Preparation and Characterization of a Novel Chemically Crosslinked Chitosane-g-Polyacrylamide Hydrogel as a Promising Adsorbent for the Removal of Methylene Blue from Aqueous Solutions

The present study aims primarily to develop a new three-dimensional chitosan-graft-polyacrylamide hydrogel through radical polymerization using sodium trimetaphosphate as a crosslinking agent. The structural confirmation of the synthesized hydrogel was carried out by Fourier transform infrared spectroscopy and X-Ray diffraction analysis. In addition, the thermal behavior of the above hydrogel was investigated using thermogravimetric analysis and differential thermal analysis. Moreover, the kinetics and swelling behavior of the resulting product were also enquired. The hydrogel obtained was used as an adsorbent to remove cationic dyes from aqueous solutions. It was found that the hydrogel possessed a high adsorption capacity that reached 872 mg/g under optimum conditions. Thus, kinetic, thermodynamic, and adsorption isotherm models were employed to describe the adsorption process of methylene blue onto the chitosan-based hydrogel. The results obtained suggested that the adsorption of methylene blue onto the hydrogel is fitted well with the pseudo-second-order and Freundlich models. According to the thermodynamic studies, it was revealed that the adsorption of methylene blue onto hydrogel was a spontaneous and exothermic process.