Growth of Single-Walled Carbon Nanotubes by the Rapid Heating of a Supported Catalyst Ya-Li Li, † Ian A. Kinloch, † Milo S. P. Shaffer, †,‡ Charanjeet Singh, †,§ Junfeng Geng, | Brian F. G. Johnson, | and Alan H. Windle* ,† Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, and Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K. Received March 22, 2004. Revised Manuscript Received September 15, 2004 Single-walled carbon nanotubes (SWNTs) have been synthesized by the rapid injection of a nickel formate/silica gel catalyst/support into a hot fluidized-bed reactor. The initial rapid heating of the catalyst in the hydrocarbon feedstock was found to be essential for the nucleation of SWNTs since only amorphous or graphitic carbon particles were formed without it. These results suggest that the rapid heating of the catalyst precursor enables the formation of the small metal particles required for SWNT growth, probably due to the accelerated thermal decomposition of the catalyst precursor and enhanced nucleation rate. The growth of the SWNTs was investigated by the adoption of different methods for introducing the catalyst, and by varying the synthesis parameters including the catalyst loading, hydrocarbon gas flow rate, and concentration. The results found that SWNTs formed only under certain reaction conditions. The nanotubes produced were characterized by electron microscopy and Raman spectroscopy. 1. Introduction The catalytic chemical vapor decomposition process (CCVD) has proved to be a feasible production route for carbon nanotubes, as demonstrated by the successful synthesis of multiwalled carbon nanotubes (MWNTs) in the form of both random aggregates and well-ordered films. 1-3 The extension of the process to the synthesis of single-walled carbon nanotubes (SWNTs), which are preferred to MWNTs for some applications because of their superior electrical and mechanical properties, 2,3 is a current objective. In recent years, numerous studies have been made of different catalysts and precursors based upon Fe, Co, and Ni compounds supported on various substrates such as SiO 2 , MgO and Al 2 O 3 . Typically, either the catalysts are physically impreg- nated onto the substrate or both the catalyst and the substrate are formed by a sol-gel process. 4-14 These studies showed that the growth of SWNTs is more difficult to control than that of MWNTs. SWNT synthesis has been reported to be affected by many conditions, including the combination of the catalyst and support used, the metal loadings on the supports, 4-6,9-11 their preheat treatment, 6 the hydro- carbon gas flow rate and its concentration, 12 the reaction temperature, 9,11,12 and the chemical properties of the carbon feedstock. 14 In particular, the physical and chemical properties of the catalyst/support are found to be important to the growth of SWNTs, since some systems show quite a wide synthesis window for SWNT production, while many others yield only MWNTs or amorphous carbon regardless of the synthesis condi- tions. Currently, the detailed mechanism for SWNT growth is unclear. However, it is generally agreed that the presence of the small catalyst particles similar in diameter to SWNTs (less than a few nanometers) is necessary for the nucleation of SWNTs and their subsequent growth under suitable reaction conditions. The control of the formation of such small diameter catalyst particles and their stabilization at high growth * To whom correspondence should be addressed. Phone: (0044)- 1223-334321. Fax: (0044)-1223-334366. E-mail: ahw1@cam.ac.uk. † Department of Materials Science and Metallurgy. ‡ Present address: Department of Chemistry, Imperial College Science Technology & Medicine, Imperial College Rd., London SW7 2AZ, U.K. § Present address: Thomas Swan and Co. Ltd., Consett, County Durham, U.K. | Department of Chemistry. (1) Andrews, R.; Jacques, D.; Qian, D.; Rantell, T. Acc. Chem. Res. 2002, 35, 1008. (2) Baughman, R. H.; Zakhidov, A. A.; Heer, W. A. Science 2002, 297, 787. (3) Ajayan, P. M. Chem. Rev. 1999, 99, 1787. (4) Kong, J.; Cassel, A. M.; Dai, H. J. Chem. Phys. Lett. 1998, 292, 567. (5) Colomer, J. F.; Stephan, C.; Lefrant, S.; Tendeloo, G. Van; Willems, I.; Konya, Z.; Fonseca, A.; Laurent, Ch.; Nagy, J. B. Chem. Phys. Lett. 2000, 317, 83. 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