Chitosan-coated HKN-COF as a sustainable adsorbent for efficient removal of PFOA from water

Abstract: Perfluorooctanoic acid (PFOA), a persistent organic pollutant from the PFAS family, poses serious environmental and health risks due to its high stability and bioaccumulative nature. This study presents the development of a sustainable adsorbent system based on chitosan-coated covalent organic frameworks (CS@HKN-COFs) for efficient PFOA removal from water. HKN-COFs were synthesized via Schiff-base condensation using custom-synthesized L16 linkers and characterized through FTIR, PXRD, BET, SEM, and TGA analyses, confirming their high crystallinity, porosity, and thermal stability. Among the synthesized variants, HKN-COF-2 exhibited the highest adsorption performance (~2200 mg/g), which was further enhanced to ~2500 mg/g upon chitosan coating. The CS@HKN-COF composites demonstrated rapid adsorption kinetics, reaching equilibrium within 60 minutes, and followed a pseudo-second-order kinetic model, suggesting chemisorption as the dominant mechanism. Isotherm studies fitted the Langmuir model, indicating monolayer adsorption on homogeneous surfaces. These composites also showed excellent performance across a wide pH range (3–9) and retained high adsorption capacity under various ionic strengths, highlighting their robustness. Regeneration studies confirmed structural stability and reusability over multiple cycles with minimal loss in performance. The enhanced adsorption capacity, eco-friendliness, and reusability of CS@HKN-COFs underscore their potential as a viable solution for sustainable water purification and PFAS remediation.