A mechanistic study on solar energized degradation of herbicide into value-added product using -SO3H functionalized ionic liquid-polyoxometalate based heterogeneous catalyst in aqueous medium

Abstract

Two acidic ionic liquid-based hybrids of polyoxometalate, dibutyldisulphoammonium polyoxometalate, [DBDSA]3[PM12O40], (M= Mo, W) were prepared by exchanging labile halide ion of parent ionic liquid with Keggin [PM12O40]3− anions. The incorporation of N-SO3H into the ammonium cation results in intra-molecular H-bonding with POM anion, which is responsible for the preservation of heterogeneity of the catalyst throughout the reaction. Their catalytic activities were investigated for the degradation of metobromuron herbicide in aqueous medium as heterogeneous oxidative catalyst under sunlight using H2O2 as oxidant. The isolated active peroxo intermediate was responsible for the reaction. A detailed mechanistic study on degradation of metobromuron into various products at different time intervals was done. The reaction for 8 h under sunlight removed greater than 70 % of TOC and also resulted in 1‑bromo-4-isocyanatobenzene as the major value-added product for the synthesis of various unsymmetrical disubstituted urea derivatives. The recyclability experiment showed excellent stability and reusability of the catalyst.