Fabrication, Formation Mechanism, and Magnetic Properties of Metal Oxide Nanotubes via Electrospinning and Thermal Treatment

A simple procedure has been developed for preparing high aspect ratio nanotubes of alpha-Fe2O3 and Co3O4 with diameters less than 100 nm and wall thicknesses less than 25 nm based on an appropriate heat treatment of electrospun polymeric fibers containing Fe(III) and Co(II) ions. The transformation of the as-prepared nanofibers to the final nanotube structure has been studied by scanning and transmission electron microscopy as well as X-ray diffraction, differential scanning calorimetry/thermogravimetric, and X-ray photoelectron spectroscopy measurements. These measurements and comprehensive analysis have led to a semiquantitative picture of a new nanotube formation mechanism. On the basis of the principles established in this article, it is foreseeable that many other oxide nanotubes could be designed and fabricated, opening a broad avenue to investigate electrical, chemical, mechanical, and magnetic properties. In this particular case, we have shown that magnetic properties are very different between alpha-Fe2O3 nanofibers and nanotubes, and they are distinctly different from their bulk counterpart.