Purification of carbon nanotubes by high temperature chlorine gas treatment

Carbon nanotubes (CNTs) have a tremendous amount of potential to become useful components for future practical applications that may become a part of everyday life. While the sp² carbon itself is a rather chemically inert material, the issue of residual metal nanoparticle catalysts remains a prominent barrier in the utilization of CNTs in many areas due to the strong influence of these metallic impurities on the redox chemistry of biomarkers. Even with a standard purification procedure, CNTs have been shown to still contain residual metal nanoparticle catalysts. As such, presented in this paper is an improved purification technique for treating the CNTs with the highly reactive Cl₂ gas at an elevated temperature of 1000 °C for 10 min, which would result in the vaporization of the metallic impurities as M _xCl_y, leading to a large decrease in the amount of metallic nanoparticle impurities within the CNTs. By means of electrochemistry and X-ray fluorescence analysis, we demonstrate that the behaviour of such Cl₂ treated CNTs showed a significant shift towards that of high purity CNTs, with a dramatic decrease in the influence of the residual metallic impurities on the electrochemical behaviour of CNTs. Therefore it is suggested that the Cl₂ treatment of carbon nanotubes is a highly promising route towards the production of pure CNTs.