Crosslinked carboxymethyl cellulose-hydroxyethyl cellulose hydrogel films for adsorption of cadmium and methylene blue from aqueous solutions

Abstract

The present work describes the production of carboxymethylcellulose (CMC) -hydroxyethyl cellulose (HEC) hydrogel films using citric acid as a non-toxic crosslinking agent, for a potential application in wastewater treatment. After their synthesis, all films were then characterized through Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), UV-Visible spectroscopy (UV-Vis) and swelling study. During these measurements, the successful crosslinking of the hydrogel film was validated; films also possess good thermal stability, a high transmittance under the visible light region, confirming their transparency, and excellent swelling ability in neutral and in acidic media. Therefore, the as-produced films were then used as a potential adsorbent for the removal of cadmium (Cd) and methylene blue (MB) from concentrated aqueous solutions. The adsorption ability of each film was evaluated thanks to thermodynamic and kinetic studies showing that the adsorption equilibrium was reached within 1h for Cd and 3h for MB. Furthermore, the analysis of the adsorption kinetics highlights that all the data could be fitted by a pseudo-second order model, and the adsorption isotherms could be sufficiently described by Langmuir isotherm model for the two studied pollutants. From this analysis, the maximum adsorption capacities, determined by Langmuir model, are close to 126.58 and 769.23 mg/g for Cd and MB, respectively. Moreover, the sorption capacities of Cd and MB in films both increase with the temperature. According to the thermodynamic parameters, cadmium and methylene blue adsorption processes using tested films are favorable, spontaneous, and endothermic.