GOALI: The Structure Sensitivity of Photochemical Reactions on Titanium Dioxide Surfaces

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9712606 Rohrer Systems based on solar activated titania photocatalysts have the potential to effectively and economically remove or degrade toxic impurities in air and water. Recent research conducted by the principal investigator of this proposal has recently demonstrated that some surfaces of titania, TiO2, are better at catalyzing the relevant reactions than others. If the anisotropy of this catalytic property were understood more completely, it might be possible to improve the reactivity of titania photocatalysts through structural or microstructural modifications. Therefore, the objective of this project is to define this orientation-reactivity relationship and to identify the mechanism responsible for this phenomenon. The photocatalytic activity of surfaces with known orientations will be determined using direct microscopic analysis. Electron back scattered diffraction patterns will be used to determine the surface orientations of many grains in a titania polycrystal and Auger electron spectroscopy will be used to assess the surface chemical compositions of the same grains. After using atomic force microscopy (AFM) to determine the morphological structure of each surface, they will be used to photocatalyze the reduction of Ag+ from aqueous solution. The amount of silver deposited on each grain will be estimated on the basis of AFM images and taken as a measure of the relative reactivity of each surface. Parallel experiments will be conducted on low index, homogeneous, high purity titania epi-layers grown on sapphire. Based on such measurements, we will determine the orientation dependence of the relative photocatalytic activity. %%% The outcome from this GOALI project will be a surface orientation-surface property relationship for the photocatalytic activity of titania. Defining this relationship will not only advance our inowledge of titania photochemistry, it will also demonstrate methods that can be used to systematically determine the full orientation dependence of other surface phenomena such as corrosion and wear. ***