"The huge demand for fossil fuels and the risks of the environmental crisis have spurred an interest in renewable energies. Using the clean and abundant solar energy, semiconductor photocatalysis and photovoltaics have evoked tremendous interest. Titanium dioxide (titania, TiO2) has been the focus of the research trend because of its excellent crystallinity, photoreactivity, chemical and thermal stability, and low cost. The research objective presented in this dissertation is to fabricate titania nanomaterials with tunable porosities, large surface area, unique morphologies, and enhanced capacities of adsorption, electron transport, diffusion, and then apply them in photocatalysis and photovoltaics. A modified non-hydrolytic sol-gel system with calcium carbonate templating was developed to create macro/micro/nano porous anatase titanium dioxide. The hydrolysis rate was lowered by chelating ligands of valeric acid for slow and sufficient precursor coating. CaCO3 was completely removed via acidification, resulting in titania powders with a surface area ranging from 197 to 239 m2/g. The templated TiO2 with a surface area of 239 m2/g and pore diameters of 6-109 nm showed a promising 27% photocatalytic improvement compared to commercial particles, and a 180% increase compared to template-free TiO2. This increase is attributed to the increased catalyst loading capacity and active photocatalytic sites. From hard templates to soft biodegradable natural templates, the rate-controlled sol-gel method was combined with homogenized micro/nano-fibrillated cellulose (MFCs) with an average diameter below 50 nm. Cellulose was removed completely by thermal treatment, and an in-situ coating technique created thin titania films on substrates with a porous structure. The degradation efficiency of the photocatalytic films was related to film thickness and to the Ti(IV)-to-cellulose ratio. Photocatalyst on film eliminated the post separation treatment related to powder catalyst and simplified the purification process. The sol-gel/MFCs precursor was also coated in-situ as the photoanode for dye-sensitized solar cells. It was found that the thickness of the anode film was a dominant factor to the overall performance and efficiency. The 6-layer cell showed a 400303% increase in solar-to-electricity efficiency (1.75%) compared to commercial paste at the same thickness under a simulated solar light irradiation of 100 mW cm-2 (AM 1.5). From non-hydrolytic to hydrolytic, a modified liquid phase deposition (LPD) approach was combined with MFCs. An optimized solvent composition of isopropanol/water ratio of 4 to 1 was found to yield coatings with uniform spherical TiO2 possessing a chain-like morphology oriented along the axis of the decomposed cellulose fibers. The average rate constant and degradation percentage were 0.72±0.09 min-1, 95% for TiF4-cellulose-4IPA1Water films, which increased by 1.88 times over the film prepared without cellulose templates due to the beneficial surface area, pore size, and the unique morphology. The three-dimensional web structure with pseudo one-dimensional sphere-chain could retard the recombination of photogenerated electron-hole pairs and improve the charge transport."--Pages ii-iii.
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