Design of a novel 2,2′-(pyridyl)imidazole monomer for the selective recovery of Ni(II) via ion-imprinting technology

The growing industrial demand for nickel, coupled with its toxicity to the environment and human health, presents a significant challenge for its separation and recovery. To address this issue, we propose a novel chelating monomer based on 2,2′-(pyridyl)imidazole ligand and its application to prepare a Ni(II)-selective ion-imprinted polymer (IIP). The monomer was characterized by 1 H NMR spectroscopy and copolymerized with ethylene glycol dimethacrylate in the presence of Ni(II) ions. The resulting adsorbent (PIM-Ni-IIP) and its non-imprinted counterpart (PIM-NIP) were characterized by FTIR, 13 C CPMAS NMR, SEM and BET analysis. PIM-Ni-IIP exhibited a significantly higher total pore volume (0.511 cm 3 vs. 0.006 cm 3 ) and surface area (344.2 m 2 /g vs. 7.8 m 2 /g) compared to PIM-NIP, indicating that the imprinting process fundamentally altered the polymer morphology. Adsorption experiments performed at an optimal pH of 6 revealed a maximum adsorption capacity (q max ) of 26.2 mg/g for PIM-Ni-IIP, yielding an imprinting factor (IF) of 5.8. PIM-Ni-IIP exhibited good selectivity for Ni(II) over Co(II), Cd(II), and Mg(II), with selectivity coefficients ( k ) up to 1.34, 2.84, and 1.44, and relative selective coefficients ( k ´) of 1.50, 1.50 and 3.00, respectively. PIM-Ni-IIP kinetic data followed a pseudo-second-order model (R 2 of 0.990), and the adsorption process was best described by the Sips isotherm (R 2 of 0.984). Furthermore, PIM-Ni-IIP maintained 77% of its initial capacity after five adsorption-desorption cycles. These results confirm that the synergy between the novel monomer and the imprinting technique created Ni(II)-specific recognition sites, making PIM-Ni-IIP a robust and efficient candidate for Ni(II) recovery from aqueous solutions.