Synthesis,Structure And Properties Of Uranyl-organic Framework Materials

Uranium compounds have succeeded in arousing increasing interest due to the potentiality in benefiting environmental safety and in maximizing the utilization of limited natural resources.Inspired by the extensively studied in metal-organic framework materials(MOFs),researches about uranium-organic frameworks(UOFs)have shown great momentum in different fields with regard to the intriguing architectures and versatile applications,such as fluorescence,photocatalysis,X-ray detection and ions adsorption.As we all know,the change of dimension not only changes the structure of materials,but also has a great impact on its properties and even the field of application.In general,the higher the dimension of the material,the more stable,the more conducive to the practical application of materials.However,the terminal oxygen atoms of uranyl in UOFs are very chemically inert,which is not conducive to the formation of three-dimensional framework.Thus,the construction of three-dimensional UOFs materials become an important problem.Polyoxometalates(POMs)are a subset of metal oxygen clusters of the early transition metals in their high oxidation states(Mo,W,V),which shows potential applications in many fields,especially in photocatalysis.As both polyoxometalate and uranyl show good photocatalytic performance,the synthesis of POMs@MOFs materials with both polyoxometalate and uranyl is also an important topic.Because it not only enriches the topological structure of uranyl organic framework materials,but also makes it possible to explore the photocatalytic synergistic effect between them.Based on this,this paper has done the following innovative work:1.Three new Uranium-organic compounds have been synthesized under the strong acid condition.Both of the compound 1[(UO₂)(TMA)](H₂BPY)_0.5·4H₂O(TMA=trimesic acid,BPY=4,4?-bipyridine)and 2[(UO₂)(PMA)_0.5](H₂BPY)_0.5(PMA=pyromellitic acid)show a“sandwich”2D-structure.The double-protonated 4,4?-dipyridines stabilize the supramolecular structure without obvious interlayer interactions in 1,while there is weak N-H···O hydrogen bonding in 2.Compound 3[(UO₂)₂(PTA)(BPDO)](PTA=terephthalic acid)was obtained by employing 4,4?-bipyridine-N-dioxide(BPDO)as auxiliary ligand.Owing to the much weaker protonation ability,the BPDO molecules can pillar the screwy uranyl layers via U-O covalent bonds to form a 3D framework.All the title compounds are well-characterized.The results indicate the intensity of the interaction between uranyl layer and the auxiliary ligand not only affect the assembly of the architecture,but also the fluorescent and adsorption behavior.2.Polyoxometalate-supported two-dimensional uranyl organic framework material(compound 4,[(UO₂)(BPDO)₂(PW₁₂O₄₀)]))was synthesized by hydrothermal method.Its innovation lies in the introduction of polyoxometalate into uranyl organic framework material.In this compound,polyoxometalate plays the dual role of template and coordination.The study of dye adsorption shows that the material has good adsorption properties.3.On the basis of the previously synthesized polyoxometalate-based uranyl organic framework compounds,by changing the conditions,we creatively synthesized two three-dimensional supramolecular polyoxometalate-based uranyl organic framework materials(compounds 5 and 6,the molecular formulas are[(UO₂)(BPDO)₃)[Si W₁₂O₄₀]·3.7H₂O and[(UO₂)(BPDO)₃][PW₁₂O₄₀]·H₂O,respectively).Their adsorption properties were studied.