Iron-induced efficient mineralization of a cyclic perfluoroalkyl surfactant in subcritical and supercritical water

Abstract

The decomposition of [CF2(CF2SO2)2N]−, a typical cyclic perfluoroalkyl surfactant, in subcritical and supercritical water was investigated. This is the first report on the decomposition of cyclic perfluoroalkyl surfactants, which are being developed as greener alternatives to environmentally persistent and bioaccumulative perfluoroalkyl surfactants. [CF2(CF2SO2)2N]− decomposition was negligible in either pure subcritical water under argon or in subcritical water in the presence of O2. In contrast, the mineralization of [CF2(CF2SO2)2N]− to F− ions was accelerated when a zerovalent metal (copper, zinc, or iron) was used in the reaction system under argon, and iron led to the most efficient mineralization. When the reaction was performed at 350°C for 6h, the F− yield was 70.6 times that in the absence of iron. Using supercritical water enhanced the reactivity: when [CF2(CF2SO2)2N]− was heated at 380°C with iron for 18h, 82.5% of the fluorine content in the initial [CF2(CF2SO2)2N]− was transformed into F− ions. The mineralization of [CF2(CF2SO2)2N]− was accompanied by transformation of the zerovalent iron to Fe3O4.