The gas-phase derivatization procedure was employed for direct (i.e., without chemical activation of terminal carboxylic groups) amidization of oxidized single-walled carbon nanotubes (SWNTs) with simple aliphatic amines. The procedure includes treatment of SWNTs with amine vapors under reduced pressure and a temperature of 160-170 °C. Applicability of infrared (IR) spectroscopy and temperature-programmed desorption mass spectrometry (TPD-MS) for chemical characterization of the derivatized SWNTs was analyzed. It was concluded that IR spectra of oxidized SWNTs treated with amines under different conditions (described here and elsewhere) cannot correspond to amide derivatives on SWNT tips because of the very low concentration of the terminal groups relative to the whole sample mass, which implies a negligible contribution to the IR spectra. The bands detectable in the case of long-chain amines correspond to amine molecules physisorbed because of strong hydrophobic interactions of their hydrocarbon chains with SWNT walls. Energetically preferable adsorption sites are the channels inside SWNTs, according to MM+ molecularmechanics modeling. TPD-MS provided additional information on the chemical state of the amines. Heating of the amine-treated SWNTs at >200 °C causes cleavage of alkenes from the amine residues: nonene and pentene form in the case of nonylamine and dipentylamine, respectively. For the short-chain amine (dipentylamine), only one chemical form was detected, whereas two forms (amide and physisorbed amine) can be distinguished for the SWNTs treated with nonylamine. The content of physisorbed nonylamine is about 1 order of magnitude higher than the amide content. According to the results of two-level ONIOM quantum-chemistry-molecular-mechanics calculations, the direct formation of amides on armchair SWNT tips is more energetically favorable than that on the zigzag tips, although the activation barriers are of approximately equal height.

We attempted the direct solvent-free amination of closed caps of multiwalled carbon nanotubes (MWNTs) with octadecylamine (ODA), which is essentially similar to the amination of spherical fullerenes. Thermogravimetric analysis revealed a relatively high content of organics in the product of derivatization (ODA-MWNTs), suggesting that a large ODA fraction is distributed over MWNT sidewalls through chemical attachment. This was confirmed by high-resolution transmission electron microscopy observations. Quantum chemical calculations showed that the presence of pyracylene units in the closed caps is not crucial for the amine addition, although the site specificity of the reaction does depend on the mutual position of five-membered rings. If the caps contain pyracylene units, then the addition preferentially takes place on their 6,6 bonds; if they do not, then the preferential reaction sites are C−C bonds of the pentagons. Whereas ideal nanotube sidewalls composed of solely benzene rings were found to be inert with respect to amines, the real nanotube sidewalls must contain numerous reactive five-membered rings as defects. ODA-MWNTs exhibited enhanced dispersibility/solubility in propanol. The proposed amination reaction is the most direct link between carbon nanotube and fullerene chemistry, contrary to all derivatization methods designed previously.

Gold nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWNTs) functionalized with aliphatic bifunctional thiols (1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 2-aminoethanethiol) through a direct solvent-free procedure. Small gold particles, with a narrow particle size distribution around 1.7 nm, were obtained on 1,6-hexanedithiol-functionalized MWNTs. For MWNTs functionalized with the aminothiol, the average Au particle size was larger, 5.5 nm, apparently due to a coalescence phenomenon. Gatan image filter (GIF) observations show that sulfur is at the nanotube surface with a non-homogeneous distribution. A higher sulfur concentration was observed around the gold nanoparticles' location.

Morphological changes in single-walled carbon nanotubes (SWNTs) upon bombardment with 3MeV protons were monitored by transmission electron microscopy in a wide range of irradiation doses. Evident morphological alterations were observed at >0.1 mC, such as curving of the nanotubes, a loss of their straight shape, and formation of short pieces. During further irradiation (doses approaching 1 mC) SWNTs degraded into an amorphous material, although a significant fraction of them were present as pieces of different lengths.

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Using a two-level ONIOM approach, we performed a theoretical study of the direct amidation of mono-carboxyl-derivatized fragments of zigzag (10,0) and armchair (5,5) single-walled carbon nanotubes (SWNTs) with the simplest aliphatic amine, methylamine. Our results suggest that the direct formation of amides is much more energetically preferable on armchair SWNT tips than on the zigzag nanotube tips. This might open a new route to selective derivatization of different forms of carbon nanotubes.

Raman spectra of starting (pristine) and functionalized multiwalled carbon nanotubes (MWNTs) were analyzed by principal component analysis (PCA) because the original Raman spectra showed very little differences between them. The nanotubes were functionalized with amines: dodecylamine (MWNT1), nonylamine (MWNT2), phenylamine (MWNT3) and octadecylamine (MWNT4), and with dithiols: 1,4-butane dithiol (MWNT5), 1,6-hexane dithiol (MWNT6) and 1,8-octane dithiol (MWNT7). The D and G band intensity ratios (∼1338 and ∼1575 cm −1 ) of the functionalized MWNTs spectra were compared with those of the starting material. For the studied systems, PCA allowed the differentiation between starting and functionalized MWNTs. The present study demonstrated the potential of the application of PCA to the study of functionalized nanotubes by Raman spectroscopy.

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