Surface impregnated copper influence on the sunlight-assisted photocatalysis of zinc oxide nanostructures

The development of highly efficient photocatalysts requires improving the surface activity of ZnO nanostructures. The goal of this research is to improve photocatalytic functionality by creating heterojunctions on the surface of ZnO with metallic copper. Heterojunctions with different concentration of (0.5, 1, 5, 10 wt%) metallic copper on ZnO (Cu@ZnO) was obtained by hydrothermal aided impregnation method. The crystal structure of ZnO was retained as hexagonal wurtzite phase even after impregnation of copper as substantiated by XRD and Raman spectroscopy results. The bandgap of ZnO did not vary after impregnating copper due to the presence of copper on the surface of ZnO. The average lifetime of the photogenerated carriers increased from 23.09 ns for ZnO to 30.58 for 0.5% Cu@ZnO. The optimum Cu concentration for impregnation on ZnO was found to be 0.5% to achieve the highest photocatalytic activity. The XPS studies confirmed the presence of primarily metallic copper on the surface. Further, the kinetics and scavengers of the reactive species during the degradation were also investigated. A 100% degradation of methylene blue was achieved by 0.5% Cu@ZnO in 35 min. The enhancement arises from the presence of Cu–ZnO Schottky barrier which acts as electron–hole trap centres to suppress the recombination of excited electrons with holes.