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 (Vo) defects. Utilizing electron energy loss spectroscopy and density functional theory, we show that the lack of reactivity of TMA groups adsorbed at Vo's cannot be attributed to either a less active adsorption conformation or electron transfer from the Vo defect. Instead, we propose that the excess unpaired electrons associated with the Vo promptly recombine with photoexcited holes approaching the surface, effectively "screening" TMA species at the Vo site. We also show that this screening effect is predominately localized at the Vo, only mildly affecting TMA's at adjacent Ti sites. [ABSTRACT FROM AUTHOR]