High selectivity cum yield gel electrophoresis separation of single-walled carbon nanotubes using a chemically selective polymer dispersant

Abstract

Pure semiconducting single-walled carbon nanotubes (SWNTs) are appealing for many electronic circuits and devices, but the presence of parasitic metallic SWNTs in all as-synthesized nanotube samples makes this application elusive. Agarose gel electrophoresis (AGE) can be used to separate metallic from semiconducting SWNTs when applied in conjunction with the use of an appropriate surfactant or dispersant. To date, only sodium dodecyl sulfate (SDS) has been reported to permit considerable separation with AGE. In this study, we report on the considerably better separation achieved using chondroitin sulfate (CS-A) as a dispersant in AGE compared with SDS-assisted AGE. The CS-A assisted AGE technique may be used to produce in a single pass semiconducting SWNTs with purity of 95%, compared with 85% purity achieved with SDS-assisted AGE for the same arc discharge nanotubes. Further, the yield of CS-A assisted AGE is about 25%, which is in the order of 5 to 10 times the yields of other reported highly selective techniques. Semiconducting SWNTs produced via CS-A/AGE were used to fabricate field effect transistors (FET) with mobilities of 2 to 8 cm2/(V s) and on/off ratios from 102 to 105, which are significantly higher than the mobility of 0.7 cm2/(V s), and on/off ratio of 104 reported for FETs made with semiconducting SWNTs produced by SDS-assisted AGE. The excellent yield-cum-purity single-pass separation is achievable with this unique chemically selective CS-A dispersant with AGE because of its ability to wrap the nanotubes well, high degree of sulfation making the nanotube/CS-A hybrid highly charged and amine functionality resulting in preselectivity of metallic nanotubes, causing the latter to migrate much more effectively under a uniform electric field.