Synthesis and characterization of mesoporous silica/titania nanocomposites : potential additives for dye sensitized solar cells (DSSCs)
- Authors: Akawa, Mpingana Ndilimeke
- Date: 2017
- Subjects: Dye-sensitized solar cells , Nanostructured materials , Mesoporous materials , Silica , Titanium
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235628 , uj:24100
- Description: M.Sc. (Nanoscience) , Abstract: The photoanode is an important part of the DSSCs as it is the medium for dye adsorption, electron transport and electrolyte diffusion. The composition and morphology of the photoanode therefore directly influences the performance of the cell. Optimising the morphology of the photoanode is therefore one of the key factors in improving the performance of the DSSCs. This work entailed the synthesis of titania supported on silica nanocomposites for use as light scattering materials in the photoanode with the motivation of optimising the morphology of the photoanode and further enhance the energy conversion efficiency of the DSSCs. The silica support materials, specifically mesoporous silica, SBA-15 and non-mesoporous SiO2 were synthesized through the soft-template acid catalyzed sol-gel method and base catalyzed sol-gel method respectively. Two SBA-15 nanomaterials were synthesized by varying the hydrolysis and aging times which resulted in materials of different textural and morphological properties. These silica support materials (SiO2, SBA-15 A1 and SBA-15 A2) were used as support materials for the synthesis of TiO2 supported on silica nanocomposites. Also, TiO2 nanoparticles of size 19.32 ±3.70 nm (n = 193) were synthesized for use as active site of the photoanode. The physical, chemical and optical properties of the nanoparticles and nanocomposites were studied using FTIR, TEM, Nitrogen Sorption, SEM-EDS, XRD, and diffuse reflectance Ultraviolet-Visible (DR-UV-VIS) spectroscopy. The nitrogen desorption results of the 10 wt% TiO2 / SBA-15 nanocomposites just like the parent SBA-15 support, revealed the Type IV isotherms with H1 hysteresis loops which indicated that the support materials did not lose their mesoporosity and uniform pore size arrangement upon incorporation of TiO2 nanocrystals. This finding was supported by the TEM results. The energy band gaps of TiO2 supported on the mesoporous silica (SBA-15) (3.60 eV) were blue shifted relative to the unsupported TiO2 (3.44 eV) and TiO2 supported on the non-mesoporous SiO2 (3.55 eV). These results confirmed the XRD results which indicated smaller TiO2 crystallite sizes for TiO2 crystals supported on the SBA-15 support materials which were 10.60 nm as compared to the unsupported TiO2 and TiO2 supported on the non-mesoporous SiO2 (15.89 nm). The band gap increased as the crystallite sizes decreased...
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Tailoring mesoporous transition metal oxides for sustainable heterogeneous catalysis
- Authors: Akinnawo, Christianah Aarinola
- Date: 2020
- Subjects: Heterogeneous catalysis , Transition metal oxides , Mesoporous materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/473879 , uj:42694
- Description: Abstract: Chemical processes, both in the laboratory and industrial sectors, involve designing products to meet human needs. However, during these processes, more environmental problems are created due to the generation of non-useful by-products and toxic effluents that are harmful to the biosphere. Also, these chemical processes are performed under harsh reaction conditions. The conventional homogeneous catalysts often used suffer deactivation at high temperatures, and the separation problem makes reusability, recycling, and recovery difficult. Hence, for sustainable chemical processes, novel heterogeneous mesoporous transition metal oxide catalysts were designed. The catalysts were utilized in redox and acetalization conversions, both as active phase and nanoparticle support... , Ph.D. (Chemistry)
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Application of well-defined nanoparticles as catalysts for kinetic studies of model reactions, and their immobilization on mesoporous SBA-15 for olefin oxidation
- Authors: Bingwa, Ndzondelelo Sigqibo
- Date: 2015-06-26
- Subjects: Catalysis , Nanoparticles , Dendrimers , Mesoporous materials , Reactivity (Chemistry)
- Type: Thesis
- Identifier: uj:13626 , http://hdl.handle.net/10210/13807
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
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Synthesis and characterization of organic–inorganic mesoporous silica materials for use as stationary phases for solid phase extraction (SPE) and HPLC columns
- Authors: Maiga, Deogratius Titus
- Date: 2015-11-09
- Subjects: Mesoporous materials , Silica , Union of Applied Chemistry (IUPAC)
- Type: Thesis
- Identifier: uj:14525 , http://hdl.handle.net/10210/15048
- Description: M.Sc. (Chemistry) , According to the International Union of Applied Chemistry (IUPAC) mesoporous silica materials are a class of materials which contain pore size with diameters ranging from 2 to 50 nm. Due to their attractive features such as large surface area along with tunable pore size, accessible silano groups and easy functionalization make them with special properties to be employed as stationary phases for different chromatographic applications such as clean up, preconcentration, purification and separation of analytical samples. Organic–inorganic mesoporous hybrid materials are a new class of materials obtained when an inorganic material, such as mesoporous silicas are surface modified using an organic material via silylation. The main advantage of these hybrid materials is that they are formed by combining dissimilar properties of inorganic and organic materials into one material. Whereas the inorganic materials provide rigidity and thermal stability, the organic components provide flexibility, dielectric, ductility, and processability. Therefore the advantages of these hybrid materials lead them to be used over a wide range of applications. The main objective of this study was to synthesize organic-inorganic hybrid mesoporous silica materials for use as stationary phases for solid phase extraction and high performance liquid chromatography columns. The materials were prepared under basic conditions using silica gel and tetraethyl orthosilicate used as a source of silica and modified by either surface polymerization or grafting methods using octadecyltrimethoxysilane followed endcapping with hexamethyldisilazane. The materials were characterized before and after surface modification using different analytical methods. Scanning electron microscopy (SEM) pictures showed that the morphology of the materials remained unchanged after surface modification.
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Synthesis of mesoporous composite nanostructured materials for extraction of selected emerging organic pollutants
- Authors: Motlhale, Elisah
- Date: 2017
- Subjects: Mesoporous materials , Nanostructured materials , Organic water pollutants , Carbon nanotubes , Adsorption
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/244105 , uj:25241
- Description: M.Sc. (Nanoscience) , Abstract: The presence of emerging contaminants in water has become a serious concern recently, not only because of the risks they pose to human health and aquatic life, but also due to their continuous accumulation in aquatic environment. Pharmaceuticals, such as paracetamol, ibuprofen, caffeine, aspirin and nalidixic acid are commonly found within the environment and are considered to be emerging contaminants. Methods such as solid phase extraction are usually used to extract and eventually quantify pharmaceuticals from water. Dispersive micro solid phase extraction (DMSPE) is a recent development that uses nanomaterials for the extraction and eventual quantification of emerging contaminants from water. Typically nanomaterials with high surface areas and good chemical stability are used. Therefore the following study investigated the use of mesoporous silica, specifically SBA-15, acid-treated multi-walled carbon nanotubes (MWCNTs) and nanocomposite of SBA-15 coated onto the sidewalls acid-treated multi-walled carbon nanotubes (CNTs) as adsorbents for extraction of paracetamol from water. The nanomaterials were prepared and the physical and chemical properties were investigated using characterization techniques such as N2 adsorption at 77 K, high-resolution transmission electron microscopy, Fourier Transform-Infrared, Raman spectroscopy and X-ray diffraction. The aim of this project was to extract paracetamol from water using nanomaterials as adsorbents. The quantification was accomplished using high-performance liquid chromatography-photo diode array detector (HPLC-PDA). The highest recovery of paracetamol was 98.3%...
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