Carbon nanotubes as a template for mild synthesis of magnetic CoFe2O4 nanowires

Hundred nanometers outer diameter multi-walled carbon nanotubes have been used as suitable host template for synthesizing CoFe₂O₄ nanowires encapsulated inside nanotubes under mild conditions, i.e. 100 °C and atmospheric pressure, with a high filling yield of the nanotubes, using an aqueous nitrate precursor solution and the confinement effect provided by the surrounding walls. The formation of caps near the tube tips at the beginning of the nitrate decomposition led to consider each nanotube as a closed nanoreactor, in which the reaction conditions could be far different from the macroscopic conditions outside the tube. The structure of the CoFe₂O₄ nanowires could be continuously changed from a disordered hair-like dendritic structure at 100 °C to highly crystallized domains when increasing the temperature. A material with high coercivity at room temperature for small particles of about 25 nm in diameter was obtained by submitting the nanowires to an Ar treatment at 550 °C for 2 h.