Efficient removal of Cd2+ ions and methylene blue from aqueous solutions by polyanionic sodium alginate-derived hydrogel

Considering the purification technology based on the fabrication of efficient adsorbents for the effective removal of water contaminants, we developed a polyanionic superabsorbent hydrogel for its application in the adsorption of cadmium ions (Cd2+) and methylene blue (MB). The hydrogel was prepared by graft copolymerization of methacrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid onto sodium alginate. The hydrogel structure, thermal stability, surface morphology, and surface area were studied using FT-IR, SEM, EDX, TGA, and BET techniques. The hydrogel capacity to remove Cd2+ MB from aqueous solutions was investigated at different contact times, pH, sorbent dosage, contaminant concentrations, temperature salinity, and ion selectivity. To understand the hydrogel sorption behavior, different adsorption kinetics and isotherms models were employed. The hydrogel exhibited impressive efficacy in the removal of Cd2+ and MB ions, achieving removal efficiencies of up to 87% and 97.5%, respectively, under a sorbent dosage of 0.15 g/100 mL and a temperature of 25 degrees C. Utilizing the Langmuir isotherm model, the maximum sorption capacities were determined to be 526 mg/g for cadmium ions and 131.5 mg/g for methylene blue. Regeneration experiments confirmed the reusability of the hydrogel, highlighting its potential as an effective adsorbent for Cd2+ and MB dye.