Effect of Fenton-like oxidation on enhanced oxidative degradation of para-chlorobenzoic acid by ultrasonic irradiation

Abstract

Sonolysis, Fenton-like oxidation (FeOOH-H2O2), and a combination of the two processes were used to facilitate the degradation of para-chlorobenzoic acid (a model compound for free radical mediated reactions). The objective of this study was to investigate the effect of FeOOH and H2O2 dosages on the degradation of para-chlorobenzoic acid (p-CBA) using ultrasound/FeOOH-H2O2. The oxidation rate of p-CBA was measured at various concentrations of H2O2 and FeOOH particles and pH conditions. pH's below the pK(a) of p-CBA (3.98), showed significantly better degradation of p-CBA than at higher values from 5 to 9. The rates of degradation of p-CBA by FeOOH-H2O2 were enhanced in the presence of ultrasound. The first-order rate constant, k, for p-CBA degradation by ultrasound was 4.5 x 10(-3) min(-1), and in the presence of FeOOH-H2O2 this was found to be substantially faster (1.54 x 10(-2) min(-1)). The observed rate enhancements for the degradation of p-CBA can be attributed primarily to the continuous cleaning and chemical activation of the FeOOH surfaces by acoustic cavitation and the accelerated mass transport rates of reactants and products between the solution phase and the FeOOH surface. This new process provides a viable alternative to existing oxidation technologies. (C) 2003 Elsevier B.V. All rights reserved.