Purification of Single-Walled Carbon Nanotubes (SWNTs) by Acid Leaching, NaOH Dissolution, and Froth Flotation

Abstract

The SWNTs with a carbon content of approximately 3% were synthesized via the disproportionation of CO over a CoMo/SiO2 catalyst. The three sequential steps, including acid treatment, silica dissolution, and froth flotation, were proposed for the purification of the as-synthesized SWNTs. The pretreatment step for the catalyst removal by acid leaching was optimized at an HCl concentration of 6 M, 50°C, and a sonication time of 3 h, corresponding to the Co and Mo removals of 84% and 44%, respectively. For the silica dissolution, the SWNTs sample after the acid leaching step was treated with a 5 M NaOH solution at 50°C and a sonication time of 3 h, leading to a silica removal of 54%. The froth flotation was employed to separate the SWNTs from the remaining silica using SDBS as an anionic frother. The process performance was maximized at an SDBS concentration of 0.1 × CMC, an air flow rate of 120 cm3/min, and a solution pH of 5, yielding a carbon content of the purified SWNTs of 71%. It was also found that the proposed technique successfully purified the as-synthesized SWNTs sample without damaging its nanostructure.