A multi-step strategy for cutting and purification of single-walled carbon nanotubes Original Research Article

A multi-step procedure has been developed to cut and purify single-walled carbon nanotubes (SWCNTs) from the pristine soot synthesized by catalytic chemical vapor decomposition, which contains significant amount of multiwalled carbon nanotube (MWCNT) impurities. The procedure involves refluxing in dilute HNO3 solution followed by (NH4)2S2O8/H2SO4 ultrasonication and a novel ammonia heat treatment step. The metal impurities are removed in the HNO3 refluxing step. In the (NH4)2S2O8/H2SO4 treatment step, the SWCNTs are cut uniformly into micrometer long, while the MWCNTs are selectively cut into very short curled pieces. These short MWCNT pieces and the amorphous carbon impurities are partly removed in the (NH4)2S2O8/H2SO4 treatment step, and most of them are finally removed by the final ammonia heat treatment. The ammonia heat treatment step also recovers the structures of SWCNTs by healing defects on the sidewall. The final SWCNT products have purity higher than 95%, a length distribution between 1 and 2 μm, and very few defects.