Large-scale production of multi-walled carbon nanotubes by low-cost spray pyrolysis of hexane

Multi-walled carbon nanotubes (MWCNTs) were prepared by spray pyrolysis, using hexane as a carbon source and ferrocene as a catalyst precursor, followed by purification with acid leaching and air oxidation. The as-grown and purified MWCNTs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, thermogravimetry, and Raman spectroscopy. The sublimation temperature of ferrocene, the ferrocene concentration in hexane, pyrolysis temperature and time, and the flow rate of hexane and H2 were optimized to obtain MWCNTs with a high quality and a high yield. The MWCNTs have a typical sausage-like structure and their lengths are more than several tens of micrometers. The inner and outer diameters of the MWCNTs were in the range of 15-45 and 25-70 nm, respectively. The purity and yield of the purified MWCNTs were more than 95% and 70% mass fraction, respectively.