UV-enhanced exchange of O-2 with H2O adsorbed on TiO2

Ultraviolet light dramatically increases the rate of isotope exchange betwe en gas-phase O-2 and water adsorbed on TiO2 at room temperature, but it doe s not affect the rate of CO2-water exchange. Both ethanol and acetaldehyde, when coadsorbed with (H2O)-O-18, dramatically decrease the rate of O-2 exc hange, but not CO2 exchange, with adsorbed (H2O)-O-18. This decrease is att ributed to a combination of competition for adsorbed oxygen between exchang e and photocatalytic oxidation of the adsorbed organic and blocking of the oxygen adsorption sites by the organic. The same oxygen species participate in O-2-(H2O)-O-18 exchange and photocatalytic oxidation. (C) 1999 Academic Press.