【作者】 段小川；

【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】 离子液体是指在室温下呈现液态、完全由离子所组成的有机溶剂,由于其独特的物理化学性质而受到广泛关注。相比于其在有机化学和催化领域的应用,离子液体在无机纳米材料合成方面的应用研究才刚刚开始。不同于之前传统分子溶剂(水或有机溶剂),以离子液体作为合成反应的介质具有独特的优势,可以制备具有特殊物相和形貌的无机纳米材料。到目前为止,已经有大量的研究报道了使用离子液体可以可控地制备无机纳米材料,但是对于其作用机理仍然没有清晰的认识。因此,在很多的研究工作中,离子液体仅仅是被当作简单的表面活性剂,其独特的优势并没有被完全展示出来。在本文研究中,我们系统地研究了离子液体在合成无机纳米材料中的作用机制,这些研究有望为如何使用离子液体可控合成特定物相和形貌的无机纳米材料提供一定的借鉴价值。论文的具体研究内容如下：1.以NH4-Dw和7-AlOOH为目标作用物,系统地研究了离子液体在反应过程中所起作用,首次在同一反应体系中提出两种不同的离子液体作用机制。首先,通过控制反应体系温度可以实现由NH4-Dw向y-AlOOH的物相转变。其次,通过调节体系中所加离子液体[Bdmim]Cl的量,可以得到形貌不同的NH4-Dw和y-AlOOH纳米结构。研究结果表明,由于NH4-Dw和y-AlOOH具有不同的表面结构,离子液体在合成NH4-Dw和y-AlOOH过程中表现出不同的作用模式,分为阳离子作用模式和阴离子作用模式。阳离子作用模式主要表现为分散作用,可以使线束状的NH4-Dw分散为线状的NH4-Dw。阴离子作用模式主要表现为诱导自组装作用,可以使六方γ-AlOOH片自组装成为多级花状结构。根据不同的作用模式,可以根据需要来选择离子液体的阴、阳离子,对所作用的无机纳米材料进行调控,因此有望实现可控地设计合成无机纳米材料。此外,通过焙烧前驱体NH4-Dw和y-AlOOH纳米结构可以得到形貌保持不变的多孔γ-Al2O3纳米结构,测试结果表明该多孔结构具有较大的比表面积和良好的孔径性能。2.首次使用[Bmim][H2PO4]作为离子液体前驱体合成出多种形貌的羟基磷酸铁(Fe5(PO4)4(OH)3·2H2O)。究结果表明,通过调节反应体系中[Bmim][H2PO4]的相对浓度和溶剂组成,可以得到暴露有{111}晶面的双棱锥状、暴露有{001}晶面的板状、由{441}和{111}晶面所组成的四方十六面体状、凹{001}晶面的截角双棱锥状的羟基磷酸铁。不同形貌的形成可以归因于[Bmim][H2PO4]对{111}晶面的生长有一定的保护作用。此外,以反应所得的羟基磷酸铁为芬顿催化剂,系统研究了不同形貌与其光催化性能之间的关系。实验结果表明,所得产物的光催化活性与其暴露面有密切联系,而与其比表面积关系不大。这些研究结果为如何设计合成高效的芬顿催化剂提供了一定的借鉴价值。3.通过便捷的水热法一步合成出不同物相(α-,β-和8-MnO2)和形貌(棒状、线状、花状和墙状)的二氧化锰纳米结构。实验结果表明,反应体系中前驱体KMnO4的浓度对于二氧化锰最终物相和形貌起到决定性作用。其中,体系中心的浓度会影响所成MnO2晶核的物相,而MnO4-的浓度会对成核速率以及随后的生长过程起到显著影响。另外,系统地研究了反应温度对所形成二氧化锰纳米墙结构的影响。更进一步地,对所制备的二氧化锰纳米结构进行了锂电性能测试,研究了不同物相和形貌与其电化学性能之间的相互关系。测试结果表明,二氧化锰纳米墙结构表现出优良的放电循环性能,是一种理想的电级材料。4.首次提出通过改变初级生长颗粒的暴露晶面来获得稳定性良好的介观晶体。在没有高分子聚合物作为添加剂的情况下,以N,N-二甲基甲酰胺和甲醇为复合溶剂,一步法合成出高稳定性的氧化铁介观晶体。改变初级生长颗粒的暴露晶面,可以降低其表面能,阻碍其进一步融合形成单晶结构,因而可以得到稳定性良好的介观晶体。此外,由于介观晶体自身的孔道结构,菱面体形的氧化铁介观晶体表现出优良的放电循环性能。5.通过单前驱体法,首次合成出一种形貌新颖的八足状PbS超结构。通过对该超结构生长过程进行仔细地分析,认为这种独特结构的形成是由晶体的热力学和动力学生长共同作用所致。通过改变溶剂的组成可以得到形貌不同的PbS微米结构,这些研究结果有望为可控合成无机纳米材料提供一定的借鉴价值。综上,本文主要研究了使用便捷和环境友好的液相合成法来制备具有特殊物相和形貌的无机纳米材料,证明了以离子液体为反应介质所制备的材料具有新颖的形貌和优异的性能,并且有望为更多无机纳米材料的可控合成提供一些新的思路。更多还原

【Abstract】 Ionic liquids (ILs), which are liquid salts at room temperature, have attracted tremendous attention due to their unique properties. Compared the widespread application in organic chemistry and organometallic catalysis, their use in inorganic synthesis is just about to begin. It is worth mentioning that the ionothermal synthesis is quite different from hydro-or solvothermal conditions, which may lead to new materials with interesting morphologies and that are not accessible by using conventional organic solvents or water due to the unique physicochemical properties of ionic liquids. Despite great efforts have been made on controlling crystal phase and morphology of inorganic materials using ionic liquid, a consensus of the effect type between the ionic liquids and the substrate has still not been achieved. As the consequences of this situation, most of the synthesis are not be predicted and simply use an IL or a mixture of IL with conventional solvent just like common surfactant, not sufficiently exploits the main advantage of ILs. In this paper, we systematically study the effect of ILs on the formation of inorganic nanomaterials. The purposes are to explore the new functions of ILs and develop new synthetic methods of nanomaterials with desired phase and morphology. The main points can be summarized as follows:1. Well-dispersed NH4-DW and y-A100H nanostructures with controlled morphologies have been synthesized employing an ionic liquid-assisted hydrothermal process. The