Core shell ZnO-MnO₂ nanocomposites for dye degradation and DFT simulation

To enhance the photogeneration and separation of charge carriers, ZnO/MnO₂ nanocomposites were efficiently synthesized using a simple hydrothermal process and tested as photocatalyst for dye degradation. The samples of ZnO, MnO₂, and ZnO/MnO₂ nanocomposites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflection spectroscopy, and photoluminescence spectra (PL). The photocatalytic activity of the ZnO/MnO₂ prepared using 10 mg was significantly higher than that of ZnO or MnO₂, as demonstrated by optical and photoluminescence measurements. In fact, the degradation efficiency of methyl orange (MO) with ZnO/MnO₂ (10 mg) reaching to 98% after 2 h of sunlight irradiation. The enhanced degradation of MO compared with pure ZnO and MnO₂ can be attributed to the high surface area, efficient sunlight absorption, and excellent charge carrier separation of the ZnO/MnO₂ photocatalyst. Density functional theory (DFT) simulations of ZnO and MnO₂ further revealed the electronic origins of the structural properties, showing that the photocatalytic activity is due to the electron transitions between the valence and conduction bands of materials.