A new purification method for carbon nanotubes and associated atomic force microscope force–distance curve analysis

Abstract The discovery of carbon nanotubes has opened numerous cutting-edge nanoscale research fields, such as microelectronic devices and biomedical applications. Although pure nanotubes suffice for most purposes, highly purified magnetic carbon nanotubes are more suitable for specialized applications such as gene delivery. The conventional methods of purification are too harsh for nanotubes to retain their magnetic properties, hence it requires loading of magnetic nanoparticles inside individual tubes. In this paper, we propose an innovative purification method to directly extract magnetic carbon nanotubes from arc-discharged single-walled carbon nanotubes. The procedure is easy, and atomic force microscope (AFM) force–distance curve analysis combined with transmission electron microscopy (TEM) images are used to monitor the purification process. The AFM force–distance curves present the forces between the AFM tip and different sample surfaces. By comparing the peak values on a series of curves associated with different sample points, we can directly differentiate the carbon nanotubes retaining magnetic characteristics from other nanotubes after the purification process.