The Synthesis And Application Study Of Carbon Nanotubes And Graphene

Due to the structural diversity of the element carbon and compounds, carbon and its compounds have been one of the research focuses in the fields of materials, physics, chemistry. Especially in recent three decades, as the star materials of C60, carbon nanotubes (CNTs), graphene (Graphene) were continuously found, the study of carbon material is never ever so prosperous. To achieve its application of a material, the premise is that the material needs to be excellent and irreplaceable, it carried out large-scale preparation and controllable preparation as well, this is also the research focus of two new carbon nanomaterials, carbon nanotubes and graphene. In view of this, this thesis proposes a new method for the ultra-fast, large-scale preparation of graphene, which named molten carbon-containng alloy quenched carbon slfe-segregation (MQCS); Some fabrication methods of several kinds of carbon nanotubes with special structures have been proposed and designed. On basis of these works, research on the hydrogen generation performance of Al-Sn/CNTs composites which was produced by the carbon nanotube and the Al-Sn hydrogen-generation alloys firstly was presented by the thesis, as well the corrosion resistance performance of Ni alloy strip coated by graphene composite films which was produced by the method of molten carbon-containng alloy quenched carbon slfe-segregation, have been inverstgated. And the following results have been obtained:The process conditions of preparing carbon nanotubes by a floating catalyst method are studied, and the carbon nanotubes arrays and films required in experiments of this thesis were prepared. By rolling of Al-Sn alloy, a novel hydrogen-generation alloy was developed that can react with water directly and quickly and produce hydrogen at room temperature. The influence of alloying elements on the hydrogen generation rate and yield are studied, it waas found that the alloy with the aluminum content of27wt%, the volumes of Al and Sn in the alloy were at the same, hydrogen evolution rate was the highest. While if the alloy has the aluminum content of45wt%, the hydrogen yield reached maximum,2.3L/cm3(0.2g/cm3), which is superior than that of the traditional hydrogen storage alloy and can be compared with the metal hydride. Through the high temperature high pressure process, the Al-Sn alloy composite materials containing carbon nanotubes were prepared. The studies show that, with the increase of the amount of carbon nanotubes in the composite material, the hydrogen yield and hydrogen evolution rate of the composite material increased. While, When the carbon nanotube content was same in the composite, the hydrogen yield and hydrogen evolution rate of the composite containing single-walled carbon nanotubes are greater than those of composite containing multi-walled carbon nanotubes. Combined with other theoretical researches and the experimental phenomena here, we guess that the above phenomenon can be explained as the followings. The flow of water molecules in the inner of single wall carbon nanotubes is far higher than that in the multi-walled carbon nanotubes, which increases the probability of water molecules into the alloy and the reaction between Al-Sn alloy and water, thereby increases the reaction rate of the composite with water directly and the capacity for generating hydro gen.Using anodic aluminum oxide (AAO) as the template, though a new method that expands again the pores of AAO where the carbon nanotubes or nanowires were prepared, and carbon nanotubes or nanowires are grown again then, a heterostructure with a larger contact surface when the silver nanowire is connected to the carbon nanotube in axial direction, but in the radial direction is wrapped by carbon nanotube is obtained. A new structure of carbon nanotubes with depressions or windows in their walls was fabricated using the AAO template by adjusting the heat treatment temperature of the Ag nanowires having been obtained in the AAO pores and the temperature of growth of carbon nanotubes, which lets the Ag nanoparticles dispersed on the walls of AAO pores and thus changes the morphology of the walls of AAO pores and lets the carbon nanotubes copy this morphology in their growth process. On this basis, a new heterostructure with platinum nanoparticles embedded in the carbon nanotube wall, other than attached on the inner or outer surfaces of the carbon nanotubes is prepared. The above structures are firstly obtained in this these, which enrich the morphology and structure of carbon nanotubes, and may have some new performances and play special roles in fields of energy, drug delivery, nanoelectronic devices and so on. A novel method for large-scale preparation of graphene, which called the molten carbon-containng alloy quenched carbon slfe-segregation (MQCS) in the thesis was developed. This method is characterized by using preparation amprphous alloy strips with of single-roller melt-spinning equipment, jetting molten Ni/C alloy to high-speed rotating copper roller, obtained instantaneously (less than0.2seconds) the a continuous alloy strip of a few millimeters wide several meters long with its surface coated graphene composite films.Through the qualitative description of strip morphology and the half quantitative analysis of x-ray energy dispersive spectrum (EDS), the effects of carbon content in nickel alloy and the rotation speed of copper roller on the growth of graphene film were studied. It is found that:if the carbon content is less than0.2wt%, the graphene can not be gotten. The higher the content of carbon in the alloy, the higher the carbon content on alloy strip surface, the larger the graphene area it got. However, if the carbon content in the alloy is higher than0.6wt%, graphene will coat the alloy strip totally. In order to get thin graphene layer, the carbon content is better in the range of0.6-0.3wt%in present experimental condition; meanwhile, it is found that the faster coppor roller rotated, the thinner the strip was, the faster the cooling rate was, the more carbon segregated, the larger coverage the graphene films on the surface of the alloy strip had. In order to get thinner and more uniform graphene films, the appropriate speed should be at4000-6000rpra Studies on the growth mechanism of the graphene by the method is different from the carbon diffusion in the solid in the process of carburizing and depositio carbon in the common CVD method, in this method, the diffusion of carbon is mainly in melting of the Ni alloy, with the increased diffusion rate and depth, the graphene can be grown at a incomparable speed compared to the CVD method. The cooling rate ofthe quenching of melting Ni/C alloy is as high as104-106K/s, the fast diffusion of carbon Atomic caused by the great variation of temperature gradient and the chemical potential gradient is stronger than the affect of the decreasing diffusion speed due to the rapid solidification. Thus, the performace is still the precipitation of a large number of carbon atoms. At the same time, the rapid cooling causes grain refinement, provides more diffusion points of the precipitation of carbon atoms, improves the diffusion efficiency, further accelerates the carbon atoms precipitation. Therefore, a large quantities of graphene and few-layer graphene are formed on the surface of nickel alloy strips.The corrosion resistance of the alloy strip prepared by the present method has been investigated. Through the comparison of the samples’polarization curves covered with different areas of graphene composite films, it was found that corrosion potential of the Ni alloy strip fully coated with graphene composite film is significantly higher than that of pure nickel, the corrosion current is two orders of magnitude lower than that of the pure nickel. It showed that the corrosion resistance of the alloys strips with fully graphene composite film coated is far better than the pure nickel samples; and the larger the coated graphene composite films area is, the better he corrosion resistant performance of the alloy strip is. The graphene composite films can improve the corrosion resistance of the metal, because the graphene composite film plays a role as the barrier layer of ion. And by reducing the chance of reaction ofNi metal and ion, the corrosion rate is lowered.