Design of a cobalt (II)-selective ion-imprinted polymer using modified pullulan and a click-based strategy

A novel Co²⁺-ion-imprinted polymer (Co-IIP) was developed using cyanoethyl pullulan (CEP) for selective Co²⁺ recovery. The chelating ligand 2-Hydroxy-5-[(furan-2-ylmethyl)amino]benzohydrazide (FABH), synthesized from 4-aminosalicylic acid and furfural, was grafted onto CEP via nucleophilic addition, forming FAB-functionalized pullulan (FAB-Pn). Co-IIP was prepared by Co²⁺ coordination with FAB-Pn, followed by Diels-Alder (DA) crosslinking with bis(maleimido)ethane (BM) and subsequent template ion removal. Characterization via FTIR, NMR, SEM, BET, and XPS confirmed successful functionalization and imprinting. Co-IIP exhibited a high adsorption capacity (112 mg/g), significantly outperforming NIP. Selectivity studies revealed selectivity coefficients (β_r) of 11-14 and an imprinting factor (α) of 2, demonstrating strong Co²⁺ preference over Hg²⁺, Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺. Kinetic analysis showed fast adsorption equilibrium within 15 min, fitting the pseudo-second-order model. Thermodynamic studies confirmed an endothermic, spontaneous process, with ΔH⁰ = 27 kJ/mol and ΔS⁰ = 187 J/mol·K. Reusability tests showed 94 % retention after 5 cycles, confirming structural stability. These results establish Co-IIP as a highly selective, reusable material for Co²⁺ recovery in industrial and environmental applications.