β–Cyclodextrin polymerization for selective separation of long-chain per- and poly-fluorinated alkyl substances at environmentally relevant concentrations

Per- and polyfluorinated alkyl substances (PFASs), particularly long-chain compounds such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA), are pervasive contaminants of global surface and groundwater resources. They have a significant negative impact on human health. Among the existing remediation techniques, adsorption remains an effective method and widely applied for removing PFASs from water. However, the limited adsorption kinetics of conventional adsorbents have motivated the development of advanced materials. In this study, we have synthesized a β-cyclodextrin (β-CD) polymer crosslinked with decafluorobiphenyl (β-CD–DFB) for the efficient separation of multiple long- and short-chain PFASs at environmentally relevant concentrations. The β-CD–DFB polymer exhibited a significant Langmuir adsorption capacity (43.10 ± 4.30 mg g⁻¹) and 10-times better affinity (K_L = 1.10 ± 0.40 L mg⁻¹) for long-chain PFOS compared to short-chain PFASs, with kinetics comparable to powdered activated carbons (ACs) and biochars (Act-BCs). Notably, the β-CD–DFB polymer could reduce the concentrations of long-chain PFASs in water from 1 to 44 ng L⁻¹ via adsorption, significantly below the advisory level (i.e., 70 ng L⁻¹) set by the US Environmental Protection Agency and Korea Ministry of Environment. The adsorbent was easily regenerated simply by washing with methanol and maintained a high performance over five consecutive adsorption–desorption cycles. Furthermore, the performance of the adsorbent remained unaffected by natural organic matter (such as humic acid), which is a common AC foulant. Adsorption tests with real wastewater samples confirmed the potential of β-CD–DFB as a promising adsorbent for selective long-chain PFAS removal in water and wastewater treatment applications.