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 is specified. The attribution of carbonaceous materials to each fraction in the distribution was based on SEM and TEM measurements and the literature. The MWNT purified sample with 1.6 wt% metal oxide was investigated by high resolution thermogravimetry (HRTG). The quantitative assessment for the carbonaceous fractions was 25 wt% of amorphous and high defect carbonaceous materials 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 supports these results. The accuracy of the values, taking into account other measurements performed on the same batch of material, should be more sensible than +/-4 wt%.

Purification of single-walled carbon nanotubes

“…The different structural forms of carbon exhibit different reactivity towards oxidation. In general the purified tubes break down at a higher temperature than the amorphous carbon which can be seen by the higher weight loss onset temperature for the purified sample (350-400 • C), consistent with previous reports [13,32,33]. The corresponding most rapid weight loss observed in the DTG curve for the purified sample (Fig.…”

Polymeric nanomaterials as electrolyte and electrodes in supercapacitors

“…The decomposition occurs in two stages, with 584 o C being the temperature of maximum decomposition rate determined in the TG derivative curve (DTG). This two-stage decomposition is associated with the catalytic effect of the metal particles on the nanotube degradation, and the presence of defective material which decomposes fi rst [25]. The TG and SEM results indicated that the CNT used in this work can be considered moderately pure and of good structural quality [26].…”

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática

“…Amostras de nanotubos de carbono do mesmo lote que está sendo utilizado foram estudadas em detalhe pelo nosso grupo e concluiu-se que a concentração de nanotubos de carbono era de aproximadamente 54% em massa. 20 Informações complementares sobre este nanomaterial podem ser encontradas na referência 20 e permitem que outros trabalhos sobre a influência de nanotubos de carbono em compósitos poliméricos possam ser comparados com o que será apresentado. Neste trabalho, a técnica empregada para o preparo dos nanocompósitos TPU/MWCNT foi a mistura em solução, considerada mais efetiva quando são utilizadas cargas de dimensões muito pequenas 3 e envolveu três passos básicos: dispersão do nanotubo em THF, mistura com a solução do polímero (à temperatura ambiente) e recuperação do compósito por evaporação do solvente (casting) com obtenção do filme.…”