Surface chemistry and pore structure effects on per- and polyfluoroalkyl substances (PFAS) adsorption by sustainable activated carbons

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Per- and polyfluoroalkyl substances (PFAS) persist in aquatic environments, creating an urgent need for effective and sustainable adsorbents for water treatment. This study compared activated carbons derived from spent coffee grounds (CGAC), bamboo (BAC), and waste coke (WCAC), prepared under identical carbonization and steam activation conditions, to clarify how precursor-dependent physicochemical properties control PFAS adsorption. Nine representative PFAS were evaluated through batch kinetic and isotherm experiments. WCAC showed the highest overall removal efficiency among the three activated carbons, achieving more than 98% removal of most long-chain PFAS within 10 min. Based on pseudo-second-order kinetic fitting, the adsorption capacities ranged from 358.8 to 628.4 μg g⁻¹ for CGAC, 336.7 to 455.7 μg g⁻¹ for BAC, and 397.5 to 1,064.4 μg g⁻¹ for WCAC. The highest fitted capacities were obtained for PFNA on WCAC (1,064.4 μg g⁻¹) and PFOA on WCAC (930.5 μg g⁻¹), indicating strong affinity toward long-chain perfluorocarboxylates, while kinetic parameters revealed PFAS- and adsorbent-specific adsorption behavior. Isotherm analysis further confirmed the strong adsorption performance of WCAC for selected PFAS, with experimental equilibrium adsorption capacities of 2,301.6 μg g⁻¹ for PFOS, 1,952.0 μg g⁻¹ for PFHpA, 1,670.0 μg g⁻¹ for PFNA, and 1,444.0 μg g⁻¹ for PFOA. The isotherm parameters indicated heterogeneous adsorption on energetically diverse carbon surfaces. Overall, PFAS adsorption depended on pore accessibility, graphitic character, hydrophobicity, and oxygen-containing functional groups rather than surface area alone, supporting the rational design of sustainable carbon adsorbents for water treatment.