Large-scale production of high-quality multi-walled carbon nanotubes: role of precursor gas and of Fe-catalyst support

The crucial role of precursor gas (PG) and of catalyst support (CS) in the growth of multi-walled C nanotubes (MWCNTs) by iron-catalysed chemical vapour deposition (CVD) is evidenced. This is accomplished by comparing structural and morphological properties of MWCNTs synthesised by the use of different PGs (ethane and isobutane) and CSs (silica and alumina). The results of analyses, carried out on catalysts and C deposits by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermo-gravimetry (TG) and X-ray diffraction (XRD), demonstrate that Al2O3-supported catalysts are more efficient than SiO2-supported ones in decomposing hydrocarbons. The use of i-C4H10 as PG allows reducing Fe-encapsulation and improving yield (YC) and selectivity, so as the largescale production (YC >900 wt.%) of high-quality nanotubes can be operated even at moderate reaction temperature (600 °C) after proper calibration of Fe-load (29 wt.%) and catalyst reduction temperature (500 °C).