states that like dissolves like (Cao et al., 2015). The enrichment factor is directly affected by the sample volume and an increase in sample volume results in increase in enrichment factor until equilibrium between solute and adsorbate is attained (Rashidi Nodeh et al., 2017).
2.3.4 Studies on enrichment of heavy metals using Solid Phase Extraction
Solid phase extraction can be carried out in batch equilibrium or in mini-column packed with solid particles (Han et al., 2014; Martínez et al., 2013). Alumina supported on graphene oxide nanocomposite was used as a nanosorbent for Dispersive MicroSolid Phase Extraction (DMSPE) of As (V) and Cr (III) preconcentration. It proved to be a good sorbent with a good recovery of between 92-108 % and precision of 2.7 to 4.0 %. A combination of DMSPE and Energy Dispersive X-Ray Fluorescence (EDXRF) analysis was used for direct measurement of samples without the elution step (Baranik et al., 2018). A polystyrene polydimethyl siloxane polymer was loaded into a micropipette tip of a syringe as a sorbent for miniaturised solid phase microextraction. Less amount of sample and elution reagents were required. The adsorbent is free of chemical interference and has high adsorption capacity (Ali et al., 2016). Magnetic iron cobalt/silica nanocomposite was used as a sorbent for the enrichment of arsenic using micro solid phase extraction. The combination of Inductively Coupled Optical Emission Spectroscopy (ICP-OES) and preconcentration proved to be a sensitive and an effective method for determination of arsenic in river as well as tap water. The method is only suitable for total arsenic not speciation (Magoda et al., 2016). Magnesium oxide-based adsorbent was used for preconcentration and determination of As by graphite furnace atomic adsorption spectrometry (GFAAS). The sorbent proved to be effective for As preconcentration in real water samples when HNO3 was used as an eluent. The preconcentrated As was successfully transferred into the GFAAS without other matrix modifiers needed (Qiang et al., 2017). Solid phase extraction is summarized in detail in Table 2:4.
The concentration of Cd and Pb in the majority of samples is usually around the detection limit of the most sensitive analytical techniques. Accurate determination of these metals is a very important goal for analytical chemists, hence the aim of most researchers is to improve the analytical potential of the different analytical techniques (Krawczyk & Jeszkaskowron, 2016).
Table 2:4 Solid phase extraction of heavy metals using various sorbents
Illustrations are not included in the reading sample
Adsorption is usually employed as a polishing step to remove inorganic and organic contaminants in wastewater and water treatment. However, the adsorption efficiency of conventional sorbents is usually limited by the active sites, surface area, lack of selectivity and the adsorption kinetics. Nanomaterials are better sorbents with their short intraparticle diffusion distance, tuneable pore size and surface chemistry, extremely higher specific surface area and associated sorption sites (Qu et al., 2013; Zhao et al., 2018 ).
2.3.5 Adsorption isotherms
Adsorption isotherms are generally used to describe adsorption processes and they include Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The Langmuir isotherm model describes the equilibrium between the amount of solute absorbed per unit mass of adsorbent and the remaining solute in the solution at low surface coverage. It assumes a monolayer homogenous adsorption, identical energy of sorption for all sites, independent of coverage binding energy and absence of interaction between adjacent adsorbate molecules. The non-linear form of the Langmuir isothermal model can be expressed as equation 2.16 (Nanta et al., 2018),
Illustrations are not included in the reading sample
Where qmis maximum monolayer adsorption (mg/g adsorbent), b is the Langmuir equilibrium constant (L/g adsorbent). The linearized form of the Langmuir isotherm can be expressed by equation 2.17 (Yoosefian et al., 2017),
Illustrations are not included in the reading sample
A plot of — versus Ce whose slope and intercept are used to determine values of Langmuir constant qm and b.
A dimensionless constant separation factor RL is used to express the essential characteristics of the Langmuir isotherm as shown by equation 2.18 (Pathania et al., 2016),
Illustrations are not included in the reading sample
where Co is the initial adsorbate concentration (mg/L), the RL value represents the nature of adsorption process which is favourable (0<RL< 1), unfavourable (RL>1), linear ( RL=1) and irreversible ( RL = 0)
The Freundlich isotherm model describes a multilayer heterogeneous adsorbent surface with different adsorption sites and the non-linear form of the model is given by equation 2.19 (Nodehi et al., 2020),
Illustrations are not included in the reading sample
where KF is the Freundlich adsorption capacity (mg/g adsorbent) and 1/n is the surface heterogeneity parameter. The linear form of the Freundlich equation is represented by equation 2.20 (Pathania et al., 2016),
Illustrations are not included in the reading sample
the intercept value of KF and the slope of 1/n are estimated from the plot of lnqe versus lnCe.
The Dubinin-Radushkevich -model accounts for the effect of the porous structure of the adsorbent on adsorption and it’s represented by equation 2.21
Illustrations are not included in the reading sample
The linear equation of the Dubinin-Radushkevich model is represented by equation 2.22-2.23 (Nishikawa et al., 2018)
Illustrations are not included in the reading sample
overall, the equation can be rewritten as equation 2.24
Illustrations are not included in the reading sample
the parameters can be obtained by plotting lnqe against In2 Illustrations are not included in the reading sample , the slope of the curve = -KdrR2 T2 and lnqDR gives the intercept, the mean adsorption energy E is obtained by equation 2.25
Illustrations are not included in the reading sample
where the adsorption energy is related to the constant KDR (mol[2]/kj[2]),qDR(mg/g) is the adsorption capacity. e is the Polanyi potential, R is the gas constant, T is the temperature in Kelvins.
CHAPTER 3 : PRELIMINARY STUDIES
3.1 Preparation of the aqueous leaf extract
Flacourtia indica leaves (Figure 3.1) were collected during the summer of 2021 from Mutoko in Zimbabwe (32.22, 32° 13” 30.17 E -17.41, 17° 24’ 34.26” S). The leaves were washed with deionised water three times to remove dirt and dried in a shade for a week. The leaves were ground into a fine powder using a blender and sieved using a 200 gm sieve. 20 g of the plant leaf powder were dissolved in 0.5 L deionised water and heated for 0.5 hours at a temperature of 100 C using a heating mantle. The resulting water/ F. indica powder mixture was vacuum filtered with the aid of a 0.45 gm filter paper and the brown extract stored at 4 C in fridge before use. The obtained extract was used without further dilution (Soto-Robles et al., 2019).
Illustrations are not included in the reading sample
Figure 3:1 A: Flacourtia indica plant .
Illustrations are not included in the reading sample
Figure 3:2: F indica plant aqueous leaf extracts (A) and P —ZrO2CeO2ZnO nanoparticle solutions (B) at different pH.
3.2 Synthesis of P — ZrO2CeO2ZnO nanoparticles
300 mL of Zn (NO3)2.6H2O was added to 1200 mL of F. indica plant extract and heated for 0.5 h. ZrOCl2.8H2O and Ce (SO4)2.4H20 salts were subjected to the same conditions as Zn (NO3)2.6H2O. 25 mL of Hydrophosphorous acid (concentrated) solution (25 mL) was slowly added to the reacting mixture vigorous stirring. The solution was boiled until minimum liquid remains. The semi liquid containing the nanoparticles (Figure 3:2 B) was dried using an oven and a muffle furnace at 800 °C to get the P — ZrO2CeO2ZnO nanoparticles. The effect of leaf dosage concentration was determined by adding 1-5 g of the leaf powder in 100 mL deionized water to a constant concentration of metal salt solution, constant temperature and pH. The effect of metal salt concentration was determined by varying the metal concentration from 0.05 to 0.5 M and keeping temperature, leaf concentration and pH constant.
3.3 Optimization of synthetic conditions
The optimization of the synthetic conditions for green synthesis of P — ZrO2CeO2ZnO nanoparticles were carried out using the Taguchi experimental design. The independent variables which were optimized were pH., dosage, metal concentration and volume ratio. The experimentally recorded response (absorbance and signal/noise ratio) from 16 runs of the optimization are shown in Table 3:1. The optimum conditions which were obtained using the Taguchi design were volume ratio 1:4, pH. 9, dosage 4 g/ 100 mL, and metal ion concentration 0.05 M.
Table 3:1: The Taguchi design for the optimization of P —ZrO2CeO2ZnO nanoparticles synthesis.
Illustrations are not included in the reading sample
CHAPTER 4 : METHODOLOGY
4.1 Chemicals and materials
All the chemicals used during the study quality was analytical grade unless otherwise stated and used as provided. Flacourtia indica leaves, zirconyl chloride octahydrate ZrOCl2.8H2O 99.5% (Riedel-De Haen Ag Sleeze Hanover), zinc nitrate hexahydrate Zn (NO3)2.6H2O 99.5%, (Merck, RSA), cerium (IV) sulphate hydrate Ce (SO4)2.4H20 98%, (Merck, RSA), phosphoric acid (Merck, RSA), phenol (Riedel-de-Haen. AG), methanol (Avonchem, UK), propanol (ACE, RSA), sodium hydroxide NaOH (Glassworld, SA), hydrochloric acid), HCL, (Merck, RSA) (Reagent grade), disodium Ethylenediaminetetraacetic acid (Merck, SA), potassium dichromate (Merck RSA), phenol liquid (91%) (Riedel-de-Haen.AG), Sodium alginate (Sigma Aldrich USA), cadmium chloride hydrate (Sarchem, RSA), lead nitrate (Skylab’s, SA), phenol (91%) (Riedel-de-Haen, AG), methanol (Avonchem, UK), propan-2-ol (ACE, RSA), phosphoric acid (Merck, RSA), calcium chloride (Merck, RSA), arsenic oxide ( As2O3), phosphoric acid, Merck (RSA), calcium chloride (Saarchem, RSA) (reagent grade). Na2EDTA (Merck, SA), C32H22N6O6S2Na2C32H22N6O6S2Na2- Congo Red (Merck, RSA), As2O3, (Sarchem SA) and deionised water.
4.2 Equipment
The morphology of the P — ZrO2CeO2ZnO nanoparticles and P — ZrO2CeO2ZnO nanoparticles/alginate beads was determined by Scanning Electron Microscope (SEM) (Auriga Zeiss, Germany). SEM determines size, shape and surface morphology with direct visualization of nanoparticles. The nanoparticles powder was mounted onto a sample holder followed by coating with a conductive material using a sputter coater. Analysis is carried out by scanning the whole sample with a focused fine beam of electrons. The surface characteristics of the sample are determined by secondary electrons which are emitted from the sample surface. SEM provides limited information about the true population average and size distribution (Mourdikoudis & Pallares, 2018)
The size of the nanoparticles was determined using Transmission Electron Microscope (TEM) (Tecnai F20, FEI company, USA). TEM is used to determine size, shape and surface morphology of particles. Nanoparticles were deposited onto films or support grids and after dispersion they were fixed by plastic embedding. Fixing was done to make nanoparticles withstand against the instrument facilitate handling or vacuum. When the beam of electrons is transmitted through the ultra-thin sample it interacts with the sample as it passes through it. A diffraction pattern is formed when the transmitted and diffracted beams combine on a fluorescent screen. The information regarding lattice spacing and symmetry of the structure is given by the diffraction pattern (Mourdikoudis & Pallares, 2018).
The leaves were ground the leaves to fine powder using a Blender (HE-House). The synthesized nanoparticles were dried using a Muffle furnace (Carbolite, England). The crystallinity of the nanoparticles and beads was determined using X - ray Diffraction (XRD), D2- Phase Diffractometer, (Bruker, Germany).
XRD is an analytical technique for examining crystalline solids and it operates based on the Bragg equation (equation 4.1)
Illustrations are not included in the reading sample
where n is the order of reflection (n G (1,2,3...), d is the interplanar spacing, A is the wavelength, 0 is the Bragg angle which is the angle between the incident beam and lattice plane. A collimated beam of X-rays is directed at the sample and the angle at which the beam is diffracted is measured. The information regarding the crystal nature of the substance is given by the angle of diffraction which differs from that of the incident beam (Dahman, 2017).
The nitrogen adsorption and desorption properties as well as BET surface area were determined using Tristar II Plus surface and porosity analyser from Micrometrics (USA). BET technique was developed by S. Brunauer, P.H Emmet and E. Teller in 1938 and they named it Brunauer-Emmet-Teller analysis. It is used to determine surface areas of the solids by measuring nitrogen adsorption at -I96X (Mallard et al., 2015). The Brunauer-Emmett-Teller equation (Equation 4.2) is utilized to estimate the surface area from nitrogen adsorption isotherms (Song & Jhung, 20I7)
Illustrations are not included in the reading sample
Where P is the equilibrium pressure of adsorbate, P0 is the saturation pressure of adsorbate at temperature of adsorption. Va is the volume of gas reduced (at standard temperature and pressure), Vm is the gas uptake corrected to standard temperature and pressure, C is a constant related to energy of adsorption, A plot of Illustrations are not included in the reading sample gives a straight line with an intercept Illustrations are not included in the reading sample , C and VmC can be obtained from the plot and Vm can be calculated and used to determine specific surface area using equation 4.3,
Illustrations are not included in the reading sample
Where Vm is the gas uptake corrected to standard temperature and pressure, o is the average area occupied by the adsorbed molecule in Angstrong’ squared, N is the Avogadro’s number, Vois the ideal gas volume, W is the weight of the sample (g), Vm is found by determining the volume of the adsorbed gas (reduced to standard temperature and pressure) at a number of equilibrium relative pressure by use of BET equation.
The functional groups of the nanoparticles and beads were determined using Fourier Transform -Infra Red Spectrometer with Attenuated Total Reflectance (ATR-FTIR, Thermo-fisher scientific). FT-IR is an absorbance analysing technique which measures the amount of light at different wavelength that is absorbed by a sample and express the measurement in a spectrum. Different materials absorb and transmit different range and levels of light and each has its unique spectrum. FT-IR utilizes the Michelson interferometer which separate radiant beams and direct them through different optical paths and then recombines them in order to produce repetitive interference signals which are measured as a function of optical path difference by the detector. Infrared spectral information is generated by the interferometer after radiant beams pass through the sample. The technique can be used to analyse characteristics such as film thickness, optical properties of nanoparticles (Shea, 1998).
The acidity of the reactions was monitored using a pH meter (Adwa AD 1020- Romania). The source of light for photodegradation of Congo red was a Light Emitting Diode (LED) (Panasonic). The nanoparticles were recovered using a Centrifuge 5702 R, (Eppendorf) during synthesis. The liquid solution was driven through the column using a peristaltic pump (Eyela, Model: Microtube MP-3, Japan). The metal content was used to determine using an Agilent ICP-MS 7800 (Agilent Technologies-Australia). The band gap was determined using Genesis 10s UV-Visible spectrometer (Thermo-Fisher Scientific Co.). Ultraviolet-visible (UV-Vis) spectra are produced when incident radiation and the electrons in a chromophore interacts and results in an electronic transition involving the promotion of one or more of the outer shells from a ground state into a higher energy state. UV-Vis spectroscopy is used to measure the number of discrete wavelengths of ultra violet or visible light that are absorbed by or transmitted through a sample in comparison to a blank sample. Information on what is in the sample and at what concentration is obtained based on the absorption or transmittance property. The amount of light absorbed by the sample is quantitatively related to the concentration of the sample. The Beer-Lambert's law is used to obtain the concentration of the substance. It can be defined as the absorption of light is directly proportional to the path length and concentration of the substance. The Beer-Lambert's law is often applied when the path length of the light is known and the molar absorptivity and can be represented by equation 4.4
Illustrations are not included in the reading sample
Where c is concentration of the sample in mol/L, A is the absorbance and has no units and £ is the molar absorptivity in L/mol/cm and b is the path length in cm (Settle, 1998).
The solutions for absorption studies were stirred using an Orbital shaker (Griffin, Model: CTR, German). The Congo red dye was stirred using Magnetic stirrer (Stuart Scientific, Model: SM3) during photocatalysis. Nanoparticles and beads were dried using drying Oven (Biobase, Model: BOV-V4SF, China).
4.3 Preparation of stock solutions
Preparation of metal salts was carried out as follows; 0.05 M Cerium was prepared by dissolving 20.23 g of Ce (SO4)2.4H20 in 1 L of deionized water, 0.05M. Zirconium was prepared by dissolving 16.11 g of ZrOCl2.8H2O in deionized water and 0.05M Zinc was prepared by dissolving 14.87 g of Zn (NO3)2.6H2O salt in 1 L deionized water.
Arsenic (III) stock solution was prepared by dissolving 1.32 g As2O3 in 20 mL 1.0 M NaOH in a 1000 mL volumetric flask. The resulting solution was topped to the mark using deionised water. As (III) was converted to As (V) by adding 1 mL of 0.01 M KMnO4 for every 2.5 mL of As (III). The solution was stirred for a minute and left to undisturbed for 24 hr and filtered afterwards.
The amount of metal salts needed to prepare 1000 ppm metal solution was determined by the molecular weight of the salt by the molar mass of the metal. The stock solution was prepared by dissolving 0.509 g CdCL2, 0.3995 g PbNO3 in 250 mL deionised water. This solution was further diluted to prepare the other required concentrations.
4.4 Synthesis of the P — ZrO2CeO2ZnO nanoparticles
Flacourtia indica leaves were collected during the summer of 2021 from Mutoko in Zimbabwe (32.22, 32° 13” 30.17 E -17.41, 17° 24’ 34.26” S). The leaves were washed with deionised water three times to remove dirt and dried in a shade for a week. The leaves were ground into a fine powder (200^m) using a blender. 20 g of the plant leaf powder were dissolved in 0.5 L deionised water and heated for 0.5 hr at a temperature of 100C using a heating mantle. The resulting water/ F. indica powder mixture was vacuum filtered with the aid of a 0.45 gm filter paper and the brown extract stored at 4°C in fridge before use. The obtained extract was used without further dilution (Soto- Robles et al., 20I9).
The independent variables that affect the synthesis of the nanoparticles such as pH, plant extract dosage, initial metal concentration and plant extract to metal salt volume ratio (Mittal et al., 20I4) were optimized using the Taguchi experimental design. The variables used during optimizations were pH (3, 6, 9, I2), plant dosage (2, 3, 4, 5 g), initial metal concentration (0.05, 0.I, 0.2, 0.5 M), plant extract to volume ratio (I:2, 1:4, 2:1, 4:1. 300 mL of each metal salt solution (ZrOCl28H2O, Zn(N03)26H20 and Ce(S04)24H20) were added to 1200 mL of F. indica leaf extract sequentially and heated for 0.5 hr at 100°C. All salts were subjected to the same conditions. Concentrated Hydrophosphorous acid solution (25 mL) was added drop wise to metal salts under vigorous stirring in order to further dope the composite using phosphorous (Du et al., 2016). The solution was boiled until minimum liquid remains. The semi liquid containing the nanoparticles was oven dried and then the solid was then calcined at 900OC to get the oxide nanoparticles (Vidya, et al., 2017). The optimized conditions were then used to synthesize the nanoparticles before characterization.
4.5 Preparation of P — ZrO2CeO2ZnO nanoparticles/alginate
beads
P — ZrO2CeO2ZnO nanoparticles were synthesized by the method described in section 4.4. The alginate beads were formed by mixing 4 g P — ZrO2CeO2ZnO nanoparticles with 100 mL of 2 % w/v sodium alginate at room temperature for 4 hours using a magnetic stirrer (Figure 4:1). CaCl2 (20 mL of 0.1M) was slowly added to the solution with stirring using with a magnetic stirrer. The beads were placed in 2 M CaCl2 solution for 12 hours at room temperature to allow for curing. Shrinking of the microcapsules was induced by oven drying at 60 °C for 24 hours.
Illustrations are not included in the reading sample
Figure 4:1: (a) P — ZrO2CeO2ZnO nanoparticles/alginate beads being extruded from syringes and (b) wet alginate beads in a petri dish
4.6 Characterization of the P — ZrO2CeO2ZnO nanoparticles
The surface plasmon resonance of the nanoparticles composite was characterized using a UV-Vis Spectrophotometer at a wavelength of 180-800 nm. Distilled water was used as a blank. The functional groups responsible for bio-reduction of the metal ions were characterised by Fourier Transform-Infra-red spectrometer operated at a resolution of 2cm-[1], and scanning from 4000- 400 cm-[1] and an average of16 scans. FTIR was carried out on P — ZrO2CeO2ZnO nanoparticles and the F. indica plant extract. The chemical composition of the nanoparticles was determined using Energy Dispersive Spectrometer (EDX) on Scanning Electron Microscopy (SEM). The crystallinity of the nanoparticles was determined using a D2-Phaser X-Ray diffractometer using Cu K (a=1.5406) radiation. The samples were scanned continuously at 29 from 10 - 90°. The samples placed on the sample holder were fine powder only.
Brunauer-Emmet-Teller (BET) surface area analysis was used to determine the surface area of both nanoparticles and beads. A 300 mg quantity of the nanoparticles and bead was used for surface area analysis. The pore size distribution was obtained from a plot of pore size versus incremental pore volume. The total pore volume was determined from a plot of pore size versus pore volume.
The surface morphology analysis was carried out on a Scanning Electron Microscopy instrument at an acceleration of 200 V and a working distance of 6.3 mm. The P — ZrO2CeO2ZnO nanoparticles were scanned and observed after being deposited on SEM specimen stabs. The size of the nanoparticles was determined using Transmission Electron Microscopy at 20-200 kV. The nanoparticles suspension was placed on a carbon coated TEM grid and the equipment was operated at 200 kV.
X-Ray Photoelectron Spectroscopy (XPS) was used to study the surface composition and the oxidation states of the elements of the P — ZrO2CeO2ZnO nanoparticles. The analysis was performed using Kratos axis ultra with DLD equipped with monochromatic X-ray source (E=1486.6 eV) running at 225 V. The photoelectron take-off angle to the sample surface was at 46°. The electron detector was set perpendicular to the sample to avoid the shadowing effect of the ion gun at one side of the particles.
4.7 Determination of the metal’s concentration in P ZrO2CeO2ZnO nanoparticles
A weighed amount of material containing the suspected nanoparticle sample was dissolved in 20 mL of 1 M HNO3/HC1 and boiled until minimum volume was left. The sample was toped up to 25 mL using deionized water and filtered. The concentration of metal elements was determined using an Agilent ICP-MS 7900 (Agilent Technologies-Australia). The operating conditions were: with incident RF power- 1550 W, carrier gas flow rate- 1 L/min, plasma gas flow rate -15 L/min, machine warmup- 1500s, replicate analysis - 3, plasma mode-low matrix, tune mode -He.
4.8 Studies of kinetics and reaction mechanisms for photocatalytic degradation of Congo red using P — ZrO2CeO2ZnO nanoparticles photocatalyst
Congo red was used as a test dye to study the photocatalytic activity of P — ZrO2CeO2ZnO catalysts. Adsorption-desorption equilibria were achieved by dispersing the 1 g/L of the P — ZrO2CeO2ZnO catalyst in 10 mg/L of Congo red dye solution and stirring in the dark for 0.5 hours before being subjected to UV led warm white light (Figure 4.2). At 0.5 hour intervals, 4 mL aliquots were taken and the suspended catalyst was removed by centrifugation at 2500 rpm for 5 minutes. Quantification of the degraded dye was carried out using a UV-Vis spectrophotometer at 562.9 nm. The amount of Congo red degraded was calculated using Equation 4.5 (Yoosefian et al., 2017),
Illustrations are not included in the reading sample
where Co is the initial Congo red dye concentration prior to illumination with LED white light, Ct is the Congo red dye concentration after illumination with LED white light at time t.
Illustrations are not included in the reading sample
Figure 4:2. A) The LED warm white light coiled around the beaker photoreactor B) the complete photoreactor used during decolourization experiments consisting of LED light and the beaker wrapped with aluminium foil on a magnetic stirrer.
4.9 Enrichment of cadmium and lead
About 100 mg of P — ZrO2CeO2ZnO nanoparticle/alginate beads were loaded into a 5 mL syringe that was covered with glass wool at the bottom (Figure 4:3). The sorbent was prewashed using 0.1 M HNO3 and deionised water before loading the sample. The model solution consisting of 10 gg/L Pb and Cd was prepared using deionised water and pH was adjusted using 0.1 M HNO3 and 0.1 M NaOH. In this study a screening step to determine the significant variables was carried out using a Half Factorial Design (HFD) experimental design followed by optimization of the significant variables using the Taguchi design. The conditions used during the optimization experiments were amount of adsorbent (50, 100, 150 mg), sample volume (10, 50, 100 mL), sample pH (3, 6, 9), eluent volume (10 mL), eluent concentration (0.5, 1.0 and 2.0 M), eluent flow rate 3 rpm and sample flow rate 2 rpm were used during the optimization experiments. Recovery studies using real samples were used to assess the extraction efficiency from the syringe column. The retained metals were eluted using HNO3 from the syringe column and diluted prior to ICP-MS analysis. HNO3 was chosen as the sole eluent since it does not cause much interference in ICP-MS. ANOVA was used to determine the effect of parameters on sorption. The optimum eluent concentration was investigated by passing 10 mL of 0.5, 1.0, 2.0 M HNO3 through the loaded column and the one with highest desorption was used as the eluting acid. After desorption, the adsorbent was washed with the eluting acid before each new extraction cycle.
The effect of desorption conditions on the release of the metals from the surface of the beads was investigated using extraction recovery (ER %). The optimized procedure was applied on recovery of spiked cadmium and lead for well and borehole water samples. The enrichment factor (EF) was determined by calculating the ratio of concentration of the lead and cadmium in the final extract to the initial concentration in the aqueous phase with and without the P — ZrO2CeO2ZnO nanoparticle/alginate as shown in Equation 4.6 (Li et al., 2017),
Illustrations are not included in the reading sample
Extraction recovery (ER) was determined using the ratio of eluted to initial concentration by the Equation 4.7 (Ali et al., 2020a),
Illustrations are not included in the reading sample
Where Cdes, Co, Cdes, Vdes and Vo are the analyte concentration in the extraction solvent, analyte concentration in the sample, extraction solvent volume and sample volume.
Illustrations are not included in the reading sample
Figure 4:3: (A) P — ZrO2CeO2ZnO nanoparticles/alginate beads loaded onto syringe tips and covered by glass wool (B) Sample reservoir, peristaltic pump and syringe setup used during solid phase experiments.
The developed solid phase extraction method was applied on borehole and well water samples. The water samples were collected in clean empty plastic containers with filtration using a 0.45 gm filter paper. The collected water was acidified using 1 M HNO3 in order to preserve it. The samples were stored at 4 °C.
4.9.1 Adsorption studies
The adsorption capacity of P — ZrO2CeO2ZnO /alginate nanocomposite was determined using batch studies on an orbital shaker. Equilibrium adsorption experiments were carried out with initial concentration ranging from 10-100 mg/L, dosage 150 mg, volume 100 mL and pH 7.0. The solutions were filtered using a 0.45 gm filter paper after reaching equilibrium and quantified using an ICP-MS spectrometer. The adsorption capacity at different concentrations was determined using the Equation 4.8 (Huang et al., 2018),
Illustrations are not included in the reading sample
where qe is the adsorption equilibrium capacity (mg/g), v = solution volume (L), m = the amount of P — ZrO2CeO2ZnO /alginate nanocomposite in grams, Co and Ce are initial and equilibrium concentration of Cd and Pb in mg/L.
