[Photodegradation of perfluorinated carboxylic acids by 185 nm VUV light]

Perfluorinated carboxylic acids (PFCAs) especially perfluorooctanoic acid (PFOA) are a new type of persistent and bioaccumulative organic pollutants, and they have been widely detected in various environmental media. Photodegradation of five types of PFCAs i.e. PFOA, perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA) and perfluorobutanoic acid (PFBA) by 185 nm vacuum ultraviolet (VUV) were examined to develop an effective method to deal with PFCAs pollution. All five PFCAs degrade significantly under the irradiation of 185 nm light and fluoride ion correspondingly forms, though PFCAs hardly degrade under irradiation of 254 nm UV light. After 6h irradiation by 185 nm light, more than 60% of PFBA degrades, while other four PFCAs degrade more than 90%, and defluorination ratio range from 71% to 21% decreasing with increasing carbon atoms contained by PFCAs. Three reaction atmosphere i.e. nitrogen, air and oxygen have no significant effect on degradation and defluorination of PFCAs. LC/MS measurement shows, PFOA degrades to PFHpA, PFHxA, PFPeA and PFBA step by step. Under irradiation of 185 nm light, PFCA firstly is decarboxylated, and the radical thus formed reacts with water to form shorter-chain PFCA and fluoride ion.