Abstract
Abstract Transition metal catalysts (mainly: iron, cobalt and nickel) on various supports are successfully used in a largescale production of carbon nanotubes (CNTs), but after the synthesis it is necessary to perform very aggressive purification treatments that cause damages of CNTs and are not always effective. In this work a preparation of unsupported catalysts and their application to the multi-walled carbon nanotubes synthesis is presented. Iron, cobalt and bimetallic iron-cobalt catalysts were obtained by co-precipitation of iron and cobalt ions followed by solid state reactions. Although metal particles were not supported on the hard-to-reduce oxides, these catalysts showed nanometric dimensions. The catalysts were used for the growth of multi-walled carbon nanotubes by the chemical vapor deposition method. The syntheses were conducted under ethylene - argon atmosphere at 700°C. The obtained catalysts and carbon materials after the synthesis were characterized using transmission electron microscopy (TEM), X-ray diffraction method (XRD), Raman spectroscopy and thermogravimetric analysis (TG). The effect of the kind of catalyst on the properties of the obtained carbon material has been described.
Highlights
Carbon nanotubes (CNTs) have unique properties, such as: mechanical, chemical or electrical, and for this reason, are of great interest in many areas of science and technology
All the catalysts revealed the presence of small amounts of calcium and aluminum oxides, which have been added as structural promoters
For iron catalyst 2.8 wt.% of Al2O3 and 1.6 wt.% of CaO and for cobalt catalyst 3.5 wt.% of Al2O3 and 0.2 wt.% of CaO was calculated. For both mixed catalyst 2.1wt.% of Al2O3 as well as 2.3 wt.% and 1.8 wt.% of CaO was determined for Fe:Co (65:35) Fe:Co (50:50), respectively. For this reason the peaks corresponding to these phases were not observed on the diffraction patterns, because these values were below detection of the X-ray diffraction method
Summary
Carbon nanotubes (CNTs) have unique properties, such as: mechanical, chemical or electrical, and for this reason, are of great interest in many areas of science and technology. One of the most popular methods to obtain carbon nanotubes is the catalytic chemical vapor deposition method[4], which is characterized by a simple experimental system, available reagents and allowing the synthesis of carbon nanotubes in the continuous regime This technique is based on the hydrocarbons decomposition on the metallic catalysts e.g. iron, nickel, cobalt[5,6,7], yttrium or molybdenum[8]. As in the case of silica, the properties of alumina can be tuned to create high surface area, mesoporous materials[13], the majority of studies using large-scale alumina supported catalysts for CNTs synthesis show the as-produced bulk alumina with promising CNTs growth results[15,16,17]. The obtained carbon materials have good properties and do not require any removal of supports of catalyst, which is difficult, expensive and time consuming
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