Preparation of porous chromium oxide nanotubes using carbon nanotubes as templates and their application as an ethanol sensor.

Chromium oxide nanotubes were successfully prepared using multi-walled carbon nanotubes (MWCNTs) as a template via a supercritical fluid-mediated route. In this method, with chromium (III) nitrate nonahydrate as precursor, chromium oxide was first deposited on MWCNTs in supercritical ethanol in the presence of NH(4)HCO(3). The as-prepared chromium oxide/MWCNT nanocomposites were characterized by transmission electron microscopy, x-ray diffraction, infrared spectroscopy and thermogravimetric analysis. It was demonstrated that the MWCNTs were coated with a layer of amorphous Cr(2)O(3)·xH(2)O. The thickness of the Cr(2)O(3)·xH(2)O sheath on MWCNTs could be tuned by manipulating the ratio of precursor to MWCNTs. Calcining the composites at 550 °C, the MWCNTs were removed, producing polycrystalline α-Cr(2)O(3) nanotubes. The as-prepared α-Cr(2)O(3) sample was used as a sensor material to detect ethanol vapor, and it was demonstrated that the α-Cr(2)O(3) nanotubes exhibited good performance even at 400 °C.