Efficient degradation of methabenzthiazuron photoinduced by decatungstate anion in water: Kinetics and mechanistic studies
2011
Allaoui, A. | Malouki, M.A. | Wong-Wah-Chung, P.
This study concerns the elimination of methabenzthiazuron (MBTU) photocatalysed by sodium decatungstate salts W₁₀O₃₂ ⁴⁻ .(DTA) in aqueous solution under irradiation at 365nm. Ninety percentage of MBTU (10⁻⁴M) is mineralised in the presence of the photocatalyst (2×10⁻⁴M) after 7d 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 ΦMBTU=2.5×10⁻² and t₁/₂ (MBTU)=1.4h. 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 W₁₀O₃₂ ⁴⁻∗ 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.
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