Haojie Zhang

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants widely detected in terrestrial systems, where their high mobility and resistance to degradation pose long-term risks to soil and groundwater resources. Although traditional adsorbents such as activated carbon are widely used for PFAS remediation, their limited regenerability often necessitates high-temperature treatment or direct incineration with high CO₂ emissions, or the use of expensive and toxic organic solvents for desorption, thereby constraining their sustainable application in environmental systems. Here, we present a novel thermo-responsive hydrogel adsorbent that enables temperature-controlled adsorption and release of PFAS, offering a new pathway for the sustainable management and remediation of PFAS.The hydrogel was synthesized via copolymerization of N-isopropylacrylamide (NIPAM) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTAC) and exhibits a lower critical solution temperature (LCST) of approximately 35 °C. Above the LCST, the hydrogel surface becomes hydrophobic, promoting the adsorption of long-chain PFAS including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) through hydrophobic interactions. Below the LCST, the surface transitions to a hydrophilic state, weakening these interactions and enabling PFAS desorption. As a result, the adsorption coefficient (Kd) of the hydrogel for PFOA at 45 °C is 35-fold higher than that at 25 °C. By exploiting this reversible hydrophobic–hydrophilic transition, adsorption and desorption of long-chain PFAS can be achieved without the use of organic solvents. Lab-scale batch experiments demonstrated that approximately 80% of PFOA and PFOS could be desorbed through temperature control alone, with complete desorption achieved upon the addition of chloride ions (Cl⁻). Notably, after ten adsorption–desorption cycles, PFOS desorption efficiency remained above 80%, indicating excellent reusability.The environmental relevance of this approach was further evaluated using rapid small-scale column tests with tap water as a proxy for natural water matrices. Through temperature modulation and the addition of 1% NaCl, 84% of PFOS and 75% of PFOA were desorbed, with enrichment factors of 32 and 15, respectively. These results demonstrate that thermo-responsive hydrogels can provide a controllable and solvent-free strategy for PFAS retention and release, offering new opportunities for sustainable remediation and management of PFAS.

In order to address the regeneration issue of adsorbents for the elimination of per- and polyfluoroalkyl substances (PFAS), this work synthesized a novel smart hydrogel based on a temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAm). These hydrogels exhibit hydrophobicity and hydrophilicity above and below the the lower critical solution temperature (LCST) of PNIPAm, respectively. Concurrently, the monomer 2-(methacryloyloxy)ethyl)trimethylammonium chloride (MTAC), distinguished by its quaternary ammonium groups, was co-polymerized with NIPAM to augment its electrostatic effect. Utilizing perfluorooctanoic acid (PFOA) as a case study, the smart hydrogel attained an 80% desorption efficiency through the mere adjustment of temperature, obviating the necessity for salt solution or organic solvent. This work is expected to overcome the challenges associated with the regeneration of adsorbents and contribute to the sustainable management of PFAS.