Preparation of Carbon Nanotubes by Using Mesoporous Silica
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Preparation of Carbon Nanotubes by Using Mesoporous Silica Shinji Kawasaki, Shingo Komiyama, Shigekazu Ohmori, Akifumi Yao, Fujio Okino and Hidekazu Touhara Faculty of Textile Science & Technology, Shinshu University Tokida, Ueda 386-8567, JAPAN ABSTRACT Carbon nanotubes were synthesized using several mesoporous silica templates with different pore sizes in order to investigate the possibility of controlling the diameter of carbon nanotubes by changing the pore size of the mesoporous silica. TEM observation confirmed that carbon nanotubes with uniform diameter can be obtained by the present method. However, it was found that it is difficult to prepare carbon nanotubes having diameter smaller than 20 nm by the present method even if the template with small pore size is used.
INTRODUCTION Owing to their new functional properties as electrode materials and hydrogen storage materials, carbon nanotubes attract rapidly growing attention [1]. Concerning the preparation of the carbon nanotubes, one of the most important problems is how to prepare nanotubes with desired form. Another significant problem is how to obtain such nanotubes in a large scale. Chemical vapor deposition (CVD) based synthesis of carbon nanotubes using an anodic aluminum oxide (porous alumina) membrane template is an interesting way to overcome the above mentioned problems [2, 3]. However, the tunable diameter of the nanotube prepared by the template carbonization method using porous alumina is limited to 20 nm. Furthermore, it is not easy to control the pore size and the thickness of the alumina membrane simultaneously. In the last decade, several techniques for making highly ordered periodic mesoporous silica with pore sizes of 2 - 50 nm have been developed [4, 5]. There are several types of pore alignment known as cubic, 3d-hexagonal and 2d-hexagonal. The 2d-hexagonal silica has cylindrical pores arranged in the honeycomb fashion. Using the ordered mesopores, nanostructured carbon materials have been tried to be synthesized and Jun et al.[6] succeeded in making a carbon replica of mesoporous silica. In the present study, we have tried to prepare carbon nanotubes using mesoporous silica by template carbonization method. We have investigated the possibility of controlling the diameter of carbon nanotubes by changing the pore size of the mesoporous silica.
EXPERIMENTAL DETAILS Mesoporous silica with mesopores of 2 - 4 nm and 6 - 20 nm in diameter were synthesized in the presence of cetyltrimethylammmonium bromide (CTAB, Aldrich) surfactant and triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P(EO) -P(PO) -P(EO) ) copolymer (Pluronic P123, BASF), respectively. Trimethylbenzene (TMB) was used as an organic swelling agent to enlarge the mesopore. The solution mixture was aged for 24 h at 353 - 383 K. Calcination was carried out by slowly raising the temperature from room temperature to 873 K.
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CVD experiments were performed as follows. A mesoporous silica sample was evacuated in a SiO tube at 383 K for 30
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