Photocatalyzed Degradation of Agrochemicals in Water

1.本文研究了农药西玛津、苯硫威、福美双、二嗪农、杀螟松、稻瘟灵、丙炔肼、敌敌畏、仲丁威和异稻瘟净在TiO_2悬浮液中的光催化降解.光催化降解农药的速率比无TiO_2的直接光解快得多，降解速率与农药浓度的关系符合一级动力学。3.农药的降解与农药的结构有关。农药的半衰期范围为4.11-11.9min（λ> 290 nm）和5.0-24.3min（λ = 365 nm）。量子产率估计为0.0086-0.032min（λ = 365 nm）。4<2->.以异稻瘟净为降解剂，考察了影响其降解的几个因素。5. TiO_2的最佳浓度为0.5-1.0mg/ml。初始反应速率（r_0）与TiO_2吸收的光子数（I_a）和量子产率（PHI）成正比。r_0与异稻瘟净的初始浓度（C_0）和鼓泡气体中O_2的分压（pO_2）符合Langmuir-llinshelwood关系。讨论了吸附态O_2（O_2（ads））的作用。提出异稻瘟净光催化降解的经验速率为：r_0=I_aPHIpO_2，_<ads>（异稻瘟净）_<ads>。实验结果与计算结果吻合较好。6.基于对降解产物的GC/MS分析，检查了降解途径。一种途径是OH攻击异稻瘟净的α、β和γ键，另一种途径是OH攻击异稻瘟净的苯环，然后α裂解。结果表明，光催化降解技术可应用于水体污染物的降解。

1. The phtocatalyzed degradation of agrochemicals (simazine, benthiocarb, thiram, diazinon, fenitrothion, isoprothiolane, propyzamide, dichlorvos, fenobucarb, and iprobenfos) has been investigated in an aqueous suspension of TiO_2 using a ultra high-pressure mercury lamp (lambda>290nm and 365nm) at 35ﾟC.2. The degradation is much faster than direct photolysis without TiO_2 and depends on the first order kinetics to the concentrations of the agrochemicals. 3. The degradation depends on the structures of the agrochemicals. The half-lives of the agrochemicals ranged from 4.11-11.9min (lambda>290nm) and 5.0-24.3min (lambda=365nm). Quantum yields were estimated to be 0.0086-0.032min (lambda=365nm). The agrpchemicals were ultimately mineralized to form Cl^-, SO_4^<2->, NO_3^-.4.Several factors affecting the degradation were examined in details with iprobenfos. 5. Optimum concentration of TiO_2 was found to be 0.5-1.0mg/ml. The initial reaction rate (r_0) is proportional to the photons absobed by TiO_2 (I_a) and quantum yield (PHI). r_0 follows the langmuir-llinshelwood relationship with the initial concentration (C_0) of iprobenfos and the partial pressure of O_2 in the bubbling gas (pO_2). The action of adsorbed O_2 (O_2(ads)) is discussed. We propose the empirical rate of the photocatayzed degradation of iprobenfos as follows : r_0=I_aPHIpO_2, _<ads>(iprobenfos)_<ads>. Fair agreement of r_0 was found between experiment and calculation. 6. Based on the GC/MS analysis of the degradation products, degradation pathways were examined. One pathway is OH attack on alpha, beta, and gamma bond of iprobenfos, another pathways is OH attack on the benzene ring of iprobenfos followed by the alpha cleavage. It was found that the photocatalyzed degradation could be applicable to the degradation of water contaminants.