Photoelectric and photocatalytic properties of long-time annealing Mn–Co–Ni–O thin film

The Mn1.9Co0.8Ni0.3O4 (Mn–Co–Ni–O) thin films are prepared by magnetron sputtering method. We compared the resistivity of samples annealed at 400 °C (MCNO400) and 600 °C (MCNO600) separately and found that the MCNO400 sample has lower resistivity and wider band gap, which results from the discrepancy of grain morphology and ion number. Annealed Mn–Co–Ni–O thin films also exhibit similar photocatalytic effect to ZnO thin film in Fenton photo degradation of methylene blue (MB) dye solution. However, the MCNO400 film has better stability and the Mn–Co–Ni–O film has broader spectrum absorption compared with ZnO thin film, which will enhance the utilization of sunlight and the separation efficiency of photo-generated electrons and holes. This indicates that the Mn–Co–Ni–O film has potential industrial applications to replace ZnO. Furthermore, type-I N–N heterojunction is also constructed to enhance the number of electrons and holes involved in photocatalysis in Mn–Co–Ni–O thin films with ZnO coating to improve the photocatalytic effect. Experimentally, the photocatalytic rate of MCNO600/ZnO thin film overrides that of the MCNO400/ZnO thin film, and they can degrade MB dye solution stably and efficiently by the analysis of kapp values.