Stability of single-wall carbon nanotubes under hydrothermal conditions
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Jose Maria Calderon-Moreno and Masahiro Yoshimura Center for Materials Design, Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagasuta, Midori-ku, Yokohama 2226-8503, Japan (Received 11 April 2000; accepted 13 December 2001)
The stability of single-wall carbon nanotubes under hydrothermal conditions (100 MPa pressure, from 30 min to 48 h in the temperature range from 200 to 800 °C) has been investigated. The resultant products were characterized by Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. The stability range of single-wall carbon nanotubes (SWCNTs) under hydrothermal conditions suggests that they, similar to fullerenes, can only survive mild and short-term treatment in high-temperature, high-pressure water. SWCNTs gradually transform into multiwall carbon nanotubes (MWCNTs) and polyhedral graphitic nanoparticules. After 48 h at 750 °C only the Raman spectra characteristic of graphitic carbon were observed. Transmission electron microscopy revealed that after 800 °C and 48 h of treatment SWCNTs fully transformed into MWCNTs and polyhedral carbon nanoparticles.
I. INTRODUCTION
The discovery of fullerene molecules1 and carbon nanotubes2 has intensified research on nanometer-scale carbon materials. Carbon nanotubes (CNTs) can be considered as tubular crystals of graphite capped with a half fullerene. They have a unique structure, being metallic or semiconducting depending on the tube diameter and chirality.3 CNTs can be distinguished into two types depending on the structure: single wall (SWCNTs);4 multiwall (MWCNTs).2 Several recent reports show that CNTs can perform the same electronic functions as larger silicon-based devices.5–8 CNTs are considered for such applications as special capillaries,9 storage of hydrogen,10 and reinforcement for composites and nanowires.11 Nowadays, the electronic circuits have become smaller and smaller; hence, nanotubes hold the promise of creating novel devices replacing conventional siliconbased device technology. Recently, CNTs were grown directly onto the metal electrodes of circuit devices12 and circuits of single-wall carbon nanotubes were assembled.13 Finding an inexpensive method for mass production and purification/separation of these materials will clear the obstacle for their wide-scale applications. Recently, carbon materials have attracted the attention of researchers on the interaction between carbon and water in a broad range of temperatures and pressures. The earlier work showed that hydrothermal pretreatment of the carbon soot increases efficiency of the fullerene 734
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J. Mater. Res., Vol. 17, No. 4, Apr 2002 Downloaded: 13 Mar 2015
extraction,14,15 and purification of CNTs using hydrothermal treatment16,17 or via other routes using aqueous solutions18 has been achieved. In the previous report,19 the hydrothermal behavior of C60 fullerene and the stability region of fullerene under hydrothermal conditions have been established. In this work, as emphasis has been made on the
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