Sustainable kaolin-crosslinked kappa-carrageenan hydrogel as an efficient adsorbent for cationic dye removal from wastewater

Dissolution of biopolymers in water is indeed a challenge for water treatment applications. By developing strong 3D gels through ionic crosslinking, biopolymers can be effectively utilized for water treatment applications. In this study, a sustainable and cost-effective kaolin-crosslinked κ-carrageenan (Kln-crosslinked κCg) hydrogel was developed by crosslinking kaolin clay with the κ-carrageenan biopolymer to eliminate cationic dyes, crystal violet (CV) and methylene blue (MB), from wastewater. The developed hydrogels were characterized using XRD, FTIR, SEM, and BET techniques. The effects of dye concentration, adsorbent dosage, pH, and temperature on the adsorption process were assessed. The pseudo-second-order and Elovich models most accurately depicted the adsorption kinetics, implying that chemisorption was the predominant mechanism. The Langmuir isotherm effectively represented the experimental data, indicating monolayer adsorption with saturation capacities of 188.4 ± 5.07 mg/g for CV and 124 ± 2.21 mg/g for MB. Thermodynamic analysis showed an endothermic, spontaneous process, increasing system disorder. Additionally, the hydrogel showed high reusability, ∼70 % removal efficiency after three cycles. A multi-objective genetic algorithm II (MOGA-II) effectively optimized the adsorption parameters. The artificial neural network model, with 10 neurons, yielded good predictive results, aligning closely with experimental data. R² values were 0.9953 for CV and 0.9519 for MB.