表层土壤半导体物质对残留有机氯农药光分解催化作用

本申请项目重点研究表层土壤中存在的半导体物质对有机农药的光解催化作用；考察土壤主要成分对光解的协同或拮抗效应，从土组成层次定量描述有机氯农药在表层土壤中的光解动力学过程；通过阶段产物的分析推测可能的光解机理。该项研究对认识有机氯农药在土壤中的环境行为、完善难降解有机物在土壤中的迁移转化理论具有重要意义。为难降解有机物的环境管理和风险评价提供科学依据。

Phototransformation is a kind of important environmental behaviors of pesticides on soil surfaces. Soil in our country is rich in iron oxides, and hematite is a kind of semiconductors with band gap 2.2eV. This study focused on the effect of natural photosensitizers (iron oxides, fulvic acids and TiO2 et al) on photodecomposition of typical organochlorine pesticides. The concrete study included: (1) identification the photosensitizers in soils and investigation of the effects of these substances on photocatalysis; (2) study of photocatalytic kinetic constants of organochlorine pesticides on soil surfaces in the presence of photosensitizers; (3) analyzation of the intermediate products and study of the photodecomposition pathway; (4) study about the effect of additional photosensitizers of soils on photocatalytic decomposition.The primary study results were listed as follows: (1) photocatalytic rates fit pseudo-first-order kinetics in the presence of photosensitizers when the content of organic carbon was below 0.08%. The kinetic constants increased with the increase of the content of hematite, the results can be described as k (h-1)=0.0057x + 0.0051(x percentage content). (2) Natural organic matters inhibited the photodecomposition of lindane. The photolytic rates were increased with the reduction of natural organic matters. (3) the quantitative model between sediment components and photocatalytic rate constants were established by partial least squares, the obtained experiment data were analyzed by multiple factor analyzation. The results indicated that photodecomposition of lindane was inhibited by organic carbon and inorganic carbon; however lindane was photodecomposed by Fe2O3 and TiO2. (4) The experiment results was further evidenced by additional hematite、natural organic carbon and TiO2.(5)Pentachlorocyclohexane, tetrachlorocyclohexane and trichlorobenzene et al were detected by GC-MS at the beginning of photoirradiaton, however these products disappeared gradually during the irradiation. The result indicated that lindane was decomposed by way of dehydrochlorination and dechlorination. At the last phase of the photoirradiation, intermediate products were decomposed and mineralized.