【作者】 李静；

【导师】 魏雨； 李艳廷；

【作者基本信息】 河北师范大学 ， 物理化学， 2008， 硕士

【摘要】 纳米氧化钛（TiO₂）作为一种新型的无机纳米功能材料,具有很多常规TiO₂所不具备的光、电、热、磁、力学等特殊性质,如比表面积大、表面活性高、热导性好、光吸收性能好、分散性好等,因此具有非常广泛的用途。我国对TiO₂的研究十分重视,已把TiO₂工业列为当前优先发展的高技术产业重点。因此,开展TiO₂纳米材料诸多特性（如光致发光特性、化学性质稳定特性及光敏、气敏、压敏等特性）在分析化学中的应用研究,从而拓宽分析化学的研究领域就具有十分重要的意义。硅胶基质固定相开发最早,研究深入,但其容易引起色谱峰拖尾,虽经键合改性后仍不能从根本上解决其使用的pH范围窄的问题。使它在一些重要领域中的应用受到了限制。纳米结构TiO₂色谱填料与SiO₂相比,有其独特的优势:化学稳定性良好、机械强度高、表面性质独特等。但传统方法制备的氧化钛比表面积和孔体积较小,孔结构不理想,粒径分布范围宽,表面物理化学性质不良、渗透性差,载体表面积小则负载或键合的固定相量小。要制备具有大比表面积、适宜孔体积、理想孔结构、孔径分布窄、渗透性好、颗粒均匀的氧化钛基质填料需要新的制备方法。本文通过利用钛醇盐醇热法制备了纳米结构TiO₂空心微球,借助扫描电子显微镜、X-粉末衍射、透射电子显微镜等手段对产物的形貌、表面物理化学性质进行了表征,考察了一系列制备条件和外部环境对产物形貌的影响。并对微球的生成机理进行了初步探索,考察了TiO₂微球的色谱性能。另外,在对制备过程中得到的TiO₂纳米粉体在水介质中的分散稳定性进行研究发现,经一定温度煅烧处理后的TiO₂纳米粉体出现了分散稳定性反常的现象。通过与其它方法（TiCl4酸性条件下沸腾回流水解）所得TiO₂纳米粉体的比较,研究了粉体表面结构和性质与热处理温度的关系。本论文的主要内容可以概括如下:1.纳米结构TiO₂空心微球制备在氮气气氛中,将Ti（OC₄H₉ⁿ）₄缓慢的滴加到低碳醇、浓硫酸和微量水的混合体系中,强烈电磁搅拌得到无色透明反应前驱物;反应前驱物在配有聚四氟乙烯内罐的高压釜中经180℃热处理得到纳米结构TiO₂空心微球;对产物进行物理化学性质表征,得出该TiO₂微球粒径在5-10μm之间,结构破损微球显示其内部为空心结构。借助扫描电子显微镜（SEM）和XRD表征手段,证明醇热法所制备微球表面是由锐钛矿型纳米TiO₂颗粒构成。2.考察不同试验条件对空心微球形貌的影响分别考察了包括热压时间、热压温度、热压方式、所用酸的种类、反应物的不同配比等对TiO₂空心微球结构的影响。实验结果表明,在诸多影响因素中,反应物（水）、催化剂硫酸与钛酸四丁酯的摩尔比是影响产物形貌的两个重要因素,通过改变二者的用量可以控制微球粒径的大小及壳层厚度。在此基础上,对TiO₂空心微球的形成机理进行了初步探讨,提出了高温高压下溶剂分子“自动定向聚集”的微球形成模型。3.对纳米结构TiO₂空心微球的物理化学性质、色谱性能进行表征通过氮吸附法研究了TiO₂空心微球的表面物理化学性质,表明所制多孔微球颗粒均匀（5-7μm）,孔径在中孔范围内（7.4 nm）,平均孔体积（0.31 cm3·g-1）、比表面积（146.1 m2·g-1）及孔径分布等性质较其它常用方法所制备产品都有较大提高;电位滴定结果显示微球表面酸性弱于常规硅胶。同时,以苯、甲苯和乙苯为测试化合物,以乙腈水溶液为流动相,测定了该TiO₂微球作为HPLC固定相的疏水选择性和灵敏度。结果表明该TiO₂微球具有反相固定相特征。将其用于分离中性和碱性化合物时,显示出较好的色谱性能。同时该固定相除了在较强酸碱条件下保留行为稳定之外,其所用流动相为含有浓度较低有机溶剂的水体系,因此在发展制备规模的HPLC廉价分离药物和降低对环境的污染方面具有实际意义。4. TiO₂纳米粉体的分散稳定性研究对醇热法制备的TiO₂纳米粉体与其它方法（TiCl₄酸性条件下沸腾回流水解）所得TiO₂纳米粉体在分散稳定性方面进行了比较研究。通过自然沉降法对两种产品经不同温度煅烧处理后的样品进行了水体系中分散稳定性考察。结果发现,经一定温度煅烧处理后的两种TiO₂纳米粉体都出现了分散稳定性反常的现象,二者唯一不同之处在于,不同的制备方法导致这一现象出现的温度不同。借助XRD、TEM、傅立叶变换红外光谱仪（FT-IR）及激光粒度分析仪等相关表征手段,研究了粉体表面结构和性质与热处理温度的关系。在此基础上,将产生这种现象的可能原因归结为:高温煅烧处理使TiO₂纳米颗粒发生晶相转化,这种转化过程使颗粒由不规则结构向类球型结构转变,而类球型结构表面曲率的增大利于水分子在其表面的吸附,导致颗粒表面水分子的溶剂化作用此时成为控制分散稳定性的关键因素。这一结果对研究纳米TiO₂表面水分子吸附机理及其防止团聚都有重要意义,同时对解释科研人员在TiO₂纳米粉体光催化反应中观察到的某些现象也将有所帮助。更多还原

【Abstract】 Titania （TiO₂） has previously been studied over the years. In the nanoscale regiment, it often exhibits very unusual electric, optical, magnetic and chemical properties, which cannot be achieved by their bulk counterparts. These unique physical and chemical properties are of technological importance and scientific research interests. So far, the most actively pursued research on TiO₂ is its use for photo-assisted degradation of a variety of toxic chemicals, as a promising electrode material in dye-sensitized solar cells, and as gas sensor. Therefore, it is very significant to research and apply of many characteristics of TiO₂ in analytical chemistry, such as photoluminescence, chemical stability, photosensitive and gas-sensitive, et al.The silica-based phases are the most widely used materials in HPLC. Silica supports are superior to other supports in terms of efficiency, rigidity and