Efficient degradation of perfluorooctanoic acid (PFOA) by photocatalytic ozonation

Perfluorooctanoic acid (PFOA) could be efficiently degraded by the combined process of photocatalysis and ozonation, its degradation intermediates were fluoride ions and short-chain perfluorocarboxylic acids (PFCAs) including C 6 F 13 COOH, C 5 F 11 COOH, C 4 F 9 COOH, C 3 F 7 COOH and C 2 F 5 COOH. After 4   h reaction time, its degradation efficiency was 99.1% and defluorination ratio only reached to 44.3%. The degradation mechanism of PFOA by photocatalytic ozonation was proposed and found to be similar to Photo-Kolbe reaction: PFOA anion was degraded to produce PFOA radical by a direct electron transfer from its carboxyl group to photo-generated hole (h + ). Then PFOA radical was decarboxylated to produce perfluoroheptyl radical, and then be oxidized to form C 7 F 15 OH by hydroxyl radical ( OH) which was produced from ozone trapping photo-generated electron. Because of its thermal instability, C 7 F 15 OH would be converted to C 6 F 13 COF, which was further hydrolyzed to generate C 6 F 13 COO − . Therefore the combined process of photocatalysis and ozonation was efficient for PFOA degradation.