Eslam A Mohamed, Mahmoud F Mubarak, H A Abdel Samad
An eco-friendly hybrid biohydrogel adsorbent, namely GK-SA/AlO(OH)-NiO (Gum Karaya-Sodium Alginate/ Aluminum oxide hydroxide-Nickel Oxide nanocomposite), was successfully synthesized via a green ionic gelation technique followed by Ca2+ crosslinking-bead formation and subsequent thermal stabilization of the embedded nanoparticles. Characterization through FTIR, XRD, SEM, EDX, and BET surface analysis confirmed the successful integration of the biopolymer matrix and metal oxides. SEM micrographs revealed a highly porous, three-dimensional, and rough surface morphology ideal for mass transfer. Furthermore, BET analysis demonstrated a significant textural enhancement, where the specific surface area increased from ~42 m2/g for the pristine hydrogel to ~118 m2/g for the GK-SA/AlO(OH)-NiO composite. The batch adsorption performance was evaluated using aqueous solutions of anionic Congo red (CR) dye. Under optimized operational conditions (pH 5.0, dosage 0.2 g, and 25 °C), the composite exhibited an exceptional maximum monolayer adsorption capacity (qmax) of 298.6 mg/g within a rapid equilibrium time of 90 min. Equilibrium data were accurately represented by the Langmuir isotherm model, while the capture kinetics followed tightly to the pseudo-second-order model. The apparent activation energy was determined to be +42.9 k J.mol-1, confirming that the interfacial uptake process is highly temperature-dependent and chemically accelerated. Mechanistic evaluations revealed that the efficient remediation process is governed by a synergistic combination of electrostatic attraction between the anionic dye and the protonated hybrid matrix, hydrogen bonding, n-π stacking, and robust surface complexation reactions. Overall, the successful synthesis of GK-SA/AlO(OH)-NiO nanocomposite offers a promising environmentally sustainable framework for highly efficient remediation of toxic CR dyes from industrial wastewater.