Transmission Electron Microscopy Analysis Of The Crystalline Microporous Materials

With the development of material science, more and more materials have been synthesized. Microporous materials have been widely used in gas adsorption and separation, ion exchange, catalysis and other fields, because of their large specific surface area and the advantages of molecular selectivity. However, whether one kind of material has attractive application prospect, it is closely related with its structure. So it is very important for us to study the structure of materials. On the basis of their crystallinity, microporous materials can be divided into two parts, amorphous microporous materials(such as activated carbon and porous aromatic frameworks(PAFs)) and crystalline microporous materials(such as Zeolites and metal-organic Frameworks(MOFs)). Amorphous materials are disordered or short-range ordered in atomic scale, so it is difficult to be described by using an accurate model. Thereby we mainlyfocus on the structure of crystalline microporous materials. The traditional methods to determine the structure of materialsinclude Single Crystal X-Ray Diffraction(SXRD), Powder X-Ray Diffraction(PXRD) and Transmission Electron Microscopy(TEM).In this thesis, we mainly use TEM to explore the structure of Zeolites and MOFs. Especially, we will introduce a new analysis technique of TEM, three dimensional(3D) electron diffraction tomography(EDT),and its application in the structure determination of Zeolites and MOFs. This thesis includes the following five sections:The first chapter is the introduction. In this section, we summarize the development history of microporous materials and TEM, introduce the application and achievements of traditional TEM, and focus on the development of 3D EDT and its principle. Furthermore, we also introduce the research tool of 3D EDT, RED software, in detail.In the second chapter, we will introduce the application of conventional TEM in the study of the structure of Zeolites. First of all, we study the problem of the intergrowth of A and B phase in the A enriched Zeolite Beta by High Resolution Transmission Electron Microscopy(HRTEM). We also analyze the packing mode of A and B phase at the atomic level, and calculate the proportion of A phase in the different samples. Secondly, we study the crystallization of pore-wall of hierarchical Zeolite Beta and the whole sample, and prove that the sample is a highly ordered crystalline micro- and meso-porous composite material. Finally, we explore the crystallization of hierarchical ZSM-5 Zeolite, and the problem of the growth orientation of small crystals inside the sample particles.About the third chapter, we mainly study the possibility of the EDT technology in the structure determination of MOFs. Currently, there have been a lot of articles to determine the structure of Zeolites by using EDT, but it has not been reported to resolve the structure of MOFs by this technology. Here we expand the EDT technology to determine the structure of the MOFs. As we all know, most of Zr-MOFs have good stability, and UiO-66 is the representative of them. UiO-66 has a uniform particle size(usually 100-300nm) and good stability, and therefore it’s suitable to determine its structure by the EDT technique. After we obtain the structure of UiO-66 by EDT, we compare it with the result obtained by HRTEM, which shows that they are consistent. At last, we compare it with the result from PXRD, and we can see that these two results have the similar atom positions. Only the positionof one oxygen atom has the deviation of 0.35 ?, and the deviation for the rest of the atom positions is less than 0.1 ?. This implies that it is feasible to determine the structure of MOFs by using EDT.In the fourth chapter,we focus on the use the EDT technology to study terminal oxygen atoms of a MOF, JUC-32. The physical and chemical properties of materials are largely determined by the nature of the terminal atoms. Therefore, the study of the terminal atoms has great significance. With the development of TEM technology, especially the Cs corrector TEM, we can directly "observe" oxygen atoms in the metal oxide by TEM. If we want to "see" oxygen atoms directly, it will require very high magnification. In this condition, the electron irradiation dose perarea is very high, and the damage of the sample is also very serious. So the Cs corrector TEM can only be used to study the stable materials. Most of MOF materials are very sensitive under electron beam, and it is difficult to study them by the Cs corrector TEM. In addition, it is also rarely reported to study terminal atoms of MOFs materials by the use of other TEM method. So it has an important significance to determine the position of terminal oxygen atomsin JUC-32 by using EDT technology.For the fifth chapter, we use the EDT technology tosuccessfully resolve the structure of a new phosphorus aluminum Zeolite, PST-6. We compare these results with the HRTEM images, and find that both of them are consistent, which further confirms that 3D EDT technology can be used in the structure analysis of the complicated Zeolites.In conclusion, in this thesis we discuss the application of the conventional TEM method in the study of the structure of materials. Wealso compare EDT technology with the traditional method of structure analysis in detail, and study the feasibility of the application of EDT in the structure analysis of MOF materials. At last, we use EDT technology to successfully resolve the structure of an unknown phosphorus aluminum Zeolite, PST-6. We believe that our research will further improve the development of EDT technology andthe application of TEM technology in the study of the structure of materials.