Synthesis of (9,8) single-walled carbon nanotubes on CoSO4/SiO2 catalysts: The effect of Co mass loadings

Abstract

Selective synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chirality distribution at high production yield is critical to realize their applications in electronics and medicine. However, there is a significant trade-off between chirality selectivity and SWCNT yield. In this study, a series of CoSO4/SiO2 catalysts containing from 1 to 9 wt% of Co were prepared to systematically study how Co mass loadings affect the chirality selectivity and carbon production yield. SWCNTs were analyzed by spectroscopies and microscopes, while catalysts at three stages of SWCNT synthesis were studied by multiple characterization tools. Our results show that all CoSO4/SiO2 catalysts can grow (9,8) tubes. Specifically, the catalyst containing 3 wt% Co has the highest yield of (9,8) tubes, which grow from metallic Co particles with a size of around 1.2 nm. These Co particles are in-situ produced by reducing small Co9S8 particles of 2 nm in size, while unreduced Co9S8 particles help to stabilize metallic Co particles. High Co mass loadings lead to the formation of large Co and Co9S8 particles, which favor the formation of graphitic carbon and multi-walled carbon nanotubes. These findings provide useful insights to guide the development of novel catalysts for the chiral selective production of SWCNTs.