Fully Chitosan-Based Thermoresponsive Hydrogel for Efficient Cu²⁺ Adsorption and Regeneration

Abstract

To efficiently remove Cu²⁺ from wastewater, a fully chitosan thermoresponsive hydrogel (IPS_gel) was prepared using chitosan as the raw material. IPS_gel exhibited pronounced thermoresponsive behavior as well as a high adsorption capacity toward Cu²⁺. When the temperature exceeded its volume phase transition temperature (VPTT = 35.4 °C), enhanced hydrophobic interactions among with the alkyl groups along the polymer chains induced rapid dehydration, shrinkage, and a reversible volume phase transition. The effects of initial Cu²⁺ concentration and pH on adsorption performance were systematically evaluated. The adsorption process followed the Langmuir isotherm and pseudo-second-order kinetic models, and a maximum adsorption capacity of 24.5 g/g was achieved. During regeneration, only 0.23 L of 0.1 M hydrochloric acid per gram of IPS_gel was required for rapid Cu²⁺ desorption, representing a reduction of approximately 88 to 95% compared to the conventional acid consumption (2 to 5 L/g) of traditional hydrogels. These findings indicate that by integrating thermoresponsiveness, high adsorption capacity, and efficient regeneration, the chitosan-based IPS_gel shows strong potential for wastewater treatment applications and provides a new strategy for the green design of purification materials.