Purity evaluation of carbon nanotube materials by thermogravimetric, TEM, and SEM methods

Abstract

Raw and purified samples of carbon nanotubes are considered as multicomponent systems with a distribution of carbonaceous, amorphous, multishell graphitic particles and nanotubes, together with the particles of metal compounds from the catalyst. With respect to the carbon nanotube fractions, a distribution of size, defect concentrations and functionalities needs to be taken into account. In order to address the problem of quantitative evaluation of purity it is necessary to measure the quality and distribution of the carbon nanotubes. In this research conventional and high resolution thermogravimetry are applied to quantify different fractions of carbonaceous and metallic materials in raw and moderately purified single walled and multiwalled carbon nanotubes. For each oxidized fraction, defined by careful line shape analysis of the derivative thermogravimetric curves (DTG), the temperature of maximum rate of oxidation, the temperature range for this oxidation, related to the degree of homogeneity, and the amount of associated material was specified

The assignments of a type of carbonaceous material to each fraction in the distribution were based on several works from the literature and SEM and TEM measurements. The MWNT purified sample (1.6 wt% metal oxide) was investigated by high resolution thermogravimetry and the quantitative assessment for the carbonaceous fractions in this sample was as follow: 25 wt% of amorphous and other very defective carbonaceous including nanotubes, 54 wt% MWNT and 20 wt% multishell graphitic particles. A qualitative evaluation of these fractions was obtained from the SEM and TEM images and corroborates these results. The accuracy of the values, take into account other measurements performed for the same batch of material, should be better than ±4wt%.