Highly Efficient Removal of PFAS from Water Using Surface-Modified Regenerable Quaternized Chitosan Hydrogels

In this study, surface-modified bio-based hydrogels derived from crosslinked quaternized chitosan (MQCGs) were developed to treat PFAS-contaminated water. The novelty of this work lies in the surface modification and engineering of the hydrogels to enhance the surface area and positive charge of the hydrogels through sacrificial templating. By blending the chitosan solution with polyethylene glycol (PEG) and then removing PEG via sacrificial templating, microscale channels were created on the surface of the hydrogels. This increased the availability of the hydrogel's positive charges for increased electrostatic interactions with PFAS, achieving >98% PFOS (a long-chain PFAS) adsorption in less than 30 min. Batch adsorption experiments demonstrated that surface-modified quaternized chitosan hydrogels (MQCGs) removed both long- and short-chain PFAS across a pH range of 3 to 12, maintaining their performance over 10 regeneration cycles. The adsorption behavior followed the Freundlich isotherm model and pseudo-second-order kinetics, indicating fast multilayer adsorption on heterogeneous active sites via the combined actions of electrostatic, hydrophobic, and physical interactions. Using PFOS and PFOA as model long-chain PFAS and PFBS and PFHxA as short-chain surrogates, respectively, MQCGs achieved a complete removal of PFOS and PFOA and over a 99.9% removal of PFBS and PFHxA, each at a low concentration of 500 µg/L in water. Moreover, MQCGs exhibited highly efficient removal of PFAS at environmentally relevant concentrations of 20 µg/L in tap water containing MgSO₄ and NaCl as competing electrolytes, demonstrating the potential of MQCGs as a new class of efficient, selective, and regenerable materials for PFAS sequestration.