Highly carboxylated chitosan-based thermosensitive hydrogel: Preparation and efficient adsorption of heavy metal ions

Chitosan thermosensitive hydrogels can modulate their internal structure in response to temperature changes, enabling specific functions and thus holding great promise for environmental and energy materials. However, their application in heavy metal wastewater treatment still faces challenges such as low adsorption capacity and poor selectivity. In this study, a novel carboxylated chitosan thermosensitive hydrogel (CPNM) was successfully prepared via a one-pot method using N-isopropylacrylamide (NIPAM) and maleic acid (MA) as monomers. CPNM exhibited a fast adsorption rate, reaching near saturation within 1 h, and showed extremely high selectivity for Cu 2+ with a maximum adsorption capacity of 494.1 mg·g −1 . The adsorption process followed pseudo-second-order kinetics (chemical adsorption) and conformed to the Langmuir isotherm model (monolayer adsorption, spontaneous endothermic process). The mechanism primarily involves complexation of N/O atoms from -COOH, -NH 2 , -OH, and -CO-NH- groups. Benefiting from its temperature-responsive property, CPNM enabled efficient regeneration using EDTA-2Na at 50 °C, retaining a high adsorption capacity of 110.4 mg·g −1 for Cu 2+ after five cycles. This material therefore represents a promising candidate for alleviating heavy metal water pollution. Environmental implication This work addresses the environmental challenges posed by Cu 2+ , Cr 3+ , and Ni 2+ —persistent heavy metal contaminants in industrial wastewater. Conventional chitosan-based adsorbents suffer from low capacity and poor selectivity, limiting their practical application. Our novel carboxylated chitosan thermosensitive hydrogel (CPNM) achieves a record-high Cu 2+ adsorption capacity (494.1 mg·g −1 ) and excellent Cu 2+ selectivity under competitive conditions. The temperature-responsive property enables efficient regeneration with EDTA-2Na at 50 °C, maintaining 110.4 mg·g −1 after five cycles. This work provides a sustainable, high-performance material for heavy metal remediation, directly contributing to safer water resources and environmental protection.