| Abstract
| - The gas-phase derivatization procedure was employed for direct (i.e., without chemical activation of terminalcarboxylic groups) amidization of oxidized single-walled carbon nanotubes (SWNTs) with simple aliphaticamines. The procedure includes treatment of SWNTs with amine vapors under reduced pressure and atemperature of 160−170 °C. Applicability of infrared (IR) spectroscopy and temperature-programmeddesorption 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 (describedhere and elsewhere) cannot correspond to amide derivatives on SWNT tips because of the very lowconcentration of the terminal groups relative to the whole sample mass, which implies a negligible contributionto the IR spectra. The bands detectable in the case of long-chain amines correspond to amine moleculesphysisorbed because of strong hydrophobic interactions of their hydrocarbon chains with SWNT walls.Energetically preferable adsorption sites are the channels inside SWNTs, according to MM+ molecular-mechanics modeling. TPD-MS provided additional information on the chemical state of the amines. Heatingof the amine-treated SWNTs at >200 °C causes cleavage of alkenes from the amine residues: nonene andpentene 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 isabout 1 order of magnitude higher than the amide content. According to the results of two-level ONIOMquantum-chemistry-molecular-mechanics calculations, the direct formation of amides on armchair SWNTtips is more energetically favorable than that on the zigzag tips, although the activation barriers are ofapproximately equal height.
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