Post-annealing temperature effects on the structural and optical properties and Cr(VI) removal performance of laser-ablated copper oxide nanoparticles

In this study, laser-ablated nanoparticles were produced by laser ablation of a copper target in deionized water by the increased first harmonic of Nd:YAG laser and the influence of the subsequent annealing temperature on the structural and optical properties of produced nanoparticles was studied. Also, the annealing temperature influence on the photocatalytic reduction of aqueous Cr(VI) ion with the nanoparticles was investigated. Its X-ray diffraction (XRD) results indicate that the laser-ablated nanoparticles are completely oxidized into CuO nanoparticles by annealing and by increasing the temperature from 400 to 800°C, the mean crystallite size of nanoparticles increased from 11 to 90 nm, and the bandgap decreased from 1.2 to 1.9 eV. The bandgap increased with a size reduction due to the quantum confinement effect. The morphological analysis by field-emission scanning electron microscope and transmission electron microscope confirm that spherical-shaped CuO nanoparticles are formed and the size of particles increased with the increase in the annealing temperature. The photocatalytic activity results of nanoparticles show maximum Cr(VI) reduction for nanoparticles annealed at 600°C. The decrease as the temperature of annealing rises is associated with the surface area reduction and the temperature reduce is attributed to the expansion of the bandgap.