Structure and texture of phenol-based carbon nanofibers heat-treated at high temperatures

Commercially available phenol-based carbon nanofibers (CNFs) and activated carbon nanofibers (ACNFs) about 200–500 nm in diameter were heated to 900 °C and then heat-treated further at temperatures of 3000–3200 °C. The texture and structure of the both heat-treated samples were investigated by SEM and TEM observations and measurements of XRD and Raman spectra. A large number of fine graphite particles 300–1000 nm in diameter were observed for ACNF much more than for CNF after heat treatment at high temperatures. The result supports the mechanism of generation of the particles by evaporation of carbon species at high temperatures from the nanofibers followed by the deposition, because ACNF has much larger external surface area than CNF. A large volume of graphitic regions and rather small volume of turbostratic regions were observed in the nanofibers of all heat-treated CNFs and ACNFs. The graphitic region was believed to be formed due to surface graphitization as reported for carbon sheets derived from bacteria cellulose nanofibers heat-treated at high temperatures.