The Preparation And Growth Mechanism Of Coiled Carbon Nanofibers With Symmetrical Structure And Multi-Branched Carbon Fibers

Recently, the investigation of carbon nanofibers attracted the attention of many researchers. Carbon nanofibers have many unique properties, such as low density, high modular ratio, high strength ratio, high conductivity, high specific surface area, and profound potential applications in catalysts and catalyst supports, Li-ion batteries, electrochemical double-layer capacitors and field emission displays, and so on.In this paper, several kinds of nano copper catalysts with different size were synthesized through different preparation methods, and carbon fibers were synthsized with these copper catalysts. It was discussed that the effect of the size of nano copper catalyst particles on the morphology of carbon fibers. The effect of reaction temperature on the growth mode of carbon fibers was also studied. Through the observation of the carbon fibers with different growth periods, multi-branched carbon fibers with different growth modes were investigated and corresponding growth models were established. Through the surface reconstruction of catalyst particles, the induction of hydrogen has a serious effect on the formation of Y shaped carbon fibers. Through HRTEM analysis, the growth mechanism of coiled carbon nanofibers was studied. The main content as follows:(1) The size of nano copper catalyst particles and reation temperature have effect on the morphology of carbon fibers. Nano copper catalyst with different size can synthesis straight carbon fibers, coiled carbon nanofibers and the mixture of above-mentioned two kinds of carbon fibers. In a word, the size of nano copper catalyst particles not only dicided the diameter of carbon fibers, but also affect the morphology of carbon fibers directly, that is, the smaller catalyst particles are apt to synthesize coiled carbon nanofibers, the bigger ones to straight carbon fibers. In addition, the reaction temperature also affects the morphology of carbon fibers and can change the growth rate of carbon fibers. In this paper, straight carbon fibers have been obtained using copper tartrate catalyst precursor at 200 oC.(2) The agglomeration phenomenon of nano copper catalyst particles was studied in the initial growth period of carbon fibers. The growth mechanism of multi-branched carbon fibers was explained through the preparation and characterization of carbon fibers with different growth periods, and the growth models of carbon fibers were established.The TEM and SEM results show that it is the growth directions of carbon fibers over nano-copper catalyst particles in their agglomerations are not parallel, which lead to the existence of inner stress between carbon fibers, and multi-branched carbon fibers was obtained finally.(3) Due to the reconstruction of the surface of nano copper catalyst particles with the participation of hydrogen gas, Y-shaped carbon fibers were synthesized successfully. At the reaction temperature (279 o), hydrogen gas has reconstructed the surface of nano copper catalyst particles, which lead to the formation of three carbon fiber growth faces on the surface of catalyst particle. During the period of carbon fibers growth, each nano copper catalyst particle can synthesize three pieces of carbon fibers simultaneously, and then Y-shaped carbon fibers were obtained finally.(4) Through TEM and SEM analysis, the growth mechanism of coiled carbon nanofibers was investigated. The anisotropy of nano copper catalyst particles to the growth of carbon fibers is the key for the formation of coiled carbon nanofibers. There maybe has oxide of copper in the surface of nano copper catalyst particles. The angle between two pieces of coiled carbon nanofibers grown from a nano copper catalyst particle usually is 70 o or 110 o.