Continuous and low-cost synthesis of high-quality multi-walled carbon nanotubes by arc discharge in air

We have developed a continuous and low-cost approach to prepare high-quality multi-walled carbon nanotubes (MWCNTs) using direct current arc discharge with a horizontal graphite anode and a vertical rotating cylindrical graphite cathode in air. The most important features of this promising process are continuously preparing nanotubes and simply adopting the cheapest and most accessible air as the buffer gas. When the cylindrical cathode rotates constantly, film-like MWCNT products are continuously deposited on the surface of cathode and immediately taken out of the arc discharge region by the rotating cathode. This process is quite favorable for the formation of nanotubes due to the easier condensation of carbon vapor quickly away from the arc region. Fine MWCNTs with random orientation can be obtained and they are nearly free of carbon nanoparticles and curved graphite sheet in them after simple purification at 750 °C for 30 min in air. The purified MWCNT film shows a good field emission property, and the open-on and threshold electric fields are 1.15 V/μm and 1.66 V/μm, respectively.