Hydrothermal preparation of long nanowires of vanadium oxide
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Long beltlike nanowires were successfully synthesized for a semiconducting oxide of vanadium by a hydrothermal route at 180 °C for 5 h and were characterized by x-ray powder diffraction, energy dispersive x-ray spectroscopy, and electron diffraction microscopy. The product is mainly layered V2O5 ⭈ 0.3H2O with a small fraction of V2O5 ⭈ xH2O (0.3 < x < 1.7) and V2O5 phases. The obtained nanowires, several tens of micrometers long and a few of tens of nanometers wide, are crystallized well, growing along the [010] direction. The effects of preparation conditions on the formation of the nanowires are discussed. I. INTRODUCTION
One-dimensional wirelike nanostructures have attracted much attention in recent years because of their great potential for addressing some basic issues about dimensionality and space-confined transport phenomena as well as potential applications in nanodevices.1 Recently, vanadiam pentoxide nanowires have been found to possess some interesting properties and some novel applications.2,3 V2O5 belongs to the family of semiconducting oxides with cations of different valence states, and its one-dimensional structures often adopt novel beltlike (ribbonlike) morphology.4,5 Vanadium pentoxide has an interesting layered structure, which permits a wide variety of other molecules or cations embedded between the layers without a far reaching restructuring.2 Also, the oxide nanowires have been revealed to exhibit unusual liquid-crystal3 and N-type enhancement field-effect transistor-like behaviors.5 With these properties, the functional material can be potentially used to fabricate antistatic coatings, mineral liquid-crystal display devices, and nanoscaled field-effect transistors.5–9 V2O5 nanowires have been synthesized by polycondensation of vanadic acid in water at room temperature.10–13 The preparation of poly(vanadic acid) solutions involved ion exchange between Na+ and H+ ions in a resin from sodium metavanadate solutions. Due to the slow synthesis at room temperature, a long reaction time was needed (several weeks), and long nanowires were hard to obtain. Recently, Krumeich et al.2 have developed a sol-gel method followed by hydrothermal treatment to prepare nanotubes and nanowires of V2O5 using suitable organic molecules as templates. However, they a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 8, Aug 2002
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used toxic vanadium(V) alkoxide precursors. Mild hydrothermal methods have been extensively used in the synthesis of oxide materials, and various layered phases of V2O5 have been synthesized with metal or organic cations (Ag+, Cu2+, Na+, K+, tetramethylammonium cations) embedded between the layers.14–20 Here, we extend this technique to prepare V 2 O 5 nanowires. We successfully obtained long V2O5 nanowires (up to 80 m) at 180 °C for 5 h using NH4VO3 as an initial material and HNO3 for pH control. The product is mainly layered V2O5 with 0.3 H2O molecules embedded between the V2O5 layers,
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