Abstract
Hexagonal molybdenum oxide (h-MoO3) was synthesized by a solution based chemical precipitation technique. Analysis by X-ray diffraction (XRD) confirmed that the as-synthesized powder had a metastable hexagonal structure. The characteristic vibrational band of Mo–O was identified from Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly depicted the morphology and size of h-MoO3. The morphology study showed that the product comprises one-dimensional (1D) hexagonal rods. From the electron energy loss spectroscopy (EELS) measurement, the elemental composition was investigated and confirmed from the characteristic peaks of molybdenum and oxygen. Thermogravimetric (TG) analysis on metastable MoO3 revealed that the hexagonal phase was stable up to 430 °C and above this temperature complete transformation into a highly stable orthorhombic phase was achieved. The optical band gap energy was estimated from the Kubelka–Munk (K–M) function and was found to be 2.99 eV. Finally, the ethanol vapor-sensing behavior was investigated and the sensing response was found to vary linearly as a function of ethanol concentration in the parts per million (ppm) range.
Highlights
Considerable research interest has been focused on metastable nanocrystalline materials due to their unusual and enhanced properties as compared to their bulk counterparts
By adjusting the hydrothermal reaction temperature, metastable (h-MoO3) and stable (α-MoO3) MoO3 nanoparticles were successfully synthesized by Chithambararaj et al [15]
The powder subjected to TGA measurements was subjected to X-ray diffraction (XRD) analysis, and the result confirmed that above 450 °C the product is in a stable orthorhombic structure (Figure not included)
Summary
Considerable research interest has been focused on metastable nanocrystalline materials due to their unusual and enhanced properties as compared to their bulk counterparts. The optical band structure and ethanol vapor-sensing behavior were studied by means of diffuse reflectance spectroscopy (DRS) and fiber optics spectroscopy, respectively. The size of the crystallite is in the nanometer range, significant structural defects such as dislocations, staking faults, twin boundaries and intergrowth, etc., induce strain in the material, which results in considerable broadening of the diffraction peak profile.
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