Effective defluorination of novel hexafluoropropylene oxide oligomer acids under mild conditions by UV/sulfite/iodide: mechanisms and ecotoxicity

Abstract

It has recently been discovered that HFPO-TA (a processing aid in the production of fluoropolymers) has high levels of bioaccumulation and biotoxicity. Hydrated electrons (eaq−) have been proposed to be potent nucleophiles that may decompose PFAS. Unlike previous studies in which the generation of eaq− was often restricted to anaerobic or highly alkaline environments, in this study, we applied the UV/SO32−/I− process under mild conditions of neutrality, low source chemical demand, and open-air, which achieved effective degradation (81.92 %, 0.834 h−1) and defluorination (48.99 %, 0.312 h−1) of HFPO-TA. With I− as the primary source of eaq−, SO32− acting as an I− regenerator and oxidizing substances scavenger, UV/SO32−/I− outperformed others under mild circumstances. The eaq− were identified as the main active species by quenching experiments and electron paramagnetic resonance (EPR). During degradation, the first site attacked by eaq− was the ether bond (C6-O7), followed by the generation of HFPO-DA, TFA, acetic and formic acid. Degradation studies of other HFPOs have shown that the defluorination of HFPOs was accompanied by a clear chain-length correlation. At last, toxicological experiments confirmed the safety of the process. This study updated our understanding of the degradation of newly PFASs and the application of eaq− mediated photoreductive approaches under mild conditions.