Mechanistic insight into sulfite-enhanced diethyl phthalate degradation by hydrogen atom under UV light

Abstract

As one of the attractive photochemical technologies, sulfite combined with UV light has been demonstrated to be efficient for recalcitrant organic pollutant degradation, but the underlying mechanism of these processes under aerobic conditions has not been fully explored. In this study, we found that diethyl phthalate (DEP) could be efficiently degraded by sulfite/UV under aerobic conditions. Quenching studies combined with electron paramagnetic resonance spectrometry indicated that oxidative radicals (SO3•−, SO4•− and •OH), hydrated electron (eaqs-) and hydrogen atom (H•) were generated in sulfite/UV system under aerobic conditions. H• was found to be the dominant reactive species for DEP degradation while other oxidative radicals had a limited role. It was interesting to found that ethanol and tert-butyl alcohol could promote DEP degradation. This was mainly ascribed to that ethanol and tert-butyl alcohol could quench the reaction of oxidative radicals with sulfite and the generated H•/eaqs-, which favored DEP degradation. DEP degradation was largely dependent on solution pH and alkaline conditions favored DEP degradation. Anions (CO32– and Cl-) and low concentration of organic acid (citrate and oxalate) had neglect effects on DEP degradation, while humic acid greatly inhibited the degradation of DEP. Our results indicated that H• generated during sulfite/UV process might also played an important role in pollutant degradation and the presence of oxidative radical quenchers (e.g. alcohols) favored the reductive degradation of pollutant in the process.