A borax crosslinked hydrogel of 2-methyl-2-propene-1-sulphonate grafted onto guar gum for removing cationic dyes and Cr6+ ions

Abstract

This study describes the effective removal of cationic dyes and Cr⁶⁺ ions from aqueous solutions by employing a borax crosslinked hydrogel of guar gum (GG) grafted with 2-methyl-2-propene-1-sulphonate (MPS), GG@MPS@H, by free radical polymerization. The well characterized GG@MPS@H hydrogel was examined as an adsorbent for cationic dyes, methylene blue (MB) and crystal violet (CV), and Cr⁶⁺ ions by batch adsorption experiments. The values of maximum %removal for CV, MB, and Cr⁶⁺ ions were found to be 98.01%, 95.80%, and 92.82%, respectively. The pseudo-2nd order kinetic and Langmuir isotherm models showed the highest values of correlation coefficients (R²) and least values of error functions (χ²), root mean square errors (RMSE) and normalized standard deviations (Δq%) for all the adsorbates, indicating the best fitting of the models to the adsorption data. The results showed GG@MPS@H's maximal adsorption capacity of 231.95, 263.72, and 215.60 mg g⁻¹ for CV, MB, and Cr⁶⁺ ions, respectively. The observations of thermodynamic analysis showed that adsorption was spontaneous and exothermic. Additionally, GG@MPS@H displayed remarkable regeneration and recyclability after nine adsorption–desorption cycles without any appreciable loss of adsorption performance. The results of the studies performed to investigate the practical utility of the hydrogel for the treatment of real industrial wastewater indicated its significant potential as an effective adsorbent for real wastewater treatment. The studies demonstrated GG@MPS@H as a cost effective and sustainable adsorbent with high adsorption efficacy for removing cationic dyes and Cr⁶⁺ ions with prospective applications for real wastewater treatment.