High-pressure carbon monoxide (HiPco)-synthesized single-walled carbon nanotubes (SWCNTs) have been a widely studied carbon nanomaterial for nearly two decades. It has been the de facto standard for SWCNT research, be it functionalization, separation and purification, or composites, as a result of the consistent, high-quality material that was made available at an affordable price to researchers worldwide. The recent shutdown of the HiPco reactor at Rice University has resulted in a scarcity of HiPco material available to the research community, and a new source of similar SWCNTs is desperately needed. Continued research and development on the design, materials used, and the overall process have led to a new HiPco material, referred to as NoPo HiPCO^®, as an alternative to the erstwhile Rice HiPco SWCNTs. In this work, we have compared the two HiPco materials, and aim to provide more clarity for researchers globally on the state of HiPco SWCNTs for research and applications alike in 2019.

An efficient, economic and easy method for removing 99% of catalyst particle from high pressure carbon monoxide (HiPCO) single walled carbon nanotubes (SWCNT) is reported. The experiment is carried out at low temperature followed by acid treatment. The process exploited here is oxidation of the carbon impurities to gaseous phase as CO₂ and removal of oxidized catalyst debris using acid treatment. Stability of SWCNT at these temperatures does not allow any damage to the nanotubes, however, some damage is observed which can be attributed to the oxidation of catalyst particles and their removal. The purified sample showed very less/no amount of amorphous carbon and catalyst impurities. Characterization of the material was carried out using Raman spectroscopy, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Transmission electron microscope (TEM) and Energy Dispersive Spectroscopy (EDAX). The resultant SWCNT were found to be highly pure. EDAX spectroscopy showed that the purified sample had only 0.5wt% of catalyst impurities whereas the as prepared once have 9.09wt%, also, TGA curve of the treated sample showed a very significant increase in the oxidation temperature indicating less defect and less catalyst content in the sample. The non- carbonaceous residue after purification is about 0.3%. highly efficient purification of SWCNT using the proposed method. This work provides a basis on removing the catalyst particles completely.