Study On The Design,Synthesis,Structure And Performance Of Actinium-Based Extractants And Their Coordination Polymers

Minerals are important energy substances.With the increasing demand for energy,nuclear energy,as a new generation of high-efficiency and clean energy,has become an important part of our country's energy composition.The development of nuclear energy is inseparable from the exploitation and utilization of uranium ore.The thorium-based molten salt reactor(TMSR),as a representative of the fourth-generation advanced nuclear energy system,is very suitable for our country's rich thorium resources and is an important guarantee for national energy security.However,the chemical interaction of uranium and thorium with a variety of inorganic or organic oxygen-containing ligands is involved in the mining and utilization of uranium and thorium ore,the treatment of tailings,and the reprocessing of spent fuel.Inorganic acid radicals in the environment and carboxylate radicals of soil organic matter can also form complexes with uranium and thorium,which may affect their migration and adsorption behavior.Studying the structure of uranium/thorium-coordination polymers can provide basic structural parameters for the extraction,separation,adsorption or migration of uranium and thorium elements,and provide scientific support and a large amount of data for the efficient utilization of uranium and thorium resources and environmental governance model.The chemical research on uranium and thorium elements runs through the entire nuclear industry system of molten salt reactors and spent fuel reprocessing.At this stage,the existence form,molecular structure and coordination environment of thorium,uranium and its fission products in various processes are still not completely clear.The research on coordination chemistry of uranium,thorium and their fission products is of great significance to the development of nuclear industry and mining.The work of this thesis starts from the design of ligands,and based on the nitrogen-containing carboxylic acid ligands for mineral separation,a series of novel uranium/thorium-coordination polymers have been constructed.Analyze its precise structure through single crystal X-ray diffraction technology,and study its physical and chemical properties through fluorescence,ultraviolet,infrared spectroscopy,and other methods;Through mass spectrometry combined with DFT(density functional theory)calculations,the coordination chemical behavior of ligands and uranyl ions in solution was studied,and the extraction and separation behavior of transuranic elements(americium)was studied through theoretical calculations.In addition,the application of uranium/thorium-coordination polymer as a new type of actinium material in dye adsorption,iodine removal,and carbon dioxide catalytic conversion was further explored.The specific research content is as follows:(1)Starting from the design of ligands,the in-situ synthesis of ligands(ISLS)has some unique advantages,not only can reduce the reaction process,but also can synthesize some products that cannot be directly synthesized by conventional methods,and realize the diversity of complex structures.We used the semi-rigid dicarboxylic acid ligand H₂bc Hba with imino-reactive sites,through p H and auxiliary ligand regulation,and found that with the decrease of p H,the ligand gradually began to undergo in-situ nitrosylation.Four uranyl coordination polymers were successfully constructed due to different degrees of nitrosolation reaction of ligands,and studied the influence of nitroso groups on the configuration of uranyl coordination polymers based on theoretical calculations.Subsequently,a nitrogen-rich two-dimensional anion uranyl organic framework was successfully constructed by self-assembly of a triazine ring based ternary carboxylic acid ligand H₃TBPCA with uranyl ions.The semi-rigid tridentate ligands and uranyl ions present various coordination modes,and instead of forming a graphene-like honeycomb network plane,a two-dimensional layered network with a certain thickness is formed.The anionic skeleton can selectively adsorb positively charged dye molecules,and the skeleton has a high density of Lewis acidic metal centers and basic-NH-groups,which can also be used to effectively catalyze the cycloaddition reaction of carbon dioxide and epoxy compounds.(2)Based on the theory of soft and hard acids and bases,we constructed two kinds of hybrid transitional uranyl metal organic frameworks by using a mixed ligand containing nitrogen and oxygen atoms-terpyridine carboxylic acid(Hcptpy).Among them,Hcptpy and transition metal ion will form a metalized linear bidentate carboxylic acid ligand after pre-assembly.The metallized ligand then forms a one-dimensional uranyl chain with uranyl ion as the node.The space between the chains is filled with a large number of solvent molecules,which can be exchanged with neutral guest molecule I₂,and has a good adsorption capacity for iodine.When the formate on the uranyl equatorial plane is replaced by biphenyl dicarboxylic acid,the one-dimensional(1D)uranyl chain is transformed to a 2D+2D?3D polycatenated framework structure.In addition,this hybrid uranyl metal organic framework can be used to catalyze the cycloaddition reaction of CO₂ and epoxy compounds.(3)Pre-assembled by hydrolysis condensation to form Th₆ metallized clusters,then reassembled with pyrazole acid and picolinic acid ligands,explored the solution chemical behavior of thorium clusters,and synthesized hexanuclear thorium cluster based on pyrazole and picolinic acid.Then,by introducing the coordination of transition metal and the nitrogen end of the ligand,a metal-organic framework based on thorium cluster-different metal was constructed,and their adsorption behavior for Re O₄^-was further explored.(4)In order to reveal the coordination chemical behavior of U(?)ions with three different alkyl chain PDAM ligands in solution,a study was carried out in combination with electrospray mass spectrometry(ESI-MS)and density functional theory(DFT).Mass spectrometry experiments show that[UO₂L(NO₃)]⁺is the dominant complex formed.Theoretical calculations also confirmed that[UO₂L(NO₃)]⁺is more stable than[UO₂L(OH)·H₂O]⁺.The length of the ligand alkyl chain has little effect on the coordination structure of the uranyl complex,but the steric hindrance effect of the chain length will affect the thermodynamic behavior during the coordination process.(5)Transuranic element(Am)is a high-level waste in spent fuel.Studies have shown that nitrogen-containing pyridine pyrazole ligands have excellent selective extraction capabilities for it,but the extraction mechanism is still unclear.Explore the electronic structure of extractants and their complexes from the molecular level through theoretical calculations,and study the influence of the ligand chain length and pre-organized structure on its extraction ability,including the thermodynamic behavior in the extraction process,etc.,to provide theoretical guidance for the design and use of the extractant in the experiment.