Separation and purification of carbon nanotubes using froth flotation with three sequential pretreatment steps of catalyst oxidation, catalyst removal, and silica dissolution

Carbon nanotubes (CNTs) with a carbon content of 3% were synthesized via the disproportionation of CO over a CoMo/SiO 2 catalyst. The proposed purification technique consisted of four sequential steps: oxidative treatment, acid leaching, silica dissolution, and froth flotation. The as‐synthesized CNTs were oxidized at 250 °C before being treated with a 5‐ m HCl solution at 80 °C and a sonication time of 6 h, resulting in a catalyst removal of 90% and an increase in carbon content to 4%. For the silica dissolution, the CNTs were treated with a 0.5‐ m NaOH solution at 70 °C and a sonication time of 12 h, leading to a silica removal of 70% and an increase in carbon content to 35%. The froth flotation technique was employed to separate the CNTs from the remaining silica using two types of surfactants: linear ethoxylated alcohol with an average degree of polymerization of 7 and a linear alkyl chain of 12–14 carbon number (Surfonic L24‐7) and sodium dodecyl benzene sulfonate (SDBS). The separation performance was maximized at a Surfonic L24‐7‐to‐SDBS molar ratio of 1 : 12 with a total surfactant concentration of 230 mg/L, yielding a carbon content of 76%. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.