4.10 Enrichment of Arsenic and Chromium by pipette tip solid phase extraction
A known amount of P — ZrO2CeO2ZnO nanoparticle/alginate composite beads were loaded on top of a small layer of glass wool in the pipette tip and covered by glass wool on top (Figure 4.4). 1.0 M HNO3 followed by deionized water at a flow rate of 1 mL/min were used to condition the sorbent bed before use in solid phase experiments. 5 iig/L As and Cr solution was prepared from ultrapure water. The variables which are significant for the enrichment of As and Cr were screened for using Pareto analysis and a Half Factorial Design (HFD). A L27 (3[4]) Full Factorial Design (FFD) matrix was used to carry out the optimization step. 1.0 M HN03 or NaOH solutions were used to adjust the pH of the solution to the desired levels. The spiked water samples were passed through the column at a flow rate of 1 mL/min. Nitric acid was used to elute the retained compounds prior to ICP-MS analysis. The desorption step was investigated by vortexing the beads with 10 mL of 0.01, 0.10, 0.50, 1.00 M HN03 and the one with highest desorption was used as the eluting acid. The highest enrichment factor was obtained by investigating the effect of sample volume on enrichment. The experiments were repeated three times in order to obtain reproducible results. The washed beads were used again for a new cycle of extraction. The effect of desorption conditions on the release of the metals from the surface of the beads was determined using extraction recovery (ER%).
The ratio of concentration of the metal ions in the final extract to the initial concentration in the aqueous phase with and without the P — ZrO2CeO2ZnO alginate was used to calculate the enrichment factor (EF) using Equation 4.6.
Extraction recovery (ER) was determining the ratio of eluted to initial concentration by the Equation 4.7,
The adsorption capacity which is used to determine the effect of different conditions on adsorption was determined using Equation 4.8.
Illustrations are not included in the reading sample
Figure 4:4: Pipette tips loaded with P — ZrO2CeO2ZnO nanoparticles/alginate beads and glass wool
The proposed method was validated in terms of linearity, precision, recovery, limit of detection, limit of quantification and correlation. Calibration curves were obtained over a range of six standards prepared in deionised water and the procedure was used to obtain the method linearity. The precision was determined from the relative standard deviation of five extractions. The sensitivity was determined by establishing the limit of quantification (LOQ) which gives a signal to noise ratio of 10:1 which is derived from equation 4.9.
Illustrations are not included in the reading sample
Limit of detection (LOD) which leads to the solute concentration that led to signal to noise of 3:1 and is derived from equation 4.10
Illustrations are not included in the reading sample
where m is the slope of calibration curve and 5b is the standard deviation of the blank.
Recovery tests were performed by spiking effluent and well water in triplicate in order to study the extraction recovery at optimum conditions.
The developed solid phase extraction method was applied on effluent collected in Avondale Harare S17°48’57.3478, E31°2’43.7208 and well water samples from Retreat Waterfalls, Harare, Zimbabwe S17°55’21.17388, E31°3’5.814. Effluent water was collected in Avondale because the sampling point lies at laboratory which produces effluent water from its analysis. The well water sample was from an informal settlement without proper sanitary facilities.
CHAPTER 5 : RESULTS AND DISCUSSION
5.1 Optimization of the method for the green synthesis of P- ZrO2CeO2ZnO nanoparticles using aqueous extracts from Flacourtia indica leaves
5.1.1 Optimization of synthetic conditions
The optimization of green synthesis of P — ZrO2CeO2ZnO nanoparticles was carried out using the Taguchi L16 orthogonal design array and the experimentally recorded response (absorbance and signal/noise ratio) from 16 runs of the optimization are shown in Table 5.1. The optimum conditions for P — ZrO2CeO2ZnO synthesis which were determined using the Taguchi experimental design were leaf extract concentration 4 g/100 mL, pH 9, metal ion salt concentration of 0.05 M and metal to leaf extract volume ratio 1:4. The P — ZrO2CeO2ZnO nanoparticles were then synthesized using the optimized conditions and characterized.
Table 5:1 Optimization of synthetic conditions of P — ZrO2CeO2ZnO nanoparticles.
Illustrations are not included in the reading sample
5.1.2 Evaluation of interactions and significant factors for the synthesis of P — ZrO2CeO2ZnO using ANOVA
ANOVA analysis of the data obtained from the green synthesis of P — ZrO2CeO2ZnO nanoparticles was evaluated using Minitab Version 18 as shown in Table 5.2 in order to obtain the probable interactions and most important effects between variables. The probability values less than 5 % shows the statistical significance of related effects at 95 % confidence level. The most significant variables with p values less than 0.05 were leaf extract dosage, metal salt concentration and pH. The volume ratio was statistically insignificant because the p value was above 0.05. Minitab statistical software was used to generate the relationship between tested variables and response as shown in Equation 5.1.
Absorbance (response) = 12.0 - 1.35 P + 9.28 D - 134 M+ 9.7 V+ 0.155 P[2]- 0.427 D + 79.6 M[2]- 1.05 V[2] - 0.429 P*D+ 3.57 P*M+ 0.222P*V + 14.5D*M - 2.04 D*V + 5. M*V. [5.1]
where P is pH, D is leaf extract dosage or concentration, M is metal salt concentration, V is metal salt to leaf extract volume ratio.
A positive value in the equation means the factor is enhanced and a factor which is not enhanced is represented by a negative value for the green synthesis of the nanoparticles in Equation 5.1. The synthesis of P — ZrO2CeO2ZnO nanoparticles was enhanced by concentration of the leaf extract, positive interactions between metal salt concentration, pH, volume ratio of the metal ion concentration to leaf extract concentration. Equation 5.1 describes the effect of various factors on nanoparticle synthesis. The R-squared value obtained from ANOVA was found to be 0.9831 suggesting that the model is appropriate for describing the green synthesis of P — ZrO2CeO2ZnO nanoparticles. Dosage or leaf extract concentration is significant since at high concentration segregation can occur and at low concentration unstable nanoparticles are formed.
Table 5:2: ANOVA results for the determination of the most significant factors for synthesis of P — ZrO2CeO2ZnO nanoparticles.
Source DF Seq SS Adj SS Adj MS F P
Illustrations are not included in the reading sample
5.1.3 Main effects of variables on nanoparticle synthesis
Figure 5.1 shows the main effects of variables such as dosage, pH, metal ion concentration and metal salts to leaf extract volume ratio. Figure 5.1 a show that the mean response decreased as the pH raised from 3.0 to 6.0 then it started to rise again from 9.0 and dropped at 12.0 when all the other factors were constant. The change in pH affected electrical charges of the phytochemicals present in the leaf extracts which in turn affects their capping and stabilizing abilities, hence overall affected the growth of the nanoparticles. A particular pH favoured the formation of nanoparticles of certain shapes in order to achieve greater stability. Change in pH can also result in formation of nanoparticles with different size and shape as well as favour aggregation of nanoparticles to form larger ones or nucleation to form new nanoparticles (Machalova et al., 2013). The reduction process is accelerated by alkaline conditions because under alkaline conditions the a glucose (cyclic structure) turns to P glucose (open chain structure) which is more reactive since it has an exposed CHO group which can readily reduce the metal ions (Kumar et al., 2016) .
The mean response of nanoparticle synthesis increased as leaf extract dosage increased assuming all factors are kept constant (Figure 5.1 b). The concentration of the plant biomass extract used during the nanoparticles synthesis determines the extent of reduction and stabilization which could affect the resulting shapes and sizes of the nanoparticles (Ghodake et al., 2010).
Figure 5.1 c shows that the mean response for nanoparticle synthesis decreased as the concentration of metal salts increased from 0.05 to 0.10 M and it increased again from 0.10 to 0.20 M and then it decreased again as concentration increased from 0.20 to 0.50 M metal ion concentration. At low metal concentration the rate of metal reduction reached its maximum. The reducing agent became the limiting factor when the metal concentration was increased and the reaction reached equilibrium. Figure 5.1 d shows that the synthesis of nanoparticles was only possible when the phytochemicals in the leaf extracts and metal ions were within suitable range for nucleation. The rate of nucleation is mainly affected by the availability of the capping and reducing agents as they determine whether metal precursors will be reduced (Prathna et al., 2011).
Illustrations are not included in the reading sample
Figure 5:1 The main effects of change in (a) pH, (b) leaf extract concentration or dosage (c) metal ion precursor concentration and (d) metal ion to leaf extracts volume ratio on P — ZrO2CeO2ZnO nanoparticles synthesis.
5.1.4 Evaluation of interactions between influencing factors by response surface methodology for P — ZrO2CeO2ZnO nanoparticle synthesis
The three-dimensional plots were used to determine the interaction between dosage, volume ratio, pH, and metal concentration. Figure 5.2 (a) shows that nanoparticle synthesis decreased as metal ion concentration increases and increases with volume ratio of metal to plant extract. At low concentration the metal is less than the plant extract so all the metal ions are reduced and as the metal ions concentration increases the plant functional groups are saturated. Volume ratio affected nanoparticle synthesis as more reducing agent is available and less metal ions are in solution, thus more active sites are available for reduction of the metal ions to form nanoparticles.
Figure 5.2 (b) shows that nanoparticle synthesis decreased with increase in volume ratio and increased with increase in plant extract dosage. At higher plant extract dosage more, functional groups are available for synthesis than at low dosage and at higher volume ratio the functional groups responsible for reduction are saturated with high metal concentration. Figure 5.2 (c) shows that nanoparticle synthesis decreased with increase in dosage and increased as metal ion concentration increased. The response decreased as dosage increased due to early attainment of equilibrium between plant and metal ions and the response increased as the metal ion concentration increased. Figure 5.2 (d) shows that nanoparticle synthesis increases with a pH increase and decrease with an increase in volume ratio. The observation is due to the increase in reactive sites responsible for reduction of the metal ions. At low pH, the plants functional groups are protonated whereas at high pH they are deprotonated or lose a proton easily and hence can reduce the metal ion to form the nanoparticles. Figure 5.2 (e) suggests that nanoparticle synthesis increase as both pH and metal ion concentration increased. The reason is that at high metal ion concentration more metals ions are available for reduction until saturation is reached. Figure 5.2 (f) demonstrates that nanoparticle synthesis increased as both dosage and pH were increased. This shows that there is interaction between pH and dosage as the increase in both factors resulted in increase in response.
Illustrations are not included in the reading sample
Figure 5:2: Response surface plot for interaction of (a) volume ratio and metal concentration, (b) volume ratio and dosage, (c) metal concentration and dosage, (d) volume ratio and pH, (e) metal concentration and pH, (f) dosage and pH
5.1.5 Possible reaction mechanism for P — ZrO2CeO2ZnO nanoparticles synthesis
F. indica leaf extracts contain phytochemicals such as alkaloids, ketones, flavonoids, aldehydes, phenols and carboxylic acid ester. All the phytochemicals have free n electrons or hydroxyl groups which are all potential reducing and stabilizing agents for nanoparticles synthesis. Metal salts containing zinc, zirconia and cerium are reduced to Zr[0], Ce[0] and Zn[0] nanoparticles by the reducing agents and free electrons from the plant extracts (Kumari & Meena, 2020). The first step involves complexation between the phytochemicals in the F indica leaf extract and the metal salts. The second step involves formation of a transition complex between the hydroxyl groups of the flavonoids and phenolic compounds and zirconia, cerium and zinc ions. Zero valent nanoparticles are formed when electrons are transferred to the metal ion as shown in Equations 5.2 to 5.4.
Illustrations are not included in the reading sample
The oxide nanoparticles were formed when zero valent phytochemical stabilized nanoparticles were oxidized at 900 °C as shown in Equation 5.5 to 5.7.
Illustrations are not included in the reading sample
The other possible reaction involves reducing sugars donating electrons to metal ions which results in formation of zero valent Zr, Ce and Zn nanoparticles directly. An alternative mechanism involves hydrolysis of sugars into their component reducing sugars before the nanoparticles are reduced. The aldehyde group is oxidized to the carboxyl group by nucleophilic addition of the hydroxyl group. The carboxyl group then reduces the metal ions to nanoparticles. The reduction of Zr[4]+, Ce[2]+ or Zn[2]+ to Zr[0], Ce[0] and Zn[0] occurs under basic conditions.
5.1.6 Comparison with other studies
A comparison of the optimization of the synthesis of P — ZrO2CeO2ZnO nanoparticles with other studies is shown in Table 5.3. The results of the P — ZrO2CeO2ZnO nanoparticles synthesis agrees with other studies for total nanoparticle synthesis time and the size distribution of the nanoparticles.
Table 5:3: A comparison of the current study for the synthesis of P — ZrO2CeO2ZnO nanoparticles with other studies.
Illustrations are not included in the reading sample
In summary the synthesis of the P — ZrO2CeO2ZnO nanoparticles were affected by experimental variables such as pH, metal ion concentration and leaf extract dosage. There is interaction between factors during the synthesis stage and these were between pH and dosage, metal concentration and volume ratio, pH and metal concentration, plant dosage to volume ratio, pH and volume ratio and between plant dosage to metal concentration. The results obtained allow for the selection of the optimum conditions without interactions. The synthesized nanoparticles have active sites for hydrogen bonding on the C — O, P = O, C = O, C = ONH and OH bands which enhances the particles application for environmental remediation such as catalysis and adsorption.
5.2 Characterization of surface composition
5.2.1 UV- Vis Spectroscopy Characterisation
The colour of the P — ZrO2CeO2ZnO nanoparticles changed from brown to yellowish after 1.5 hr of reaction time. The UV-Vis spectrum of the P — ZrO2CeO2ZnO at different pH and concentration in the wavelength range 300 to 900 nm is shown in Figure 5.3. The maximum adsorption occurred from 300 to 350 nm for all samples at different pH and concentrations.
Illustrations are not included in the reading sample
Figure 5:3: UV-Vis spectrum of the P — ZrO2CeO2ZnO nanoparticles at a. 0.05M nanoparticles at pH 3, 5, 9 and 12, b. 0.1M nanoparticles at pH 3, 5, 9, and 12, c. 0.2M nanoparticles at pH 3, 5, 9 and 12.
The UV-Vis spectra of the P — ZrO2CeO2ZnO nanoparticles (Figure 5.4 a) showed a maximum at 349 nm and the ZrO2CeO2ZnO nanoparticles (Figure 5.4 b) showed a maximum at 300 nm. The bandgap of the P — ZrO2CeO2ZnO nanoparticles was determined using Ultraviolet Diffuse Reflectance Spectroscopy (UV-DRS) analysis. The optical band gap was determined using the equation 5.8,
Illustrations are not included in the reading sample
Where a is the absorption coefficient, E(hv) is the photon energy E (hv), A is a constant, n=1/2 is a directly allowed transition, n=2 is an indirectly allowed transition (Soto-Robles et al., 2019). The optical band gap energy was determined using Tauc plots where (a hv)n vs hv were plotted as shown in Figure 5.4 c-f. The experimental determined bandgap of the P — ZrO2CeO2ZnO nanoparticles was found to be 2.4 eV (Figure 5.4 c). The bandgap for the ZrO2CeO2ZnO nanoparticles determined experimentally was found to be 2.65 eV (Figure 5.4 d). Results of the study suggests that phosphorous doping can reduce the optical band gap and hence improve the catalytic properties of the photocatalyst.
Illustrations are not included in the reading sample
Figure 5:4 UV Vis spectrum of (a) P —ZrO2CeO2ZnO nanoparticles and (b) ZrO2CeO2ZnO nanoparticles and determination of band gap (c)and e) for P — ZrO2CeO2ZnO nanoparticles at n=2 and n=1/2 respectively and (d) and (f) for ZrO2CeO2ZnO nanoparticles at n = 2 and n=1/2 respectively.
5.2.2 Fourier Transform Infrared Spectroscopy (FT-IR)
The role of phytochemicals in green synthesis of P — ZrO2CeO2ZnO nanoparticles was investigated using FT-IR analysis. The spectrum of the F. indica leaf extract is shown in Figure 5.5 a. The presence of the O — H group in the leaf extract is attributed to phenolic compounds and is confirmed by a band at 3285 cm-[1] (Ramezanpour et al., 2019) and a medium band at 2917 cm-[1] represent the C — H stretch of alkanes (Sharmila et al., 2017). A small band at 1706 cm-[1] is due to the C = O stretch of a and P unsaturated aldehydes and ketones (Repo et al., 2011) and the other small band at 1024 cm-[1] is due to the C — O of carboxylic acid ester (Shahwan et al., 2011).
The P — ZrO2CeO2ZnO nanoparticles (Fig 5.5 b) have extra bonds which appear in the region below 1000 cm-[1] and these can be attributed to formation of metal oxide nanoparticles, Ce — O appears at 712 cm-[1] (Senthilkumar et al., 2017), Zr — O stretching band at 508 cm-[1] (Mersian et al., 2018) and Zn — O at 493 cm-[1] (Jayachandraiah et al., (2014), Kirankumar & Sumathi, (2017 ). The location of bands in P — ZrO2CeO2ZnO nanoparticles is different from those of the plant extracts demonstrating a proper linkage between functional groups present in plant extracts and nanoparticles (Vaseghi et al., 2018a). The phenolic O — H band appears at 3285 cm-[1] in plant and in P — ZrO2CeO2ZnO nanoparticles it appears at 3616 cm'[1]. The C = 0 is due to flavonoids or reducing sugars aldehydes and ketones band shift 1706 cm'[1] in raw plant extract to 1682 cm'[1] in P — ZrO2CeO2ZnO nanoparticles (Wicaksono et al., 2020), C —O band shift 1024 cm'[1] in plant to 1055 cm'[1] in P — ZrO2CeO2ZnO
nanoparticles. The P = 0 phosphoryl bond appears at 1267 cm-[1] (Alexandratos &
Zhu, (2018); Zhi et al., (2018 ).
Illustrations are not included in the reading sample
Figure 5:5: FT-IR Spectrum of (a) raw plant (b) P — ZrO2CeO2ZnO nanoparticles.
The FT-IR spectrum of 1 % P — Zr02Ce02Zn0 nanoparticles/alginate beads before and after sorption is shown in Figure 5.6. The spectrum of 1 % P — Zr02Ce02Zn0 nanoparticle/ alginate beads (Figure 5.6 a) shows a 0 — H band at 3332 cm-[1] (Monier et al., 2018), C — 0 stretching of amide at 1601 cm-[1], C — N stretching of amines at 1127 cm-[1] (Joshy et al., 2018) and a C — 0 — C saccharide stretching of alginate at 1061 and 1018 cm-[1] (Geetha et al., 2016). After sorption (Figure 5.6 b) the 0 — H band shifts to 3231 cm-[1], C — 0 group shifts to 1601 cm-[1] , and C — 0 — C shifts to 1027 cm-[1] indicating that those groups may have participated in enrichment of Pb and Cd.
Illustrations are not included in the reading sample
Figure 5:6: FT IR spectrum of a 1% P — ZrO2CeO2ZnO nanoparticles/alginate composite (a) before and (b) after adsorption
5.2.3 Brunauer-Emmet-Teller (BET) analysis
The surface area, pore volume and diameter of the nanoparticles were investigated using BET analysis and the results are shown in Figure 5.7. The physisorption isotherms for both plant leaves (Figure 5.7 a) and P — Zr02Ce02Zn0 phytochemical caped nanoparticles (Figure 5.7 b) are similar suggesting that the surface properties are influenced by the capping material from the plant. Both plant and nanoparticles exhibited Type III physisorption isotherm which is obtained when interactions between the adsorbent and adsorbate are weak, the material has no identifiable monolayer formation and the adsorbed molecules are clustered around the most favourable sites on the surface of the nonporous solid (Thommes et al., 2015). The surface area, pore size and pore volume of the P — ZrO2CeO2ZnO nanoparticles were 0.4593 m[2]g-[1], 6.80 nm, 0.000734 cm[3]g-[1] respectively. The pore size is within the range of 2-50 nm hence the material is classified as mesoporous (Ravi et al., (2019; Zhang et al., 2009) and physisorption takes place in two or less distinct stages which is capillary condensation and monolayer-multilayer adsorption (Sing et al., 1985).
Illustrations are not included in the reading sample
Figure 5:7: N2 adsorption-desorption curves of (a) raw plant and (b) P — ZrO2CeO2ZnO nanoparticles
The BET surface area of the 1% P — ZrO2CeO2ZnO nanoparticles/alginate beds was determined using BET N2 adsorption-desorption isotherms and the material exhibited type V physisorption isotherm as shown in Figure 5.8. The statistical thickness of the beads is shown in Figure 5.9 and it ranges from 0 - 1 Ä.
Illustrations are not included in the reading sample
Figure 5:8: Surface plots for alginate and 1% P —ZrO2CeO2ZnO nanoparticle/ alginate composite.
Illustrations are not included in the reading sample
Figure 5:9: Statistical thickness of (a) alginate and (b) 1% P — ZrO2CeO2ZnO NP alginate.
The effect of inclusion of P — ZrO2CeO2ZnO into the calcium alginate beads is shown in Table 5.4 and the results show that the surface area increased from 4.38 to 7.33 m[2]g -[1], micropore volume from 0.00087 to 0.0016 cm[3]g-[1], and pore size decreased from 423.94 to 386.48 A respectively. The volume, micropore area and surface area of the alginate increased after encapsulation with 1 % P — ZrO2CeO2ZnO nanoparticles. Saturation of the pores occurred when the nanoparticle content was increased to 4 and 6 %. Hence in the study the 1 % P — ZrO2CeO2ZnO nanoparticle/alginate composite beads were selected for the enrichment of Pb, As, Cd and Cr due to their larger pore volume and higher surface area of the composite beads which enhances better uptake and interaction. Both calcium alginate and P — ZrO2CeO2ZnO nanoparticles /alginate beads exhibits type V physisorption isotherm which shows weak adsorbent-adsorbate interactions and is obtained with certain porous materials (Thommes et al., 2015).
Table 5:4: BET Surface area analysis of alginate and P — ZrO2CeO2ZnO nanoparticle loaded beads.
Illustrations are not included in the reading sample
nanoparticles/alginate beads
5.2.4 Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy characterisation
The morphology and topography of the P — ZrO2CeO2ZnO nanoparticles were determined by SEM and the SEM images are shown in Figure 5.10 (a). Small irregular shaped particles embedded within flakelike structures are visible in the SEM images. Figure 5.10 (b) shows the results of SEM-EDX elemental mapping of the nanoparticles. The quantities of the elements present were, cerium (5.9%), carbon (7.66%), iron (1.57%), oxygen (41.14%), calcium (0.29%), phosphorous (24.5%), zirconium (10.39%) potassium (0.92%) and zinc (4.34%). The carbon, potassium, oxygen, calcium and iron, which were detected were from impurities present in the plant leaf extracts and metal salts used to synthesize the nanoparticles. The size of the nanoparticles was determined from transmission electron microscopy (TEM) micrographs or images using ImageJ software. The images are shown in Figure 5.10 (c; d). The respective particle size distribution plots in Figure 5.10 (e). The P — ZrO2CeO2ZnO nanoparticles particle size range was 0.10-4.51 nm and they demonstrated some dispersion and a few clusters. The majority of the nanoparticles was within 0.10- 0.59 nm range. The mean nanoparticle size was 0.255 nm. Both TEM and SEM images also confirms that the nanoparticles have an irregular shape.
The selected area electron diffraction (SAED) patterns were also recorded and are shown in Figure 5.10 (f; g). The ring like structure of the SAED pattern confirms the polycrystalline nature of the nanoparticles (Lian et al., 2017). The Odpin online software was used to index the SAED images with a diffraction constant of 440 and the results showed that the diffraction pattern at a,/>’ and y = 90 °, a (Â) = 4.05, b (Â) = 4.05, c (Â)= 4.05. The (hkl)1 circle corresponding to 211 was indexed to ZrO2 26 = 60.1. The SAED indexing results pointed out to the formation of oxides of zirconia and cerium nanoparticles. The other circle with (hkl)1 corresponding to 220 can be indexed to 26 =54.54 of CeO2. Figure 5.11 shows the selected area electron mapping of a) oxygen, 16 b) phosphorous, 16 c) zinc 16 d) Cerium, 16 e) zirconium. The inclusion of the elements during nanoparticle synthesis is shown by EDX elemental mapping images which show that the elements are evenly distributed.
Illustrations are not included in the reading sample
Figure 5:10: (a) SEM image, (b) EDS spectrum, (c & d) TEM image, (e) Particle distribution (f) and (g) SAED images of P — ZrO2CeO2ZnO.
Illustrations are not included in the reading sample
Figure 5:11: EDX mapping images for (a) oxygen, (b) phosphorous, (c) zinc, (d) cerium, (e) zirconium within the P — ZrO2CeO2ZnO nanoparticles.
The morphology of the P — ZrO2CeO2ZnO nanoparticles/alginate beads was determined by scanning electron microscopy and the images of the P — ZrO2CeO2ZnO nanoparticles/alginate beads are shown in Figure 5.12 (a), (b) and (c). The beads have a microporous structure with the nanoparticles embedded within the beads.
Illustrations are not included in the reading sample
Figure 5:12: a), b), c) SEM image of P — ZrO2CeO2ZnO nanoparticles/alginate beads
5.2.5 X-ray Diffraction characterisation
Powder X-ray Diffraction (XRD) and Profex software version 4.2.4 were used to investigate the crystalline nature, phase identification and composition analysis of the P — ZrO2CeO2ZnO nanoparticles. The pure wurtzite structure of bulk ZnO was indexed by the corresponding XRD patterns shown in Figure 5.13 (Ali et al., 2016; Bandeira et al., 2020; Joint Committee on powder Diffraction Standards, JCPDS NO. 36-1451; Khorsand Zak et al., 2017). The diffraction peaks observed at 29=36.33, 37.48 and 48.17 were indexed to the Bragg reflections (020), (101) and (102) planes of the wurtzite structure of ZnO. Similar findings were observed on ZnO synthesis ( Güy and Ozacar, (2016); Choudhary et al., (2010). The monoclinic phase of ZrO2 (JCPDS No. 01-0731523) was attributed by diffraction peaks at 29=30.19, 50.25, 60.10 indexed to the Bragg reflections (101), (112), (211). Various authors assigned the diffraction peaks to ZrO2 nanoparticles ( da Silva et al., 2019; Mangla & Roy, 2018; Sharma et al., 2019). The presence of CeO2 was confirmed by diffraction peaks at 29 = 28.5, 33.08, 54.54 and 59.08 which were indexed to the (111), (200), (220) and (222) face centred cubic structure of CeO2 (JCPDS No. 34-0394). Similar diffraction pattern was observed during CeO2 synthesis (Aboutaleb and El-Salamony, 2019; Akbari et al., 2017; Chen et al., 2012; da Silva et al., 2019; Krishnan et al., 2019; Mishra and Rai, 2019; Ravi and Shashikanth, 2017) The peak at 29 = 21.59 and 26.51 can be indexed to the amorphous carbon in the nanoparticles (Koç et al., 2019;
Mohammadi & Veisi, 2018). The peak at 29 =24.16 can be indexed to the (012) of
Fe3O2 from the leaf extract (Benhammada et al., 2020).
