(247f) Selective Synthesis of (9,8) Single Walled Carbon Nanotubes Using CoSO4/SiO2 Catalyst

A new chirality selective catalyst (CoSO₄/SiO₂) has been developed for single walled carbon nanotube (SWCNT) synthesis. The CoSO₄/SiO₂ catalystis prepared by dispersing cobalt (II) sulphate heptahydrate on high surface area porous silica using an incipient wetness impregnation method. Photoluminescence, absorption and Raman spectroscopy results show the CoSO₄/SiO₂ catalyst has high selectivity toward (9,8) nanotubes. The chirality selectivity of the catalysis can be tuned by varying catalyst reduction conditions. At an optimal reduction condition, when the catalyst is reduced under H₂ up to 540 ^oC, photoluminescence results show the (9,8) nanotubes count for 51.7 % of all semiconducting SWCNTs. Theoretical study shows that the diameter of structurally stable metal nanoparticles is scattered, other than continual. The Co₁₄₇ cluster is the most stable cluster in its diameter range. The selectivity toward the (9,8) nanotube is credited to large Co nanoparticles with diameter comparable with that of (9,8) nanotubes. Forming such large Co nanoparticles is because of the lower reduction temperature (470 ^oC) of Co species in the CoSO₄/SiO₂ catalyst. We also found that sulfur compounds resulting from reducing SO₄^2- ions play a critical role in stabilize such large Co nanoparticles. This research opens up routes toward highly selective growth of SWCNTs.