Porous organic polymers driven by bis-urea anion receptor sites for adsorption of perfluoroalkyl carboxylic acids

Perfluoroalkyl carboxylic acids (PFCAs), a representative class of per- and polyfluoroalkyl substances (PFASs), have drawn increasing attention due to their extreme persistence and potential health risks. Conventional adsorbents for adsorption of PFCAs mainly rely on hydrophobic and electrostatic interactions. Herein, we developed an "anion-receptor-site engineering" strategy by polycondensing methylidynetri-p-phenylene triisocyanate with 3,3'-diaminobenzidine to fabricate a porous organic polymer BD(NH₂)₂-POP with ortho-phenylene bis-urea linkages. The adsorbent was systematically evaluated for adsorption of C4-C10 PFCAs, covering removal efficiency, interference response, regeneration, and trace-level enrichment. BD(NH₂)₂-POP features a mesoporous structure (∼13.47 nm), hydrophobic interface (contact angle ∼126.5°), and tunable surface charge (pH_PZC≈4.42), affording rapid kinetics and high adsorption capacity. Competitive experiments revealed that oxygen-containing anions (e.g., carboxylates) strongly inhibit PFCA uptake, indicating that directional, multipoint hydrogen bonding between the bis-urea N-H motifs and carboxylate headgroups plays a key role, while hydrophobic and electrostatic interactions provide synergistic enhancement. The adsorbent can be regenerated through an alkaline organic solvent plus high-concentration urea system and exhibits robust enrichment capability at trace levels (0.1-20 ng/mL, R² = 0.963-0.999). This work proposes and validates a "headgroup anchoring-hydrophobic stabilization" adsorption framework, offering guidance for molecular recognition-based POP design for PFASs remediation.