Development of guar gum-sodium alginate based hydrogel for sustainable and efficient removal of crystal violet dye...

A Guar gum‑sodium alginate (GG-SA) based hydrogel was synthesized through free radical polymerization, incorporating both covalent and ionic crosslinking. FTIR, XRD, TGA, FESEM, and XPS analyses confirmed the formation of a stable, porous network with relevant functional groups. Swelling studies showed a high swelling percentage of 1480 % in basic conditions, indicating significant water uptake ability. This hydrogel served as an adsorbent to remove crystal violet dye during batch experiments performed at ambient temperature. Adsorption studies demonstrated that under optimized conditions- 0.3 g adsorbent dose, 5 mg L^-1 dye concentration, neutral pH, and 25 °C -the hydrogel achieved complete removal of crystal violet dye. The adsorption mechanism involves several interactions, i.e., electrostatic interactions, hydrogen bonding, and π-π stacking. Thermodynamic studies indicated an exothermic and spontaneous process. The adsorption data are best modelled using the Freundlich isotherm, while the maximum adsorption capacity was calculated as 3.245 mg g^-1. Kinetics studies following a pseudo-second-order model, suggesting multilayer adsorption on a heterogeneous surface and a chemisorption process. Furthermore, reusability studies across four cycles revealed consistent performance, confirming the hydrogel's potential for sustainable dye removal in wastewater treatment applications.