Differences between reductive defluorination of perfluorooctanoic acid by chlorination, bromination, and iodization in the vacuum-ultraviolet/sulfite process.

The introduction of iodide (I) has broad perspectives on the decomposition of perfluorocarboxylates (PFCAs, CFCOO). However, the iodinated substances produced are highly toxic synthetic chemicals, hence, it is urgent to find a similar alternative with less toxicity. In this work, the defluorination of perfluorooctanoic acid (PFOA) by I, bromide (Br) and chlorine (Cl) was systematically compared in the VUV/sulfite process. Results indicated that the PFOA defluorination rates increased with increasing nucleophilicity of halogens (I > Br > Cl). Meanwhile, the introduction of I, Br, and Cl reduced the interference of the coexisting water matrix on the degrading influence of PFOA. The in situ produced e, SO, H•, and HO• were recognized, among the addition of I maximized the relative contribution of e but Br and Cl decreased that of H• and other radicals. Additionally, HPLC/MS analysis revealed the presence of I, Br, and Cl had a vital impact on the difference in product concentrations, while they had a negligible effect on the change in the pathway of degradation. Overall, this study demonstrated the similarities and differences between I, Br, and Cl, which has significant implications for further understanding VUV/sulfite degradation.