Synthesis of single-walled carbon nanotubes with narrow diameter distribution by calcination of a Mo-modified Fe/MgO catalyst

The Fe-Mo/MgO catalyst for the synthesis of single-walled carbon nanotubes (SWNTs) from methane decomposition by chemical vapor deposition was pretreated by calcination at 900 degrees C for 10 h. A comparison of SWNT growth on the catalysts with and without Mo confirmed that Mo addition in the calcined catalyst was crucial in stabilizing and dispersing Fe nanoparticles to a small size, and thus, to synthesize SWNTs with uniform diameters. The products were characterized by energy dispersive spectroscopy, high-resolution transmission electron microscopy, X-ray diffraction, Ar adsorption, Raman spectroscopy, and thermogravimetric analysis. The results showed that Fe-rich nanoparticles were the active sites for SWNT growth and the diameter of the SWNTs depended on the size of the Fe nanoparticles. The calcination led to the formation of the FeMoO4 phase when Mo was added, which is a more stable phase than the MgFe2O4 phase. The Mo/Fe ratio was also important in preparing SWNTs of high density, high purity, and with a narrow diameter distribution. These results are useful for the precise control of the synthesis of SWNTs.