Separation of Double-Wall Carbon Nanotubes by Electronic Type and Diameter
Jason K. Streit, Stephanie Lam, Yanmei Piao, Angela R. Hight Walker, Jeffrey A. Fagan, Ming Zheng
In this work, we introduce a new procedure for the efficient isolation and subsequent separation of double-wall carbon nanotubes (DWCNTs). A simplified rate zonal ultracentrifugation (RZU) process is first applied to obtain samples of highly enriched DWCNTs from a raw carbon nanotube material that has both single- and double-wall tubes. Using the purified DWCNT suspension, we demonstrate for the first time that DWCNTs can be further processed using aqueous two-phase extraction (ATPE) for the effective sequential separation by electronic structure and diameter. Additionally, we introduce analytical ultracentrifugation (AUC) as a new method of DWCNT characterization, capable of providing quantitative estimation of single-wall carbon nanotube (SWCNT) and DWCNT composition. Results from AUC analysis are utilized to compare two DWCNT separation schemes. We find that RZU processing followed by sequential bandgap and diameter sorting via ATPE provides samples of high DWCNT enrichment, whereas single-step redox sorting of the same raw material through ATPE yields mixture of SWCNTs and DWCNTs of similar diameter and electronic character. The presented methods offer significant advancement in DWCNT processing and separation while also providing a promising alternative for DWCNT sample analysis.