Photodegradation of methyl parathion and dichlorvos from drinking water with N-doped TiO2 under solar radiation

Abstract

Methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate) are the most commonly used pesticides in India. These pesticides are often found in many surface and groundwater sources and their concentration levels often exceed the drinking water permissible limits recommended by Indian and European drinking water standards. In this study, doping of nitrogen on TiO2 was carried out with different nitrogen containing organic compounds such as triethylamine, urea, ethylamine and ammonium hydroxide. Nitrogen (N) doped TiO2 from triethylamine precursor showed better photocatalytic activity under visible and solar radiation for the degradation of methyl parathion and dichlorvos. Studies for the photodegradation of analytical and commercial grade methyl parathion and dichlorvos were carried out with N-doped TiO2 and Degussa P-25 TiO2 under UV, visible and solar radiation using batch reactor. N doped TiO2 showed higher photocatalytic activity under solar radiation compared to UV and visible light. GC–MS analysis of commercial grade methyl parathion showed intermediates such as para-nitrophenol and O,O-dimethyl phosphonic ester in the middle of the photodegradation process. Similarly, commercial grade dichlorvos showed intermediates such as 2,2-dichlorvinyl-O-methyl phosphate and O,O,O-trimethyl phosphonic ester during the reaction. However, at the end of the reaction none of the intermediates were present in the system. Photodegradation of mixed pesticides showed that methyl parathion and dichlorvos were degrading simultaneously. However, the rates of reaction were different from single pesticide degradation.