UV/nitrilotriacetic acid process as a novel strategy for efficient photoreductive degradation of perfluorooctane sulfonate

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.