Effect of sulfur on the growth of carbon nanotubes by the floating catalyst method

Sulfur added to the starting materials is a crucial factor for Fe catalysts to grow carbon nanotubes by the floating catalyst method. This work shows that only the optimal amount of sulfur additive (thiophene) can produce filamentous carbon product. The effect of sulfur on the catalytic activity was then discussed. The sulfur composition in the iron catalyst particles is too low to liquefy them. Thermodynamic and kinetic analyses indicate that not sulfur element's iron particles but the geometric effect of the sulfur atoms on the outer-layers of the Fe catalyst particles increases the catalytic activity, and carbon nanotubes can grow continuously from them.