V2O5/polypyrrole core-shell nanotubes for gas sensor.

V2O5/polypyrrole core-shell nanotubes have been synthesized through an in situ polymerization of pyrrole monomers in the presence of prepared vanadium oxide nanotubes. Formation of polypyrrole in core-shell structure was endorsed by FTIR spectral analyses. Transmission electron microscopy images revealed that one dimensional morphology of vanadium oxide nanotubes remained undisturbed upon coating of polypyrrole, and polypyrrole was uniformly coated on the surface of vanadium oxide nanotubes, with a thickness of 30 nm. XRD suggested certain synergetic interaction existed in the core-shell structure, probably resulting in the enhanced thermal stability of polypyrrole coatings. The gas tests showed that the core-shell structure exhibited a high response, good stability and a short response/recovery time in the detection of different concentrations of ethanol at room temperature, implying its potential application for gas sensors. The enhanced gas sensing properties due to the synergic interaction between intimately contacted polypyrrole and vanadium oxide nanotubes lead to the formation of a hetero p-n junction with a depletion region, which is similar to a field effect transistor. The gas effects a change of the depletion region and thus modulates the conductivity of the junction.