Microstructural investigation and magnetic properties of CoFe2O4 nanowires synthesized inside carbon nanotubes

Cobalt ferrite nanowires with an average diameter of 50 nm and lengths up to several micrometers were synthesized inside multi-walled carbon nanotubes under mild reaction conditions, i.e. 100degreesC and atmospheric pressure, using an aqueous nitrate precursor salt filling the tubes. The concept of a confinement effect inside carbon nanotubes has been advanced to explain the formation of CoFe2O4 under such mild reaction conditions. The formation of caps near the tube tips at the beginning of the nitrate decomposition meant that each nanotube was considered as a closed nanoreactor, in which the reaction conditions could be very different to the macroscopic conditions outside the tube. A post-synthesis treatment under inert atmosphere allowed the growth of CoFe2O4 particles, from a disordered hair-like dendritic structure at 100degreesC to highly crystallized domains at higher temperatures. A material with high coercivity at room temperature for small particles of about 25 nm in diameter was obtained by submitting the CoFe2O4 nanowires after calcination in air at 100degreesC to an argon treatment at 550degreesC for 2 h.