Abatement kinetics of 30 sulfonylurea herbicide residues in water by photocatalytic treatment with semiconductor materials.

Sulfonylurea herbicides (SUHs) are a family of environmentally compatible herbicides but their high water solubility, moderate to high mobility through the soil profile, and slow degradation rate make them potential contaminants of groundwater as demonstrated in this paper. The photodegradation of a mixture of 30 SUHs in aqueous suspensions of semiconductor materials (ZnO and TiO2 in tandem with Na2S2O8 as electron acceptor) under artificial light (300-460 nm) irradiation was investigated. As expected, the influence of both semiconductors on the degradation of SUHs was very significant in all cases. Photocatalytic experiments show that the addition of photocatalyst, especially for the ZnO/Na2S2O8 system, greatly improves the removal of SUHs compared with photolytic tests, significantly increasing the reaction rates. The first-order equation (monophasic model) satisfactorily explained the disappearance process although it overlooked small residues remaining late in the process. These residues are important from an environmental point of view and the Hoerl function (biphasic model), was a better predicter of the results obtained. In our conditions, the average time required for 90% degradation was about 3 and 30 min for ZnO/Na2S2O8 and TiO2/Na2S2O8 systems, respectively.