A Rapid Microwave Synthesis at Low Temperatures, Electron Microscopy and Raman Study of MoO₃ and WO_x Nanostructures

Microwave (MW) synthesis of various nanostructures of MoO₃ and WO_x have been carried out at low temperatures. MoO₃/WO_x nanoparticles and nanobelts/nanorods were obtained starting from the respective Mo(W) chloride and carbonyl precursors. Transmission electron microscopy (TEM and HRTEM) and TEM-EDAX have been carried out in great detail to investigate the nature and the composition of the nanostructures that have been obtained. The nanostructures of molybdenum and tungsten oxides synthesized by the present method and characterized using electron microscopy have been found to be single-crystalline in nature and have large aspect ratios. A detailed Raman spectroscopic study of the synthesized nanostructures were carried out to ascertain the individual and distinct Raman characteristics. The Raman Spectrum of MoO₃ in the range 600–1000 cm⁻¹, displays three well-defined peaks located at 996.0, 819.1 and 664.6 cm⁻¹ which are the fingerprints of the orthorhombic α-MoO₃ crystalline phase. The peaks of the Raman spectrum in the sample of the MoO₃ nanoparticles shift towards lower wavenumbers in comparison to that of the MoO₃ nanobelts. In the case of the Raman spectrum of the WO₃ nanoparticles the peaks broaden with respect to the full width at half-maximum (FWHM), which may be due to the scattering and the size effects.