Effect of Mineralizer (KNO<sub>3</sub>) on the Structural and Optical Properties of h-MoO<sub>3</sub> Nanocrystals

Abstract

Single phase hexagonal molybdenum oxide (h-MoO3) nanocrystals were successfully synthesized by solution based chemical precipitation method. The effect of mineralizer (KNO3 salt) on hexagonal phase, crystallite size, and surface morphologies of MoO3 was investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. The XRD result indicates that the diffractograms exhibit characteristic hexagonal phase of MoO3. From the line broadening analysis, the average crystallite size was calculated and estimated. A less crystallite size of 34 nm was obtained in the presence of mineralizing agent KNO3 in comparison to without mineralizer (46 nm). The particle exhibits rod like morphology with perfect hexagonal cross-section and well faceted top and side surfaces. Further, the thermal and optical properties were studied by thermo gravimetric analysis (TGA) and diffuse reflectance spectroscopy (DRS) measurements. The weight loss due to decomposition of intercalated water and ammonia were observed. By TGA analysis, the mineralizer assisted sample shows higher phase stability with the phase transition temperature of 520 °C due to the incorporation of K+ in MoO3 structure. The optical band gap energy was calculated using Kubelka-Muck function and the values were found to be 3.11 eV and 2.97 eV for KNO3 assisted and non-assisted MoO3 samples respectively. The observed increase in optical band gap (Eg) for h-MoO3 synthesized in the presence of KNO3 was attributed to the size dependent optical properties.