Molybdenum Dioxide and Vanadium-Doped Molybdenum Dioxide Microcrystals in a Polymer Container.
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Molybdenum Dioxide and Vanadium-Doped Molybdenum Dioxide Microcrystals in a Polymer Container. Alexandru C. Pavel1, Dwight K. Romanovicz1, John T. McDevitt1 1 Department of Chemistry & Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, TX 78712-0165. ABSTRACT Molybdenum dioxide and vanadium-doped molybdenum dioxide microcrystals were synthesized by a totally new method involving a redox-active monomer route. The two related dioxides had virtually identical crystal structures and the three precursors used in the process could be subsequently divided in two subgroups of two members each, based on their strong similarities in composition and crystal structure, respectively. Molybdenum trioxide (orthorhombic and hexagonal forms) and the vanadium-doped (10%, molar) molybdenum trioxide (hexagonal form) were used in the redox process with excess pyrrole, and at relatively high temperature (325°C) and long reaction time (12 days), formed a heterogeneous new type of organic-inorganic microcomposite. The new material could be described as a molybdenum dioxide crystal in a polymer box, with the size of the crystallite grain depending on the dimensions of the initial molybdenum trioxide grain and the ratio between the unit cell volumes of the initial and final oxide. The procedure took advantage of the relatively high reduction potentials of the Mo6+ and V5+ oxide surface centers towards the oxidative polymerization of pyrrole at intermediate temperatures, and the high catalytic activity of the metal cations in the molybdenum trioxide-based materials towards the total oxidation of the carbon atoms in the organic moiety, at elevated temperatures. This new synthetic route offers good perspectives as precursor composites for nanocrystal engineering in practical applications like heterogeneous catalysis, chemical sensing, nanostructured metallic catalysts, etc.
INTRODUCTION Hybrid organic-inorganic nano- and microcomposites have received great attention during the past two decades due to the prospect of synthesizing composite materials with novel physical and chemical properties, which otherwise cannot be solely derived using the individual parent compounds. Composites made by intercalation of organic moieties into layered or micro- and mesoporous inorganic lattices have been studied the most, based on the optimized combination of mechanical, electronic, optical or chemical properties, desired for the targeted practical applications [1]. Polypyrrole has been among the most investigated electron conductive polymers owing its straightforward chemical and electrochemical synthesis methods, tunable electronic conductivity and the ability to produce smooth, conductive thin films. The relatively high oxidation potential and the good chemical stability of pyrrole have made this monomer an excellent candidate for the in situ polymerization in layered and channel-like micro- and mesoporous inorganic matrices, thus leading to new hybrid composites with enhanced electronic and mechanical properties [2
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