Syntheses,Structures And Iodine Adsorption Properties Of Thorium-based Metal-organic Frameworks

Metal Organic Frameworks（MOFs）are a new class of long-range ordered crystalline porous materials formed by the self-assembly of metal ions or metal clusters and organic linkers through coordination bonds.Such materials not only have the selectivity of metal nodes and the diversity and modifiability of organic linkers,but also have the characteristics of diverse structures,high specific surface area,well-developed voids,easy modification,and tunable pore size.Catalysis,molecular absorption and separation,fluorescence,drug transport,electrochemistry and many other fields have been widely used.With the increasing demand for electricity,the nuclear power industry has also developed rapidly.However,the nuclear power generation process produces spent fuel containing a large amount of radionuclides.Therefore,how to effectively enrich and separate the radionuclides produced in the process of nuclear power generation is the focus of environmental protection and nuclear energy development.Among them,the radionuclide iodine(mainly composed of ¹³¹I and ¹²⁹I)mainly exists in the form of I₂,CH₃I,C₂H₅I,and has the characteristics of being volatile and soluble in water,so it is easy for air and water to diffuse into the spontaneous combustion environment,causing environmental pollution.endanger human health.In this study,based on the characteristics of Th-MOFs with good acid-base stability,high specific surface area,adjustable pore size,and functional modification,three new MOFs materials using Th4+as metal source were designed and synthesized.Single crystal X-ray diffraction,powder X-ray diffraction,infrared spectroscopy,thermogravimetric analysis,surface area testing,scanning electron microscopy and other tests have investigated the structure of the material.According to the structural characteristics of the material,the adsorption performance of the material under different conditions was explored.The adsorption mechanism of iodine was analyzed by means of infrared spectroscopy,ultraviolet-visible spectroscopy,EDS elemental analysis,X-ray photoelectron spectroscopy and Raman spectroscopy.details as follows:1.Synthesis of Th₆（μ₃-O）₄（μ₃-OH）₄（BPDC）₁₂（H₂O）₆（DMF）₁₁（H₂O）₉（Th-BPDC）by solvothermal method via 4,4’-biphenyldicarboxylic acid（BPDC）and thorium nitrate hydrate.The structure is an octahedral structure.It has good stability at p H=1-10.At the same time,it also has good stability under different organic solvents.Thermal stability temperature 517℃.The specific surface area is 845.56 m²/g.2.Synthesis of Th₆（μ₃-O）₄（μ₃-OH）₄（BPYDC）₁₂（H₂O）₆（DMF）₁₁（H₂O）₉（Th-BPYDC）by solvothermal method via 2,2’-bipyridine-5,5’dicarboxylic acid（BPYDC）and thorium nitrate hydrate.The structure is an octahedral structure.It also has good stability at p H=1-10.At the same time,it also has good stability under different organic solvents.Thermal stability temperature 486℃.The secific surface area is 647.53m²/g.3.The ligand 4,4’-azophthalic acid（AZB）was synthesized by p-nitrobenzoic acid and D-glucose,followed by solvothermal method,using4,4’-azophthalic acid（AZB）and thorium nitrate hydrate to synthesize Th₆（μ₃-O）₄（μ₃-OH）₄（AZB）₁₂（H₂O）₆（DMF）₁₁（H₂O）₉（Th-AZB）.This structure is also an octahedral structure.It has good stability at p H=5-9.At the same time,it also has relatively good stability under different organic solvents.Thermal stability temperature 500℃.The specific surface area is 1333.84 m2/g.4.The iodine adsorption was studied on Th-BPDC and Th-BPYDC to prove the influence conditions of iodine adsorption.The difference between the removal rate and adsorption capacity of the two materials in cyclohexane kinetics,isotherm and iodine vapor kinetics was judged.At the same time,after adsorption of iodine,the two materials were subjected to X-ray diffraction analysis,infrared spectroscopy analysis,ultraviolet spectroscopy Visible spectroscopy,scanning electron microscopy,EDS elemental analysis,X-ray photoelectron spectroscopy,and Raman spectroscopy were used for characterization.Through this study,it provides important theoretical guidance for radioactivity adsorption research,and the reserve materials provide new ideas,with a certain value.