ESR Spin-Trapping Study of Active Oxygen Radicals from Photoexcited Semiconductors in Aqueous H2O2 Solutions

Abstract

Abstract Experiments were carried out concerning the relation between the production of active oxygen radicals from three semiconductors [TiO2 (anatase and rutile) and WO3] and the concentration of H2O2 by the ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. Two natures of hydroxyl radicals were produced from photoexcited semiconductors in aqueous H2O2 solutions. These originated in the reduction of H2O2 and the oxidation of water, which were confirmed using 17O-labeled water. The mechanism for the generation of active oxygen radicals is discussed regarding the energy band structures of the semiconductors, the redox potentials of the oxygen radicals, and the surface acidity and basicity of semiconductors.