Investigation of Different Pre-Treated Multi-Walled Carbon Nanotubes by Raman Spectroscopy

Abstract

Raman spectroscopy is a common method of studying carbon-based materials such as multi-walled carbon nanotubes (MWCNT). However, the analysis of this technique is non-trivial since recorded spectra may be a convolution of both molecular vibrations and phonon resonances. The energies of these physical processes may occur in the same energy regime, and hence several analytical approaches can be necessary for a full analysis. Due to the negligible quantities of non-graphitic carbon in MWCNT, the present fitting procedure focuses on understanding phonon resonances to elucidate how varying mod-ifications of MWCNT ultimately influence their graphitic bulk structure. We have found this approach to provide greater insight into the structure of MWCNT when low quantities of amorphous carbon are present, when com-pared with methods which try to interpret both phonon scattering and mole-cular vibrations simultaneously. Different pre-treatments for the modification of the graphitic structure of MWCNT are compared, including aqueous acidic and gas phase methods, and statistically evaluated. Focusing on phonon re-sonances enables one to analyze the reaction process of nitrosulfuric acid pre-treatment at different temperatures. Thereby, it is possible to control the ratio between defects and graphitic structures in MWCNT samples and pre-pare samples with reproducible D/G ratios.