Low temperature assembly of fullerene arrays in single-walled carbon nanotubes using supercritical fluids

Molecules assembled inside nanotubes to form 1D arrays exhibit functional properties different to the bulk crystal and have been proposed for many applications ranging from catalysis to quantum computing. We have discovered that single-walled carbon nanotubes can be efficiently filled with fullerenes in supercritical fluids at temperatures as low as 30–50 °C. Despite the low solubility of fullerenes in supercritical fluids, the nanotube filling was particularly effective in supercritical carbon dioxide producing Cn@SWNT structures in 70% yield at 50 °C. This method was also applied for functionalized and endohedral fullerenes and allows insertion of thermally unstable molecules which would be impossible to insert in nanotubes using standard techniques. We discuss the advantages of using supercritical fluids as compared to conventional solvents and propose mechanisms for fullerene encapsulation at low temperatures.