Preparation and characterization of chitosan/AMPS/kaolinite composite hydrogels for adsorption of methylene blue

This study aims to evaluate a new synthesized composite hydrogel prepared by gamma radiation polymerization of chitosan (CS) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with kaolinite. The enhancement of kaolinite on the swelling, diffusion, and adsorption properties of CS/AMPS/Kaolinite hydrogels was studied using methylene blue (MB) as model compound. Effect of chloride ion on swelling and MB adsorption was also studied. A non Fickian behavior was observed for diffusion of water and MB into hydrogels. Adsorption capacities of the hydrogels significantly improved to be 52.9 mg/g, 39.7 mg/g, 30.7 mg/g, and 21.7 mg/g dry gel for CS/AMPS/Kaolinite-2, CS/AMPS/Kaolinite-1, CS/AMPS, and CS hydrogels, respectively by the addition of kaolinite. The equilibrium data for dye adsorption showed that Langmuir isotherm better fitted the MB adsorption with a high correlation (R2 > 0.99) than Freundlich, Temkin, and Elovich isotherms for all types of synthesized hydrogels. The chloride content affected the adsorption of MB in the order of AlCl3 > CaCl2 > NaCl. CS/AMPS/Kaolinite hydrogels can be used for adsorption of cationic dyes such as MB as an effective and promising adsorbent. It is to be emphasized that the addition of AMPS and kaolinite in the gel structure improved swelling and adsorption capability of the new composite hydrogels.