Single-Walled Carbon Nanotube Chiral Selectivity Exhibited by Commercially Available Hydrogels of Varying Composition

Abstract

Despite the commercial availability of many different hydrogel formulations, the effective gel-based purification of single-walled carbon nanotubes (SWNT) remains exclusive to the gel Sephacryl S-200. In this study, 12 commercially available gels and two custom-synthesized gels were investigated for their ability to effectively purify SWNT, as determined through quantification of SWNT adsorption, elution, chiral selectivity, and overall process efficiency. The ability of each gel to separate SWNT was found to correlate with physiochemical properties, such as hydrogel pore size, the presence of ionic ligands, and both polysaccharide backbone and cross-linker compositions. While Sephacryl S-200 demonstrated superior separation efficiency and chiral selectivity among the gels studied, Superose 6 was found to adsorb more SWNT than Sephacryl S-200 per cm2 of the gel surface area and exhibited a unique preference for the (7,3) and (7,5) SWNT chiralities, in contrast to the established selectivity of Sephacryl S-200 for the (6,5) chirality. Collectively, this work both identifies gels that exhibit unique SWNT chiral selectivity and provides insights into the rational design of gels tailored for SWNT purification.

Gel Chromatography for Separation of Single-Walled Carbon Nanotubes

“…The mechanism of unique chirality selectivity of Superose 6 has not been clearly identified yet. This selectivity was not found in other agarose-based gels with an agarose backbone and epichlorohydrin (ECH) crosslinker [ 86 ]. Sepharose 6FF, which consists of agarose and ECH similar to Superose 6, succeeded in high purity m-SWNT separation, while the purity of s-SWNT was low.…”

“…When the gel was synthesized with 1.0-4.0 mmol isomaltodextrin, SWNTs could not be separated due to the too large pore size [92]. That is, too small pores interfere with the diffusion of SWNTs, and too large pores degrade the surface interaction of SWNTs [86]; hence, a gel with an appropriate pore size must be chosen. Therefore, an appropriate gel structure must be utilized for targeted SWNT separation.…”

“…The single strands in allyl dextran-based gel make it less rigid than agarose gel. Moreover, the degree of orientation of the functional groups is lower than that of agarose gel; therefore, the former is expected to interact less with other substances [ 76 , 86 ].…”

“…The increase in the gelled area is expected to enable active interaction between SWNT and MBA within Sephacryl gels. Considering that non-Sephacryl gels do not include an amide group, it is estimated that the amide groups in MBA are at the core of SWNT–gel interaction [ 77 , 86 ].…”

“…The increase in the gelled area is expected to enable active interaction between SWNT and MBA within Sephacryl gels. Considering that non-Sephacryl gels do not include an amide group, it is estimated that the amide groups in MBA are at the core of SWNT-gel interaction[77,86].Dolan et al (2021) analyzed the effect of the APS concentration (i.e., the radical initiator) on the repulsive interaction between Sephacryl gel and SDS-SWNT assemblies (Figure 9). In addition, they explained the adsorption and desorption mechanisms of SWNTs on organosulfate by the electrostatic forces of APS.…”