Moringa oleifera wood-derived biochar for efficient silver removal from aqueous systems: adsorption performance and mechanistic insights

ABSTRACT

The growing interest in biochar as an environmentally sustainable adsorbent has encouraged exploration of alternative biomass sources for removing toxic contaminants from aqueous systems. This study investigates the potential of biochar derived from Moringa oleifera wood for silver remediation, with a particular focus on how pyrolysis temperature influences its physicochemical properties and adsorption performance. Characterization of the material, kinetic, isotherm, and thermodynamic analyses and the effects of different experimental parameters on adsorption behaviour were evaluated. Biochar synthesized at 550 °C achieved the highest removal efficiency of 99.65 ± 0.02%. The adsorption capacity increased with silver concentration, reaching 125.69 ± 0.09 mg/g at 300 mg/L. This value is close to the maximum adsorption capacity of 131.58 mg/g obtained from the Langmuir isotherm model. Notably, biochar produced at 350 °C also demonstrated a high removal efficiency, exceeding 96%. Adsorption kinetic data were best described by the pseudo-second-order model, indicating that chemisorption was the rate-controlling mechanism. Thermodynamic evaluation showed that the process is spontaneous and endothermic. Silver removal may involve possible contributions from pore filling, surface complexation, electrostatic attraction, ion exchange, and reduction of silver ions. This study highlights that Moringa wood can be converted into high-performance biochar, as a promising and efficient adsorbent for removing silver from aqueous systems.