Production of single-walled carbon nanotubes by decomposition of carbon-containing gases over heterogeneous catalysts and their purification by using froth flotation

Abstract

In this study, the effects of catalyst formulation, carbon-containing gases, type of catalyst metals, and type of catalyst supports on the synthesis of single-walled carbon nanotube (SWNT) were investigated. It was found that disproportionation of carbon monoxide (CO) over Co-Mo(1:2)/SiO2 provides a maximum selectivity towards SWNTs. However, when using the Co-Re/SiO2 catalysts with CO gas, the maximum of both yield and selectivity toward SWNTs were obtained on a Co:Re ratio of 1:4, a pre-reduction temperature of 800C, and a reaction temperature of 850C. Furthermore, the catalyst characterization suggests different growth mechanisms of SWNTs on the Co-Re/SiO2 catalyst from the Co-Mo/SiO2 catalyst. To study the pruification of the as-prepared SWNTs, carbon black was first used as a representative of SWNTs and tested for separation from SiO2 by using froth flotation. The maximum carbon black recovery of 70% with an enricvhment ratio of 3.5 was achieved with an initial surfactant concentration of 75% of the critical micelle concentration (CMC), a feed solid concentration of 0.02%w/v, an air flow rate of 200 mL/min, an initial foam height of 50 cm, and no use of an electrolyte. Subsequently, the as-prepared SWNTs were experimentally purified by the NaOH leaching and then froth flotation. From the results, the maximum carbon content of 78%, with a 71% selectivity of SWNTs, was achieved at a surfactant concentration of 75% CMC, a solid loading of 1.0 mg/mL, an air flow rate of 100 mL/min, and a foam height of 22 cm. Furthermore, based on pre- and post-treatment characterization, the physical structures of SWNTs were retained after these purification steps.