【作者】 陈擘威；

【导师】 张林；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2014， 博士

【摘要】 气凝胶是具有低密度、高孔隙率以及高比表面积等特点的新型纳米材料,可广泛应用于催化、吸附、高能物理等领域。锌基气凝胶成型性差,难于制备出完整的块状气凝胶,限制了其应用,因此目前对其研究较少。本论文系统的研究了锌基复合气凝胶的制备、氧化以及还原过程。以锌的无机盐为前驱体,研究在不同的制备参数(前驱体、溶剂、模板剂、水解比、凝胶促凝剂等)下所得到的湿凝胶,经超临界干燥工艺获得相应的锌基复合气凝胶样品；利用高级流变仪研究了不同反应体系的粘度变化,考察了体系储能模量和耗能模量的变化；用氮气和氧气的混合气氛氧化处理,制备了氧化锌气凝胶；采用一氧化碳与氮气的混合气体为还原锌基复合气凝胶,成功制备得到碳气凝胶。用聚丙烯酸和柠檬酸都制备出锌基复合气凝胶,说明聚丙烯酸和柠檬酸都具有模板剂的功能,但是制备的气凝胶在微观结构上却有很大的差异,这是与模板剂的分子链的长短具有直接联系。在制备锌基复合气凝胶过程中,模板剂的分子量和ZnCl2的含量都会对气凝胶的微观结构造成关键影响：用分子量为1800聚丙烯酸与ZnCl2的摩尔比为1：40制备的气凝胶微观颗粒间的孔隙率高,孔洞结构均匀,比表面积为470m2/g,总的孔体积为1.846cm3/g；以柠檬酸为模板剂制备的气凝胶的胶体颗粒之间较为致密,孔洞结构不明显,孔隙率低,比表面积为54m2/g,总的孔体积为0.126cm3/g。在溶胶—凝胶过程中,系统的研究了水量、环氧丙烷用量、聚丙烯酸用量对体系凝胶时间、气凝胶密度和比表面积的影响。利用高级流变仪研究了反应体系的粘度变化,对溶胶—凝胶过程进行研究。通过粘度的变化考察了体系储能模量和耗能模量变化,确定了凝胶时间；并研究了影响气凝胶比表面积和密度因素。运用分子动力学方法计算了不同分子量同浓度及同分子量不同浓度的聚丙烯酸的回旋半径和径向分布函数。用分子量1800的聚丙烯酸作为模板剂,将其浓度控制在0.11g·mL-1制备出锌基复合气凝胶的微观结构较好,这与实验的结果是相一致的。在气凝胶氧化处理中,研究了不同气体气氛、退火温度以及升温速率对气凝胶的成型性和微观结构的影响。在氮气：氧气为50：1的混合气氛中,500℃C的高温下,对锌基复合气凝胶进行退火处理,得到的氧化锌气凝胶孔隙率较高,骨架结构纤细,孔洞分布均匀,比表面积为125m2/g,总的孔体积为0.25cm3/g。制备的氧化锌气凝胶具有六方晶系的单一物相晶体结构,并运用Rietveld计算模拟方法对氧化锌气凝胶的晶体结构进行精修。测试氧化锌气凝胶的荧光光谱,发现随着温度升高,氧化锌气凝胶的发光光谱峰没有发生红移或者蓝移,发光强度随着温度升高增强。开发出了一种制备高纯度碳气凝胶的新技术。在一氧化碳：氮气为100：1的混合气氛中,980℃的高温下,对锌基复合气凝胶进行还原,制备出碳气凝胶。该方法制备的碳气凝胶密度低、比表面积高,这对其修饰、复合、改性等更进一步研究提供了良好的基础。XPS测试发现气凝胶中碳元素的单质的形式存在,EDS测试表明碳元素占96.8%；前驱物不同配比对样品的多孔结构、比表面积有较大影响；碳气凝胶比表面积可达1560cm2/g,总孔体积为1.760cm3/g,该材料属于介孔材料。更多还原

