Thermoresponsive shrinkage-driven chitosan hydrogel boosts sustainable Cu²⁺ removal

Developing adsorbents with efficient regeneration and long-term stability and reusability remains a critical challenge for sustainable heavy-metal removal. In this study, chitosan (CS) was molecularly engineered into a thermoresponsive hydrogel (TR-ICS_g) capable of integrating efficient Cu²⁺ adsorption with rapid, low-consumption regeneration. Under thermal stimulation, enhanced interactions among hydrophobic alkyl groups promoted hydrogel dehydration, resulting in pronounced volume shrinkage. Further, during regeneration, this thermally induced shrinkage enabled efficient elution with only 200 mL·g^-1 of 0.1 M HCl, reducing acid consumption by 67.2% compared to the swollen state. The shrunken TR-ICS_g achieved a Cu²⁺ desorption efficiency of 92.7% within 5 min, demonstrating rapid regeneration under low-eluent conditions. Under a standardized adsorption-desorption protocol (pH 6.0, 25 °C, initial Cu²⁺ concentration of 200 mg·L^-1, 10 min), TR-ICS_g sustained 20 consecutive cycles within 300 min, achieving a cumulative Cu²⁺ uptake of 905 mg·g^-1, while the single-cycle uptake decreased only modestly from 52.4 to 38.2 mg·g^-1. This study provides a scalable, low-consumption regeneration strategy for sustainable and continuous heavy-metal wastewater treatment.