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Title: Spectroscopic and microscopic study of vanadium oxide nanotubes

Abstract

V{sub 2}O{sub 5} nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V{sub 2}O{sub 5} nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5{sup +} oxidation state in the nanotubes. However, V{sub 2}O{sub 5} nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V{sub 2}O{sub 5}. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V{sub 2}O{sub 5} nanotubes.

Authors:
; ; ; ; ; ; ; ; ;  [1];  [2];  [2]
  1. Institut fuer Physik, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz (Germany)
  2. (Germany)
Publication Date:
OSTI Identifier:
20982827
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 8; Other Information: DOI: 10.1063/1.2716157; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ELECTRONIC STRUCTURE; ELECTRONS; ENERGY-LOSS SPECTROSCOPY; NANOTUBES; OXIDATION; SOL-GEL PROCESS; VANADIUM; VANADIUM OXIDES; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Gloskovskii, A., Nepijko, S. A., Schoenhense, G., Therese, H. A., Reiber, A., Kandpal, H. C., Fecher, G. H., Felser, C., Tremel, W., Klimenkov, M., Institut fuer Anorganische und Analytische Chemie, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz, and Institut fuer Materialforschung I, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe. Spectroscopic and microscopic study of vanadium oxide nanotubes. United States: N. p., 2007. Web. doi:10.1063/1.2716157.
Gloskovskii, A., Nepijko, S. A., Schoenhense, G., Therese, H. A., Reiber, A., Kandpal, H. C., Fecher, G. H., Felser, C., Tremel, W., Klimenkov, M., Institut fuer Anorganische und Analytische Chemie, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz, & Institut fuer Materialforschung I, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe. Spectroscopic and microscopic study of vanadium oxide nanotubes. United States. doi:10.1063/1.2716157.
Gloskovskii, A., Nepijko, S. A., Schoenhense, G., Therese, H. A., Reiber, A., Kandpal, H. C., Fecher, G. H., Felser, C., Tremel, W., Klimenkov, M., Institut fuer Anorganische und Analytische Chemie, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz, and Institut fuer Materialforschung I, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe. Sun . "Spectroscopic and microscopic study of vanadium oxide nanotubes". United States. doi:10.1063/1.2716157.
@article{osti_20982827,
title = {Spectroscopic and microscopic study of vanadium oxide nanotubes},
author = {Gloskovskii, A. and Nepijko, S. A. and Schoenhense, G. and Therese, H. A. and Reiber, A. and Kandpal, H. C. and Fecher, G. H. and Felser, C. and Tremel, W. and Klimenkov, M. and Institut fuer Anorganische und Analytische Chemie, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz and Institut fuer Materialforschung I, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe},
abstractNote = {V{sub 2}O{sub 5} nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V{sub 2}O{sub 5} nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5{sup +} oxidation state in the nanotubes. However, V{sub 2}O{sub 5} nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V{sub 2}O{sub 5}. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V{sub 2}O{sub 5} nanotubes.},
doi = {10.1063/1.2716157},
journal = {Journal of Applied Physics},
number = 8,
volume = 101,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • Vanadium oxide nanotubes (VOx-NTs) have been synthesized via one-step hydrothermal treatment. The compounds were analyzed through X-ray powder diffraction; scanning electron microscope, UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS) and complex impedance spectroscopy. The electrical and dielectric properties dependence on temperature (302–523 K) and on frequency (5 Hz to 13 MHz) of VOx-NTs have been reported. The complex impedance plots exhibits the presence of grain and grain boundaries. Dielectric data were analyzed using complex permittivity and complex electrical modulus for the sample at various temperatures. The presence of non-Debye type of relaxation has been confirmed by the complex modulus analysis. ACmore » conductivity exhibits two conduction mechanisms: at high temperature, a translational motion with a sudden hopping and at low temperature, a localized hopping with a small hopping or reorientational motion. DC conductivity indicated, negative temperature coefficient of resistance (NTCR) type behavior. - Graphical abstract: The imaginary part of dielectric constant decreases with the increase in frequency at all temperatures and the values of ε´´ exhibit considerable frequency dispersion in the lower frequency range . Highlights: •Vanadium oxide nanotubes (VOx-NTs) were synthesized. •Non-debye type of relaxation has been confirmed. •AC conductivity exhibits two conduction mechanisms. •DC conductivity indicated negative temperature coefficient of resistance type behavior.« less
