Efficient degradation of perfluorooctanoic acid (PFOA) by photocatalytic ozonation

[Display omitted] •Degradation ratio was enhanced by photocatalytic ozonation process.•Defluorination of PFOA was greatly influenced by initial pH of solution.•Photo-generated hole was the main active species in PFOA degradation.•Several of intermediates were detected by LC–MS. 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 C6F13COOH, C5F11COOH, C4F9COOH, C3F7COOH and C2F5COOH. After 4h 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 C7F15OH by hydroxyl radical (OH) which was produced from ozone trapping photo-generated electron. Because of its thermal instability, C7F15OH would be converted to C6F13COF, which was further hydrolyzed to generate C6F13COO−. Therefore the combined process of photocatalysis and ozonation was efficient for PFOA degradation.