Identifying and quantifying active sites in heterogeneous catalytic systems is crucial to understanding and evaluating performance across different types of materials. This challenge is made more difficult for photocatalytic systems where the dynamics of light capture and charge separation are involved. It has previously been hypothesized that tetrahedral sites at the interface of anatase and rutile titania composites act as photocatalytic hotspots.[1] However, it is difficult to investigate this specific claim due to additional charge trapping and light absorption phenomena occurring in these materials. Here we utilize the natural tetrahedral coordination of silica to template titania materials in different ways that allow us to tune the structure of the solid-solid titania-silica interface, and thus probe the effect of tetrahedral Ti on photocatalytic activity. Crystalline titania was either grown or deposited onto a silica support yielding materials with different interfacial structures. We utilized newly-developed phosphorous-based titration techniques to quantify the number of accessible and tetrahedral Ti sites, [2] and measure the rate of benzyl alcohol photo-oxidation as a reaction probe. Our work allows us to examine the effects of interfacial coordination, particle size, and synthesis method. For example, when normalizing per surface-accessible Ti, the observed photocatalytic turnover frequency is 0.6 h-1 across three sets of titania-silica materials, independent of particle size. Time permitting we will also discuss other combined thermo- and photocatalytic systems where tetrahedral Ti plays a critical role. [1] a) D. C. Hurum, A. G. Agrios, K. A. Gray, T. Rajh, M. C. Thurnauer, Journal of Physical Chemistry B. 2003, 107, 4545-4549; b) G. Li, N. Dimitrijevic, L. Chen, J. Nichols, M. Graham, T. Rajh, K. A. Gray, Journal of the American Chemical Society 2008, 130, 5402-5403. [2] a) T. R. Eaton, M. P. Campos, K. A. Gray, J. M. Notestein, Journal of Catalysis 2014, 309, 156-165; b) T. R. Eaton, A. M. Boston, A. B. Thompson, K. A. Gray, J. M. Notestein, ChemCatChem 2014, 6, (online).

Controlling the titania-silica interface for enhanced (photo)catalytic performance

249th National Meeting (2015)

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