Biopolymer-grafted hydrogel composites based on activated carbon: structural properties, adsorption mechanism, and RSM-BBD optimization

This study presents a novel hydrogel composite synthesized by grafting guar gum with itaconic acid and N-isopropylacrylamide, combined with bio-derived activated carbon. While these components have been individually explored, their unique integration imparts dual pH and temperature-responsive behaviour, significantly enhancing adsorption capacity and regeneration performance compared to conventional hydrogels. Comprehensive characterization through FESEM-EDX, TEM, XRD, FTIR, and BET confirmed the composite’s structural and morphological features conducive to efficient dye adsorption. The adsorption of methylene blue (MB) was systematically evaluated under varying conditions and optimized via response surface methodology (RSM). The hydrogel exhibited a high swelling capacity (SP% = 1100%) and gel content (Gc% = 90%), with adsorption kinetics fitting the pseudo-first-order model and equilibrium data aligning with the Freundlich isotherm, indicating multilayer adsorption on heterogeneous sites. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic. Notably, the composite maintained substantial adsorption efficiency after six regeneration cycles, demonstrating excellent reusability. The novelty of this research lies in the strategic design of a dual-responsive natural polymer network functionalized with sustainable activated carbon, yielding a highly effective, reusable adsorbent for dye removal. This composite material offers a promising, eco-friendly approach for treating industrial wastewater contaminated with cationic dyes such as MB dye.