Degradation of fenitrothion by a falling-film plasma reactor

Abstract

The contamination of surface water with organophosphates is an environmental concern due to their acute toxicity to wildlife and humans. This study reports an evaluation of the efficacy of a falling-film plasma reactor (FFPR) for degrading fenitrothion, which is an organophosphate insecticide and a simulant for nerve agents. An FFPR setup was demonstrated to effectively degrade fenitrothion in aqueous solutions. The degradation kinetics of the aqueous fenitrothion was found to follow an exponential decaying function and to have a destruction removal efficiency (DRE) of up to 95% within 60 min. The effectiveness of the FFPR treatment was attributed to its ability to efficiently generate reactive oxygen species, particularly hydroxyl radicals, to oxidize fenitrothion and byproducts. Four transient intermediate products from the fenitrothion degradation reaction were detected and identified. Their concentrations were found to increase in the first ca.15 min of the reaction and then follow exponential decay patterns. Quantum chemical calculations revealed that hydroxyl radicals react with fenitrothion through three major pathways. The first pathway involves the attack of the hydroxyl radical at the phosphorus atom and the subsequent leaving of the 3-methyl-4-nitrophenol radical, leading to two major products observed in experiments. The second pathway involves the hydrogen abstraction by hydroxyl radicals at the methoxy groups on the phosphorus atom and converts the methoxy groups to hydroxyl groups, resulting in a major product in experiments. The third pathway involves the hydrogen abstraction by hydroxyl radicals at the methyl group on the nitrophenol ring and converts the methyl group to a carboxyl group, resulting in another major product detected in experiments.