摘要
The photooxidation of organophosphorus pesticides (OPP) such as methamidophos, phorate, malathion, diazion and EPN, was investigated in UV-TiO <sub>2</sub> , UV-H <sub>2</sub> O <sub>2</sub> and UV-TiO <sub>2</sub> -H <sub>2</sub> O <sub>2</sub> systems. Apparent first-order rate constants were used to describe the photodecomposition behaviors of OPP. Batch results demonstrate that the degradation efficiencies of OPP increased in the order of phorate >methamidophos >malathion ≈diazion >EPN. The photooxidation of methamidophos and phorate is primarily attributed to direct photolysis. Whereas the presence of TiO <sub>2</sub> promotes the degradation efficiencies of diazion, malathion and EPN. Hydrogen peroxide was found to be an intermediate in UV-TiO <sub>2</sub> system during the photocatalytical reaction process. Longer irradiation decreased H <sub>2</sub> O <sub>2</sub> concentration due to the high electron-hole recombination rate on the surface of TiO <sub>2</sub> . Adding H <sub>2</sub> O <sub>2</sub> is more effective on the photocatalytic oxidation of OPP than TiO <sub>2</sub> . Threefold to tenfold of the quantum efficiency of the UV-H <sub>2</sub> O <sub>2</sub> system was obtained for the UV-TiO <sub>2</sub> system. Moreover, the quantum efficiencies for degradation of OPP decreased when light intensity is increased from 100 to 450 W, although increasing light intensity can increase the apparent first-order rate constants of OPP. © 1997 Elsevier Science S.A.