Influence of gas-mixture composition on yield, purity and morphology of carbon nanotubes grown by catalytic isobutane-decomposition

Present work concerns iron-catalyzed growth of multi-walled C nanotubes (MWCNTs) by decomposition of isobutane (C4H10). MWCNTs are prepared, by chemical vapor deposition (CVD) at 600 °C, in C4H10-H2-He atmosphere over 29 wt.þ/Al2O3 catalysts. After purification, reaction products are analyzed by scanning electron microscopy (SEM), Raman spectroscopy (RS) and thermo-gravimetric analysis (TGA). The influence of the gas-mixture composition on the reaction issue is investigated by considering different gas-flowing setups: H2 or C4H10 flow is varied in the range 15-90 cc/min while keeping hydrocarbon or H2 constant. The total flow is kept at 120 cc/min by using He as a balance-gas. Owing to these changes, diverse selectivity towards nanotubes, morphologies, size distributions, purity degrees and crystallinity are obtained, as evidenced by the characterization results.