performance. However, there are several disadvantages with silica-based materials such as severe peak tailing in the chromatography of basic compounds and limited pH stability. The defects of silica limit its application in some important fields. There has been an increasing importance in application of titania-based HPLC packings for their excellent chemical, high-temperature, mechanical stability as well as bioanalysis suitability. But titania prepared by the traditional methods has some deficiency, such as less specific surface area and hole volume, imperfect hole structure , wider range of size distribution, etc.. Therefore, it is essential that develop a new method to prepare titania-based packing materials,which should have the good features such as larger specific surface area, proper pore volume, narrow hole scope distribution and more homogeneous particle size distribution.In this paper nanostructured TiO₂ hollow microspheres were prepared via a facile alcohothermal method using tetra-n-butyl titanate as a precursor, including subsequent thermal treatment. The products were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD） and transmission electron microscope. The effects of experimental and environment conditions on hollow microspheres have been investigated, and the further discussion has been carried out to understand the forming mechanism of nanostructured TiO₂ hollow microspheres. Meanwhile, the chromatogram performance of hollow TiO₂ microspheres was studied. At the same time, TiO₂ nanoparticles were prepared by alcohothermal method. An abnormal fine re-dispersibility and stability of them in aqueous medium was observed during phase transformation from Anatase to Rutile. Compared with TiO₂ nanoparticles prepared by hydrolysis of titanium tetrachloride （TiCl₄） in an acid aqueous solution, this phenomenon had nothing to do with their preparation methods.The main work includes the following aspects:1. Preparation of nanostructured TiO₂ hollow microspheresA solution containing absolute ethanol, concentrated H2SO4 and purified water was stirred heavily in a purified nitrogen flushed system at room temperature for 30 min. After that, Ti（OC4H9n）4 was added slowly via a dropping pipette under vigorous stirring during another 30 min. The final reaction mixture was sealed in a Teflon-lined stainless steel 30 ml autoclave, which was employed to obtain a high temperature and pressure for the nucleation and growth of TiO₂ hollow microspheres. As shown in the SEM images, TiO₂ microspheres with a relatively uniform particle size distribution of 5-10μm present in our transparent sol. In addition, since these TiO₂ microspheres have small crystal grains, which present a process of amorphous-crystalline transition tendency during thermal treatment according to XRD images, they might have good potential application in catalyst supports, coatings and catalysis in wastewater treatment, etc.2. Effects of experimental and environment conditions on hollow microspheresA