Hydroxyl radical initiated photodegradation of 4-chloro-3,5-dinitrobenzoicacid in aqueous solution

The photodegradation of 4-chloro-3,5-dinitrobenzoic acid (CDNBA) in aqueous solution was investigated using advanced oxidation processes (AOP) involvi ng hydroxyl radical production: (i) UV-C photolysis of H2O2 using low or me dium pressure Hg arcs (UV/H2O2 process) and (ii) vacuum ultraviolet (VUV) p hotolysis of water at 185 nm (low pressure Hg are with Suprasil envelope) a nd at 172 nm (Xe-excimer lamp). These processes were shown to be efficient methods for CDNBA mineralization, in contrast to CDNBA photolysis. For the UV/H2O2 process, the optimal concentration of H2O2 leading to the fastest d egradation rate could be evaluated as a function of the initial CDNBA conce ntration using a simplified equation based on the main reactions involved i n the first stages of the degradation process. Chloride ions were produced at the same rate as CDNBA was depleted, independently of the method used fo r the production of hydroxyl radicals. In contrast, the production of nitra te and nitrite ions was strongly process dependent, the differences being r elated to the formation of primary reducing intermediates by VUV photolysis of water. (C) 2000 Elsevier Science B.V. All rights reserved.