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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Green technology extraction and characterisation of silica nanoparticles from palm kernel shell ash via sol–gel
- Authors: Imoisili, Patrick E. , Ukoba, Kingsley O. , Jen, Tien-Chien
- Date: 2020
- Subjects: Palm kernel shell ash , Silica , Sol–gel
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/435667 , uj:37761 , Citation: Imoisili, P.E., Ukoba, K.O. & Jen, T.C. 2020. Green technology extraction and characterisation of silica nanoparticles from palm kernel shell ash via sol–gel. , DOI: https://doi.org/10.1016/j.jmrt.2019.10.059
- Description: Abstract: Silica nanoparticles have numerous applications including drug delivery, lightweight aggre-gates, and energy storage. It has been manufactured from different agricultural bioresourceswith limited research on palm kernel shell ash (PKSA). This study produced silica nanoparti-cles from palm kernel shell ash. Modified sol–gel extraction technique was used to producethe silica nanoparticles from PKSA. The extracted silica nanoparticles were characterizedusing X-ray diffraction (XRD), Scanning electron microscope (SEM) with Energy dispersiveX-ray (EDX), Fourier transform infrared (FT-IR) techniques, Brunauer–Emmett–Teller (BET)method and Thermogravimetric analysis (TG). The microstructural analysis reveals that theunit size of the extracted silica nanoparticles is between 50–98 nm, with a very high specificsurface area (438 m2g−1). EDX confirmed the presence of SiO2in the sample. FT-IR analysisshows the existence of silanol and siloxane groups. This success means, decrease in envi-ronmental contamination caused by indiscriminate disposal of palm kernel shell (PKS) andsilica nanoparticles for advanced material applications.
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Environmental silica dust exposure and pulmonary tuberculosis in Johannesburg, South Africa
- Authors: Kootbodien, Tahira , Iyaloo, Samantha , Wilson, Kerry , Naicker, Nisha , Kgalamono, Spo , Haman, Tanya , Mathee, Angela , Rees, David
- Date: 2019
- Subjects: Pulmonary tuberculosis , Occupational dust exposure , Silica
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/397414 , uj:33031 , Citation: Kootbodien, T. et al. Environmental silica dust exposure and pulmonary tuberculosis in Johannesburg, South Africa. Int. J. Environ. Res. Public Health 2019, 16, 1867; doi:10.3390/ijerph16101867
- Description: Abstract: Background: Occupational crystalline silica dust exposure is associated with an elevated risk of pulmonary tuberculosis (PTB). However, there is less evidence for an association with environmental silica dust exposure. Methods: A cross-sectional study of 310 participants was conducted in an exposed community living within 2 km of gold mine tailings and an unexposed population residing more than 10 km from the nearest gold mine tailing. Chest radiographs (n = 178) were read for PTB, past or current, by three readers. Results: Past or current PTB was radiologically identified in 14.4% (95%CI 9.2–21.8) in the exposed and 7.5% (95%CI 2.8–18.7) in the unexposed groups. Multivariate logistic regression models suggested that PTB prevalence was independently associated with exposure to second-hand smoke (OR = 8.13, 95%CI 1.16–57.22), a lower body mass index (OR = 0.88, 95%CI 0.80–0.98), previous diagnosis and treatment of PTB (OR = 8.98, 95%CI 1.98–40.34), and exposure to dust in the workplace from sand, construction, and/or mining industries (OR = 10.2, 95%CI 2.10–50.11). Conclusion: We found no association between PTB and environmental exposure to gold mine tailing dust. However, workplace silica dust exposure is a significant risk factor for PTB in South Africa, and PTB patients of working age should be screened for silica exposure.
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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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