Selective growth of chirality-enriched semiconducting carbon nanotubes by using bimetallic catalysts from salt precursors

Abstract

Bimetallic catalysts play important roles in the selective growth of single-walled carbon nanotubes (SWNTs). Using the simple salts (NH₄)₆W₇O₂₄·6H₂O and Co(CH₃COO)₂·4H₂O as precursors, tungsten-cobalt catalysts were prepared. The catalysts were composed of W₆Co₇ intermetallic compounds and tungsten-dispersed cobalt. With the increase of the W/Co ratio in the precursors, the content of W₆Co₇ was increased. Because the W₆Co₇ intermetallic compound can enable the chirality specified growth of SWNTs, the selectivity of the resulting SWNTs is improved at a higher W/Co ratio. At a W/Co ratio of 6 : 4 and under optimized chemical vapor deposition conditions, we realized the direct growth of semiconducting SWNTs with the purity of ∼96%, in which ∼62% are (14, 4) tubes. Using salts as precursors to prepare tungsten-cobalt bimetallic catalysts is flexible and convenient. This offers an efficient pathway for the large-scale preparation of chirality enriched semiconducting SWNTs.