【作者】 陈超；

【导师】 王智宇；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2014， 博士

【摘要】 研究纳米晶形貌控制的方法、探索纳米晶形貌与性能之间的关系,实现纳米材料的性能设计与优化是目前材料科学研究领域中的重大主题。介观尺度下,纳米晶体的晶粒粗化与生长机制既包括经典晶体生长理论所描述的“奥斯特瓦尔德熟化(Ostwald Ripening)"也包括非经典晶体生长理论所涵盖的“定向附着生长(Oriented Attachment)"和“介观晶体生长(Mesocrystal)"等。非经典晶体生长理论基于初级纳米晶体的组装与融合,为纳米晶的形貌控制与结构设计提供了崭新的思路和更多的可能性。本文以两种典型的过渡金属氧化物：锐钛矿相的二氧化钛(TiO2)与黑锰矿相的四氧化三锰(Mn3O4)为研究对象,探索不同晶体生长机制的诱导方式过程控制方法,研究不同晶体生长机制对纳米晶体形貌的影响规律,解决纳米晶形貌控制中的一些相关问题。根据纳米晶自身的形貌与结构特点,开展它们在光催化降解有机污染物、染料敏化太阳能电池以及锂离子电池等方面的性能研究,解决纳米材料功能应用中的一些相关问题。论文的研究工作分为以下几个方面：一、奥斯特瓦尔德熟化机制下TiO2纳米晶体的生长控制在双表面配体控制纳米晶生长的基础上,提出以卤素离子作为表面配体协同油酸分子控制TiO2纳米晶体形貌的方法。发现卤素离子中的氟离子对锐钛矿(001)晶面的吸附能力最强,在其参与下TiO2纳米晶的形貌为截角四方双锥体,其暴露晶面包括两个(001)晶面和八个(101)晶面。二、定向附着生长机制下TiO2纳米项链的生长控制发展了一种两步溶剂热的策略制备了具有一维单晶结构的锐钛矿TiO2纳米项链。第一步溶剂热过程被经典结晶过程所主导,获得具有一定程度(001)晶面暴露的初级TiO2纳米晶粒。第二步溶剂热过程被定向附着生长过程所主导,通过初级晶粒在[001]晶向上的组装与晶面融合,获得一维项链状纳米结构。在此合成策略的基础上我们研究了诱发和控制定向附着生长的关键条件。三、TiO2纳米项链对染料敏化太阳能电池性能的影响规律通过TiO2纳米项链增强了染料敏化太阳能电池的性能。利用TiO2纳米项链独特的一维单晶结构减少电子在纳米晶薄膜中的散射和复合,增强薄膜对电子的传输性能。当纳米晶薄膜内TiO2纳米项链的质量百分比为30～40%时,电池的光电转换效率为7.5%与基于纳米颗粒的薄膜电极的光电转换效率(4.2%)相比提升了78%。四、非经典结晶过程中Mn3O4介观/介孔晶体的生长控制发展了一种简单易于放大化生产的化学沉淀法制备了Mn3O4纳米晶。所得的纳米晶具有均一的尺寸和形貌,通过调节锰源的种类或添加量以及水合肼的添加量实现了对纳米晶的形貌控制(类长方体状介观晶体、圆盘状介观晶体、介孔纳米片、介孔纳米方台、介孔纳米多面体等)。考察介孔纳米方台的形貌演变过程,发现其晶体生长过程包括两个阶段：初期的晶粒自组装以及后期介观晶体的熟化。晶粒的自组装也是介孔晶体中产生孔结构的原因,在其生长过程中会出现具有介观晶体结构特征的中间产物。五、研究Mn3O4/氧化石墨烯纳米复合材料在锂离子电池上的应用在室温化学沉淀法合成Mn3O4介观晶体和介孔晶体的基础上,合成出Mn3O4纳米晶体/氧化石墨烯纳米复合材料。介观晶体与介孔晶体内部具有较高的孔隙率,可以吸收因为锂离子进出而引起的体积变化。同时将Mn3O4与氧化石墨烯复合,解决了Mn3O4导电性不足的问题。该纳米复合材料在锂离子电池的应用中表现出优异的循环稳定性和倍率性能。更多还原

