Epoxidation and Deoxygenation of Single-Walled Carbon Nanotubes:  Quantification of Epoxide Defects

Abstract

Epoxidation of single-walled carbon nanotubes (SWNTs) may be carried out by the reaction of SWNTs with either trifluorodimethyldioxirane or 3-chloroperoxybenzoic acid; the resulting O-SWNTs are spectroscopically similar to those formed by ozonolysis. Quantification of the epoxide substituents is possible through the catalytic de-epoxidation reaction using MeReO3/PPh3 and the 31P NMR spectroscopy. The de-epoxidation methodology may be used to determine that wet air oxidation is preferable to either acid or O2/SF6 purification. We have demonstrated that previously assumed "pure" SWNTs are actually "doped" to a level of at least 1 oxygen per 250 carbon atoms.

Catalyst Residue and Oxygen Species Inhibition of the Formation of Hexahapto-Metal Complexes of Group 6 Metals on Single-Walled Carbon Nanotubes

“…The analysis of the high resolution O 1s XPS signal of the as received tubes (Figure 4) shows that the oxygen containing species comprise iron oxides (530.3 eV), in addition to a range of oxygen moieties associated with the side walls of the SWCNTs. Prior studies suggest that the latter are due to the single and double bonds that oxygen makes to carbon in carboxylic acid, ketone, epoxide, and alcohol groups [16,29]. Annealing the tubes in argon or under vacuum reduces these oxygen moieties relative to the iron oxide peak (Table 3) epoxide, and alcohol groups [16,29].…”

“…Prior studies suggest that the latter are due to the single and double bonds that oxygen makes to carbon in carboxylic acid, ketone, epoxide, and alcohol groups [16,29]. Annealing the tubes in argon or under vacuum reduces these oxygen moieties relative to the iron oxide peak (Table 3) epoxide, and alcohol groups [16,29]. Annealing the tubes in argon or under vacuum reduces these oxygen moieties relative to the iron oxide peak (Table 3) An analysis of the Fe 2p3/2 signals ( Figure 5 and Table 3) shows that the majority (ca.…”

“…In reality, SWCNTs comprise a myriad of species that are dependent on the route of their synthesis and the method of purification. Open termini contain oxygen functional groups such as hydroxides and carboxylic acids [15], while side-walls have significant concentrations of epoxides [16]. The concentration of the latter functional group can be one oxygen per 123 carbon atoms in as prepared samples and as high as one oxygen per 105 carbon atoms in "purified" samples [16].…”

“…Open termini contain oxygen functional groups such as hydroxides and carboxylic acids [15], while side-walls have significant concentrations of epoxides [16]. The concentration of the latter functional group can be one oxygen per 123 carbon atoms in as prepared samples and as high as one oxygen per 105 carbon atoms in "purified" samples [16]. Clearly, this dramatically alters the chemical nature of the surface of the SWCNT, although this is often used as an advantage when reacting species at the surface [17,18].…”

Photophysics of Individual Single-Walled Carbon Nanotubes

“…212 In addition, the presence of defect sites, impurities, and oxygen is expected to decrease the QY via hole doping, which effectively removes an electron from the valence band and provides a trap for the excited state. 213,219 Another conjecture is that these processes may accelerate intersystem crossing to triplet states, which sequesters excited state carriers and lowers the observed QY. 220 Promisingly, SWNT sample quality is continuing to improve, and tailoring the environment immediately surrounding SWNTs could make it possible to suppress competing processes that arise from extrinsic factors, enabling more carriers to decay by radiative relaxation pathways.…”