Both XRD and SAED analysis confirmed the crystalline nature of the P — ZrO2CeO2ZnO nanoparticles. The crystalline size was calculated using the Debye - Scherrer’s formula, Equation 5.9 (Birajdar et al., 2016),
Illustrations are not included in the reading sample
where 1 is the X-ray wavelength (1.5406 A), P is the Full Width Half Maximum (FWHM) of the most intense peak and 9 is the Bragg’s angle position. The crystalline size of ZnO nanoparticles at 29 = 36.2 was 0.247 nm. The size of ZrO2 was 0.296 nm at 29 = 30.198. At 29 = 47.48 the crystalline size of CeO2 was 0.191 nm. The sizes of the nanoparticles were found to be in the same range when size determination was carried out by both XRD and TEM. The results from EDX, ICP-MS and XRD investigations revealed that zinc, phosphorous, zirconia and cerium were successfully incorporated into the P — ZrO2CeO2ZnO nanoparticles. FT-IR, UV Vis, ICP-MS, SEM, TEM, SAED, XRD and elemental imaging maps investigations point out to the formation of P — ZrO2CeO2ZnO nanoparticles.
Illustrations are not included in the reading sample
Figure 5:13: XRD pattern of the P — ZrO2CeO2ZnO nanoparticles.
The crystallinity of the P — ZrO2CeO2ZnO nanoparticles/alginate beads was determined using a D2-Phaser Powder Diffractometer and the pattern is shown in Figure 5.14. The beads were amorphous as shown by the disordered pattern suggesting that the nanoparticles were incorporated into the structure of the beads. This suggested that the nanoparticles did not retain their original structure but disturbed the structure of the alginate by penetrating into its pores. Larosa et al., (2018) characterized bare and tannese loaded calcium alginate beads and found out that tannese loaded beads were not crystalline.
Illustrations are not included in the reading sample
Figure 5:14: XRD pattern of P — ZrO2CeO2ZnO nanoparticles/alginate beads
5.2.6 X-ray photoelectron spectroscopy characterisation
The XPS spectra of elements present in P — Zr02Ce02Zn0 nanoparticles are presented in Figure 5:15. The spectra confirm the presence of P 2p, Zr 3d[5], C 1s sp[2] and sp[3], O 1s, Ce d[5] and Zn 2p[3] as summarized in Table 5.5. The Zr 3d[5] at 181.9 and 184.6 eV could be ascribed to Zr[4]+ ions (Nascimento et al., 2022). The peaks at 883.1 and 901.2 eV are ascribed to Ce[3]+ whilst the peak at 917.4 is due to Ce[4]+ ions (Zhang et al., 2015). The peak at 133.5 eV could be ascribed to P[5]+ ions (Omer et al., 2019). The peaks at 1022.4 and 1046.6 eV could be ascribed to Zn 2p[3] of Zn[2]+ ions (Zhou et al., 2018). The peaks at 284.6, 285.8, 293.4 and 298.2 eV are due to the C — C, C — 0, C = 0,0 — C = 0 of Carbon1s respectively (Chen et al., 2022). The peaks at 168.8 and 170 eV are due to S 2sp[3] and 2 p[1] from the sulphate of starting salts (Kafashan, 2019).The peaks at 198.8 and 200.4 eV is due to Cl 2p[3] and 2p[1] respectively from to the metal chloride of the starting salts. From XPS results the suggested structures are P-ZrO2CeO2ZnO and P - ZrO2CeOZnO.
Illustrations are not included in the reading sample
Figure 5:15 XPS showing the elements present in the P— ZrO2CeO2ZnO nanoparticles (a) sodium, (b) zinc, c) cerium, (d) carbon, (e) chlorine, (f) zirconium, (g) sulphur, (h) phosphorous
Table 5:5 XPS Chemical ID and Quantification
Illustrations are not included in the reading sample
5.2.7 Determination of metal composition by Inductively Coupled Plasma-Mass Spectrometry
The concentration of zinc, zirconia and ceria metals in P —ZrO2CeO2ZnO nanoparticles and P — ZrO2CeO2ZnO nanoparticles encapsulated into alginate was investigated by ICP-MS. The results of the investigation are shown in Table 5.6 and they prove that the nanoparticles were successfully incorporated in the alginate beads.
Table 5:6: Quantification of metal concentration in P — ZrO2CeO2ZnO nanoparticles and 1% P — ZrO2CeO2ZnO NP/alginate.
Illustrations are not included in the reading sample
5.3 Kinetics and reaction mechanisms for photocatalytic degradation of Congo red using P — ZrO2CeO2ZnO nanoparticles
5.3.1 Catalytic activity of the P — ZrO2CeO2ZnO
The catalytic activity of P — ZrO2CeO2ZnO nanoparticles was evaluated for the photodegradation of Congo red with the aid of UV LED light. The parameters which were optimized during the study includes amount of catalyst, initial Congo red concentration and degradation time.
5.3.2 The effect of catalyst amount on degradation of Congo red
The evaluation of the effect of catalyst amount was carried out at a fixed concentration of Congo red (10 mg/L) and varied P — ZrO2CeO2ZnO nanoparticles catalyst amount (0.5, 1.0 and 2.0 g/L). The outcome of the evaluation is shown in Figure 5.16. UV- Vis spectrometry was used to quantify the amount of Congo red remaining in solution. Before light illumination the removal efficiencies were 32.6, 20.46 and 7.13% and after light illumination they increased to 77.82, 59.90 and 35.55 % for 0.5, 1.0 and 2.0 g/L catalyst concentrations, respectively. A similar trend was observed by Aboutaleb and El-Salamony, (2019) whereby an increase in the amount of catalyst gave rise to a decrease in removal efficiencies. The observed phenomenon is attributed to the reduction in active sites of the catalyst which occurs when it becomes saturated with substrate.
The higher removal efficiency at low catalyst concentration is due to the increased amount of catalyst surface available for uptake of the Congo red molecules and corresponding increased absorption of photon energy leading to production of more free reactive radicals for dye decomposition. Higher catalyst concentration results in lower rate of decolouration due to the accumulation of particles, which leads to dispersion and reduced penetration of light and subsequently limited decolourization (Arbab et al., 2018; Guo et al., 2012).
Illustrations are not included in the reading sample
Figure 5:16 The effect of 0.05, 1 and 2 g/L catalyst dosage on decolouration of 10 mg/L Congo red and insert colour changes with time after degradation.
5.3.3 The effect of changing Congo red concentration on its degradation
The determination of effect of changing Congo red dye concentration on its degradation was investigated using 10, 15 and 25 mg/L of Congo red and 1 g/L catalyst concentration. The results of the investigation are as shown in Figure 5.17. Before light illumination the removal efficiencies of Congo red were 27.57, 43.17 and 15.87 % and after light illumination the removal efficiencies were 85.85, 82.07 and 66.19 % at 10, 15 and 25 mg/L Congo red concentrations respectively. A similar trend was observed by Shekardasht et al., (2020) who suggested that more light exposure would be required for higher concentrations of Congo red. The removal efficiencies were very high when the dye concentrations were low due to high absorption-desorption equilibria. When the concentration of the dye increased, more Congo red molecules, intermediates and photoproducts competed for absorption onto the active sites of the catalyst surface leading to an effective reduction in the reaction rate (Martínez et al., 2013).
Illustrations are not included in the reading sample
Figure 5:17. The effect of changing Congo red concentrations (10, 15 and 25 mg/L) on photodegradation by 1 g/L of P — ZrO2CeO2ZnO nanoparticles catalyst and insert colour changes as the reaction progressed.
5.3.4 The effect of reaction time on degradation of Congo red
The reaction time for the degradation of Congo red was optimized using 100 mL of 15 mg/L of Congo red dye and 1 g/L of P — ZrO2CeO2ZnO nanoparticles catalyst. The reaction was followed by taking samples between 30-300 min for every 30 min. Figure 5.18 shows the experimental results and the optimum reaction time for the catalytic degradation of the dye was 250 min. Arunadevi et al., (2018) reported an optimum time of 180 min using Cd, Ba — CuO nanoparticles. In similar studies, Aboutaleb and
El-Salamony, (2019) also managed to reach optimum degradation time of 180 min using Fe2O3 — CeO2 nanoparticles. Clamping of the P — ZrO2CeO2ZnO nanoparticle photocatalyst and the low strength of the LED light source contributed to the longer degradation time experienced in this study.
Illustrations are not included in the reading sample
Figure 5:18. The effect of varying reaction time on the photocatalysis of 15 mg/L Congo red by 1 g/L P — ZrO2CeO2ZnO nanoparticles.
5.3.5 Reaction kinetics for the degradation of Congo red
In catalysis studies, kinetic modelling is crucial because it gives the rate of Congo red degradation which indicates the amount of time needed for the reaction go towards completion. The degradation of Congo red was investigated using pseudo zero order, pseudo second order and Langmuir-Hinshelwood (L-H) kinetic models.
The pseudo zero, pseudo first and pseudo second order kinetic models as shown in Figure 5:19 were used to model the results of the kinetic study. The apparent rate constant and reaction rates are shown in Table 5.7. At low concentration (10 mg/L) the reaction best fitted pseudo first order kinetics with rate constant 0.0069 min-[1] and a similar trend was observed (Boudiaf et al., (2020), Zhang and Yan, (2019) and Vattikuti et al., (2016). Pseudo first order reactions are heterogeneous photocatalysis and adsorption-desorption process on the photocatalyst is not disturbed by decomposing reactions (Duta & Visa, 2015). In the study the reaction followed pseudo first order kinetics meaning the reaction rate depended only on Congo red and excess reactant did not affect the reaction. The reaction followed pseudo second order kinetics at 15 mg/L with R2 = 0.9401 with a rate constant of 0.2376 min-[1]. The degradation reactions followed zero order kinetics with a rate constant of 0.0775 min-[1] at 25 mg/L Congo red concentration. The reaction rate is independent of the concentration of all reacting species and constant for zero order kinetics.
Illustrations are not included in the reading sample
Figure 5:19. Kinetic modelling for the degradation of 10, 15 and 25 mg/L Congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles (a) Pseudo zero order, (b) Pseudo first order, (c) pseudo second order.
Table 5:7. Parameters of kinetic study of the photocatalytic degradation of 10, 15 and 25 mg/L Congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles.
Illustrations are not included in the reading sample
5.3.6 Regeneration of the P —ZrO2CeO2ZnO nanoparticle catalyst
The experiments to determine the regeneration of catalyst were run using 20 mg/L Congo red concentration, 1 g/L catalyst amount, and uncontrolled pH for four cycles. The used catalyst was regenerated by centrifugation followed by washing with distilled water followed by oven drying at 110 °C. Figure 5:20 shows the extraction efficiencies obtained during the experiment and they were 75, 46.6, 47.7 and 51.1 % for the first, second, third and fourth cycle respectively. The general decrease in photocatalytic activity of the P — ZrO2CeO2ZnO catalyst can be ascribed to photo-corrosion under light irradiation and loss of some weakly bound nanoparticles on the catalyst surface (Zhu et al., 2016). The increase between the third and fourth cycles can be attributed to trace amount of Congo red remaining on the catalyst surface during catalyst regeneration. The residual Congo red has a cumulative effect on the total concentration of the dye upon addition of fresh dye after each cycle.
Illustrations are not included in the reading sample
Figure 5:20. The recycling experiments for degradation of 20 mg/L Congo red using 1 g/L P — ZrO2CeO2ZnO nanoparticles.
5.3.7 The reaction mechanism for the catalytic degradation of Congo red
The reaction mechanism for Congo red photodegradation was investigated using scavenging experiments using 15 mg/L Congo red solution with (a) no scavenger, (b) 1 mM isopropanol (c) 1 mM Ethylenediaminetetraacetic acid (EDTA) and (d) 1 mM potassium dichromate. The progress of the reaction was monitored by withdrawing samples every 30 min and analysing using UV-Vis spectrometry. The results of the investigation are shown in Figure 5:21. Ethylenediaminetetraacetic acid was used to scavenge for holes (Zhu et al., 2016). Isopropanol and Potassium dichromate were used to scavenge for hydroxyl and superoxide radicals, respectively (Zeghioud et al., 2018). Addition of potassium dichromate caused a decrease in the reaction efficiency by 76.01%. The relatively large decrease confirms that the superoxide species played a major role in oxidative degradation of Congo red. Similar observations were noted by Adam et al., (2018) during their studies on degradation of Congo red. The major role played by h + holes in the degradation of Congo red was shown by a decrease in efficiency by 53% upon addition of ethyleaminetetraacetic acid. The hydroxyl radicals had a minor role as indicated by a 49.9% decrease in efficiency upon addition of isopropanol. Photolysis also played a minor role in the reaction as evidenced by a 53.0% decrease in efficiency when light was the limiting factor in the reaction.
Figure 5:21. Effect of different scavengers on degradation of 15 mg/L Congo red
The kinetics of the inhibition reaction were studied and the results are shown in Figure 5:22 and Table 5.8. The inhibition reactions using potassium dichromate, ethyleaminetetraacetic acid, t-butanol and light only without catalyst were best described by second order kinetics with rate constants of 0.0652, 0.0651, 0.0889 and 0.0889 min-[1], respectively. Both Congo red and the inhibitors played a key role during the degradation reaction at different levels. The reaction rate is proportional to the product of the concentration of the two reactants or the square of the molar concentration if the reactant is only one for pseudo second order reactions. Zero order kinetics with a rate constant of 0.0306 min-[1] best described the reaction without inhibitor. The concentration of Congo red and other reactants had a significant effect on the photodegradation reaction.
Illustrations are not included in the reading sample
Figure 5:22. (a) Pseudo zero order, (b) pseudo first order, (c) pseudo second order kinetic modelling for the inhibition reactions of 15 mg/L Congo red
Table 5:8. Kinetic parameters for the EDTA, t-butanol, potassium dichromate inhibition reactions.
Illustrations are not included in the reading sample
When irradiated with visible light P —ZrO2CeO2ZnO nanoparticles absorbed the photons possessing energy greater than their bandgap and the electrons got excited. The electrons got excited in the valence band (VB) and moved to the conduction band (CB). Electrons and holes were transferred between ZrO2, CeO2 and ZnO when an equal number of holes (h+) were generated in the VB. Electrons jumped from ZnO to CeO2 to ZrO2 in the conduction band. The holes were transferred from ZrO2 to CeO2 to ZnO in the valence band. The holes and electrons took part in the chemical reaction which resulted in separation of photo induced electron-hole pairs and a decrease of recombination rate in the catalyst (Qin et al., 2018). Positive holes were formed when electrons reside in the conduction band as shown in Equation 5.10
Illustrations are not included in the reading sample
Excited electrons were transferred from a conduction band of ZnO which has better electrical conductivity and a lower fermi level, Equations 5.11 (Vidya et al., 2017) to 5.13.
Illustrations are not included in the reading sample
The generated photoelectrons were scavenged by dissolved oxygen in water producing oxygen radicals, Equation 5.14.
Illustrations are not included in the reading sample
The generated oxygen radicals combined with hydrogen ions to form HOO-, Equation 5.15.
Illustrations are not included in the reading sample
HOO- combined with trapped electrons to generate hydrogen peroxide, Equation 5.16.
Illustrations are not included in the reading sample
Hydrogen peroxide combined with trapped electrons to form hydroxyl radicals, Equation 5.17.
Illustrations are not included in the reading sample
The positive holes on the VB reacted with water or the surface hydroxyl groups to form hydroxyl radicals as shown by Equations 5.18 and 5.19.
Illustrations are not included in the reading sample
equations 5.14-5.19 were adapted from (Darabdhara & Das, 2018)
The hydroxyl and superoxide radicals reacted with Congo red to form carbon dioxide, water and other non-toxic products as shown by Equation 5.20.
Illustrations are not included in the reading sample
Figure 5:23 shows the proposed reaction mechanism summarising the above discussed equations. Electrons were transferred within the metal element in the photocatalyst resulting in creation of positive holes. The electrons reacted with oxygen and hydroxides to form radicals which oxidizes Congo red to non-toxic compounds.
Illustrations are not included in the reading sample
The effectiveness of the P — ZrO2CeO2ZnO nanoparticles catalyst was compared with other catalysts as shown in Table 5.9. The photocatalyst compared well with other catalysts in terms of degradation efficiency and rate.
Table 5:9. A comparison of photodegradation efficiency of catalysts using Congo red as substrate
Illustrations are not included in the reading sample
The major findings were low catalyst of 10 mg/L concentration promoted increased rate of reaction due to availability of free active sites until equilibrium is reached. High catalyst concentration of 25 mg/ L resulted in lower rate of degradation due to the aggregation of nanoparticles which leads to low dispersion and reduced penetration of photons and subsequently reduced photodegradation. Removal efficiencies were enhanced by low dye concentrations due to high absorption- desorption equilibria. Congo red molecules, intermediates and photoproducts competed for adsorption onto the active sites of the catalyst surface leading to an effective reduction in the reaction rate due to the high concentration of dye. The reaction required more time to enable the catalyst to reach equilibrium and degrade optimum molecules. At lower concentration the reaction follows pseudo first order kinetics, at medium concentration it follows pseudo second order kinetics and at high concentration follows zero order kinetics. The reaction mechanism for the efficient degradation of Congo red was determined by superoxide, h+ holes and light. The high removal efficiency for the P — ZrO2CeO2ZnO catalyst means it can be used to degrade the toxic Congo red dye effectively.
5.4 Enrichment of lead and cadmium from water using P — ZrO2CeO2ZnO Nanoparticles/Alginate Beads: Optimization and determination of significant factors and interactions using response surface methodologies
5.4.1 Adsorption equilibrium studies
The performance of a sorbent is evaluated by determining the adsorption capacity which establishes how much sorbent is required to quantitatively concentrate the analyte from aqueous matrices. The adsorption equilibrium studies were determined by varying the Cd and Pb concentration from 10 - 100 mg/L, the sample volume was kept at 100 mL, the optimum pH was 7, the adsorbent dosage was 150 mg. The maximum adsorption capacity was estimated by fitting adsorption data into Freundlich, Langmuir, Temkin and Dubinin-Radushkevich models. The fitness of the isotherms was judged using the correlation coefficient R[2]. The isotherm plots for Cd and Pb are shown in Figures 5:24 and 5:25 respectively.
Illustrations are not included in the reading sample
Figure 5:25: (a) Langmuir (b) Freundlich (c) Temkin and (d) Dubinin-Radushkevich plots for Pb adsorption
The maximum adsorption capacity was 62.89 mg/g for Cd and 292.93 mg/g for
Pb according to the Dubinin Radushkevich equation. Cd fitted the Dubinin
Radushkevich equation with R = 0.992 and represented by Equation 5.21,
Illustrations are not included in the reading sample
and sorption mechanism was mainly physical in nature. Pb fitted into the Freundlich isotherm model with R = 0.975 and represented by Equation 5.22,
Illustrations are not included in the reading sample
The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm model parameters are shown in Table 5.10.
Table 5:10: Langmuir, Freundlich, D-R and Temkin isotherm parameters.
Illustrations are not included in the reading sample
5.4.2 Screening of Significant Factors for Cd and Pb extraction
The significant variables which affect the removal efficiency of Cd and Pb were screened by carrying out a half factorial design with 8 runs using Minitab 18. The optimised variables included sample flow rate, dosage, pH, sample volume, eluent flow rate and eluent concentration.
The significant variables for Cd recovery was selected according to their estimated effects which are represented by normal plots (Figure 5: 26) and Pareto chart (Figure 5: 27). Each variable which exceeded the reference line was considered to be significant at 95% confidence interval. Sample volume was found to be the most significant variable for Cd recovery and the other variables were insignificant. The other factors were kept constant in the subsequent experiments. In the case of Pb,, no variable was found to be significant at 95% confidence interval.
Illustrations are not included in the reading sample
Figure 5:26: Normal plots for effects of flow, dosage, pH, sample volume, eluent flow rate and eluent concentration on extraction recovery.
Illustrations are not included in the reading sample
Figure 5:27: Pareto chart for the effects on flow, dosage, pH., sample volume, eluent flow rate and eluent concentration on extraction recovery of lead and cadmium.
5.4.3 Optimization of the significant extraction conditions for Cd and Pb using the Taguchi experimental design
Optimization of the significant variables was carried out by the Taguchi experimental design and included 16 runs in order to determine the varied variables which are sample volume, dosage, and pH and eluent concentration. The model to predict the enrichment factor of Cd and Pb is shown in Equations 5.23 to 5.24 respectively. A positive value indicates enhancement and a negative value vice versa.
Illustrations are not included in the reading sample
The predicted responses are shown in Table 5.11 and actual optimum conditions were sample volume 100 mL, dosage 50 mg, and pH 7.0 and for recovery, the optimum elution conditions were 0.1 MHNO3 from results in Table 5.12. The predicted responses only agreed on sample volume and the rest were different which is expected since the model fit is not 100 %.
Table 5:11: Multiple Response Prediction Parameters
Illustrations are not included in the reading sample
Table 5:12: Results of the optimization of the most significant extraction conditions for CD and Pb
Illustrations are not included in the reading sample
The residual plot is shown in Figure 5:28 and the residuals are randomly scattered in a constant band with about the zero-line indicating the appropriateness of the model.
Illustrations are not included in the reading sample
Figure 5:28: Residual plots for the enrichment of Cd and Pb.
5.4.4 Evaluation of significant factors and interactions using Analysis of Variance (ANOVA)
To test the probable interaction and important effects between variables, ANOVA was carried out using Minitab 18 and the probability values less than 5% indicated statistical significance at a 95% confidence level. In this case, the linear model and sample volume were statistically significant parameters. The coefficient of determination (R[2]) for the model is 0.9159 implying the model can explain 91.59% of the observed variation in the experimental results by changing variables of the modelled parameters.
ANOVA was used to test the significance of the Taguchi design model for Pb and Cd enrichment. The responses and the results of the ANOVA analysis are presented in Tables 5.13 and 5.14 respectively. In all cases for the enrichment of Pb the values of p were above 5% at a 95% confidence interval meaning that they were not statistically significant at selected variables. Hence enrichment of Pb is independent of any change in variables and can be carried out under any conditions. However, for the enrichment of Cd, the effect of sample volume was statistically significant as well as the model itself.
Table 5:13: Taguchi model for optimization of enrichment of Pb.
Illustrations are not included in the reading sample
Model Summary
Illustrations are not included in the reading sample
Table 5:14: Taguchi model for optimization of enrichment of cadmium from water samples.
Illustrations are not included in the reading sample
Model Summary
Illustrations are not included in the reading sample
5.4.5 Main effects of sample volume, dosage and pH on the enrichment of Cd and Pb using P — ZrO2CeO2ZnO nanoparticles/alginate
The sample volume is an important parameter in preconcentration studies since high preconcentration factors are desirable when analysing trace metals in real samples. There was an exponential increase in enrichment factor for Cd (Figure 5:29 A) when sample volume changes from its lowest level to its highest level assuming all other factors are kept constant. There is a decrease at first followed by an increase in enrichment factor for Pb (Figure 5:29 B) when sample volume changes from 10 mL to 100 mL assuming all other factors are kept constant. The use of a large sample volume allows the enrichment factor to be improved in this case; hence 100 mL was selected as the optimum sample volume in this study. Further higher volumes above 100 mL were avoided since the recoveries decrease swiftly with increasing sample volume for each analyte (Tokay et al., 2021).
There was a decrease in the enrichment factor for Pb and Cd when sorbent dosage changes from 10 mg to 150 mg when all other factors are kept constant. As the amount of adsorbent increases in solid-phase extraction methods, desorption of the analytes attached to the adsorbent becomes difficult since a higher eluent volume is needed resulting in a decrease in sensitivity and extraction efficiency(Ulusoy et al., 2019). The extraction efficiency does not increase with the increase in dosage because the concentration of the metal ions is kept constant (Yuan et al., 2020).
Illustrations are not included in the reading sample
Figure 5:29: Main effect of sample volume, dosage and pH on enrichment factor of (A) Cd and (B) Pb
A gradual increase in enrichment factors for Cd under acidic conditions followed by a decrease from pH 6.0 was observed when pH changed from pH 3.0 to 9.0 when all the other factors were kept constant was observed. There was a decrease in the enrichment factor for Pb when pH changes from pH 3.0 to 9.0 when all the other factors are kept constant. At lower pH values there was protonation of the functional groups of P — ZrO2CeO2ZnONanoparticles/alginate beads nanocomposite which caused the reduction of hydrogen bonding between adsorbent and Cd. Sorption of Pb was found to be high at low pH. In basic solution, hydroxide ions may form complexes with metal ions and precipitate them whereas in acidic solutions protonation of binding sites of chelating molecules may also occur thereby affecting the enrichment of the Pb and Cd as shown in Figure 5:30 (Urns et al., 2013).
Illustrations are not included in the reading sample
Figure 5:30 Distribution of lead hydroxide and cadmium hydroxide at various pH Optimum conditions were obtained using the half-factorial design and the levels which produced the highest enrichment factors with few interactions were selected as the optimum conditions
5.4.6 Evaluation of the most significant factors and interactions using response surface methodology and interaction plots
The enrichment factor increased with enhancing sample volumes from 10 to 100 mL whereas increasing sorbent dosage from 10 to 150 mg resulted in a decline in enrichment factor and this was due to the sample reaching equilibrium earlier as shown in surface plots in Figure 5:31. Interactions occurred between sample volume and dosage as shown in Figure 5:32. Interactions were observed at sample volume below 30 mL for both. Cd (Figure 5:32 a) and Pb (Figure 5:32 g). Dosages also experienced interactions above 80 mg for Cd (Figure 5:32 c) whereas for Pb they were observed below 40 mg and above 100 mg (Figure 5:32 i).
The enrichment factor was enhanced when the sample volume was increased from 5 to 100 mL. When pH was increased from 3 to 9 for the same experiment the enrichment factor decreased due to analytes and surface properties of sorbent being affected such that they favour or hinder sorption as shown in the surface plots in Figure 5:31. Interaction occurred between sample volume and pH as shown in Figure 5:32. Interactions occurred for sample volume less than 30 mL and above 70 mL for Cd (Figure 5:32 b) and only below 50 ml for Pb (Figure 5:32 h). Interactions were observed below pH 5.0 and above 7.0 for Pb (Figure 5:32 k).
Surface plots in Figure 5:31 show that when the adsorbent dosage was increased from 50 to 150 mg, a decrease in enrichment factor due to early attainment of equilibrium was observed. An increase in pH resulted in an increase in the enrichment factor up until neutral pH and the enrichment factor started to decline thereafter because the forms of analytes and sorbent surface chemistry changed as pH was increased and some forms favoured uptake whilst others inhibited it. The interaction plots are shown in Figure 5:32. Interactions were observed for dosages below 50 mg for Cd (Figure 5:32 b) and above pH 7 for Cd (Figure 5:32 f).
