Controlled Preparation Of Carbon Nanotubes And Their Composites Via Chemical Vapor Deposition

As an emerging class of one-dimensional materials, carbon nanotubes(CNTs), seamlessly rolled up from graphite sheets, have attracted tremendous research attention due to their unique electrical, mechanical and chemical properties. Over the past two decade, the efforts on CNT research has shift to their applications in the fields of biology, electronics and composites, after the initial fundamental research mainly focusing on the synthesis of high-quality nanotubes. The development of the nanoscience and nanotechnology has been promoted greatly by the work on CNTs. Up to now, there are still several challenges or obstacles restrict the industrial applications, such as the approaches for the synthesis of low-cost and high-quality CNTs in large-scale; efficient strategy for the tuning of structure and electronic properties of the produced CNTs; and the thorough understanding of the growth mechanism of CNTs.In this work, we fabricate CNTs, CNT-assembly and CNT-based composites by chemical vapor deposition (CVD), including both fixed catalyst and floating catalyst methods, as mentioned in detail in the following:We focus on the extending lifetime of catalyst and growth rate of CNTs by tuning the experimental conditions, such as the growth time, especially the gas composition of the atmosphere. It is found that the yield and purity are significantly influenced by the addition of weak oxidant and/or sulfur-containing precursors (CO2 or SO2) during chemical vapor deposition over CoMo/MgO porous catalyst prepared by a sol-gel combustion method.Various flower-like morphologies consisting of CNTs have been synthesized on the surface of pretreated silicon substrate, and numerous micrometer-sized tubes made of CNTs have been synthesized on the silicon substrate in the presence of weak oxidizer (CO2).CNT/cement composites have been achieved by the floating catalytic chemical vapor deposition with cement as substrates. The results show that adhesion strength in the CNT/cement composites can be classified into two types in view of the coalition mode:(1) strong bond, that is CNTs grown directly on the surface of cement particulates; (2) weak bond, CNTs attaching on the surface of cement particulates. In addition, nanocarbons with novel helical structures have been fabricated over Fe/cement catalyst prepared with impregnation method.