Our society depends overwhelmingly on carbon based resources (coal, natural gas and oil). The use of carbon based resources to meet the current energy needs of our society is associated with two critical drawbacks, that are: i) carbon based resources are not renewable and ii) burning hydrocarbons and venting the waste gases into atmosphere, e.g., carbon dioxide (CO2), leads to worsening of the greenhouse effect. As a response to these issues, the strategy of so-called “green carbon” has been proposed. This strategy consist of obtaining energies that foresees a gradual transition from carbon based resources to hydrogen based fuel, i.e., “hydrogen economy”, while simultaneously increasing the role of renewable energies. Carbon based resources would ultimately be used for synthesis of high-value chemicals and hydrogen (H2) generation. This strategy is possible to become a reality only if innovations in materials, chemistry, catalysis, and other engineering related fields are to occur. From a materials science perspective, extensive research is currently underway to develop materials able to store H2, to capture CO2, or to separate H2 from byproducts such as CO2, CO, or N2. This work aims to explore the opportunities, as well as the associated limitations of the use of silicon oxycarbonitride ceramics derived from preceramic polymers by NH3-assisted route for the above-mentioned applications, such as H2 gas separation membranes, and H2 or CO2 capture or storage materials in form of powders.
A simple and general synthesis method to tune the chemical composition and pore size, as well as the surface area of oxycarbonitride ceramics has been developed. This method is based on modifying the structure of preceramic polymers through chemical reactions with NH3 at 300 – 800 oC, followed by a thermolysis under an Ar atmosphere at 750 oC. Under these synthesis conditions a polysiloxane and a polysilazane transform to microporous ceramics, while materials derived from a polycarbosilane remain nonporous, as revealed by N2 and CO2 adsorption isotherms. Small angle X-ray scattering (SAXS) characterization indicates that samples prepared from the polycarbosilane possess latent pores (pore size < 0.35 nm) which are not accessible in the gas adsorption experiments. [...]
Table of contents
1. Introduction and motivation
2. Part I. Basics
3. Chapter 1. Literature survey
1.1. NH3-assisted synthesis of silicon nitrides and carbonitrides
1.1.1. Silicon nitrides
1.1.2. Carbonitrides
1.1.3. Porosity evolution during polymer-to-ceramic conversion. Strategies to retain microporosity in polymer-derived ceramics at high temperatures.
1.2. Microporous materials for H2 and CO2 gas capture and storage
1.2.1. Materials for H2 storage: current research trends and perspectives
1.2.1.1. Conventional H2 storage
1.2.1.2. Materials-based H2 storage
1.2.1.3. Materials demands for H2 storage by physisorption
1.2.2. Materials for CO2 capture and storage: current research trends and perspectives
1.2.2.1. Traditional CO2 capture method: Chemical absorption with monoethanolamine (MEA)
1.2.2.2. Materials-based CO2 capture
1.2.2.3. Materials demands for CO2 capture by physisorption
1.2.3. Commercial prospectives for materials for gas capture and storage
1.3. Gas separation methods. Membranes for H2 separation
1.3.1. General considerations and gas permeation mechanisms
1.3.1.1. Hagen-Poiseuille mechanism
1.3.1.2. Knudsen diffusion mechanism
1.3.1.3. Surface diffusion mechanism
1.3.1.4. Gas-translational mechanism
1.3.1.5. Molecular sieving
1.3.1.6. Solid state diffusion mechanism
1.3.1.7. Gas transport regime within pores of different size and composition
1.3.2. Membranes derived from polymer-derived ceramics (PDCs)
4. Part II. Experimental
5. Chapter 2. Experimental procedures
2.1. Materials and synthesis parameters
2.2. Characterization of silicon oxycarbonitride (SiCNO) ceramics
2.2.1. Elemental analysis
2.2.2. Fourier transformation infrared spectroscopy (FTIR)
