The influence of bimetallic catalyst composition on single-walled carbon nanotube yield

We show that the yield of single-walled carbon nanotubes (SWCNTs) grown with bimetallic catalysts is a strong function of their atomic-scale composition. A series of compositionally-tuned Ni(x)Fei(1-x) bimetallic catalysts with a constant mean diameter of 2.0 nm are used to catalyze the growth of nanotubes via a floating catalyst method. Increasing the Fe content in the catalysts is found to lower the fraction of SWCNTs in the collected as-grown product. Based on a simple surface-to-volume model, these results are explained by the higher carbon solubility of Fe compared to Ni which results in a larger amount of carbon precipitation and the formation of multi-walled tubes when the nanotubes are nucleated from catalysts with high Fe content. Overall, our study demonstrates that the size and composition of bimetallic catalysts must be precisely controlled to obtain high yields of SWCNTs for large-scale production. (C) 2011 Elsevier Ltd. All rights reserved.