A novel ion-responsive hydrogel based on quaternized chitosan and hydroxyethyl cellulose for high efficient chloride ion adsorption

Abstract

Chloride removal is crucial for industrial wastewater discharge, seawater purification and concrete structure durability. In this study, a novel hydrogel with excellent chloride adsorption property was prepared and the adsorption capacity in relation to external pH and other ions was evaluated. The hydrogel was synthesized using a one-pot method with quaternized chitosan (HACC), hydroxyethyl cellulose (HEC), and carboxymethyl chitosan (CMC) as monomers. By adjusting the material compositions, we effectively modulated the microstructure and charge characteristics of hydrogel, achieving a balanced swelling ratio and optimal adsorption performance. The optimal process conditions were identified as 25 °C and a chloride ion concentration of 40 mmol L⁻¹, achieving a maximum adsorption capacity of 1080 mg g⁻¹. Isotherm modeling showed that the adsorption fits well with the Freundlich isotherm, suggesting multilayer adsorption. The quaternary ammonium groups serve as fixed positive charge sites or active adsorption sites, enabling the hydrogel to efficiently adsorb anions through the synergistic effects of electrostatic interactions, physical adsorption, and amino protonation. The varied adsorption capacities of quaternary ammonium groups for different anions give rise to competitive adsorption phenomena among them. The incorporation of silver ions into the hydrogel greatly enhances its selective adsorption of chloride ions through chemical combination. This work presents a comprehensive strategy for designing a novel hydrogel with exceptional adsorption properties specifically tailored for chloride ions.