Improved filling rate and enhanced magnetic properties of Fe-filled carbon nanotubes by annealing and magnetic separation

The filling rate of Fe nanowires in carbon nanotubes (CNTs) was improved by a post-treatment which involved annealing and magnetic separation. The annealing process transformed γ-Fe to ferromagnetic α-Fe, resulting in α-Fe-filled CNTs with improved magnetic properties. The Fe-filled CNTs were then separated from those unfilled CNTs due to the different attractive forces under magnetic field. Thermal gravimetric analysis (TGA) revealed that the purity of CNTs was improved after magnetic separation and the filling rate can be up to 40.0 wt.%, which is increased about 8.1% comparing with annealed CNTs. The saturation magnetization of CNTs reached 31.45 emu/g after magnetic separation.