Oxidation products and pathway of ceramic honeycomb-catalyzed ozonation for the degradation of nitrobenzene in aqueous solution

Semi-continuous experiments on catalytic ozonation of nitrobenzene (NB) in aqueous solution using ceramic honeycomb as catalyst have been investigated. Experimental results showed that the presence of ceramic honeycombs significantly increased the ozonation degradation rate of NB compared to the case of non-catalytic ozonation. With addition of the radical scavenger tert-butanol, the evident reduction of NB removal indicated that NB was oxidized primarily by hydroxyl radical ((OH)-O-center dot) in the both systems of ozonation alone and ozonation/ceramic honeycomb. The total organic carbon removal suggested that in the process of ozonation/ceramic honeycomb NB was more quickly mineralized than that by ozonation alone. The absorbance of UV-vis spectra confirmed that carboxylic acids and aromatic compounds were predominant oxidative organic products of NB by catalytic ozonation. The oxidative decomposition products (o-, p-, m-nitrophenols, phenol, 4-nitrocatechol, hydroquinone, p-quinone, 1,2,3-trihydroxy-5-nitrobenzene, maleic acid, malonic acid, oxalic acid, acetic acid and nitrate ion) have been identified by GC/MS and IC, indicating that degradation proceeded via (OH)-O-center dot oxidation. A general reaction pathway for the degradation of NB was proposed by the evidence presented in this study. (C) 2007 Elsevier B.V. All rights reserved.