Hierarchical microporous miscanthus-derived activated carbon enables entropy-driven high-efficiency dye removal

Abstract Thermochemically treated lignocellulosic biomass represents a sustainable route to high-performance activated carbons for water purification. In this study, a miscanthus-derived activated carbon (ACM) was synthesized via one-step high-temperature KOH activation and evaluated for methylene blue (MB) removal from aqueous solutions. ACM exhibits a high specific surface area (SSA BET = 1,290 m 2 /g), dominant microporosity, and a hierarchical pore structure, enabling rapid dye diffusion. Adsorption kinetics follow a pseudo-second-order model, while intraparticle diffusion analysis reveals a two-stage mass-transfer mechanism. The weak pH dependence suggests that electrostatic interactions are not the sole controlling factor. Equilibrium data are best described by the Redlich–Peterson isotherm, indicating heterogeneous surfaces and mixed adsorption behavior. The maximum adsorption capacity increases from 410.2 to 463.8 mg/g as temperature rises from 298 to 318 K, confirming endothermic adsorption. Thermodynamic parameters indicate spontaneous, entropy-driven adsorption. FTIR analysis shows that MB uptake is predominantly governed by strong non-covalent interactions, including π–π stacking and hydrogen bonding with ACM surface functionalities, with partial contribution from pore filling rather than classical chemisorption. Reusability tests demonstrate an 80.7 % removal efficiency after three adsorption–desorption cycles without detectable mass loss, highlighting ACM as a cost-effective and sustainable sorbent for wastewater treatment.