Surface modification of activated carbon for enhanced PFAS adsorption and regeneration

• PDADMAC modification significantly enhanced PFAS adsorption on GAC • PFAS removal was resilient to chloride while moderately inhibited by organic matter • Column tests confirmed delayed breakthrough and scalable packed-bed performance • PDADMAC-modified AC exhibited good reusability with NaCl-based regeneration A surface modification strategy was employed to functionalize activated carbon (AC) with the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) for the efficient removal of per- and polyfluoroalkyl substances (PFAS) from aqueous solutions. The modification introduces permanent positive charges at the carbon–water interface, promoting electrostatic attraction with anionic PFAS head groups while preserving the intrinsic hydrophobic interactions between the carbon matrix and fluorinated tails. Systematic optimization of PDADMAC loading (0–12 wt%) identified 8 wt% as optimal, yielding 0.4–1.2-fold increases in adsorption capacity and accelerated uptake kinetics, with particularly pronounced enhancement for short-chain PFAS. Rapid small-scale column tests and bench-scale fixed-bed experiments using simulated natural waters demonstrated that the surface modification extended PFAS breakthrough volumes to 2.0–3.4 times those of raw AC. Notably, the functionalized surface enabled efficient regeneration using a simple 1% NaCl solution, retaining 79% (perfluorobutanoic acid) and 98% (perfluorooctanoic acid) of initial removal efficiency after five adsorption–desorption cycles, in contrast to conventional regeneration approaches that rely on harsh organic solvents. This work provides the first comprehensive evaluation of PDADMAC-modified activated carbon for PFAS remediation, systematically elucidating synthesis–structure–performance relationships across diverse water chemistries, continuous-flow operation, and multi-cycle regeneration.