Iron removal from carbon nanotubes and metal catalyst recycle

A method of purifying carbon nanostructured material comprising the steps of:

• (a) obtaining a quantity of unpurified carbon nanostructured material, the unpurified carbon nanostructured material being contaminated with metal catalyst particles and amorphous carbon structures;
• (b) oxidizing the unpurified carbon nanostructured material by exposure to carbon dioxide at an elevated temperature, wherein the oxidizing removes the amorphous carbon structures to form a carbon dioxide-treated carbon nanostructured material and carbon monoxide;
• (c) exposing the carbon dioxide-treated carbon nanostructured material to a flowing gas comprising at least the carbon monoxide produced in step (b), wherein at least 500 mol % excess of carbon monoxide is used with respect to the stoichiometric quantity needed to react with the contaminating metal in the carbon nanostructured material;
• (d) raising the temperature of the carbon dioxide-treated carbon nanostructured material and the flowing gas from about 20° C. to about 200° C. to produce a purified carbon nanostructured material and a gaseous stream comprising a volatile metal species, wherein the carbon monoxide's pressure in the flowing gas is of 50-120 bar and the purified carbon nanostructured material contains less than about 10 wt. % metal catalyst;
• and (e) transporting the gaseous stream away from the purified carbon nanostructured material.