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 modifications 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 compared with methods which try to interpret both phonon scattering and molecular 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 resonances 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 prepare samples with reproducible D/G ratios.

Nitrogen‐Functionalized Hydrothermal Carbon Materials by Using Urotropine as the Nitrogen Precursor

“…An unambiguous evaluation is aggravated by the fact that MS signals of N‐functional groups overlap with signals of the O‐functional groups. The recently developed isothermal segregation procedure and semiquantitative analysis of the O‐functional groups could therefore not be applied . Nevertheless, trends within the synthesized HTCs can be determined.…”

“…All in all, D, G, 2D, and combined G+D bands provide information about structural defects within graphitic systems . Therefore, detailed analyses, by applying different fitting methods, to obtain insights into the defect entities were not successful because these fitting methods were developed for graphitic or soot materials . XRD patterns of the measured HTC samples support the absence of highly structured domains due to a very broad band at around 10–20° (Figure S23 in the Supporting Information).…”

Atomically dispersed vanadium oxides on multiwalled carbon nanotubes via atomic layer deposition: A multiparameter optimization

“…The D * /G ratio by Raman spectroscopy was determined by focusing on single phonon resonances which is only possible in highly graphitic materials. 10 The high inert carbon content (low D * /G ratio) and structural properties emphasize that long diffusion times are necessary to guarantee contact between precursor and all available active sites, which are located at defect sites in the graphitic lattice. The high surface area and tubular structure of the MWCNT impede the deposition of vanadium oxide via ALD.…”

“…Functionalized MWCNTs were dried in a vacuum oven at 80 C for 12 h to eliminate residual water. 10 Before its use as a support material in the ALD process, MWCNTs were annealed (under inert atmosphere) at defined temperatures to remove specific functional groups. Table I lists some properties of untreated MWCNT to give a detailed view of the support material character.…”

Probing the intrinsic catalytic activity of carbon nanotubes for the metal-free oxidation of aromatic thiophene compounds in ionic liquids

“…Finally, the resulting samples were dried at 80 °C for 12 h (oCNTs). More detailed information can be found in our previous work [39] . oCNT x ( x indicates the annealing temperature) was synthesized by annealing oCNTs under argon with a heating rate of 5 °C/min to 252, 310, 510, 60 0, 80 0 and 10 0 0 °C, respectively, maintaining the target temperature for 30 min.…”