Preparation Of One Dimension Alumina Nanomaterials By Solution-Phase Methods

Alumina is one of the most important inorganic materials. Nanostructured alumina has broad applications in catalysts, catalyst supports, ceramic materials, reinforces of composites, biological materials, semiconducting materials and optical materials. In the past decade, the synthesis of 1D alumina nanomaterials has received considerable interest due to their unique properties, such as high elastic modulus, high electric medium constant, low magnetic conductibility, and unique optical characteristics.Various methods have been employed for the preparation of 1D nanomaterials. Among them, solution-phase approaches are especially powerful synthetic routes due to their mild reaction condition, controllability of size, structure and component for products and large production. In this dissertation, novel solution-phase methods are investigated to synthesize several kinds of typical 1D alumina nanomaterials, such as alumina nanorods, nanowires, nanofibers and alumina/carbon nanotubes 1D nanocomposites. The results and discussion are shown as follows:1,γ-AlOOH precursor nanorods and nanowires were prepared by rolling ofγ-AlOOH layers. The effect of processing parameter on the morphology, phase, specific surface area and pore volume of theγ-AlOOH, and the effect of pH value and temperature on the velocity of dissolution–reprecipitation were studied.During Ostwald ripening, higher pH value and temperature enhance the velocity of dissolution–reprecipitation. Increasing of pH value and temperature will promote the Ostwald ripening of theγ-AlOOH. When the pH value increase from 4 to 5, or the temperature increase from 180℃to 200℃, the effect of Ostwald ripening become adequate.If the effect of Ostwald ripening is not adequate, the obtained products are needle-likeγ-AlOOH with irregular shape and unsmooth surface, someγ-AlOOH nanosheets are adsorbed on their surface, their preferred orientation is not apparent, their specific surface area and pore volume are biggish. If the effect of Ostwald ripening is adequate, the obtained products areγ-AlOOH nanorods with regular shape and smooth surface, noγ-AlOOH nanosheets are adsorbed on their surface, their preferred orientation is apparent, their specific surface area and pore volume are lesser.Compared withγ-AlOOH nanorods, the length ofγ-AlOOH nanowires with big aspect ratio is much longer. At the initial stage of their growth, the effect of oriented attachment is not apparent.3, Heat decomposition course of the 1Dγ-AlOOH nanomaterials was studied. Because the proportion of hydroxyl groups on the surface of 1Dγ-AlOOH nanomaterials is very large, their heat decomposition course can not be regarded as a single rate controlling process, their associated activation energy is not constant, the activation energy of desorption of chemisorbed water and conversion into transition alumina are -17.71 and -155.72, respectively.4, Alumina nanofibers were prepared by catalytic oxidation of Al. The function of Hg during catalytic oxidation, the effect of processing parameter on the velocity of catalytic oxidation, specific surface area and average diameter of the obtained products, the nucleation and growth of alumina nanofibers were investigated.During the oxidation of Al, Hg serves as a medium to transfer Al atoms. Increasing of temperature, purity of Al and content of oxygen will accelerate the oxidation of Al, raise the degree of supersaturation of alumina in liquid Hg, and then result alumina nanofibers with bigger specific surface area and smaller average diameter. The concentration of HgCl2 solution and the soaking time have no apparent effect on their specific surface area and average diameter.The catalytic oxidation was employed to fabricate other metal oxide nanostructures, such as ZnO nanoparticles and nanosheets, cube-like CuO2 nanoparticles, ZnO hollow spheres and CuO2 hollow structures, etc.5, Alumina/carbon nanotubes 1D nanocomposites with continuous alumina layers on the surface of carbon nanotubes were prepared with the carbon nanotubes modified by PVA. The modification of carbon nanotubes by PVA will increase dispersibility of carbon nanotubes, and improve combination of carbon nanotubes and alumina.In a word, in this dissertation, the preparation of 1D alumina nanomaterials by novel solution-phase methods are studied for their controllable synthesis, investigating their new properties in the future, and providing supplementary for solution-phase methods of 1D nanomaterials.