Carbon nanotubes as removable templates for metal oxide nanocomposites and nanostructures

Abstract

SEVERAL techniques have been developed recently for fabricating nanocomposite structures by filling1–3 carbon nanotubes4,5. Here we show that surface-tension effects can induce the growth of uniform, thin metal oxide filmsa€"sometimes only a monolayer thicka€"on the outside of nanotubes, along with oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes. We report the preparation of such nanotube–oxide composites by annealing a mixture of partially oxidized nanotubes and V2O5 powder in air above the melting point of the oxide. The external coatings of the tubes are crystalline sheets of the V2O5 layer-like structure, which grow with the c axis parallel to that of the nanotube layers. Intercalation of the oxide occurs where there are missing shells in the nanotubes. We also show that the nanotubes can be partially removed by oxidation, leaving behind layered oxide fibres. Given the importance of vanadium oxides as catalysts and functional ceramics, this role of nanotubes as removable templates might lead to useful new kinds of nanostructured materials.