The effect of sulfur on the structure of carbon nanotubes produced by a floating catalyst method

The effect of sulfur on the structures (shell number and diameter distribution) of carbon nanotubes (CNTs) was investigated in detail using high resolution transmission electronic microscopy (HRTEM) and Raman spectroscopy. Single-walled (SWNTs), double-walled (DWNTs), and multi-walled carbon nanotubes (MWNTs) with different diameter distributions were obtained only by increasing the sulfur addition amount with methane as carbon source. A similar structure change was found for ethanol as carbon source with changing the sulfur addition amount. These results indicate that addition of sulfur is necessary to enhance the growth of SWNTs and DWNTs, independent of the carbon source for our method. Based on the growth parameter study, HRTEM observations and kinetic considerations, the role of sulfur in the nucleation and growth of CNTs was discussed.