Efficient decomposition of a new fluorochemical surfactant: Perfluoroalkane disulfonate to fluoride ions in subcritical and supercritical water

Decomposition of –O3SC3F6SO3− in subcritical and supercritical water was investigated, and the results were compared with the results for C3F7SO3−. This is the first report on the decomposition of perfluoroalkane disulfonates, which are being introduced in electronics industry as greener alternatives to environmentally persistent and bioaccumulative perfluoroalkyl surfactants. Addition of zerovalent iron to the reaction system dramatically increased the yield of F− in the reaction solution: when the reaction of –O3SC3F6SO3− was carried out in subcritical water at 350 °C for 6 h, the F− yield was 70%, which was 23 times the yield without zerovalent iron. Prolonged reaction increased the F− formation: after 18 h, the F− yield from the reaction of –O3SC3F6SO3− reached 81%, which was 2.1 times the F− yield from the reaction of C3F7SO3−. Although the reactivity of FeO toward these substrates was lower than zerovalent iron in subcritical water, the reactivity was enhanced when the reaction temperature was elevated to supercritical state, at which temperature FeO underwent in situ disproportionation to form zerovalent iron, which acted as the reducing agent. When the reaction of –O3SC3F6SO3− was carried out in the presence of FeO in supercritical water at 380 °C for 18 h, the F− yield reached 92%, which was the highest yield among tested.