Eco-friendly GG-g-poly(AAc-VBS) Hydrogel for the Adsorptive Removal of Congo Red Dye from Wastewater

Abstract

Synthetic dyes like Congo Red (CR) are poisonous, mutagenic, and non-biodegradable, making their release into waterways a severe environmental issue. A novel biopolymer-based hydrogel was created by free-radical polymerisation of acrylic acid (AAc) and 4-vinylbenzenesulfonic acid sodium salt (VBS) onto gum ghatti (GG) with N,N′-methylenebisacrylamide as the crosslinker and potassium persulfate as the initiator. FTIR, XRD, and FESEM indicated effective grafting, the amorphous polymeric backbone, and the creation of a highly porous, interconnected dye-uptake network in the GG-g-poly(AAc-VBS) hydrogel. CR adsorption was examined as a function of pH, contact time, initial dye concentration, adsorbent dosage, and temperature. Optimal removal (≈94%) occurred at pH 3 with an equilibrium contact period of 90 min. The pseudo-secondorder model (R² = 0.998) fit kinetic data, while the Langmuir isotherm fit equilibrium data, indicating a monolayer adsorption process with a maximum capacity of 412.7 mg g⁻¹. Adsorption was spontaneous and endothermic, according to thermodynamics. After five adsorption–desorption cycles, the hydrogel retained over 82% of its initial removal effectiveness. These data suggest GG-g-poly(AAc-VBS) is a good, sustainable dye-contaminated wastewater adsorbent.