Freon-CO₂-assisted purification of single-walled carbon nanotubes

With the rapidly growing applications, efficient purification of single-walled carbon nanotubes (SWCNTs) has become one of the key problems. This paper proposes Freon-CO₂-assisted purification of SWCNTs, where CO₂ can oxidize the graphitized carbon layer to expose iron (Fe) impurities, while the chlorine from Freon can react with the Fe impurities to form low-boiling-point metal chlorides that can be eliminated in a gas stream. After an acid washing with a very small amount of hydrochloric acid, the last remaining metal impurities are removed and highly pure SWCNTs are produced. Compared with traditional strong-acid-oxidation purification or high-temperature-vacuum purification, this method can maintain the structure and length of the SWCNTs. Raman spectra show that an I _G/I _D ratio of more than 100 can be obtained. This purification method can maintain the microstructure and excellent properties of SWCNTs and provide a solution for the preparation of high-quality SWCNTs to exert their properties.