Surface Chemistry and Interfacial Charge-Transfer Mechanisms in Photoinduced Oxygen Exchange at O2-TiO2 Interfaces

Experimental results obtained over the last three decades on photoinduced oxygen isotopic exchange (POIE) of TiO2 oxygen atoms with those of adsorbed water molecules and gaseous O-2 are analyzed in the light of recent information from the literature on the interaction of water and O-2 species with the TiO2 surface (obtained by application of surface spectroscopy techniques in combination with high-resolution scanning tunnelling microscopy). The analysis emphasizes the singular role that bridging oxygen ions and bridging oxygen vacancies play in TiO2 surface chemistry and interfacial electron transfer at the gas phase-TiO2 interface in the absence and presence of water. The observed competition between POIE and the photo-oxidation (PO) of organic compounds is analyzed in terms of the recently developed direct-indirect (D-I) kinetic model for heterogeneous photocatalysis (D. Monllor-Satoca et al., Catal. Today, 2007, 129, 247, and references therein).