basic strategies used in this work are (i) controllable phase transition from NH4-DW to y-A100H can be realized with increasing the reaction temperature, and (ii) morphological evolution of NH4-DW and γ-AlOOH nanostructures could be affected by ionic liquid concentration. Based on the experimental results, the main objective of this work is to clarify the ionic liquid effect models on the synthesis of NH4-DW and γ-AlOOH nanostructures, which can be divided into cationic or anionic dominant effect model determined by the different surface structure of the targets. Specifically, under the cationic dominant regime, ionic liquids mainly show dispersion effect for NH4-DW nanostructures meanwhile the anionic dominant model can induce y-AlOOH particles self-assembly to form hierarchical structures. Under the guidance of the models proposed, the effect of ionic liquids would be optimized by the appropriate choice of cations or anions considering different effect model with substrate surface. It is highly expected that such effect models between ionic liquids and target products are helpful to understand and design rational ionic liquids consisting of specific functional groups, thus open up new opportunities for synthesis of inorganic nanomaterials with novel morphology and improved property. In addition, the as-prepared NH4-Dw and y-AlOOH nanostructures can then be converted to porous γ-Al2O3nanostructures by thermal decomposition while preserving the same morphology. By HRTEM and nitrogen adsorption analysis, the obtained γ-Al2O3samples have excellent porous properties and might be useful in catalysis and adsorption.2. Well-dispersed ferric giniite microcrystals with controlled sizes and shapes are solvothermally synthesized from ionic liquid precursors using1-n-butyl-3-methy-limidazolium dihydrogenphosphate ([Bmim][H2PO4]) as phosphate source. The success of this synthesis relies on the concentration and composition of the ionic liquid precursors. By adjusting the molar ratios of Fe(NO3)3·9H2O to [Bmim][H2PO4] as well as the composition of ionic liquid precursors, we obtained uniform microstructures such as bipyramids exposing{111} facets, plates exposing{001} facets, hollow sphere, tetragonal hexadecahedron exposing{441} and{111} facets, truncated bipyamids with carved{001} facets. The crystalline structure of the ferric giniite microcrystals is disclosed by various characterization techniques. It was revealed that [Bmim][H2PC>4] played an important role in stabilizing the{111} facets of ferric giniite crystals, leading to the different morphologies in the presence of ionic liquid precursors with different composition. Furthermore, since these ferric giniite crystals were characterized by different facets, they could serve as model Fenton-like catalysts to uncover the correlation between the surface and the catalytic performance for photodegradation of organic dyes under visible-light irradiation. Our measurements indicate that the photocatalytic activity of as-prepared Fenton-like catalysts is highly depended on the exposed facets, and the surface area has essentially no obvious effect on the photocatalytic degradation of organic dyes in the present study. It is highly expected that these findings are useful in understanding the photocatalytic activity of Fenton-like catalysts with different morphologies, and suggest a promising new strategy for crystal facet engineering of photocatalysts for wastewater treatment