Supercritical Fluids as Reaction Media for Scalable Production of Carbon Nanomaterials

We have demonstrated scalable and selective synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and onion-like carbons (OLCs) in a batch reactor using supercritical fluids (SCFs) as reaction media. The process utilizes toluene and alcohols (ethanol, propanol, and butanol) as carbon precursors in combination with ferrocene. Growth with supercritical toluene at 600 °C in the absence of water yields large diameter CNTs while introduction of 92.5 mmol/L of water enhances product yield by 50%, promoting formation of smaller diameter CNTs and decorating the exterior surface of CNTs with Fe nanoparticles. At 400 and 500 °C, in the absence of water, supercritical toluene produces mainly OLCs and CNFs, respectively. For alcohols, a gradual evolution of the morphology of nanocarbons forms from mainly OLCs to tube-like structures as the ratio of C/O atoms increases, possibly due to a decrease in the tendency of graphitic sheets to minimize their energies by curling into onion-like structures as chain length increases. This study provides a framework for utilizing SCF reaction media in a batch reactor to achieve scalable and selective growth of different nanocarbons and nanocarbon–metal nanocomposites.