Substituent effects on photodegradation of phenols in binary mixtures by hybrid H2O2 and TiO2 suspensions under UV irradiation

The use of hybrid H2O2 and TiO2 suspensions for photodegradation of phenol, o-cresol, and 4-chlorophenol (4-CP) in single and binary solutions was investigated under UV irradiation. The degradation of each phenol in either single or binary systems could be fitted well by the pseudo-first-order kinetics based on the Langmuir-Hinshelwood model. The degradation rates of these phenols in single system decreased in the order 4-CP > phenol > o-cresol using UV alone (photolysis), H2O2/UV, TiO2/UV, or H2O2/TiO2/UV process, which could be explained by the types and positions of phenyl-ring substitution of phenols. In contrast to single systems, the depression in degradation rate of each reactant was observed in binary systems, particularly when the second reactant was in excess. Reaction intermediates during the degradation of binary mixtures of phenol/o-cresol and phenol/4-CP by H2O2/TiO2/UV process were also identified and discussed. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.