Hydrogen peroxide photoproduction sensitized with rose bengal with semicarbazide as the electron source

Abstract

The xanthene dye rose bengal was used to sensitize the photochemical production of hydrogen peroxide with semicarbazide as a sacrificial electron donor. The optimum experimental conditions concerning pH, light quality, photon flux density, concentration of the different components, sensitizer immobilization etc. were selected so that the final peroxide yield was enhanced and the pigment photobleaching slowed down. The overall reaction was found to proceed via reductive quenching of the photoexcited rose bengal in its triplet state by semicarbazide; the reduced rose bengal in turn reducing oxygen to superoxide and hydrogen peroxide. Alternatively, an energy transfer mechanism by which rose bengal tranfers its excitation energy to molecular oxygen appears to take place simultaneously, with the consequent formation of singlet oxygen, which would be responsible for the observed pigment bleaching.