Fe-catalysed synthesis of carbon nanotube by i-C4H10 decomposition: advantages and problems deriving from H2 addition to the growth ambient

This work is a continuation and a completion of our previous studies on the synthesis of multi-walled carbon nanotubes (MWCNTs) by i-C4H10 decomposition at moderate temperature (600 °C). It intends to show the existence of well-defined relationships between the variations of the reaction parameters and the changes of yield and graphitization degree of the grown MWCNTs. For this purpose, MWCNTs prepared by catalysed chemical vapour deposition (CCVD) in i-C4H10-H2-He environment over Fe/Al2O3 catalysts (metal load: 29%; reduction temperature: 500 or 700 °C) are considered. The results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (RS) and thermo-gravimetry (TG) analyses, performed on purified MWCNTs, evidence the changes in morphology, crystalline arrangement, purity and thermal stability produced by the use of different i-C4H10 and H2 partial pressures (0.25-0.75 atm) and catalyst amount (0.25-2.00 g). The empirical correlations established, by fitting the data, between issue of reactions, in terms of yield and MWCNT graphitization degree, and relative (to catalyst) carbon-and hydrogen-supply rates allow highlighting, on a quantitative basis, benefits and problems deriving from H2 addition to the growth atmosphere, topic on which, as in our knowledge, only qualitative information is available in literature.