Purification of single-wall carbon nanotubes by functionalization and ultracentrifugation

An alternative method is developed for the removal of impurity residuals (metallic nanoparticles, amorphous carbon and fullerenes) resulting from the synthesis of single wall carbon nanotubes (SWNT) by electric arc discharge. For the separation of fullerenes and amorphous carbon, an 'as grown' single wall carbon nanotube sample was subjected to leaching with a Soxhlet apparatus using toluene as solvent. Single wall carbon nanotubes were then functionalized by oxidation for forming carboxylic and hydroxyl groups to increase their solubility for their efficient dispersion with centrifugation. Oxidation was performed with H₂SO₄ and HNO₃ in the presence of potassium persulfate and later they were centrifuged at 23,000 rpm (20,000 g). After these procedures, metallic particles precipitated and the single wall carbon nanotube remained suspended on the water surface from which they were removed by decantation. The purified single wall carbon nanotube sample was characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy with results showing evidence of impurity removal with the applied procedures.