Synthesis And Properties Of Guest Molecule/ion Responsive Fluorescent MOFs Materials

Metal-organic frameworks（MOFs）have been widely used in gas storage,adsorption and separation,catalysis,electrochemistry and other fields due to their large specific surface area,high porosity,and adjustable pore size.Luminescent MOFs materials belong to an important branch of MOFs materials,and have huge applications in the field of chemical sensing.At present,a large number of constructed sensors have many shortcomings such as high detection limit,low selectivity or low sensitivity due to the complex composition of the target detection object or the weak interaction between the target object and the sensing material.To deal with these problems,this thesis is devoted to designing and synthesizing sensors with high selectivity and high sensitivity,which can be applied to detect and identify ions,antibiotics,organic solvents and biological macromolecules in water systems.The main research contents of this paper are as follows:In this paper,1,1’-ethylbiphenyl-3,3’,5,5’-tetracarboxylic acid（H₄L）,two nitrogen-containing ligands and transition metal ions were selected and successfully synthesized by solvothermal method,[Zn₃（L）_1.5（DMF）₃]·C₂H₇N（1）,Zn（L）_0.5（bpb）_0.5（H₂O）₂（2）,[Zn（L）（4,4′-bpy）]（3）,Cd（L）_0.5（4,4′-bpy）_0.5·H₂O（4）,[Cd₂（L）（bpb）（H₂O）₄]·0.5H₄L（5）,[Cd₆Na₄（L）₄（DMF）₂（μ-H₂O）₃]（6）.H₄L=1,1’-ethylbiphenyl-3,3’,5,5’-tetracarboxylic acid,4,4′-bpy=4,4′-bipyridine,bpb=1,4-di（pyridin-4-yl）benzene.It was characterized by X-ray single crystal diffraction,infrared,thermogravimetric,X-ray powder diffraction and other means.Fluorescence sensing experiments were performed to detect organic solvents,antibiotics,amino acid,etc.Finally,ion encapsulation experiments were carried out,and luminescent materials with anti-counterfeiting applications were prepared.1.MOFs materials 1-3 were synthesized under hydrothermal conditions,with H₄L as organic carboxylic acid ligands,bpb and 4,4′-bpy as nitrogen-containing ligands,and Zn as the central metal ion.Structural analysis showed that MOFs materials 1-3 were all three-dimensional network structures.Fluorescence sensing experiments showed that 1exhibited high selectivity and sensitivity to triethylamine（TEA）and tetracycline（TET）,2to nitrobenzene（NB）,and 3 to tetracycline.inally,the ultraviolet absorption spectrum of triethylamine,tetracycline,and nitrobenzene aqueous solution and the fluorescence emission spectrum of 1-3 were used to reveal the reason of fluorescence quenching combined with density functional theory.The reason for the quenching of triethylamine may be the fluorescence inner filter effect,and the reason for the quenching of tetracycline and nitrobenzene may be energy resonance transfer or electron transfer.2.MOFs materials 4 and 5 were synthesized under hydrothermal conditions,with H₄L as organic carboxylic acid ligands,bpb and 4,4′-bpy as nitrogen-containing ligands,and Cd as the central metal ion.Structural analysis showed that 4 was a three-dimensional network structure,and 5 was a two-dimensional planar structure.Fluorescence sensing experiments showed that 4 exhibited high selectivity and sensitivity to tetracycline and nitrobenzene,and 5 to roxithromycin（ROX）and B O.Then,the UV absorption spectra of aqueous solutions of tetracycline,nitrobenzene,roxithromycin,and B O and the emission spectra of 4 and 5 were used to analyze the reasons for fluorescence quenching combined with density functional theory.The reason for the quenching of fluorescence by tetracycline and nitrobenzene may be energy resonance transfer or electron transfer,and the reason for the quenching of fluorescence by roxithromycin and B O may be the fluorescence inner filter effect.Finally,Tb³⁺was encapsulated into 4,and the composite material was made into a fluorescent ink by using its special luminescent properties.This ink has great potential for anti-counterfeiting applications.3.MOFs material 6 was successfully synthesized under hydrothermal conditions with H₄L as the organic carboxylic acid ligand and Cd and Na as the central metal ions.Structural analysis shows that:6 is a three-dimensional network structure.Fluorescence sensing experiments showed that 6 exhibited high selectivity and sensitivity to cysteine,ornidazole and nitrobenzene.The reason of fluorescence quenching was analyzed by UV absorption spectrum of ornidazole and nitrobenzene solution,emission spectrum of 6 and density functional theory.The fluorescence quenching mechanism may be energy resonance transfer or electron transfer.Notable,the processed 6 can detect glucose with a low detection limit（3.5μM）.6 was soaked in glucose solution to form a MOF hydrogel（Glu@Cd Na-MOF）,and it was found that Glu@Cd Na-MOF exhibited high selective sensitivity to both metronidazole and tetracycline.Finally,Eu³⁺was encapsulated into 6,and the composite material was made into a fluorescent ink by using its special luminescent properties.This ink has great potential for anti-counterfeiting applications.