Photochemical decomposition of environmentally persistent short-chain perfluorocarboxylic acids in water mediated by iron(II)/(III) redox reactions

The photochemical decomposition of short-chain (C3–C5) perfluorocarboxylic acids (PFCAs) was investigated. Direct photolysis in water proceeded slowly with the 220- to 460-nm light emission from a xenon–mercury lamp to form F−, CO2, and shorter-chain PFCAs. Addition of a small amount of Fe3+ to the aqueous solutions of the PFCAs dramatically enhanced their photochemical decomposition under an oxygen atmosphere: when the (initial PFCA)/(initial Fe3+) molar ratio was 13.5 (initial PFCA concentration = 67.3 mM), the pseudo-first-order rate constants for the PFCA decomposition were 3.6–5.3 times those with photolysis alone, and the turnover number for the catalytic PFCA decomposition [i.e., (moles of decomposed PFCA)/(moles of initial Fe3+)] reached 6.71–8.68 after 24 h of irradiation. The catalysis can be explained by photoredox reactions between PFCA, Fe3+/Fe2+ and oxygen via photo-induced complexation of Fe3+ with the PFCAs.