【作者】 杨琪；

【导师】 胡文彬；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 氧化铝是一种非常重要的无机材料,其纳米材料广泛应用于催化剂或催化剂载体、陶瓷材料、复合材料增强物、生物医学材料、半导体材料和光学材料等领域。氧化铝一维纳米材料还具有高弹性模量、高电介质常数、低导磁性、高热传导性和独特的光学性能等特性。因此有关氧化铝纳米材料,特别是氧化铝一维纳米材料的制备成为材料科学界的研究热点。由于液相法具有反应条件容易实现、产物尺寸、结构和成分可控性好、能大量制备的特点,本论文主要研究新的液相制备方法制备几种典型的氧化铝一维纳米材料:如氧化铝纳米棒和纳米线、氧化铝纳米纤维、氧化铝/碳纳米管一维纳米复合材料,主要研究内容及结果如下:1、利用γ-AlOOH独特的层状结构合成γ-AlOOH前驱体纳米棒和纳米线,考察制备条件对产物形貌、物相、比表面积和孔体积的影响,重点研究反应溶液的pH值和反应温度对γ-AlOOH熟化过程的影响。在熟化过程中,反应溶液的pH值和反应温度的升高均加快熟化过程溶解-再结晶速度,使熟化过程进行得更充分。当反应溶液的pH值为4,γ-AlOOH的熟化过程进行得不充分;当反应溶液的pH值升高至5,γ-AlOOH的熟化过程进行得较充分。当反应温度为180℃,γ-AlOOH的熟化过程进行得不充分;当反应温度升高至200℃,γ-AlOOH的熟化过程进行得较充分。熟化过程进行得不充分,生成的产物是形状不规则、表面不光滑的γ-AlOOH条状物,有γ-AlOOH纳米片吸附在其表面,其择优取向不明显,比表面积和孔体积较大;熟化过程进行得较充分,生成的产物是形状规则、表面光滑的γ-AlOOH纳米棒,没有γ-AlOOH纳米片吸附在其表面,其择优取向明显,比表面积和孔体积较小。与γ-AlOOH纳米棒相比,大长径比的γ-AlOOH纳米线的生长初期,通过卷曲生长机制(rolling growth)形成的γ-AlOOH一维纳米结构长度较长,其方向附着机制(oriented attachment)的效应不明显。2、研究γ-AlOOH前驱体一维纳米材料的热分解过程。由于表面羟基的比例很大,γ-AlOOH前驱体一维纳米材料的热分解过程不能视为单速度控制的反应过程,其激活能不是恒定的,其化学吸附水脱出的激活能和其结构水脱出,并转变为氧化铝中间相的激活能分别为-17.71和-155.72kJ/mol。3、利用催化氧化反应合成氧化铝纳米纤维,分析催化氧化反应中汞的作用,考察制备条件对催化氧化反应速度、产物的比表面积和平均直径的影响,研究氧化铝纳米纤维的形核长大过程,并对催化氧化反应制备其他金属氧化物纳米材料进行探讨。在催化氧化反应中,汞不被消耗,它只是作为铝原子传输的媒介,充当催化剂的作用。随着反应温度、铝纯度、反应气氛中氧含量的升高,氧化铝纳米纤维的生长速度加快;随着反应温度、铝纯度、反应气氛中氧含量的升高,氧化铝纳米纤维的比表面积增大,平均直径减小;而HgCl2溶液浓度、铝浸入HgCl2溶液的时间对氧化铝纳米纤维的比表面积和平均直径没有明显影响。通过催化氧化反应还可以制备出其他金属氧化物纳米结构如:氧化锌纳米粒子和纳米片、立方或近立方形貌的氧化亚铜纳米粒子等。引入聚乙二醇胶束为模板,还可以制备出氧化锌纳米空心球、氧化亚铜空心结构等。4、对碳纳米管进行PVA改性,制备出氧化铝连续覆盖碳纳米管表面的氧化铝/碳纳米管一维纳米复合材料,为碳纳米管在复合材料中的应用做准备,研究PVA改性对氧化铝/碳纳米管一维纳米复合材料制备的影响。碳纳米管经过PVA改性,能在碳纳米管表面形成一层连续的PVA覆盖层,提高碳纳米管在水中的分散性,改善氧化铝与碳纳米管的结合。本论文通过对氧化铝一维纳米材料新的液相制备方法进行研究,为今后实现其可控制备,研究其新的物理化学性能提供材料基础,并为进一步完善一维纳米材料的液相制备方法提供新的思路。更多还原

【Abstract】 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.更多还原