Activation of persulfate by UV and Fe2+ for the defluorination of perfluorooctanoic acid

Efficient defluorination of perfluorooctanoic acid (PFOA) was achieved by integrating UV irradiation and Fe2+ activation of persulfate (S2O82-). It was found that the UV-Fe2+, Fe2+-S2O82-, and UV-S2O82-processes caused defluorination efficiency of 6.4%, 1.6% and 23.2% for PFOA at pH 5.0 within 5 h, respectively, but a combined system of UV-Fe2+-S(2)O(8)(2-)dramatically promoted the defluorination efficiency up to 63.3%. The beneficial synergistic behavior between Fe2+-S(2)O(8)(2-)and UV-S2O82-was demonstrated to be dependent on Fe2+ dosage, initial S(2)O(8)(2-)concentration, and solution pH. The decomposition of PFOA resulted in generation of shorter-chain perfluorinated carboxylic acids (PFCAs), formic acid and fluoride ions. The generated PFCAs intermediates could be further defluorinated by adding supplementary Fe2+ and, S(2)O(8)(2-)and re-adjusting solution pH in later reaction stage. The much enhanced PFOA defluorination in the UV-Fe2+-S(2)O(8)(2-)system was attributed to the fact that the simultaneous employment of UV light and Fe2+ not only greatly enhanced the activation of S(2)O(8)(2-)to form strong oxidizing sulfate radicals (SO4(center dot-)), but also provided an additional decarboxylation pathway caused by electron transfer from PFOA to in situ generated Fe3+.