Thermodynamics and Kinetic Study of Lead Removal from Aqueous Solution Using Ag-CdO Nanoparticle Synthesized with Vernonia amygdalina Plant Extract

Abstract

Water pollution caused by heavy metal contamination is a major environmental concern due to the toxic effects of metals such as Lead Pb (II)), which pose serious health risks. Conventional methods for removing heavy metals from wastewater, including chemical precipitation, ion exchange, and membrane filtration. Nanomaterials, particularly metal oxide nanoparticles, have emerged as promising adsorbents due to their high surface area and unique physicochemical properties. In this study, we synthesized and characterized cadmium oxide (CdO) nanoparticles (NPs) and Ag-CdO nanocomposites for their application in Pb (II) removal from aqueous solutions. The FT-IR spectra revealed characteristic peaks corresponding to Cd-O stretching vibrations around 478 cm⁻¹, and metal-oxygen bonds near 569 cm⁻¹, confirming the formation of CdO and Ag-CdO composites. Scanning Electron Microscopy (SEM) revealed changes in morphology upon Ag-CdO, with smaller pores and a more homogeneous surface observed in Ag-CdO NCs.Zeta potential analysis indicated moderate electrostatic stability for both CdO and Ag-CdO, with the point showing a more stable colloidal system. UV-Visible Spectroscopy (UV-Vis) measured the optical properties and band gap energies, which were found to be 2.7 eV for CdO and 2.5 eV for Ag-CdO. X-ray Diffraction (XRD) Confirmed the cubic crystalline phase of both CdO NPs and Ag-CdO NCs. The diffraction peaks for CdO NPs were observed at 2θ = 26.75° and 33.10°, while Ag-CdO NCs showed peak shifts to higher 2θ values at 44.38°, 64.55°, and 77.47°, indicating successful Ag incorporation. The crystallite sizes were calculated using the Scherrer equation, yielding 28 nm for CdO NPs and 17 nm for Ag–CdO NCs. Removal efficiency of Pb(II) was studied under various conditions, including Pb concentration, catalyst dose, pH, temperature, and contact time. The results showed that Ag-CdO NCs achieved superior Pb(II) removal (97 %) compared to CdO NPs (87 %), with optimal conditions at a catalyst dose of 0.30 g, pH 6, and 40 °C. The Langmuir isotherm model confirms monolayer adsorption, while the pseudo-second-order kinetics indicate strong chemical interactions. The study demonstrates that Ag-CdO NCs exhibit enhanced catalytic properties, making them a promising material for water treatment and environmental remediation applications