Ozonation of chloronitrobenzenes in aqueous solution: kinetics and mechanism

Abstract

BACKGROUND: Chloronitrobenzenes (ClNBs) are a family of toxic and bio-resistant organic compounds. Ozone treatment is specifically suitable for partial or complete oxidation of non-biodegradable components. However, few studies on the decomposition of ClNBs by ozone are available, and kinetics and mechanisms of ClNBs ozonation have not been thoroughly investigated. The kinetics and mechanism of ozonation degradation of ClNBs in aqueous solution were investigated, and the contribution of both molecular ozone and hydroxyl radicals was also evaluated. RESULTS: The results demonstrated that the decomposition of ClNBs was a pseudo-first-order reaction with respect to the pollutant concentration and the overall rate constant increased with an increase in pH. It declined, however, with an increase in pollutant and radical scavenger concentration. Furthermore, TOC removal rate was significantly lower than that of ClNBs, but the same order o-ClNB < m-ClNB < p-ClNB was followed. Ozonation could not reduce TOC significantly, p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol and 5-chloro-2-nitrophenol were detected as primary degradation intermediates in ozonation of p-ClNB. Rate constants of the direct reaction between ozone and ClNBs at 25 °C had been found to be lower than 1 M−1S−1. More than 95% of ClNBs removal was due to hydroxyl radical oxidation at pH ≥ 7. CONCLUSION: Advanced oxidation processes may be the preferred choice for the elimination of ClNBs from the environment. Copyright © 2008 Society of Chemical Industry