Identification of large fullerenes formed during the growth of single-walled carbon nanotubes in the HiPco process

Iron-catalyzed, gas-phase disproportionation of carbon monoxide under high pressures is known to produce single-walled carbon nanotubes (SWNT) in high yields. Small amounts of nontubular nanocarbons and iron encapsulated-graphitic shelled nanoparticles are produced concomitantly. Differences in the oxidation kinetics among the SWNT, nontubular carbon, and iron core-graphitic shell nanoparticles have been exploited as a tool for the quantitative determination of high-molecular-weight nontubular, carbon products. The nontubular carbon materials were eliminated by selective oxidation wherein the raw material was subjected to increasing oxidation thresholds followed by acid leaching in an aqueous or gas-solid reaction. Relative concentrations of nontubular nanocarbons in differentially oxidized samples were determined employing laser desorption ionization-mass spectrometry (LDI-MS) with C-60 and bismuth triphenyl as internal markers. The identity of the nontubular carbon was examined by nondestructive extraction through fluorination in a gas-solid reaction followed by LDI-MS and electron microscopic and polarized Raman spectroscopies. The extracted nontubular carbon was found to be comprised predominantly of large, closed-shell carbon structures spanning the range of C-120 to C-400.