Oxide nanotubes prepared using carbon nanotubes as templates
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Oxide nanotubes prepared using carbon nanotubes as templates B. C. Satishkumar, A. Govindaraj, Erasmus M. Vogl, Lipika Basumallick, and C. N. R. Raoa) Solid State and Structural Chemistry Unit and CSIR Center of Excellence in Chemistry, Indian Institute of Science, Bangalore 560 012, and Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur, Bangalore 560 064, India (Received 23 April 1996; accepted 29 October 1996)
Hollow nanotubes of SiO2 , Al2 O3 , V2 O5 , and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis. Preparation of hollow nanotubes of ceramic oxides such as silica has recently attracted wide attention.1 Hollow tubes of silica have been synthesized by hydrolyzing tetraethylorthosilicate (TEOS) in a mixture of ethanol, ammonia, water, and tartaric acid.2 Nanotubes of oxides such as V2 O5 have been prepared by annealing a mixture of partially oxidized carbon nanotubes along with the oxide powder above the melting point of the oxide.3 We have been exploring the synthesis of oxidic nanotubes by employing closed or opened carbon nanotubes as templates. It may be noted that carbon fibers have been coated with SiO2 by the decomposition of an organometallic precursor.4 The procedure employed by us involves coating the carbon nanotubes with tetraethylorthosilicate or other such precursors and then oxidizing the carbon of the nanotubes. Experiments carried out in this direction with SiO2 , Al2 O3 , and V2 O5 have been reasonably successful, and we report the preliminary results in this Communication. Since such nanotubes could be of use in catalysis, we have also prepared SiO2 nanotubes containing transition metal ions. Carbon nanotubes were prepared by the arc vaporization of graphite rods in an inert atmosphere (550 Torr) of helium gas at 10 V, 50 A dc.5 The nanotubes formed in the core region of the cathode deposit were dispersed in methanol and sonicated for 2 h in a separation funnel. The suspension was allowed to settle and the bulky graphitic carbon removed. The remaining solid suspension was dried and heated in air at 1023 K for 10 min to oxidize the graphitic carbon.5 The pure carbon nanotubes thus obtained were closed at both ends or open at one end in some instances. These nanotubes were used for various experiments. We have also used the carbon nanotubes treated with boiling HNO3 for 24 h. Such nanotubes are almost always open and contain acidic sites on the surface.6,7 These were washed with water and dried in an oven at 330 K for 12 h.
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http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 3, Mar 1997
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