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 (DMP O) and N-r-butyl-or-phenyl-nitrone (PBN) as spin-trap reagents has been app lied to detect free radical intermediates generated during the in situ visi ble irradiation of aqueous sulforhodamine B (SRB)-TiO2 air-saturated disper sion. 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 oxyge n radicals and the role of these photogenerated active oxygen radicals in t he photo-oxidation process are discussed. It is suggested that the oxygen m olecules rather than these active oxygen radicals are the main oxidizing ag ent and play an important role in the visible photo-oxidation of SRB mediat ed by TiO2 particles. (C) 2000 Elsevier Science S.A. All rights reserved.