Inducing growth of highly ordered molybdenum oxide nanoplates under ambient conditions
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Large area uniform nanoplates of molybdenum oxide (MoO3), a typical semiconductor material, have been synthesized under soft conditions by using carboxymethyl cellulose (CMC) as template. Under ambient condition, hydrolysis of ammonium molybdate into layered molybdenum oxide, and its subsequent inclusion of CMC polymers results in formation of lamellar CMC/molybdenum oxide hybrid. Calcinations of this lamellar hybrid at 500 °C lead to formation of large area uniform nanoplates of orthorhombic phase of MoO3. Scanning electron microscopy and transmission electron microscopy images show that these MoO3 nanoplates are regularly packed, about 100 nm in thickness and 10–100 m in length. The mechanism of the hybrid reaction and the templating ability of CMC polymers have been extensively discussed. The oriented growth of short molybdenum oxide flakes into long-range ordered plates has been induced by CMC polymers because of the shrinking of CMC during the hybrid reaction. This is the first report that large area highly ordered molybdenum oxide nanometer materials have been obtained under soft reaction conditions.
I. INTRODUCTION
Low-dimensional functional materials have received numerous attentions because of their promising optical, electrical, magnetic, and ionic-transport properties.1–9 Fabrication of these materials with lowered dimensionality often leads to unexpected wonderful properties and applications. Moving to lower dimensionality to fabricate rods, disks, tubes, or belts has always been innovative and resulted in diverse applications.10–13 Molybdenum oxide (MoO3) is a low-dimensional material, which has been widely used in photochromic and electrochromic devices, gas sensors, catalysts, and also rechargeable battery electrodes because of its layered structure and wide band gap n-type semiconductor behavior.14–17 However, for these applications, especially for rechargeable battery electrodes, the fundamental research has been significantly hindered by the fact that these MoO3 materials are usually disordered and do not possess long-range order and contain morphological inhomogeneities.18 Scientists have tried to control the architectures and morphological patterns of MoO3 materials. Examples include intercalation of primary amine into molybdic acid via sol-gel ion exchange,11 reaction of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0344 2602
J. Mater. Res., Vol. 23, No. 10, Oct 2008
bulk MoO3 or ammonium heptamolybdate tetrahydrate under hydrothermal reaction conditions,12,13 or use of carbon nanotubes template.19 Among these examples, the sol-gel ion exchange method is almost a solid-state reaction with very low reaction rate and yield, while the hydrothermal reaction is carried out under critical conditions and always takes several days. All of the above methods are not economical to synthesize highly ordered molybdenum oxide materials. To obtain highly ordered molybdenum oxide materials with low cost, new reaction routes are required. Our group has been wo
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