South African Journal of Chemistry
On-line version ISSN 1996-840X
Print version ISSN 0379-4350
MHLANGA, Sabelo D. et al. The effect of synthesis parameters on the catalytic synthesis of multiwalled carbon nanotubes using Fe-Co/CaCO3 catalysts. S.Afr.j.chem. (Online) [online]. 2009, vol.62, pp.67-76. ISSN 1996-840X.
Fe-Co bimetallic catalysts supported on CaCO3 were prepared by a wet impregnation, a deposition-precipitation and a reverse micelle method. The sizes of the Fe and Co particles were not affected by the Fe and Co sources (nitrate, acetate) when the wet impregnation and deposition-precipitation methods were used. 'Clean' multi-walled carbon nanotubes (MWCNTs) were obtained from all three Fe-Co synthesis procedures under optimal reaction conditions. The CNTs produced gave yields ranging from 623 % to 1215 % in 1 h under the optimal conditions, with similar outer diameters (o.d.) of 20-30 nm and inner diameters (i.d.) ~10 nm. The Fe/Co catalyst formed in the wet impregnation method revealed that the yield, diameter and purity of the CNTs were influenced by the C2H2/N2 ratio, time and temperature. All the methods gave high-quality CNTs after short reaction times but the quality deteriorated as the synthesis time was increased from 5 to 360 min. Indeed, the most influential parameter in controlling CNT purity, length and o.d. was found to be the synthesis time. The as-synthesized CNTs were purified using a single-step mild acid treatment process (30 % HNO3), which readily removed the support and metal particles.
Keywords : Carbon nanotubes; synthesis; bimetallic catalyst; iron; cobalt.