【作者】 戚克振；

【导师】 郑文君；

【作者基本信息】 南开大学 ， 材料物理与化学， 2013， 博士

【摘要】 离子液体作为一种新型的绿色环保溶剂在无机纳米材料的合成领域得到了广泛的关注。本论文将离子液体的分子特征与材料表面结构特点相结合,采用密度泛函理论(DFT)方法辅助计算,分析得出离子液体在纳米材料合成中可与晶体表面形成氢键及静电作用。离子液体与晶面的这种相互作用改变了正在生长中的纳米晶的表面化学,从而实现了对形貌和微观结构的调控。本论文以离子液体控制TiO2形貌为研究主体,采用第一性原理DFT计算,系统地考察了离子液体与TiO2表面之间相互作用的本质。基于DFT计算的表面能和Wulff定律,得出了离子液体生长环境对纳米材料的形貌影响的因素及其形貌演化规律。在此基础上,研究几何匹配与离子液体选择性吸附的微观联系和规律,提出了几何匹配原则。本文具体的研究内容包括：(1)结合周期平板模型,通过密度泛函计算模拟离子液体[Emim]Br在Ti02低指数晶面上的吸附情况,以此来研究离子液体环境对TiO2纳米晶形貌的影响。发现离子液体[Emim]Br优先选择吸附在金红石的(110)面和锐钛矿的(101)面。吸附的离子液体能有效的改变TiO2纳米晶的表面能,使得晶面间的表面能差距明显增大,特别是锐钛矿(101)和(001)之间,以及金红石(110)和(001)之间。这一变化增加了锐钛矿(100)晶面的暴露比例,增加了金红石纳米晶的长径比。这一计算结果已经得到了我们的实验验证。(2)利用DFT计算和实验相结合的方法分析了离子液体与晶面的匹配程度对离子液体吸附选择性的影响。首先对一种典型的离子液体[Emim]Br在Ti02表面的吸附做了详细的计算,得到离子液体的最稳定吸附状态。通过吸附热与结构参数比较发现,离子液体[Emim]Br的吸附强度与几何匹配程度存在着一致性。通过该匹配关系选择氨基离子液体辅助成功合成了一维ZnO纳米线。由此得到了一个具有普适的规律：离子液体的几何结构与晶面参数的匹配将有助于我们判断其吸附的选择性。这一几何匹配原则为导向合成纳米材料提供了一个新方法。(3)利用离子液体辅助水热方法合成形貌可控的ZnO纳米环并对其荧光性质进行了初步研究。采用简单的水热反应体系,通过选用离子液体[C3mim]Br作为结构导向剂,在适当的pH值、反应温度等条件配合下,成功合成了ZnO纳米环,并且实现了ZnO纳米环产物的长径比可控。结合第一性原理DFT辅助计算,对纳米环的形成机理和[C3mim] Br所发挥的重要作用给出了详细的阐述。纳米环的形成主要源于离子液体[C3mim]Br对ZnO侧面(10-10)的保护作用以及(000-1)晶面上较高的缺陷密度导致该面腐蚀较快而消失,从而形成环状结构。更多还原

【Abstract】 Ionic liquids as functional solvents have been attracted great attention to prepare inorganic nanomaterials. Recently, ILs have become a kind of fascinating reaction medium component for the synthesis of inorganic materials, because they offer the potential for morphology control that is not possible from other synthetic methods. ILs can form highly ordered structures on the growing crystal facets through their wealth non-covalent interactions, and this modification of surface chemistry and energetics of primary nanocrystals are both important factors for affecting the shape of nanocrystals. On the basis of DFT calculations and experiment, we proposed a new concept, geometric matching principle, in which is meaningful for prediction of the adsorption selectivity of ILs on crystal facets and clarification of the mechanism for shape-controlled chemistry. We think this geometric matching principle opens a new perspective for creating new nanosructures and is a significant step toward the ultimate goal of controlling synthesis of inorganic nanomaterials. The main content is as follows:(1) We obtain a profound understanding of ionic liquids affect the morphologies of TiO2nanocrystals. DFT calculations have been performed to study [Emim]Br adsorption of the TiO2surfaces, and the equilibrium crystal shape of TiO2has been predicted using the Wulff construction. The gap of surface energy is shown an obvious increase after [Emim]Br adsorption, especially, between (101) and (001) for anatase, and also between (110) and (001) for rutile. This gap variation results in increasing the (100) facet exposure of anatase, and an increase in the aspect ratio of rutile nanocrystals, which is verified by our experiments.(2) We proposed a new concept, geometric matching principle, in which the adsorption site of substrate should not only meet the space requirement for interionic stacking of imidazole cations, but also maximize the interaction of the adsorbed imidazole cations within ILs. In this case, the interaction between adsorbed ILs and substrate is thus maximized. This geometric matching principle is a significant step toward the ultimate goal of controlling synthesis of inorganic nanomaterials. (3) Morphology-controllable ZnO nanorings with high crystallinity were synthesized by a simple hydrothermal approach, using ionic liquid as a stabilizing agent or template. The growth mechanism of these ring-like ZnO nanocrystals was explored based on first-principles calculations and a series of controlled experiments where the concentration of [C3mim]Br was tuned. The photoluminescence spectra reveal that the as-prepared ZnO nanorings exhibit blue emission.更多还原