Eco-friendly guar gum-montmorillonite composite hydrogels crosslinked with N, N′-methylene bisacrylamide for selective adsorption of methylene blue, crystal violet and safranin

With rapid industrial growth, the discharge of dyes from textile industries poses a serious threat to water quality and environmental health. Cationic dyes, specifically methylene blue (MB), crystal violet (CV), and safranin (Sf), are commonly used in textile and biological applications and are known for their toxicity and persistence. This study reports the development of a Guar Gum-montmorillonite (GG-MMT) composite hydrogel crosslinked with N, N '-methylene bisacrylamide (MBA). The hydrogel was synthesized through free radical polymerization and modified by incorporating MMT-nanoclay. This composite hydrogel was then characterized using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), and zeta potential. Batch experiments were performed to evaluate the adsorption efficiency of selective cationic dyes under varying conditions of adsorbent dosage, initial dye concentration, contact time, pH, and temperature. Adsorption followed the Freundlich isotherm, with maximum adsorption capacities of 338.17 mg/g for MB, 349.09 mg/g for CV, and 467.56 mg/g for Sf under optimal adsorption conditions (pH 8, 40 degrees C, 240 min, 20 mg adsorbent, 20 mg/L dye). Thermodynamic studies confirmed that the process is spontaneous (Delta G < 0) and exothermic (Delta H < 0). Analysis of Variance (ANOVA) followed by Tukey's post hoc test validated the effect of different adsorption parameters. The adsorption mechanism involved multiple interactions, including cation exchange, electrostatic interactions, dipole-dipole interactions, hydrogen bonding, pi-pi stacking, n-pi interactions, and van der Waals forces. The composite hydrogel demonstrated excellent reusability over 9 cycles. These findings highlight the potential of the GG-MMT composite hydrogel for practical applications in large-scale wastewater treatment.