2.2.3. Simultaneous thermal analysis (STA)
2.2.4. X-ray scattering
2.2.4.1. Powder diffraction (XRD)
2.2.4.2. Total X-ray scattering experiments-pair distribution function (PDF)
2.2.4.3. Small angle X-ray scattering (SAXS)
2.2.5. Solid-state nuclear magnetic resonance (NMR)
2.2.6. Transmission electron microscopy (TEM)
2.2.7. Gas adsorption experiments
2.2.7.1. N2 physisorption
2.2.7.2. CO2 physisorption
2.2.8. High pressure CO2 adsorption experiments
2.2.8.1. Calculation of the isosteric heat of adsorption (Qst)
2.2.9. H2 adsorption experiments
2.3. Gas separation membranes
2.3.1. Substrates
2.3.1.1. Alumina substrates
2.3.1.2. Zirconia substrates
2.3.2. Preparation of preceramic polymer solution and slurry for dip-coating
2.3.3. Deposition of preceramic polymers on porous substrates by dip-coating
2.3.4. Gas permeance measurements
6. Part III. Results and discussion
7. Chapter 3. Structure and porosity characteristics of silicon oxycarbonitride ceramics
3.1. Structure and composition
3.2. Thermal transformation of ceramers to ceramics as revealed by thermogravimetric (TG) and FTIR characterization
3.3. Nitrogen incorporation as revealed by total X-ray scattering experiments
3.4. Local structures as revealed by 29Si NMR
3.4.1.1. Ceramics derived from SMP-10 and HTT-1800
3.4.1.2. Ceramics derived from SPR-212a
3.5. Local structures as revealed by 13C NMR and 1H NMR
3.6. Heterogeneity of elemental distribution in microporous SPR600NHAr and nonporous SMP600NHAr as revealed by TEM-EELS characterization.
3.7. Porosity development and BET surface area as revealed by N2 adsorption
3.8. The homogeneity and size of the pores
3.9. Nature of the adsorbing surfaces
3.10. Porosity characteristics as revealed by small angle X-ray scattering study
3.11. Porosity – structure relationship
3.12. Summary
8. Chapter 4. Silicon oxycarbonitride ceramics for gas capture and separation
4.1. Ultramicroporous silicon nitride based ceramic for CO2 capture
4.1.1. CO2 capture capacity measured at 0 and 100 oC
4.1.2. Physical nature of CO2 adsorption on the ultramicroporous silicon nitride as confirmed by the isosteric heat of adsorption (Qst)
4.1.3. Dependence of the CO2 storage capacity on the pore size
4.2. H2 adsorption isotherms
4.3. Silicon oxycarbonitride ceramics for gas separation: ceramic membranes
4.3.1. Gas permeation properties of ceramic membranes derived from polycarbosilane (SMP600NHAr1, SMP600NHAr2, SMPAr)
4.3.1.1. Gas transport through SMP600NHAr1 membrane
4.3.1.2. Gas transport through SMPAr membrane
4.3.1.3. Gas transport through SMP600NHAr2 membrane
4.3.1.4. Summary of gas permeance mechanism for ceramic membranes derived from polycarbosilane
4.3.2. Gas permeation properties of ceramic membranes derived from polysiloxane (SPR600NHAr1, SPR600NHAr2)
4.3.2.1. Gas transport through SPR600NHAr1 membrane
4.3.2.2. Gas transport through SPR600NHAr2 membrane
4.3.2.3. Summary of gas permeance mechanism for ceramic membranes derived from polysiloxane
4.3.3. Gas permeation properties of ceramic membranes derived from polysilazane (HTT600NH, HTT600NHAr, HTTAr)
4.3.3.1. Gas transport through HTT600NHAr and HTTAr membrane
4.3.3.2. Gas transport through HTT600NH membrane
4.3.3.3. Summary of gas permeance mechanism for ceramic membranes derived from polysilazane
9. Chapter 5. Conclusions and outlook
Research Objective and Topics
This doctoral dissertation aims to investigate the potential and limitations of silicon oxycarbonitride ceramics, synthesized via an NH3-assisted thermolysis route from preceramic polymers, for use as H2 gas separation membranes and as powder-based materials for H2 or CO2 capture and storage. The core research question addresses whether these materials can be engineered with tailored chemical compositions and microporous structures that remain stable at high temperatures, thereby facilitating sustainable "green carbon" energy transitions.
- Synthesis and characterization of polymer-derived microporous silicon oxycarbonitride ceramics.
