Modified Sol-Gel Synthesis of Vanadium Oxide Nanocomposites Containing Surfactant Ions, and Their Partial Removal
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Modified Sol-Gel Synthesis of Vanadium Oxide Nanocomposites Containing Surfactant Ions, and Their Partial Removal Arthur Dobley, Peter Y. Zavalij, Jürgen Schulte, and M. Stanley Whittingham Chemistry Department and the Institute for Materials Research, State University of New York at Binghamton, Binghamton, New York 13902-6016, U.S.A. ABSTRACT Recently, there has been much interest in creating new layered transition metal oxides. Vanadium oxides may be used as sorbents, catalysts, and cathodes in lithium batteries. The modified sol-gel technique allows for some control towards the final structure of the compound. Using this technique, a new layered vanadium oxide phosphate material, containing the surfactant dodecylphosphate, has been synthesized. The compound was analyzed using powder XRD, TGA, SEM, FTIR, TEM, and solid state NMR for both 51V and 31P. V2O3(PO4C12H25)3Na2-x Kx(H2O)3.2 is the general formula of the layered product with an interlayer spacing of 36.6 Å. The initial compound is composed of a vanadium oxide phosphate layer sandwiched between two hydrocarbon layers. The synthesis, composition, and structure of the initial compound will be discussed. Interestingly, when this compound is calcined to 400°C, the structure changes and is possibly hexagonal. Preliminary results are presented on this calcined material. INTRODUCTION Since the discovery at Mobil [1, 2] of MCM-41, a mesoporous structured aluminum silicate, there has been great interest in extending the research to include transition metals [3, 4]. However, very little of this work has targeted vanadium oxides. This is surprising as many vanadium oxide compounds are of particular interest as they have many potential commercial applications such as molecular sieves, sorbents, catalysts, and energy storage devices. Vanadium oxides have a particularly rich structural chemistry [5] and have also been found to form a wide range of inorganic/organic materials [6]. Along with the quest of discovering new materials analogous to MCM-41, new techniques are being used to synthesize these compounds. One of the techniques is the modified sol-gel method. Sol-gel synthesis involves a sol (a fluid colloidal system) turning into a gel (jelly-like mass with 3D system). This occurs by a metal alkoxide undergoing hydrolysis and polymerization. Further drying yields a xerogel. Organics present in the product make it a ‘modified’ sol-gel. Templating, done by surfactants, forms micelles (shapes) in solution. Metal oxides can be fashioned to a particular shape (i.e. tunneled, layered structures) around these micelles. The surfactants can then be removed to leave behind the metal oxide with the desired nano-structure. Earlier work in our laboratory showed that vanadium oxide surfactant materials were not mesoporous, despite TEM indications of a 40 Å lattice, but rather were composed of Keggin-like vanadium oxide clusters [7, 8]. Single crystal X-ray diffraction confirmed the presence of clusters and of organic/inorganic systems swellable by a wide range of solvents [9].
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