Adsorptive removal of rhodamine B using sustainable gum acacia- activated carbon hydrogel composites from aqueous systems: Isotherm, and kinetic insights.

An activated carbon incorporated gum acacia-based hydrogel was synthesized via chemically induced free radical polymerization route using acrylic acid and itaconic acid as co-monomers to develop an effective adsorbent for removing dye (Rhodamine B) from aqueous solution. The composite hydrogel exhibited high swelling ability (≈2000% in basic medium), good gel content, and yield, indicating a stable three-dimensional polymeric network. The structural, physiochemical, morphological, and thermal characteristics were confirmed through FTIR, XRD, FESEM, AFM, XPS, and TGA analyses. Batch adsorption studies were carried out by varying pH (2-12), dye concentration (1-15 ppm), adsorbent dose (100-600 mg), and contact time (24 h). Maximum dye removal ~100% was achieved at 10 ppm dye concentration, 300 mg adsorbent dose, and at acidic pH. The results of the adsorption experiments fitted best to the Langmuir isotherm (R2 = 0.977), which indicate monolayer adsorption on a surface with identical active sites, while the pseudo-second-order kinetic model described the rate process accurately (R2 = 0.994), and maximum adsorption capacity 2.48 mg/g, suggesting chemisorption as the dominant mechanism. The negative ΔG° values (-9 to -15 kJ/mol) confirmed the spontaneous nature of adsorption, and negative ΔH° values (-73.08 kJ/mol) confirmed adsorption process is exothermic. The hydrogel maintained ~85% removal efficiency after five reuse cycles and showed negligible interference from salt concentrations under study. Thus a sustainable bio-based, affordable hydrogel composite was developed from renewable gum acacia base enabling selective and efficient removal of Rhodamine B from water.