ESR Study of Active Oxygen Radicals from Photoexcited Semiconductors Using the Spin-Trapping Technique

The ESR spin-trapping technique was used to detect active oxygen radicals by photoexcitation of powdery semiconductors (TiO2, WO3, CdS, and Fe2O3) in water and aqueous H2O2 solutions using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as spin trap. Superoxide ion (O2−), hydroperoxyl radical (·O2H) and hydroxyl radical (·OH) were detected under photoexcitation. The mechanism for the generation of active oxygen radicals is discussed referring to the energy band structures of the semiconductors and the redox potentials of the oxygen radicals.