Mass production of high-purity bamboo-shaped carbon nanotubes from ethanol using a plasma jet

Bamboo-shaped carbon nanotubes (BCNTs) were synthesized continuously in high yields from ethanol in an arc plasma jet under atmospheric pressure with ferrocene as catalyst. The products obtained were characterized by TEM and HRTEM. The typical arc plasma conditions for the mass production of BCNTs at atmospheric pressure that can be achieved in about 120s are direct current, 220-240A; voltage, 140-150V; the injecting rate of ethanol and ferrocene mixture (100∶1 by weight), 50mL/min. It was found that the as-prepared BCNTs with a fishbone-type wall exist in an entangled state and have a uniform outer diameter of ca. 20nm and a length of several microns. The purity of BCNTs in the final product is estimated to be over 90%. BCNTs with branched morphologies are also observed occasionally. It is believed that several steps are involved in the growth of BCNTs. Once the mixture of ethanol and ferrocene is injected into the arc plasma reactor, ethanol undergoes decomposition reactions, releasing a large amount of active carbon species that work as the building blocks of BCNTs. At the same time, ferrocene is decomposed, yielding aggregated Fe particles that function as a catalyst for the growth of BCNTs. Active carbon species are immediately adsorbed by or dissolved inside the catalyst particles formed in situ, and graphene layers nucleate on the surfaces of the catalyst particle and finally grow into bamboo-shaped tubular structures because of the diffusion of carbon species inside the catalyst particles, and more importantly because of the difference in the mobilities of the catalyst particles and the graphitic shell.