Senthilnathan J, Philip Ligy
Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, India.
J Environ Sci Health B. 2009 Mar;44(3):262-70. doi: 10.1080/03601230902728328.
Lindane (1alpha, 2alpha, 3beta, 4alpha, 5alpha, 6beta-hexachloro cyclohexane), methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate) are removed from water individually and as a mixture by photo degradation using suspended and immobilized forms of TiO(2) (Degussa P-25). Studies were conducted to optimize the coating thickness of immobilized photo catalyst. The rate of degradation of pesticides was compared in both suspended and immobilized TiO(2) systems. Degradation studies of mixed pesticides were carried out with low concentrations (1.0 and 2.5 mg/L) of pesticides. Only three intermediate byproducts such as methyl paraoxon, O,O,O-trimethyl phosphonic thionate and p-nitrophenol were observed during the methyl parathion degradation in suspended, immobilized TiO(2) systems and mixed pesticides degradation studies. At the end of the reaction methyl parathion and its by-products were completely degraded. During lindane degradation hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene, 1-hydroxy 2,3,4,5,6-chlorocyclohexane, 1-hydroxy 2,3,4,5,6-chlorobenzene, pentachloro cyclopentadiene, 1,2,3,4,5-hydroxy cyclopentene and 1,2,3-hydroxy cyclobutane were identified in suspended and immobilized TiO(2) systems, whereas only hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene and pentachloro cyclopentadiene were observed during mixed pesticides degradation. No intermediate by-product was observed during the photo degradation of dichlorvos. Langmuir-Hinshelwood pseudo first order kinetic equation showed that there was not much change in the rates of degradation in both suspended and immobilized TiO(2) systems irrespective of the pesticide. During mixed pesticides degradation, the degradation pattern was not similar to that of single pesticide.
林丹（1α, 2α, 3β, 4α, 5α, 6β-六氯环己烷）、甲基对硫磷（O,O-二甲基-O-4-硝基苯基硫代磷酸酯）和敌敌畏（2,2-二氯乙烯基-O,O-二甲基磷酸酯）可通过使用悬浮和固定化形式的TiO₂（德固赛P-25）进行光降解，从水中单独或混合去除。进行了研究以优化固定化光催化剂的涂层厚度。比较了悬浮和固定化TiO₂体系中农药的降解速率。对低浓度（1.0和2.5 mg/L）的混合农药进行了降解研究。在悬浮、固定化TiO₂体系中的甲基对硫磷降解以及混合农药降解研究过程中，仅观察到三种中间副产物，如甲基对氧磷、O,O,O-三甲基硫代磷酸酯和对硝基苯酚。反应结束时，甲基对硫磷及其副产物被完全降解。在林丹降解过程中，在悬浮和固定化TiO₂体系中鉴定出六氯环己烷、五氯环己烷、六氯苯、1-羟基-2,3,4,5,6-氯环己烷、1-羟基-2,3,4,5,6-氯苯、五氯环戊二烯、1,2,3,4,5-羟基环戊烯和1,2,3-羟基环丁烷，而在混合农药降解过程中仅观察到六氯环己烷、五氯环己烷、六氯苯和五氯环戊二烯。在敌敌畏的光降解过程中未观察到中间副产物。朗缪尔-欣谢尔伍德准一级动力学方程表明，无论农药种类如何，悬浮和固定化TiO₂体系中的降解速率变化不大。在混合农药降解过程中，降解模式与单一农药的降解模式不同。
