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Vanadium Pentoxide Nanostructures: An Effective Control of Morphology and Crystal Structure in Hydrothermal Conditions

2009; American Chemical Society; Volume: 9; Issue: 8 Linguagem: Inglês

10.1021/cg900373f

1528-7505

Waldir Avansi, Cauê Ribeiro, Edson R. Leite, Valmor Roberto Mastelaro,

Gas Sensing Nanomaterials and Sensors

A systematic study was made of the synthesis of V2O5·nH2O nanostructures, whose morphologies, crystal structure, and amount of water molecules between the layered structures were regulated by strictly controlling the hydrothermal treatment variables. The synthesis involved a direct hydrothermal reaction between V2O5 and H2O2, without the addition of organic surfactant or inorganic ions. The experimental results indicate that high purity nanostructures can be obtained using this simple and clean synthetic route. On the basis of a study of hydrothermal treatment variables such as reaction temperature and time, X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) revealed that it was possible to obtain nanoribbons of the V2O5·nH2O monoclinic phase and nanowires or nanorods of the V2O5·nH2O orthorhombic phase. Thermal gravimetric analysis (TGA) shows also that the water content in the structure can be controlled at appropriate hydrothermal conditions. Concerning the oxidation state of the vanadium atoms of as-obtained samples, a mixed-valence state composed of V4+ and V5+ was observed in the V2O5·nH2O monoclinic phase, while the valence of the vanadium atoms was preferentially 5+ in the V2O5·nH2O orthorhombic phase. The X-ray absorption near-edge structure (XANES) results also indicated that the local structure of vanadium possessed a higher degree of symmetry in the V2O5·nH2O monoclinic phase.