(20b) Fluorinated Activated Carbon-Grafted Chloromethylated Polysulfone Ultrafiltration Adsorptive Membranes for Selective and Enhanced PFOS and Pfbs Removal

The persistent presence of per- and polyfluoroalkyl substances (PFAS) in aquatic environments has raised critical concerns due to their high mobility, environmental persistence, and resistance to conventional treatment methods. In particular, the removal of short-chain PFAS, such as perfluorobutane sulfonic acid (PFBS), remains a significant challenge due to their low concentrations in water and varying physicochemical properties. In this study, a novel adsorptive ultrafiltration (UF) membrane was developed by grafting fluorinated superfine activated carbon (FSFAC) onto the surface of chloromethylated polysulfone (CM-PSF) membranes. The goal was to combine the advantages of adsorption and membrane separation to achieve enhanced selectivity, improved permeability, and energy-efficient PFAS removal. Surface functionalization of the UF support membrane offers key advantages over conventional thin-film composite (TFC) nanofiltration (NF) membranes, including lower energy demand and higher water permeability.

Fluorination of activated carbon significantly improved its affinity toward both long- and short-chain PFAS (removal >90%) through combined hydrophobic and fluorine–fluorine (F···F) interactions. Isothermal adsorption studies demonstrated that FSFAC outperformed its unmodified counterpart (SFAC), requiring only 2 ppm to achieve >99% removal of 2 ppm perfluorooctane sulfonic acid (PFOS) within 30 minutes, compared to 50 ppm for SFAC. For perfluorobutane sulfonic acid (PFBS), FSFAC achieved >90% removal at 50 ppm, while SFAC showed only ~70% removal at similar high concentrations. At environmentally relevant lower concentrations (50 ppb), FSFAC achieved >99% PFOS removal in 30 minutes, whereas SFAC reached only 85% after 2 hours. When grafted onto UF membranes, FSFAC imparted strong adsorptive properties without compromising membrane permeability. The resulting FAC-CM-PSF membranes demonstrated removal efficiencies exceeding 90% for both PFOS and PFBS, comparable to nanofiltration membranes, while offering up to 20 times higher water flux. Adsorption was identified as the dominant removal mechanism, as control membranes (PSF and CM-PSF) showed <20% PFOS removal. Moreover, the membranes maintained >80% removal efficiency for both PFOS and PFBS after three reuse cycles. Overall, this work presents a tunable membrane platform that addresses key limitations of current PFAS treatment technologies by enabling selective removal of diverse PFAS contaminants from water systems.