Metal cations inserted in vanadium-oxide nanotubes

Vanadium-oxide nanotubes (VOx-NTs) consist of nanosize cylinders of thin, easily bent vanadyl (VOx) wall chains, which are open at both ends. Surfactant molecules (e.g. C12H27N) can be easily trapped in the interior of the nanotube walls. The structure of as-synthesized VOx-NTs are observed to collapse to an amorphous vanadium oxide at temperatures greater than 250 degrees C. This happens, even under a protective atmosphere. This property makes the VOx-NTs unusable as a catalyst at temperatures between 400-500 degrees C, which is the temperature range where many applications would exist. In order to increase the thermal stability of VOx-NTs several exchange reactions have been used to modify the original nanotubes. In these reactions metallic cations (Cd2+, Co2+, Mn2+ or Zn2+) were introduced. It was observed that that the morphology of the nanotubes remained unchanged after the exchange reactions were performed. In order to characterize the exchanged VOx-NTs the following analytic techniques were used: scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared, particle-induced X-ray emission and Rutherford backscattering spectrometry. The results showed that the VOx-NTs exchanged with metallic cations have preserved their tubular morphology. However, it has not been possible to fully perform a 100% efficient exchange reaction. (c) 2007 Elsevier B.V. All rights reserved.