ESR spin-trapping detection of radical intermediates in the TiO2-assisted photo-oxidation of sulforhodamine B under visible irradiation

The ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and N-r-butyl-or-phenyl-nitrone (PBN) as spin-trap reagents has been applied to detect free radical intermediates generated during the in situ visible irradiation of aqueous sulforhodamine B (SRB)-TiO2 air-saturated dispersion. Hydroxyl radical ((OH)-O-.), hydroperoxyl radical (HO2.) and hydrated electrons (e,g) were detected in the TiO2-assisted photo-oxidation of SRB under visible irradiation. The mechanism for the generation of active oxygen radicals and the role of these photogenerated active oxygen radicals in the photo-oxidation process are discussed. It is suggested that the oxygen molecules rather than these active oxygen radicals are the main oxidizing agent and play an important role in the visible photo-oxidation of SRB mediated by TiO2 particles. (C) 2000 Elsevier Science S.A. All rights reserved.