Oxygen-Containing Functional Groups on Single-Wall Carbon Nanotubes:  NEXAFS and Vibrational Spectroscopic Studies

Abstract

Single-walled nanotubes (SWNTs) produced by plasma laser vaporization (PLV) and containing oxidized surface functional groups have been studied for the first time with NEXAFS. Comparisons are made to SWNTs made by catalytic synthesis over Fe particles in high-pressure CO, called HiPco material. The results indicate that the acid purification and cutting of single-walled nanotubes with either HNO3/H2SO4 or H2O2/H2SO4 mixtures produces the oxidized groups (O/C = 5.5-6.7%), which exhibit both pi*(CO) and sigma*(CO) C K-edge NEXAFS resonances. This indicates that both carbonyl (C=O) and ether C-O-C functionalities are present. Upon heating in a vacuum to 500-600 K, the pi*(CO) resonances are observed to decrease in intensity; on heating to 1073 K, the sigma*(CO) resonances disappear as the C-O-C functional groups are decomposed. Raman spectral measurements indicate that the basic tubular structure of the SWNTs is not perturbed by heating to 1073 K, based on the invariance of the ring breathing modes upon heating. The NEXAFS studies agree well with infrared studies which show that carboxylic acid groups are thermally destroyed first, followed by the more difficult destruction of ether and quinone groups. Single-walled nanotubes produced by the HiPco process, and not treated with oxidizing acids, exhibit an O/C ratio of 1.9% and do not exhibit either pi*(CO) or sigma*(CO) resonances at the detection limit of NEXAFS. It is shown that heating (to 1073 K) of the PLV-SWNTs containing the functional groups produces C K-edge NEXAFS spectra very similar to those seen for the HiPco material. The NEXAFS spectra are calibrated against spectra measured for a number of fused-ring aromatic hydrocarbon molecules containing various types of oxidized functional groups present on the oxidized SWNTs.

Chemistry of Single-Walled Carbon Nanotubes

“…6 The aromatic ring system of the SWNTs can be disrupted by the application of extremely aggressive reagents. When sonicated 51 in the presence of strong oxidizing agents such as HNO 3 or H 2 SO 4 or a mixture of the two, 52 the nanotubes can be functionalized as carboxylic acids or quinones, [53][54][55][56] whereas sonication in organic solvents produces dangling bonds in the SWNTs that undergo further chemical reactions. 57 As expected from the foregoing discussion, the oxidative power necessary to incorporate acidic sites into carbon nanotubes varies with the tube diameter.…”

Low-Potential Nicotinamide Adenine Dinucleotide Detection at a Glassy Carbon Electrode Modified with Toluidine Blue O Functionalized Multiwall Carbon Nanotubes

“…28,29 The purification of carbon nanotubes is mainly done to remove any metal catalyst and amorphous carbon, although this yields small amounts of oxygen-containing functional groups, such as carboxylic groups. 30 However, these groups mainly are located at the open ends of the CNTs, so the hydrophobic surface of CNTs still remaining and will not affect the interaction of TBO and MWNTs. Figure 1 displays the typical morphology of the MWNTs (A) and TBO-MWNTs (B) characterized by scanning electron microscopy (SEM).…”

An efficient method for the carboxylation of few-wall carbon nanotubes with little damage to their sidewalls

“…The results indicate that KMnO 4 creates an oxidized tube that is free from amorphous carbon; however, additional steps are needed to remove the MnO 2 that is generated during the oxidation process. Kuznetsova et al [32] have demonstrated that both carbonyl and ether groups are produced when SWNTs are purified using H 2 SO 4 /HNO 3 and H 2 SO 4 /H 2 O 2 mixtures. The effect of partial chemical oxidation of SWNTs using various oxidizing agents has also been reported by Yang and co-workers [19].…”