Synthesis And Properties Of Rare Earth Metal Organic Framework Materials

Metal-organic Framework?MOFs?is a crystal porous material with periodic network structure formed by self-assembly of Metal ions or Metal clusters and Organic ligands.Metal-organic framework have attracted much attention due to their permanent porosity and unique optical and electronic properties.In recent years,it has been widely used in gas phase storage/separation,sensing,drug delivery,polyphase catalysis,proton conduction and other fields.Among these organic framework materials,lanthanide organic framework?Ln-MOFS?is regarded as one of the most promising chemical sensors due to their advantages of short response time,easy operation,high selectivity and good sensitivity.However,lanthanide metal ions are affected by transition forbidden and their molar fluorescence absorption coefficient is low.Therefore,they need to be sensitized by chelating appropriate organic chromomeres as antennas.It is shown that the lanthanide ions have a high affinity for the oxygen atoms that provide lone pair electrons,and benzoic acid and its derivatives are a good choice for the fluorescence emission of sensitized lanthanide ions.Therefore,the choice of ligands containing carboxylic acids is a better sensitization antenna.In this thesis,a series of researches were carried out on the synthesis of MOFs materials and their corresponding fluorescence properties.This paper is mainly divided into the following parts:Chapter 1:This chapter mainly introduces the research progress,synthesis methods and applications of MOFs in recent years.Chapter 2:In this chapter,three compounds with different pore structures were prepared by solvothermal method with appropriate ligands 3,4',5-biphenyl-tricarboxylic acid?H₃bpt?and lanthanide metal salts.The metal ions in these three compounds all coordinate with oxygen atoms.The difference is that the coordination mode of crystal is regulated by changing reaction conditions,such as reaction temperature,pressure,PH of solution and changing reaction solvent,so as to construct Ln-MOFS with different pore structure.The three compounds were characterized.Compound 1 was found to emit bright green light under ultraviolet light.So,compound 1?Tb-MOFS?was used as the fluorescent probe for detect 11 metal ions including Mg²⁺,Cd²⁺,Al³⁺,K⁺,Cu²⁺,Co²⁺,Ag⁺,Li⁺,Na⁺,Cr³⁺,Fe³⁺,(immersed in DMF,The metal ion concentration was 10^-3 mol.L^-1)and 10 anions(MnO₄^-,NO₃^-,Cl^-,H₂PO₄^-,CO₃^2-,Br^-,F^-,HCO₃^-,PO₄^3-,I^-,mol.L^-1).It was found that compound 1?Tb?lost its original green light and fluorescence quenching occurred in DMF solution containing mol.L^-1 Fe³⁺and MnO₄^-.The results showed that Fe³⁺solution could make the fluorescence quenching ratio of compound 1 reach 99.1%,and the detection limit was 3.54mM.MnO₄^-solution could make the fluorescence quenching ratio of compound 1reach 99.6%and the detection limit was 4.6 m.This indicates that compound 1has potential fluorescence sensing ability of Fe³⁺and MnO₄^-.Chapter 3:In this chapter,the pyridine carboxylic acid ligands nicotinic acid,lanthanide metal Gadolinium?Gd?and cupreous iodide?CuI?were selected as metal sources to synthesize MOFs of two bimetallic centers with three-dimensionalstructurebysolventthermal method,[Sm₂?BPYDC?₃?DMF?₂?H₂O?]·2DMF?4?,[Sm₂?BPYDC?₃?DMA?₂?H2O?_0.5]·1.5DMA?5?.Compounds 4 and 5 with the same copper?I?-halide clusters of secondary structural unit?cubane Cu₄I₄?,the difference is that Gd³⁺of the adjacent seven coordination in compound 4 is linked with carboxylic acid groups to become a one-dimensional carboxylate-gadolinium chain that extends infinitely along the C direction.Two adjacent crystallographic independent Gd1and Gd2 in compound 5,are linked with organic ligands containing carboxylic acid groups to form a one-dimensional carboxylate-gadolinium chain that extends infinitely along two directions,Cu₄I₄ cluster and carboxylic acid oxygen-gadolinium chain are linked by organic ligand to form the three-dimensional skeleton with one-dimensional channel structure.By fluorescence characterization,we found that compounds 4 and 5 had wide and strong green light emission,and this emission peak came from Cu₄I₄ cluster of cubane type.At the same time,compounds 4 and 5 had strong fluorescence in dilute solution,but their fluorescence intensity decreased significantly in solid state.In addition,compounds 4 and 5 were used as fluorescent probes to detect a series of anions and metal cations.The results showed that CrO₄^2-and Cr₂O₇^2-solutions could make the fluorescence quenching ratio of compound 4 reach 80%and that of compound 5 reach 76%,with detection limits of 5.16×10^-5M and8.25×10^-6M,respectively.Fe³⁺solution can make the fluorescence quenching ratio of compound 4 reach 84%and reach 80%for compound 5.The detection limits are 4.02×10^-5M and 1.86×10^-6M respectively.The results of ULTRAVIOLET absorption spectrum showed that the strong ultraviolet absorption of Fe³⁺or Cr₂O₇^2-for the excitation energy hindered the energy absorption of compounds 1 and 2,leading to the reduction of luminescence intensity or even completely quenching.The reasonably and effectively designed and synthesized copper?I?halogen cluster rare earth bimetallic center MOFs as a recyclable multi-response luminescent sensor has a certain potential in the field of dual-function sensing.Chapter 4:The summary and prospect of this thesis.