(323c) Supercritical Fluids As Reaction Media for Scalable Production of Carbon Nanomaterials

We have demonstrated scalable synthesis of a variety of nanocarbons including carbon nanotubes (CNTs), carbon nanofibers (CNFs), and onion-like carbon (OLC) in a batch reactor using supercritical fluids as a reaction media. The process utilizes toluene, ethanol, or butanol as a carbon precursor in combination with ferrocene that serves the dual role of a catalyst precursor and a secondary carbon source. Growth with supercritical toluene at 600ºC in the absence of water yield large-diameter CNTs and CNFs while the introduction of 0.05 ml of water enhances the product yield by 50% and promotes the formation of smaller-diameter CNTs. The exterior surface of CNTs was decorated with highly monodispersed Fe nanoparticles. At lower temperature (400ºC) in the absence of water, supercritical toluene produces mainly OLC; similarly, high OLC selectivity was achieved by increasing the amount of added water to 5.55 mol/L. The tendency for alcohols to produce tubular structures increases in the order C₂H₅OH < C₃H₇OH < C₄H₉OH, which suggests a direct correlation between the aliphatic chain length of alcohol and the tendency to form a tubular structure. The use of supercritical fluids for growth does not only provide a route for selective and scalable growth of a variety of carbon nanomaterials, but also provides a unique one-step approach that is free of aggressive acid treatment for synthesis of CNT-supported or encapsulated Fe composites with potential applications in catalysis and energy storage.