The Chloroalkoxide Route to Transition Metal Oxides. Synthesis of V 2 O 5 Thin Films and Powders from a Vanadium Chloromethoxide
2009; American Chemical Society; Volume: 21; Issue: 8 Linguagem: Inglês
10.1021/cm803242m
ISSN1520-5002
AutoresMauro Epifani, Teresa Andreu, Carlos Magaña, Jordi Arbiol, Pietro Siciliano, Massimiliano D’Arienzo, Roberto Scotti, Franca Morazzoni, J.R. Morante,
Tópico(s)Catalysis and Oxidation Reactions
ResumoVanadium chloromethoxide was prepared by the methanolysis of VCl4. The addition of water with a H2O:vanadium molar ratio ranging between 0 and 16 changed the solution color from green to deep blue at a rate increasing with water concentration. UV−vis, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy investigations showed that VCl4 precursor is initially methanolyzed to (VO)Clx(OCH3)y (x + y = 4) monomers. Upon water addition, methoxo ligands undergo hydrolysis. The presence of chlorine ligands and of the vanadyl group explains the long-term stability of the solutions. V2O5 thin films and powders were prepared, respectively, by spin-coating onto silicon substrates and drying of the solutions, followed by heat-treatments at temperatures up to 500 °C. Films and powder precursors were characterized by X-ray diffraction, FTIR, Raman, UV−vis, and EPR spectroscopy, transmission electron microscopy, and thermal analyses. The structural evolution begins by condensation of the initial monomers to form amorphous structures with poor extension of the three-dimensional network. Heat-treatment at higher temperatures induces further condensation and the elimination of the chlorine ligands, which leave an oxygen-defective structure and cause the initial formation of substoichiometric V3O7 phase. When the samples were annealed at T ≥ 400 °C, only the V2O5 phase was found. V2O5 powders annealed at 500 °C were used in chemoresistive gas sensing devices and were able to detect reducing gases such as ammonia and ethanol over a broad range of concentrations by stable and reliable signal.
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