Synthesis Of Carbon Nanotubes By Chemical Vapor Deposition With Natural Nano-minerals As Catalyst And Studies On Hydrogen Absorption In Carbon Nanotubes

Great attentions have been paid in the studies of synthesis and applications of carbon nanotubes (CNTs) since the last decade. Several methods have been developed to synthesize nanotubes, including arc-discharge, laser ablation of graphite and chemical vapor deposition (CVD). The experimental results and theoretical calculations have proved that CNTs are of excellent properties in electronic and thermal conducting, as well as mechanics, which enable them to be used in nano-electronic devices, flat panel display, sensors, probes of tunneling microscopes and composites with good electronic, thermal conducting and mechanical reinforcements. All these potential application fields promote researchers to synthesize of CNTs in a high yield. The CVD method, because of its simplicity and low cost, will probably become the method of choice to produce the large quantities of CNTs necessary for fundamental as well as nano-technological purposes.In the thesis, the morphologies, structures, physical properties and preparation methods of CNTs were briefly reviewed. The syntheses of CNTs by CVD method were discussed in details, especially the effects of catalyst carriers (support) on the CNTs syntheses. Thereafter, the ideas of special natural nano-mineral materials and nanocrystalline CaCO₃ as catalyst carriers came into consideration. The previous reports on hydrogen storage in CNTs were also reviewed. The obviously dispersed data reported in literatures stimulated the author to perform the experimental measurements of H₂ absorption abilities in CNTs and related materials in order to evaluate its capacity of H₂ storage.The naturally formed minerals of hormites in the earth, such as sepiolite and palygorskite, are very similar to those of artificial nanomaterials (CNT) in size, morphology and structure. Experimental results proved that both of them could support metallic catalyst by precipitation, and directly decompose acetylene to prepare multiwalled CNTs. The intensive interaction between the supports and catalytic metal kept the formed catalyst nanoparticles from agglomeration at high temperature and gave rise to the uniform diameters of CNTs grown over the supports. The catalytic metal nanoparticles with a smaller size could nucleate CNTs, while nanoparticles with a larger size tended to be covered by graphene sheets and deactivated its catalysis property.At previous cases, the nano-minerals only played a role of catalyst carrier. What nucleated CNTs and was responsible for their growth were transition metallic nanoparticles. Titanate modified palygorskite could change the conditions of ferric components in the mineral under reductive atmosphere at elevated temperature. They could transform into iron nanoparticles and catalyze CNTs growth. The catalytic activity of the modified mineral was strongly correlated with temperature, for the mineral phase would be changed at higher temperature. Judging from TEM observations, the central cores of the CNTs were usually filled with single-crystalline nanowires which were formed using CNT as template at high temperature,>800. Marine manganese nodules powders could decompose acetylene to synthesize CNTs without any prior modification, which was proved by further experimental performance. A large fraction of helically coiled CNT product could be obtained by facilely changing the experimental conditions. In the product, a unique category of carbon nanostructure with harmoniously triple helices was firstly observed. A typically dual growth mode of CNT was developed in the thesis based on the TEM observations, i.e., a combination of based growth and tip growth.In order to easily remove catalyst impurities, nanocrystalline CaCO3 was also used as catalyst carrier. Some important parameters were investigated in the paper, such as category and content of metallic catalyst, reaction temperature and time, et al. The purification of the raw product could be achieved in one step, possessing little structural destructivity. All these results might broaden the application fields of nanocrystalline...