Effective catalyst on SiO2 in ethanol CVD for growth of single-walled carbon nanotubes

We have compared catalytic activity of Co and Fe in a growth process of single-walled carbon nanotube (SWNT) by chemical vapor deposition using ethanol as a carbon source and SiO2 as a catalyst-supporting material. Changes of the catalyst precursors (Co- and Fe acetate) in the growth process were carefully observed at three different stages: (i) after oxidation in air at 400 °C but before heating to the growth temperature (800 °C), (ii) after heating to the growth temperature in flowing Ar and H2 but before starting the nanotube growth and (iii) after the growth process is over. During the growth of SWNT, the Co catalyst took the form of β-Co, resulting in a high yield growth. On the contrary, the Fe catalyst formed a silicate, Fe2SiO4, showing a poor catalytic ability. Our result shows that chemical reactions between the catalyst precursors and their supporting materials sensitively affect the catalytic ability.