High-Affinity Cationic Organic Molecular Cages for Efficient PFAS Remediation to Ultralow Levels

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent water contaminants that require adsorbents capable of rapid uptake, high affinity, and effective regeneration under environmentally relevant conditions. Here, we report ICC3, a charge-engineered organic amine molecular cage (OAMC) with 12 accessible protonation sites, for broad-spectrum PFAS removal. The high cationic charge density, hydrophilicity, conformational flexibility, and intrinsic cavity structure of ICC3 enabled fast and selective adsorption of both carboxylate- and sulfonate-terminated PFAS. ICC3 showed high uptake capacities for PFOA (2983 mg g–1) and PFOS (3515 mg g–1) at pH 7, while maintaining rapid adsorption kinetics and resistance to common competing ions. Experimental analyses and theoretical calculations are consistent with an electrostatic association between the protonated amine groups of ICC3 and the anionic PFAS headgroups through N+···O– ion-pair formation. This reversible binding mechanism allowed efficient regeneration by alkaline treatment followed by reprotonation, with adsorption capacity retained at ≥96% of the initial value. Immobilization of ICC3 on silica enabled continuous-flow treatment, achieving removal efficiencies exceeding 99% for PFOA and 97% for PFOS. These results demonstrate that molecular-level charge engineering of OAMCs provides a viable strategy for designing regenerable adsorbents for rapid and deep PFAS removal from water.