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.