  • Vanadium(V) oxide supported on ..gamma..-Al/sub 2/O/sub 3/,CeO/sub 2/,Cr/sub 2/O/sub 3/,SiO/sub 2/,TiO/sub 2/, and ZrO/sub 2/ was studied by x-ray fluorescence, by x-ray diffraction, and especially by the combination of Raman spectroscopy and temperature programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from approx. 1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At mediummore » and high surface concentrations, the wet-impregnated samples already contain crystalline V/sub 2/O/sub 5/. At equal surface concentrations the ion-exchanged catalysts contain no V/sub 2/O/sub 5/ crystallites. An exception is SiO/sub 2/ on which also crystalline V/sub 2/O/sub 5/ is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order Al/sub 2/O/sub 3/ > TiO/sub 2/ > CeO/sub 2/, whereas on heating ion-exchanged V/SiO/sub 2/ the crystalline V/sub 2/O/sub 5/ spreads out over the silica surface. The reducibilities of the ion-exchanged catalysts, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500 to 800 K, this interaction ranges from strong with titania to weak with silica as a carrier.« less
  • We present detailed resonance Raman spectroscopic results excited at 220 and 287 nm for alumina-supported VO{sub x} catalysts. The anharmonic constant, harmonic wavenumber, anharmonic force constant, bond dissociation energy, and bond length change in the excited state for double bonded V{double_bond}O and single bonded V-O were obtained from fundamental and overtone frequencies. Totally symmetric and nontotally symmetric modes could be discerned and assigned on the basis of the overtone and combination progressions found in the resonance Raman spectra. Selective resonance enhancement of two different vibrational modes with two different excitation wavelengths was observed. This allowed us to establish a linearmore » relationship between charge transfer energy and VO bond length and, consequently, to assign the higher-energy charge transfer band centered around 210?250 nm in the UV?vis spectra to the V{double_bond}O transition.« less
  • The molecular structure of silica-supported vanadium oxide (VOx) catalysts over wide range of surface VOx density (0.0002 8 V/nm2) has been investigated in detail under dehydrated condition by in situ multi-wavelength Raman spectroscopy (laser excitations at 244, 325, 442, 532, and 633 nm) and in situ UV-Vis diffuse reflectance spectroscopy. Resonance Raman scattering is clearly observed using 244 and 325-nm excitations while normal Raman scattering occurs using excitation at the three visible wavelengths. The observation of strong fundamentals, overtones and combinational bands due to selective resonance enhancement effect helps clarify assignments of some of the VOx Raman bands (920, 1032,more » and 1060 cm-1) whose assignments have been controversial. The resonance Raman spectra of dehydrated VOx/SiO2 show V=O band at smaller Raman shift than that in visible Raman spectra, an indication of the presence of two different surface VOx species on dehydrated SiO2 even at sub-monolayer VOx loading. Quantitative estimation shows that the two different monomeric VOx species coexist on silica surface from very low VOx loadings and transform to crystalline V2O5 at VOx loadings above monolayer. It is postulated that one of the two monomeric VOx species has pyramidal structure and the other is in partially hydroxylated pyramidal mode. The two VOx species show similar reduction-oxidation behavior and may both participate in redox reactions catalyzed by VOx/SiO2 catalysts. This study demonstrates the advantages of multi-wavelength Raman spectroscopy over conventional single-wavelength Raman spectroscopy in structural characterization of supported metal oxide catalysts.« less
  • No abstract prepared.