Selective-Controlled Synthesis And Properties Of Micro/Nano-sized Carbon Materials Via Arc Plasma

Micro/nano-sized carbon materials have attracted extensive research interests across the world in recent years due to their unique physical and chemical properties as well as potential applications in many high-tech fields. Selective and controlled preparation with low price is the precondition of commercial application of these functional carbon materials. Based on the specific structure and chemical composition of coals, a series of functional carbon materials have been successfully fabricated via the technique of arc plasma or arc plasma coupled with chemical vapor deposition (CVD) and the results obtained are summarized as follows.A multi-functional device of arc plasma system was designed and built. Various hydrocarbons could be introduced into the plasma zone via the hole in the cathode for making different carbon materials. The process of arc plasma could be diagnosed in-situ by optical emission spectroscopy (OES).One-dimensional (1 D) nanomaterials, single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs), were synthesized by arc plasma method using coal-based carbon rods as the evaporating anode. The influences of experimental parameters, such as the catalyst, atmosphere, pressure, coal types and carbonization temperature of rods, on the production of SWCNTs were investigated systematically. The results show that Taixi anthracite is a suitable carbon source for mass production of SWCNTs with Y2O3 and Ni as catalysts at a helium pressure of 0.05 MPa. The yield of the SWCNTs could reach up to 10%. The species in the arc plasma during the preparation process were analyzed using OES. The OES analysis reveals that active species such as C2 dimers and CN species were present in the arc plasma and the active intermediates involved in the formation and growth of SWCNTs. The impurity was removed by mixture acids combined with air and the purity of the SWCNTs was about 90 wt.%. High quality DWCNTs could be obtained in large scale in the mixture of hydrogen and helium using FeS as catalyst. The production rate of DWCNTs was 25 mg/min. The CH species as well as C2 dimers were identified in the preparation process of DWCNTs.Zero-dimensional (0 D) nanomaterials, nano onions-like fullerences (NOLFs) and carbon-encapsulated magnetic nanoparticles (CEMNs), were fabricated on a large scale by arc plasma combined with CVD in acetylene atmosphere. The NOLFs have several hundred graphene layers with concentric circle structure. The as-obtained CEMNs with well-ordered graphitic shells have narrow diameter distribution and ferromagnetic properties at room temperature. The results suggested that the magnetic nanoparticles could be well protected from the acid eroding.A series of micrometer sized carbon materials were selectively prepared with high efficiency on a large scale by arc plasma coupled with CVD in the presence of hydrocarbons, of which coal-based carbon rods were used as consuming anode. The synthesis of micrometer carbon materials, such as carbon belts, carbon micrcoils (CMCs), carbon microtrees, carbon strings and hierarchical carbon microfibers, have been accomplished by adapting the experimental condition. It is found that the carbon belts obtained have the width of 1.5-2.5μm, the thickness of 50-200 nm and the length of hundreds of micrometers, of which possess a large width-to-thickness ratio. A combination process has been demonstrated in which catalyst grain with a shape of cuboid formed during arc plasma was responsible for the growth of carbon belts during the subsequent chemical vapor deposition. The CMCs are composed of almost amorphous carbon without any pore in the fiber axis, existing both left-chirality and right-chirality. It is found that the carbon micro-trees grew on the anode surface with highly-oriented arrays when iron was used as catalyst in the presence of acetylene. The carbon micro-trees have a solid inner core and an anisotropic yet highly graphitized structure. The Young's modulus of the micro-trees is comparable to that of carbon nanotubes reported in literature. In the case of the un-treated coal-based anodes, a large amount of whisker-like strings that are perpendicular to the anode surface in aligned arrays and composed of nano-sized carbon fibers in diameter 50-200 nm are obtained. When the coal-based anodes are impregnated with salt solution, thorn-shaped fibers act as their basic building blocks.