Photocatalytic mineralization of hydroperfluorocarboxylic acids with heteropolyacid H4SiW12O40 in water

The decomposition of hydroperfluorocarboxylic acids [H-PFCAs; HCnF2nCOOH (n = 4 and 6)] induced by heteropolyacid photocatalyst H4SiW12O40 in water was investigated, and the results are compared with the results for the corresponding perfluorocarboxylic acids (PFCAs; CnF2n+1COOH). This is the first report on the photochemical decomposition of H-PFCAs, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative PFCAs. H-PFCAs were not decomposed by irradiation with UV–Visible light (>290 nm) in the absence of H4SiW12O40. In contrast, UV–Visible light irradiation of H-PFCAs in the presence of H4SiW12O40 efficiently decomposed H-PFCAs to F− and CO2. The decomposition reactions showed pseudo-first-order kinetics, and the decomposition rate constants were 1.8–2.5 times higher than those for the corresponding PFCAs. The reaction mechanism can be explained by elimination of H+ from the ω-H atom of the H-PFCAs by the excited catalyst, followed by formation of perfluorodicarboxylic acids.

Research highlights
► H4SiW12O40 photocatalyst to mineralize hydroperfluorocarboxylic acids (H-PFCAs).
► H-PFCAs are alternatives to harmful perfluorocarboxylic acids (PFCAs).
► The decomposition rates for H-PFCAs were 1.8–2.5 times those for PFCAs.
► The decomposition of H-PFCAs proceeds via formation of perfluorodicarboxylic acids.
► The catalyst can be used at relatively high pH up to 5.2.