Synthesis of stacked-cup carbon nanotubes in a metal free low temperature system

Stacked-cup carbon nanotubes wereeformed by either Fischer-Tropsch type or Haber-Bosch type reactions in a metal free system. Graphite particlescwere used as the catalyst. The samples were heated at 600 °C in a gas mixture of CO;75 Torr, N₂ 75 Torr and H₂ 550 Torr for three days. Transmission electron microscope analysis of the catalyst surface at the completion of the experiment recognized the growth of nanotubes. They were 10-50 nm in diameter and ∼1 μm in length. They had a hollow channel of 5-20 nm in the center. The nanotubes may have grown on graphite surfaces by the CO disproportionation reaction and the surface tension of the carbon nucleus may have determined the diameter. Although, generally, the diameter of a carbon nanotube depends on the size of the catalytic particles, the diameter of the nanotubes on graphite particles was independent of the particle size and significantly confined within a narrow range compared with that produced using catalytic amorphous iron-silicate nanoparticles. Therefore, they must have an unknown formation process that is different than the generally accepted mechanism.