Effect of fuel structure on synthesis of carbon nanotubes in diffusion flames

Carbon nanotubes (CNTs) were synthesized on nickel nitrate coated nickel foam in co-flow diffusion flames. Two different fuel structures, methane and ethylene, were used to synthesize CNTs. The effect of fuel structure on CNTs was systematically studied. Results showed that carbon nanomaterials, including nanotubes and nanofibers, were successfully synthesized in all conditions in methane flames, while, in ethylene flames, bamboo-like CNTs were synthesized in limited conditions. It was also found that carbon nanomaterials synthesized in ethylene flames had more defects than that of in methane flames. In addition, metal nickel nanoparticles acted as catalysts in the synthesis of CNTs, and carbon nanomaterials diameter was dependent on the catalyst particle size. Flame-synthesized CNTs were based on the vapor-liquid-solid mechanism, and a “recursive growth mechanism” for CNTs growth was proposed, which would be more conducive to the understanding of CNTs growth mechanism. This method offers another possibility for low-cost, large-scale synthesis of carbon nanomaterials.