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

Abstract

The photodegradation of 4-chloro-3,5-dinitrobenzoic acid (CDNBA) in aqueous solution was investigated using advanced oxidation processes (AOP) involving hydroxyl radical production: (i) UV-C photolysis of H 2O 2 using low or medium pressure Hg arcs (UV/H 2O 2 process) and (ii) vacuum ultraviolet (VUV) photolysis of water at 185 nm (low pressure Hg arc with Suprasil envelope) and 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/H 2O 2 process, the optimal concentration of H 2O 2 leading to the fastest degradation rate could be evaluated as a function of the initial CDNBA concentration using a simplified equation based on the main reactions involved in the first stages of the degradation process. Chloride ions were produced at the same rate as CDNBA was depleted, independently of the method used for the production of hydroxyl radicals. In contrast, the production of nitrate and nitrite ions was strongly process dependent, the differences being related to the formation of primary reducing intermediates by VUV photolysis of water.