Iodosulfuron degradation by TiO2 photocatalysis: Kinetic and reactional pathway investigations

The photocatalytic degradation of a sulfonylurea herbicide, iodosulfuron methyl ester (IOME), has been studied in TiO2 aqueous suspensions under UV irradiation. The influence of various parameters such as initial concentration, TiO2 concentration and light intensity on the kinetic process was investigated. Disappearance rate of iodosulfuron followed pseudo-first order kinetics. A special attention was devoted to the identification of intermediates, using a new analytical approach which consists of coupling HPLC–DAD (UV), HPLC–ESI-MS and HPLC–1H NMR techniques after a SPE pre-concentration step. By combining UV, MS and NMR data, up to 20 degradation products were unambiguously identified. Furthermore, 1H NMR data allowed the differentiation of several positional isomers, in particular those of hydroxylation resulting from the attack of OH radicals on the benzene ring of IOME. Kinetic evolution profiles of main intermediates, end products (NO3−, NH4+, SO42−) and total organic carbon (TOC) were also examined in detail. From obtained kinetic and analytical results, the presence of privileged sites for the attack of OH radicals was shown and a detailed degradation pathway was proposed.