Raman study of multiwalled carbon nanotubes functionalized with oxygen groups

Abstract

We present changes in the first and second order Raman spectra of multiwalled carbon nanotubes ͑MWNTs͒ functionalized with oxygenated groups. The oxygen groups were introduced onto the nanotube surface through two strong acid purification routes: ͑1͒ reflux in concentrated ͑70%͒ HNO 3 acid for 4 h at 80°C and ͑2͒ ultrasonification in 3 HNO 3 ͑70% ͒ :1H 2 SO 4 ͑98%͒ for 8.5 h. Raman spectroscopy, using two laser excitation wavelengths ͑514.5 and 632.8 nm͒, x-ray photoelectron spectroscopy, and thermal gravimetric analysis were employed to study the evolution of the products. All the techniques revealed a higher degree of functionalization for scheme 2 compared to scheme 1. Charge transfer phenomena were manifested by a shift of the C1s core level towards higher binding energies. We found that the intensity of both the D and G energy Raman modes if normalized to the second order mode D * mode follows similar trends upon acid treatments. We interpret this result together with the observed dispersion of G mode as an indication that the G mode in carbon nanotubes is defect induced in a double resonant process. Both acid schemes cause an upshift of D and G Raman modes, due to intercalation of acid molecules, exerting pressure on the sp 2 structure and an electron transfer from the states in MWNTs to the oxygen atoms.

Surface properties of oxidized and aminated multi-walled carbon nanotubes

“…7,8,24,34 Figure 3 presents the curves corresponding to the mass loss as a function of temperature (Figure 3a) and the derivative of the TGA curve (DTG) (Figure 3b). The thermogram in Figure 3a shows only one stage of decomposition for the MWCNT sample at temperatures between 450 and 650 ºC, which is a typical result for a MWCNT.…”

“…The effects of acid treatment on the structure and morphology of the tubes have been described in depth in previous studies. [7][8][9][10][11][12] Methods based on carboxylation present advantages in that CNT can be Vol. 23, No.…”

Raman spectroscopy of covalently functionalized single‐wall carbon nanotubes

“…In fact, the intensity ratio I D /I G 0 is suggested to be a sensitive measure for the defect concentration in carbon nanotubes by some authors. 57,58 An assignment of additional modes visible in the Raman spectra of SWCNTs can be found in the review articles by Saito et al 59 and Dresselhaus et al…”

Influence of architecture on the Raman spectra of acid-treated carbon nanostructures

“…The maximum intensity of the G and (Figure 3a). This shift may have been caused by the heavy functionalisation and electron transfer to the nanotube bundle to form NO À 3 anions [31,34]; the interstitial volume in SWCNT bundles is usually easily accessed to form such a charge-transfer compound, while MWCNTs or CNFs do not tend to form such tube bundles [35]. For the other CNSs the changes are within the standard deviation.…”

“…The I G /I D ratios were determined by analysing the band heights (instead of their areas), since the Raman spectra of some CNSs do not show well resolved G and D bands to allow band area measurements or unique deconvolutions by fitting, for example with Lorentzian line shapes. It is important to point out that it has been shown that use of intensity or area ratios in this kind of analysis yields similar results [31].…”