Study of carbon nanotubes synthesis by spray pyrolysis and model of growth

Multi-walled carbon nanotubes (MWCNTs) were grown inside of quartz tubing by spray pyrolysis of ferrocene/benzene under argon flow. Carbon nanotubes (CNTs) with length of 200 μm were produced with reaction time of 10 min. The diameter of CNTs was influenced by the size of droplets formed in the nebulizer and the length was greatly influenced by ferrocene concentration and argon gas flow. It was found that temperature is a critical variable to produce CNTs at the experimental conditions used in this work. It was also found that CNTs only grew if ferrocene is added to gas flow, even if CNTs are previously seeded and formed on substrate, benzene cannot produce the CNTs without ferrocene. A model of CNTs formation and growth is proposed for spray pyrolysis of ferrocene/benzene, this mechanism consist of the formation of carbon/Fe nanoparticles during pyrolysis in the gas phase, these nanoparticles reach the walls of substrate, and the nanoparticles attach to substrate surface or to the nanotubes. Under proper conditions the displacement of Fe inside the graphitic structure induces the alignment of carbon walls, straightening this way the nanotubes.