Study of single-walled carbon nanotubes via the catalyst lifetime - Study of single-walled carbon nanotubes via the catalyst lifetime - HRI-US
Study of single-walled carbon nanotubes via the catalyst lifetime
The effect of catalyst composition, hydrocarbon flow rate, and synthesis temperature on the single-walled carbon nanotubes (SWCNTs) grown was studied through the evolution of the corresponding catalyst lifetime. Catalyst lifetime was estimated based on the analysis of Raman spectra of SWCNTs obtained by sequential introduction of 12CH4 and 13CH4 gases at different stages of the catalyst activity during bulk nanotube growth. We found that proper modification of the Fe catalyst composition with Mo increases the lifetime around 3 times, increasing the catalytic activity and yield of tubes grown. A 9 times increase in the hydrocarbon flow rate (from 6.4 × 10-4 to 3.8 × 10-2 CH4 mol/s g Fe) results in a decrease in the catalyst lifetime; however, the formed carbon atoms rate increases around 2 times (from 1.8 × 1021 to 3.5 × 1021 C atoms/s g Fe) increasing the nanotube growth rate (from 1.2 to 2.4 nm/s), along with improving the nanotube quality. An increase in the synthesis temperature of ΔT ∼ 140 °C shortened the lifetime around 9 times (from ∼90 to ∼10 min), increasing, however, the growth rate and resulting in a similar nanotube yield. The kinetics of nanotube formation in terms of carbon atoms diffusion ability and solubility is discussed.