Adsorbability of Single-Wall Carbon Nanotubes onto Agarose Gels Affects the Quality of the Metal/Semiconductor Separation

Although the metal/semiconductor separation of single-wall carbon nanotubes (SWCNTs) using an agarose gel column has been successfully developed, little is known about the mechanism of the separation. In this study, we examined the agarose concentration dependence of the separation using this column. The amount of SWCNTs obtained from the eluate decreased with increasing agarose concentration, indicating that a smaller amount of SWCNTs was adsorbed onto the agarose gels at higher concentrations. To clarify the relation between the adsorbability of SWCNTs and the agarose concentration, various concentrations of SWCNTs were adsorbed onto 2, 4, and 6% agarose gels in a quasi equilibrium state. The results showed that the concentration of the unadsorbed SWCNTs increased with increasing agarose concentration. By assuming that the adsorption follows the Langmuir isotherm, it was found that the effective gel volume for the adsorption was negatively correlated with the agarose concentration; specifically, the adsorbability was associated with the effective gel volume Finally, an effect of the adsorbability on the separation using the agarose gel columns was considered. With decreasing adsorbability of SWCNTs onto agarose, the amount of SWCNTs adsorbed onto the top of the column decreased and the distribution of the SWNCNTs became broadened along the column. Thus, the agarose concentration dependence of the separation quality is attributable to the adsorbability of SWCNTs onto the agarose gels.