Synthesis of VOx-NT

Synthesis

Tubes have been synthesized by a similar method as it is described in Ref. [1]. A mixture of vanadium (V⁵⁺) tri-isopropoxide [VO(iOPr)₃] and dodecylamine [CH₃-(CH₂)₁₁-NH₂] was used as the starting material. Applying a hydrothermal procedure, the chemicals were kept for 8 days at a temperature of 220°C. The final product is a black powder. TEM and SEM investigations have been carried out to check the yield and the purity of the tubes.

         TEM picture of a multiwalled VOx-NT

Two kinds of tubular nanostructures are present in the material. On one hand there are concentric vanadium oxide layers forming multi walled nanotubes. On the other hand there are also structures where only one or two rolled-up vanadium oxide sheets form a scroll.
In the vanadium oxide planes, edge coupled VO₆ octahedra form zig-zag chains. Arrays of these chains build up the walls of the tubes. Also, rather isolated tetrahedrally coordinated vanadium ions are located next to the chains. Organic spacer molecules are sandwiched between the walls serving as a template to stabilize the structure.
From XPS and EELS measurements a non-zero occupation of the V 3d shell was observed and the averaged vanadium valency was determined to be 4.4+ which suggests the presence of 60% vanadium ions in a 4+ oxidation state and another 40% V⁵⁺-sites [2].

[1] F. Krumeich et al., J. Am. Chem. Soc. 121, 8324 (1999)
[2] X. Liu et al., Phys. Rev. B 72, 115407 (2005)