Inhibitive Influence of Oxygen Vacancies for Photoactivity on TiO2(110)

Scanning tunneling microscopy results reveal a pronounced site selectivity in the hole-mediated photooxidation of trimethyl acetate (TMA) on TiO2(110), wherein the reaction readily occurs at regular Ti sites but is completely inhibited at oxygen vacancy (V-O) defects. Utilizing electron energy loss spectroscopy and density functional theory, we show that the lack of reactivity of TMA groups adsorbed at V-O's cannot be attributed to either a less active adsorption conformation or electron transfer from the V-O defect. Instead, we propose that the excess unpaired electrons associated with the V-O promptly recombine with photoexcited holes approaching the surface, effectively "screening" TMA species at the V-O site. We also show that this screening effect is predominately localized at the V-O, only mildly affecting TMA's at adjacent Ti sites. DOI: 10.1103/PhysRevLett.109.266103