Gas-phase synthesis of single-walled carbon nanotubes on catalysts producing high yield

Composite catalysts are employed for high yield gas-phase synthesis of single-walled carbon nanotubes (SWCNTs). Specifically, silicon is investigated as an additive to iron catalysts for synthesis of SWCNTs in inverse diffusion flames. While silicon is often used as a substrate in supported-catalyst processes to promote nanotube growth, this study demonstrates that it can also be beneficial for gas-phase nanotube synthesis in diffusion flames. An oxy-fuel ethylene inverse diffusion flame is employed to provide a soot-free, carbon-rich environment for nanotube growth. Iron and silicon precursors are added to the fuel stream for nucleation of iron/silicon/oxygen catalyst particles, with the amount of particle oxidation determined by the amount of oxygen-enrichment and fuel dilution at a given temperature. Under optimum conditions, nearly 90% of the catalyst particles produce single-walled carbon nanotubes as compared to less than 10% when the catalyst consists of only iron and oxygen. The effect of silicon addition is investigated through variation of the iron/silicon ratio and measurement of nanotube growth rates. Silicon is shown to primarily affect SWCNT inception with minimal influence on growth rate.