【Abstract】 Controlling the morphology of nanocrystals and exploring the relationship between their morphologies and properties are the most interesting topics in material science and technology. Controlling the nanocrystal growth process is essential for its morphology tuning, property designing and functionalizing. In mesoscopic scales, crystal growth process normally follows the classical mechanism "Ostwald ripening" and the non-classical mechanisms, including "Oriented attachment" and "Mesocrystal". Generally the non-classical crystal growth mechanisms are based on the assembly and fusion of primary nanocrystals. Providing innovative pathways and diverse possibility for controlling the morphologies of nanocrystals.Anatase TiO2nanocrystals and hausmannite Mn3O4nanocrystals are two typical transition metal oxide nanomaterials. In this article we investigated the influence of crystal growth mechanism on the morphology of nanocrystals, aiming at solving the related problem on the crystal growth controlling. The potential applications of nanocrystals with specified morphology on photocatalytic degradation of organic pollutants, dye-sensitized solar cells and lithium-ion batteries were investigated. The thesis consists of following contents:1. The TiO2nanocrystals were synthesized by solvethermal method, using halogen ion and oleic acid as surfactants to control the morphology. The two surfactants showed distinct absorption capability on specified facets, tuning the growth rate of different facets. Thus, with the help of surfactants, the morphology of TiO2nanocrystals could be effectively controlled. It was also found that fluoride had stronger tendency to selectively absorb on (001) facet compared with other halogen ions. Using fluoride as surfactant, truncated nanobipyramids were obtained, surfaced by two (001) and eight (101) facets.2. A two step synthetic strategy has been developed to prepare one-dimension chain-like TiO2nanocrystals via oriented attachment process. The primary crystals followed oriented attachment and were able to assemble in solution and fuse along specified facets, forming one-dimension chain-like TiO2nanocrystals with single crystal characteristic. The two-step strategy employed in the experiment effectively separated the Ostwald ripening and oriented attachment growth process. The different absorption capability of fluoride and oleic acid on different facets of TiO2 nanocrystals reduced steric hindrance on (001) facet, facilitating oriented attachment growth. It is worth noticing that relative high temperature drives the crystals to overcome the energy barrier for fusion. Moreover, the hydroxyl in the reaction system has great influence on the length of TiO2nanochains.3. Applying TiO2nanochain to enhance the photoelectric conversion efficiency in dye-sensitized solar cells (DSSCs). TiO2nanocrystal film is the most important component in DSSCs. It has been proved that one-dimensional TiO2nanochains with single crystal structure possessed high electron conductivity. In this work, TiO2nanochains and nanoparticles were mixed to prepare nanocrystal films. TiO2nanochains could reduce the possibility of scattering and annihilation of electrons in the transmission process, thus increasing the conductivity of the film. It was found that the addition of30～40wt.%TiO2nanochains in the film increased the photoelectric conversion efficiency to7.5%, which is a78%increase comparing with nanoparticle films (4.2%).4. Preparation of Mn3O4mesoscopic crystals and mesoporous crystals through non-classical crystallization process. The synthesis was carried out at room temperature via chemical precipitation. Mn3O4nanocrystals with uniform morphology were obtained using hydrazine as precipitation agent. The size and morphology of Mn3O4could be effectively controlled by adjusting experiment conditions. The growth process of mesoporous nanocrystals was monitored. It was found that based on the assembly and fusion of primary nanoparticles, nanocrystals with mesoscopic characteristic were formed, then a ripening process occurred, resulting mesoporous nanocrystals. It was also found that the magnetic properties of Mn3O4nanocrystals were affected by the size and morphology.5.Applying Mn3O4mesoscopic and mesoporous nanocrystals as the cathode for high-performance lithium-ion battery. The high porous rate in nanocrystals could mitigate the volume change cause by insertion of lithium ions. Mn3O4/graphene oxide composites were prepared to compensate the conductivity. Such nanocomposites exhibit high performance in lithium-ion batteries更多还原