UV/Nitrilotriacetic Acid Process as a Novel Strategy for Efficient Photoreductive Degradation of Perfluorooctanesulfonate

摘要

Perfluorooctanesulfonate (PFOS) is a toxic, bioaccumulative, and highly persistent anthropogenic chemical. Hydrated electrons ( e _(aq)~(–)) are potent nucleophiles that can effectively decompose PFOS. In previous studies, e _(aq)~(–) are mainly produced by photoionization of aqueous anions or aromatic compounds. In this study, we proposed a new photolytic strategy to generate e _(aq)~(–) and in turn decompose PFOS, which utilizes nitrilotriacetic acid (NTA) as a photosensitizer to induce water photodissociation and photoionization, and subsequently as a scavenger of hydroxyl radical (~(•)OH) to minimize the geminate recombination between ~(•)OH and e _(aq)~(–). The net effect is to increase the amount of e _(aq)~(–) available for PFOS degradation. The UV/NTA process achieved a high PFOS degradation ratio of 85.4% and a defluorination ratio of 46.8% within 10 h. A pseudo-first-order rate constant ( k ) of 0.27 h~(–1) was obtained. The laser flash photolysis study indicates that e _(aq)~(–) is the dominant reactive species responsible for PFOS decomposition. The generation of e _(aq)~(–) is greatly enhanced and its half-life is significantly prolonged in the presence of NTA. The electron spin resonance (ESR) measurement verified the photodissociation of water by detecting ~(•)OH. The model compound study indicates that the acetate and amine groups are the primary reactive sites.