Demonstration of covalent sidewall functionalization of single wall carbon nanotubes by NMR spectroscopy: Side chain length dependence on the observation of the sidewall sp3 carbons

Abstract

Carboxylic acid-functionalized single walled carbon nanotubes (SWNTs) prepared via the reaction of an amino acid, NH 2 (CH 2 ) n CO 2 H where n = 1 (glycine, GLY), 5 (6-aminohexanoic acid, AHA), 10 (11-aminoundecanoic acid, AUDA), with fl uorinated single walled carbon nanotubes (F-SWNTs) have been characterized by MAS 13 C NMR spectroscopy. The ease of observing the aliphatic CH 2 groups and the resolution of the signal are dependent on the length of the amino acid's aliphatic chain. We have proposed that where substituent chains are short (making NMR data collection difficult) chemical modification to extend the chain length should alleviate analysis problems. In this regard, we have investigated the esterifi cation of the carboxylic acid termini. The amino acid-functionalized SWNTs were esterified with an appropriate alcohol to ensure parity of the overall substituent length, i.e., GLY-SWNT (C 1 ) + 1-dodecanol (C 12 ) = DOD-GLY-SWNT (1), AHA-SWNT (C 5 ) + 1-octanol (C 8 ) = OCT-AHA-SWNT (2), and AUDA-SWNT (C 10 ) + 1-propanol (C 3 ) = PRO-AUDA-SWNT (3). The 13 C NMR shift for the sp 3 nitrogen-substituted carbon atoms of the SWNT sidewall is observed at ≈ 75 ppm. Increasing the length of SWNT sidewall functional groups enhances the ability to observe the sidewall sp 3 carbon. The methylene carbon signal intensity is less attenuated in the dipolar dephasing spectrum of the ester-functionalized SWNTs than their associated amino acid derivatives, suggesting more motional freedom of the side chain in the solid state. The confi rmation of the dipolar dephasing spectral effects was assisted by the characterization of the ester of AUDA-SWNT with 1,3-propanediol: PPD-AUDA-SWNT (4).

Polyethyleneimine functionalised nanocarbons for the efficient adsorption ofcarbon dioxide with a low temperature of regeneration

“…[18] Proof of covalent attachment of amine functions to fluorinated SWNTs has also been given previously. [21] In our current study, the same approach was initially taken with MWNTs (see Section 2).…”

Coupled thermogravimetry, mass spectrometry, and infrared spectroscopy for quantification of surface functionality on single-walled carbon nanotubes

“…Despite its obvious importance, the ability to characterize the types and quantities of functional groups attached to SWCNT has proven to be a difficult task. A number of methods have been applied to try to estimate the degree of functionalization of a carbon nanotube (CNT) sample, including titration [6] and deoxygenation [7]r e a ctions, NMR [8], XPS [9,10] and fluorescence spectroscopy [11], as well as AFM, STM [12], and STEM imaging techniques [13]. Though each of these techniques has shown some capability at estimating the quantity of sidewall functional groups, they also have limitations.…”

Phosphine functionalized single-walled carbon nanotubes

“…However, as seen in Table 1, there is no apparent relationship with regard to 31 P chemical shifts of SWNT-phosphine derivatives [16]. We have previously shown that 13 C NMR signals for substituted SWNTs are also difficult to assign in comparison with traditional organic analogs [21,22]. Thus, it is not possible to make peak assignments by direct analogy with small molecular phosphines.…”