A new purification method of single-wall carbon nanotubes using H2S and O2 mixture gas

A purification process of single-wall carbon nanotubes (SWNTs) combining both the acid treatment to remove metal particles and the gas-phase purification to remove impurity carbon particles has been developed. Acid solution of 3 M HCl was used to remove catalyst metal particles out of the arc-discharge grown SNWTs. Thermal oxidation method using H2S–O2 gas mixture was followed to preferentially remove carbon particles. Hydrogen sulfide played a role of enhancing the removal of carbon particles as well as suppressing the oxidation of nanotubes. After the combined liquid–gas cleaning process, we achieved carbon nanotubes purity of >95% with yield of 20–50%.