Synthesis of a cationic olefin-linked covalent organic framework for the selective removal of per-and polyfluoroalkyl substances

Per -and polyfluoroalkyl substances (PFASs) have become a pressing global concern for environmental and public health due to their extreme persistence and association with severe adverse effects, underscoring the urgent need for efficient and sustainable remediation technologies. In this study, we present a cost-effective, one-pot melt polymerization approach for the synthesis of an ionic covalent organic framework (COF) adsorbent, TMB-TPA-COF(Br − ), using 2,4,6-trimethylpyridine (TMB) and terephthalaldehyde (TPA) as inexpensive molecular building blocks. The material is subsequently functionalized via in-situ quaternization with bromoethane to introduce cationic sites that enable strong electrostatic interactions for selective PFAS capture. The resulting TMB-TPA-COF(Br − ) exhibits well performance in the removal of perfluorooctanoic acid (PFOA), achieving a maximum adsorption capacity of 411.5 mg/g and reaching adsorption equilibrium within 30 min. It maintains high removal efficiency for five perfluoroalkyl carboxylic acids (PFCAs) over a broad pH range (2–5), and the presence of humic acid induces only a marginal decrease (<10 %) in PFOA uptake, demonstrating remarkable resilience in complex environmental matrices. Notably, TMB-TPA-COF(Br − ) surpasses commercial activated carbon and conventional anion exchange resins in the simultaneous removal of 14 structurally diverse PFASs, achieving ≥75 % removal for 13 compounds, with the exception of perfluorobutanoic acid (PFBA). Moreover, the adsorbent exhibits excellent chemical stability, retaining over 88 % of its initial removal efficiency after five regeneration cycles, and consistently maintains high performance across seven real-world water samples, including groundwater, wastewater, and surface water, where it achieves >75 % removal of PFCAs. This study highlights the potential of TMB-TPA-COF(Br − ) as a high-performance and cost-effective adsorbent for PFASs remediation, offering a scalable and practical solution to address widespread PFASs contamination.