摘 要

近年来，由于多孔材料在比表面积、孔洞体积与孔状结构可调节等方面的巨大优势，人们在基础研究以及应用方面都对其投入了大量努力。其中，金属有机骨架材料（metal-organic frameworks, MOFs）成为了多孔材料中的焦点之一。Yaghi课题组在1995年首次提出了MOFs这一概念，自此出现了大量关于MOFs新结构的开发，性能的优化，孔结构的改良以及气体吸附和催化性能研究。MOFs材料主要由金属离子与起到连接作用的有机配体构成，加上其合成条件相对温和，使得人们可以通过二级结构单元构建的方法来设获得多种优良的性能。

类沸石咪唑酯骨架材料（zeolitic imidazole frameworks, ZIFs）是MOFs材料的一种，这种材料集合了沸石与MOFs材料的优良性能，不仅表现出比沸石更好的可调控性（通过金属离子与有机连接配体的调控来获得新结构）而且具有比MOFs更好的化学稳定性与热稳定性，同时其具有极高的表面积、单峰微孔结构、高结晶度、功能多样性。

本研究选取了ZIF-4、ZIF-8、ZIF-62三种典型结构，深入探究了它们的原子结构、电子结构与光学性能，帮助科研工作者更加直观、详尽的了解ZIFs的结构与性能的关系，为应用研究提供重要的理论基础。更重要的是，我们通过对比ZIFs的结构与性能，分析ZIFs结构与性能的内在联系，为以后ZIFs的改性、新结构开发、应用研究提供了重要的实验方向，具有重要的指导意义。主要研究结果如下：

1. ZIF-4的有机配体为ZIFs中比较简单的咪唑环，晶格参数的a、b、c分别为15.71Å、15.98Å、18.27Å，空隙率为91.20%；C-N键相比其他结构较长，因为其配体结构相对简单，空间上排布相对不紧密，C、N成键时受到的束缚较小；径向分布函数有很多明显的尖峰，结构中所有化学键的键长分布都非常集中，具有显著的晶体结构特征；禁带宽度约为5eV，介电函数、吸收光谱、反射普、能量损失谱的第一峰都出现在5eV附近，符合其带隙宽度。
2. ZIF-8与ZIF-4 相比，配体可以视为采用了甲基修饰，晶格参数的a、b、c均为为17.20Å，空隙率为93.06%，是选取的三种ZIFs结构中最大的，为其在气体吸附方面的大量应用研究奠定了基础；甲基的存在，增加了有机连接体的复杂性，Zn离子在三维空间的分布更加分散；DOS的禁带宽度约为5eV，与ZIF-4相近；光学性质方面，甲基的引入对吸收光谱、能量损失谱、介电函数、反射谱的第一峰位置影响较小。
3. ZIF-62替换了ZIF-4中的部分配体为苯并咪唑，且本研究ZIF-62体系中，咪唑环与苯并咪唑的摩尔比为3:1，晶格常数a、b、c为14.90Å、17.38Å、19.16Å，原子数密度（0.064atoms/ų）是三种结构中最大的，空隙率（90.64%）则最小；苯并咪唑的引入对导带的DOS产生了显著影响，使禁带宽度减小为4eV;光学性能方面；光学性质方面，此种替换使介电函数虚第一峰处向小能量处发生移动，增加了外加电场下形成电偶极子的能量，吸收光谱和反射光谱均的第一峰向长波长移动，材料对电子的非弹性散射增强。

关键词：第一性原理；ZIFs；原子结构；电子结构；光学性能

Abstract

In recent years, porous materials show great superiority in specific surface area, pore volume and tunable pore structure, so scientists pay more and more efforts to properties research and applications. In this states, MOFs (metal-organic frameworks) turns into one of the most popular objects. In 1995, Yaghi et. al. proposed the concept of MOFs for the first time, fron then on, a great deal of researches on new structure exploiting, performance optimization, pore improvement as well as gas adsorption occurred. This material compose of metal ions and organic ligands which play the role of connection, and the synthesis conditions are relatively mild, so that people can obtain more excellent properties by the construction of secondary building units.

ZIFs (Zeolite imidazole frameworks) are included in MOFs, which combine the advantages of zeolite anf MOFs. This porous not only be more controllable (adjustment of ligands and metal ions leading to novel structure), but also exhibit better chemical and thermal stabilities compare to MOFs. In addition, they are of extremely high surface area, crystallinity,and functional diversity.

Our study chooses representative ZIF-4, ZIF-8, ZIF-62 subject to explores their atomic, electronic, and optical properties, aiming to provide more intuitive and detailed structure information in order to offer theoretical basis for application research. What is more important is that we put forwards new ideas from the point of structure affecting properties. Our results will direct later experiments about ZIFs modification, new frameworks finding, applications. This article mainly have the following outcoming and conclusions:

1. For ZIF-4, the ligand is imidazole ring which is relatively simple, the lattice parameter a, b, c is 5.71Å, 15.98Å, 18.27Å respectively, and the porosity is 91.20%. As for bonds, the C-N bond is longer than the other chosen ZIFs, because the bonding process of C and N atoms is relatively less restrained due to the simple organic linker. There are many narrow peaks in radical distribution function and the bonds length distribution is very concerned which are typical characteristics of crystal. In addition, the band gap is 5 eV being consistent with the first peak of dielectric function, absorption, reflection, energy loss spectrum at around 5 eV.

(b) Compared with ZIF-4, ZIF-8’s ligand is modified with methyl, and the lattice parameter a, b, c is all 17.20Å. ZIF-8 has the biggest porosity of 93.06%, which accounts for its promising application on gas absorption. The exist of methyl contributes to the framework complexity, so the distribution of Zn ions is more dispersed. Moreover, the method of adding extra methyl will not have obvious effect on band gap (around 5 eV) and the first peak’s energy of optical spectrum.

(c) In ZIF-62, benzimidazole replaces part of midazole rings, and the molar ratio of imidazole ring to benzimidazole is 3:1. The lattice parameters a, b, c is 14.90Å、17.38Å、19.16Å respectively, and ZIF-62 has the largest atomic number density of 0.064atoms/ų with the least porosity of 90.64%. The induced benzimidazole has significant influence on the conduction band with de energy gap decreased to 4eV. In optical properties, the replacement lead to the energy of dielectric function imaginary part’s first peak becoming lower, the increasing the energy in the formation of electric dipole, the movement of absorption and reflection spectrum to longer wavelength, the enhancement of electrons inelastic scattering.

Key Words: first principle calculation; atomic structure; electron structure; optical property

目 录

第1章 绪论 1

1.1 ZIFs材料简介 1

1.2 ZIFs材料的结构 2

1.3 ZIFs材料的合成 3

1.3.1 有溶剂参与的ZIFs合成方法 4

1.3.2 无溶剂参与的ZIFs合成方法 6

1.4 ZIFs材料的性能及应用 7

1.4.1 气体分离与选择性吸附 7

1.4.2 催化性能及应用 7

1.5 本论文的主要研究内容与意义 11

1.5.1 主要研究内容 12

1.5.2 本论文的研究意义 12

第2章 理论基础及研究方法 14

2.1 第一性原理计算 14

2.2 密度泛函理论 15

2.2.1 Hohenberg-Kohn与Kohn-Sham定理 15

2.2.2 局域密度近似与广义梯度近似 16

2.3 光学理论基础 16