Raman Studies of Solutions of Single-Wall Carbon Nanotube Salts

Abstract

Polyelectrolyte solutions of Na-doped single-wall carbon nanotube (SWNT) salts are studied by Raman spectroscopy. Their Raman signature is first compared to undoped SWNT suspensions and dry alkali-doped SWNT powders, and the results indicate that the nanotube solutions consist of heavily doped (charged) SWNT. Raman signature of doping is then used to monitor in situ the oxidation reaction of the nanotube salt solutions upon exposure to air and to an acceptor molecule (benzoquinone). The results indicate a direct charge-transfer reaction from the acceptor molecule to the SWNT, leading to their gradual charge neutralization and eventual precipitation in solution. The results are consistent with a simple redox titration process occurring at the thermodynamical equilibrium.

About the solubility of reduced SWCNT in DMSO

“…Incidentally, the increase in the D-band in the Raman spectrum obtained from reduced SWCNT subjected to DMSO is clearly apparent in figure 2 of [1]b u tw a s left without further explanation. The D-band increase was noted and somewhat discussed in [2] but was attributed to Na intercalation. Also noted in [2] is the stability of the dispersion even after oxidation which was attributed to a number of possible factors, none of them including chemical functionalization as we demonstrate here.…”

“…The D-band increase was noted and somewhat discussed in [2] but was attributed to Na intercalation. Also noted in [2] is the stability of the dispersion even after oxidation which was attributed to a number of possible factors, none of them including chemical functionalization as we demonstrate here.…”

“…Furthermore, they concluded that the thus reduced SWCNT dissolve spontaneously in polar aprotic solvents such as sulfolane, dimethyl sulfoxide (DMSO), Nmethylformamide (NMF), dimethylformamide (DMF) and 1-methyl-2-pyrrolidone. Indeed, these solvents do appear to dissolve reduced SWCNT and therefore they have been used to conduct chemistry and processing of reduced SWCNT with the expectation that pristine neutral SWCNT can be recovered through oxidation by exposure to air [2,3]. Here we report our discovery of the solubility and reactivity of reduced SWCNT in DMSO solution.…”

Carbon Nanotube–Purification and Sorting Protocols

“…Other techniques such as thermal gravimetric analysis (TGA), near-infrared (NIR) spectroscopy 84 , Raman spectroscopy [85][86][87][88][89][90] , were introduced for quantitative analysis. The TGA of CNT sample is carried out in air/O 2 to study oxidative response.…”

“…But one needs to be very careful while taking spectra as both spectroscopic techniques are dependent on environmental conditions. Anglaret 87 ,et al, observed monotonic Raman frequency upshift and intensity reduction when a laser spot was moved along the same SWNT. Thus instead of single characterisation technique a combination of microscopic and spectroscopic techniques are used to verify the results such as TEM-Raman 90 or TEM-NIR.…”