Illustrations are not included in the reading sample
Figure 5:31: Surface plots for sample volume, dosage and pH vs enrichment factor of Pb (A) and Cd (B)
Illustrations are not included in the reading sample
All displayed terms are in the model,
Figure 5:32: Interaction plots for sample volume, dosage and pH vs enrichment factor for Pb and Cd
5.4.7 Interference studies
Metals and other coexisting ions associated with heavy metals show interference in the presence of some heavy metal ions. The interference occurs through redox reactions, formation of precipitates and participating in complexation reactions (Ahmad et al., 2019). The effect of anions and metals have been investigated by several authors and results show that metal interactions are mainly antagonistic (Mahamadi & Madocha, 2013). The effect of organic contaminants has been rarely investigated hence in this study the effect of alcohol on recoveries of Cd and Pb metals were determined by varying the concentration from 1, 5, and 10 % phenol and propane-2-ol at pH 7, sorbent dosage 50 mg and 10 pg/L Cd and Pb concentration and the results are shown in Figure 5:33. Phenol-enhanced Cd and Pb recovery at low concentrations up to 5 % and depressed recovery at high concentrations. Propanol enhanced recovery at 1 % and depressed recovery at 5 and 10 % concentrations. Both alcohols depressed recovery at 10% concentration due to enhancement of bonding between sorbent and analyte.
Illustrations are not included in the reading sample
Figure 5:33: The effect of increasing the concentration of phenol and propanol on recoveries of Cd and Pb from water samples.
5.4.8 Desorption cycles for Cd and Pb recoveries
Five adsorption-desorption cycles were carried out to assess the effectiveness of the sorbent to recover Cd and Pb from water samples as shown in Figure 5:34. The extraction recovery of Cd and Pb were almost constant for four cycles however it is depressed at the fifth cycle. The lower recovery values of between 20-30% may be due to strong adsorption which hinders the desorption step leading to a decrease in the recovery values (Maranata et al., 2021).
Illustrations are not included in the reading sample
Figure 5:34: Cd and Pb adsorption desorption cycles
5.4.9 Acceptance criteria
The linearity was determined over a range of six calibration standards ranging from
31.25-1000 gg/L. The calibration points were fitted to linear regression. Five extractions of 50 pg/L Cd and Pb by P — ZrO2CeO2ZnO nanoparticles/alginate composite and calculating the relative standard deviation were used to determine method precision (repeatability). The limit of quantification (LOQ) was calculated using equation 4.5. The limit of detection (LOD) was calculated using equation 4.6. The acceptance criteria are shown in Table 5.15.
Table 5:15: Results of acceptance criteria for the analysis
Parameter
Illustrations are not included in the reading sample
Recovery (ER)% 57.0 -147.70 33.12- 116.5
5.4.10 Analytical applications
The validation of the proposed procedure was determined by carrying out addition recovery experiments on real water samples and the results are shown in Table 5.16. It was done by spiking real samples from well and borehole water with analyte ions and recoveries were calculated using Equation 4.3. Spiking was done at three different levels i.e., at 1.0, 5.0 and 10 pg/L for each metal ion. The borehole water sample was collected from Avondale, Harare and the well water sample was collected from Retreat farm in Waterfalls, Harare, Zimbabwe.
Table 5:16 Recoveries for well water and borehole water
Illustrations are not included in the reading sample
5.4.11 Comparison with other methods
The analytical performance of the method was compared with other reported methods as shown in Table 5.17. The limit of detection, precision, recovery and enrichment factors of the present method compares well with other methods in literature.
Table 5:17. Comparison of this study with some enrichment studies in literature.
Illustrations are not included in the reading sample
The major findings were the experimental results showed that 0 — H, C — 0, and C — 0 — C bonds played a role on enrichment of Cd and Pb because they did not appear in the FTIR spectrum after uptake. Sorption of Cd was mainly physical in nature and Pb involved multilayer adsorption. Sample volume was selected as the most significant factor for Cd recovery during screening experiments whereas Pb could be analysed under any conditions. High sample volume 100 mL, low sorbent dosage 10 mg and acidic pH below 7 favoured enrichments of both Cd and Pb. The recoveries of the metal ions were enhanced by low concentration at 1% of propanol and phenol and depressed their high concentrations at 10%. The method showed great potential for enrichment of the selected metals because a very low limit of detection was obtained.
5.5 Enrichment of Arsenic and Chromium by pipette tips loaded with P — ZrO2CeO2ZnO nanoparticles /alginate beads
5.5.1 Adsorption experiments
The sorption capacity of the adsorbent is important since it determines how much adsorbent is required to remove a specific amount of the metal ions from solution. Adsorption capacity was calculated using Equation 4.4.
The adsorption capacity was determined by varying initial As and Cr concentration from 5 to 20 mg/mL, 100 mL sample volume, dosage 20 mg, at pH. 7.0, at 1 mL/ min flow rate and the results are shown in Table 5:18. Both Cr and As sorption followed Dubinin Radushkevich isotherm model meaning the main mechanism of sorption was physical. The equilibrium isotherm equation forCr was lnqe = In 2.0 + 0.015e[2] and the equation model of As was In qe = In 1.84 — 0.012 e[2]. The maximum sorption capacity for Cr was 137.12 mg/g and 154.74 mg/g for As according to the Dubinin Radushkevich model.
Table 5:18: Langmuir, Freundlich, D-R and Temkin isotherm parameters
Illustrations are not included in the reading sample
5.5.2 Optimization of SPE experiments
The screening of the most significant factors on Cr and As enrichment was determined using the half fractional factorial design with eight experimental runs. The screened factors were eluent concentration, pH, sorbent dosage, sample volume, eluent flow rate. The eluent concentration (2.0 M), amount of adsorbent (10;40 mg), eluent flow rate (2 rpm) sample volume (5;100 mL), sample pH (3;9) and eluent volume (10 mL) were used during the optimization experiments. The extraction efficiency was assed using recovery studies.
A Pareto chart in Figure 5:35 was used to select the significant variables from sample volume, pH, eluent concentration, eluent flow rate and sample flow rate based on their absolute values. The values which exceeded the reference determining line were considered significant variables at 95% confidence interval. Data from the Pareto chart shows that dosage, eluent flow rate and sample volume were the most significant factors on removal of Cr. For subsequent experiments significant variables were considered for optimization using the full factorial design and the others were fixed (Abbaspour et al., 2013).
Illustrations are not included in the reading sample
Figure 5:35: Pareto chart for optimization of the significant effect for solid phase extraction of a) As and b) Cr.
5.5.3 Full factorial designs and response surface methodology for
optimization of the significant conditions for Cr an As enrichment A full factorial design with 21 runs was used to optimize the screened significant variables (dosage, eluent flow rate and sample volume). Figure 5:36 shows the residual plots for the optimization process. The model is appropriate for the study since the points are scattered around the centre.
Illustrations are not included in the reading sample
Figure 5:36: Residual plots for enrichment of a) Cr and b) As
The optimum conditions which gave favourable results for As and Cr enrichment were eluent flow rate- 1 mL/min, sample volume-5 mL, pH 7 and dosage 40 mg. The obtained values were close to the predicted values in Table 5.19.
Table 5:19: Multiple Response Prediction Parameters
Illustrations are not included in the reading sample
The responses of the runs and the independent variables runs are shown in Table 5.20.
The data in the table was used to model the interactions between the factors, main factors and to predict the enrichment factors of arsenic and chromium.
Table 5:20: Results for optimization of significant extraction conditions for As and Cr.
Illustrations are not included in the reading sample
Equations 5.25 and 5.26 shows the model to predict the EF of As and Cr respectively. An enhancement relationship among responses is shown by positive value whilst a negative value indicates decline between responses among terms.
Illustrations are not included in the reading sample
where D is dosage or amount of beads sorbent, P is pH and S is sample volume.
5.5.4 Effects of sample volume, pH and dosage on enrichment factors of As and Cr and the interactions between factors
Interaction plots were used to determine interactions between the variables. The results are displayed in the Figure 5.37. Interactions between sample volume and dosage were observed for Cr and As. The interactions for Cr occurred at 50 mL sample volume (Figure 5:37 a), 12-15 mg sorbent dosage (Figure 5:37 c). The interactions for As were observed between 40 to 50 mL and above 80 mL (Figure 5:37 iii) and at 10, 20 and 40 mg sorbent dosage (Figure 5:37 i). Interactions between sample volume and pH were also observed during the study. Interactions between pH and sample volume were observed at pH 4 and 7 (Figure 5:37 e) and at 40-60 mL sample volume (Figure 5:37 b) for Cr enrichment. Interactions were also observed between sample volume and pH for As enrichment. Other interactions occurred as below pH 4 (Figure 5:37 ii) and between 10- 40 mL and at 100 mL (Figure 5:37 v). Interactions were observed between pH and dosage for Cr enrichment at 15 mg and above 35 mg of sorbent dosage (Figure 5:37 d) and at pH 4 and 5 (Figure 5; 37 f). Similar interactions were noted during As enrichment between pH 4-6 and above pH 8 (Figure 5:37 iv) and at 15, 20-30 mg sorbent dosage (Figure 5:37 vii). The results from interaction studies shows regions to avoid when choosing optimum conditions.
Illustrations are not included in the reading sample
5.5.5 The effect of main factors on As and Cr enrichment
Figure 5:38 shows main effects of sample volume, dosage and pH on the enrichment of As and Cr enrichment.
The pH of the enrichment solution plays an important role in uptake of ions. An increase in enrichment factor was observed for both Cr and As when the pH was increased from 3.0 to 9.0. However, after pH 7.0 a decline in enrichment was observed for Cr from pH 7 to 9 whereas for As the mean response was almost constant. The optimum pH chosen for the enrichment of As and Cr in this study was pH 7.0. Serkan Yalgin et al., (2020) obtained quantitative recoveries for Cr (III) at similar pH range of 6.0 to 8.0 using Phallus impudicus loaded with YFe2O3. Hydroxyl groups on the sorbent are mainly responsible for sample uptake. The groups retain anions under acidic conditions and under basic conditions they retain cations (Baranik et al., 2018).
A general increase in the enrichment factor was observed when the dosage was increased from10 to 40 mg as shown in Figure 5:38. The enrichment factor was higher for Cr than As suggesting it was preferentially enriched. This is due to the fact that at low dosage more of the metal ions remain in solution since the sorption sites becomes saturated quickly. The enrichment factor increased at higher sorbent dosage because a lot of free active sites were available for the uptake of Cr and As. Ghorbani et al., (2020) also observed a similar trend for recovery of Cr . They suggested the reason for the trend was due to an increase in free active sites for the uptake of the analytes and surface area.
The other parameter which was evaluated in this study which can influence the extraction efficiency was the sample volume. A decrease in enrichment of As and Cr was observed when sample volume was increased from 5 to 100 mL as shown in Figure 5:38. Zhang et al., (2010) also observed a similar trend when they enriched As. Huang et al., (2007) found that quantitative recoveries of Cr were found when sample volumes were less than 30 mL.
5.5.6 Effect of organic interferences on As and Cr enrichment
The effect of ethanol and methanol on solid phase extraction of As and Cr enrichment was determined at pH 7.0 by varying the alcohol concentration from1, 5 and 10 % fo r methanol 1, 2 and 10 % for ethanol. The results of the determination are shown in F igure 5:39. During the experiment the dosage of the adsorbent was 20 mg; the sample and eluent volumes were 10 mL and As and Cr concentration was 10 gg/L.
Illustrations are not included in the reading sample
Figure 5:39: Effect of (a, b) methanol and (c, d) ethanol on recovery of As and Cr Increase in methanol concentration depresses the recovery of both As by 6 % and Cr by over 100 %. The increase in ethanol concentration from 1 to 10 % results in increase in recovery of As by 3 %, however increase in concentration of ethanol results in Cr enrichment increasing by up to 5 %. At higher ethanol concentrations recovery of As and Cr was depressed.
5.5.7 Regeneration studies for As and Cr enrichment
Adsorption desorption cycles were carried out to assesses the regeneration and reusability of the sorbent for As and Cr enrichment. As recovery was constant during the desorption cycles, however Cr recoveries dropped during the second cycle from 102 to 39% and in the fourth cycle it was 19% as shown in Figure 5:40.
Illustrations are not included in the reading sample
Figure 5:40 Extraction recovery cycles for As and Cr
5.5.8 Evaluation of the enrichment of As and Cr method performance
Six standards ranging from 31.25, 62.5, 125, 250, 500, 1000 gg/L were used to determine the linearity of the method. Linear regression analysis was used to fit the calibration points. In order to confirm that the selected regression and linearity are appropriate a sample spiked with a standard was analysed. Five extractions of As and Cr 20 gg/L using P — ZrO2CeO2ZnO nanoparticle/alginate composite were used to determine the precision of the method. A single analytical run was carried out in a single day respectively to determine precision as relative standard deviation RSD %. The limit of quantification was calculated using equation 4.5 and the limit of detection was calculated using equation 4.6. The results for the validation data for the analysis is shown in Table 5.21.
Table 5:21: Results of the validation data for the analysis
Illustrations are not included in the reading sample
5.5.9 Application in real samples
Addition recovery experiments were carried out to determine the accuracy of the method for As and Cr enrichment by spiking real samples from well and effluent water and the results are shown in Table 5.22. Spiking of the water samples was carried out at 2, 5.0 and 10 pg/L for Cr and As. Recovery as % was calculated from mass in the analyte of spiked sample towards added mass after replicate analysis of spiked samples at various concentrations using Equation 4.7.
Table 5:22: Recovery tests from well and effluent water samples.
Illustrations are not included in the reading sample
5.5.10 Comparison with other methods
The developed method was compared with previous methods reported in literature as shown in Table 5:23. The LOD, recoveries and precision of the current method were comparable or even lower than other methods on As and Cr recovery based on enrichment before spectroscopy analysis.
Table 5:23: Comparison of As and Cr enrichment and determination using other methods.
Illustrations are not included in the reading sample
During As and Cr enrichment study the most significant factors were screened using a half factorial design. The number of factors were reduced from five to three. The three were dosage, eluent flow rate and sample volume. Interactions were observed for sample volume and dosage at 50 mL between 12-15 mg for Cr, sample volume and pH at pH 4 and 7 between 40-60 mL for Cr and for As above pH 4 between 10-40 mL, dosage and pH at pH 4 and 5 above dosage 35mg for Cr and for As at pH 4-6 at 20-30 mg sorbent dosage. The method shows great potential for enrichment of arsenic and chromium due to its low limit of detection.
CHAPTER 6 : CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
A green method for the synthesis of P — ZrO2CeO2ZnO nanoparticles was established. The synthesis of nanoparticles was shown to be affected by variables such as pH, dosage and metal concentration. There were interactions between factors during the synthesis stage. These interactions were between metal concentration and volume ratio, plant dosage to volume ratio, plant dosage to metal concentration, pH and volume ratio, pH and metal concentration, pH and dosage. The FTIR results suggest that phytochemicals such as flavonoids, aldehydes, ketones, reducing and sugars, participated in the synthesis and stabilization of P — ZrO2CeO2ZnO nanoparticles. Their functional groups shifted or were totally absent in the nanoparticle band. The synthesised nanoparticles have active sites for hydrogen bonding on the C — O, P = O, C = O, C = O and O — H bands which enhances the particles application for environmental remediation such as catalysis and adsorption.
P — ZrO2CeO2ZnO nanoparticles show high activity for Congo red degradation under domestic LED light irradiation in aqueous medium. Low catalyst concentration at 0.5 g/L promotes an increase in rate of reaction due to availability of active sites and high catalyst concentration results in lower rate of decolouration due to the accumulation of particles which leads to dispersion and reduced penetration of light and subsequently limited decolourization. Low dye concentrations at 10 mg/L resulted in large removal efficiencies due to high absorption desorption equilibria. High dye concentrations at 25 mg/L result in more Congo red molecules, intermediates and photoproducts competing for absorption onto the active sites of the catalyst surface leading to an effective reduction in the reaction rate. The reaction requires a longer time to enable the catalyst to degrade optimum molecules and reach equilibrium. The reaction follows pseudo first order kinetics at 10 mg/L dye concentration, pseudo second order kinetics at 15mg/L concentration and zero order kinetics at 25 mg/L concentrations of Congo red. The results of the photocatalytic studies reveal that superoxide, h+ holes and light are the main determinants of the reaction mechanism for the efficient degradation of Congo red.
For Cd and Pb enrichment on P — ZrO2CeO2ZnO nanoparticles/ alginate beads the experimental results showed that O — H, C — O, and C — O — C bonds played a role on enrichment of Cd and Pb. Sorption of Cd was mainly physical in nature and Pb involved multilayer adsorption. Sample volume was selected as the most significant factor for Cd recovery during screening experiments whereas Pb could be analysed under any conditions. The significance of sample volume for the recovery of Cd was reinforced as the statistically significant parameter during evaluation of significant parameters by ANOVA. High sample volume of 100 mL, low sorbent dosage of 10 mg and acidic pH at 4 favoured enrichments of both Cd and Pb. The recoveries of the metal ions were enhanced by low concentration of propanol and phenol and depressed their high concentrations.
Novel P — ZrO2CeO2ZnO nanoparticles/ alginate beads were successfully used for As and Cr enrichment. The most significant factors were screened using a half factorial design and the number was reduced from five to three namely sample volume, dosage and eluent flow rate. Interactions were observed for sample volume and dosage at 50 mL between 12-15 mg for Cr, sample volume and pH at pH 4 and 7 between 40-60 mL for Cr and for As above pH 4 between 10-40 mL, dosage and pH at pH 4 and 5 above dosage 35 mg for Cr and for As at pH 4-6 at 20-30 mg sorbent dosage.
6.2 Recommendations for future work
Specific phytochemical can be extracted from plants using organic solvent and utilized during synthesis of nanoparticles. Samples from each different condition in the experimental design can be analysed using TEM and SEM to determine effect of factors on size and morphology. The effect of temperature on nanoparticle synthesis can also be explored. The optimization of green synthesis can be carried out using other experimental design techniques as well as response surface methodology.
Nanoparticles can also be immobilized in different matrix and form membranes which can be explored for the enrichment of heavy metals. Multielement enrichment can also be explored for solid phase extraction studies.
Further studies need to be carried out to determine the exact causes of the colour changes which occurred to Congo red in the presence of LED light and P —ZrO2CeO2ZnO nanoparticles. The products at each stage of the decolourization reaction can be identified using Gas ChromatographyMass Spectrometry (GC-MS) or Liquid chromatography Mass spectrometry (LC- MS).
CHAPTER 7 LIST OF PUBLICATIONS
A. Hokonya, N., Mahamadi, C., Mukaratirwa-Muchanyereyi, N., Timothy Gutu, T. and Zvinowanda, C., (2022). Green synthesis of P — ZrO 2CeO 2ZnO nanoparticles using leaves extract of Flacourtia indica and their application for photocatalytic degradation of a model toxic dye, Congo red, Heliyon, 8 (8). https://doi.Org/10.1016/j.heliyon.2022.e10277
B. Hokonya, N., Mahamadi, C., Mukaratirwa-Muchanyereyi, N., Timothy Gutu, T. and Zvinowanda, C., (2022). Enrichment of lead and Cadmium from water using P — ZrO 2CeO 2ZnO Nanoparticles/Alginate Beads: Optimization and determination of significant factors and interactions using response surface methodologies. Scientific African, 17. https://doi.org/10.1016/j.sciaf.2022.e01 340
C. Hokonya, N., Mahamadi, C., Mukaratirwa-Muchanyereyi, N., Timothy Gutu, T. and Zvinowanda, C., (2022). Evaluation of effects of factors and interactions on enrichment of Arsenic and Chromium by pipette tip solid phase extraction using novel P — ZrO 2CeO 2ZnO nanoparticles /alginate beads. European Journal of Chemistry. https://doi10.5155/eurjchem.13.3.327-336.2295
D. APTER 8 : REFERENCES
Aazam, E. S. (2015). Photocatalytic degradation of Congo red under visible light irradiation using Pd-Bi3.84W0.16O6.24 nanocomposite. Journal of Alloys and Compounds, 644 (3), 1-6. https://doi.Org/10.1016/j.jallcom.2015.04.163.
Abazari, R., Heshmatpour, F., & Balalaie, S. (2013). Pt/Pd/Fe trimetallic nanoparticle produced via reverse micelle technique: Synthesis, characterization, and its use as an efficient catalyst for reductive hydrodehalogenation of aryl and aliphatic halides under mild conditions. ACS Catalysis, 3 (2), 139-149. https://doi.org/10.1021/cs300507a
Abbaspour, M., Makhmalzadeh, B. S., Arastoo, Z., Jahangiri, A., & Shiralipour, R. (2013). Effect of anionic polymers on drug loading and release from clindamycin phosphate solid lipid nanoparticles. Tropical Journal of Pharmaceutical Research, 12 (4), 477-482. https://doi.org/10.4314/tjpr.v12i4.5
Abdelwahab, N. A., & Helaly, F. M. (2017). Simulated visible light photocatalytic degradation of Congo red by TiO2coated magnetic polyacrylamide grafted carboxymethylated chitosan. Journal of Industrial and Engineering Chemistry, 50, 162-171. https://doi.org/10.1016/j.jiec.2017.02.010
Aboutaleb, W. A., & El-salamony, R. A. (2019). Effect of Fe 2 O 3 -CeO 2 nanocomposite synthesis method on the Congo red dye photodegradation under visible light irradiation. Materials Chemistry and Physics, 236, 121724. https://doi.org/10.1016/j.matchemphys.2019.121724
Adam, R. E., Pozina, G., Willander, M., & Nur, O. (2018). Synthesis of ZnO nanoparticles by co-precipitation method for solar driven photodegradation of Congo red dye at different pH. Photonics and Nanostructures - Fundamentals and Applications, 32, 11-18. https://doi.Org/10.1016/j.photonics.2018.08.005
Ahmad, H., Cai, C., & Liu, C. (2019). Separation and preconcentration of Pb(II) and Cd(II) from aqueous samples using hyperbranched polyethyleneimine- functionalized graphene oxide-immobilized polystyrene spherical adsorbents. Microchemical Journal, 145, 833-842. https://doi.org/10.1016/j.microc.2018.11.032
Ahmad, S., & Soleymanpour, A. (2016). Application of l -cystine modified zeolite for preconcentration and determination of ultra-trace levels of cadmium by flame atomic absorption spectrometry. Journal of Chromatography A, 1436, 34-41. https://doi.org/10.1016/j.chroma.2016.01.065
Ahsan, M. A., Katla, S. K., Islam, M. T., Hernandez-Viezcas, J. A., Martinez, L. M., Diaz-Moreno, C. A., Lopez, J., Singamaneni, S. R., Banuelos, J., Gardea- Torresdey, J., & Noveron, J. C. (2018). Adsorptive removal of methylene blue, tetracycline and Cr(VI) from water using sulfonated tea waste. Environmental Technology and Innovation, 11, 23-40. https://doi.org/10.1016/j.eti.2018.04.003 Akbari, A., Khammar, M., Taherzadeh, D., Rajabian, A., Khorsand Zak, A., &
Darroudi, M. (2017). Zinc-doped cerium oxide nanoparticles: Sol-gel synthesis, characterization, and investigation of their in vitro cytotoxicity effects. Journal of Molecular Structure, 1149, 771-776. https://doi.org/10.1016/j.molstruc.2017.08.069
Akhtar, A., Kazi, T. G., Afridi, H. I., Baig, J. A., & Khan, M. (2020). Simultaneous preconcentration of toxic elements in eye makeup products through single drop ionic liquid based non-dispersive microextraction method using narrow glass column: Multivariate application. Microchemical Journal, 157, 104963. https://doi.org/10.1016/j.microc.2020.104963
Alamelu, K., Raja, V., Shiamala, L., & Jaffar Ali, B. M. (2018). Biphasic TiO2nanoparticles decorated graphene nanosheets for visible light driven photocatalytic degradation of organic dyes. Applied Surface Science, 430, 145154. https://doi.org/10.1016/j.apsusc.2017.05.054
Ali, J., Tuzen, M., Kazi, T. G., & Hazer, B. (2016). Inorganic arsenic speciation in water samples by miniaturized solid phase microextraction using a new polystyrene polydimethyl siloxane polymer in micropipette tip of syringe system. Talanta, 161, 450-458. https://doi.org/10.1016/j.talanta.2016.08.075
Ali, K., Dwivedi, S., Azam, A., Saquib, Q., Al-said, M. S., Alkhedhairy, A. A., & Musarrat, J. (2016). Aloe vera extract functionalized zinc oxide nanoparticles as nanoantibiotics against multi-drug resistant clinical bacterial isolates. Journal of Colloid and Interrface Science, 472, 145-156. https://doi.org/10.1016/j.jcis.2016.03.021
Ali, Y., Mehdi, S., & Ghani, M. (2020a). Derived N-doped carbon through core-shell structured metal-organic frameworks as a novel sorbent for dispersive solid phase extraction of Cr ( III ) and Pb ( II ) from water samples followed by quantitation through flame atomic absorption spectrometry. Microchemical Journal, 155, 104786. https://doi.org/10.1016/j.microc.2020.104786
Ali, Y., Mehdi, S., & Ghani, M. (2020b). Derived N-doped carbon through core-shell structured metal-organic frameworks as a novel sorbent for dispersive solid phase extraction of Cr ( III ) and Pb ( II ) from water samples followed by quantitation through flame atomic absorption spectrometry. Microchemical Journal, 155, 104786. https://doi.org/10.1016/j.microc.2020.104786
Alipanahpour Dil, E., Ghaedi, M., Asfaram, A., Mehrabi, F., & Bazrafshan, A. A. (2018). Optimization of process parameters for determination of trace Hazardous dyes from industrial wastewaters based on nanostructures materials under ultrasound energy. Ultrasonics Sonochemistry, 40, 238-248. https://doi.org/10.1016/j.ultsonch.2017.07.022
Allaedini, G., Tasirin, S. M., & Aminayi, P. (2015). Synthesis of Fe-Ni-Ce trimetallic catalyst nanoparticles via impregnation and co-precipitation and their application to dye degradation. Chemical Papers, 70 (2), 231-242. https://doi.org/10.1515/chempap-2015-0190
Amran, M. B., Aminah, S., Rusli, H., & Buchari, B. (2020). Bentonite-based functional material as preconcentration system for determination of chromium species in water by flow injection analysis technique. Heliyon, 6 (5), e04051. https://doi.org/10.1016/j.heliyon.2020.e04051
Anwar, A., Ul Qader, S. A., Raiz, A., Iqbal, S., & Azhar, A. (2009). Calcium alginate : a support material for immobilization of proteases from newly isolated strain of Bacillus subtilis KIBGE-HAS. World Applied Sciences Journal, 7 (10), 12811286.