based on heterogeneous Fenton-like process.3. Four well-defined morphologies, including nanorod, nanowire, nanoflower and nanowall, of MnO2nanostructures with different crystal phases (α-, β-, and8-MnO2) have been synthesized employing a simple hydrothermal process. Our experimental results demonstrate that the concentration of KMnO4plays a key role of forming different shapes and phases of MnO2nanostructures. Specifically, the K+concentration can affect the crystal phase of MnO2seeds in the nucleation processes and the decomposition rate of MnO4can influence the number of MnO2nucleus at the initial nucleating stage and also can affect the subsequent crystal growth process. Moreover, the effects of reaction temperature on the morphology of8-MnO2nanowall are systematically studied. The electrochemical performances of the as-prepared MnO2as the positive material of rechargeable Li-ion batteries have also been researched. It is found that8-MnO2nanowall possess largely enhanced electrochemical activity compared to a-MnO2nanowires and β-MnO2nanorods. The vast difference in electrochemical activity is discussed in terms of the morphology, crystal phase and specific surface area of MnO2nanostructures. It is highly expected that these findings are useful in understanding the formation of MnO2nanocrystals with different morphologies, which are also applicable to other metal oxides nanocrystals.4. High-stability hematite mesocrystals were prepared by a facile route using N,N-dimethylformamide (DMF) and methanol as the mixed solvent without polymer additives. The success of this synthesis relies on (i) carefully analzed the time-resolved structure formation process of pesudocubic hematite single-crystal, and (ii) tuned the crystallograpically aligned orientations of primary particle units by crystal facet engineering to prevent the crystallographic fusion to single-crystal. To the best our knowledge, this is the first attempt to investigate the role of crystal facet engineering on the formation of stable mesocrystals. In particular, the rhombic hematite mesocrystals exhibit excellent lithium insertion behavior compared to the hematite single-crystals.5. A novel PbS hierarchical superstructure, denoted as octapodal dendrites with a cubic center, has been synthesized employing a simple single-source precursor route. Our experimental results demonstrate that the novel hierarchical superstructure was generated through the delicate balance between the kinetic growth and thermodynamic growth regimes. Moreover, the morphology of PbS crystals can be controlled by adjusting the solvent under thermodynamically or kinetically controlled growth regime. It is highly expected that these findings are useful in understanding the formation of PbS nanocrystals with different morphologies, which are also applicable to other fcc nanocrystals.In summary, we presented some facile and environmentally friendly methods for the controllable synthesis of inorganic nanomaterials in this dissertation. It has been proved that the ionic liquid possessing the extraordinary potential is favorable for the fabrication of nanomaterials with novel morphologies and improved properties. We believe the understanding that we develop of effect model of ILs on the formation of nanostructures is of fundamental importance. Furthermore, it is hoped that this findings will aid in the design of new synthetic methodologies for preparation of inorganic materials using ILs.更多还原