【作者】 徐冰；

【导师】 高宏； 王晶；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2010， 博士

【摘要】 自组装已成为合成纳米材料的一种有效且有发展前景的方法。近年来,利用自组装技术已制备出许多零维、一维、二维和三维结构的纳米/微米材料,并且提出了各种关于自组装合成纳米材料的反应机理。本论文采用自组装技术,通过水热方法合成了几种三维海胆状和花状的纳米/微米薄水铝石和氧化铝,系统研究了制备工艺参数对产物形貌的影响,在实验结果的基础上,详细分析了薄水铝石三维结构的形成机理,建立了晶体的生长模型。本论文的主要内容概括如下：在乙醇—水溶液体系中,利用结晶氯化铝作为反应物,水热合成三维海胆状薄水铝石,经过高温焙烧得到γ-Al2O3,采用一系列手段对产物进行表征,考察了不同铝盐前体、不同醇种类、水醇比例、反应温度及反应时间等因素对三维海胆状薄水铝石形貌的影响。在上述实验结果的基础上推断了海胆状薄水铝石的形成机理,在整个晶体生长过程中,表面自由能F与自组装自由能△G互相竞争和酸侵蚀协同作用机理起到关键作用。起始阶段,由薄水铝石的层状晶体结构决定首先形成不规则片状结构,为了降低表面自由能,片状结构通过氢键聚集形成块体,此阶段表面自由能F占主导地位；随着反应时间的延长,不规则的片状结构在盐酸作用下逐步进化为规则均匀的棒状结构,并且自组装形成海胆状结构,纳米棒之间通过氢键连接,此阶段自组装自由能占主导地位。最后运用此机理解释了各种反应因素对产物形貌的影响。在水溶液体系中,利用阳离子表面活性剂辅助水热合成三维花状薄水铝石,经过高温焙烧得到γ-Al2O3,采用一系列手段对产物进行表征,考察了加料顺序、铝盐与尿素摩尔比、CTAB摩尔数、填充度、反应温度及反应时间等因素对三维花状薄水铝石形貌的影响。在实验结果基础上,推断了花状薄水铝石的形成机理,并运用其形成机理阐释了各种反应因素对产物形貌的影响。在花状薄水铝石的生长过程中,模板剂CTAB起到关键作用,通过CTAB与铝离子的有机—无机协同作用,CTAB形成三维花状胶束,随反应时间的延长,铝离子直接在花状胶束内沉积,最终形成三维花状结构。在水溶液体系中,利用偏铝酸钠和尿素为反应物,采用种分—水热耦合法合成三维花状薄水铝石,经过高温焙烧得到y-Al2O3,采用一系列手段对产物进行表征,考察了偏铝酸钠与尿素摩尔比、反应温度及反应时间等因素对花状薄水铝石形貌的影响。在三维花状薄水铝石的生长过程中,定向附着和碱侵蚀协同作用决定了产物的形貌,运用此机理解释了反应因素对产物形貌的影响。起始阶段,薄水铝石形成的片状结构通过晶间融合自组装形成不规则棒状结构,棒状结构在碱侵蚀作用下逐渐规则均匀,随着反应时间的延长,棒状结构通过氢键定向附着自组装行成花状结构。更多还原

【Abstract】 Self-assembly is becoming an efficient and promising method to obtain nanomaterials. In present years, nano/micro materials with zero dimensional, one dimensional, two dimensional and three dimensional structures have been synthesized by self-assembly and their formation mechanisms have been brought out. In the dissertation, nano/micro boehmite and alumina with three dimensional urchin-like and flowerlike structures were synthesized hydrothermally by self-assembly. The influences of preparation parameters on the morphologies were investigated. The formation mechanisms and growing models of three dimensional boehmite structures are proposed and established on the basis of experimental results. The main points are summarized as follows:Three dimensional urchin-like boehmite structures were synthesized hydrothermally with AlCl3·6H2O serving as the precursor in an ethanol-water mixed solution system. Gamma-alumina with the same morphology was obtained when the samples were calcined at 600℃. The samples were characterized by a series of methods and the influence of precursor type, alcohol type, volume ratio of EtOH/H2O, reaction temperature and reaction time on the final morphologies of boehmite were investigated. The formation mechanism was proposed on the basis of experimental results. The cooperative mechanism between the competition between the surface free energy (F) and the self-assembly free energy (△G) and acid erosion plays a key role. In the beginning, the boehmite nanoplates were obtained resulted with the crystal layer structure of boehmite. Then the nanoplates aggregated into blocks via hydrogen bonds to minimize the surface free energy. The surface free energy was dominant in the stage. The irregular nanoplates evolved uniform nanorods on the effect of hydrochloric acid with increasing time. Finally, the urchin-like AlOOH structures consisting of nanorods were prepared. The nanorods contacted each other via hydrogen bonds. The self-assembly free energy was dominant in the stage. The reason·of the effect of the reaction factors on the final morphologies was explained by the mechanism.Three dimensional flowerlike AlOOH structures were obtained with cetyl trimethyl ammonium bromide (CTAB) serving as the template via a hydrothermal method in a water solution system. After calcination, the boehmite structures could be transformed into gamma-alumina nanostructures while keeping their morphology. The samples were characterized by a series of methods and the influence of mixing sequence, molar ratio of aluminum salts to urea, molar amount of CTAB, reaction temperature and reaction time on the final morphologies of boehmite were investigated. The formation mechanism was proposed on the basis of experimental results and explained the reason of the influence of the reaction factors on the morphologies. The template reagent CTAB plays a crucial role on the formation of the flowerlike boehmite.The novel three dimensional boehmite structures were prepared with sodium aluminate and urea serving as precursors via a seed separation and hydrothermal reaction coupling method in a water solution system. Gamma-alumina with the same morphology was obtained when the samples were calcined at 600℃. The samples were characterized by a series of methods. The influences of molar ratio of sodium aluminate to urea, reaction temperature and reaction time on the final morphologies of boehmite were investigated. The cooperative mechanism between the oriented attachment and base erosion is responsible for the morphology of boehmite and explain the reason of the effect of reaction factors on the morphology of boehmite. In the beginning, the formed nanosheets self-attached through stacking by lattice fusion to generate irregular nanorods. Then the boehmite nanorods became uniform and self-assembled the flowerlike structures via hydrogen bonds by an oriented attachment mechanism with increasing time.更多还原