Carbon Nanotube Growth on Calcium Carbonate Supported Molybdenum-Transition Bimetal Catalysts
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Carbon Nanotube Growth on Calcium Carbonate Supported Molybdenum-Transition Bimetal Catalysts Zhongrui Li Æ Enkeleda Dervishi Æ Yang Xu Æ Viney Saini Æ Meena Mahmood Æ Olumide Dereck Oshin Æ Alexandru R. Biris Æ Alexandru S. Biris
Received: 6 April 2009 / Accepted: 4 June 2009 / Published online: 30 June 2009 Ó Springer Science+Business Media, LLC 2009
Abstract A comparison of different catalyst systems (Fe–Mo, Co–Mo or Ni–Mo nanoparticles supported on calcium carbonate) has been performed in order to optimize the carbon nanotube (CNT) growth. The influences of the reaction temperature, metal loading and carbon source on the synthesis of CNTs were investigated. Dense CNT networks have been synthesized by thermal chemical vapor deposition (CVD) of acetylene at 720 °C using the Co–Mo/ CaCO3 catalyst. The dependence of the CNT growth on the most important parameters was discussed exemplarily on the Co catalyst system. Based on the experimental observations, a phenomenological growth model for CVD synthesis of CNTs was proposed. The synergy effect of Mo and active metals was also discussed. Keywords Carbon nanotubes CVD Co–Mo/CaCO3 catalyst hydrocarbon
1 Introduction As the carbon nanotube (CNT) applications continuously increase, high quality CNTs in large quantities are demanded. Catalytic chemical vapor deposition (cCVD) method attracts a lot of interest by making possible the
Z. Li (&) E. Dervishi Y. Xu V. Saini M. Mahmood O. D. Oshin A. S. Biris Nanotechnology Center and Applied Science, University of Arkansas at Little Rock, Little Rock, AR 72204, USA e-mail: [email protected] A. R. Biris National Institute for Research and Development of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj-Napoca, Romania
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large-scale and high-quality production of CNTs at a relatively low cost. Additionally, with the cCVD method, the growth of CNTs can be controlled by adjusting the reaction conditions and choosing proper catalysts. In the cCVD process, CNTs are produced from the thermal decomposition of the carbon-containing molecules on desirable metal catalysts. Many efforts have been put to optimize catalyst formulations and operating conditions [1, 2]. Strong adhesion between CNTs and the metal clusters from which they are produced is a requirement for CNT growth. This adhesion must be larger than the energy gained by the CNT when carbon dangling bonds form a cap. The catalyst composition (controlled by its preparation method) affects the efficiency and the selectivity of the catalysts towards the synthesis of desired CNTs. Using thermal cCVD, Co and Fe catalysts generally tend to form hollow and well graphitized nanotubes whereas Ni and Cu produced structures which were not as well graphitized [3, 4]. Besides the commonly used Fe, Co, and Ni catalysts, other metals (such as Mo, Cu) or metal mixtures (like Fe–Ni, Fe–Co, Co–Ni, and Co–Mo) have been used for nanotube synthesis [5]. However, the mechanism for bi-metallic catalysts affect the CNT growth is still poorly understood. In this work, we
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