Comparative study on photocatalytic degradation of methomyl and parathion over UV-irradiated TiO2 particles in aqueous solutions

Photodegradation of methomyl and parathion, the representatives of carbamate and organophosphorus pesticides, respectively, over TiO2 particles under 400-W UV irradiation was investigated and compared at 40 degrees C. All experiments were conducted at different initial pH values (4.0-10.0), initial pesticide concentrations (10-30 mg/L), and TiO2 doses (0-1.5 g/L). The Langmuir-Hinshelwood kinetic model was used to evaluate the apparent first-order rate constants of both pesticides at their initial stages of degradation processes. It was seen that methomyl was degraded much faster than parathion under comparable conditions, primarily due to more complicated structures of parathion molecules. The mineralization processes of methomyl and parathion by TiO2/UV were also studied on the basis of the measured total organic carbon (TOC) data. Finally, the possible degradation paths of methomyl and parathion were inferred by following the variations of the concentrations of final mineralized products with time. (c) 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.