Micro-Raman spectroscopy analysis of catalyst morphology for carbon nanotubes synthesis

Multiwall carbon nanotubes (CNTs) were grown using the chemical vapor deposition method by applying C2H2 fluxed over FexCo5−x/CaCO3 catalyst under radio frequency heating. Micro-Raman scattering investigations of the metal active species over the oxidic support allowed the understanding of the relationship between the compositional distribution among the catalyst particles and the nanotube production rate, diameter distribution and morphology. It was proved that the catalyst chemical and structural non-uniformities of the active metals relative ratios (FexCo5−x) strongly influence the carbon deposition rate as well as the nanotube crystallinity characteristics. The catalytic activity of the FexCo5−x alloy relative to pure metals was correlated with the better relative permeability and polarizability contributed by certain ratios of Fe and Co as active catalytic species. It was also found evidence that catalyst pretreatment plays an active role on the nanotube yield and morphology. Micro-Raman spectroscopy of the catalytic systems was used successfully to predict the quality and crystallinity of the corresponding carbon nanotubes.