CHARACTERIZATION OF SONOCHEMICALLY PREPARED UNSUPPORTED AND SILICA-SUPPORTED NANOSTRUCTURED PENTAVALENT MOLYBDENUM OXIDE

We describe the preparation and characterization of unusual pentavalen t molybdenum oxide stabilized by water molecules, Mo2O5 . 2H(2)O. Ultr asound irradiation of a slurry of molybdenum hexacarbonyl, Mo(CO)(6), in Decalin for 3 h under ambient air yields blue-colored Mo2O5 . 2H(2) O. Infrared (FT-IR) spectrum analysis of the resulting blue product re veals that the Mo ions possess molybdenyl bonds (Mo=O) and Mo-O charac ter and also shows the presence of hydrogen-bonded, as well as coordin ated, water molecules. The DSC profile of the blue oxide shows the pre sence of two endothermic peaks at around 100 degrees C and 140 degrees C, corresponding to the elimination of hydrogen-bonded and coordinate d water molecules, respectively. The amount of water molecules was det ermined by thermogravimetric analysis (TGA). Characterization using po wder X-ray diffraction (XRD) and transmission electron microscopy (TEM ) with selected area electron diffraction (SAED) shows the amorphous n ature of the blue product. The TEM picture shows that the blue oxide i s composed of spongy platelet nanoparticles (similar to 20 nm). Heatin g the initial blue powder at 300 degrees C for 2 days under an oxygen, hydrogen, and nitrogen atmosphere yields X-ray crystalline MoO3, MoO2 , and a mixture of MoO3 and MoO2, respectively. X-ray photoelectron sp ectroscopy (XPS), along with the potentiometric titration analysis of the blue oxide, confirms the formation of pentavalent molybdenum oxide . UV-visible absorption studies of the blue product demonstrate that t he characteristic absorption of the Mo(V) (d(1)-cation) oxide system a nd the Mo ions probably consists of two types of coordination symmetry (T-d and O-h). Electron spin resonance (ESR) experimental results rev ealed an unusual doublet pattern, which is ascribed to superhyperfine coupling of pentavalent molybdenum with a proton of coordinated water. The nanostructured amorphous pentavalent molybdenum oxide (blue oxide ) thus formed has also been successfully deposited on Stober's silica micropheres (250 nm) ultrasonically. The TEM images of silica-supporte d blue oxide reveal uniform distribution and strong adhering nature of the blue oxide. FT-IR spectroscopy illustrated the structural changes that occur when the amorphous SiO2 is coated sonochemically with the blue oxide.