Production, characterization, and adsorption modeling of Pb(II) ions using eco-friendly pomegranate peel, biochar, and activated carbon

Abstract

Pomegranate peel was transformed into three adsorbent materials, including raw pomegranate peel (RPP), biochar produced by pyrolysis (BPP), and activated carbon (PPAC), and comparatively evaluated for Pb2+ removal from aqueous solutions. The main objective of this study is to investigate the effect of thermal conversion and chemical activation on the adsorption performance of pomegranate peel-derived materials and to develop a sustainable and high-efficiency biosorbent for heavy metal remediation. PPAC was produced via pyrolysis and subsequent ZnCl2 chemical activation of pomegranate peel biomass. Batch experiments identified optimal conditions at pH 5.31 and 120 min contact time with an initial Pb2+ concentration of 250 mg/ L. At 298 K, equilibrium capacities (Qm) reached 53.19 mg/ g (RPP), 147.05 mg/ g (BPP), and 370.37 mg/ g (PPAC), revealing a pronounced enhancement after thermal conversion and especially after chemical activation. This significant improvement demonstrates the effectiveness of structural and surface modifications in enhancing metal adsorption capacity. The superior performance of PPAC is associated with its highly developed porous framework and enriched surface chemistry, which intensify metal-surface interactions. Adsorption behavior followed the pseudo-second-order kinetic model, indicating that Pb2+ uptake is governed primarily by surface-controlled chemical processes. Thermodynamic analysis revealed a spontaneous and endothermic adsorption process, with negative Delta Go values ranging from - 15.92 to - 20.54 kJ/mol, a positive Delta Ho value of 41.57 kJ/mol, and positive Delta So values of 192.92-195.32 J/mol.K. These findings highlight the environmental relevance of converting agricultural waste into efficient adsorbents for sustainable wastewater treatment applications. The findings confirm that activation of pomegranate peel substantially upgrades its adsorption efficiency, highlighting PPAC as a viable material for sustainable Pb2+ remediation.