Removal of catalytic metal impurities from SWNTs by in situ chelation/SFE in supercritical carbon dioxide

Catalytic metal impurities produced in the production process of single-walled carbon nanotubes (SWNTs) can be removed by a Lewis acid-base complex and an β-diketone by in situ chelation/supercritical fluid extraction (SFE) using supercritical carbon dioxide (ScCO2) at 60 °C and 200 atm. Sonication appears to be a necessary step prior to SFE, in which it loosens and diminishes the interaction between SWNTs and metal impurities. Addition of a surfactant (SDS) significantly improves the dispersion of these SWNT bundles, which facilitates the removal of entrapped nanoparticles. Quantitative removal of nanometallic impurities from SWNTs using either SFE or sonication alone, cannot be achieved. Supercritical carbon dioxide, acting as a green solvent, can be used for the dissolution and transportation of catalytic metal impurities from SWNTs, which significantly reduces the generation of acid and organic solvent wastes in the purification processes. Methods for dissolving metallic particles in ScCO2are not only significant for potential applications in cleaning SWNTs, but also are important in many other chemical processes for various fields.