Hydrothermal synthesis of hexagonal and orthorhombic MoO3 nanoparticles

Molybdenum oxide (MoO3) with two different crystal structures (hexagonal and orthorhombic) was successfully synthesized by an effective and environmental friendly hydrothermal method. The phase confirmation and structural properties of the sample was elucidated by X-ray diffraction (XRD) method. The reaction temperature has great impact on the crystal structure, size, shape and chemical composition of the samples. Vibration behavior of chemical bonds was characterized by Fourier transform infrared spectroscopy (FT-IR) and the observed peaks confirm the formation of MoO3. Scanning electron microscopy (SEM) observation shows that an increase in reaction temperature, the shape was drastically changed from one dimensional (1D) to two dimensional (2D) layered structures. Energy dispersive X-ray analysis (EDX) reveals that the as-prepared samples are in non-stoichiometric composition and their composition varies with reaction temperature. The thermal study was acquired by thermo gravimetric analysis and it demonstrates the process of dehydration and deammonization, observed below 260 °C and phase transformation from hexagonal to highly stable orthorhombic phase at 400–450 °C. Additionally, the optical absorption properties were measured using diffuse reflectance spectroscopy (DRS) and the band gap energy, estimated from Kubelka–Munk function (K–M) was found to be in the range of 3.01–3.24 eV.