Periodic Janus structure based on ionic covalent organic framework for selective removal of perfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that often show an adverse impact on human health. Rational design of porous adsorbents for selective and reversible removal of PFAS, such as perfluorooctane sulfonate (PFOS), is imperative and challenging. Herein, a Janus strategy based on an ionic covalent organic framework (iCOF-DG_Cl) composed of the alternately hydrophobic aromatic domains and hydrophilic guanidinium moieites has been proposed to meet the requirement of high-performance adsorbents. iCOF-DG_Cl shows fast adsorption kinetics (970.9 mg g⁻¹ min⁻¹) and ultrahigh uptake capacity (2491 mg g⁻¹) toward PFOS, making it one of the most effective materials among the reported PFOS adsorbents. Moreover, the PFOS removal by iCOF-DG_Cl remains highly selective in the presence of disturbing anions, and the adsorbent could be well recovered for reuse. Mechanism studies have demonstrated that the Janus structure units of iCOF-DG_Cl form both hydrophobic and electrostatic interactions with the amphiphilic PFOS, thus achieving cooperative adsorption of PFOS. This work provides a facile approach based on Janus structure of COFs adsorbent for wastewater remediation.