Formation of carbon nanotubes from methane decomposition: effect of concentration of Fe₃O₄ on the diameters distributions

Fe₃O₄ was used to synthesize narrow diameter of carbon nanotubes (CNTs). The effect of concentration of Fe₃O₄ on the diameters of carbon nanotubes (CNTs) synthesized by methane decomposition at 1000°C was investigated. We used conventional impregnation method to prepare Fe₃O₄/MgO catalysts. The results show that the concentration of Fe₃O₄ greatly affects the diameter distributions of produced CNTs. The CNTs formed by Fe₃O₄/MgO catalysts, with the mole ratio set at 0.25:9.75 and 1:9 had diameter of 3.23 ± 1.71 and 49.04 ± 33.62nm, respectively, showing that a decrease in concentration of Fe₃O₄ yields smaller diameter and narrower diameter distribution. A growth model explaining tip-growth and base-growth mechanism is proposed for understanding formation of CNTs.