The sonochemical preparation of tungsten oxide nanoparticles

Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO)₆ in diphenylmethane (DPhM) in the presence of an Ar (80%)-O₂ (20%) gaseous mixture at 90°C. Heating this amorphous powder at 550°C under Ar yields snowflake-like dendritic particles consisting of a mixture of monoclinic and orthorhombic WO₂ crystals. Annealing of the as-prepared product in Ar at 1000°C causes the formation of a WO₂-WO₃ mixture containing nanorods (around 50 nm in diameter) and packs of these nanorods. Heating the product in air for 3 hours leads to triclinic WO₃ crystal formation, with a basic size of 50-70 nm. The prepared oxides have been characterized by elemental analysis, X-ray powder diffraction measurements, FTIR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX).