Design And Synthesis Of Two-dimensional Metal-organic Framework Nanomaterials And Their Applications In Fluorescence/Electrochemical Sensing

Metal-organic frameworks（MOFs）are self-assembled porous crystalline materials composed of metal ions and organic ligands.MOFs have become a hot research material due to their high surface area,pore size and tunable chemical function.Two-dimensional MOFs have the porous network structure of MOFs materials combined with the advantages of large specific surface area of two-dimensional materials,and thus show outstanding advantages in sensing and other aspects.1.Three kinds of fluorescent MOF₁-MOF₃ were designed and synthesized from three kinds of linear polyconjugated nitrogen-containing ligands（2,5-2CH₃-bpeb、Bpht、CH₃-bpeb）,metal ions Zn²⁺and two kinds of“V”carboxylic acids.MOF₁and MOF₂are layered structures,and the layers are stacked by weak interaction.The external mechanical force can break the weak interaction between the layers and exfoliate the bulk MOF₁ and MOF₂ into two-dimensional nanosheets（thickness is4.14 nm and 1.27 nm,respectively）.The nanosheet shows stronger photoluminescence performance,specifically detects folic acid（FA）,and has a detection limit as low as 0.11μM,and higher sensitivity than a traditional folic acid detection material.2.A novel strippable layered structure MOF₄ with larger pores and stronger intra-layer rigidity was synthesized from“V”type tri-nitrogen ligand,metal ion Cd²⁺and p-Fluorobenzoic acid.Single crystal X-ray diffraction analysis reveals that MOF₄ is bridged by the“V”ligands Bpvb,Cd²⁺and p-Fluorobenzoic acid to form a hexagonal window with the size of 35.96（?）×24.36（?）,much larger than MOF₁（19.94（?）×14.18（?））and MOF₂（13.48（?）×18.12（?））.Its larger pores can increase the diffusion rate of macromolecular analytes,thereby improving the detection sensitivity of the sensor.The fluorescence spectrum study shows that MOF₄ can be used as a high sensitive multi-response fluorescence sensor for multiple sensing of FA,Fe³⁺and nitrobenzene,with detection limit of 0.03μM,1.18μM and 0.62μM,respectively.3.Anthraquinone-based ligands with redox activity were selected to self-assemble with metal Zn²⁺to form exfoliated layered structure MOF₅.The electrochemical sensor MOF₅/GCE based on MOF₅ nanosheets was constructed and used to detect L-Cys,with good electrochemical performance.MOF₅/GCE has a wide linear range in the range of 1-150μM,the detection limit of 1.91μM,high sensitivity and selectivity.Due to high surface tension of the anthraquinone group gives the anthraquinone-based two-dimensional MOF₅ has better hydrophilicity.The two-dimensional material can be used for detection of body fluids or other biological samples.In addition,after the interaction between the anthraquinone-based MOF₅and the analyte forms hydrogen bonds,the electron cloud density of the anthraquinone increases,so it is easier to conduct electron transfer with hydrogen ions in the solution,thereby generating a strong current signal.