Sulfur-induced chirality changes in single-walled carbon nanotube synthesis by ethanol chemical vapor deposition on a Co/SiO2 catalyst

Abstract

Selective synthesis of single-walled carbon nanotubes (SWCNTs) with different chiral structures is highly desirable for their potential applications ranging from electronics, photovoltaics to medicine. Here, we have shown that introducing sulfur-containing compounds into carbon feedstock may efficiently alter the chiral selectivity of a Co/SiO₂ catalyst toward different chiral species. When carbon disulfide (0.0001 wt%) was added to ethanol, the carbon yield increased significantly from 4.8 to 14 wt% without chirality changes. The changes in chiral selectivity are correlated with the significant changes in the carbon yield. With further increase of carbon disulfide concentration, the chirality distribution shifted from smaller diameter chiral nanotubes, such as (7,6) at 0.9 nm, toward larger diameter chiral ones, such as (8,7) at 1 nm and (9,8) at 1.2 nm, in addition to a sharp decrease in the carbon yield. Further, when a different sulfur-containing compound was used, the chiral selectivity changed differently. Thiophene (0.1 wt%) in ethanol led to a good chiral selectivity toward (9,8) nanotubes with a relative abundance of 43.1% among all semiconducting nanotubes. We propose that sulfur may selectively block active sites on Co particles through dynamic interactions among sulfur, hydrogen, carbon and Co metal particles. Our results suggest that sulfur-containing compounds may be used as an efficient additive to tune the chiral selectivity of catalysts in SWCNT synthesis.