Large-Scale Synthesis, Annealing, Purification, and Magnetic Properties of Crystalline Helical Carbon Nanotubes with Symmetrical Structures

Authors

  • N. J. Tang,

    1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (P.R. China)
    2. Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (P.R. China)
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  • W. Zhong,

    1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (P.R. China)
    2. Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (P.R. China)
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  • C. T. Au,

    1. Chemistry Department and Center for Surface Analysis and Research, Hong Kong Baptist University , Hong Kong (P.R. China)
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  • A. Gedanken,

    1. Department of Chemistry and Kanbar Laboratory for Nanomaterials, Bar-Ilan University, Ramat-Gan 52900 (Israel)
    2. Center for Advanced Materials and Nanotechnology, Bar-Ilan University, Ramat-Gan 52900 (Israel)
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  • Y. Yang,

    1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (P.R. China)
    2. Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (P.R. China)
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  • Y. W. Du

    1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (P.R. China)
    2. Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (P.R. China)
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  • This work was financially supported by the National Natural Science Foundation (Grant Nos. 50602023 and 10674059) and the National Major Project of Fundamental Research: Nanomaterials and Nanostructures (Grant No. 2005CB623605), P.R. China. The authors also thank the Chinese and Israeli Ministries of Science for a Binational Grant through the Sino–Israeli Program in Materials Science.

Abstract

Crystalline helical carbon nanotubes (HCNTs) are synthesized as the main products in the pyrolysis of acetylene at 450 °C over Fe nanoparticles generated by means of a combined sol–gel/reduction method. Transmission electron microscopy (TEM) images reveal that there are two HCNTs attached to each Fe3C nanoparticle, and that the two HCNTs are mirror images of each other. Annealing in Ar at 750 °C and purification by immersion in hot (90 °C) HCl solution do not significantly change the structure of the HCNTs, despite the partial removal of Fe nanoparticles by the latter treatment. The magnetic properties of the as-prepared, annealed, and purified HCNTs have been systematically examined. The annealed sample shows relatively high magnetization due to the ferromagnetic α-Fe nanoparticles encapsulated in the HCNT nodes. In the case of HCl treatment, relatively pure HCNTs are obtained by the removal of ferromagnetic nanoparticles from the double-HCNT nodes. The effects of the amount of catalyst used in the synthesis process on the morphology and yield of the carbon products have also been investigated.

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