Scalable Method for the Reductive Dissolution, Purification, and Separation of Single-Walled Carbon Nanotubes

Abstract

As synthesized, bulk singlewalled carbon nanotube (SWNT) samples are typically highly agglomerated and heterogeneous. However, their most promising applications require the isolation of individualized, purified nanotubes, often with specific optoelectronic characteristics. A wide range of dispersion and separation techniques have been developed, but the use of sonication or ultracentrifugation imposes severe limits on scalability and may introduce damage. Here, we demonstrate a new, intrinsically scalable method for SWNT dispersion and separation, using reductive treatment in sodium metal-ammonia solutions, optionally followed by selective dissolution in a polar aprotic organic solvent. In situ small-angle neutron scattering demonstrates the presence of dissolved, unbundled SWNTs in solution, at concentrations reaching at least 2 mg/mL; the ability to isolate individual nanotubes is confirmed by atomic force microscopy. Spectroscopy data suggest that the soluble fraction contains predominately large metallic nanotubes; a potential new mechanism for nanotube separation is proposed. In addition, the G/D ratios observed during the dissolution sequence, as a function of metal: carbon ratio, demonstrate a new purification method for removing carbonaceous impurities from pristine SWNTs, which avoids traditional, damaging, competitive oxidation reactions.

Practical applications of small-angle neutron scattering

“…106,107,109 In the case shown in Fig. 8, the slope in the high Q of 1.0 disappearing into the background strongly indicates extensive unbundling of the tubes.…”

Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

“…[18][19][20] An alternative ink fabrication method known as reductive dissolution has been developed to produce solutions of highly dispersed and unbroken SWNTs. [21][22][23] In these processes, SWNTs are chemically reduced in the presence of an alkali metal either in liquid ammonia or in a naphthalenide solution in tetrahydrofuran. The reactive media is then removed, leaving a nanotubide salt that dissolves with only gentle mechanical stirring, without sonication, in a polar organic solvent such as dimethylsulfoxide (DMSO) or dimethylformamide.…”

“…CVD-grown SWNTs were purified and processed at Linde Nanomaterials. The organic SWNT ink was prepared using the liquid ammonia reductive dissolution technique developed by Fogden et al 21,22 In this process, SWNTs were chemically reduced in the presence of sodium and liquid ammonia, and the resulting nanotubide salt was dissolved in DMSO with magnetic stirring. Processing and deposition of the organic ink was performed in a glovebox; after deposition by spray coating, the films were maintained under clean dry air overnight to oxidize the nanotubide to the neutral species.…”

Giant cationic polyelectrolytes generated via electrochemical oxidation of single-walled carbon nanotubes

“…In particular, charging provides a means to process single-walled carbon nanotubes (SWCNTs), whilst avoiding aggressive sonication and time consuming centrifugation processes. Anionic nanotube (nanotubide) polyelectrolytes have been generated using reductive chemical (alkali metal naphthalide/THF 3 , alkali metal/ liquid ammonia 4,5 ) and electrochemical approaches 6 . The covalent chemistry of reduced carbon nanomaterials has also been studied extensively, extending to a whole library of electrophilic addition and radical-based surface modifications [7][8][9] that can be tailored to specific applications.…”