Synthesis of Carbon Nanotubes

1. Catalytic chemical vapour deposition (CCVD)

Carbon nanotubes (CNTs) are unique nanostructures with remarkable electronic and mechanical properties and have attracted tremendous interest worldwide. Catalytic chemical vapour deposition (CCVD) is currently the most promising technique to produce carbon nanotubes (CNTs) at large-scale, low cost and on a dedicated place on a substrate. The method consists in the decomposition of a carbon containing gas over a supported catalyst. Contrasting with the abundant types of carbon sources used for the growth of CNTs, their synthesis is restricted to the thermal decomposition reaction of the carbon source. The optimization of growth parameters remains mostly empirical.

Our research aims at developing new CNT growth processes suitable for applications as well as for the understanding of CNTs growth mechanism. For instance, we have recently shown that the chemical mechanism in the synthesis of carbon nanotubes can be modified by the presence of CO2 in the reactor. Mixing the carbon source with CO2 provides outstanding kinetic characteristics of the reaction. [1] When CO2 is produced in situ by thermal decomposition of a carbonate used as a substrate, the yield of the reaction is enhanced to such an extent that 85% of acetylene is converted into CNTs [2]. For the mass production of CNTs, we have developed a continuous production process based on a rotary tube furnace [3,4]. Large quantities of catalyst can be processed simultaneously and 1.5kg/day of high quality, amorphous carbon free CNTs can be produced [2].

View of the rotary tube oven used for the CVD, large-scale synthesis of  carbon nanotubes. It allows 1.5 kg/day production of high quality tubes, suitable for applications in composites

 

Zoom on the flow of CNTs in a 2 inch quartz tube at the exit of the active zone of the furnace.

 

In addition to the large scale production, we are producing by CVD millimeter thick carpets of aligned CNTs from ethylene at 750°C in the presence of water traces. The height of the carpet is strongly related to the pH control of the substrate [8]. When the catalyst film is patterned by lithography, complex structures like pillars or sheets can be produced as well. [5]

CNT forests with a height of about 1mm have been produced by the water assisted CVD growth process. Large scale structures with well defined shape can be produced from a patterned catalyst. TEM micrographs of CNTs produced at 750°C.

2. Arc discharge method

MWNTs

SWNTs  bundle

We master the synthesis of multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) by the arc discharge method. The high temperature of the arc enables the formation of CNTs of a very high structural quality suitable for fundamental research. They often exhibit properties, close to the ones predicted by theory. (View of our arc discharge chamber and HRTEM images of the produced CNTs).

References:
[1] A. Magrez, J.W. Seo, V.L. Kuznetsov and L. Forró, Angew. Chem. Int. Ed. 46, 441 (2007)
[2] M. Mionic, D.T.L. Alexander, L. Forró and A. Magrez, Phys. Status Solidi B 245, 1915 (2008)
[3] A. Magrez, J.W. Seo, C. Miko, K. Hernadi and L. Forró, J. Phys. Chem. B 109, 10087 (2005)
[4] E. Couteau, K. Hernadi, J.W. Seo, l. Thien-Nga, C. Miko, Chem. Phys. Lett. 378, 9 (2003)
[5] R. Smajda, J. C. Andresen, M. Duchamp, R. Meunier, S. Casimirius, K. Hernadi, L. Forró and A. Magrez, Phys. Status Solidi B 246, 2457 (2009)
[6] J.W. Seo, A. Magrez, M. Milas, K. Lee, V. Lukovac and L. Forró, J. Phys D-Applied Physics 40, R109 (2007)
[7] J. W. Seo, E. Couteau, P. Umek, K. Hernadi, P. Marcoux, B. Lukic, Cs. Mikó, M. Milas, R. Gaál, and L. Forró, New J. Phys. 5, 120.1 (2003
[8] A. Magrez et al,, ACS Nano 5, 3428 (2011).