Purification of Carbon Nanotubes for Dissolution in Chlorosulfonic Acid

Carbon nanotubes (CNTs) can be scalably processed into high-performance fiber with a low environmental footprint by solution spinning from chlorosulfonic acid (CSA). CNTs are produced by numerous manufacturers, but CNTs typically need to undergo purification to improve solubility in CSA. For over two decades, oxidative techniques have been used to remove amorphous carbon species to improve CNT dissolution in acid. However, more recent work has attributed the improved solubility after single-walled carbon nanotube (SWCNT) oxidation is due to the inclusion of oxygen groups in the sidewall of the SWCNT. Here, we refute the recent claim that oxidation incorporates oxygen into the sidewall of CNTs to improve CNT dissolution to CSA. Instead, we provide experimental evidence in support of classical purification literature: at the appropriate time and temperature, oxidation removes amorphous carbon shells and defective SWCNTs without oxidizing the SWCNT sidewall. Once these amorphous carbon shells are removed, CSA can access and protonate the sp2-bonded carbon sites, which results in SWCNT dissolution. Additionally, we explore how oxidation conditions impact SWCNT aspect ratio (length of CNT divided by CNT diameter), which directly controls macroscale fiber properties.