Single-walled carbon nanotubes (SWCNTs) display interesting electronic and optical properties desired for many advanced thin film applications, such as transparent conductive electrodes or thin-film transistors. Large-scale production of SWCNTs generally results in polydispersed mixtures of nanotube structures. Since SWCNT electronic character (conducting or semiconducting nature) depends on the nanotube structure, application performance is being held back by this inability to discretely control SWCNT synthesis. Although a number of post-production techniques are able to separate SWCNTs based on electronic character, diameter, or chirality, most still suffer from the disadvantage of high costs of materials, equipment, or labor intensity to be relevant for large-scale production. On the other hand, chromatographic separation has emerged as a method that is compatible with large scale separation of metallic and semiconducting SWCNTs.
In this work, SWCNTs, in an aqueous surfactant suspension of sodium dodecyl sulfate (SDS), are separated by their electronic character using a gel chromatography process. Metallic SWCNTs (m-SWCNTs) are collected as initial fractions since they show minimum interaction with the gel medium, whereas, semiconducting SWCNTs (sc- SWCNTs) remain adsorbed to the gel. The process of sc-SWCNT retention in the gel is found to be driven by the packing density of SDS around the SWCNTs. Through a series of separation experiments, it is shown that sc-SWCNTs can be eluted from the gel simply by disturbing the configuration of the SDS/SWCNT micellar structure. This is achieved by either introducing a solution containing a co-surfactant, such as sodium cholate (SC), or solutions of alkali metal ionic salts. Analysis of SWCNT suspensions by optical
absorption provides insights into the effect of changing the metal ion (M+ = Li+, Na+, and K+) in the eluting solution. Salts with smaller metal ions (e.g. Li+) require higher concentrations to achieve separation. By using salts with different anionic groups (cholate, Cl-, I-, and SCN-), it is concluded that the SWCNT separation using salt solutions is mainly driven by the cations in the solution.
Additionally, different methods for depositing separated SWCNTs on glass substrates are described. In one method, SWCNTs are first isolated from their surfactant by introducing organic solvents such as methanol or acetone to aqueous suspensions of previously separated m- and/or sc-SWCNTs. Following the induced SWCNT dissolution, desired nanomaterials can be redispersed directly in another solvent, such as methanol, for deposition on substrates. In another method, separated SWCNTs are deposited on glass substrates by the process of evaporation driven self-assembly. Different morphologies on the substrate are formed by changing the viscosity of the evaporating SWCNT/SDS suspensions. The results are described using the Stokes-Einstein equation for diffusion in one dimension.
Library of Congress Subject Headings
Carbon nanotubes--Synthesis; Alkali metals
Materials Science and Engineering (MS)
Department, Program, or Center
School of Chemistry and Materials Science (COS)
John-David R. Rocha
Christopher J. Collison
Michael S. Pierce
Ashour, Rakan F., "Use of Alkali Metal Salts to Prepare High Purity Single-Walled Carbon Nanotube Solutions and Thin Films" (2014). Thesis. Rochester Institute of Technology. Accessed from
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