Second Generation Photocatalysts: TiO2-Based Nanocomposites by dc Reactive Sputtering

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While the anatase phase of TiO2 is generally the best single-phase material in terms of its redox efficiency in air and water, mixed phase TiO2 (anatase + rutile) often exhibits higher photoactivity than pure phases alone. A detailed explanation of these phenomena, however, is lacking. Recent work in Gray's group has revealed insights into the nature of charge separation, trapping and recombination in mixed phase titania. There is a nanostructured morphology comprised of interwoven crystallites of rutile and anatase creating solid-solid interfaces across which photoexcited electrons are transferred from rutile to lower energy anatase lattice trapping sites. Physical vapor deposition of thin films offers a direct approach to systematically explore the structural aspects of solids (phase composition, grain size, defects. orientation and interfaces) in relation to the observed phenomena. By developing appropriate process controls, controlled synthesis and characterization will be correlated with functionality to understand interfacial structure and function, including its role in providing active sites for enhanced photocatalytic response. Functionality will be measured in terms of the reduction of CO2 in response to UV and visible radiation exposure.