Activation of persulfate by UV and Fe 2+ for the defluorination of perfluorooctanoic acid

Efficient defluorination of perfluorooctanoic acid (PFOA) was achieved by integrating UV irradiation and Fe 2+ activation of persulfate (S2O8 2- ). It was found that the UV-Fe 2+ , Fe 2+ -S2O8 2- , and UV-S2O8 2- 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-Fe 2+ -S2O8 2- dramatically promoted the defluorination efficiency up to 63.3%. The beneficial synergistic behavior between Fe 2+ -S2O8 2- and UV-S2O8 2- was demonstrated to be dependent on Fe 2+ dosage, initial S2O8 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 Fe 2+ and, S2O8 2- and re-adjusting solution pH in later reaction stage. The much enhanced PFOA defluorination in the UV-Fe 2+ -S2O8 2- system was attributed to the fact that the simultaneous employment of UV light and Fe 2+ not only greatly enhanced the activation of S2O8 2- to form strong oxidizing sulfate radicals (SO4 •- ), but also provided an additional decarboxylation pathway caused by electron transfer from PFOA to in situ generated Fe 3+ .