Local environment of Co2+ ions intercalated in VOx/hexadecylamine nanotubes

SALETA, M; AURELIO, G.; F. BARDELLI; SÁNCHEZ, R. D.

Madrid

Conferencia; IUCr2011; 2011

International Union of Crystallography

The synthesis of nanostructures of oxides is an actual challenge among the scientific community. Many efforts are dedicated toward the development of material and structures with at least one dimension on the nanometer scale. One of these systems is the vanadium oxide nanotube (VOx NT), which presents potential applications in catalysis and electrochemisty, as cathode of Li-ion batteries [1]. The VOx NT?s are a multiwall nanostructre, where the walls are constituted by alternated layers of VOx and organic surfactant. The surfactant acts as template, providing support and hardness to the structure. The layers of VOx are constituted by V ions in two oxidation states (4+ and 5+). The V4+ ions are essential for the rolling up of the VOx layers, which form the NT . Unfortunately the presence of this ion reduces the performance of the cathodes. In this point appears the necessity of obtaining VOx NT?s where the amount of V4+ ions is reduced and the tubular shape is preserved. With this aim, we have performed doping treatments with transition metal ions to VOx/hexadecylamine (HDA) NT?s, in order to study the influence of doping ions on the magnetic properties of the system. We found that the doping treatments with Co and Ni ions reduce significantly the content of V4+ keeping the tubular morphology. [2] In this work we present a characterization of VOx/HDA NT?s doped with Co ions performed by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRPD) and X-ray absorption spectroscopy (XAS). The first result obtained by XAS was the corroboration of our magnetic and electron spin resonance results, where we assign C324 to the intercalated Co ions the 2+ oxidation state. This confirmation was obtained comparing the XANES (X-ray Absorption Near Edge Structure) spectra of our NT?s with standards (LaCo3+O3, Co2+O and metallic Co). By XAS characterization we obtained the first image of the local environment of the Co2+ ions intercalated in the VOx/HDA NT?s. The cobalt ions are located in the region of the surfactant close to two oxygen atoms of the oxide layer.