Ga₂O₃-Photoassisted and Photolytic Degradation of the Flubendiamide Agrochemical in Aqueous Media under UVC Irradiation

抄録

The photoassisted degradation of the recalcitrant and persistent Flubendiamide insecticide was examined in the presence of the metal-oxide semiconductor Ga₂O₃ in air-equilibrated and inert conditions (Ga₂O₃/air and Ga₂O₃/N₂, respectively) under Ultraviolet C (UVC) irradiation at 254 nm; for comparison, the degradation of this insecticide was also investigated in catalyst-free/air and catalyst-free/N₂ under UVC irradiation. The time course of the degradation was monitored by examining the yields of inorganic ions formed (fluoride, iodide, sulfate, nitrate and ammonium ions) and analyzed quantitatively by ion chromatographic techniques. Mechanistic considerations are described from calculating partial charges and electron densities on each of the functionalities in the Flubendiamide structure in aqueous media. Reactive oxygen species, such as the electrophilic •OH radicals and singlet oxygen, are inferred to attack the insecticide at positions where the functional groups possess the highest electron densities and highest negative partial charges, which led ultimately to defluorination, deiodination, desulfonation, and denitrogenation (i.e., formation of ammonium and nitrate ions). The total yields of decomposition followed expectations in the increasing order: N₂ < Ga₂O₃/N₂ < air < Ga₂O₃/air.