Synthesis And Fluorescence Sensing Properties Of Rare Earth Metal-organic Framework Compounds

Metal-organic frameworks?MOFs?are new organic-inorganic hybrid materials composed of metal ions and organic ligands.Since its discovery,MOFs materials have great application prospects in the fields of ion sensing,gas adsorption and storage,luminescence,magnetism,biomedicine and so on due to its rich functional points,strong structural designability and sensitivity to external stimuli.Because of the rare earth ions exhibit high color purity,visible light emission and large stokes shift and relatively long life f-f transition,rare earth metal compounds of rare earth metal-organic frameworks?RE-MOFs?have rich luminescence sites,the wavelength range,the material characteristics easy to modify,so they are widely used in lighting,sensing and other fields.In this paper,six novel RE-MOFs materials were prepared by solvent-thermal method with 2,5-furan dicarboxylic acid?H₂FDA?and 1,3,5-benzoic acid?H₃BTC?as ligands and rare-earth metal ions(Tb³⁺,Y³⁺,Sm³⁺)as luminescence centers.The structure and phase purity were analyzed and verified by single crystal X-ray diffraction,powder X-ray diffraction and elemental analysis,and the single crystal sutcture was simulated and optimized by combining first-principles calculatuons.Using thermogravimetric analysis,fluorescence spectroscopy and other analytical methods,the potential applications in metal ions and organic small molecule sensing were studied.The main research work includes the following three aspects:1?By using H₂FDA as the organic ligand,three isomorphic RE-MOFs materials[RE?FDA?_1.5?DMF?].DMF were prepared by self-assembling with rare earth ions at high temperature and atmospheric pressure(RE=Tb³⁺,Y³⁺,Sm³⁺,FDA=furan dicarboxylic acid,DMF=N,N-dimethyl formamide).The three RE-MOFs materials all have the crystal structure of pure crystal phase.The crystals crystallize in the orthogonal crystal space group Pnma.Under the excitation of the wavelength of 296nm,the maximum emission peaks of the three RE-MOFs materials appeared at 543 nm,544 nm and 643 nm respectively,which were attributed to the characteristic emission of Tb³⁺,Y³⁺and Sm³⁺.In addition,[Tb?FDA?_1.5?DMF?]·DMF showed specific recognition of Fe³⁺ions and nitrobenzene,with detection range of 0.01?g/ml-0.1?g/m and 5 mg/L-4000 mg/L,respectively.[Y?FDA?_1.5?DMF?]·DMF showed specific recognition of Cu²⁺ions,nitrobenzene and o-chlorophenol,with detection range of 0.1?g/ml-20?g/ml,5 mg/L-5000 mg/L and 10 mg/L-2000 mg/L,respectively.[Sm?FDA?_1.5?DMF?]·DMF does not exhibits specific recognition of metal ions or aromatic hydrocarbons due to the influence of solvent DMF.2?Two isomorphic co-doped MOFs materials[Sm_0.1Tb_0.9?FDA?_1.5?DMF?]·DMF and[Sm_0.2Y_0.8?FDA?_1.5?DMF?]·DMF were prepared by hydrothermal method with Sm³⁺and Tb³⁺as rare-earth ions luminescence centers and H₂FDA as organic ligands,respectively.Two co-doped MOFs materials have similar structures as the single-doped MOFs materials.At the excitation wavelength of 296 nm,the maximum emission peaks attributed to Tb³⁺and Y³⁺appeared at 544 nm and 566 nm,respectively.Both RE-MOFS materials showed specific recognition of As³⁺ions,and the detection range was 0.1 mg/L-1000 mg/L and 0.01 mg/L-100 mg/L,respectively.In addition,[Sm_0.2Y_0.8?FDA?_1.5?DMF?]·DMF also exhibits enhanced fluorescence for Mg²⁺,with detection range of 500 mg/L-3000 mg/L.3?By using 2,5-furan dicarboxylic acid?H₂FDA?and 1,3,5-benzoic acid?H₃BTC?as ligands and Tb³⁺as the metal center,water-stable and thermally stable dual-ligand MOF[Tb₂?FDA?_1.5?BTC??DMF?]·DMF was prepared by hydrothermal method.At the excitation wavelength of 296 nm,MOF material appeared at 542 nm due to characterisitc energy level transition of Tb³⁺.MOF material has exhibits excellent adsorption capacity to nitrogen.Brunauer-emmett-teller?SBET?and Langmuir?SLangmuir?of nitrogen adsorption isotherm have surface areas of 790.4cm³g^-1and 1440.3 cm³g^-1respectively,and the maximum adsorption capacity of N₂is124 cm³g^-1.