The purification of HiPco SWCNTs with liquid bromine at room temperature

A new procedure to purify HiPco single-walled carbon nanotubes (SWCNTs) from iron catalyst impurity is introduced. The protocol, which uses liquid bromine at room temperature (RT) as an oxidant, improves nanotube purity from iron by a factor of approximately 10, while maintaining good nanotube integrity as demonstrated by near infrared (NIR) luminescence and absorbance measurements. When HiPco SWCNTs are dissolved in RT Br₂(l) (free of O₂ and H₂O), the metallic iron impurity is quickly oxidized to its bromide salt and easily removed by aqueous washing or by washing with dilute acid. The iron content (by ICP-AE) for the purified SWCNT material was 2.8-3.6% by weight (for three different samples) for a single purification step, but could be lowered to 1.6-1.8% with an additional purification cycle. Characterization of the resulting purified SWCNT material has been achieved by TEM imaging, XPS, ICP-AE analysis, Raman spectroscopy, electronic absorption spectroscopy, and by NIR photoluminescence measurements. Finally, the new Br₂(l) purification procedure has been compared to and contrasted with other established purification procedures for HiPco SWCNTs and found to be a highly desirable alternative.