Efficient mineralization of hydroperfluorocarboxylic acids with persulfate in hot water

The persulfate (S2O82−)-induced decomposition of hydroperfluorocarboxylic acids (H-PFCAs), that is, HCnF2nCOOH (n = 4, 6, and 8), in hot water was investigated, and the results were compared with the results for perfluorocarboxylic acids (PFCAs). This is the first report on the use of hot water to decompose H-PFCAs, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative PFCAs. Although H-PFCAs showed almost no decomposition in hot water at 80 °C in the absence of S2O82−, the addition of S2O82− to the reaction solution led to efficient mineralization to F− ions, with F− yields [(moles of F−)/(moles of fluorine in initial H-PFCAs)] of 96.7–98.2% after 6 h of treatment. The decomposition of H-PFCAs induced by S2O82− also proceeded even at 60 °C, at which the initial decomposition rates were 7.1–12.7 times those for the corresponding PFCAs. The reaction mechanism can be explained by nucleophilic substitution by SO4radical dot− at the carbon atom attached to the ω-H atom of the H-PFCAs, followed by formation of perfluorodicarboxylic acids (HOOCCn−1F2n−2COOH), which react with SO4radical dot− to give shorter-chain perfluorodicarboxylic acids; this process eventually resulted in complete mineralization to F− ions.