A study of photocatalytic degradation of methomyl and its commercial product Lannate-90

Abstract

Photocatalytic degradation of the carbamate insecticide methomyl and its commercial product Lannate-90 in aqueous suspension of TiO2 and ZnO using an Osram ultra-vitalux  lamp (315-400 nm) was investigated. The objective of the investigation was to study and compare the rates of photochemical degradation of the pure active compound and its formulated product in order to find out the impact of inert ingredients on degradation processes. The photochemical degradation of pure methomyl was found to be slower than the degradation of its commercial product Lannate-90. Photodegradation was investigated by UV-VIS spectrometry and HPLC, while mineralization was monitored using IC and TOC analyses. Light absorption capabilities of catalysts were characterized by ultravioletvisible diffuse reflectance spectroscopy method, while the stability of catalysts was studied by Infrared analyses. Degradation products of methomyl and its formulated product were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) results and tentative photodegradation pathways were proposed. Article Highlights• Photocatalysis of pure methomyl and its commercial product Lannate-90 were investigated.• The kinetics of methomyl and Lannate-90 were studied and pseudo first-order was determined.• Photodegradation of Lannate-90 was much faster than photodegradation of pure methomyl.• TiO2 is a better catalyst than ZnO for both methomyl and Lannate-90.• Three major transformation products of photocatalytical degradation were identified.