Abstract
Singlet molecular oxygen (¹O₂), which was produced with a significant yield, was detected from a powder-type TiO₂ photocatalyst irradiated with a 355-nm laser pulse by monitoring its near-infrared phosphorescence at 1270 nm. Lifetime measurements for the 1O2 produced at TiO₂ (Degussa P25) in various environments, such as in air and in suspensions of H₂O, D₂O and ethanol, indicated that quenching takes place mainly at the TiO₂ surface in the absence of reactants. Quantum yields for ¹O₂ generation were measured for ten commercial TiO₂ photocatalysts in air and ranged from 0.12 to 0.38, while the lifetimes ranged from 2.0 to 2.5 us. Since the quenching by the TiO₂ surface is quite fast, the formation and decay processes of ¹O₂ have not been distinguished from the recombination of the photogenerated electron-hole pairs. The values of quantum yield suggest that ¹O₂ may contribute to the oxidation of some organic molecules at the irradiated TiO₂ surface.

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