Enhanced solar photocatalytic performance of Cu-doped nanosized ZnO

Abstract

We report the controlled synthesis of nanostructured undoped and Cu-doped ZnO by a simple one-step hydrothermal treatment, characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Raman spectroscopy and photoluminescence (PL). XRD results showed that all samples present a hexagonal wurtzite structure. The SEM micrographs revealed that the particles have a hexagonal shape and a uniform size distribution. Optical band gap was found to vary with Cu content. The photoluminescence spectra indicate that the introduction of Cu into pure nano-ZnO causes a decrease in surface defects, such as oxygen and zinc vacancy. In fact, this study shows that the intensity of the PL decreases initially when the concentration of Cu doping increases (greater than 1%). Whereas, when the concentration of the Cu doping rate is 0.5% the PL intensity increases. The result indicates that doping with Cu with a suitable concentration can effectively inhibit the recombination of the free charge carriers. The as-synthesized nanostructures were used as photocatalysts for the degradation of methyl orange (MO) under solar irradiation. The PL and photocatalysis results reveal that the highest photocatalytic activity is obtained with the 1% Cu-doped ZnO photocatalyst. In fact, this study shows that the photodegradation follows first-order kinetics. Therefore, in the absence of ZnO photocatalyst a low kinetic rate constant of 5.634.10−4 min−1 is estimated while the introduction of undoped or 1% Cu-doped ZnO increases the kinetic constant by approximately 9 and 20 times, respectively.