Breeson, Andrew; (2017) Control of Crystallinity in Photocatalytic Titanium Dioxide. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Powders and thin films of titanium dioxide (TiO2) were synthesised via wet chemical methods in two ways: a sol-gel synthesis, and a liquid phase deposition. Crystalline mixed phase powders, highly oriented films, and non-crystalline films of titanium dioxide have all been investigated. Specifically this investigation revealed dramatic differences in the XPS valance band spectra of the crystalline polymorphs of anatase and rutile, and subsequently a novel procedure for extracting quantitative phase information from X-ray photoelectron spectroscopy valence band spectra was developed. A linear relationship between the mixed phase TiO2 surface structure determined by this novel technique, and the ensuing photocatalytic activities were discovered. Additionally, highly oriented thin films of TiO2 were synthesised on single crystal substrates. Nitrogen doping of the films was achieved in two ways, and the distribution of the dopant within the films was revealed to be dramatically different for each method. Furthermore, N doping induced a phase transformation from highly aligned rutile to polycrystalline anatase. This result of a rutile to anatase transition at high temperature and not been observed previously. As before, these results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy valance band analysis. Lastly, non-crystalline, unaligned films of TiO2 on glass substrates were synthesised. The film structure was revealed to be porous, and successively exhibited superhydrophilic abilities without ultraviolet light irradiation. Further investigation via X-ray absorption spectroscopy techniques revealed the films to have anatase-like short range order with a significant tetrahedral titania component. The films were also shown to be highly photocatalytically active.Powders and thin films of titanium dioxide (TiO2) were synthesised via wet chemical methods in two ways: a sol-gel synthesis, and a liquid phase deposition. Crystalline mixed phase powders, highly oriented films, and non-crystalline films of titanium dioxide have all been investigated. Specifically this investigation revealed dramatic differences in the XPS valance band spectra of the crystalline polymorphs of anatase and rutile, and subsequently a novel procedure for extracting quantitative phase information from X-ray photoelectron spectroscopy valence band spectra was developed. A linear relationship between the mixed phase TiO2 surface structure determined by this novel technique, and the ensuing photocatalytic activities were discovered. Additionally, highly oriented thin films of TiO2 were synthesised on single crystal substrates. Nitrogen doping of the films was achieved in two ways, and the distribution of the dopant within the films was revealed to be dramatically different for each method. Furthermore, N doping induced a phase transformation from highly aligned rutile to polycrystalline anatase. This result of a rutile to anatase transition at high temperature and not been observed previously. As before, these results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy valance band analysis. Lastly, non-crystalline, unaligned films of TiO2 on glass substrates were synthesised. The film structure was revealed to be porous, and successively exhibited superhydrophilic abilities without ultraviolet light irradiation. Further investigation via X-ray absorption spectroscopy techniques revealed the films to have anatase-like short range order with a significant tetrahedral titania component. The films were also shown to be highly photocatalytically active.

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