Oxygen-assisted synthesis of SWNTs from methane decomposition

Single-walled carbon nanotubes (SWNTs) were prepared from CH4 decomposition by an Fe - Mo/MgO catalyst. A small amount of O-2 ( about 0.04% - 0.20%) was introduced into the process to tailor the activity of the catalyst. By comparing the effect of adding O-2 at different stages of SWNT growth, the online BET and gas chromatography detection indicated the effective regeneration of the catalyst at the early stage of SWNT growth. In addition, TEM, Raman and TGA characterizations revealed that the effect of O-2 was to remove the amorphous carbon and other carbon impurities to increase the purity and yield of the SWNTs. Furthermore, detailed characterization of the TGA and Raman spectra indicated that a slight increase in the O-2 concentration was effective for preparing SWNTs with a narrower diameter distribution without decreasing their total yield. The mechanism was attributed to the cycle of oxidation and reduction of iron nanocrystallites on the MgO lattice, in the presence of O-2. This in situ oxidation, regeneration and purification method with O-2 is useful for the controlled mass production of SWNTs at low cost.