Mixed-linker Zn(II) coordination polymer with structurally accessible binding sites for recyclable trace-level...

The persistence of pharmaceutical residues in aquatic systems necessitates the development of robust and recyclable adsorbents for trace-level contaminant removal. In this work, a Zn(II)-based mixed-linker coordination polymer, [Zn(Phen)(5-NIP)]ₙ (Phen = 1,10-phenanthroline; 5-NIP = 5-nitroisophthalate) (Zn-CP), was synthesized via a solvothermal method and evaluated for the adsorption of the antibiotic Trimethoprim (TMP) from aqueous media. Structural characterization by single-crystal X-ray diffraction revealed a one-dimensional zigzag chain architecture featuring periodically exposed aromatic and carboxylate moieties that provide accessible adsorption sites. Batch adsorption experiments quantified by UHPLC-MS/MS demonstrated high TMP removal efficiency (up to ~ 97%) at trace concentrations under optimized conditions. Adsorption kinetics were reasonably described by both pseudo-first-order and pseudo-second-order models, with the pseudo-first-order model giving a slightly better empirical fit, while nonlinear isotherm analysis showed that both Langmuir and Freundlich models described the equilibrium data well, with Freundlich giving a marginally better fit and the Langmuir model providing a model-estimated apparent capacity of 84.27 µg g^-1, suggesting suitability for low-concentration pharmaceutical remediation rather than high-load adsorption applications. Thermodynamic analysis indicated a spontaneous and predominantly physisorption-driven interaction. The material exhibited excellent chemical stability and retained its adsorption performance over 10 regeneration cycles, retained 97.4% of its initial adsorption capacity, and showed a mass recovery of 96.5%. FTIR, XPS, and DFT analyses suggest that hydrogen bonding and π-π interactions between TMP and the exposed functional groups of Zn-CP govern the adsorption mechanism. This study highlights the potential of structurally robust mixed-linker coordination polymers as recyclable adsorbents for trace-level and environmentally relevant pharmaceutical polishing/remediation in aqueous systems.