核壳结构纳米材料的制备、调控与功能化特性

发布时间：2018-06-17 06:47

本文选题：纳米能源材料 + 核壳结构　；参考：《清华大学》2015年博士论文

【摘要】：作为一类新型功能复合材料,核壳结构纳米材料不仅实现了内核材料和壳材料的结合与互补,而且具有结构和化学成分的多样性及可调性,所以该设计概念逐渐被引入到能量存储、催化和隔热等领域。但作为一种未来新能源和环境领域的重要候选材料,目前核壳纳米材料的制备还局限于实验室小规模、不计成本的阶段,并且调控程度有限,合成壳厚均一、单分散的颗粒具有一定挑战性;另外,核壳结构对离子/电子传输、电化学反应、相变等的影响及机理还很不清晰。因此,本论文以核壳型纳米材料的制备、表征和能源方面的应用为研究对象,并进行了一些初级的机理分析和设计。材料体系选择了过渡金属氧化物、Al金属和La2Zr2O7,结合模板法、原位化学反应沉积法和粒子表面化学处理等技术,合成了可规模化生产的三类核壳结构,包括核壳紧贴型、半空型(蛋黄-蛋壳结构)和全空型纳米材料,并分别对其微观形貌、结构调控及功能化特性进行了系统的研究。在探索核壳紧贴型结构纳米材料的可控合成和性能优化方面,利用KMn O4与还原性碳球模板的原位氧化还原反应制备了C@MnO2核壳紧贴型结构。尽管获得了改善的电容性质,但距MnO2比容量的理论值仍有较大差距。因此在对MnO2充放电机理理解的基础上,本研究又设计并合成了尺寸小于10nm的MnO2@C核壳紧贴型结构。当扫描速率为1mV/s时,该材料的比容量达到1103F/g,5000次循环后容量保持率仍超过96%。另外,为发展核壳结构纳米材料在锂离子电池负极中的应用,本研究以Al为核心,在其表面合成能够同时传导Li+和电子的TiO2壳层,并在核-壳之间引入适当的空隙,制备出Al@TiO2蛋黄-蛋壳结构。电化学测试结果表明,其首次循环的可逆容量为1237 mAh/g,并且在1C倍率下的容量可稳定在1170 mAh/g,平均库伦效率约为99.2%,平均每次循环容量衰减小于0.01%;在10C倍率下的可逆容量达到690 mAh/g。为进一步得到全空型核壳结构纳米材料,本研究以有机碳球为模板,制备了具有多级孔结构和高比表面积的Co3O4空心球,并通过对碳球模板酸处理或碱处理,实现了空心球球壳厚度和孔结构的调节,获得了优异的催化CH4燃烧的活性和催化稳定性。为证明这种制备陶瓷空心球技术的普适性,本研究还利用同样的方法制备出TiO2-Ag空心结构,并表征了其光催化性能。最后,在核壳结构纳米粉体合成的基础上,发展一种两步煅烧工艺,成功地制备超低热导率(0.016Wm-1K-1)、超高强度(251.3MPa)和良好的热稳定性(1400oC)的空心晶粒La2Zr2O7高强度超级隔热材料和优异催化性能的多级孔结构的Co3O4蜂窝结构块体。
[Abstract]:As a new class of functional composites, core-shell nanocomposites not only realize the combination and complementarity of core and shell materials, but also have the diversity and adjustability of structure and chemical composition. So the design concept is gradually introduced into energy storage, catalysis and heat insulation. However, as an important candidate material in the field of new energy and environment in the future, the preparation of core-shell nanomaterials is still confined to the small scale of laboratory, regardless of cost, and the degree of regulation is limited, and the thickness of synthetic shell is uniform. In addition, the effect of core-shell structure on ion / electron transport, electrochemical reaction and phase transition is not clear. Therefore, the preparation, characterization and energy applications of core-shell nanomaterials were studied in this paper, and some primary mechanism analysis and design were carried out. Three kinds of core-shell structures which can be produced on a large scale have been synthesized by using transition metal oxide Al and La _ 2Zr _ 2O _ 7, combined with template method, in-situ chemical reaction deposition method and particle surface chemical treatment, including core-shell close type. The micromorphology, structural regulation and functionalization of semicircle (egg yolk-eggshell) and hole-type nanomaterials were systematically studied. In order to explore the controllable synthesis and performance optimization of core-shell structure materials, CMnO2 core-shell structure was prepared by in-situ redox reaction of KMnO _ 4 and reductive carbon sphere template. Although the improved capacitance properties are obtained, there is still a big gap between the theoretical value and the specific capacity of MNO _ 2. Therefore, on the basis of understanding the mechanism of MNO _ 2 charge and discharge, we have designed and synthesized the core-shell structure of MNO _ 2 @ C core-shell with a size smaller than 10nm. When the scanning rate is 1 MV / s, the specific capacity of the material reaches 1103 F / g 5 000 cycles and the capacity retention rate is still over 96%. In addition, in order to develop the application of core-shell nanomaterials in the anode of lithium ion batteries, the TIO _ 2 shell layer, which can conduct Li and electrons at the same time, was synthesized on the surface of Al, and an appropriate void was introduced between the core and shell. Alpha-TiO2 yolk-eggshell structure was prepared. The electrochemical test results show that the reversible capacity of the first cycle is 1237 mg / g, and the capacity at 1C ratio can be stabilized at 1170 mAh/ g, the average Coulomb efficiency is about 99.2%, the average capacity attenuation per cycle is less than 0.01g, and the reversible capacity at 10C ratio reaches 690mAh.g. Co3O4 hollow spheres with multilevel pore structure and high specific surface area were prepared using organic carbon spheres as template in order to obtain full hollow core-shell structure nanomaterials. The thickness and pore structure of hollow spherical shell were adjusted, and excellent catalytic activity and catalytic stability of Ch _ 4 combustion were obtained. In order to prove the universality of this technique, the hollow structure of TIO _ 2-Ag was prepared by the same method, and its photocatalytic properties were characterized. Finally, based on the synthesis of nanocrystalline core-shell powders, a two-step calcination process was developed. Hollow La _ 2Zr _ 2O _ 7 with high strength and excellent catalytic performance were successfully prepared by the fabrication of hollow La2Zr _ 2O _ 7 super thermal insulation material with high strength and excellent catalytic performance, and the multilevel pore structure Co _ 3O _ 4 honeycomb block with excellent catalytic performance and excellent thermal stability (1400oC).
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1

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