Efficient degradation of methabenzthiazuron photoinduced by decatungstate anion in water: Kinetics and mechanistic studies

This study concerns the elimination of methabenzthiazuron (MBTU) photocatalysed by sodium decatung-state salts W10O324-center dot(DTA) in aqueous solution under irradiation at 365 nm. Ninety percentage of MBTU (10(-4) M) is mineralised in the presence of the photocatalyst (2 x 10(-4) M) after 7 d under exposure and the formation of nitrate, sulphate and ammonium confirmed this phenomenon. In aerated conditions, the photodegradation rate of MBTU clearly increased in the presence of DTA by a factor of 40 when compared to direct photolysis with Phi(MBTU) = 2.5 x 10(-2) and t(1/2) (MBTU) = 1.4 h. Oxygen appeared essential since 2 times inhibition of MBTU disappearance and the photocatalytic cycle interrupt were observed in the absence of oxygen. The degradation mechanism has been elucidated through the photoproducts identification by LC-ESI-MS analysis. Two processes were implied in the degradation: electron transfer and H atom abstraction reactions both involving W10O324-center dot excited state species. In the primary steps of the degradation, the aromatic ring hydroxylation was observed by electron transfer leading to OH-MBTU isomers and H atom abstraction reaction gave benzthiazuron and a supposed demethylated product. Secondary oxidations permitted the hydroxylation of both products. (C) 2011 Elsevier Ltd. All rights reserved.