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

M.E. SALETA; G. AURELIO; F. BARDELLI; H. E. TROIANI; R.D. SÁNCHEZ; M. MALTA; R. M. TORRESI

Madrid

Congreso; XXII International Congress and General Assembly of the IUCr; 2011

IUCr

The synthesis of nanostructures of oxides is an actual challengeamong the scientifi c community. Many efforts are dedicated towardthe development of material and structures with at least one dimensionon the nanometer scale. One of these systems is the vanadium oxidenanotube (VOx NT), which presents potential applications in catalysisand electrochemisty, as cathode of Li-ion batteries [1]. The VOxNT’s are a multiwall nanostructre, where the walls are constituted byalternated layers of VOx and organic surfactant. The surfactant acts astemplate, providing support and hardness to the structure. The layers ofVOx are constituted by V ions in two oxidation states (4+ and 5+). TheV4+ ions are essential for the rolling up of the VOx layers, which formthe NT . Unfortunately the presence of this ion reduces the performanceof the cathodes. In this point appears the necessity of obtaining VOxNT’s where the amount of V4+ ions is reduced and the tubular shape ispreserved.With this aim, we have performed doping treatments with transitionmetal ions to VOx/hexadecylamine (HDA) NT’s, in order to study theinfl uence of doping ions on the magnetic properties of the system.We found that the doping treatments with Co and Ni ions reducesignifi cantly the content of V4+ keeping the tubular morphology. [2]In this work we present a characterization of VOx/HDA NT’s dopedwith Co ions performed by Transmission Electron Microscopy (TEM),X-ray powder diffraction (XRPD) and X-ray absorption spectroscopy(XAS). The fi rst result obtained by XAS was the corroboration ofour magnetic and electron spin resonance results, where we assignto the intercalated Co ions the 2+ oxidation state. This confi rmationwas obtained comparing the XANES (X-ray Absorption Near EdgeStructure) spectra of our NT’s with standards (LaCo3+O3, Co2+O andmetallic Co).By XAS characterization we obtained the fi rst image of the localenvironment of the Co2+ ions intercalated in the VOx/HDA NT’s. Thecobalt ions are located in the region of the surfactant close to twooxygen atoms of the oxide layer.[1] M.E. Spahr, P. Stoschitzki-Bitterli, R. Nesper, O. Haas, P. Novák, J.Electrochem. Soc. 1999, 146, 2780. [2] M.E. Saleta, H.E. Troiani, S. RibeiroGuevara, G. Ruano, R.D. Sánchez, M. Malta, R.M Torresi. J. App. Phys. 2011,in press.