Sustainable valorization of sugarcane bagasse into a hierarchical γ-Al2O3/activated carbon composite: synergistic adsorption of cationic dyes

The development of sustainable hybrid adsorbents is crucial for advancing adsorption-based water treatment technologies. In this work, a hierarchical AC/γ-Al 2 O 3 composite derived from sugarcane bagasse was synthesized via a mild H 2 SO 4 -assisted activation process at 120 °C, providing a low-energy alternative to conventional high-temperature activation routes. The resulting material exhibited a hierarchical porous structure and a high specific surface area of 1740 m²/g. Methylene blue (MB) was used as a model cationic pollutant to evaluate adsorption performance. The composite achieved over 99% MB removal within 40 min using 20 mg of adsorbent at pH 10, outperforming its individual components. The strong pH dependence indicated that electrostatic attraction plays a major role in the adsorption process. Kinetic data were best described by the pseudo-second-order model, while equilibrium data were well fitted by the Langmuir and Redlich–Peterson isotherms, yielding a maximum adsorption capacity of 1023 mg/g. Thermodynamic parameters revealed a spontaneous, endothermic, and entropy-driven process (ΔG° < 0, ΔH° = 15.0 kJ/mol, ΔS° = 65 J/mol.K). Adsorption involved multiple mechanisms, including electrostatic interactions, π–π stacking, hydrogen bonding, and pore-filling effects. The interaction between the carbon matrix and γ-Al 2 O 3 phase contributed to enhanced adsorption through complementary surface chemistry and interfacial coupling effects. The composite retained more than 91% of its initial efficiency after eight regeneration cycles, demonstrating excellent stability and reusability. The combination of agricultural waste valorization, low-temperature synthesis, and high adsorption performance highlights the potential of this material for sustainable wastewater treatment applications.