【作者】 史非；

【导师】 王立久；

【作者基本信息】 大连理工大学 ， 材料学， 2007， 博士

【摘要】 SiO₂气凝胶是一类轻质介孔材料，具有超低密度、高孔隙率、高比表面积和低热导率等特点，在许多领域具有潜在的应用前景。传统上，SiO₂气凝胶的制备多采用超临界干燥工艺，但超临界干燥工艺复杂、成本高，而且有一定的危险性。为了实现SiO₂气凝胶的大规模生产以及在诸多领域的实际应用，研究低成本常压干燥工艺制备SiO₂气凝胶非常必要。本文分别以工业硅溶胶、水玻璃和工业废渣粉煤灰为原料，通过常压干燥工艺制备了疏水的介孔SiO₂气凝胶，研究确定了常压干燥工艺中对水凝胶进行一步溶剂交换-表面改性处理的工艺路线；以正硅酸乙酯为原料，通过常压干燥工艺制备了疏水的SiO₂气凝胶薄膜；利用红外光谱（FT-IR）、差热-热重分析（DTA-TG）、X射线衍射分析（XRD）、扫描电镜（SEM）、透射电镜（TEM）和BET吸附等手段对气凝胶的表面基团、热稳定性、微观形貌和结构进行了研究；利用紫外／可见（UV／VIS）分光光度计等初步分析了SiO₂气凝胶对水中甲基橙和三氯甲烷等有机溶剂的吸附性能，以及气凝胶对硫酸庆大霉素药物的吸附和释放性能。以工业硅溶胶和水玻璃为硅源，用乙醇／三甲基氯硅烷／庚（己）烷（EtOH／TMCS／Heptane（Hexane））溶液对SiO₂水凝胶进行处理，在常压干燥条件下合成了疏水的介孔SiO₂气凝胶，分析了EtOH／TMCS／Heptane（Hexane）溶液对水凝胶进行一步溶剂交换-表面改性的机理，并对EtOH／TMCS／Heptane（Hexane）和TMCS／HMDSO（六甲基二硅醚）两种改性工艺得到的SiO₂气凝胶的性质进行了比较，探讨了热处理对SiO₂气凝胶的微观形貌、疏水／亲水性、比表面积和孔分布影响。结果表明，用EtOH／TMCS／Heptane（Hexane）对水凝胶进行改性处理更有利于获得大块的低密度SiO₂气凝胶，所合成的SiO₂气凝胶为轻质介孔固体，呈现出海绵状结构，密度0.128～0.197g／cm³，最可几孔直径7～18 nm，比表面积559～699m²／g，孔隙率91％-94％，孔隙分布均匀。在150～450℃温度范围内，随热处理温度升高，气凝胶的比表面积、孔体积和孔径逐渐增大；经500℃热处理后，孔体积有所减小，但比表面积达到最大值，气凝胶由疏水性完全转变为亲水性。以正硅酸乙酯为硅源，采用溶胶-凝胶法，通过三种不同的工艺常压干燥制备了SiO₂气凝胶薄膜，分析了不同工艺对薄膜结构性质的影响，结果表明，三种工艺均能够获得疏水性较好的SiO₂气凝胶薄膜，涂膜后进行溶剂交换-表面改性的制备工艺能够获得高可见光透过率的气凝胶薄膜。以工业废渣粉煤灰为原料，对制备多孔轻质SiO₂气凝胶及超细粉进行了研究，研究了由粉煤灰制备SiO₂气凝胶的两种工艺过程。工艺Ⅰ为：由粉煤灰制得水玻璃后，用硫酸催化得到水凝胶，用去离子水浸泡水凝胶一定时间，再经EtOH／TMCS／Hexane改性和常压干燥后可以制得SiO₂气凝胶超细粉体；随去离子水浸泡时间延长，所得气凝胶的纯度增加，粒度分布范围变窄。工艺Ⅱ为：由粉煤灰制得水玻璃后，首先经过离子交换树脂交换，然后再经胶凝、EtOH／TMCS／Hexane改性和常压干燥，可得到微观形貌和孔分布接近于由工业水玻璃制得的SiO₂气凝胶，比表面积635.19m²／g，最可几孔直径6.67nm。研究了气凝胶对水中染料甲基橙和有机物质三氯甲烷等的吸附性能，经450℃热处理的亲水性SiO₂气凝胶对甲基橙有较高的吸附能力，但亲水性气凝胶在空气中放置一段时间后其吸附性能会有所下降；疏水性气凝胶能够高效吸附三氯甲烷等有机溶剂，吸附后气凝胶的高比表面积和高孔隙率特点不会发生明显变化，因此，疏水性SiO₂气凝胶可以多次反复使用，在水的净化和有机物质吸附方面应用前景广阔。研究了SiO₂气凝胶对硫酸庆大霉素的吸附和释放性能，气凝胶的亲水／疏水性程度对药物的吸附和释放性能有重要影响，在450～500℃之间，随热处理温度升高，SiO₂气凝胶对硫酸庆大霉素的吸附能力增强，载药量增加；经500℃处理的SiO₂气凝胶能够均匀吸附药物，吸附载药率可达122.42％，并且具有均匀的药物释放效果。更多还原

