Probing Carbon Nanotube–Surfactant Interactions with Two-Dimensional DOSY NMR

Abstract

Two-dimensional diffusion ordered spectroscopy (2D DOSY) NMR was used to probe the micellar structure of sodium dodecyl sulfate (SDS) and sodium cholate (SC) in aqueous solutions with and without semiconducting and metallic single-walled carbon nanotubes (SWCNTs). The solutions contain SDS and SC at weight ratios of 1:4 and 3:2, the ratios commonly used to isolate semiconducting and metallic SWCNTs through density gradient ultracentrifugation (DGU). These results show that the coverage of surfactant on the semiconducting and metallic SWCNTs is nearly identical in the 1:4 surfactant mixture, and a lower degree of bundling is responsible for the greater buoyancy of semiconducting SWCNTs. In the 3:2 surfactant mixture, the metallic SWCNTs are only encapsulated in SC while the semiconducting SWCNTs remain encapsulated in a poorly packed two-surfactant micelle, leading to a large buoyant density difference between the electronic species. This work provides insight into future directions to increase the purity of semiconducting and metallic SWCNTs sorted through DGU and demonstrates the utility of 2D DOSY NMR in probing SWCNT-surfactant complexes.

Assembly and Electronic Applications of Colloidal Nanomaterials

“…Depending on the density of the targeted nanomaterial, the original nanomaterial dispersion is either layered at the top or bottom of the density gradient. [132,189] For example, SWCNTs with metallic or semiconducting purities in excess of 99% have been prepared and are available commercially. [185] Furthermore, by exploiting the differential affinity of sodium cholate and sodium dodecyl sulfate for metallic and semiconducting SWCNTs, the ratio of these two surfactants has been optimized to realize high-purity metallic or semiconducting SWCNT dispersions.…”

“…[185] Furthermore, by exploiting the differential affinity of sodium cholate and sodium dodecyl sulfate for metallic and semiconducting SWCNTs, the ratio of these two surfactants has been optimized to realize high-purity metallic or semiconducting SWCNT dispersions. [132,189] For example, SWCNTs with metallic or semiconducting purities in excess of 99% have been prepared and are available commercially. [190] In addition, isopycnic DGU has been extended to the sorting of 2D nanomaterials, such as graphene, [119] h-BN ( Figure 3E,F), [121] and 2D TMDs, [125] using iodixanol-based density-gradient media.…”

Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions

“…The resulting aqueous dispersions were characterized for semiconducting purity. Surfactants were removed from the SWCNTs by flocculating in ethanol, filtering onto a nylon membrane, and rinsing the membrane in acetone and IPA33. The resulting dry film was weighed and retained for later use.…”

High Precision Fractionator for Use with Density Gradient Ultracentrifugation

“…Since it was introduced into the SWCNT community in 2006, density gradient ultracentrifugation (DGU) has become widely established as an effective method for such sorting. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] In DGU processing, mixtures of individualized, surfactant-suspended SWCNTs are placed in a centrifuge tube filled with a medium that varies in density from top to bottom. Under prolonged centrifugation, the different nanotube structures migrate to form distinct layers at isopycnic points, positions where their specific buoyant density matches the density of the surrounding medium.…”

“…1,6,9,[20][21] In our experience, these approaches do not provide the fractionation convenience and performance needed to realize the separation potential of SWCNT DGU processing. We describe here the construction and operation of a novel, high precision fractionator designed specifically for automated extraction of layers from DGU tubes.…”