Aranishi, K., Jiang, H. L., Akita, T., Haruta, M., & Xu, Q. (2011). One-step synthesis of magnetically recyclable Au/Co/Fe triple-layered core-shell nanoparticles as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane. Nano Research, 4 (12), 1233-1241. https://doi.org/10.1007/s12274-011-0174-1
Arbab, P., Ayati, B., & Ansari, M. (2018). Reducing the use of nanotitanium dioxide by switching from single photocatalysis to combined photocatalysis-cavitation in dye elimination. Process Safety and Environmental Protection. https://doi.org/10.1016/j.psep.2018.10.012
Arslan, Z., Oymak, T., & White, J. (2018). Triethylamine-assisted Mg(OH)2 coprecipitation/preconcentration for determination of trace metals and rare earth elements in seawater by inductively coupled plasma mass spectrometry (ICP- MS). Analytica Chimica Acta, 1008, 18-28. https://doi.org/10.1016/j.aca.2018.01.017
Arumugam, J., Dhayal Raj, A., Albert Irudayaraj, A., Thambidurai, M., Raj, Ad., & Irudayaraj, Aa. (2018). Solvothermal synthesis of Bi 2 S 3 nanoparticles and nanorods towards solar cell application. Materials Letters. https://doi.org/10.1016/j.matlet.2018.02.123
Arunadevi, R., Kavitha, B., Rajarajan, M., Suganthi, A., & Jeyamurugan, A. (2018a). Investigation of the drastic improvement of photocatalytic degradation of Congo red by monoclinic Cd, Ba-CuO nanoparticles and its antimicrobial activities. Surfaces and Interfaces, 10, 32-44. https://doi.Org/10.1016/j.surfm.2017.11.004
Asfaram, A., Ghaedi, M., & Goudarzi, A. (2016). Optimization of ultrasound-assisted dispersive solid-phase microextraction based on nanoparticles followed by spectrophotometry for the simultaneous determination of dyes using experimental design. Ultrasonics Sonochemistry, 32, 407-417. https://doi.org/10.1016/j.ultsonch.2016.04.009
Bandeira, M., Possan, A. L., Pavin, S. S., Raota, C. S., Vebber, M. C., Giovanela, M., Roesch-Ely, M., Devine, D. M., & S. Crespo, J. (2020). Mechanism of formation, characterization and cytotoxicity of green synthesized zinc oxide nanoparticles obtained from Ilex paraguariensis leaves extract. Nano-Structures and NanoObjects, 24, 100532. https://doi.org/10.1016/j.nanoso.2020.100532
Baranik, A., Gagor, A., Queralt, I., Margui, E., Sitko, R., & Zawisza, B. (2018). Determination and speciation of ultratrace arsenic and chromium species using aluminium oxide supported on graphene oxide. Talanta, 185, 264-274. https://doi.org/10.1016/j.talanta.2018.03.090
Barciela-Alonso, M. C., Plata-García, V., Rouco-López, A., Moreda-Piñeiro, A., & Bermejo-Barrera, P. (2014). Ionic imprinted polymer based solid phase extraction for cadmium and lead pre-concentration/determination in seafood. Microchemical Journal, 114, 106-110. https://doi.org/10.1016/j.microc.2013.12.008
Basavegowda, N., Mishra, K., & Lee, Y. R. (2017). Trimetallic FeAgPt alloy as a nanocatalyst for the reduction of 4-nitroaniline and decolorization of rhodamine B: A comparative study. Journal of Alloys and Compounds, 701, 456-464. https://doi.org/10.1016/j.jallcom.2017.01.122
Benhammada, A., Trache, D., Kesraoui, M., Tarchoun, A. F., Chelouche, S., & Mezroua, A. (2020). Synthesis and characterization of a-Fe2O3 nanoparticles from different precursors and their catalytic effect on the thermal decomposition of nitrocellulose. Thermochimica Acta, 686, 178570. https://doi.org/10.1016/j.tca.2020.178570
Benzaouak, A., Ellouzi, I., Ouanji, F., Touach, N., Kacimi, M., Ziyad, M., El Mahi, M., & Lofti, E. M. (2018). Photocatalytic degradation of Methylene Blue (MB) dye in aqueous solution by ferroelectric Li1-xTa1-xWxO3materials. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 553, 586-592. https://doi.org/10.1016/j.colsurfa.2018.06.011
Bhagwat, U. O., Wu, J. J., Asiri, A. M., & Anandan, S. (2017). Sonochemical Synthesis of Mg-TiO2nanoparticles for persistent Congo red dye degradation. Journal of Photochemistry and Photobiology A: Chemistry, 346, 559-569. https://doi.org/10.1016/j.jphotochem.2017.06.043
Bhunia, K., Khilari, S., & Pradhan, D. (2017). Trimetallic PtAuNi alloy nanoparticles as an efficient electrocatalyst for the methanol electrooxidation reaction. Dalton Transactions, 46 (44), 15558-15566. https://doi.org/10.1039/C7DT02608K
Bing, X., Jian, X., Chu, J., Li, J., & Guo, C. (2019). Hierarchically porous BiOBr/ZnAl1.8Fe0.2O4and its excellent adsorption and photocatalysis activity. Materials Research Bulletin, 110, 1-12. https://doi.org/10.1016/j.materresbull.2018.10.006
Birajdar, S. D., Bhagwat, V. R., Shinde, A. B., & Jadhav, K. M. (2016). Effect of Co2+ ions on structural, morphological and optical properties of ZnO nanoparticles synthesized by sol-gel auto combustion method. Materials Science in Semiconductor Processing, 41, 441-449. https://doi.org/10.1016/j.mssp.2015.10.002
Bkour, Q., Zhao, K., Scudiero, L., Jung, D., Won, C., Marin-flores, O. G., Norton, M. G., & Ha, S. (2017). Synthesis and performance of ceria-zirconia supported Ni- Mo nanoparticles for partial oxidation of isooctane. Applied Catalysis B: Environmental, 212, 97-105. https://doi.org/10.1016/j.apcatb.2017.04.055
Blanchet-Chouinard, G., & Lariviere, D. (2018). Determination of Pb in environmental samples after cloud point extraction using crown ether. Talanta, 179, 300-306. https://doi.org/10.1016Zj.talanta.2017.11.015
Boudiaf, S., Nasrallah, N., Mellal, M., Belabed, C., Belhamdi, B., Meziani, D., Mehdi, B., & Trari, M. (2020). Synthesis and characterization of semiconductor CoAl2O4 for optical and dielectric studies: Application to photodegradation of organic pollutants under visible light. Optik, 219, 165038. https://doi.org/10.1016/j.ijleo.2020.165038
Bouju, H., Buttiglieri, G., & Malpei, F. (2008). Perspectives of persistent organic pollutants (POPS) removal in an MBR pilot plant. Desalination, 224 (1-3), 1-6. https://doi.org/10.1016/j.desal.2007.04.071
Boutra, B., Guy, N., Ozacar, M., & Trari, M. (2020). Magnetically separable MnFe2O4/TA/ZnO nanocomposites for photocatalytic degradation of Congo Red under visible light. Journal of Magnetism and Magnetic Materials, 497, 165994. https://doi.org/10.1016/j.jmmm.2019.165994
Bozkurt, P. A. (2017). Sonochemical green synthesis of Ag / graphene nanocomposite. Ultrasonics - Sonochemistry, 35, 397-404. https://doi.org/10.1016/j.ultsonch.2016.10.018
Bradha, M., Vijayaraghavan, T., Suriyaraj, S. P., Selvakumar, R., & Ashok, A. M. (2015). Synthesis of photocatalytic La(1-x)AxTiO3.5-6 (A=Ba, Sr, Ca) nano perovskites and their application for photocatalytic oxidation of congo red dye in aqueous solution. Journal of Rare Earths, 33 (2), 160-167. https://doi.org/10.1016/S1002-0721(14)60397-5
Briffa, J., Sinagra, E., & Blundell, R. (2020). Heavy metal pollution in the environment and their toxicological effects on humans. Heliyon, 6, e04691. https://doi.org/10.1016/j.heliyon.2020.e04691
Cai, X.-L., Liu, C.-H., Liu, J., Lu, Y., Zhong, Y.-N., Nie, K.-Q., Xu, J.-L., Gao, X., Sun, X.-H., & Wang, S.-D. (2017). Synergistic Effects in CNTs-PdAu/Pt Trimetallic Nanoparticles with High Electrocatalytic Activity and Stability. Nano-Micro Letters, 9 (4), 48. https://doi.org/10.1007/s40820-017-0149-1
Calderilla, C., Maya, F., Leal, L. O., & Cerdá, V. (2018). Recent advances in flowbased automated solid-phase extraction. TrAC - Trends in Analytical Chemistry, 108, 370-380. https://doi.org/10.1016/j.trac.2018.09.011
Cao, W., Hu, S. S., Ye, L. H., Cao, J., Xu, J. J., & Pang, X. Q. (2015). Trace-chitosan- wrapped multi-walled carbon nanotubes as a new sorbent in dispersive micro solid-phase extraction to determine phenolic compounds. Journal of Chromatography A, 1390, 13-21. https://doi.org/10.1016/j.chroma.2015.02.060
Castilhos, N. D. B., Sampaio, N. M. F. M., da Silva, B. C., Riegel-Vidotti, I. C., Grassi, M. T., & Silva, B. J. G. (2017). Physical-chemical characteristics and potential use of a novel alginate/zein hydrogel as the sorption phase for polar organic compounds. Carbohydrate Polymers, 174, 507-516. https://doi.org/10.1016/j.carbpol.2017.06.079
Chang, M. J., Cui, W. N., Wang, H., Liu, J., Li, H. L., Du, H. L., & Peng, L. G. (2019). Recoverable magnetic CoFe2O4/BiOI nanofibers for efficient visible light photocatalysis. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 562, 127-135. https://doi.org/10.1016/j.colsurfa.2018.11.016
Chen, F., Jiang, X., Zhang, L., Lang, R., & Qiao, B. (2018). Single-atom catalysis: Bridging the homo- and heterogeneous catalysis. Chinese Journal of Catalysis, 39 (5), 893-898. https://doi.org/10.1016/S1872-2067(18) 63047-5
Chen, J., Han, X., Fu, G., Tang, W., Row, K. H., & Qiu, H. (2022). Preparation of magnetic nitrogen-doped porous carbon by incomplete combustion with solvothermal synthesis for magnetic solid-phase extraction of benzoylurea insecticides from environmental water. Journal of Chromatography A, 1685, 463600. https://doi.org/10.1016/j.chroma.2022.463600
Chen, J. R., Chen, J. R., & Su, C. K. (2022). Solution Foaming-Treated 3D-Printed monolithic packing for enhanced solid phase extraction of trace metals. Talanta, 241 (January). https://doi.org/10.1016/j.talanta.2022.123237
Chen, J., Xu, T., Ding, J., Ji, Y., Ni, P., & Li, Z. (2012). Mn - Ce - Co complex oxide nanoparticles : Hydrothermal synthesis and their catalytic subcritical oxidation of 4 , 4 -Dibromobiphenyl. Journal of Hazardous Materials, 235 - 236, 85-91. https://doi.org/10.1016/j.jhazmat.2012.07.013
Cheng, S. I., Rick, J., Pan, C. J., Chou, H. L., Su, W. N., Chen, K. J., Liu, C. C., Yang, Y. W., Wang, C. H., & Hwang, B. J. (2014). Trimetallic (Aurod-Pdshell- Ptcluster) catalyst used as amperometric hydrogen peroxide sensor. Biosensors, 4 (4), 461-471. https://doi.org/10.3390/bios4040461
Chi, J. Q., Yan, K. L., Xiao, Z., Dong, B., Shang, X., Gao, W. K., Li, X., Chai, Y. M., & Liu, C. G. (2017). Trimetallic Ni-Fe-Co selenides nanoparticles supported on carbon fiber cloth as efficient electrocatalyst for oxygen evolution reaction. International Journal of Hydrogen Energy, 42 (32), 20599-20607. https://doi.org/10.1016/j.ijhydene.2017.06.219
Choudhary, B., Chawla, S., Jayanthi, K., Sood, K. N., & Singh, S. (2010). Synthesis and surface modification of ZnO:Cu nanoparticles by silica and PMMA. Current Applied Physics, 10 (3), 807-812. https://doi.org/10.1016/j.cap.2009.09.019
Cruz-Martinez, H., Tellez-Cruz, M. M., Rojas-Chavez, H., Ramirez-Herrera, C. A., Calaminici, P., & Solorza-Feria, O. (2019). NiPdPt trimetallic nanoparticles as efficient electrocatalysts towards the oxygen reduction reaction. International Journal of Hydrogen Energy, 4, 12463-12469. https://doi.org/10.1016/j.ijhydene.2018.07.142
da Silva, A. F. V., Fagundes, A. P., Macuvele, D. L. P., de Carvalho, E. F. U., Durazzo, M., Padoin, N., Soares, C., & Riella, H. G. (2019). Green synthesis of zirconia nanoparticles based on Euclea natalensis plant extract: Optimization of reaction conditions and evaluation of adsorptive properties. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 583, 123915. https://doi.org/10.1016/j.colsurfa.2019.123915
Dahaghin, Z., Mousavi, H. Z., & Sajjadi, S. M. (2017). Trace amounts of Cd ( II ), Cu ( II ) and Pb ( II ) ions monitoring using Fe 3 O 4 @ graphene oxide nanocomposite modi fi ed via 2-mercaptobenzothiazole as a novel and ef fi cient nanosorbent. Journal of Molecular Liquids, 231, 386-395. https://doi.org/10.1016/j.molliq.2017.02.023
Dahman, Y. (2017). Generic Methodologies for Characterization**By Yaser Dahman, Caroline Halim, Oswaldo Matos, and Louisa Chan. Nanotechnology and Functional Materials for Engineers, 1986, 19-45. https://doi.org/10.1016/B978- 0-323-51256-5.00002-2 Darabdhara, G., & Das, M. R. (2018). Bimetallic Au-Pd nanoparticles on 2D supported graphitic carbon nitride and reduced graphene oxide sheets: A comparative photocatalytic degradation study of organic pollutants in water. Chemosphere, 197, 817-829. https://doi.org/10.1016/j.chemosphere.2018.01.073
Darroudi, M., Hoseini, S. J., Kazemi Oskuee, R., Hosseini, H. A., Gholami, L., & Gerayli, S. (2014). Food-directed synthesis of cerium oxide nanoparticles and their neurotoxicity effects. Ceramics International, 40 (5), 7425-7430. https://doi.org/10.1016/j.ceramint.2013.12.089
Devatha, C. P., Thalla, A. K., & Katte, S. Y. (2016). Green synthesis of iron nanoparticles using different leaf extracts for treatment of domestic waste water. Journal of Cleaner Production, 139, 1425-1435. https://doi.org/10.1016/j.jclepro.2016.09.019
Dimpe, K. M., Ngila, J. C., & Nomngongo, P. N. (2018). Preparation and application of a tyre-based activated carbon solid phase extraction of heavy metals in wastewater samples. Physics and Chemistry of the Earth, 105, 161-169. https://doi.org/10.1016/j.pce.2018.02.005
Dodson, J. J., Neal, L. M., & Hagelin-Weaver, H. E. (2011). The influence of ZnO, CeO2 and ZrO2 on nanoparticle-oxide-supported palladium oxide catalysts for the oxidative coupling of 4-methylpyridine. Journal of Molecular Catalysis A: Chemical, 341 (1-2), 42-50. https://doi.org/10.1016/j.molcata.2011.03.022
Du, X., Cai, P., Luo, W., & Cheng, G. (2016). Facile synthesis of P-doped Rh nanoparticles with superior catalytic activity toward dehydrogenation of hydrous hydrazine. International Journal of Hydrogen Energy, 42 (9), 6137-6143. https://doi.org/10.1016/j.ijhydene.2016.12.049
Dubey, R. S., Rajesh, Y. B. R. D., & More, M. A. (2015). Synthesis and Characterization of SiO 2 Nanoparticles via Sol-gel Method for Industrial Applications. Materials Today: Proceedings, 2 (4-5), 3575-3579. https://doi.org/10.1016/j.matpr.2015.07.098
Duta, A., & Visa, M. (2015). Simultaneous removal of two industrial dyes by adsorption and photocatalysis on a fly-ash-TiO2composite. Journal of Photochemistry and Photobiology A: Chemistry, 306, 21-30. https://doi.org/10.1016/j.jphotochem.2015.03.007
Dutta, P. P., Bordoloi, M., Gogoi, K., Roy, S., Narzary, B., Bhattacharyya, D. R., Mohapatra, P. K., & Mazumder, B. (2017). Antimalarial silver and gold nanoparticles: Green synthesis, characterization and in vitro study. Biomedicine & Pharmacotherapy, 91, 567-580. https://doi.org/10.1016/j.biopha.2017.04.032
El-Sheikh, A. H., Nofal, F. S., & Shtaiwi, M. H. (2019). Adsorption and magnetic solid-phase extraction of cadmium and lead using magnetite modified with schiff bases. Journal of Environmental Chemical Engineering, 7 (4), 103229. https://doi.org/10.1016/j.jece.2019.103229
Erdogan, H., Yalginkaya, Ö., & Türker, A. R. (2011). Determination of inorganic arsenic species by hydride generation atomic absorption spectrometry in water samples after preconcentration/separation on nano ZrO2/B2O3 by solid phase extraction. Desalination, 280 (1-3), 391-396. https://doi.org/10.1016/j.desal.2011.07.029
Ezhilarasi, A. A., Vijaya, J. J., Kaviyarasu, K., Maaza, M., Ayeshamariam, A., & Kennedy, L. J. (2016). Green synthesis of NiO nanoparticles using Moringa oleifera extract and their biomedical applications: Cytotoxicity effect of nanoparticles against HT-29 cancer cells. Journal of Photochemistry and Photobiology B: Biology. https://doi.org/10.1016/j.jphotobiol.2016.10.003
Fang, B., Wanjala, B. N., Yin, J., Loukrakpam, R., Luo, J., Hu, X., Last, J., & Zhong, C. J. (2012). Electrocatalytic performance of Pt-based trimetallic alloy nanoparticle catalysts in proton exchange membrane fuel cells. International Journal of Hydrogen Energy, 37 (5), 4627-4632. https://doi.org/10.1016/j.ijhydene.2011.05.066
Fayazi, M., Taher, M. A., Afzali, D., Mostafavi, A., & Ghanei-Motlagh, M. (2016). Synthesis and application of novel ion-imprinted polymer coated magnetic multiwalled carbon nanotubes for selective solid phase extraction of lead(II) ions. Materials Science and Engineering C, 60, 365-373. https://doi.org/10.1016/j.msec.2015.11.060
Fazlzadeh, M., Rahmani, K., Zarei, A., Abdoallahzadeh, H., Nasiri, F., & Khosravi, R. (2017). A novel green synthesis of zero valent iron nanoparticles (NZVI) using three plant extracts and their efficient application for removal of Cr(VI) from aqueous solutions. Advanced Powder Technology, 28 (1), 122-130. https://doi.org/10.1016/j.apt.2016.09.003
Fedorenko, S. V., Mustafina, A. R., Mukhametshina, A. R., Jilkin, M. E., Mukhametzyanov, T. A., Solovieva, A. O., Pozmogova, T. N., Shestopalova, L. V., Shestopalov, M. A., Kholin, K. V., Osin, Y. N., & Sinyashin, O. G. (2017). Cellular imaging by green luminescence of Tb(III)-doped aminomodified silica nanoparticles. Materials Science and Engineering C, 76, 551-558. https://doi.org/10.1016/j.msec.2017.03.106
Fei, Y., Li, Y., Han, S., & Ma, J. (2016). Adsorptive removal of ciprofloxacin by sodium alginate/graphene oxide composite beads from aqueous solution. Journal of Colloid and Interface Science, 484, 196-204. https://doi.org/10.1016/j.jcis.2016.08.068
Fu, J., Li, D., Li, G., Huang, F., & Wei, Q. (2015). Carboxymethyl cellulose assisted immobilization of silver nanoparticles onto cellulose nanofibers for the detection of catechol. Journal of Electroanalytical Chemistry, 738, 92-99. https://doi.org/10.1016/j.jelechem.2014.11.025
Fu, L., Cheng, G., & Luo, W. (2017). Colloidal synthesis of monodisperse trimetallic IrNiFe nanoparticles as highly active bifunctional electrocatalysts for acidic overall water splitting. Journal of Materials Chemistry A, 5 (47), 24836-24841. https://doi.org/10.1039/C7TA08982A
Gan, P. P., & Li, S. F. Y. (2012). Potential of plant as a biological factory to synthesize gold and silver nanoparticles and their applications. In Reviews in Environmental Science and Biotechnology, 11(2), 169-206). https://doi.org/10.1007/s11157- 012-9278-7
Gao, T., Jin, Z., Liao, M., Xiao, J., Yuan, H., & Xiao, D. (2015). A trimetallic V-Co- Fe oxide nanoparticle as an efficient and stable electrocatalyst for oxygen evolution reaction. Journal of Materials Chemistry A, 3 (34), 17763-17770. https://doi.org/10.1039/C5TA04058B
Geetha, P., Latha, M. S., Pillai, S. S., Deepa, B., Santhosh Kumar, K., & Koshy, M. (2016). Green synthesis and characterization of alginate nanoparticles and its role as a biosorbent for Cr(VI) ions. Journal of Molecular Structure, 1105, 54-60. https://doi.org/10.1016/j.molstruc.2015.10.022
Gharagozlou, M., Baradaran, Z., & Bayati, R. (2015). A green chemical method for synthesis of ZnO nanoparticles from solid-state decomposition of Schiff-bases derived from amino acid alanine complexes. Ceramics International, 41 (7), 8382-8387. https://doi.org/10.1016/j.ceramint.2015.03.029
Ghavaminejad, A., Kalantarifard, A., Su, G., & Sang, C. (2016). Microporous and Mesoporous Materials In-situ immobilization of silver nanoparticles on ZSM-5 type zeolite by catechol redox chemistry , a green catalyst for A 3 -coupling reaction. Microporous and Mesoporous Materials, 225, 296-302. https://doi.org/10.1016/j.micromeso.2015.12.050
Ghiaci, M., Aghabarari, B., Botelho Do Rego, A. M., Ferraria, A. M., & Habibollahi, S. (2011). Efficient allylic oxidation of cyclohexene catalyzed by trimetallic hybrid nano-mixed oxide (Ru/Co/Ce). Applied Catalysis A: General, 393 (1-2), 225-230. https://doi.org/10.1016/j.apcata.2010.12.006
Ghodake, G., Deshpande, N., Lee, Y., & Jin, E. (2010). Pear fruit extract-assisted room temperature biosynthesis of gold nanoplates. Colloids and Surfaces B, 75 (2), 584-589.
Gholivand, M. B., Jalalvand, A. R., Goicoechea, H. C., Paimard, G., & Skov, T. (2015). Surface exploration of a room-temperature ionic liquid-chitin composite film decorated with electrochemically deposited PdFeNi trimetallic alloy nanoparticles by pattern recognition: An elegant approach to developing a novel biotin biosensor. Talanta, 131, 249-258. https://doi.org/10.1016/j.talanta.2014.07.040
Ghorbani, M., Aghamohammadhassan, M., Ghorbani, H., & Zabihi, A. (2020). Trends in sorbent development for dispersive micro-solid phase extraction. Microchemical Journal, 158, 105250. https://doi.org/10.1016/j.microc.2020.105250
Gionco, C., Hernández, S., Castellino, M., Gadhi, T. A., Muñoz-Tabares, J. A., Cerrato, E., Tagliaferro, A., Russo, N., & Paganini, M. C. (2019). Synthesis and characterization of Ce and Er doped ZrO2 nanoparticles as solar light driven photocatalysts. Journal of Alloys and Compounds, 775, 896-904. https://doi.org/10.1016/j.jallcom.2018.10.046
Gnanamoorthi, K., Balakrishnan, M., Mariappan, R., & Ranjith Kumar, E. (2015). Effect of Ce doping on microstructural, morphological and optical properties of ZrO2 nanoparticles. Materials Science in Semiconductor Processing, 30, 518526. https://doi.org/10.1016/j.mssp.2014.10.054
Grassi, M., Sandolo, C., Perin, D., Coviello, T., Lapasin, R., & Grassi, G. (2009). Structural characterization of calcium alginate matrices by means of mechanical and release tests. Molecules, 14 (8), 3003-3017. https://doi.org/10.3390/molecules14083003
Guo, H. X., Lin, K. L., Zheng, Z. S., Xiao, F. Bin, & Li, S. X. (2012). Sulfanilic acid- modified P25 TiO2 nanoparticles with improved photocatalytic degradation on Congo red under visible light. Dyes and Pigments, 92 (3), 1278-1284. https://doi.org/10.1016/j.dyepig.2011.09.004
Guy, N., & Ozacar, M. (2016). The influence of noble metals on photocatalytic activity of ZnO for Congo red degradation. International Journal of Hydrogen Energy, 41 (44), 20100-20112. https://doi.org/10.1016/j.ijhydene.2016.07.063
Hagiwara, K., Koike, Y., Aizawa, M., & Nakamura, T. (2015). On-site quantitation of arsenic in drinking water by disk solid-phase extraction/mobile X-ray fluorescence spectrometry. Talanta, 144, 788-792. https://doi.org/10.1016/j.talanta.2015.07.002
Haik, M. Y., Ayesh, A. I., Abdulrehman, T., & Haik, Y. (2014). Novel organic memory devices using Au-Pt-Ag nanoparticles as charge storage elements. Materials Letters, 124, 67-72. https://doi.org/10.1016/j.matlet.2014.03.070
Hakova, M., Chocholousova Havlikova, L., Solich, P., Svec, F., & Satinsky, D. (2019). Electrospun nanofiber polymers as extraction phases in analytical chemistry -
The advances of the last decade. TrAC - Trends in Analytical Chemistry, 110, 81 96. https://doi.org/10.1016/j.trac.2018.10.030
Halonen, N., Sapi, A., Nagy, L., Puskas, R., Leino, A. R., Maklin, J., Kukkola, J., Toth, G., Wu, M. C., Liao, H. C., Su, W. F., Shchukarev, A., Mikkola, J. P., Kukovecz, A., Konya, Z., & Kordas, K. (2011). Low-temperature growth of multi-walled carbon nanotubes by thermal CVD. Physica Status Solidi (B) Basic Research, 248 (11), 2500-2503. https://doi.org/10.1002/pssb.201100137
Han, L., Sapozhnikova, Y., & Lehotay, S. J. (2014). Streamlined sample cleanup using combined dispersive solid-phase extraction and in-vial filtration for analysis of pesticides and environmental pollutants in shrimp. Analytica Chimica Acta. https://doi.org/10.1016/j.aca.2014.04.005
Hapeshi, E., Achilleos, A., Vasquez, M. I., Michael, C., Xekoukoulotakis, N. P., Mantzavinos, D., & Kassinos, D. (2010). Drugs degrading photocatalytically: Kinetics and mechanisms of ofloxacin and atenolol removal on titania suspensions. Water Research, 44 (6), 1737-1746. https://doi.org/10.1016/j.watres.2009.11.044
He, M., Huang, L., Zhao, B., Chen, B., & Hu, B. (2017). Advanced functional materials in solid phase extraction for ICP-MS determination of trace elements and their species - A review. Analytica Chimica Acta, 973, 1-24. https://doi.org/10.1016/j.aca.2017.03.047
Hemraj-Benny, T., Tobar, N., Carrero, N., Sumner, R., Pimentel, L., & Emeran, G. (2018). Microwave-assisted synthesis of single-walled carbon nanotube- supported ruthenium nanoparticles for the catalytic degradation of Congo red dye. Materials Chemistry and Physics, 216, 72-81. https://doi.org/10.1016/j.matchemphys.2018.05.081
Henríquez-Hernández, L. A., Luzardo, O. P., Boada, L. D., Carranza, C., Pérez Arellano, J. L., González-Antuña, A., Almeida-González, M., Barry-Rodríguez, C., Zumbado, M., & Camacho, M. (2017). Study of the influencing factors of the blood levels of toxic elements in Africans from 16 countries. Environmental Pollution, 230, 817-828. https://doi.org/10.1016/j.envpol.2017.07.036
Hu, S., Munoz, F., Noborikawa, J., Haan, J., Scudiero, L., & Ha, S. (2016). Carbon supported Pd-based bimetallic and trimetallic catalyst for formic acid electrochemical oxidation. Applied Catalysis B: Environmental, 180, 758-765. https://doi.org/10.1016/j.apcatb.2015.07.023
Huang, C., Jiang, Z., & Hu, B. (2007). Mesoporous titanium dioxide as a novel solidphase extraction material for flow injection micro-column preconcentration online coupled with ICP-OES determination of trace metals in environmental samples. Talanta, 73 (2), 274-281. https://doi.org/10.1016/j.talanta.2007.03.046
Huang, X., Yang, J., Wang, J., Bi, J., Xie, C., & Hao, H. (2018). Design and synthesis of core-shell Fe3O4@PTMT composite magnetic microspheres for adsorption of heavy metals from high salinity wastewater. Chemosphere, 206, 513-521. https://doi.org/10.1016/j.chemosphere.2018.04.184
Huerta-Aguilar, C. A., Palos-Barba, V., Thangarasu, P., & Koodali, R. T. (2018). Visible light driven photo-degradation of Congo red by TiO2-ZnO/Ag: DFT approach on synergetic effect on band gap energy. Chemosphere, 213, 481-497. https://doi.org/10.1016/j.chemosphere.2018.09.053
Jaime-Acuna, O. E., Villavicencio, H., Petranovskii, V., & Raymond-Herrera, O. (2016). Disperse orange 30 dye degradation by assisted plasmonic photocatalysis using Ag-CdZnSO/zeolitic matrix nanocomposites. Catalysis Communications, 75, 103-107. https://doi.org/10.1016/j.catcom.2015.11.009
Jassal, V., Shanker, U., & Gahlot, S. (2016). Green synthesis of some iron oxide nanoparticles and their interaction with 2-Amino, 3-Amino and 4- Aminopyridines. Materials Today: Proceedings, 3 (6), 1874-1882. https://doi.org/10.1016/j.matpr.2016.04.087
Jayachandraiah, C., Krishnaiah, G., & Siva Kumar, K. (2014). Ce induced structural and optical properties of Ce doped Zno nanoparticles. International Journal of ChemTech Research, 6 (6), 3378-3381.
