Estimation of •OH radical reaction rate constants for phenol and chlorinated phenols using UV/H2O2 photo-oxidation

A detailed investigation on UV/H2O2 photooxidation has been carried out in order to determine the kinetics of the oxidative degradation of phenol and 2- and 4-chlorophenols in dilute aqueous solutions. Effects of different process parameters, such as initial substrate and H2O2 concentrations, substrate to H2O2 ratio on the degradation kinetics of the phenolic substrates, have been studied. Degradation rates of phenol and chlorophenols are insignificantly small with ultraviolet radiation only and also with hydrogen peroxide (in the absence of UV radiation), but the synergistic effect of UV/H2O2 results in a marked enhancement of the rates of degradation. A mechanistic model for UV/H2O2 photooxidation has been developed. Room temperature (27 degrees C) rate constants for the reaction of (OH)-O-. radical (formed by absorption of photons) with the substrates have been estimated by using the model equation. The calculated rate constants are of the same order of magnitude as reported for other similar aromatic compounds. (C) 1999 Elsevier Science B.V. All rights reserved.