|STUDIES ON THE SEPARATION OF ACTINIDES BY NITROGEN HETEROCYCLIC LIGANDS AND NITROGEN CONTAINING COFs
|Place of Conferral
|氮杂环配体 N-heterocyclic ligands 共价有机框架 Covalent organic frameworks 锕系元素 Actinides 分离 Separation
论文第二章采用硬、软原子结合的策略，将四氢喹啉基团与2, 2'-联吡啶和1, 10-邻菲罗啉刚性骨架相结合，成功制备出了两种具有四齿配位结构的氮杂环二酰胺配体，QL-DABP和QL-DAPhen。通过系统的萃取实验研究了两个配体对镧系和錒系离子的萃取性能，同时采用紫外-可见光谱（UV-Vis）、傅里叶变换红外光谱（FT-IR）、电喷雾质谱法(ESI-MS)、核磁共振（NMR）等光谱以及密度泛函(DFT)理论计算等实验和理论相结合的手段，深入探究QL-DAPhen配体对三价镧锕离子的配位化学及萃取机理。研究结果表明氮供体骨架是实现三价镧锕分离的关键，且酰胺附属基团的空间位阻影响络合物种的分布。
论文第三章首次采用工业级的吡啶杂环和芳香醛（对苯二甲醛）作为sp2C-COFs材料的单体，通过固相熔融法成功规模化制备出二维共价有机框架材料（sp2C-COFs），并进一步后修饰使其甲基离子化。然后将得到的两种具有不同阴离子交换能力的sp2C-COF-1和sp2C-COF-1-MeNO3用于硝酸体系中Th(IV)的分离研究。该类型COFs材料具有良好的结晶性、稳定性、多孔性以及规整片层块体结构。通过酸度、时间接触、离子浓度、离子选择性、循环利用、辐照性能测试等一系列的吸附实验探究材料对Th(IV)的吸附性能。sp2C-COF-1，sp2C-COF-1-MeNO3在9 M硝酸下对Th(IV)具有最佳的吸附性能。动力学快，20 min左右达到吸附平衡，且最大饱和吸附容量可达35.5 mg/g。在包含常见乏燃料伴生离子的高放废液中可选择性的分离Th(IV)。
论文第四章将对苯二甲醛替换成1, 4-联苯二甲醛作为sp2C-COFs的单体，再次采用固相熔融法进一步制备出孔径尺寸更大且同样具有阴离子交换功能的sp2C-COF-2和sp2C-COF-2-MeNO3，并将它们用于对Pu(IV)吸附研究。分析结果表明两个COFs材料同样具有良好的结晶性、稳定性、多孔性和规整的片层结构。通过系统的吸附实验和理论计算考察了它们对四价锕系（Th、Np、Pu）离子的分离性能和吸附机理。在8 M硝酸下对Pu(IV)具有良好的吸附性能。动力学快，10 min左右达到吸附平衡，且平衡时的去除率高达96%。在包含多种常见乏燃料伴生离子的高放废液中可实现对Pu(IV)的选择性分离。COFs材料有效片段的DFT理论分析表明，甲基离子化的COFs材料相比氢质子化的COFs材料具有更优的吸附性能，且对四价锕系的亲和力大小为Pu(IV)>Np(IV)>Th(IV)。
Green and sustainable development are the main theme of contemporary society. Therefore，in order to develop the atomic energy business efficiently and safely, it is necessary to properly and safely deal with and dispose of radioactive materials produced in the process of nuclear industry. As important nuclear materials, uranium, thorium and plutonium occupy a central position in the nuclear fuel cycle, and their separation and recovery are a necessary part of achieving sustainable development of nuclear energy.
Based on the current status and problems of actinides separation in the nuclear fuel cycle, this thesis synthesizes different structures of N-heterocyclic diamide ligands and uses them for the selective separation of actinides in high acid to provide basic theoretical support for the design of lanthanides and actinides extractants. In addition, the N-heterocyclic structure was further introduced into COFs materials to prepare highly crystalline nitrogen-containing sp2-carbon hybridized COFs(sp2C-COFs) on a large scale and the COFs were used for the separation of actinides in high acid systems. The details of the study are as follows:
The thesis firstly briefly outlines the current status of nuclear fuel cycle and spent fuel treatment, introduces the development of nitrogen-containing ligands and their application in actinides separation, then introduces the development of covalent organic frameworks and their research progress in actinides and other radionuclides separation application. Based on the above research progress, the topic idea and research content of this thesis are proposed.
