Polyacrylonitrile fiber functionalized with fluorous hyperbranched polyethylenimine for selective removal of perfluorooctane sulfonate (PFOS) in firefighting wastewaters

Perfluorooctane sulfonate (PFOS) is a well-known persistent organic pollutant in water systems, especially in firefighting wastewaters. It is highly desirable to develop new adsorbents that can remove PFOS efficiently and selectively from firefighting wastewaters. In this work, polyacrylonitrile (PAN) fiber was functionalized by adding fluorous hyperbranched polyethylenimine (F-PEI) under hydrothermal conditions, generating a series of fluorous PAN-g-F-PEI fibers. Compared with the fiber without perfluoroalkyl chains, the existence of perfluoroalkyl chains significantly shortened the equilibrium adsorption time. Lowering solution pH and increasing the F-PEI content were two more efficient ways to improve the maximum equilibrium adsorption capacity. The introduction of enough perfluoroalkyl chains into the fiber effectively suppressed the adverse effect of zwitterionic surfactants, nonionic surfactants and organic solvents on the PFOS removal efficiency, and also alleviated the adverse effect of anionic surfactants. The PAN-g-F-PEI fiber with the largest amount of perfluoroalkyl chains could efficiently and selectively remove PFOS from the firefighting wastewaters containing a high concentration of PFOS and the residual PFOS concentration could reach below 10 ng/L, satisfying the standard of the U.S. Environmental Protection Agency. Moreover, after adsorption, PAN-g-F-PEIs could be easily regenerated by methanol washing and reused for five times without pronounced loss of adsorption capacity.