Jia, X., Zhao, P., Ye, X., Zhang, L., Wang, T., Chen, Q., & Hou, X. (2017). A novel metal-organic framework composite MIL-101(Cr)@GO as an efficient sorbent in dispersive micro-solid phase extraction coupling with UHPLC-MS/MS for the determination of sulfonamides in milk samples. Talanta, 169, 227-238. https://doi.org/10.1016/j.talanta.2016.08.086
Joshy, K. S., Susan, M. A., Snigdha, S., Nandakumar, K., Laly, A. P., & Sabu, T. (2018). Encapsulation of zidovudine in PF-68 coated alginate conjugate nanoparticles for anti-HIV drug delivery. International Journal of Biological Macromolecules, 107 (PartA), 929-937. https://doi.org/10.1016/j.ijbiomac.2017.09.078
Jung, E., & Baek, K. (2015). Enhanced reductive extraction of arsenic from contaminated soils by a combination of dithionite and oxalate. Journal of Hazardous Materials, 284, 19-26. https://doi.org/10.1016/j.jhazmat.2014.11.004
Kafashan, H. (2019). Optoelectronic properties of In-doped SnS thin films. Ceramics International, 45 (1), 334-345. https://doi.org/10.1016/j.ceramint.2018.09.172
Kang, S. W., Lee, Y. W., Park, Y., Choi, B.-S., Hong, J. W., Park, K.-H., & Han, S. W. (2013). One-Pot Synthesis of Trimetallic Au@PdPt Core-Shell Nanoparticles with High Catalytic Performance. ACS Nano, 7 (9), 7945-7955. https://doi.org/10.1021/nn403027j
Kant, S., Pathania, D., Singh, P., Dhiman, P., & Kumar, A. (2014). Removal of malachite green and methylene blue by Fe0.01Ni0.01Zn0.98O/polyacrylamide nanocomposite using coupled adsorption and photocatalysis. Applied Catalysis B: Environmental, 147, 340-352. https://doi.org/10.1016/j.apcatb.2013.09.001
Karimi, M., Dadfarnia, S., Shabani, A. M. H., Tamaddon, F., & Azadi, D. (2015). Deep eutectic liquid organic salt as a new solvent for liquid-phase microextraction and its application in ligandless extraction and preconcentraion of lead and cadmium in edible oils. Talanta, 144, 648-654. https://doi.org/10.1016/j.talanta.2015.07.021
Karthikeyan, B., & Loganathan, B. (2012). Strategic green synthesis and characterization of Au/Pt/Ag trimetallic nanocomposites. Materials Letters, 85, 53-56. https://doi.org/10.1016/j.matlet.2012.06.070
Kasa, N. A., Sel, S., Chormey, D. S., & Bakirdere, S. (2019). Determination of cadmium at trace levels in parsley samples by slotted quartz tube-flame atomic absorption spectrometry after preconcentration with cloud point extraction. Measurement, 147, 106841. https://doi.org/10.1016/j.measurement.2019.07.069
Khorsand Zak, A., Ghanbari, A., & ShekoftehNarm, T. (2017). The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet-Visible region. Advanced Powder Technology, 28 (11), 2980-2986. https://doi.org/10.1016/j.apt.2017.09.006
Kim, S. R., Ali, I., & Kim, J. O. (2017). Electrochemical synthesis of co-doped RGO- Bi-TiO2nanotube composite: Enhanced activity under visible light. Journal of Industrial and Engineering Chemistry, 54, 316-323. https://doi.org/10.1016/j.jiec.2017.06.006
Kog, M. M., Aslan, N., Erkovan, M., Aksakal, B., Uzun, O., Farooq, W. A., & Yakuphanoglu, F. (2019). Electrical characterization of solar sensitive zinc oxide doped-amorphous carbon photodiode. Optik, 178, 316-326. https://doi.org/10.1016/j.ijleo.2018.10.008
Krawczyk, M., & Jeszka-skowron, M. (2016). Multiwalled carbon nanotubes as solid sorbent in dispersive micro solid-phase extraction for the sequential determination of cadmium and lead in water samples. Microchemical Journal, 126, 296-301. https://doi.org/10.1016/j.microc.2015.12.027
Krishnan, A., Beena, S., & Chandran, M. (2019). ScienceDirect Fabrication and evaluation of CeO 2 -Fe 2 O 3 mixed oxide for hydrogen evolution by photo water splitting reaction under visible light irradiation. Materials Today: Proceedings, 18, 4968-4976. https://doi.org/10.1016/j.matpr.2019.07.489
Krukowska, A., Trykowski, G., Winiarski, M. J., Klimczuk, T., Lisowski, W., Mikolajczyk, A., Pinto, H. P., & Zaleska-Medynska, A. (2018). Mono- and bimetallic nanoparticles decorated KTaO3photocatalysts with improved Vis and UV-Vis light activity. Applied Surface Science, 441, 993-1011. https://doi.org/10.1016/j.apsusc.2018.02.077
Kumar, N., Sheo, L., & Upadhyay, B. (2016). Facile and green synthesis of highly stable l -cysteine functionalized copper nanoparticles. Applied Surface Science, 385, 225-233. https://doi.org/10.1016/j.apsusc.2016.05.125
Kumar, N., & Upadhyay, L. S. B. (2016). Facile and green synthesis of highly stable L-cysteine functionalized copper nanoparticles. Applied Surface Science, 385, 225-233. https://doi.org/10.1016Zj.apsusc.2016.05.125
Kumari, P., & Meena, A. (2020). Green synthesis of gold nanoparticles from Lawsoniainermis and its catalytic activities following the Langmuir- Hinshelwood mechanism. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 606, 125447. https://doi.org/10.1016/j.colsurfa.2020.125447
Kuzmanoski, A., Pankratov, V., & Feldmann, C. (2016). Energy transfer of the quantum-cutter couple Pr -Mn 2 p in CaF 2 :Pr 3 p , Mn 2 p nanoparticles. Journal of Luminescence, 179, 555-561. https://doi.org/10.1016/j.jlumin.2016.07.040
Larosa, C., Salerno, M., de Lima, J. S., Merijs Meri, R., da Silva, M. F., de Carvalho, L. B., & Converti, A. (2018). Characterisation of bare and tannase-loaded calcium alginate beads by microscopic, thermogravimetric, FTIR and XRD analyses. International Journal of Biological Macromolecules, 115, 900-906. https://doi.org/10.1016/j.ijbiomac.2018.04.138
Lee, J., Li, P., Choi, C., & Dong, X. (2010). Synthesis of Mn - Al alloy nanoparticles by plasma arc discharge. 519, 81-85. https://doi.org/10.1016/j.tsf.2010.07.063
Li, H., Zhao, Y., Yin, C., Jiao, L., & Ding, L. (2019). WO 3 nanocrystal prepared by self-assembly of phosphotungstic acid and dopamine for photocatalytic degradation of Congo red. Colloids and Surfaces A: Physicochemical and
Engineering Aspects, 572, 147-151. https://doi.org/10.1016/j.colsurfa.2019.03.092
Li, L., Huang, Y., Wang, Y., & Wang, W. (2009). Hemimicelle capped functionalized carbon nanotubes-based nanosized solid-phase extraction of arsenic from environmental water samples. Analytica Chimica Acta, 631 (2), 182-188. https://doi.org/10.1016/j.aca.2008.10.043
Li, L., Wang, Z., Zhang, S., & Wang, M. (2017). Directly-thiolated graphene based organic solvent-free cloud point extraction-like method for enrichment and speciation of mercury by HPLC-ICP-MS. Microchemical Journal, 132, 299-307. https://doi.org/10.1016/j.microc.2017.02.011
Li, M., Wang, P., Pei, F., Yu, H., Dong, Y., Li, Y., Liu, Q., & Chen, P. (2018). A novel signal amplification system fabricated immunosensor based on Au nanoparticles and mesoporous trimetallic PdPtCu nanospheres for sensitive detection of prostate specific antigen. Sensors and Actuators, B: Chemical, 261, 22-30. https://doi.org/10.1016/j.snb.2018.01.136
Li, W., Zhao, W., Zhou, X., Su, L., Zhang, H., Lu, L., & Zhang, S. (2014). Fabrication and catalytic activity of Pt/Ni/Fe trimetallic nanoparticles for hydrogen generation from NaBH. Gaodeng Xuexiao Huaxue Xuebao/Chemical Journal of Chinese Universities, 35 (10). https://doi.org/10.7503/cjcu20140362
Lian, X., Li, Y., Tong, X., Zou, Y., Liu, X., An, D., & Wang, Q. (2017). Synthesis of Ce-doped SnO2nanoparticles and their acetone gas sensing properties. Applied Surface Science, 407, 447-455. https://doi.Org/10.1016/j.apsusc.2017.02.228
Liang, R., Luo, S., Jing, F., Shen, L., Qin, N., & Wu, L. (2015). A simple strategy for fabrication of Pd@MIL-100(Fe) nanocomposite as a visible-light-driven photocatalyst for the treatment of pharmaceuticals and personal care products (PPCPs). Applied Catalysis B: Environmental, 176 - 177, 240-248. https://doi.org/10.1016/j.apcatb.2015.04.009
Liang, Z., Xiao, X., Yu, X., Huang, X., Jiang, Y., Fan, X., & Chen, L. (2018b). Nonnoble trimetallic Cu-Ni-Co nanoparticles supported on metal-organic frameworks as highly efficient catalysts for hydrolysis of ammonia borane. Journal of Alloys and Compounds, 741, 501-508. https://doi.org/10.1016/j.jallcom.2017.12.151
Lima, E. C., Dotto, G. L., Federal, U., & Maria, D. S. (2018). Adsorption Of Reactive Red 141 Using Corn Stover Modified With Adsorption Of Reactive Red 141 Using Corn Stover Modified With 3 - Aminopropyltriethoxysilane.
Lin, M., Kim, G. H., Kim, J. H., Oh, J. W., & Nam, J. M. (2017). Transformative Heterointerface Evolution and Plasmonic Tuning of Anisotropic Trimetallic Nanoparticles. Journal of the American Chemical Society, 139 (30), 1018010183. https://doi.org/10.1021/jacs.7b04202
Liu, G., Ping, L., & Li, H. (2007). C-H---O hydrogen bond in chloroform-triformylmethane complex: Blue-shifted or red-shifted? Spectrochimica Acta -
Part A: Molecular and Biomolecular Spectroscopy, 66 (3), 643-645. https://doi.org/10.1016/j.saa.2006.04.004
Lobiak, E. V, Shlyakhova, E. V, Bulusheva, L. G., Plyusnin, P. E., Shubin, Y. V, & Okotrub, A. V. (2015). Ni - Mo and Co - Mo alloy nanoparticles for catalytic chemical vapor deposition synthesis of carbon nanotubes. JOURNAL OF
ALLOYS AND COMPOUNDS, 621, 351-356. https://doi.org/10.1016/j.jallcom.2014.09.220
Lokanathan, M., Patil, I. M., Navaneethan, M., Parey, V., Thapa, R., & Kakade, B. (2018). Designing of stable and highly efficient ordered Pt2CoNi ternary alloy electrocatalyst: The origin of dioxygen reduction activity. Nano Energy, 43, 219227. https://doi.org/10.1016/j.nanoen.2017.11.041
Lopez-Garcia, I., Marin-Hernandez, J. J., & Hernandez-Cordoba, M. (2018). Magnetic ferrite particles combined with electrothermal atomic absorption spectrometry for the speciation of low concentrations of arsenic. Talanta, 181, 6-12. https://doi.org/10.1016/j.talanta.2017.12.086
Luo, F., Yang, D., Chen, Z., Megharaj, M., & Naidu, R. (2016). One-step green synthesis of bimetallic Fe/Pd nanoparticles used to degrade Orange II. Journal of Hazardous Materials, 303, 145-153. https://doi.org/10.1016/j.jhazmat.2015.10.034
Lv, X., Jiang, G., Xue, X., Wu, D., Sheng, T., Sun, C., & Xu, X. (2013). Fe0-Fe3O4 nanocomposites embedded polyvinyl alcohol/sodium alginate beads for chromium (VI) removal. Journal of Hazardous Materials, 262, 748-758. https://doi.org/10.1016/j.jhazmat.2013.09.036
Ma, C., Wang, F., Zhang, C., Yu, Z., Wei, J., Yang, Z., Li, Y., Li, Z., Zhu, M., Shen, L., & Zeng, G. (2017). Photocatalytic decomposition of Congo red under visible light irradiation using MgZnCr-TiO2 layered double hydroxide. Chemosphere, 168, 80-90. https://doi.org/10.1016/j.chemosphere.2016.10.063
Ma, H., Zhang, X., Li, X., Li, R., Du, B., & Wei, Q. (2015). Electrochemical immunosensor for detecting typical bladder cancer biomarker based on reduced graphene oxide-tetraethylene pentamine and trimetallic AuPdPt nanoparticles. Talanta, 143, 77-82. https://doi.org/10.1016/j.talanta.2015.05.029
Ma, J., Wang, J., Zhang, G., Fan, X., Zhang, G., Zhang, F., & Li, Y. (2015). Deoxyribonucleic acid-directed growth of well dispersed nickel-palladium- platinum nanoclusters on graphene as an efficient catalyst for ethanol electrooxidation. Journal of Power Sources, 278, 43-49. https://doi.org/10.1016/j.jpowsour.2014.12.040
Machalova, K., Straska, J., Krizek, M., & Tucek, J. (2013). Formation of zero-valent iron nanoparticles mediated by amino acids. Procedia Environmental Sciences, 18, 809-817. https://doi.org/10.1016/j.proenv.2013.04.109
Madan, S., Shaw, R., Tiwari, S., & Tiwari, S. K. (2019). Adsorption dynamics of Congo red dye removal using ZnO functionalized high silica zeolitic particles. Applied Surface Science, 487, 907-917. https://doi.org/10.1016/j.apsusc.2019.04.273
Magoda, C., Nomngongo, P. N., & Mabuba, N. (2016). Magnetic iron - cobalt / silica nanocomposite as adsorbent in micro solid-phase extraction for preconcentration of arsenic in environmental samples. Microchemical Journal, 128, 242-247. https://doi.org/10.1016/j.microc.2016.05.005
Mahamadi, C., & Madocha, B. (2013). Adsorptive Removal of Ni(II) from Water Using Alginate-Fixed Water Hyacinth: Effect of Organic Substances. American Journal of Analytical Chemistry, 04 (08), 373-378. https://doi.org/10.4236/ajac.2013.48047
Mahdavi, M., Namvar, F., Ahmad, M. Bin, & Mohamad, R. (2013). Green biosynthesis and characterization of magnetic iron oxide (Te:O.i) nanoparticles using seaweed (Sargassum muticum) aqueous extract. Molecules, 18, 5954-5964. https://doi.org/10.3390/molecules18055954
Maldonado-larios, L., Mayen-mondragón, R., Martínez-orozco, R. D., & Páramo- garcía, U. (2020). Electrochemically-assisted fabrication of titanium-dioxide / polyaniline nanocomposite fi lms for the electroremediation of congo red in aqueous e ffl uents. Synthetic Metals, 268, 116464. https://doi.org/10.1016/j.synthmet.2020.116464
Mallard, I., Stade, L. W., Ruellan, S., Jacobsen, P. A. L., Larsen, K. L., & Fourmentin, S. (2015). Synthesis, characterization and sorption capacities toward organic pollutants of new P-cyclodextrin modified zeolite derivatives. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 482, 50-57. https://doi.org/10.1016/j.colsurfa.2015.04.014
Mandal, S., Senthil Kumar, S., Krishnamoorthy, B., & Basu, S. K. (2010). Development and evaluation of calcium alginate beads prepared by sequential and simultaneous methods. Brazilian Journal ofPharmaceutical Sciences, 46 (4), 785-793. https://doi.org/10.1590/S1984-82502010000400021
Mangla, O., & Roy, S. (2018). Monoclinic Zirconium Oxide Nanostructures Having Tunable Band Gap Synthesized under Extremely Non-Equilibrium Plasma Conditions. Proceedings, 3 (1), 10. https://doi.org/10.3390/iocn_2018-1-05486
Maranata, G. J., Surya, N. O., & Hasanah, A. N. (2021). Optimising factors affecting solid phase extraction performances of molecular imprinted polymer as recent sample preparation technique. Heliyon, 7 (1), e05934. https://doi.org/10.1016/j.heliyon.2021.e05934
Martinez-Hurtado, J. L. (2011). Metallic Nanoparticle Block Copoloymer Vesicles with Enhanced Optical Properties. Nanomaterials, 1 (1), 20-30. https://doi.org/10.3390/nano1010020
Martínez, C., Vilariño, S., Fernández, M. I., Faria, J., Canle, M. L., & Santaballa, J. A.
(2013). Mechanism of degradation of ketoprofen by heterogeneous
photocatalysis in aqueous solution. Applied Catalysis B: Environmental, 142 -
143, 633-646. https://doi.org/10.1016Zj.apcatb.2013.05.018
Matin, M. A., Jang, J. H., & Kwon, Y. U. (2014). One-pot sonication-assisted polyol synthesis of trimetallic core-shell (Pd,Co)@Pt nanoparticles for enhanced electrocatalysis. International Journal of Hydrogen Energy, 39 (8), 3710-3718. https://doi.org/10.1016/j.ijhydene.2013.12.137
Matinise, N., Fuku, X. G., Kaviyarasu, K., Mayedwa, N., & Maaza, M. (2017). ZnO nanoparticles via Moringa oleifera green synthesis: Physical properties & mechanism of formation. Applied Surface Science, 406, 339-347. https://doi.org/10.1016/j.apsusc.2017.01.219
Meng, X., Yang, L., Cao, N., Du, C., Hu, K., Su, J., Luo, W., & Cheng, G. (2014). Graphene-supported trimetallic core-shell Cu@CoNi nanoparticles for catalytic hydrolysis of amine borane. ChemPlusChem, 79 (2), 325-332. https://doi.org/10.1002/cplu.201300336
Mersian, H., Alizadeh, M., & Hadi, N. (2018). Synthesis of zirconium doped copper oxide ( CuO ) nanoparticles by the Pechini route and investigation of their structural and antibacterial properties. Ceramics International, 44 (16), 2039920408. https://doi.org/10.1016/j.ceramint.2018.08.033
Mihir, H., & Siddhivinayak, B. (2015). Calcination and Microwave Assisted
Biological Synthesis of Iron Oxide Nanoparticles and Comparative Efficiency
Studies for Domestic Wastewater Treatment. 4 (6), 28-36.
Mishra, K., Basavegowda, N., & Lee, Y. R. (2015). AuFeAg hybrid nanoparticles as an efficient recyclable catalyst for the synthesis of a,ß- and ß,ß-dichloroenones. Applied Catalysis A: General, 506, 180-187. https://doi.org/10.1016/j.apcata.2015.09.014
Mishra, P. K., & Rai, P. K. (2018). Ultrafast removal of arsenic using solid solution of aero-gel based Ce1-XTixO2-Y oxide nanoparticles. Chemosphere, 217, 483-495. https://doi.org/10.1016/j.chemosphere.2018.11.003
Mittal, A. K., Chisti, Y., & Banerjee, U. C. (2013). Synthesis of metallic nanoparticles using plant extracts. In Biotechnology Advances (Vol. 31, Issue 2, pp. 346-356). Elsevier Inc. https://doi.org/10.1016/j.biotechadv.2013.01.003
Mittal, J., Batra, A., Singh, A., & Sharma, M. M. (2014). Phytofabrication of nanoparticles through plant as nanofactories. Advances in Natural Sciences: Nanoscience and Nanotechnology, 5 (4). https://doi.org/10.1088/2043-6262/5/4/043002
Mittal, M., Sharma, M., & Pandey, O. P. (2014). UV-Visible light induced photocatalytic studies of Cu doped ZnO nanoparticles prepared by coprecipitation method. Solar Energy, 110, 386-397. https://doi.org/10.1016/j.solener.2014.09.026
Mohammadi, A., & Veisi, P. (2018). High adsorption performance of P-cyclodextrin- functionalized multi-walled carbon nanotubes for the removal of organic dyes from water and industrial wastewater. Journal of Environmental Chemical Engineering, 6 (4), 4634-4643. https://doi.org/10.1016/jjece.2018.07.002
Mohan, S., Oluwafemi, O. S., Kalarikkal, N., & Thomas, S. (2015). Antibacterial and Sensing Properties of Dextrose Reduced Starch-Capped Silver Nanoparticles Synthesised via a Completely Green Method. Materials Today: Proceedings, 2 (7), 3943-3949. https://doi.org/10.1016/j.matpr.2015.08.023
Mohanan, D., Sumina, N. B., Thomas, R. T., Mohamed, A. P., Hareesh, U. S., Ray, A. K., & Pillai, S. (2019). Cucurbit[7]uril encapsulated dye-sensitized enhanced solar photocatalysis using positively charged sheet-like anatase TiO2 mesocrystals. Applied Surface Science, 488, 911-920. https://doi.org/10.1016/j.apsusc.2019.05.323
Molaei, K., Bagheri, H., Asgharinezhad, A. A., Ebrahimzadeh, H., & Shamsipur, M. (2017). SiO2-coated magnetic graphene oxide modified with polypyrrolepolythiophene: A novel and efficient nanocomposite for solid phase extraction of trace amounts of heavy metals. Talanta, 167, 607-616. https://doi.org/10.1016/j.talanta.2017.02.066
Monier, M., Shafik, A. L., & Abdel-Latif, D. A. (2018). Surface molecularly imprinted amino-functionalized alginate microspheres for enantio-selective extraction of L- https://doi.org/10.1016/j.carbpol.2018.04.106
Mourdikoudis, S., & Pallares, R. M. (2018). Characterization techniques for nanoparticles: comparison and complementarity upon studying. 12871-12934. https://doi.org/10.1039/c8nr02278j
Muchanyereyi-Mukaratirwa, N., Moyo, J. N., Nyoni, S., & Cexton, M. (2017). Synthesis of silver nanoparticles using wild Cucumis anguria: Characterization and antibacterial activity. African Journal of Biotechnology, 16 (38), 1911-1921. https://doi.org/10.5897/ajb2017.16076
Munonde, T. S., Maxakato, N. W., & Nomngongo, P. N. (2018). Preparation of magnetic Fe3O4nanocomposites modified with MnO2, Al2O3, Au and their application for preconcentration of arsenic in river water samples. Journal of Environmental Chemical Engineering, 6 (2), 1673-1681. https://doi.org/10.1016/j.jece.2018.02.017
Muradov, M. B., Balayeva, O. O., Azizov, A. A., Maharramov, A. M., Qahramanli, L. R., Eyvazova, G. M., & Aghamaliyev, Z. A. (2018). Infrared Physics & Technology Synthesis and characterization of cobalt sulfide nanoparticles by sonochemical method. Infrared Physics and Technology, 89, 255-262. https://doi.org/10.1016/j.infrared.2018.01.014
Muruganandam, S., Anbalagan, G., & Murugadoss, G. (2017). Structural, electrochemical and magnetic properties of codoped (Cu, Mn) CdS nanoparticles with surfactant PVP. Optik. https://doi.org/10.1016/j.ijleo.2016.12.001
Mystrioti, C., Xenidis, A., & Papassiopi, N. (2014). Application of Iron Nanoparticles Synthesized by Green Tea for the Removal of Hexavalent Chromium in Column Tests. Journal of Geoscience and Enviromental Protection, 28-36.
