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 (VV(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.