Synthesis and characterization of ferromagnetic Fe₃C/C composite nanoparticles as a catalyst for carbon nanotube growth

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. These template particles dispersed in aqueous solution have been used for the entrapment of ferrocene by a swelling process of methylene chloride emulsion droplets containing ferrocene within these particles, followed by evaporation of methylene chloride. The effects of CH₂Cl₂ volume and the [CH₂Cl₂]/[FeC₁₀H₁₀] (w/w) ratio on the size and size distribution of the swollen template particles were elucidated. Air-stable Fe₃C nanoparticles embedded in amorphous carbon matrix (Fe₃C/C) have been prepared by thermal decomposition of the ferrocene-swollen template polystyrene particles at 500 C for 2 h in a sealed cell. Decomposition of these swollen template particles for 2 h at higher temperatures led to the formation of carbon nanotubes (CNTs) in addition to the Fe₃C/C composite nanoparticles. The yield of the CNTs increased as the annealing temperature was raised. An opposite behavior was observed for the diameter of the formed CNTs. The size and size distribution, crystallinity, and magnetic properties of the different Fe₃C/C composite nanoparticles have also been controlled by the annealing temperature.