Preparation of chitosan derivatives/oxidized carboxymethyl cellulose hydrogels by freeze-thaw method: Synthesis, characterization, and utilization in dye absorption

This study successfully synthesized hydrogels by modifying chitosan with water-soluble and carboxyethyl groups, followed by crosslinking with oxidized carboxymethyl cellulose (OCMC). Structural analyses substantiated the establishment of robust imine linkages between the amino and aldehyde groups, affirming the hydrogel's architecture. Using scanning electron microscopy and texture analysis, it was observed that incorporating water-soluble chitosan significantly increased the hydrogel's porosity and hardness. Simultaneously, the addition of carboxyethyl groups enhanced the network structure, rendering it more compact and thereby improving the hydrogel's mechanical strength. The adsorption performance of the carboxyethyl chitosan (CEC)/ OCMC hydrogel towards methylene blue was meticulously evaluated, demonstrating a substantial enhancement in adsorption capacity from 7.74 mg/g to 39.57 mg/g following the carboxyethyl modification of chitosan. Adsorption kinetics and isotherm analysis indicated that the adsorption behavior of the hydrogel followed the pseudo-second-order kinetic model and the Langmuir isotherm model. Furthermore, the maximum adsorption capacity of the hydrogel for methylene blue was predicted to be 111.60 mg/g using the Langmuir isotherm model.