Comparison of nitrogen adsorption and transmission electron microscopy analyses for structural characterization of carbon nanotubes

Highlights: • Five different MWCNTs were thoroughly characterized with N₂ adsorption and TEM. • Limitations of N₂ adsorption analysis were discussed as compared to HRTEM results. • N₂ adsorption does not accurately predict internal pore width and pore volume of CNTs. • N₂ condensation on inter-tubes & external surfaces cause inaccuracy in textural characterization. - Abstract: Carbon nanotubes (CNTs) are different from other porous substrates such as activated carbon due to their high external surfaces. This structural feature can lead in some uncertainties in the results of nitrogen adsorption analysis for characterization of CNTs. In this paper, the results of microscopic analyses and nitrogen adsorption method for characterization of carbon nanotubes were compared. Five different types of CNTs with different structures were either synthesized or purchased. The CNT samples were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and N₂ adsorption analysis. The comparisons between the results from the microscopic analyses and N₂ adsorption showed that the total pore volume and BET surface measurements include the internal and external porosity of CNTs. Therefore, the interpretation of N₂ adsorption data required accurate TEM analysis. In addition, the evaluation of pore size distribution curves from all CNT samples in this study and several instances in the literature revealed the presence of a common peak in the range of 2–5 nm. This peak does not explain the inner pore size distribution. The presence of this common peak can be attributed to the strong adsorption of N₂ on the junction of touched and crossed nanotubes.