Chemical differentiation of carbon nanotubes in a carbonaceous matrix

To determine the purity of carbon nanotubes (CNTs), the effectiveness of some inorganic substances to catalyze the Boudouard reaction, investigated by thermogravimetric experiments, was studied. The performance, in terms of ability to separate the feature of CNTs from the features of other components, of various catalyst powders (NiO, Rh, Cr2O3), thoroughly mixed with carbonaceous simulated mixtures, was checked under a pure CO2 stream and compared without catalyst in the same operating conditions. The sequential removal of carbon up to 1200 °C by pure CO2 from a real sample of MWCNTs was characterized by TEM, XRD, and micro-Raman spectroscopy the carbonaceous fraction residues at each stopping temperature. Some evidence of the poor reliability of Raman spectroscopy in detecting the CNT purity are discussed. The procedure to perform thermogravimetry of simulated mixtures under pure CO2 at different weight compositions constituted by active carbon, MWCNTs, graphite, and Cr2O3 as catalyst was tested. The average relative error between the expected and found weight contents was within ±6%. The same procedure was also adopted to solve a simulated mixture of two kinds of MWCNTs having external diameter in a ratio of 1:10 and a very different number of walls.