【Abstract】 Silica aerogels are a class of light mesoporous materials with low density, high porosity, high surface area and low thermal conductivity. Because of their unique properties, silica aerogels have great potential application future in many fields. Conventionally silica aerogels have been made by a supercritical drying process. However, supercritical drying process is complicated and expensive, and it is unsafe to a certain extent. In order to actualize the production of silica aerogels on a large scale and practical applications in many fields, research on preparation of silica aerogels via ambient pressure drying at a reasonable cost is very necessary. In this study, using industrial silica sols, water glass and waste residue fly ash as raw materials respectively, hydrophobic mesoporous silica aerogels have been prepared via ambient pressure drying. The routes of one-step solvent exchange-surface modification of the hydrogels in the ambient pressure drying process have been investigated and determined. The surface group, thermal stability, morphology and microstructure of silica aerogels have been investigated by FT-IR, DTA-TG. XRD, SEM, TEM and BET adsorption method. Silica aerogel films have been prepared by ambient pressure drying using tetraethoxysilane (TEOS) as raw materials. The properties of adsorbing methyl orange in the water and organic solvent such as chloroform, as well as loading and releasing of gentamicin sulfate for silica aerogels have been analyzed primarily by UV/VIS spectrometer.Using industrial silica sols and water glass as silica sources, hydrophobic silica aerogels have been synthesized via ambient pressure drying by using ethanol/trimethylchlorosilane/ heptane(hexane) (EtOH/TMCS/Heptane(Hexane)) solution for modification of the hydrogel. The mechanism of one-step solvent exchange-surface modification for the hydrogel by EtOH/TMCS/Heptane(Hexane) solution was analyzed, and the comparative study of the properties of silica aerogels prepared by two modification process using EtOH/TMCS /Heptane(Hexane) and TMCS/HMDSO(hexamethyldisiloxane) respectively were conducted. Additionaly, the effects of heat-treatment on the morphology, hydrophobicity, specific surface area and pore size distribution of silica aerogels were discussed. The results indicate that modification treatment of hydrogel using EtOH/TMCS/Heptane(Hexane) is favorable for obtaining monolithic low density silica aerogels. The synthesized silica aerogel is a light-weight mesoporous solid, exhibiting a sponge structure, with the density of 0.128～0.197g/cm~3 and pore diameter 7～18nm. The specific surface area of silica aerogels are 559～699m~2/g, with 91%-94% porosity and uniform pore size distribution. It was found that the specific surface area, pore volume and pore size increased with increasing of heat-treatment temperature at 150-450℃. After heat treatment at 500℃, the pore volume decreased, but specific surface area increased to the highest, and hydrophobicity of silica aerogel turned into hydrophilia completely.Using tetraethoxysilane (TEOS) as silica sources, silica aerogel films were prepared via three different ambient pressure drying process by sol-gel method. The influences of different process on the structure and properties of silica aerogel films were analyzed. The results indicate that silica aerogels films with good hydrophobicity could be obtained by three ambient pressure drying process. However, the silica aerogels films prepared by first coating and then solvent exchange-surface modification have better optical transmission.Using industrial waste residue fly ash as raw materials, preparation of porous light-weight silica aerogels and ultra-fine powders was studied. Two different processes of preparing silica aerogels from fly ash were investigated. The processⅠis as follows: the obtained waterglass from fly ash was first catalyzed with H2SO4 so as to promote gelation, and then silica aerogel ultra-fine powders could be formed by immersing the hydrogel in the deionized water for a period and succedent modification with EtOH/TMCS/Hexane and ambient pressure drying. With the increasing of immersing time in the deionized water, the purity of silica aerogel increased and particle size distribution became narrow. The processⅡis as follows: the obtained waterglass from fly ash was first ion exchanged with cation exchange resin, and then silica aerogels could be obtained by treating the gel with EtOH/TMCS/Hexane and drying at ambient pressure. The morphology and pore size distribution of the obtained silica aerogels are similar to that of the aerogels prepared from industrial waterglass, with specific surface area 635.19 m~2/g and pore diameter 6.67nm.The adsorbability of methyl orange in the water and organic solvent chloroform for silica aerogels were investigated. Hydrophilic silica aerogels heat-treated at 450℃have higher adsorbability of methyl orange. However, the adsorbability of hydrophilic aerogels decreased a little after they were laid in the air for a period. Hydrophobic silica aerogels are capable of adsorbing organic solvents chloroform etc effectually, and the characteristics of high specific surface area and porosity of aerogels almost not changed after adsorption. Thus hydrophobic silica aerogels can be used repetitiously, and the application future is good in the aspect of waste water treatment and organic substance adsorption.The adsorption and release of gentamicin sulfate for silica aerogels were investigated. The hydrophilia or hydrophobicity of silica aerogels had important effects on the adsorption and release of drug. In the range of 450-500℃, the adsorbability and drug loading amount of gentamicin sulfate for silica aerogels increased with the increasing of heat treatment temperature. Silica aerogels heat-treated at 500℃could adsorb drug uniformly with a larger drug loading percent of 122.42%, and have a uniform drug releasing rate.更多还原