Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes

Abstract

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.

Aqueous two-polymer phase extraction of single-wall carbon nanotubes using surfactants

“…29 Fortunately, narrow groupings of (n,m) species are readily separable with only 2 to 3 separation steps, even for larger, >1.5 nm diameter SWCNTs, at bench scale by hand. 19,45 These sub-populations should then succumb to sequential application of additional ATPE step if the partition coefficients vary by even 5% as in classical separations such as distillation. Unfortunately, these small steps, and difficulty in rapid assessment of progress, are tedious to perform in practice, leaving purication of large diameter species to heroic efforts.…”

Separation of Specific Single-Enantiomer Single-Wall Carbon Nanotubes in the Large-Diameter Regime

“…Much effort, including a combination of both selective growth and a wealth of processing techniques, , has enabled the preparation of SWCNT populations with tailored diameter, length, wall number and wall type, , electronic properties, and chirality (species) . Notably, the development of W 6 Co 7 , Mo 2 C, and WC catalysts and separation methods such as polymer extraction, − gel permeation chromatography, − density gradient ultracentrifugation (DGU), ,− aqueous two-phase extraction (ATPE), − and selective DNA strands have all allowed for rapid progress in this area. In the small SWCNT diameter regime ( D t = 0.8 to 1 nm), these techniques have now made accessible a vast library of chirality-pure SWCNTs and have even allowed for the discrimination of single enantiomers. ,− Regrettably, however, for SWCNT diameters larger than 1 nm, the list of isolated single-chiral species is dramatically smaller, and enantiomer enrichment has yet to be demonstrated …”

Polymethyl(1–Butyric acidyl)silane–Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single–Walled Carbon Nanotubes

“…Even though some dispersing agents display a selective dispersion for metallic or semiconducting SWNTs to some extent, the achieved dispersions are still mixtures of them with various chiral indices. For effective sorting of individually dispersed SWNTs, researchers turn to gel chromatography [40,41], two-phase aqueous extraction [42,43], dielectrophoresis [44,45], and density gradient ultracentrifugation (DGU) [46,47]. Among these techniques, DGU has the advantages of easy operation, large-scale separation, and universal utility for various SWNTs over the others, making it the most popular technique to separate SWNTs in line with their diameter, electronic type, chirality, or even-handedness.…”