Nd-doped CuO/ZnO and ZnO/CuO heterojunctions for simultaneous UV blocking and malachite green detoxification

Abstract

A novel two-step wet-chemical synthesis produced neodymium-doped core/shell heterojunctions, Copper(II) oxide (neodymium)/Zinc oxide(CuO(Nd)/ZnO and Zinc oxide (neodymium)/Copper(II) oxide ZnO(Nd)/CuO), with tunable optoelectronic and photocatalytic properties. Structural characterization via x-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals uniform crystallite sizes (6.3-31.4 nanometers- nm) and distinct morphologies: hexagonal for CuO(Nd)/ZnO and spherical for ZnO(Nd)/CuO. Incorporating neodymium induced lattice strain (7.8-10.2 × 10⁻⁴) and increased Urbach energies (5.0-15.3 millielectron volts-meV), enhancing defect states. Tauc analysis demonstrated bandgap narrowing to 2.49-3.17 eV for ZnO and 1.49-1.55 eV for CuO. ZnO(Nd)/CuO achieved a remarkable 94.6% degradation of malachite green (MG) under cost-effective 500 W (W) white light irradiation. This significantly surpasses the performance of undoped systems (by 5%) and generally exceeds that reported for other nanocomposites (≤ 90%) in the literature. Conversely, CuO(Nd)/ZnO exhibited 89.04% ultraviolet blocking efficiency at 280-315 nm (UV-B), outperforming polymethyl methacrylate (PMMA) with ZnO quantum dots (50-60%) and ZnO nanoparticles with polylactic acid composite films (15-75%). These enhancements stem from neodymium(III) (Nd³)-mediated trap states, optimized band alignment, and charge separation at the heterojunction interface. Integrating rare-earth doping with core/shell architecture provides a scalable route for high-performance photocatalytic and ultraviolet-protective materials.