Improvement of carbon nanotube stability by high temperature oxygen/chlorine gas treatment

Carbon nanotubes are interesting for applications in numerous fields. Nevertheless the as-produced samples prepared from bulk synthesis methods contain impurities and remain entangled if neither mechanical nor chemical treatment is applied. Such treatments are known to damage the carbon nanotube structure and to reduce their stability which induces drastic diminution of their properties. We have developed a purification method based on the use of a gas-phase treatment under an oxygen/chlorine mixture at high temperature (around 1000 °C). We were able to efficiently remove metal-based impurities from catalyst residue without damaging carbon nanotubes. We show that their stability is improved thanks to the presence of chlorine-containing functional groups at the carbon nanotube surface. Under the used conditions, the functionalization level remains low preserving the SWCNT structure and efficiently protects SWCNTs from combustion by oxygen.