RESEARCH ARTICLE

 

The effect of synthesis parameters on the catalytic synthesis of multiwalled carbon nanotubes using Fe-Co/CaCO₃ catalysts

 

 

Sabelo D. Mhlanga^{I, II}; Kartick C. Mondal^{I, II}; Robin Carter^{I, II}; Michael J. Witcomb^{II, III}; Neil J. Coville^{I, II}

^IMolecular Sciences Institute and School of Chemistry, University of the Witwatersrand, Johannesburg, WITS 2050, South Africa
^IIDST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, Johannesburg, WITS 2050, South Africa
^IIIMicroscopy and Microanalysis Unit, University of the Witwatersrand, Johannesburg, WITS 2050, South Africa

 

 

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ABSTRACT

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

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Full text available only in PDF format.

 

Acknowledgements

We gratefully acknowledge financial support from the National Research Foundation, Mellon Postgraduate Mentoring Scheme, the CSIR and the University of the Witwatersrand. We also thank Mr Rudolf Erasmus for his assistance with Raman spectral collection and analysis.

 

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Received 17 December 2007
Revised 22 December 2008
Accepted 7 February 2009

 

 

* To whom correspondence should be addressed. E-mail: neil.coville@wits.ac.za.