Systematic comparison of conventional and reductive single-walled carbon nanotube purifications

As-synthesised single-walled carbon nanotubes (SWCNTs) are often contaminated with amorphous carbon and residual catalyst particles. These contaminants have a detrimental effect on the effective mechanical and electronic properties, limiting their performance in many applications. A comparative series of SWCNT purifications including acid treatments, gas phase purifications and recently-developed reductive purifications have been conducted using a single commercial SWCNT type (Tuball™). Each of the purification procedures was selected for its potential scalability to bulk quantities and evaluated for the extent of impurity removal, SWCNT damage, and overall yield. Raman spectra confirmed that reductive purification using sodium naphthalide gave the lowest D/G ratio, suggesting that the sp2 carbon framework was most effectively preserved, whilst removing a large proportion (∼74%) of the metal impurities. Conversely, nitric acid treatment was most effective at removing virtually all the metal impurities, but the sp2 carbon framework was most heavily damaged in the process. The development of scalable, one pot, reductive separations provides a useful new approach to SWCNT purification.