Calorimetric, NEXAFS and XPS studies of MWCNTs with low defectiveness

Abstract

DSC and calorimetric studies of multi-walled carbon nanotubes (MWCNTs) with average diameters in the range 7, 9 and 18 nm were carried out. MWCNTs were obtained by the CVD method. The kinetic processes in MWCNTs were studied from room temperature to 550 °C in a nitrogen flow using differential scanning calorimetry (DSC) on a Perkin – Elmer — 8000. It was found that exo- and endothermic peaks are not observed on the DSC curves after water evaporation. This indicates that all studied MWCNTs have a small number of defects, functional groups, and other impurities. The heat capacity of MWCNTs was measured by the relaxation method in the temperature range from 2 to 275 K by using PPMS. In the temperature dependences of the specific heat were observed that for MWCNTs with the decrease of the temperature below 20 K the curves shift to lower values with an increase the average diameter. The main result was that at temperatures below 45 K with the decreasing of the nanotubes diameter the ratio of heat capacity of nanotubes to the heat capacity of graphite increases. The perfection of structure and low amount of the defects, functional groups and impurity contamination for MWCNTs were demonstrated in the comparison of the XPS and NEXAFS spectra for these nanotubes with CVD prepared nanotubes (18 nm) after mechanical and chemical functionalization.