A process of non-destructive purification of carbon nanotubes (CNTs) was discussed. CNTs samples were produced by a catalytic chemical vapor deposition method, which have defects along the graphite tube walls and include impurities, such as catalyst particles, amorphous carbon, carbon nanoparticles, etc. Taking advantage of the fact that different structure and thermal oxidation rates exist between CNTs and other carbonaceous particles, samples were annealed at 1800 ℃ for 3 h in an Ar protective atmosphere. The morphologies of the as-received and high-temperature annealed samples were characterized by scanning electron microscopy. Most of CNTs cap were opened, which were in agreement with transmission electron microscopy observation. The elemental compositions of the specimens were identified by energy dispersive spectrometry. As-received sample impurities such as Al, Si, Ni and Cu (their mass fraction values were 4.67%, 0.27%, 40.12% and 1.34%, respectively) were efficiently removed. The purity and the graphitization were determined by Raman spectroscopy. After the annealing, the area of the D-line peak and the G-line peak decreased from 1314900 to 474921 and from 767157 to 566292, respectively. The intensity of D-line peak decreased, while that of G-line peak increased. These results imply that some defects have been healed. The purity and the graphitization of annealed CNTs are high. High-temperature annealing has been confirmed as an effective means of removing both the catalyst particles and microstructures defects within nanotubes.

Key words: carbon nanotube, high-temperature annealing, non-destructive purification, characterization