Characterization of Sonochemically Prepared Unsupported and Silica-Supported Nanostructured Pentavalent Molybdenum Oxide

Abstract

We describe the preparation and characterization of unusual pentavalent molybdenum oxide stabilized by water molecules, Mo2O5·2H2O. Ultrasound irradiation of a slurry of molybdenum hexacarbonyl, Mo(CO)6, in Decalin for 3 h under ambient air yields blue-colored Mo2O5·2H2O. Infrared (FT-IR) spectrum analysis of the resulting blue product reveals that the Mo ions possess molybdenyl bonds (MoO) and Mo−O character and also shows the presence of hydrogen-bonded, as well as coordinated, water molecules. The DSC profile of the blue oxide shows the presence of two endothermic peaks at around 100 °C and 140 °C, corresponding to the elimination of hydrogen-bonded and coordinated water molecules, respectively. The amount of water molecules was determined by thermogravimetric analysis (TGA). Characterization using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) shows the amorphous nature of the blue product. The TEM picture shows that the blue oxide is composed of spongy platelet nanoparticles (∼20 nm). Heating the initial blue powder at 300 °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 spectroscopy (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 the characteristic absorption of the Mo(V) (d-cation) oxide system and the Mo ions probably consists of two types of coordination symmetry (T d and O h ). Electron spin resonance (ESR) experimental results revealed 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-supported 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.

Substitution‐ and Elimination‐Free Phosphorylation of Functionalized Alcohols Catalyzed by Oxidomolybdenum Tetrachloride

“…[19,22] Further supportive insights were provided by H NMR analyses. [19] ESI-MS analysis (CH 3 CN as the eluent) of an aliquot from a catalytic reaction mixture with benzyl alcohol in CD 2 Cl 2 suggests the formation of an adduct between Cl 3 Mo(O)A C H T U N G T R E N N U N G (OCH 2 Ph) and NEt 3 (i.e., adduct …”

Nanocrystalline materials and coatings

“…The cooling achieved during the cavitation collapse is estimated to be greater than 2 Â 10 9 K. This process is commonly referred to as sonochemical method. Transition metal nanoparticles can be produced via sonication of their respective chemical precursors [194][195][196][197]. For example, Suslick et al sonicated Ni(CO) 4 under argon atmosphere to obtain amorphous nickel [194].…”

Morphological and electronic properties of ultrathin crystalline silica epilayers on a Mo(112) substrate

“…Furthermore, the assignment of this phonon band to an asymmetric Si-O mode which is influenced by the formation of Si-O-Mo species at the interface is supported by IR studies of silica supported molybdenum oxide catalysts. 37 When the molybdenum oxide catalysts are dispersed on the silica support by wet impregnation techniques, these IR studies report ͑depending on the oxidation state of the molybdenum oxides͒ the appearance of new asymmetric Si-O absorption bands in the spectral range from 925 to 1110 cm…”