Selective adsorption of OBS (sodium p‑perfluorous nonenoxybenzenesulfonate) as an emerging PFAS contaminant from aquatic environments by fluorinated MOFs: Novel mechanisms of F–F exclusive attraction

Selectivity is the key for adsorption or recovery of per- and polyfluoroalkyl substances (PFAS) from aqueous environments. In this study, the fluorinated metal–organic frameworks (MOFs) with different fluorine contents were prepared and investigated to evaluate the selective adsorption of an emerging PFAS, sodium p‑perfluorous nonenoxybenzenesulfonate (OBS). Adsorption of OBS increased with the increasing fluorine content of MOFs, and the best fluorinated MOFs showed an excellent selective adsorption capacity. The influence of various co-existing hydrocarbon substances on OBS adsorption was slight. The adsorption amount of OBS was 15-fold to that of the hydrocarbon surfactants (n-caprylic acid). The selectivity was attributed to the fluorinated structures of MOFs whose oil contact angle was up to 101°, and thus the oleophobicity of fluorinated structures made MOFs repel hydrocarbon compounds. Molecular dynamics simulations and density functional theory calculations indicated that the fluorinated structures were able to capture OBS molecules from the long distances (roughly 1–100 nm) via hydrophobic interaction, and then formed a F–F non-covalent interaction which was highly probable to be driven by a dispersion force to further attract OBS fluorinated tails within shorter distances (less than 3.5 Å). The combination of oleophobic and fluorophilic effects contribute to the exclusive selectivity of fluorinated MOFs for OBS molecule.