| AVS 64th International Symposium & Exhibition | |
| Surface Science Division | Monday Sessions |
| Session SS+AS+HC-MoA |
| Session: | Surface Science for Energy and the Environment |
| Presenter: | Amanda Muraca, Stony Brook University |
| Authors: | A.R. Muraca, Stony Brook University M.G. White, Brookhaven National Lab and Stony Brook University |
| Correspondent: | Click to Email |
Organic photooxidation processes on the TiO2(110) surface often show enhanced photoproduct yields in the presence of oxygen. For a series of simple ketones, it has widely been established that the photoactive surface species is a ketone-oxygen complex (η2-ketone diolate) formed by interaction with O-adatoms, whereas the η1-bound ketone is mostly photo-inactive.1 The question remains, however, why the ketone-oxygen complexes are more photoactive than the adsorbed ketone alone. One possible explanation is that the diolate species have higher densities of molecular states near the valence band maximum (VBM) of TiO2, where resonant electron transfer to thermalized holes is expected to occur. To test this hypothesis, a series of methyl photoyield measurements, with and without co-adsorbed oxygen, were compared for a number of substituted ketone molecules (R(CH3)CO; R = H, methyl, ethyl, butyl, propyl, phenyl, and trifluoromethyl) with varying ionization potentials (IPs). Experimentally, we observe a near linear correlation between the methyl photoproduct enhancement yields (diolate vs ketone) and the IPs of the bare ketone. These results suggest that as the ketone IP moves to higher energies, its hybridized orbitals move further (deeper) from the VBM and thereby exhibit a larger photoproduct enhancement when forming the ketone-diolate. This explanation points to orbital band alignment as the key factor determining ketone photoxidation activity, but this conclusion is largely based on the gas-phase properties and well established ideas of substituent effects. To gain more insight on our experimental results, we are currently using electronic structure calculations, both cluster models and periodic DFT, that could potentially provide more detail on band alignments for these molecules bound on the TiO2(110) surface.
1. M. A. Henderson, N. A. Deskins, R. T. Zehr, M. Dupuis, J. Catal.2011, 279, 205; N. G. Petrik, M. A. Henderson, G. A. Kimmel, J. Phys. Chem. C 2015, 119, 12262.