Physical investigations and photocatalytic activity test of NiMoO₄ thin films prepared by spray pyrolysis technique

Semiconductor photocatalysts, especially nickel molybdenum oxide with a monoclinic structure, have been frequently used to address environmental pollution issues. Many advantages have been discovered for photocatalytic applications using this material, so, in this study, we have studied the physical properties of NiMoO₄ thin film prepared using the spray approach. The structural properties have been characterized by X-ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The structural analysis shows a monoclinic structure with space group C₂/m and a grain size equal to 150 nm. In addition, the optical measurements show direct optical transitions with a bandgap equal to 3.56 eV, revealed by an ellipsometric spectroscopy study. Using a spectroscopy impedance analysis, we have also investigated the frequency relaxation phenomenon and determined the activation energy, which was equal to 1.16 eV. Finally, the photocatalytic degradation of methylene blue was performed on this thin layer under sunlight irradiation. The monoclinic structure and possible defects in the lattices were used to discuss the effective photocatalytic activity. (author)