| Recently, carbon nanomaterials (CNMs) are produced mainly by vapor-phase reactions. However, the structures of the materials could be hardly controlled as a result of the rapid reactions involved. Thus, some effects have been made to prepare CNMs by solid-state reactions. For this purpose, it is critical to have a homogeneous precursor for successful synthesis in solid-state. The precursors used in previous studies are prepared by sol-gel methods or polycyclic aromatic hydrocarbons. They suffer from time-consuming, high cost, and difficult scale-up. Furthermore, a precursor can be used to make only one kind of CNMs. Hence, it is necessary to search for a novel precursor from which different kinds of CNMs can be prepared.In this dissertation, a precursor with homogeneously mixed iron and carbon is fabricated by thermal pyrolysis of C2H2 and a ferrous organic catalyst. By heating the precursor in solid state under different conditions, different CNMs are successfully prepared, including giant fullerene-cages (GFCs), carbon nanotubes (CNTs) and carbon encapsulated magnetic ferrous (Fe@C) nanoparticles.Hollow GFCs are synthesized having one or two walls and sizes of 3-12 nm. This new material may be considered as expansions of single-walled C60 (~0.7 nm) to much higher varieties of C1140 to C18280. This verifies the existence of giant fullerenes beyond C60. The synthetic method involves the heat treatment of the precursor containing 43 wt.% Fe at much lower temperatures (~1000°C) than those used for C60 (> 2000°C) by arc discharge and laser ablation. Using the GFCs with a high specific surface area (535 m2 g-1) and good graphitization as a support material, the prepared Pt catalyst shows apparent improvement in electrochemical activity comparing with the commercial catalyst from Johnson Matthey Co. (electrochemical active surface area: 700 vs. 300 cm2 mg-1).CNTs are synthesized having sizes of 20-50 nm and lengths of 60-2000 nm by solid-phase reaction. For the fabrication, the precursor is enclosed in a quartz tube and the tube is rapidly heated to a temperature of 1300°C for 5 times at a heating rate of approximately 1000°C min-1. High temperature, rapid heat treatment and cycling are the three key factors which are favorable for solid-state diffusion, controlling the size of the Fe catalytic particle, and nucleation of CNTs, respectively. When heated, an embryo of CNT nucleates with a catalyst from the precursor at first and then carbon is dissolved at one side of the catalyst and deposits at the other side. This process leads to CNT growth.Magnetic Fe@C nanoparticles are prepared by heating the precursor at 500-800°C. Heat treatment at low temperatures (<600°C) generates fine nanoparticles (7-8 nm) with superparamagnetic properties, but that at high temperatures (700-800°C) give rise to larger nanoparticles (>10 nm) exhibiting permanent magnetic behaviors. If the precursor is air-oxidized first and then heated to 800°C, a magnetic carbon with a nanoporous and graphitic structure and a high surface area (395 m2 g-1) is obtained. The advantages of the present solid-phase approach over previous gas-phase ones include good controllability of the particle size and thus magnetic properties and suitability for large-scale production. |
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