Rim‐Based Binding of Perfluorinated Acids to Pillararenes Purifies Water

Deca-ammonium-functionalized pillar[5]arenes (DAF−P5s) show unprecedent binding towards perfluoroalkyl acids with a 1 : 10 ratio and K≥10⁶ M⁻¹. A proof-of-concept experiment shows that DAF−P5s immobilized on silica can purify perfluorooctane sulfonic acid (PFOS) polluted water down to 13 ng/L.

Abstract

Per- and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects.^[1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water,^[2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale-up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host–guest interaction between deca-ammonium-functionalized pillar[5]arenes (DAF−P5s) and perfluoroalkyl acids. DAF−P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X-ray crystallographic studies, and high binding constants (up to 10⁶ M⁻¹) to various polyfluoroalkyl acids. In addition, non-fluorinated acids do not hamper this process significantly. Immobilization of DAF−P5s allows a simple single-time filtration of PFAS-contaminated water to reduce the PFOS/PFOA concentration 10⁶ times to 15–50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS-absorbing materials.

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