Single-Walled Carbon Nanotubes Prepared by Large-Scale Induction Thermal Plasma Process: Synthesis, Characterization, and Purification

Characterization and purification studies have been performed on the single-walled carbon nanotubes (SWNTs), prepared by the large-scale (i.e., at production rates of ∼100 g h−1) induction thermal plasma process. The main impurities present in the as-produced soot materials are first identified by various material analyses and turn out to be amorphous carbon, graphitic carbon particles, and metal/metal−oxide catalysts, but without significant content of fullerenes. In particular, the amounts of graphitic particles present were high in comparison with those of other plasma arc or laser-grown SWNTs, and it is believed that these graphitic particles mainly originate from the remains of the feedstock materials. On the basis of this observation, different purification protocols have been explored by combining the two-step processes of thermal oxidation in air and liquid oxidation in a variety of acids. At each step of the purification, the changes in the SWNT samples are monitored by various analytical techniques, and the results reveal that the air oxidation at 350 °C for 1 h, followed by refluxing in 7 M HNO3 for 6 h, provides for the best efficiency in conducting the purification of the thermal plasma-grown SWNT. The material properties of the purified samples, such as the electrical resistivity and the specific surface area (SSA), have also been analyzed by using the Brunauer−Emmett−Teller (BET) and the four-probe methods, the measured values being ∼500 m2 g−1 and ∼2 × 10−3 Ω cm, respectively.