Gas-phase purification process of carbon nanotubes: reaction selectivity and nanotube quality.

摘要

Single walled carbon nanotubes (SWCNTs) are usually produced using arc discharge, laser ablation and chemical vapor deposition techniques. SWCNT .synthesis methods have been largely improved leading to assess to the mass production, however the produced soot inexorably contains a non negligible amount of noncarbon species. Indeed, metal catalyst is needed for the growth of SWCNT-type. These non-carbon particles that differently behave from the SWCNTs are particularly undesired. They forbid benefitting of intrinsic electronic transport or magnetic properties that are considered as useful for many applications. Nevertheless, their elimination without damaging the SWCNTs remains a long-standing issue [1,2,3]. Whatever the synthesis method used, the residual metallic particles are surrounded by several carbon layers in the case of SWCNT samples. The resulting protecting effect in favor of the metallic particles drastically diminishes the accessibility to standard chemical reagent. The alternative process we have developed avoids utilizing standard oxidation or acid reflux treatment and it allows to selectively remove metallic impurities with high yields. It merely consists in heating up the raw SWCNT powder under a chlorine flux [4]. We will show that this gas-phase process combines several advantages. The results presented will be focused on the characterization of the surface state and the structural quality of the purified SWCNTs after the chemical treatment using several complementary techniques: TEM, TGA, Raman spectroscopy and adsorption volumetry. We will especially discuss on a believed annealing effect within the temperature range we used (around 1000 °C).