Morphology of multi-walled carbon nanotubes affected by the thermal stability of the catalyst system

High-quality multi-walled carbon nanotubes (MWCNTs) were efficiently synthesized on the CaCO3 supported Fe-Co catalyst with catalytic chemical vapor deposition method using acetylene as carbon source. The relationship between the catalyst structure and the carbon nanotube growth was systematically studied by using multiple techniques including SEM, TEM, TGA, Raman spectroscopy, and XRD. It was found that the MWCNT product demonstrates two groups in the outer diameter distribution, which is associated with the partial decomposition of CaCO3. This thermal decomposition was found to have as a result the coexistence of two catalytic systems throughout the entire synthesis process: Fe-Co/CaCO3 and Fe-Co/CaO. It was also found that the smaller diameter nanotubes grow on the Fe-Co/CaO system, while Fe-Co/CaCO3 produces larger diameter tubes.