Modified Urtica dioica Leaves as a Low-Cost and Effective Adsorbent for the Simultaneous Removal of Pb(II), Cu(II), Cd(II), and Zn(II) from Aqueous Solution

This study investigates the simultaneous adsorption of Pb(II), Cu(II), Cd(II), and Zn(II) ions from aqueous solutions using <i>Urtica dioica</i> leaves (UDLs) modified with sulfuric acid, followed by heat treatment to enhance adsorptive properties. The heat treatment significantly increased the adsorbent's specific surface area to 451.93 m²·g^-1. Batch adsorption experiments were performed to determine the influence of the contact time, pH of the aqueous solution, adsorbent dosage, temperature, and initial metal concentration on the adsorption efficiency. The material (modified UDLs) was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Maximum removal efficiencies were determined as 99.2%, 96.4%, 88.7%, and 83.6% for Pb(II), Cu(II), Cd(II), and Zn(II) ions, respectively. Adsorption isotherms and kinetics revealed that the process follows the Langmuir equation and pseudo-second-order models, indicating monolayer adsorption and chemisorption mechanisms. Furthermore, thermodynamic analysis indicated that the adsorption processes are spontaneous and endothermic in nature. The influence of competing ions on the adsorption of multiple heavy metals was also discussed. The results suggest that sulfuric acid and heat-treated <i>Urtica dioica</i> leaves can offer a promising, low-cost, and eco-friendly adsorbent for removing heavy metal ions from contaminated water.