Efficient defluorination of PFOA by vacuum ultraviolet coupling with sulfite and iodide

Perfluorooctanoic acid (PFOA), as an anthropogenic persistent contaminant, is widely distributed in the natural aquatic environment and has been a considerable threat to ecological security and human health. In this work, we propose and evaluate the vacuum ultraviolet (VUV)/sulfite-iodide system under N₂ saturated condition for the decomposition of PFOA. The in situ generated hydrated electrons (e_aq⁻) were demonstrated to be the main active species responsible for the PFOA degradation. With observation of the intermediate products, two major degradation pathways of PFOA in VUV/sulfite-iodide system were proposed: H/F exchange and chains shortening. A significant enhancement of PFOA defluorination was observed with increasing pH values from 9.0 to 12.0, which can be explained by the decreasing quenching effect of e_aq⁻ and accelerated disproportionation of I₂ to I⁻ and IO₃⁻. Meanwhile, VUV/sulfite-iodide system also exhibited satisfactory performance in degrading high concentration of PFOA (200 μM). However, the presence of Cl⁻, NO₃⁻, and humic acid inhibited the removal of PFOA via various reaction mechanism. The VUV/sulfite-iodide system was effective toward the chosen PFCAs (trifluoroacetic acid (TFA) and perfluorobutyric acid (PFBA)), demonstrating a chain length independence on the degradation of PFCAs, supporting its broad applicability.