Insect-infested Ferula stem mesoporous activated carbon for Methylene Blue and Congo Red removal: biologically...

This study compares activated carbons prepared from normal (AC-FN) and insect-infested (AC-FI) Ferula stem biomass for Methylene Blue (MB) and Congo Red (CR) adsorption. Insect-induced structural modification was evaluated for its effect on pore development and adsorption performance after chemical activation. Among the tested conditions, H₂SO₄ activation produced the most efficient carbons. AC-FI exhibited superior textural properties with a BET surface area of 993.79 m²/g and micropore surface area of 770.82 m²/g, compared to 617.08 m²/g and 324.27 m²/g for AC-FN, respectively. The pHpzc values (6.81 for AC-FI, 6.34 for AC-FN) explained the pH-dependent adsorption: CR removal was favored under acidic conditions, and MB was enhanced near neutral to slightly basic pH. Equilibrium data fitted the Freundlich model, indicating heterogeneous surfaces. Langmuir maximum capacities were 78.60 mg/g (MB) and 71.20 mg/g (CR) on AC-FI. Kinetics followed the pseudo-second-order model, suggesting surface interactions dominate the process. Thermodynamic parameters revealed an endothermic process with positive entropy changes. Overall, insect-infested Ferula biomass is a promising biologically pre-modified precursor for producing efficient activated carbon with enhanced microporosity, favorable surface chemistry, and improved dye adsorption performance.