- Evaluation of CO2 capture capacities and H2 storage properties in these ceramic materials.
- Fabrication of ceramic membranes on porous supports for H2/N2 gas separation.
- Elucidation of nitrogen incorporation mechanisms and their role in developing stable microporosity.
- Analysis of gas permeation mechanisms through ceramic membranes under various temperature regimes.
Excerpt from the book
3.1. Structure and composition
Commercially available polycarbosilane (SMP-10), polysiloxane (SPR-212a) and polysilazane (HTT-1800) have been subjected to an intermediate thermolysis step under an NH3 atmosphere (ammonolysis step) at temperatures between 300 – 800 °C with the subsequent thermolysis under an Ar atmosphere at 750 °C for 3 h as explained in section 2.1. Detailed synthesis parameters, polymer structure and resulted samples are summarized in Figure 2-1.
Resulted samples and their colour variation in dependence on synthesis parameters are displayed in Figure 3-1. The XRD characterization (Figure 3-2) reveals that all specimens studied in this work are amorphous. Table 3-1 summarizes the chemical composition of the specimens.
Summary of Chapters
Chapter 1. Literature survey: Provides a comprehensive overview of current research trends in microporous materials for H2 and CO2 storage and separation, including the mechanism of polymer-derived ceramics.
Chapter 2. Experimental procedures: Details the synthesis parameters, characterization techniques such as XRD, NMR, TEM, and gas adsorption, as well as the fabrication methods for ceramic membranes.
Chapter 3. Structure and porosity characteristics of silicon oxycarbonitride ceramics: Discusses the structural analysis and nitrogen incorporation, confirming that NH3-assisted thermolysis effectively produces microporous ceramics.
Chapter 4. Silicon oxycarbonitride ceramics for gas capture and separation: Evaluates the experimental performance of the synthesized ceramics for CO2 capture and H2 gas separation membranes.
Chapter 5. Conclusions and outlook: Summarizes the key findings regarding the effectiveness of the NH3-assisted synthesis route and offers perspectives for future material optimization.
Keywords
Silicon oxycarbonitride, Polymer-derived ceramics, Microporosity, NH3-assisted thermolysis, Gas capture, CO2 adsorption, H2 storage, Gas separation membranes, Ceramic membranes, Nitrogen incorporation, Solid-state NMR, Small angle X-ray scattering, Material characterization.
Frequently Asked Questions
What is the primary focus of this dissertation?
The thesis explores the synthesis, structural characterization, and application of silicon oxycarbonitride ceramics derived from preceramic polymers, specifically targeting gas storage and separation applications.
What are the central research themes?
The central themes include the NH3-assisted synthesis route, the development of stable microporosity, and the evaluation of these materials for CO2 capture and H2 gas separation.
What is the primary goal of the research?
The research aims to develop a cost-effective, scalable synthesis method to create microporous ceramic materials with tailored pore sizes and surface chemistry suitable for sustainable "green carbon" energy applications.
Which scientific methods were utilized?
The study employs a variety of techniques including solid-state NMR, total X-ray scattering (PDF), Small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and gas adsorption isotherms (N2 and CO2).
What does the main body of the work cover?
The main body investigates the relationship between synthesis parameters and final material properties, specifically the role of nitrogen incorporation in forming stable micropores and the gas permeation behaviors of derived membranes.
What are the characteristic keywords of this work?
Key terms include silicon oxycarbonitride, polymer-derived ceramics, microporosity, gas capture, H2 storage, gas separation, and NH3-assisted thermolysis.
Why is the role of nitrogen important in these materials?
Nitrogen incorporation during the NH3-assisted thermolysis is critical because it facilitates the formation of SiN4 and SiO2N2 building blocks, which help stabilize the microporous network even at high temperatures.
What specific result was achieved for the membrane performance?
The polycarbosilane-derived membranes demonstrated a high permselectivity for H2 over N2 of 7.2 at 300 °C, indicating potential for efficient high-temperature gas separation.
- Quote paper
- Cristina Schitco (Author), 2015, NH3-Assisted Synthesis of Silicon Oxycarbonitride Ceramics for Gas Capture and Separation, Munich, GRIN Verlag, https://www.grin.com/document/335128