Najafi, N. M., Eidizadeh, M., Seidi, S., Ghasemi, E., & Alizadeh, R. (2009). Developing electrodeposition techniques for preconcentration of ultra-traces of Ni , Cr and Pb prior to arc-atomic emission spectrometry determination. Microchemical Journal, 93 (2), 159-163. https://doi.org/10.1016/j.microc.2009.06.004
Namdarian, A., Goljanian Tabrizi, A., Arsalani, N., Khataee, A., & Mohammadi, A. (2020). Synthesis of PANi nanoarrays anchored on 2D BiOCl nanoplates for photodegradation of Congo Red in visible light region. Journal of Industrial and Engineering Chemistry, 81, 228-236. https://doi.org/10.1016/j.jiec.2019.09.012
Nan, M., Lei, S., Jin, B., Saint, C., & Chow, C. W. K. (2009). Optimisation of an annular photoreactor process for degradation of Congo Red using a newly synthesized titania impregnated kaolinite nano-photocatalyst. Separation and Purification Technology, 67 (3), 355-363. https://doi.org/10.1016/j.seppur.2009.04.001
Nanta, P., Kasemwong, K., & Skolpap, W. (2018). Isotherm and kinetic modeling on superparamagnetic nanoparticles adsorption of polysaccharide. Journal of https://doi.org/10.1016/j.jece.2017.12.063
Nasrollahzadeh, M., Mohammad Sajadi, S., Rostami-Vartooni, A., Alizadeh, M., & Bagherzadeh, M. (2016). Green synthesis of the Pd nanoparticles supported on reduced graphene oxide using barberry fruit extract and its application as a recyclable and heterogeneous catalyst for the reduction of nitroarenes. Journal of Colloid and Interface Science, 466, 360-368. https://doi.org/10.1016/j.jcis.2015.12.036
Nasrollahzadeh, M., Sajadi, S. M., & Hatamifard, A. (2015). Anthemis xylopoda flowers aqueous extract assisted in situ green synthesis of Cu nanoparticles supported on natural Natrolite zeolite for N-formylation of amines at room temperature under environmentally benign reaction conditions. Journal of Colloid and Interface Science, 460, 146-153. https://doi.org/10.1016/j.jcis.2015.08.040
Nassar, M. Y., Amin, A. S., Ahmed, I. S., & Abdallah, S. (2016). Sphere-like Mn2O3nanoparticles: Facile hydrothermal synthesis and adsorption properties. Journal of the Taiwan Institute of Chemical Engineers. https://doi.org/10.1016/j.jtice.2016.03.041
Nekouei, S., Nekouei, F., Tyagi, I., Agarwal, S., & Gupta, V. K. (2016). Mixed cloud point/solid phase extraction of lead(II) and cadmium(II) in water samples using modified-ZnO nanopowders. Process Safety and Environmental Protection,
99 (li), 175-185. https://doi.org/10.1016Zj.psep.2015.11.005
Ngulube, T., Ray, J., Masindi, V., & Maity, A. (2016). An update on synthetic dyes adsorption onto clay based minerals: A state-of- art review An update on synthetic dyes adsorption onto clay based minerals : A state-of-art review. Journal of Environmental Management, 191, 35-57. https://doi.org/10.1016/j.jenvman.2016.12.031
Nishikawa, E., Gurgel, M., Gurgel, M., & Vieira, A. (2018). Cadmium biosorption by alginate extraction waste and process overview in Life cycle assessment context. Journal of Cleaner Production, 178, 166-175. https://doi.org/10.1016/j.jclepro.2018.01.025
Nodehi, R., Shayesteh, H., & Kelishami, A. R. (2020). Enhanced adsorption of congo red using cationic surfactant functionalized zeolite particles. Microchemical Journal, 153, 104281. https://doi.org/10.1016/j.microc.2019.104281
Nordmeier, A., Woolford, J., Celeste, L., & Chidambaram, D. (2017). Sustainable batch production of biosynthesized nanoparticles. Materials Letters, 191, 53-56. https://doi.org/10.1016/j.matlet.2017.01.032
O’Sullivan, J. E., Watson, R. J., & Butler, E. C. V. (2013). An ICP-MS procedure to determine Cd, Co, Cu, Ni, Pb and Zn in oceanic waters using in-line flowinjection with solid-phase extraction for preconcentration. Talanta, 115, 9991010. https://doi.org/10.1016/j.talanta.2013.06.054
Omer, K. M., Tofiq, D. I., & Ghafoor, D. D. (2019). Highly photoluminescent label free probe for Chromium (II) ions using carbon quantum dots co-doped with nitrogen and phosphorous. Journal of Luminescence, 206, 540-546. https://doi.org/10.1016/j.jlumin.2018.10.100
Ota, A., Istenic, K., Skrt, M., Segatin, N., Znidarsic, N., Kogej, K., & Ulrih, N. P. (2018). Encapsulation of pantothenic acid into liposomes and into alginate or alginate-pectin microparticles loaded with liposomes. Journal of Food Engineering, 229, 21-31. https://doi.org/10.1016/j.jfoodeng.2017.06.036
Oualid, H. A., Essamlali, Y., Amadine, O., Daanoun, K., & Zahouily, M. (2017). Green synthesis of Ag/ZnO nanohybrid using sodium alginate gelation method. Ceramics International, 43 (16), 13786-13790. https://doi.org/10.1016/j.ceramint.2017.07.097
Özdemir, S., Kiling, E., Okumus, V., Poli, A., Nicolaus, B., & Romano, I. (2016). Thermophilic Geobacillus galactosidasius sp. nov. loaded Y—Fe2O3 magnetic nanoparticle for the preconcentrations of Pb and Cd. Bioresource Technology, 201, 269-275. https://doi.org/10.1016/j.biortech.2015.11.052
Özzeybek, G., §ahin, i., Erarpat, S., & Bakirdere, S. (2020). Reverse phase dispersive liquid-liquid microextraction coupled to slotted quartz tube flame atomic absorption spectrometry as a new analytical strategy for trace determination of cadmium in fish and olive oil samples. Journal of Food Composition and Analysis, 90. https://doi.org/10.1016/j.jfca.2020.103486
Pallela, P. N. V. K., Ummey, S., Ruddaraju, L. K., Gadi, S., Cherukuri, C. S. L., Barla, S., & Pammi, S. V. N. (2019). Antibacterial efficacy of green synthesized a- Fe2O3 nanoparticles using Sida cordifolia plant extract. Heliyon, 5 (11). https://doi.org/10.1016/j.heliyon.2019.e02765
Pandey, P. C., & Pandey, G. (2016). One-pot two-step rapid synthesis of 3- aminopropyltrimethoxysilane-mediated highly catalytic Ag@(PdAu) trimetallic nanoparticles. Catal. Sci. Technol., 6 (11), 3911-3917. https://doi.org/10.1039/C5CY02040A
Pandey, P. C., Pandey, G., & Walcarius, A. (2017). 3-Aminopropyltrimethoxysilane mediated solvent induced synthesis of gold nanoparticles for biomedical applications. Materials Science and Engineering C, 79, 45-54. https://doi.org/10.1016/j.msec.2017.05.009
Parham, H., & Saeed, S. (2014). Ultrasound-assisted solid phase extraction of nitro- and chloro- ( phenols ) using magnetic iron oxide nanoparticles and Aliquat 336 ionic liquid. Journal of Chromatography A, 1336, 34-42. https://doi.org/10.1016/j.chroma.2014.02.012
Pascariu, P., Cojocaru, C., Olaru, N., Samoila, P., Airinei, A., Ignat, M., Sacarescu, L., & Timpu, D. (2019). Novel rare earth ( RE-La , Er , Sm ) metal doped ZnO photocatalysts for degradation of Congo-Red dye : Synthesis , characterization and kinetic studies. Journal of Environmental Management, 239, 225-234. https://doi.org/10.1016/j.jenvman.2019.03.060
Pathania, D., Sharma, A., & Siddiqi, Z. M. (2016). Removal of congo red dye from aqueous system using Phoenix dactylifera seeds. Journal of Molecular Liquids, 219, 359-367. https://doi.org/10.1016Zj.molliq.2016.03.020
Patra, S., & Yang, H. (2009). Synthesis of trimetallic Au@Pb@Pt core-shell nanoparticles and their electrocatalytic activity toward formic acid and methanol. Bulletin of the Korean Chemical Society, 30 (7), 1485-1488. https://doi.org/10.5012/bkcs.2009.30.7.1485
Pedro S Nascimento, J., Martins, A. J., de Cássia F Bezerra, R., Bertoldo, G. M., Oliveira, A. C., Bezerra, J. R., Araujo, R. S., Lang, R., Otubo, L., Rodríguez- Aguado, E., & Rodríguez-Castellón, E. (2022). Designed synthesis of nanostructured ZrO2 as active support for glycerol valorization reaction. Ceramics International, 9, 1-15. https://doi.org/10.1016/j.ceramint.2022.09.140
Phiri, I. (2016). Magnetic nanopore composite beads for simultaneous removal of organic and inorganic pollutants in highly acidic water. University of Zimbabwe.
Plotka-Wasylka, J., Szczepanska, N., Owczarek, K., & Namiesnik, J. (2017). Miniaturized Solid Phase Extraction. In Comprehensive Analytical Chemistry (76), 279-318. https://doi.org/10.1016/bs.coac.2017.03.001
Poggialini, F., Campanella, B., Giannarelli, S., Grifoni, E., Legnaioli, S., Lorenzetti, G., & Pagnotta, S. (2018). Green-synthetized silver nanoparticles for Nanoparticle-Enhanced Laser Induced Breakdown Spectroscopy ( NELIBS ) using a mobile instrument. Spectrochimica Acta Part B: Atomic Spectroscopy, 141, 53-58. https://doi.org/10.1016Zj.sab.2018.01.005
Pol, R., Guerrero, M., Garcia-Lecina, E., Altube, A., Rossinyol, E., Garroni, S., Baro, M. D., Pons, J., Sort, J., & Pellicer, E. (2016). Ni-, Pt- and (Ni/Pt)-doped TiO<inf>2</inf> nanophotocatalysts: A smart approach for sustainable degradation of Rhodamine B dye. Applied Catalysis B: Environmental, 181, 270278. https://doi.org/10.1016/j.apcatb.2015.08.006
Pouretedal, H. R., & Keshavarz, M. H. (2010). Synthesis and characterization of Zn 1 - X Cu X S and Zn 1 - X Ni X S nanoparticles and their applications as photocatalyst in Congo red degradation. Journal of Alloys and Compounds 501 (1 ), 130-135. https://doi.org/10.1016/j.jallcom.2010.04.058
Pradeep, E. K. C., Habu, T., Tooriyama, H., Ohtani, M., & Kobiro, K. (2015). Ultrasimple synthetic approach to the fabrication of CeO2-ZrO2 mixed nanoparticles into homogeneous, domain, and core-shell structures in mesoporous spherical morphologies using supercritical alcohols. Journal of Supercritical Fluids, 97, 217-223. https://doi.org/10.1016/j.supflu.2014.12.004
Prasse, C., Stalter, D., Schulte-oehlmann, U., & Ternes, T. A. (2015). Spoilt for choice : A critical review on the chemical and biological assessment of current wastewater treatment technologies. Water Research, 87.
https://doi.org/10.1016/j.watres.2015.09.023
Prathna, T. C., Chandrasekaran, N., Raichur, A., & Mukherjee, A. (2011). Biomimetric synthesis of silver nanoparticles by citrus lem(lemon) aqueous extract and theoretical prediction of particle size. Colloids and Surfaces B, 82 (1), 152-159.
Qiang, W., Zhuanni, Y., Jing, L., Aifeng, L., & Yong, T. (2017). Bifunctional magnesium oxide crystal successively as adsorbent and matrix modi fi er for preconcentration and determination of arsenic by graphite furnace atomic absorption spectrometry. Microchemical Journal, 133, 412-416. https://doi.org/10.1016/j.microc.2017.04.004
Qiao, P., Xu, S., Zhang, D., Li, R., Zou, S., Liu, J., Yi, W., Li, J., & Fan, J. (2014). Sub-10 nm Au-Pt-Pd alloy trimetallic nanoparticles with a high oxidationresistant property as efficient and durable VOC oxidation catalysts. Chem. Commun., 50 (79), 11713-11716. https://doi.org/10.1039/C4CC04596C
Qin, R., Meng, F., Khan, M. W., Yu, B., & Li, H. (2018). Fabrication and enhanced photocatalytic property of TiO 2 -ZnO composite photocatalysts. Materials Letters, 2019. https://doi.org/10.1016/j.matlet.2018.12.139
Qin, Y., Hu, H., & Luo, A. (2006). The Conversion of Calcium Alginate Fibers into Alginic Acid Fibers and Sodium Alginate Fibers. Journal of Applied Polymer Science, 101, 4216-4221. https://doi.org/10.1002/app.24524
Qu, X., Alvarez, P. J. J., & Li, Q. (2013). Applications of nanotechnology in water and wastewater treatment. Water Research, 47 (12), 3931-3946. https://doi.org/10.1016/j.watres.2012.09.058
Raghu, H. S., & Rajeshwara, N. A. (2015). Immobilization of a- amylase (1, 4-a-D- glucanglucanohydralase) by calcium alginate encapsulation. International Food Research Journal, 22 (2), 869-871.
Ramezanpour, M., Raeisi, S. N., Shahidi, S. A., Ramezanpour, S., & Seidi, S. (2019). Polydopamine-functionalized magnetic iron oxide for the determination of trace levels of lead in bovine milk. Analytical Biochemistry, 570, 5-12. https://doi.org/10.1016/j.ab.2019.01.008
Ramsden, J. J. (2018). What is Nanotechnology? In Applied Nanotechnology (pp. 313). https://doi.org/10.1016/B978-0-12-813343-9.00002-0
Rani, M., & Shanker, U. (2018). Photocatalytic degradation of toxic phenols from water using bimetallic metal oxide nanostructures. Colloids and Surfaces A, 553, 546-561. https://doi.org/10.1016/j.colsurfa.2018.05.071
Rao, K. J., & Paria, S. (2015). Mixed phytochemicals mediated synthesis of multifunctional Ag-Au-Pd nanoparticles for glucose oxidation and antimicrobial applications. ACS Applied Materials and Interfaces, 7 (25), 14018-14025. https://doi.org/10.1021/acsami.5b03089
Rashidi Nodeh, H., Wan Ibrahim, W. A., Kamboh, M. A., & Sanagi, M. M. (2017). New magnetic graphene-based inorganic-organic sol-gel hybrid nanocomposite for simultaneous analysis of polar and non-polar organophosphorus pesticides from water samples using solid-phase extraction. Chemosphere, 166, 21-30. https://doi.org/10.1016/j.chemosphere.2016.09.054
Ravi, R., Iqbal, S., Ghosal, A., & Ahmad, S. (2019). Novel mesoporous trimetallic strontium magnesium ferrite ( Sr 0.3 Mg 0.7 Fe 2 O 4 ) nanocubes : A selective and recoverable magnetic nanoadsorbent for Congo red. Journal of Alloys and Compounds, 791, 336-347. https://doi.Org/10.1016/j.jallcom.2019.03.305
Ravi, S., & Shashikanth, F. W. (2017). Preparation of Mn doped CeO 2 nanoparticles with enhanced ferromagnetism. Materials Chemistry and Physics, 194, 37-41. https://doi.org/10.1016/j.matchemphys.2017.03.032
Repo, E., Warchol, J. K., Bhatnagar, A., & Sillanpää, M. (2011). Heavy metals adsorption by novel EDTA-modified chitosan-silica hybrid materials. Journal of Colloid and Interface Science, 358 (1), 261-267. https://doi.org/10.1016/j.jcis.2011.02.059
Rosseler, O., Ulhaq-Bouillet, C., Bonnefont, A., Pronkin, S., Savinova, E., Louvet, A., Keller, V., & Keller, N. (2015). Structural and electronic effects in bimetallic PdPt nanoparticles on TiO2for improved photocatalytic oxidation of CO in the presence of humidity. Applied Catalysis B: Environmental, 166 - 167, 381-392. https://doi.org/10.1016/j.apcatb.2014.12.001
Sabri, N. S., Yahya, A. K., & Talari, M. K. (2012). Emission properties of Mn doped ZnO nanoparticles prepared by mechanochemical processing. Journal of Luminescence. https://doi.org/10.1016/j.jlumin.2012.02.020
Sacco, O., Vaiano, V., & Matarangolo, M. (2018). ZnO supported on zeolite pellets as efficient catalytic system for the removal of caffeine by adsorption and photocatalysis. Separation and Purification Technology, 193, 303-310. https://doi.org/10.1016/j.seppur.2017.10.056
Sahayam, A. C., Venkateswarlu, G., & Chaurasia, S. C. (2005). Determination of Cr(VI) in potable water samples after selective preconcentration on oxalate form of Dowex-1 and electro thermal atomic absorption spectrometric determination. Analytica Chimica Acta, 537 (1-2), 267-270. https://doi.org/10.1016/j.aca.2005.01.017
Sasmal, D., Maity, J., Kolya, H., & Tripathy, T. (2017). Study of congo red dye removal from its aqueous solution using sulfated acrylamide and N, N- dimethyl acrylamide grafted amylopectin. Journal of Water Process Engineering, 18, 719. https://doi.org/10.1016/j.jwpe.2017.05.007
Sathish, S., & Balakumar, S. (2017). Effect of synthesis parameters of polyol technique on photoluminescence properties of ZnSe nanoparticles. Journal of Luminescence, 190, 272-278. https://doi.org/10.1016/j.jlumin.2017.05.033
Senthilkumar, R. P., Bhuvaneshwari, V., Ranjithkumar, R., Sathiyavimal, S., Malayaman, V., & Chandarshekar, B. (2017). Synthesis, characterization and antibacterial activity of hybrid chitosan-cerium oxide nanoparticles: As a bionanomaterials. International Journal of Biological Macromolecules, 104, 1746-1752. https://doi.org/10.1016Zj.ijbiomac.2017.03.139
Serkan Yalgin, M., Kiling, E., Özdemir, S., Yüksel, U., & Soylak, M. (2020). Phallus impudicus loaded with Y—Fe2O3 as solid phase bioextractor for the preconcentrations of Zn(II) and Cr(III) from water and food samples. Process Biochemistry, 92, 149-155. https://doi.org/10.1016/j.procbio.2020.03.012
Settle, F. A. (1998). Handbook of instrumental techniqufoers for analytical chemistry. In IEEE Electrical Insulation Magazine (Vol. 14, Issue 6, p. 42). https://doi.org/10.1109/MEI.1998.730821
Shahwan, T., Sirriah, S. A., Nairat, M., Boyaci, E., Ero, A. E., Scott, T. B., & Hallam, K. R. (2011). Green synthesis of iron nanoparticles and their application as a Fenton-like catalyst for the degradation of aqueous cationic and anionic dyes. 172, 258-266. https://doi.org/10.1016/j.cej.2011.05.103
Shamsipur, M., Fattahi, N., Assadi, Y., Sadeghi, M., & Sharafi, K. (2014). Speciation of As(III) and As(V) in water samples by graphite furnace atomic absorption spectrometry after solid phase extraction combined with dispersive liquid-liquid microextraction based on the solidification of floating organic drop. Talanta, 130, 26-32. https://doi.org/10.1016/j.talanta.2014.06.049
Shang, C., Hong, W., Wang, J., & Wang, E. (2015). Carbon supported trimetallic nickel-palladium-gold hollow nanoparticles with superior catalytic activity for methanol electrooxidation. Journal of Power Sources, 285, 12-15. https://doi.org/10.1016/j.jpowsour.2015.03.092
Sharma, G., Bhogal, S., Kumar, V., Agarwal, S., Kumar, A., Pathania, D., Tessema, G., & Stadler, F. J. (2019). Algal biochar reinforced trimetallic nanocomposite as adsorptional / photocatalyst for remediation of malachite green from aqueous medium. Journal of Molecular Liquids, 275, 499-509. https://doi.org/10.1016/j.molliq.2018.11.070
Sharma, G., Bhogal, S., Naushad, M., Kumar, A., & Stadler, F. J. (2017). Microwave assisted fabrication of La / Cu / Zr / carbon dots trimetallic nanocomposites with their adsorptional vs photocatalytic ef fi ciency for remediation of persistent organic pollutants. “Journal of Photochemistry & Photobiology, A: Chemistry,” 347, 235-243. https://doi.org/10.1016/j.jphotochem.2017.07.001
Sharma, G., Gupta, V. K., Agarwal, S., Bhogal, S., Naushad, M., Kumar, A., & Stadler, F. J. (2018). Fabrication and characterization of trimetallic nano-photocatalyst for remediation of ampicillin antibiotic. Journal ofMolecular Liquids, 260, 342-350. https://doi.org/10.1016/j.molliq.2018.03.059
Sharma, G., Kumar, A., Sharma, S., Naushad, M., Ahamad, T., Al-saeedi, S. I., Al- senani, G. M., Al-kadhi, N. S., & Stadler, F. J. (2018). Facile fabrication of Zr 2 Ni 1 Cu 7 trimetallic nano-alloy and its composite with Si 3 N 4 for visible light assisted photodegradation of methylene blue. Journal of Molecular Liquids, 272, 170-179. https://doi.org/10.1016Zj.molliq.2018.09.063
Sharma, G., Kumar, A., Sharma, S., Naushad, M., Ahamad, T., Al-Saeedi, S. I., Al- Senani, G. M., Al-kadhi, N. S., & Stadler, F. J. (2018). Facile fabrication of Zr2Ni1Cu7 trimetallic nano-alloy and its composite with Si3N4 for visible light assisted photodegradation of methylene blue. Journal of Molecular Liquids, 272, 170-179. https://doi.org/10.1016/j.molliq.2018.09.063
Sharma, G., Kumar, D., Kumar, A., Al-Muhtaseb, A. H., Pathania, D., Naushad, M., & Mola, G. T. (2017). Revolution from monometallic to trimetallic nanoparticle composites, various synthesis methods and their applications: A review. In Materials Science and Engineering C (Vol. 71, pp. 1216-1230). https://doi.org/10.1016/j.msec.2016.11.002
Sharma, J. K., Srivastava, P., Ameen, S., Akhtar, M. S., Sengupta, S. K., & Singh, G. (2017). Phytoconstituents assisted green synthesis of cerium oxide nanoparticles for thermal decomposition and dye remediation. Materials Research Bulletin, 91, 98-107. https://doi.org/10.1016/j.materresbull.2017.03.034
Sharmila, G., Farzana Fathima, M., Haries, S., Geetha, S., Manoj Kumar, N., & Muthukumaran, C. (2017). Green synthesis, characterization and antibacterial efficacy of palladium nanoparticles synthesized using Filicium decipiens leaf extract. Journal of Molecular Structure, 1138, 35-40. https://doi.org/10.1016/j.molstruc.2017.02.097
Shea, J. J. (1998). Handbook of instrumental techniques for Analytical Chemistry. In IEEE Electrical Insulation Magazine, 14(6), 42-42). https://doi.org/10.1109/MEI.1998.730821
Shekardasht, M. B., Givianrad, M. H., Gharbani, P., Mirjafary, Z., & Mehrizad, A. (2020). Preparation of a novel Z-scheme g-C3N4/RGO/Bi2Fe4O9 nanophotocatalyst for degradation of Congo Red dye under visible light. Diamond and Related Materials, 109. https://doi.org/10.1016/j.diamond.2020.108008
Shen, L., Liang, R., & Wu, L. (2015). Strategies for engineering metal-organic frameworks as efficient photocatalysts. In Cuihua Xuebao/Chinese Journal of Catalysis (Vol. 36, Issue 12, pp. 2071-2088). Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. https://doi.org/10.1016/S1872- 2067(15)60984-6
Shet, A., & Vidya, S. K. (2016). Solar light mediated photocatalytic degradation of phenol using Ag core - TiO2 shell (Ag@TiO2) nanoparticles in batch and fluidized bed reactor. Solar Energy, 127, 67-78. https://doi.org/10.1016/j.solener.2015.12.049
Shoueir, K., El-Sheshtawy, H., Misbah, M., El-Hosainy, H., El-Mehasseb, I., & El- Kemary, M. (2018). Fenton-like nanocatalyst for photodegradation of methylene blue under visible light activated by hybrid green DNSA@Chitosan@MnFe2O4. Carbohydrate Polymers, 197, 17-28. https://doi.org/10.1016/j.carbpol.2018.05.076
Sing, K. S. W., Everett, D. H., Haul, R. A. W., Moscou, L., Pierotti, R. A., Rouquerol, J., & Siemieniewska, T. (1985). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity.
Pure and Applied Chemistry, 57 (4), 603-619. https://doi.org/10.1351/pac198557040603
Singh, A. T., & Khandpekar, M. M. (2016). Synthesis and structural studies of LaF3:Ce nanoparticles modified by Tyrosine for bioimaging and biotagging applications. Materials Today: Proceedings, 3 (10), 4260-4265. https://doi.org/10.1016/j.matpr.2016.11.107
Singh, R., & Soni, R. K. (2014). Plasmonics properties of trimetallic Al@Al2O3@Ag@Au and Al@Al2O3@AuAg nanostructures. Applied Physics A: Materials Science and Processing, 116 (3), 955-967. https://doi.org/10.1007/s00339-014-8455-7
Sithara, R., Selvakumar, P., Arun, C., Anandan, S., & Sivashanmugam, P. (2017). Economical synthesis of silver nanoparticles using leaf extract of Acalypha hispida and its application in the detection of Mn(II) ions. Journal of Advanced Research. https://doi.org/10.1016/j.jare.2017.07.001
Soltani, T., Tayyebi, A., & Lee, B. K. (2018). Quick and enhanced degradation of bisphenol A by activation of potassium peroxymonosulfate to SO4[rad]-with Mn-doped BiFeO3nanoparticles as a heterogeneous Fenton-like catalyst. Applied Surface Science. https://doi.org/10.1016/j.apsusc.2018.02.063
Song, J. Y., Jang, H., & Kim, B. S. (2009). Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts. Procedia Technology. https://doi.org/10.1016/j.procbio.2009.06.005
Song, J. Y., & Jhung, S. H. (2017). Adsorption of pharmaceuticals and personal care products over metal- organic frameworks functionalized with hydroxyl groups : Quantitative analyses of H-bonding in adsorption. Chemical Engineering Journal, 322, 366-374. https://doi.org/10.1016Zj.cej.2017.04.036
Soto-Robles, C. A., Luque, P. A., Gomez-Gutierrez, C. M., Nava, O., Vilchis-Nestor, A. R., Lugo-Medina, E., Ranjithkumar, R., & Castro-Beltran, A. (2019). Study on the effect of the concentration of Hibiscus sabdariffa extract on the green synthesis of ZnO nanoparticles. Results in Physics, 15. https://doi.org/10.1016/j.rinp.2019.102807
Sravanthi, K., Ayodhya, D., & Swamy, P. Y. (2019). Green synthesis , characterization and catalytic activity of 4-nitrophenol reduction and formation of benzimidazoles using bentonite supported zero valent iron nanoparticles. Materials Science for Energy Technologies, 2 (2), 298-307. https://doi.org/10.1016/j.mset.2019.02.003
Subhan, M. A., Ahmed, T., & Uddin, N. (2015). Synthesis, structure, PL and photocatalytic activities of la2O2CO3i^^CeO2i^^ZnO fabricated by coprecipitation method. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 138, 827-833. https://doi.Org/10.1016/j.saa.2014.10.114
Subhan, M. A., Ahmed, T., Uddin, N., Azad, A. K., & Begum, K. (2015). Synthesis, characterization, PL properties, photocatalytic and antibacterial activities of nano multi-metal oxide Ni(O CeO2^ ZnO. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 136 (PB), 824-831. https://doi.org/10.1016/j.saa.2014.09.100
Sudachom, N., Warakulwit, C., Prapainainar, C., Witoon, T., & Prapainainar, P. (2017). One step NaBH4 reduction of Pt-Ru-Ni catalysts on different types of carbon supports for direct ethanol fuel cells: Synthesis and characterization. Journal of Fuel Chemistry and Technology, 45 (5), 596-607. https://doi.org/10.1016/S1872-5813(17)30031-2
Sun, A., Dong, X., Wang, X., Duan, B., & Wang, D. (2013). Synthesis of novel core - shell Cu @ Mo nanoparticles with good sinterability. Journal of Alloys and Compounds, 555, 6-9. https://doi.org/10.1016/j.jallcom.2012.12.033
Suwannarat, K., Thongthai, K., Ananta, S., & Srisombat, L. (2018). Synthesis of hollow trimetallic Ag/Au/Pd nanoparticles for reduction of 4-nitrophenol. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 540 (October 2017), 73-80. https://doi.org/10.1016/j.colsurfa.2017.12.046
Szekalska, M., Pucilowska, A., Szymanska, E., Ciosek, P., & Winnicka, K. (2016).
