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Fenuron,isopronuron,linuron and metobromuron,belonging to substituted urea herbicides,are make significant contribution of the use of plant protection products in agriculture.However,owing to its persistence,these kinds of herbicides have remained in soil,river and sea water[1].Urea herbicides in water,which has raised a concern about their potential impact on environment.But the information concerning the environmental fate of the substituted urea herbicides residues has not been adequately solved.On the other hand,heterogeneous photocatalysis,one example of advanced oxidation processes(AOPs),can achieve complete oxidation of organic and inorganic species.The formation of reactive oxygen species(ROSs)on the surface of photocatalysts induced by UV light,such as ·OH,·O2-,·HO2 and H2O2,results in mineralization of a large variety of organic compounds[2,3].With the help of heterogeneous photocatalysis,the effects of the ROSs on substituted urea herbicides in environmental water can be evaluated properly.So the photocatalytic degradation kinetics and mechanism of the substituted urea herbicides in aqueous TiO2 suspension using Xe lamp were studied in detail in this study.The results indicated that different substituted groups affected the degradation kinetics significantly,and its was also found that ·OH radicals played an important role in degradation of the substituted urea herbicides in aqueous solution,while the other ROSs did the minor contributions.The photocatalytic degradation mechanism of the substituted urea herbicides by ROSs was also tentatively attempted based on not only the experimental evidence of degradation products identified by LC/MS/MS analysis,but also calculated data,such as the frontier electron densities(FEDs),Points Charges(PCs),activation barriers Ea of the main degradation products[3-5].The results suggested that substitution of the halogen atom,addition of ?OH,and the cleavage of urea side chain were the predominant degradation pathways during the initial stage of photocatalytic process.