Immobilization of CNT on Bamboo Charcoal by TEOS Vapor
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1081-P04-06
Immobilization of CNT on Bamboo Charcoal by TEOS Vapor Jiangtao Zhu, Fung Luen Kwong, and Dickon Hang Leung Ng Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China, People's Republic of ABSTRACT Carbon nanotubes (CNTs) are successfully immobilized on a bamboo charcoal by chemical vapor deposition of gaseous tetraethyl orthosilicate (TEOS). Electron microscopies, Raman spectroscopy and electron energy loss spectroscopy are used to characterize the sample. The CNTs found on the bamboo charcoal support were several microns long, and their diameters ranged from 50nm to 300nm. From the high resolution transmission electron microscopic analysis, we found that the CNTs were composed of ~30 layers of graphitic carbon sheets. Amorphous droplets were also found at the tips of the CNTs. This suggested that the growth of the CNT was via a vapor-liquid-solid mechanism. The amorphous droplets contained calcium, silicon and oxygen. The calcium impurity was originated from the bamboo while the silicon impurity was supplied by the TEOS. CNTs partially filled with calcium silicate were also found. It was evident that calcium silicate had played a critical role in the formation of these CNTs. INTRODUCTION CNT is the focus of attention because of its large absorbance which can exceed that of activated carbon. CNT could effectively absorb dioxin [1], fluoride [2], uraemic toxins [3], natural organic matter [4] and many other types of metal ions [5,6]. However, loosely scattered and randomly oriented CNT are difficult to handle in applications. They are required to be immobilized and anchored on supports [7]. Many types of supports have been studied, such as SiO2 [8], Al2O3 [9], MgO [10], CaCO3 [11], clay [12], and zeolite [13]. Activated carbon is an ideal support for CNTs because they have the same chemical ingredient and similar adsorptive property. At the same time, suitable transition metal catalyst which is needed for the growth of the CNTs should also be uploaded on the support prior to the fabrication of the CNTs [8, 9]. In our study, a simple process was developed to immobilize CNT on a bamboo charcoal support in the presence of TEOS vapor. This bamboo charcoal support contained the source of calcium while the TEOS provided silicon. They have been identified to be the catalysts for the growth of CNTs in our work. EXPERIMENTAL DETAILS Bamboo charcoal was prepared from fresh bamboo with the similar procedure as previously described [14]. Fresh bamboo was annealed to charcoal at 1000oC for 10h in flowing Ar. The bamboo charcoal support was then placed at one end of an alumina tube. The other end of the tube was connected to a bath of TEOS solution (Sigma-Aldrich, St. Louis, MO). The system was repeatedly pumped down to 10-2 torr and flushed with Ar, before the temperature of
the system was raised to temperatures between 1250~1350oC in flowing Ar at a rate of 40 ml/min. When the furnace reached the target temperature, the Ar gas was re-routed into the TEOS bath at 50oC
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