Centrifugal purification of chemically modified single-walled carbon nanotubes

A wet chemistry procedure which couples chemical functionalization and a dispersion-centrifugation cycle was applied to the dissolution and purification of as-prepared electric-arc produced single-walled carbon nanotubes (SWNTs). It is validated that K2S2O8 treatment generates hydrophilic groups such as carboxyl and hydroxyl on the surfaces of varying carbons, whereas such treatment also causes no severe destruction on the structure of SWNTs. Amidation of the K2S2O8-treated and mixed acids shortened SWNTs leads them largely soluble in tetrahydrofuran (THF) or other organic solvents. The soluble sample was fractionated via a dispersion-centrifugation cycle and highly pure and well-separated SWNTs were successfully obtained in the middle fractions. The purity of the centrifugally fractionated samples is qualitatively estimated with Raman spectroscopy, scanning electron microscope (SEM), and atomic force microscopy (AFM). Quantitative optical absorption spectroscopy and thermogravimetric analysis show that about 60% nanotubes in the starting material are transferred into liquid phase and the carbonaceous purity reaches as high as 129% of a reference sample R2, an 'impurity-free' fragment of soot directly from the arc chamber.