Kinetics of the photosensitized degradation of benzyl 4-hydroxybenzoate in homogeneous aqueous solution under visible-light irradiation

Abstract

The photosensitized oxidation of benzyl 4-hydroxybenzoate (benzylparaben, BeP), the endocrine disrupting compound, in homogenous aqueous solution of 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzenesulphonic acid) (TPPS4) as photosensitizer was examined. A xenon lamp simulating solar radiation was used as a light source. The influence of pH of the reaction mixture, oxygen content and initial concentrations of photosensitizer and BeP on the reaction rate was studied. The major role of singlet oxygen in BeP degradation was proved by the experiments performed in the presence of hydroxyl radicals scavengers and singlet oxygen quenchers. The rate constants of singlet oxygen quenching by BeP in D2O buffer (pD 7, 9 and 10.8) were determined. Based on the kinetic model, the rate constants of singlet oxygen quenching and reaction with BeP as well as the rate constant of excited photosensitizer quenching by BeP were determined.