On the Stacking Behavior of Functionalized Single-Wall Carbon Nanotubes

Abstract

Single-wall carbon nanotubes (SWNTs) were oxidatively functionalized by nitric acid treatment. The presence of carboxyl groups was proven by IR spectroscopy, matching earlier IR and NMR observations. Raman spectra in the radial breathing mode (RBM) and G line spectral windows were measured with six laser lines ranging from 457 to 647 nm. The RBM mode was observed to upshift by the functionalization with very little change in the spectral line shape. By the analysis of the spectral moments of the lines, this upshift is interpreted as a change in an empirical intertube interaction function. In agreement with previous TEM results, we have found that bundles in a pristine SWNT sample are significantly thinner (<10 tubes) than those in the oxidized samples (>30 tubes). Changes observed in solvatation properties and sample morphology could be explained on this basis. Our observations suggest that carboxyl related secondary bonding forces might also play a role in the stacking of oxidized SWNTs.

Reversible electron charge transfer in single-wall carbon nanotubes

“…In addition, the intensity of the remaining peaks dropped. The decrease in the intensity of the optical absorption spectra in both samples can be assigned to the fact that the introduction of dopant molecules, such as HNO 3 , provokes oxidation 15,16 or 1,3-cycloaddition…”

“…Modifications in the SWCNT structure can be explained by the H-bonding promoted by -COOH groups as suggested by Kukovecz et al 15 . One of the main sources of the reactivity of SWCNT is the curvature given by the non-planar geometry of sp 2 carbon atoms.…”

Raman spectroscopy of covalently functionalized single‐wall carbon nanotubes

“…upon nitric acid treatment, 15 given for this observation. In many cases, different sample morphologies were made responsible for the upshift of the RBM wavenumbers, either an increase in bundle size 15,127 or the opposite, a debundling of the SWCNTs. 89,126,133 However, in many cases it cannot be decided whether the reported shift of the RBMs is a true shift of the individual modes.…”

Functionalization of carbon nanotubes

“…In the course of the work reported here first the simplest functionalized SWCNTs were studied: nanotubes with -COOH groups formed upon purification treatment in refluxing HNO 3 [35] (see Fig. 3A for a schematic representation of the material).…”