Preparation And Fluorescence Sensing Of Lanthanide Metal-Organic Frameworks (Ln-MOFs) With Pyridine Carboxylate Ligand

Lanthanide Metal-Organic Frameworks materials(Ln-MOFs)have been widely studied owing to their potential applications prospects in different fields such as fluorescence,gas adsorption and separation,catalysis and so on.In the assembly process of these materials,organic ligands and metal centers are not only the structural units,but also the key factors to determine the properties of MOFs.In this paper,two new Ln-MOFs were prepared through the combination of the 2-(4-pyridyl)terephthalic acid ligands and lanthanide metal ions under hydrothermal conditions.And then,other four new Ln-MOFs were constructed using mixed ligands of oxalic acid and 2-(4-pyridyl)terephthalic acid.Their structures and composition were characterized.The thermostability,water stability,chemical stability and luminescent property for these Ln-MOFs have been investigated,and the MOFs that possess excellent fluorescence performance were selected to explore the fluorescence sensing propety.The main researches are as follows:1.The hydrothermal reaction of Ln(NO3)3·6H2O with 2-(4-pyridyl)terephthalic acid(H2pta)gave the lanthanide metal-organic frameworks(Ln-MOFs),(Ln=Eu 1,Gd 2).Single-crystal X-ray analysis reveals that compounds 1-2 are isostructural and display a 3D 6-connected net with the point symbol of {4^12.6^3}.The thermostability,water stability,chemical stability and luminescent property for 1-2 have been investigated in the solid state at room temperature.The results show that 1 and 2 have satisfactory water stability and acid alkali stability in aqueous solution.The excellent luminescence as well as good water stability of 1 makes it a highly selective and sensitive multiresponsive luminescent sensor for Fe3+.Furthermore,the Stern-Volmer quenching constant is calculated to be 11236 mol/L and the limit of detection is 3.5×10-5 mol/L.The results show that compound 1 is an ideal photoluminescence sensing material which can be used to detect metal Fe3+ions.2.Four mixed-ligand lanthanide metal-organic frameworks,namely:[Tb(pta)(COO)2]·H2O(3),[Dy(pta)(COO)2]·H2O(4),[Er(pta)(COO)2]·H2O(5)and[Ho(pta)(COO)2]·H2O(6)obtained under the water and ethanol mixed system in the presence of Oxalic acid(C2O4H2)and 2-(4-pyridyl)terephthalic acid(H2pta).Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses,IR spectra,powder X-ray diffraction(PXRD),and thermogravimetric(TG)analyses.Studies revealed that these compounds are 3D 6-connected net with the point symbol of {4^12.6^3}.Compounds 3-6 are good thermally stability and water stability,and have a high stability in water with a wide pH range(pH=4-11),MOFs 3 display bright green fluorescence emission in water,which can be quenched by trace amounts of Fe3+/Cr2O72-ions and nitrofuran.The detection limits and quenching constant towards Fe3+/Cr2O72-and nitrofuran are estimated to be 2.6×10-5 mol/L/12211 mol/L;3.8×10-5 mol/L/10276 mol/L and 8.1×10-5 mol/L/10970 mol/L respectively.The results suggest 3 is the multifunctional of fluorescence sensor to detect Fe3+/Cr2O72-and nitrofuran.