The Construction And Properties Of Mono/Bimetallic Organic Frameworks(MOFs) And Composite Materials

Metal-Organic Frameworks（MOFs）are emerging porous materials with n D（n=0-3）network structures composed of organic ligands connecting metal ions or clusters.The diversity of their compositions and structures is mainly attributed to their designable components and tunability at the micro/mesoscopic scale.So far,the structural design and application studies of MOFs have received extensive attention.In recent years,Heterometallic-Organic Frameworks（HMOFs）have stimulated the interest of chemists owing to their attractive physicochemical properties.In addition,metal nanoparticles（MNPs）are frequently used in heterogeneous catalysis because of their high chemical activity and specificity.However,the high surface energy of MNPs limits their application range.Previous studies have shown that MOFs can provide a solution for stabilizing MNPs by virtue of their unique porous structure.In view of the above considerations,new structure and functional of fourteen MOFs and their composites were constructed by using an asymmetric nitrogen-containing carboxylic acid ligand 2-（pyrimidin-5-yl）terephthalic acid（H₂L）and different metal ions.This dissertation contains five chapters:Chapter 1 introduces the definition,research background and progress,synthesis methods,influencing factors and applications of MOFs,design of stable MOFs,construction of HMOFs and MNPs@MOFs as well as their properties,etc.Chapter 2 contains monometallic MOFs with nine different structures composed of H₂L and different metal ions.1 and 2 are 3D porous frameworks with SBUs synthesized based on Ln（III）ions modified with exposed Lewis basic pyrimidine-based active sites.3-9 are2D/3D frameworks based on Cu（II）,Ni（II）,Co（II）,Zn（II）,Cd（II）,and Pb（II）ions.In view of the special structures of 1 and 2 and the strong luminescence properties of 1 and 8,it was found that 1 and 2 exhibited unique selective adsorption to CR dyes,with adsorption amounts of 322 mg g^-1and 326 mg g^-1,respectively.1 and 8 could be used as fluorescent probes for the efficient detection of Fe³⁺and Cr₂O₇^2-in water with detection limits of 10^-6～10^-4M.Chapter 3 adopts the same preparation conditions as MOF 2,the composite Ag@2 and HMOF 10 are gradually obtained by changing the amount of Ag NO₃during the synthesis of 2.This is a facile strategy to realize the“self-sublimation”transformation from monometallic MOF to the composite Ag@MOF and then to HMOF.Meanwhile,it is found that Ag@2 is directly obtained in situ by a one-step hydrothermal method without adding additional reducing agents,and the formation of Ag NPs was due to the interaction of the porous framework decorated with bare N atoms.Besides,catalytic experiments show that Ag@2 and HMOF 10 are excellent heterogeneous catalysts for CO₂fixation,especially the conversion is as high as 99%for smaller sizes epoxides.And the catalytic efficiency of Ag@2 is better than that of HMOF 10 because of the uniformity Ag NPs dispersed in the framework,which showed stronger catalytic ability than the Ag（I）ions participating in the coordination.The facile synthesis strategy in this chapter provides a new idea for the synthesis of Ag@MOFs composites.In Chapter 4,a new stable 3D porous In-MOF 11 with 1D channels is synthesized via H₂L and main group metal In（III）ions,which contains 1D open channels decorated with uncoordinated N atoms.Single-crystal testing results indicate that the1,4-benzenedicarboxylate anions(bdc^2-)is formed during the synthesis of 11 by cleaving the C（sp²）-C（sp²）σbond between two parts of partial L^2-ligands.With the addition of H₂bdc during the synthesis of complex 11,another new isomorphic porous In-MOF 12 is formed,eliminating the possibility of impure H₂L ligand.Furthermore,only Ag@11 was successfully obtained by one-step hydrothermal method,which further verified that the formation of Ag NPs was the result of the interaction with the uncoordinated pyrimidine groups in the framework.Gas adsorption experiments showed that 11 presented higher adsorption capacities for C₂H₂and CO₂(86 and 72 cm³g^-1,respectively)and selectivity for C₂H₂/CH₄and CO₂/CH₄（21.25 and 7.10,respectively）.Therefore,11 can be used as good gases adsorption material.Furthermore,11 and Ag@11 are excellent catalysts for the cyclization reaction of immobilized CO₂,with catalytic efficiency of up to 99%for smaller-sized substrates,and the catalytic efficiency of Ag@11 is higher than that of the monometallic MOF 11,proving that the synergistic effect between Ag NPs and MOF in Ag@11 promotes the catalytic process.The comparative work in this chapter is more conducive to further enriching the research on the preparation of Ag@MOF composites using the in situ one-step strategy,which has a good reference for the research in this field.Chapter 5 uses H₂L and Co（II）ion to construct a 3D porous MOF 13 with trinuclear SBUs and pyrimidine groups on the channel along the c direction.Based on the similarity between H₂bdc and H₂L,14 is successfully designed by introducing the auxiliary ligand H₂bdc with a larger pore size than that of complex 13.In addition,only the composite Ag@13 was successfully obtained by adding the precursor Ag NO₃during the synthesis of13 and 14.However,the partial substitution of L^2-by bdc^2-in 14 makes the modification of the channel lacking N-containing groups,which have not obtained Ag NPs in 14 all the time.This phenomenon confirms the view in previous chapters that the formation of Ag NPs is the result of the interaction of Ag（I）ions with the host framework,and the framework structure must satisfy the porous channels containing uncoordinated functional groups,both of which are indispensable.Furthermore,catalytic experiments show that 13,14 and Ag@13 are all good heterogeneous catalysts for immobilizing CO₂cyclization,and the catalytic efficiency for smaller-sized substrates can reach about 90%under mild conditions.The catalytic activity of Ag@13 is higher than that of monometallic MOFs 13and 14 thanks to the synergistic catalysis.