Exploiting the Physiochemical Interactions between Single-Walled Carbon Nanotubes and Hydrogel Microspheres To Afford Chirally Pure Nanotubes

Abstract

Single-walled carbon-nanotubes (SWNTs) exhibit unique electronic, optical, and mechanical properties; however, a narrow availability of chirally pure (single electronic structure) material can limit effective integration within novel devices and schemes. This work focuses on understanding, modeling, and advancing methodology used to generate preparative quantities of single-chirality SWNT: the iterative adsorption/desorption of SWNT from aqueous surfactant suspensions to/from hydrogel microspheres. Commercially available hydrogel microspheres (Sephacryl S200) were sorted by radius and exposed to SWNT, affording a direct correlation between microsphere surface area and quantity of SWNT adsorbed using differential absorbance spectroscopy. This relationship elucidates a SWNT/gel purification scheme interaction mechanism exclusively involving the gel surface. High-concentration surfactant was used to elute SWNT from the gel with desorption efficiencies dependent on both SWNT chirality and hydrogel microsphere radius, ranging from 25–45%. A thermodynamic model for SWNT desorption that accounts for hydrogel microsphere curvature effects is presented and suggests that (when compared with experimental data) SWNT with greater than ∼41% of their length adsorbed to a hydrogel surface bind irreversibly, while others are desorbed in the presence of high-concentration surfactant. These findings inspired the generation and application of mechanically fractured hydrogel microspheres (exhibiting greater surface area) for use as SWNT purification media in per-iteration quantities far less than traditional gels. A 10-iteration SWNT purification procedure demonstrated a marked improvement in process efficiency, as mechanically fractured gels afford a 10-fold reduction in gel-media use (the major expense of the process) while yielding equivalent SWNT purification.

Gel Chromatography for Separation of Single-Walled Carbon Nanotubes

“…Interestingly, grinding the gel and increasing the gel surface area could achieve the same effect as using a large amount of the gel. For example, when 21 mg of Sephacryl S-200 and 2.1 mg of mechanically fractioned Sephacryl S-200 were used as mediums for gel chromatography, a similar level of chirality separation ability was observed, despite the 10-fold mass difference between the two media, suggesting that the cost of the gel filtration process can be greatly reduced [ 87 ].…”

Mechanism and Mitigation of Irreversible Material Loss within Gel-Based Single-Walled Carbon Nanotube Purification Schemes

“…In terms of the introduction of neat vs reclaimed SWCNTs to either neat or reclaimed gel, the SWCNT uptake data in Table 1 is consistent with previous interpretations of how amorphous carbon (a-C) generated during the sonication process outcompetes SWCNTs for Sephacryl bindings sites due to its larger binding rate constant. 29 Because a-C does not elute from Sephacryl in appreciable amounts upon addition of 175 mM SDS, the reclaimed SWCNTs employed here are expected to be absent of a-C, while a-C generated during sonication remains present within the neat SWCNT suspension. This assumption is supported by the relatively large a-C background signal 61 in the absorbance spectrum of the neat SWCNTs, while that of the reclaimed SWCNTs remains relatively flat, Figure 5A.…”

“…Importantly, addition of an equimolar quantity of the most kosmotropic agent studied, NaF, increases elution efficiency over the SDS control from 54 to 88%, a significant increase and the highest elution efficiency reported in this work or elsewhere. 29,30 This demonstration of extremely efficient elution using kosmotropic salts represents a novel method to significantly increase process efficiency and potential commercial viability of gel-based SWCNT purification methods.…”

“…A typical surfactant-mediated SWCNT/gel interaction first involved preparation of fritted plastic columns, one which acts as a control absent of gel and one or more containing equivalent surface areas 29 of spherical Sephacryl gel beads, each of which was equilibrated with neat surfactant prior to SWCNT interaction. Given that the SWCNT suspensions passed through a column are diluted by collection of the neat surfactant wash volume, Figure 1C, the post-centrifugation SWCNT suspension was diluted with aqueous surfactant solution to a maximum optical density (OD) of ∼3.0 (1 cm path length) in the E 11 region, divided to equal volume aliquots, and passed through each column multiple times to ensure maximum uptake of SWCNTs.…”

“…44,47,48 Recently, our group demonstrated that differential spectroscopy can be employed to quantitatively track both the total and chirality-dependent amount of SWCNT introduced to, adsorbed to, eluted from, and irreversibly bound to beds of Sephacryl S200. 29,30,45 Therefore, although system parameters such as surfactant concentration, 44 SWCNT concentration, 37, 49 and presence of salts 41 have previously been studied with respect to gel-based SWCNT purification, this report provides additional insight through both complete quantitative tracking of SWCNTs throughout the SWCNT/gel interaction process; with a focus on novel experiments that provide mechanistic insight into how and why SWCNTs bind in an irreversibly bound state (IrBS) vs. a reversibly bound state (ReBS).…”