Semi-interpenetrating chitosan-styrene sulfonate-acrylamide hydrogel as a rapid and recyclable adsorbent for methylene blue dye.

In this study, a novel, eco-friendly superadsorbent semi-interpenetrating hydrogel (CSAm) was successfully synthesized in aqueous solution via free-radical polymerization from chitosan, sodium styrene sulfonate, and acrylamide. The chemical structure and morphological characterizations of the semi-interpenetrating hydrogel were investigated by various techniques. The adsorption performance of the semi-interpenetrating hydrogel was tested under various conditions. The optimization process demonstrated that the ratio of chitosan, styrene sulfonate, and acrylamide is 1: 1:1, resulting in a maximum adsorption capacity of 561.76 mg/g at neutral pH and 40 °C according to the Langmuir-Freundlich isotherm. The semi-interpenetrating hydrogel showed remarkably rapid adsorption behavior, removing 97.14%, 96.68%, and 95.77% of methylene blue dye from initial concentrations of 50, 100, and 200 mg/L, respectively, within the first 5 min, following pseudo-first-order kinetics. The prepared hydrogel exhibited high selectivity for the cationic dye and maintained its adsorption capacity over eight regeneration cycles, without significant loss of performance.