Photoinitiated carboxymethyl chitosan interpenetrating network hydrogel with hydrophobic modification: Coordination...

Efficient removal of Co²⁺ and Ni²⁺ from industrial effluents is essential to mitigate escalating toxicological risks to ecosystems and human health. However, conventional hydrogel adsorbents often suffer from limited network rigidity and disordered coordination sites, which thereby hinder effective multidentate chelation. To circumvent these challenges, this study synthesized a carboxymethyl chitosan (CMCS) interpenetrating network (IPN) hydrophobically modified hydrogel (designated as HNCIG) via rapid photoinitiated polymerization that was completed within 30 s. This architecture featured an interconnected mesoporous framework and optimized coordination geometry through synergistic design principles: dual cross-linking reinforced network rigidity, hydrophobic modification regulated swelling to enhance site accessibility, and the CMCS-IPN facilitated spatial refinement of active sites. FTIR, XRD, and XPS analyses confirmed the synergistic coordination mechanism involving carboxyl and amino groups. Under optimal conditions (pH 5, 328 K), HNCIG achieved maximum adsorption capacities of 190.97 mg/g for Co²⁺ and 191.16 mg/g for Ni²⁺. The adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating chemisorption-dominated uptake with spontaneous and endothermic characteristics and a multi-stage mass transfer process (ΔG° < -23 kJ/mol). After five regeneration cycles, HNCIG maintained a capacity retention above 75%, significantly outperforming the single-network hydrogel (HNG). Post-cycling characterizations further demonstrated that the IPN architecture effectively preserved both mechanical integrity and chemical functional group stability. This work offers a sustainable, high-performance, and scalable strategy for industrial heavy metal remediation.