Forest Residue-Derived Thermoresponsive Nanocellulose Adsorbent for Efficient Removal of Short- and Long-Chain PFAS from Water

This study presents the development of a novel thermoresponsive nano-adsorbent for efficient and regenerable removal of both short- and long-chain per- and polyfluoroalkyl substances (PFAS) from water. The adsorbent was synthesized by functionalizing cellulose nanocrystals (CNC) derived from forest residue biomass (FRB) with poly(N-isopropylacrylamide) (PNIPAM) via a polydopamine (PDA) linker. Comprehensive characterization confirmed the synthesis of nano-adsorbent with desired morphological, structural, chemical, thermal, and surface properties. A reversible change in hydrodynamic diameter above and below the lower critical solution temperature (LCST) of PNIPAM (32 ºC) confirmed the synthesis of thermoresponsive PNIPAM-f-CNC adsorbent. Batch adsorption studies conducted at 40 °C (above LCST) demonstrated enhanced removal efficiencies—78% for long-chain PFOA and 63% for short-chain PFBA—alongside faster kinetics and higher adsorption capacities compared to unmodified CNC. Adsorption followed the Freundlich isotherm and pseudo-second-order kinetics, indicating multilayer adsorption on a heterogeneous surface with rapid equilibrium (30 min). Upon cooling below LCST (25 °C), over 73% of PFOA and 82% of PFBA were desorbed, validating the adsorbent’s regenerability. Overall, the PNIPAM-f-CNC adsorbent offers a sustainable, high-performance platform for temperature-responsive PFAS removal and recovery.