Role of Surfactants and Salt in Aqueous Two-Phase Separation of Carbon Nanotubes toward Simple Chirality Isolation

Abstract

Aqueous two-phase extraction has recently been demonstrated as a new method to separate single-wall carbon nanotubes (SWCNTs). In this work, we determined that the mechanism of separation is driven by the hydrophobicity of the surfactant, or combination of surfactants, at the SWCNT surface. This knowledge allowed us to develop a simple approach for obtaining highly enriched single-chirality suspensions in only 1 or 2 steps. These results were obtained by strategically combining multiple surfactants with different diameter-dependent binding affinities for SWCNTs and salts that readjust the surfactant structure within the mixed micelle surrounding the SWCNTs. The procedure is successfully applied to SWCNTs from different sources (CoMoCAT and HiPco) with various diameter distributions (from 0.53 to 1.2 nm). Each separation step is characterized by optical absorption, resonant Raman, and photoluminescence excitation spectroscopies. By determining the SWCNT sorting mechanism, we were able to develop a new set of parameters that separated another chirality.

Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes

“…Additionally, enrichment of the (5,5) (from CoMoCAT SG65EX source material) and (8,8) (from Rice-produced HiPco 107.1r source material) structures was provided via the recently introduced aqueous two-phase extraction technique (ATPE) [21][22][23] . Complementary results obtained on samples enriched from HiPco source material (batch HPR 189.2) using a density gradient ultracentrifugation (DGU) approach 19,24 are presented in the supporting material 25 .…”

Diameter dependence of TO phonon frequencies and the Kohn anomaly in armchair single-wall carbon nanotubes

“…1. The DGU method provides an enrichment of armchair chiralities in general, showing enrichment in armchair species (6,6)- (10,10) (6,6) and (7,7) enriched via DNA-IEX and (5,5) via ATPE using CoMoCAT SG65 and SG65i material, respectively. Finally, ATPE was also used to generate a (6,6)-enriched sample from CoMoCAT SG65i material [absorption spectrum Fig.…”

Quasiphase Transition in a Single File of Water Molecules Encapsulated in (6,5) Carbon Nanotubes Observed by Temperature-Dependent Photoluminescence Spectroscopy

“…Recent advances in chiral sorting of carbon nanotubes, [42][43][44] combined with the extreme sensitivity (and chiral selectivity [45]) of optical spectroscopy for the filling of SWCNTs with various molecules, [13][14][15][16] provides an ideal platform for studying the thermodynamic properties of single files of water molecules confined in SWCNTs with a well-defined, small diameter. In this Letter, we report temperature-dependent photoluminescence (PL) spectroscopy of empty and water-filled sorted, single-chirality (6,5) SWCNTs.…”

“…[13,47] From this suspension, (6,5) SWCNTs were extracted by a two-step acqueous twophase procedure. [43,44] The resulting chirality-sorted nanotube suspension was first dialyzed to 1%wt/V DOC, using a stirred ultrafiltration cell, and subsequently density gradient ultracentrifugation was used to separate the empty and water-filled (6,5) SWCNTs. [48,49] Similar to previous work [13][14][15][16]48, 49] a combination of optical absorption, resonant Raman and PL-excitation spectroscopy was used to asign the composition of each of the fractions, see SM [46] indicating that the amount of filled SWCNTs are negligible in the empty fraction (< 3.7%), while in the PL spectra of the filled fraction a small contribution of empty SWCNTs can be observed, with an amplitude of ∼ 20% of the total PL intensity.…”