Selective and High Sorption of Perfluorooctanesulfonate and Perfluorooctanoate by Fluorinated Alkyl Chain Modified Montmorillonite

A novel fluorinated montmorillonite (F-MT) was synthesized via exchange of cationic fluorinated surfactant to selectively adsorb perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) from water. F-MT displayed fast and high sorption for PFOS and PFOA at concentrations below 10 μg/L, and performed better than the best activated carbon and resin previously reported. The spent F-MT can be completely regenerated by methanol solution and can be reused five times without reduction in sorption capacity. Moreover, the F-MT possessed excellent selectivity for PFOS and PFOA in the presence of other organic pollutants. The coexisting phenol, pyridine, dodecylbenzenesulfonate (SDBS), and phenanthrene (PHE) exhibited no effect on PFOS and PFOA sorption. Due to the nanoscale interlayer structure and chemical nature of F-MT, macromolecular humic acid had little effect on PFOS and PFOA sorption. Also, F-MT adsorbed very little SDBS and PHE. The results of competitive sorption and density functional theory calculations verified that PFOS and PFOA were adsorbed on the C–F chain of F-MT, while PHE and SDBS sorption occurred on the hydrocarbon part of F-MT. The unique hydro-oleophobic C–F chain on the F-MT was responsible for selective sorption of perfluoroalkyl acids (PFAAs), providing a new mechanistic insight for the interactions between PFAAs and fluorinated adsorbents. In addition, F-MT offers promising potential for removal of PFOS and PFOA from contaminated water