Chemical Vapor Deposition and Synthesis on Carbon Nanofibers: Sintering of Ferrocene-Derived Supported Iron Nanoparticles and the Catalytic Growth of Secondary Carbon Nanofibers

The synthesis of homogeneously distributed carbon nanofibers with well-defined morphology on vapor-grown carbon nanofibers was achieved by a sequence of gas-phase steps, thus fully avoiding wet chemistry: first, carbon nanofibers were exposed to oxygen plasma to introduce oxygen-containing functional groups. Then, the chemical vapor deposition of ferrocene was carried out under oxidizing conditions, yielding nanofiber-supported iron oxide nanoparticles. Secondary carbon nanofibers with diameters in the range from 10 to 20 nm were subsequently grown from cyclohexane catalyzed by the sintered metallic iron nanoparticles under reducing conditions. XPS was applied to monitor the chemical changes of the surface composition and the sintering of the metallic iron particles in hydrogen. The morphology and the height distribution of the sintered iron oxide nanoparticles was derived by a unique combined application of scanning electron microscopy and scanning tunneling microscopy. The specific surface area of the nanocomposite was enhanced strongly due to the growth of secondary nanofibers, and it was possible to tune the morphology of the nanofiber−nanofiber composites by the process parameters. Thus, a significant advance in the reproducible synthesis of branched carbon fiber nanocomposites was achieved.