Dual-mode synergy in amorphous chitosan-Fe frameworks: Simultaneous Sb(III/V) capture via ligand exchange and cooperative bridging

Antimony contamination in industrial wastewater requires effective simultaneous removal of both Sb(III) and Sb( V ) species, yet their contrasting chemical characteristics pose significant challenges for conventional adsorbents. Here, we demonstrate that amorphous chitosan-Fe coordination polymer sheets (CS-Fe aCPs) achieve exceptional Sb(III/ V ) capture through a dual-mode synergistic mechanism. For Sb(III), ligand exchange dominates the adsorption process, wherein Sb(OH) 3 directly coordinates with Fe 3+ centers by displacing weakly-bound NO 3 − ligands, as evidenced by stoichiometric NO 3 − release and significant Fe 2p binding energy shifts in XPS analysis. This process further triggers sequential Sb bridging interactions, producing an S-shaped isotherm and enabling a maximum capacity of 626.97 mg/g. For Sb( V ), the persistently high positive surface charge (+15 to +30 mV across pH 2–10) facilitates electrostatic capture of [Sb(OH) 6 ] − anions, supplemented by partial ligand displacement, achieving 574.55 mg/g capacity. The amorphous coordination framework provides abundant coordinatively unsaturated Fe 3+ sites and structural adaptability essential for accommodating both Sb species without steric hindrance. This dual-mode synergy ensures pH-insensitive performance, exceptional resistance to competing ions, and stable operation in fixed-bed column and membrane filtration systems, establishing CS-Fe aCPs as a cost-effective platform for mixed Sb speciation remediation.