In the second chapter, two N-heterocyclic ligands with tetradentate coordination structures, QL-DABP and QL-DAPhen, were successfully prepared by combining tetrahydroquinoline groups with 2, 2'-bipyridine and 1, 10-phenanthroline rigid skeletons using a strategy of combining hard and soft donor atoms. The extraction performance of the ligands for lanthanides and actinides was investigated by systematic extraction experiments. A combination of experimental and theoretical means such as ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), electrospray mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) spectroscopy and the DFT theoretical calculations were also used to focus on the extraction performance and extraction mechanism of QL-DAPhen ligands for trivalent lanthanides and actinides. The research results indicate that the nitrogen donor skeleton is the key to achieving the separation of trivalent lanthanides and trivalent actinides, and the steric hindrance of amide affiliated groups affects the distribution of complex species.
In the third chapter, two-dimensional covalent organic frameworks (sp2C-COFs) were successfully prepared on a large scale by solid-phase melting using industrial-grade pyridine heterocycles and aromatic aldehydes (terephthalaldehyde) as monomers for sp2C-COFs materials, and further post-modified to methyl ionize them. The two obtained sp2C-COF-1 and sp2C-COF-1-MeNO3 with different anion exchange capacities were then used for the separation of Th(IV) in nitric acid systems. This type of COFs materials has good crystallinity, stability, porosity, and regular lamellar structure. The adsorption performance of the materials on Th(IV) was investigated by a series of adsorption experiments including acidity, time contact, ion concentration, ions selectivity, recycling, and irradiation performance tests. The sp2C-COF-1 and sp2C-COF-1-MeNO3 exhibit good adsorption performance on Th(IV) at 9 M nitric acid. The kinetics were fast, the adsorption equilibrium is reached around 20 min, and the maximum saturation adsorption capacity is up to 35.5 mg/g. Th(IV) could be selectively separated in high level solution containing common ions.
In the fourth chapter, sp2C-COF-2 and sp2C-COF-2-MeNO3 with larger pore size and the same anion exchange function were further prepared by replacing terephthalaldehyde with 1,4-biphenyldicarboxaldehyde as the monomers of sp2C-COFs, again by solid-phase melting method, and they were used for the adsorption studies on Pu(IV). The property characterization confirms that they also have good crystallinity, stability, porosity and regular two-dimensional lamellar structure. Their separation performance and adsorption mechanism for tetravalent actinides (Th, Np, Pu) were investigated by systematic adsorption experiments and theoretical calculations. It had good adsorption performance on Pu(IV) at 8 M nitric acid. The kinetics was fast, reaching equilibrium in about 10 min, and the removal rate of Pu(IV) at equilibrium was about 96%. The DFT theoretical analysis of the effective fragments of COFs materials shows that the affinity magnitude of methyl ionized COFs for tetravalent actinides is Pu(IV)>Np(IV)>Th(IV) and is larger than that of hydrogen protonated COFs.
In the fifth chapter, with the separation of U (VI)/Mo (VI) as the research objective, sp2C-COF-1 and sp2C-COF-1-MeCl ionized with chloromethyl were used as anion exchange materials for the separation of U (VI) and Mo (VI) in sulfuric acid systems. The separation factor (SFMo/U) of COFs material for U(VI)/Mo(VI) is best at around pH=1.50, which is about 84. Both sp2C-COFs hold good adsorption capacity for Mo(VI) under various anions. The adsorption results of simulated acid leaching uranium-molybdenum ore solution indicated that the COFs could selectively separate Mo(VI) from U(VI). In addition, infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) show that Mo(VI) is mainly adsorbed on COFs materials as oxygenated molybdate anion.
Finally, the research work of this thesis is summarized, and some views on the design of N-heterocyclic amides and functional covalent organic framework materials for the separation of actinides are put forward.
Keywords: N-heterocyclic ligands, Covalent organic frameworks, Actinides, Separation
|MOST Discipline Catalogue
|工学 - 核科学与技术
|王帅. 氮杂环配体及含氮COFs材料用于锕系核素的分离研究[D]. 兰州. 兰州大学,2023.
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