Spectroscopic analyses and photocatalytic properties of transition group metal oxide films with different entropy values

In this study, transition metal high-entropy oxide thin films were prepared by chemical solution deposition (CSD) method. We investigated the correlation between the maximum shift of binding energy (ΔE) and the average ion diameter (Dav) using X-ray photoelectron spectroscopy (XPS) fitting. It was found that ΔE was positively correlated with Dav, indicating the red shift of ionic binding energy caused by point defects. The presence of point defects was identified as an important factor affecting the photocatalytic performance of the thin films. We also observed that the increased mixing-entropy can reduce the bandgap of the thin films. Among the samples studied, the (Co0.2Mn0.2Fe0.2Cr0.2Cu0.2)3O4 sample exhibited the best light absorption performance and photocatalytic effect. It was able to enhance the photocatalytic efficiency for the degradation of methylene blue (MB) by up to 8.5 times compared to other samples. Moreover, the photon efficiency (ζ) in the visible waveband was approximately 3.3 times higher than that in the near-infrared waveband. This suggests that the high-entropy oxide thin films have excellent utilization of solar energy. For the ternary oxide Mn1.5Co1Ni0.5O4, which has lower entropy, the preparation of type-I N–N heterojunction ZnO/Mn1.5Co1Ni0.5O4 can greatly enhance its redox properties and photocatalytic efficiency. This heterojunction significantly enhanced the performance of the ternary oxide. Overall, these findings provide insights into the preparation of high-efficient and stable photocatalysts using transition group metal oxide films with different entropy values, and contribute to the potential applications in solar energy utilization.