Synthesis of Carbon Nanohorns by Inductively Coupled Plasma

We demonstrate a new pathway for the synthesis of carbon nanohorns (CNHs) in a reactor by using inductively coupled plasma (ICP) and gaseous precursors. Thermal plasma synthesis allows the formation of different carbon allotropes such as carbon nanoflakes, hybrid forms of flakes and nanotubules, CNHs embryos, seed-like CNHs and onion-like polyhedral graphitic nanocapsules. In this study, pressure has the greatest impact on the selectivity of carbon nanostructures: pressure below 53.3 kPa favors the growth of carbon nanoflakes and higher pressures, 66.7 kPa and above, promotes the formation of CNHs. The ratio between methane and hydrogen as well as the global concentration of CH₄?+?H₂ inside the plasma flame are also crucial to the reaction. CNHs are formed preferentially by injection of a 1:2 ratio of H₂ to CH₄ at 82.7 kPa with a production rate of 20 g/h. The synthesis pathway is easily scalable and could be made continuous, which offers an interesting alternative compared to methods based on laser-, arc- or induction-based vaporization of graphite rods.

Graphical Abstract