Properties assessment of multiwalled carbon nanotubes: A comparative study

In the last decade the interest in studies of carbon nanotubes (CNTs) from different viewpoints has been constantly increasing. In this work, we have prepared multi walled carbon nanotubes (MWCNTs) by pyrolysis of low density polyethylene (LDPE), using cobalt(II) acetate as a catalyst precursor, and then their systematic structural characterization has been carried out in parallel with the commercial MWCNTs (Nanocyl NC3100). For that purpose, scanning electron microscopy, powder X-ray diffraction, vibrational spectroscopy and thermogravimetry were used. The scanning electron microscopic images (SEM) recorded with different magnification of the synthesized product clearly showed the morphology of the carbon nanotubes. In the diffractogram of the as-prepared MWCNTs, in contrast to the commercial MWCNTs, characteristic peaks for metallic Co were observed besides the typical peaks for graphite. When studying the MWCNTs with Raman spectroscopy, an interesting effect of the laser irradiation on the spectral picture was revealed. In the Raman spectrum of the as-prepared MWCNTs recorded with laser power of 0.111 mW the appearance of the bands from cobalt(II,III) oxide (Co3O4) modes clearly demonstrated the oxidation of Co particles from the sample to Co3O4. The infrared spectra of the as-prepared and commercial MWCNTs recorded at room temperature (RT) and at liquid nitrogen temperature (LNT) are shown and compared. There is no noticeable temperature effect on the spectra appearance in both the frequency and intensity of bands. The TGA and DTG curves for investigated MWCNTs in air atmosphere are presented and the overall results are summarized. The results of TGA showed that up to 350 °C, the as-prepared MWCNTs are thermally stable in air, and above this temperature the process of thermo-oxidative decomposition proceeds fast and is completed at around 420 °C. The activation energy for the thermal decomposition of the nanotubes is 139 kJ mol−1.