Controlled purification of single-walled carbon nanotube films by use of selective oxidation and near-IR spectroscopy

Electric-arc produced as-prepared single-walled carbon nanotube (AP-SW-NT) films have been purified by a selective oxidation process. The purification is monitored by near-infrared (NIR) spectroscopy, which gives a quantitative estimate of relative purities. This technique also gives an estimate of the change in relative amounts of SWNTs and amorphous carbon impurities after each purification step, thereby providing accurate and selective control over the oxidation process. Oxidation was carried out by reaction in flowing oxygen at different temperatures and for different durations of time; the purity was evaluated after each oxidation step and compared to the starting as-prepared film. The purities and amounts of SWNTs and carbonaceous impurities were monitored as a function of oxidation temperature and time. Optimization of the process allowed a 3-fold improvement in the AP-SWNT purity with almost quantitative retention of the SWNT portion of the sample. A purification efficiency is defined, which is expressed as the ratio of the fraction of SWNTs retained to the fraction of impurities retained in the sample after application of the purification process.