Synthesis and characterization of (AAm-co-AHPS)/MMT hydrogel composites for the efficient capture of methylene blue from aqueous solution

In this study, Acrylamide-co-3-Allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt/ montmorillonite [(AAm-co-AHPS)/MMT)] hydrogel composite was synthesis via in situ free-radical copolymerization. The swelling properties and adsorption efficiency of MB were studied. Effect of AHPS ratio on the properties of hydrogel composite was investigated at different AAm/AHPS molar ratio of 100/0, 95/5, 90/10, 85/15, and 80/20. The highest swelling ratio (49.71 g/g) was observed for the composite containing 15% AHPS. The hydrogel composites were characterized using FTIR, TGA, XRD, and SEM. The effects of contact time, dye concentration, pH, adsorbent dose, and temperature on the adsorption capacity of MB were studied. Additionally, the reusability of the composite up to five consecutive cycles was also investigated. The adsorption process was found to follow the pseudo-second-order kinetics model, and the adsorption isotherm was best fitted with the Langmuir isotherm model. Hydrogel composite (15% AHPS) achieved qmax of 811.5 mg/g as calculated by Langmuir equation. The calculated thermodynamic parameters ΔH, ΔG, and ΔS revealed the endothermic nature, spontaneity of the adsorption, and the positive affinity of the composites for MB adsorption with a favorable increase in the randomness at the solid/solution interface during the adsorption process.