Oxidative degradation of fensulfothion by hydroxyl radical in aqueous medium

Oxidative degradation of fensulfothion, a model organophosphorus compound, has been investigated by pulse radiolysis and H2O2/UV photolysis. A nearly complete transformation of fensulfothion was observed within 4 min of irradiation. Very little Total Organic Carbon (TOC) reduction was obtained at this time scale. When the product studies at this stage were conducted using LC–MS/MS analyses, nearly 20 transformation products were obtained. The entire products were identified as from the reaction of OH with fensulfothion or with some of its initially transformed products. Nearly 80% reduction in TOC was observed when photolysis was conducted using higher concentrations of H2O2 at longer time scale. A reaction rate constant (bimolecular) of 1.10 × 1010 dm3 mol−1 s−1 was obtained for the reaction of OH with fensulfothion using pulse radiolysis technique. The transient absorption spectrum obtained from the reaction of OH has a maximum at 280 nm and a weak, broad maximum around 500 nm along with a small shoulder around 340 nm. The intermediate spectrum is assigned to the radical cation of fensulfothion (3) and the hydroxyl radical adducts (1 and 2). This assignment is supported by the intermediate spectrum (λmax at 280 nm) from the reaction of sulfate radical anion (SO4-) (k2 = 3.20 × 109 dm3 mol−1 s−1) which is a one electron oxidant. It is thus demonstrated that the combination of both pulse radiolysis and the product estimation using LC–MS/MS is ideal in probing the complete mechanism which is very important in the mineralization reactions using Advanced Oxidation Processes.

Figure optionsDownload as PowerPoint slideHighlights
► Degradation of fensulfothion by hydroxyl radicals from Advanced Oxidation Process.
► Complete transformation of fensulfothion, but with low TOC reduction.
► Presentation of 20 major products of transformation of fensulfothion.
► Presentation of the fast kinetics of reaction and of the absorption spectra of short lived intermediate radicals.
► Presentation of the mechanism of degradation induced by hydroxyl radicals.