Rapid Removal of Perfluoroalkanesulfonates from Water by beta-Cyclodextrin Covalent Organic Frameworks

Adsorption is an effective method for the removal of perfluoroalkanesulfonates (PFSAs) from water, and the limitation of the adsorption rate of existing adsorbents motivates efforts to develop novel adsorbents. Here, we developed four beta-cyclodextrin covalent organic frameworks (beta-CD-COFs) with a rapid removal rate and high adsorption capacity for four PFSAs in water including perfluorooctanesulfonate (PFOS), perfluorobutanesulfonate (PFBS), perfluorohexanesulfonate (PFHxS), and chlorinated polyfluorinated ether sulfonate (F53B). All beta-CD-COFs exhibited extremely fast adsorption (adsorption equilibrium <2 min) for PFSAs with high adsorption capacities (0.33-1.51 mmol/g), which were significantly better than those of traditional resins and activated carbons, probably due to the ordered pores of beta-CD-COFs and the electron-deficient cavity beta-CD. Density functional theory (DFT) calculations also showed that PFSAs could be captured in the beta-CD cavity through strong interactions with a high binding energy. The novel beta-CD-COFs were highly selective to PFSAs in simulated wastewater impacted by aqueous film-forming foams, and they could also rapidly remove them from an actual chrome plating wastewater within 2 min. Additionally, the beta-CD-COFs could be regenerated by methanol with relatively good reusability in four cycles, further highlighting their application potential as PFAS adsorbents in water or wastewater.