Alginate: Current use and future perspectives in pharmaceutical and biomedical applications. In International Journal of Polymer Science, 2016. https://doi.org/10.1155/2016/7697031
Tadjarodi, A., Abbaszadeh, A., Taghizadeh, M., Shekari, N., & Asgharinezhad, A. A. (2015). Solid phase extraction of Cd(II) and Pb(II) ions based on a novel functionalized Fe3O4@ SiO2 core-shell nanoparticles with the aid of multivariate optimization methodology. Materials Science and Engineering C, 49, 416-421. https://doi.org/10.1016Zj.msec.2015.01.013
Tang, X., Zu, Z., Bian, L., Du, J., Chen, W., Zeng, X., Wen, M., Zang, Z., & Xue, J. (2016). Synthesis of Mn doping Ag - In - Zn - S nanoparticles and their photoluminescence properties. Materials and Design, 91, 256-261. https://doi.org/10.1016/j.matdes.2015.11.080
Tarasevich, M. R., Zhutaeva, G. V, Bogdanovskaya, V. A., Reznikova, L. A., Radina, M. V, & Kazanskii, L. P. (2011). Comparison of electrocatalytic and corrosion characteristics of monoplatinum and trimetallic (PtCoCr) systems. Protection of Metals and Physical Chemistry of Surfaces, 47 (7), 895-906. https://doi.org/10.1134/S2070205111070161
Taskin, A. K., Yasar, M., Ozaydin, I., Kaya, B., Bat, O., Ankarali, S., Yildirim, U., & Aydin, M. (2013). The hemostatic effect of calcium alginate in experimental splenic injury model. Ulusal Travma ve Acil Cerrahi Dergisi = Turkish Journal of Trauma & Emergency Surgery: TJTES, 19 (3), 195-199. https://doi.org/10.5505/tjtes.2013.30676
Thommes, M., Kaneko, K., Neimark, A. V, Olivier, J. P., Rodriguez-reinoso, F., Rouquerol, J., & Sing, K. S. W. (2015). Physisorption of gases , with special reference to the evaluation of surface area and pore size distribution ( IUPAC Technical Report ). https://doi.org/10.1515/pac-2014-1117
Tian, L., Liu, L., Li, Y., Wei, Q., & Cao, W. (2016). Ultrasensitive sandwich-type electrochemical immunosensor based on trimetallic nanocomposite signal amplification strategy for the ultrasensitive detection of CEA. Scientific Reports, 6. https://doi.org/10.1038/srep30849
Tian, Z. H., Wang, Y., Yuan, F. J., Liu, W., Jin, Z. H., & Li, T. L. (2013). Preparation of nanoscale Pd-Au@Fe trimetallic catalyst particles for the dechlorination of trichloroethylene. Guocheng Gongcheng Xuebao/The Chinese Journal of Process Engineering, 13, 321-326. http://www.scopus.com/inward/record.url?eid=2- s2.0-84878177476&partnerID=40&md5=66a02f950380de80c5dd3f687d7c580c
Tokay, F., Gunaydin, R., & Bagdat, S. (2021). A novel vortex assisted dispersive solid phase extraction of some trace elements in essential oils and fish oil. Talanta, 230. https://doi.org/10.1016/j.talanta.2021.122312
Tong, Z., Chen, Y., Liu, Y., Tong, L., Chu, J., Xiao, K., Zhou, Z., Dong, W., & Chu, X. (2017). Preparation, characterization and properties of alginate/poly(Y— glutamic acid) composite microparticles. Marine Drugs, 15 (4). https://doi.org/10.3390/md15040091
Toshima, N., Ito, R., Matsushita, T., & Shiraishi, Y. (2007). Trimetallic nanoparticles having a Au-core structure. Catalysis Today, 122 (3-4), 239-244. https://doi.org/10.1016/j.cattod.2007.03.013
Trandafilovic, L. V., Jovanovic, D. J., Zhang, X., Ptasinska, S., & Dramicanin, M. D. (2017). Enhanced photocatalytic degradation of methylene blue and methyl orange by ZnO:Eu nanoparticles. Applied Catalysis B: Environmental, 203, 740752. https://doi.org/10.1016/j.apcatb.2016.10.063
Turolla, A., Fumagalli, M., Bestetti, M., & Antonelli, M. (2012). Electrophotocatalytic decolorization of an azo dye on TiO2self-organized nanotubes in a laboratory scale reactor. Desalination, 285, 377-382.
https://doi.org/10.1016/j.desal.2011.10.029
Ulusoy, H. i., Yilmaz, E., & Soylak, M. (2019). Magnetic solid phase extraction of trace paracetamol and caffeine in synthetic urine and wastewater samples by a using core shell hybrid material consisting of graphene oxide/multiwalled carbon nanotube/Fe3O4/SiO2. Microchemical Journal, 145, 843-851.
https://doi.org/10.1016/j.microc.2018.11.056
Urns, S., Purta§, S., Ceyhan, G., & Tümer, F. (2013). Solid phase extraction of Pb(II), Cu(II), Cd(II) and Cr(III) with syringe technique using novel silica-supported bis(diazoimine) ligands. Chemical Engineering Journal, 220, 420-430.
https://doi.org/10.1016/j.cej.2013.01.037
Vaseghi, Z., Tavakoli, O., & Nematollahzadeh, A. (2018a). Rapid biosynthesis of novel Cu/Cr/Ni trimetallic oxide nanoparticles with antimicrobial activity. Journal of Environmental Chemical Engineering, 6 (2), 1898-1911.
https://doi.org/10.1016/j.jece.2018.02.038
Vaseghi, Z., Tavakoli, O., & Nematollahzadeh, A. (2018b). Rapid biosynthesis of novel Cu/Cr/Ni trimetallic oxide nanoparticles with antimicrobial activity. Journal of Environmental Chemical Engineering, 6 (2), 1898-1911.
https://doi.org/10.1016/j.jece.2018.02.038
Vattikuti, S. V. P., Byon, C., & Ngo, I. (2016). Highly crystalline multi-layered WO 3 sheets for photodegradation of Congo red under visible light irradiation. Materials Research Bulletin, 84, 288-297.
https://doi.org/10.1016/j.materresbull.2016.08.008
Venkatesan, P., & Santhanalakshmi, J. (2010). Designed synthesis of Au/Ag/Pd trimetallic nanoparticle-based catalysts for sonogashira coupling reactions. Langmuir, 26 (14), 12225-12229. https://doi.org/10.1021/la101088d
Vidya, C., Manjunatha, C., Chandraprabha, M. N., Rajshekar, M., & Antony Raj, M. A. L. (2017). Hazard free green synthesis of ZnO nano-photo-catalyst using Artocarpus Heterophyllus leaf extract for the degradation of Congo red dye in water treatment applications. Journal of Environmental Chemical Engineering,
5 (4), 3172-3180. https://doi.org/10.1016Zj.jece.2017.05.058
Vijayalakshmi, K., Gomathi, T., Latha, S., Hajeeth, T., & Sudha, P. N. (2016). Removal of copper(II) from aqueous solution using nanochitosan/sodium alginate/microcrystalline cellulose beads. International Journal of Biological Macromolecules, 82, 440-452. https://doi.org/10.1016/j.ijbiomac.2015.09.070
Wang, C. L. (2018). Fractional kinetics of photocatalytic degradation. Journal of Advanced Dilectrics, 8 (5), 1-7. https://doi.org/10.1142/S2010135X18500340
Wang, H.-L., Yan, J.-M., Wang, Z.-L., & Jiang, Q. (2012). One-step synthesis of Cu@FeNi core-shell nanoparticles: Highly active catalyst for hydrolytic dehydrogenation of ammonia borane. International Journal of Hydrogen Energy, 37 (13), 10229-10235. https://doi.org/10.1016/j.ijhydene.2012.04.007
Wang, S., Guan, Y., Wang, L., Zhao, W., He, H., Xiao, J., Yang, S., & Sun, C. (2015). Fabrication of a novel bifunctional material of BiOI/Ag3VO4with high adsorption-photocatalysis for efficient treatment of dye wastewater. Applied Catalysis B: Environmental, 168 - 169, 448-457.
https://doi.org/10.1016/j.apcatb.2014.12.047
Wei, Y., Wu, X., Zhao, Y., Wang, L., Zhao, Z., Huang, X., Liu, J., & Li, J. (2018). Efficient photocatalysts of TiO2nanocrystals-supported PtRu alloy nanoparticles for CO2reduction with H2O: Synergistic effect of Pt-Ru. Applied Catalysis B: Environmental, 236, 445-457. https://doi.org/10.1016/j.apcatb.2018.05.043
Wen, Y., Ren, F., Bai, T., Xu, H., & Du, Y. (2018). Facile construction of trimetallic PtAuRu nanostructures with highly porous features and perpendicular pore channels as enhanced formic acid catalysts. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 537, 418-424.
https://doi.org/10.1016/j.colsurfa.2017.10.049
Wu, Y. J., Hong, R. Y., Wang, L. S., Di, G. Q., Li, H. Z., Xu, B., Zheng, Y., & Wei, D. G. (2009). Molten-salt synthesis and characterization of Bi-substituted yttrium garnet nanoparticles. Journal of Alloys and Compounds.
https://doi.org/10.1016/j.jallcom.2009.03.060
Xu, C., He, M., Chen, B., & Hu, B. (2022). Magnetic porous coordination networks for preconcentration of various metal ions from environmental water followed by inductively coupled plasma mass spectrometry detection. Talanta, 245, 123470. https://doi.org/10.1016/j.talanta.2022.123470
Xu, Y., Suthar, J., Egbu, R., Weston, A. J., Fogg, A. M., & Williams, G. R. (2018). Reverse microemulsion synthesis of layered gadolinium hydroxide nanoparticles.
Journal of Solid State Chemistry, 258, 320-327.
https://doi.org/10.1016/j.jssc.2017.10.031
Yang, K., Zhou, L., Xiong, X., Ye, M., Li, L., & Xia, Q. (2016). RuCuCo nanoparticles supported on MIL-101 as a novel highly efficient catalysts for the hydrolysis of ammonia borane. Microporous and Mesoporous Materials, 225, 1-8. https://doi.org/10.1016/j.micromeso.2015.12.018
Y ang, L., Luo, W., & Cheng, G. (2016). Monodisperse CoAgPd nanoparticles assembled on graphene for efficient hydrogen generation from formic acid at room temperature. International Journal of Hydrogen Energy, 41 (1), 439-446. https://doi.org/10.1016/j.ijhydene.2015.10.074
Y ang, L., Su, J., Luo, W., & Cheng, G. (2014). Strategic synthesis of graphene supported trimetallic Ag-based core-shell nanoparticles toward hydrolytic dehydrogenation of amine boranes. International Journal of Hydrogen Energy, 39 (7), 3360-3370. https://doi.org/10.1016/j.ijhydene.2013.12.089
Y ang, S., Jiang, S., Hu, K., & Wen, X. (2020). Investigation of dispersive solid-phase extraction combined with slurry sampling thermospray flame furnace atomic absorption spectrometry for the determination of cadmium. Microchemical Journal, 154, 104542. https://doi.org/10.1016/j.microc.2019.104542
Y ang, X. an, Shi, M. ting, Leng, D., & Zhang, W. bing. (2018). Fabrication of a porous hydrangea-like Fe3O4@MnO2composite for ultra-trace arsenic preconcentration and determination. Talanta, 189, 55-64.
https://doi.org/10.1016/j.talanta.2018.06.065
Y ao, L., Liu, H., Wang, X., Xu, W., Zhu, Y., Wang, H., Pang, L., & Lin, C. (2018). Ultrasound-assisted surfactant-enhanced emulsification microextraction using a magnetic ionic liquid coupled with micro-solid phase extraction for the determination of cadmium and lead in edible vegetable oils. Food Chemistry, 256, 212-218. https://doi.org/10.1016/j.foodchem.2018.02.132
Y avuz, E., Tokaliollu, §., §ahan, H., & Patat, §. (2016). Nanosized spongelike Mn3O4 as an adsorbent for preconcentration by vortex assisted solid phase extraction of copper and lead in various food and herb samples. Food Chemistry, 194, 463469. https://doi.org/10.1016/j.foodchem.2015.08.035
Y oosefian, M., Ahmadzadeh, S., Aghasi, M., & Dolatabadi, M. (2017). Optimization of electrocoagulation process for efficient removal of ciprofloxacin antibiotic using iron electrode; kinetic and isotherm studies of adsorption. Journal of Molecular Liquids, 225 (11), 544-553.
https://doi.org/10.1016/j.molliq.2016.11.093
Yu, C., Wu, Z., Liu, R., Dionysiou, D. D., Yang, K., Wang, C., & Liu, H. (2017). Novel fluorinated Bi2MoO6nanocrystals for efficient photocatalytic removal of water organic pollutants under different light source illumination. Applied Catalysis B: Environmental, 209, 1-11.
https://doi.org/10.1016/j.apcatb.2017.02.057
Yuan, Y., Wu, Y., Wang, H., Tong, Y., Sheng, X., Sun, Y., Zhou, X., & Zhou, Q. (2020). Simultaneous enrichment and determination of cadmium and mercury ions using magnetic PAMAM dendrimers as the adsorbents for magnetic solid phase extraction coupled with high performance liquid chromatography. Journal of Hazardous Materials, 386, 121658.
https://doi.org/10.1016/j.jhazmat.2019.121658
Yurderi, M., Bulut, A., Zahmakiran, M., & Kaya, M. (2014). Carbon supported trimetallic PdNiAg nanoparticles as highly active, selective and reusable catalyst in the formic acid decomposition. Applied Catalysis B: Environmental, 160 - 161 (1), 514-524. https://doi.org/10.1016Zj.apcatb.2014.06.004
Zahedifar, M., Sadeghi, E., Mozdianfard, M. R., & Habibi, E. (2013). Synthesis , characteristics and thermoluminescent dosimetry features of y -irradiated Ce doped CaF 2 nanophosphor. Applied Radiation and Isotopes, 78, 125-131. https://doi.org/10.1016/j.apradiso.2013.04.029
Zahid, M., Saqib, N., Nadia, J., Asma, S., & Adnan, A. (2015). Adsorption studies of phosphate ions on alginate-calcium carbonate composite beads. African Journal of Environmental Science and Technology, 9 (3), 274-281.
https://doi.org/10.5897/AJEST2014.1784
Zeghioud, H., Assadi, A. A., Khellaf, N., Djelal, H., Amrane, A., & Rtimi, S. (2018). Reactive species monitoring and their contribution for removal of textile effluent with photocatalysis under UV and visible lights: Dynamics and mechanism. Journal of Photochemistry and Photobiology A: Chemistry, 365, 94-102. https://doi.org/10.1016/j.jphotochem.2018.07.031
Zhai, H., Wang, P., Zhang, Q., Liu, X., Wang, Z., Liu, Y., Zheng, Z., & Huang, B. (2018). Plasmonic Au-Ag Bimetallic Alloy Nanoparticles decorated ZnO nanorod with enhanced photocatalytic activity for ethylene-oxidation. Applied Catalysis A: General. https://doi.org/10.1016/j.apcata.2018.06.019
Zhang, H., Cao, Y., Lu, L., Cheng, Z., & Zhang, S. (2014). Trimetallic Au/Pt/Rh Nanoparticles as Highly Active Catalysts for Aerobic Glucose Oxidation. Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, 46 (1), 523-530. https://doi.org/10.1007/s11663-014-0219-4
Zhang, H., Lu, L., Cao, Y., Du, S., Cheng, Z., & Zhang, S. (2014). Fabrication of catalytically active Au/Pt/Pd trimetallic nanoparticles by rapid injection of NaBH4. Materials Research Bulletin, 49 (1), 393-398.
https://doi.org/10.1016/j.materresbull.2013.09.025
Zhang, H., Okumura, M., & Toshima, N. (2011). Stable dispersions of PVP-protected Au/Pt/Ag trimetallic nanoparticles as highly active colloidal catalysts for aerobic glucose oxidation. Journal of Physical Chemistry C, 115 (30), 14883-14891. https://doi.org/10.1021/jp203457f
Zhang, H., & Toshima, N. (2011). Preparation of novel Au/Pt/Ag trimetallic nanoparticles and their high catalytic activity for aerobic glucose oxidation. Applied Catalysis A: General, 400 (1-2), 9-13.
https://doi.org/10.1016/j.apcata.2011.03.015
Zhang, H., Wang, Z., Li, R., Guo, J., Li, Y., Zhu, J., & Xie, X. (2017). TiO2supported on reed straw biochar as an adsorptive and photocatalytic composite for the efficient degradation of sulfamethoxazole in aqueous matrices. Chemosphere, 185, 351-360. https://doi.org/10.1016/j.chemosphere.2017.07.025
Zhang, J., Ma, J., Fan, X., Peng, W., Zhang, G., Zhang, F., & Li, Y. (2017). Graphene supported Au-Pd-Fe3O4alloy trimetallic nanoparticles with peroxidase-like activities as mimic enzyme. Catalysis Communications, 89, 148-151. https://doi.org/10.1016/j.catcom.2016.08.027
Zhang, J. Z., & Yan, Y. (2018). Synthesis of mesoporous sphere-like Copper(I) oxide and its enhancement of Congo red photodegradation performance and CO sensing properties. Journal of the Taiwan Institute of Chemical Engineers, 0, 1-11. https://doi.org/10.1016/j.jtice.2018.08.006
Zhang, J. Z., & Yan, Y. (2019). Synthesis of mesoporous sphere-like Copper(I) oxide and its enhancement of Congo red photodegradation performance and CO sensing properties. Journal of the Taiwan Institute of Chemical Engineers, 95, 405-415. https://doi.org/10.1016/j.jtice.2018.08.006
Zhang, L., LEI, J., TIAN, Y., HU, X., BAI, J., HU, X., LIU, D., YANG, Y., & PAN, L. (2015). Effect of precursor and precipitant concentrations on the catalytic properties of CuO/ZnO/CeO2-ZrO2 for methanol steam reforming. Journal of Fuel Chemistry and Technology, 43 (11), 1366-1374.
https://doi.org/10.1016/s1872-5813(15)30041-4
Zhang, X., Zhang, F., & Chan, K. Y. (2004). Preparation of Pt-Ru-Co trimetallic nanoparticles and their electrocatalytic properties. Catalysis Communications, 5 (12), 749-753. https://doi.org/10.1016/j.catcom.2004.09.010
Zhang, Y., & Park, S. J. (2018). Bimetallic AuPd alloy nanoparticles deposited on MoO3nanowires for enhanced visible-light driven trichloroethylene degradation. Journal of Catalysis, 361, 238-247. https://doi.org/10.1016/jjcat.2018.03.010
Zhang, Y., Wang, W., Li, L., Huang, Y., & Cao, J. (2010). Eggshell membrane-based solid-phase extraction combined with hydride generation atomic fluorescence spectrometry for trace arsenic(V) in environmental water samples. Talanta, 80 (5), 1907-1912. https://doi.org/10.1016/j.talanta.2009.10.042
Zhang, Y., Zhou, J. L., & Ning, B. (2007). Photodegradation of estrone and 17ß- estradiol in water. Water Research, 41 (1), 19-26.
https://doi.org/10.1016/j.watres.2006.09.020
Zhao, J., Li, H., Liu, Z., Hu, W., Zhao, C., & Shi, D. (2015). An advanced electrocatalyst with exceptional eletrocatalytic activity via ultrafine Pt-based trimetallic nanoparticles on pristine graphene. Carbon, 87 (C), 116-127. https://doi.org/10.1016/j.carbon.2015.01.038
Zhao, L., Deng, J., Sun, P., Liu, J., Ji, Y., Nakada, N., Qiao, Z., Tanaka, H., & Yang, Y. (2018). Nanomaterials for treating emerging contaminants in water by adsorption and photocatalysis: Systematic review and bibliometric analysis. Science of the Total Environment, 627, 1253-1263.
https://doi.org/10.1016/j.scitotenv.2018.02.006
Zhi, B., Gallagher, M. J., Frank, B. P., Lyons, T. Y., Qiu, T. A., Da, J., Mensch, A. C.,
Hamers, R. J., Rosenzweig, Z., Fairbrother, D. H., & Haynes, C. L. (2018). Investigation of phosphorous doping effects on polymeric carbon dots: Fluorescence , photostability , and environmental impact. Carbon, 129, 438-449. https://doi.org/10.1016/j.carbon.2017.12.004
Zhou, Q., Zhao, Q., Xiong, W., Li, X., Li, J., & Zeng, L. (2018). Hollow porous zinc cobaltate nanocubes photocatalyst derived from bimetallic zeolitic imidazolate frameworks towards enhanced gaseous toluene degradation. Journal of Colloid and Interface Science, 516, 76-85. https://doi.org/10.1016/j.jcis.2018.01.042
Zhou, Q., Zheng, Z., Xiao, J., & Fan, H. (2016). Talanta Sensitive determination of As ( III ) and As ( V ) by magnetic solid phase extraction with Fe @ polyethyleneimine in combination with hydride generation atomic fl uorescence spectrometry. Talanta, 156 - 157, 196-203.
https://doi.org/10.1016/j.talanta.2016.05.024
Zhu, H. Y., Jiang, R., Fu, Y. Q., Li, R. R., Yao, J., & Jiang, S. T. (2016). Novel multifunctional NiFe 2 O 4 /ZnO hybrids for dye removal by adsorption, photocatalysis and magnetic separation. Applied Surface Science, 369, 1-10. https://doi.org/10.1016/j.apsusc.2016.02.025
Zielinska-Jurek, A., Kowalska, E., Sobczak, J. W., Lisowski, W., Ohtani, B., & Zaleska, A. (2011). Preparation and characterization of monometallic (Au) and bimetallic (Ag/Au) modified-titania photocatalysts activated by visible light. Applied Catalysis B: Environmental, 101 (3-4), 504-514.
https://doi.org/10.1016/j.apcatb.2010.10.022
Zuo, H. F., Guo, Y. R., Li, S. J., & Pan, Q. J. (2014). Application of microcrystalline cellulose to fabricate ZnO with enhanced photocatalytic activity. Journal of Alloys and Compounds, 617, 823-827.
https://doi.org/10.1016/j.jallcom.2014.08.071
CHAPTER 9 APPENDIX
9.1.1.1 Tauc plots data
Table A: 1 Tauc plots for undoped nanoparticles
Illustrations are not included in the reading sample
Table A: 2 Tauc plots for dried doped P — ZrO 2CeO 2ZnO nanoparticles dried nano
Illustrations are not included in the reading sample
AE1) Power flux calculation
Power of LED light = 20 watt = work/time = 20 Js-[1] Equation A.1
Energy of photon (E) = lic/A =6.626 x10-34 Js-[1] x 3.0 x108 ms-[1]/5.95 x10-[9] m
Equation A.2
Illustrations are not included in the reading sample
Number of photons emitted per second = 20 Js-[1]/3.3408 x 10 -[39] J Equation A.3
Illustrations are not included in the reading sample
9.1.1.2 Linear Model Analysis: Means versus pH, Dosage (g), metal concentration
(M), volume ratio
Table A: 3 Estimated Model Coefficients for Means
Illustrations are not included in the reading sample
Model Summary
Illustrations are not included in the reading sample
0.3336 98.31% 91.57%
Table A: 4: Fits and Diagnostics for Unusual Observations for P — ZrO 2CeO 2ZnO nanoparticle synthesis
Illustrations are not included in the reading sample
Illustrations are not included in the reading sample
Figure A: 1: Calibration curve for Cr and As SPE
Table A: 5: Adsorption equilibrium studies parameters
Illustrations are not included in the reading sample
Table A: 6: Adsorption equilibrium studies parameters
Illustrations are not included in the reading sample
Table A:7Adsorption equilibrium parameters for Cd
Illustrations are not included in the reading sample
Table A: 8: Adsorption equilibrium parameters for Pb
Illustrations are not included in the reading sample
Table A: 9: Adsorption desorption cycles for Pb and Cd Solid phase extraction
Illustrations are not included in the reading sample
Figure A: 2Calibration curve for Cr and As SPE
9.1.1.3 Determination of hydrogen bonding active sites of the P — ZrO 2 CeO 2 ZnO nanoparticle using alcohols.
The nanoparticles were soaked in 10 cm[3] of neat solution, 1) water, 2) methanol 3) ethanol, 4) propan-2-ol, 5) phenol separately and left overnight in a tightly sealed container. The nanoparticles were air dried for 10 minutes prior to IR measurements.
The IR shifts were then recorded. The effect of adsorption from a mixture of dilute penetrants was investigated by adding about 5 cm[3] of methanol, ethanol, prop-2-ol, phenol, butanol to 15 cm[3] water and then added to the nanoparticles. The nanoparticles were air dried before FT IR analysis.
The interaction of the nanoparticles with ethanol, methanol, propanol, phenol and a mixture of alcohols was used to study hydrogen bonding. The hydrogen bonding was monitored using the IR red shift. The ATR FT-IR yields the information about the identity of active sites on the P — ZrO 2CeO 2ZnO nanoparticles. The interaction was studied using neat solution, dilute solution and mixed solution. A red shifted hydrogen bond leads to a decrease in the hydrogen bond vibrational frequency and usually to bond length elongation whereas the blue shifted hydrogen bond leads to bond length contraction and increase in vibrational frequency (Lu et al., 2005). Blue shifted hydrogen bonds are shifted towards a higher wavelength number A spectral shift towards a higher wavelength number is called a blue shift (Liu et al., 2007) and a shift towards a lower wavelength is a red shift.
Table A: 10: Effect of ethanol, methanol, propanol, phenol and mixture on bonds
Illustrations are not included in the reading sample
The IR bands for Ce — 0 at 712 cm-[1], Zr — 0 at 508 and 438 cm-[1], Zn — 0 at 493 cm-[1], does not appear in dilute and neat solutions of nanoparticles in the alcohols. Blue shifted hydrogen bonds were experienced by a) P = 0 bonds in neat methanol, b) amidel bonds in dilute mixture of alcohols, c) 0H bonds in neat and dilute methanol, neat and dilute propanol neat phenol and the dilute mixture of alcohols. The red shifted hydrogen bonds were experienced by a) C — 0 bonds in dilute propanol and neat phenol, b) C = 0 bonds in dilute mixture of alcohols, c) P = 0 bonds in dilute ethanol and dilute phenol, d) amide 1 bonds in dilute ethanol, dilute phenol, e) 0H bonds in dilute ethanol and dilute phenol. The hydrogen bonding active sites which were identified by determining the effect of neat and dilute ethanol, methanol, propanol, phenol and dilute alcohols on FT-IR spectrum of the nanoparticles were P = 0, C — 0, C = 0, Amide 1 and 0 — H.
9.1.1.4 Antiplagiarism report
Illustrations are not included in the reading sample
Illustrations are not included in the reading sample
[...]
Buy now
- Quote paper
- Nichodimus Hokonya (Author), 2024, Green Synthesis of Trimetallic Nanoparticles using Flacourtia Indica (Burm.f.) Merr. Characterization and Applications, Munich, GRIN Verlag, https://www.grin.com/document/1590457