【Abstract】 Aerogels are the one characterized by high surface area, large porosity and low density materials, consisting of three dimensional network solids with interconnected nanoscale pores. The inherent characteristics of aerogels have been widely applied, such as thermal insulators, heterogeneous catalysis, energy, space and capacitors. To the best of our knowledge, the preparations and applications of monolithic Zn-based aerogels are not studied in depth. Therefore, it is a state-of-art way to prepare Zn-based aerogels with the dispersed inorganic sol-gel method, and the aerogels have subsequent thermal and reduction treatments. The properties of the zinc-based aerogel, such as the density and surface area, are related to the amounts of catalyst, water and polyacrylic acid (PAA) in sol-gel process. The proper molar ratios between these reactants play a crucial factor in mediating the morphology of the zinc-based aerogel. The viscosities of colloidal systemsis are discussed using a rheometer, while the elastic modulus and the viscous modulus are demonstrated in the sol-gel process. With regard to the temperature in different atmospheres, it was an integrated result of the complicated decomposition of organic compounds and the preparation of the zinc oxide aerogel. The innovation demonstrates a zinc template method to prepare carbon aerogel through thermal treatment in CO. The unusual preparation of carbon aerogel was promising for advanced nanodevices because of its outstanding nanoscale porosity structures.As far as we know, this is a novel report on producing the Zn-based aerogels through the polyacrylic acid and citric acid template method. Furthermore, the aerogels are difference owing to the long or short molecular chains of the templates. This paper offers an explicit explanation on the microstructure and surface area of the Zn-based aerogels under the influence of ZnCl2and the molecular chains of the templates. The N2adsorption/desorption of the Zn-based aerogel which the molar ratio of PAA to ZnCl2is1:40has a high surface area about470m2/g and pore volume about1.846cm3/g, and the field-emission scanning electron microscope (FESEM) demonstrates the aerogel possesses the typical characteristic mesopore. Additionly, The N2adsorption/desorption of the Zn-based aerogel which is prepared with ZnCl2and citric acid has a surface area about54m2/g and pore volume about0.126cm3/g, and the characteristic mesopore is compact with FESEM measurement.The gelation mechanism of sol-gel process is discussed in the present dissertation, such as the value of water, propylene oxide (PO), and PAA of the system in gelation process. Therefore, the properties of the zinc-based aerogel of the density and surface area are studied that they are related to the amounts of water, PO, and PAA in sol-gel process. The viscosities of the reaction system are discussed using a rheometer, and the elastic modulus and the viscous modulus are measured the different amounts of water, PO, and PAA in the gelation. Molecular dynamics method to build different molecular weight PAA in ethanol solution model, while the model simulation of the ethanol solution of different concentrations of polyacrylic acid. Solution model the radius of gyration (Rg) is determined by external conditions affect different model polyacrylic acid. While the radial distribution function g(r) is calculated and found carbonyl O and on the hydroxyl group of O, and ethanol H of PAA, there are strong hydrogen bonding interactions, there is also has a strong van der Waals mutual role.As a result, the molecular weight of1800PAA is adapted to the Zn-based aerogel template, and its concentration controlled0.11g·mL"1is more reasonable.Monolithic pure zinc oxide aerogel was prepared successfully through the dispersed inorganic sol-gel method (DIS method) combined with a furnace of500℃in mixed atmosphere which the molar ratio of N2to O2is50:1. The aerogel exhibited many desirable properties, such as uniform nanoscale pores, high porosity and large specific surface area. The N2adsorption/desorption of the aerogel has a high surface area about125m2/g and pore volume about0.25cm3/g, and FESEM demonstrates the typical characteristic mesopore. It is an integrated result of the hexagonal system of the zinc oxide aerogel, and its crystalline structure is refined with Rietveld structure refinement. After being annealed at different temperatures, the photoluminescence (PL) spectra of the aerogel were measured. The PL with no temperature-dependent shifts of the maximum of the spectral PL intensity concerning the zinc oxide aerogel being investigated suggests that it is relative to the structural and optical properties.The innovation of a zinc template method is the preparation of carbon aerogel through thermal treatment in CO. As a result, the measurements of XPS and EDS confirm only the presence of C atoms. This paper offers an explicit explanation on the microstructure and surface area of carbon aerogels under the amount influence of ZnCl2and PAA. In summary, carbon oxide aerogel of high specific surface area (1560m2/g), continuous porosity, narrow particle size distribution and excellent crystallinity is successfully prepared with zinc salt and PAA. As far as we know, this is a novel report on producing carbon aerogel through the metal template method. Our work, surely, is able to provide a simple and metal tempale method for designing new porous carbon aerogel nanoarchitectures, which is promising for a wide range of future applications.更多还原