Synthesis, structural and optical properties of Cu doped ZnO and CuO–ZnO composite nanoparticles

Hydrothermal synthesis was used to obtain pure, doped and composite semiconductor oxide materials. We synthesized ZnO, CuO, Cu doped ZnO with 1, 2 and 3 wt %, and for Cu additions at 6, 8, 10, 15, 30 and 50 wt% this resulted in ZnO–CuO composites with different morphologies. X-ray diffraction (XRD) showed hexagonal and monoclinic crystalline phases for pure ZnO and CuO, respectively. Electron microscope images showed two-dimensional (2D) shaped particles. The Cu element could dope ZnO up to 3 wt%, whilst above this value, composites of ZnO–CuO were generated, with two segregated phases having flake-like shaped elongated particles. The visible-light absorption increases for the doped samples, being directly proportional to the Cu content for the dopant and the composite particles, showing a broad absorption range between 200 and 800 nm. Two bandgap energy values of 3.22 and 1.45 eV were determined for the ZnO–CuO samples. The samples were studied by X-ray photoelectron spectroscopy (XPS) in order to understand the doping process and composite formation.