Biosorption of Pb ²⁺ From Wastewater Solution Using Material Derived From <i>Cleistocalyx operculatus</i> Leaves: Kinetics, Isotherms, and Thermodynamic Studies

Despite the extensive use of bio-based materials for heavy metal removal, the adsorption potential of Cleistocalyx operculatus leaves (CO) remains unexplored. In this study, CO leaves were converted for the first time into a low-cost, efficient biosorbent for Pb²⁺ removal from aqueous solutions, addressing both performance and sustainability requirements in wastewater treatment. Characterization by FT-IR, EDX, and SEM revealed that CO has a porous structure with nitrogen- and oxygen-containing functional groups, which facilitate metal ion binding. Batch adsorption experiments evaluated the effects of pH, contact time, initial Pb² ⁺ concentration, and temperature. The results showed that Pb² ⁺ removal efficiency reached 86.82% after 60 min at pH of 6 and 303 K. Adsorption kinetics followed the pseudo-second-order model, while the isotherm data fit the Langmuir model, with a maximum uptake capacity of 64.59 mg/g, indicating monolayer biosorption on a homogeneous surface. Thermodynamic analysis confirmed that the Pb² ⁺ adsorption process is spontaneous and exothermic. The CO material maintained nearly 70% efficiency after three adsorption-desorption cycles under acidic conditions. When applied to real wastewater from battery recycling and electroplating processes, removal efficiencies of 63.50% and 71.41% were achieved, demonstrating promising applicability in complex environments.