serious of experimental conditions, such as time and temperature of thermal treatment, species of acid, the molar ratio of reactants etc., have been investigated as factors influencing upon the configuration of TiO₂ hollow microspheres. During the investigation, the results clearly indicate that the molar ratio of H2O / Ti（OC₄H₉ⁿ）₄ and H₂SO₄/ Ti（OC₄H₉ⁿ）₄ are the two main factors influencing upon the configuration of TiO₂ hollow microspheres. The size and the shell thickness of the hollow TiO₂ microspheres can be controlled by altering the molar ratio of H2O / Ti（OC₄H₉ⁿ）₄ and H₂SO₄/ Ti（OC₄H₉ⁿ）₄. On the basis of mentioned results, an auto-orientation assembly mechanism to form hollow TiO₂ microspheres is proposed.3. Investigation of the parameters of TiO₂ hollow microspheresPorous TiO₂ microspheres （surface area: 146.1 m2·g-1, average pore volume: 0.31 cm3·g-1, pore diameter: 7.4 nm, microspheres diameter: 5-7μm） with a narrow particle size distribution, were characterized by N₂ adsorption method. The results show that the physical and chemical properties of TiO₂ microspheres are better than that of the microspheres prepared by the other methods. The data of potentiometric titration demonstrate that the acid-base value of TiO₂ microspheres were lower than that of SiO₂. At the same time, the hydrophobic selectivity and sensitivity of TiO₂ microspheres as HPLC stationary phase were studied by benzene, toluene and ethyl benzene as solutes and acetonitrile solution as a mobile phase. The results show that the packing support exhibits a little of reversed-phase behavior. The good chromatographic performances and high chemical stability were showed when it was used to separate the neutral and basic solutes using acetonitrile solution as a mobile phase.4. The dispersion stability of different nanocrystalline TiO₂Although two typical TiO₂ nanoparticles were prepared by different methods, an abnormal fine re-dispersibility and stability of them in aqueous medium, which has nothing to do with their preparation methods, was observed during phases transformation from Anatase to Rutile. FT-IR and TEM data show that increasing surface curvature occurred during A-R transformation is advantageous to water adsorption on the surface of the TiO₂ nanoparticles, which induces the stronger repulsive interaction. It is believed that this hydration forces that displace upon particles aggregation result in the abnormal fine re-dispersibility and stability of TiO₂ nanoparticles in aqueous medium. The distinct zeta potentials of the different particles manifest that the surface electrostatic forces are not crucial factors in abnormal fine re-dispersibility of TiO₂ nanoparticles observed during A-R phases transformation. Consequently, it would be quite helpful for understanding the water adsorption behaviors on TiO₂ surfaces （especial for mixture of rutile and anatase）, preventing aggregation of TiO₂ nanoparticles and explaining some phenomena observed in their photocatalytic activities.更多还原