Structural and photocatalytic properties of undoped and Zn-doped CuO thin films deposited by reactive magnetron sputtering

Abstract

In this research, undoped and Zn-doped CuO thin films were successfully fabricated by the reactive magnetron sputtering method. The effect of Zn dopant concentration on the enhancement of photocatalytic behavior and structural properties of CuO thin films was investigated. To obtain the optimal conditions in terms of the highest efficiency and rate in the photocatalytic degradation of methylene blue (MB), CuO films were first deposited at different oxygen partial pressures (30 %, 40 %, and 50 %). Optimal conditions, i.e., a 70 % photodegradation efficiency with a rate of 0.279 h−1 were achieved in the undoped sample deposited at a partial pressure of 40 %. Then different Zn amounts were incorporated into the CuO lattice by controlling the RF power in the range of 10–40 W. As-prepared samples were analyzed using GIXRD, XPS, PL, EIS, and UV–vis spectroscopy. The GIXRD pattern of the Zn-doped sample showed the formation of CuO without altering its monoclinic structure. XPS spectra indicated the presence of Cu2+ and Zn2+ oxidation states, which means the successful substitution of Zn2+ at Cu2+ sites in the CuO lattice. Based on EIS results, increasing the Zn cation dopant up to 0.026 led to a decrease in the charge resistance transfer compared to the undoped CuO. By increasing the amount of Zn in the cationic ratio up to 0.02, PL peak intensity reached the lowest value. Accordingly, the MB degradation efficiency increased to above 80 % in this sample. Active species involved in the photocatalytic reactions were investigated via a scavenger test. The Zn-doped CuO film showed high MB degradation efficiency even after five cycles (77 %), which made it a potential candidate for wastewater purification.