Plant-extract-mediated synthesis of copper oxide nanoparticles for sustainable lead detoxification: experimental evaluation and docking studies

Abstract

Increasing levels of water pollution involving heavy metals have demanded the exploration and development of efficient, sustainable approaches for the decontamination of these pollutants. In this study, copper oxide nanoparticles (CuO NPs) were synthesized using Haldina cordifolia for the removal of a persistent heavy metal from water. Advanced characterization analyses confirm both their successful synthesis and their distinctive adsorption characteristics toward Pb(II) from water. The highest-ranked docked conformation attained in molecular docking simulations showed a binding energy of −0.36 kcal mol⁻¹. The negative binding energy attained indicates a favourable affinity of the CuO NPs towards Pb(NO₃)₂. The maximum adsorption capacity of Pb(II) onto CuO NPs is 1032.57 mg g⁻¹ under the optimum conditions (pH 6, dose 50 g L⁻¹, and contact time 2 h). The adsorption mechanism is driven by both chemical (complexation, precipitation, and ion exchange) and physical electrostatic attractions. The kinetic study reveals that five kinetic models, namely, pseudo-first-order, pseudo-second-order, mixed first- and second-order, Avrami, and intraparticle diffusion, can describe the adsorption of Pb(II) onto CuO NPs, depending on the initial Pb(II) concentration. Adsorption isotherm modelling shows that among the eleven models studied, Freundlich isotherm best describes the adsorption system, with strong agreement between experimental and calculated data. Future research can thus focus on enhancing the synthesis process while examining the selectivity and reusability of CuO NPs for decontaminating the diverse metals present in intricate wastewater systems.