METALS AND MATERIALS International, Vol. 14, No. 3 (2008), pp. 385~390 Carbon Nanotubes Grown over Fe-Mo-Mg-O Composite Catalysts Yanfang Chen 1 , Doh-Hyung Riu 2 , and Yun-Soo Lim 1,3,* 1 Dept. of Materials Science & Engineering, Myongji University, San 38-2, Nam-dong, Yongin-si, Gyeonggi 449-728, Korea 2 Nano Materials Team, Korea Institute of Ceramics Engineering & Technology, 233-5, Gasan-dong, Guemcheon-gu, Seoul 153-801, Korea 3 Dept. of Nano Science & Engineering, Myongji University, Gyeonggi-do, 449-728, Korea High quality, high yield carbon nanotubes were synthesized on a composite catalyst using catalytic chemical vapor deposition. The composite catalysts Fe/MgO, Mo/MgO and (Fe, Mo)/ MgO, prepared via the sol- gel method using citric acid as fuel, were investigated for the production of CNTs. Only the (Fe, Mo)/MgO catalyst could support CNTs growth with high yield in this study. The different mole ratios between Fe, Mo, and Mg resulted in changes in product structure, diameter size, and yield. Decreasing the Fe concentration reduces the structural defects, and by increasing the Mo concentration, the yields of CNTs clearly increase. Keywords: carbon nanotubes, catalyst chemical vapor deposition, composite catalyst 1. INTRODUCTION Since their discovery in 1991, carbon nanotubes (CNTs) have been the focus of many studies [1]. Ideal carbon nano- tubes can be thought of as hexagonal networks of carbon atoms that have been rolled up to make a seamless cylinder. There are three schematic models of carbon nanotubes: zig- zag, chiral, and armchair. The cylinder nanotubes can be tens of microns long. Single-wall nanotubes can be thought of as the fundamental cylindrical structures, and they constitute the building blocks of both multiwall nanotubes and the ordered arrays of single-wall nanotubes known as ropes [2]. Due to their particular structure, CNTs have many excellent properties, including unique mechanical and electrical behav- iors. They have been applied in a range of practical nano- technologies including sensor [3], FED [4], energy storage [5], reinforcements [6], and electro-catalyst support [7]. Many methods have been developed to produce CNTs, such as arc-discharge, laser evaporation, and chemical vapor dep- osition (CVD). CVD includes catalytic chemical vapor dep- osition (CCVD) [8], plasma-enhanced chemical vapor deposition (PECVD) [9], and microwave plasma-enhanced chemical vapor deposition (MPCVD) [10]. Due to benefits such as its high purity and high yield for CNT preparation along with its simple requirements related to its furnace, power, and case of manipulation, the CCVD method has attracted a great deal of attention [11]. It has been found that the structure of carbon nanotubes is dependent on growth parameter such as the reaction temperature, catalyst, or reac- tion gases [12]. Among these parameters, the catalyst is con- sidered to be the most important. Recently, the use of the composite catalysts has attracted much attention in the area of large-scale production of single-wall carbon nanotubes (SWNTs) or multiwall carbon nanotubes (MWNTs) due to their extraordinary application to electronic and composite materials. Thus far, two types of composite catalysts have been examined in the literature: M/ Oxide and M-Mo/Oxide (M = Fe, Co, Ni and Oxide = MgO, SiO2 , CaO, ZrO 2 or Al 2 O 3 ). Compared to M/Oxide, M-Mo/ Oxide is much more frequently used for the growth of CNTs [13-20]. Mehn et al. [21] synthesized SWNTs using Fe/Mo/ Al 2 O 3 and report several effective factors related to the qual- ity and quantity of SWNTs with the CCVD method. They note that there was no significant correlation between the specific surface area and the activity of the catalyst and found that the irregularly shaped micropores of alumina gel were unsuitable for SWNTs synthesis. Flahaut et al. [22] developed the Mg (1-x) Co x O solid solution as a catalysts for the synthesis of CNTs for the notable reason that MgO was easily removed from the material after a CNTs-forming reac- tion by mild non-oxidative washing with an HCl aqueous solution. Li et al. [23] also used MgO as the substrate of composite catalysts and produced large-scale SWNTs. Tang et al. [24] replaced citric acid with urea and reported better results. It was reported that an iron catalyst had a markedly less structure-sensitive interaction between formed carbon *Corresponding author: yslim@mju.ac.kr doi: 10.3365/met.mat.2008.06.385 Published 23 June 2008