Synthesis Of Novel Metal-Organic Framworks Meterials Constructed From Nitrogen-Containing Heterocycles Ligand And Their Fluorescence Sensing And Photocatalytic Degradation Properties

Metal-organic Frameworks（MOFs）is a kind of periodic structure of coordination compounds assembled by Organic ligands and Metal ions or clusters through coordination bonds.The structural diversity,modifiable sites,uniform pores,and large specific surface area of MOFs make them rapidly developed in environmental pollutant detection,catalysis,gas adsorption and separation,etc.In this paper,a series of new complexes were synthesized by nitrogen-containing ligands and transition metals,and their applications in fluorescence sensing and photocatalytic degradation were studied.The research of this paper are as follows:A novel MOF material with excellent luminescent properties was constructed by solvothermal method using dicarboxylic acid ligand 5-（benzimidazole-1-yl）isophthalic acid containing benzimidazolium group and zinc ions.Subsequently,Cu（II）ions were successfully doped into Zn-MOF in a simple and feasible way,which improved the water stability and increased the Stokes displacement of the material.This strategy enables LMOFs（Luminescent metal–organic frameworks）,which were initially limited by water stability,to implement detection in aqueous solvents.Considering the water stability,fluorescence properties and Stokes displacement of materials,Cu_0.1/Zn-MOF was selected as fluorescence sensor to detect Fe³⁺,NFT,NFZ,FZD and TC in aqueous solution.The results show that Cu_0.1/Zn-MOF has high sensitivity,fast response,high selectivity and good circulation.The mechanism of fluorescence quenching was investigated,and it was found that cationic detection,excited light competitive absorption and energy resonance transfer（FRET）were the main fluorescence quenching mechanisms.For antibiotic detection,excited light competitive absorption,energy resonance transfer（FRET）and electron transfer（PET）were the main fluorescence quenching mechanisms.The subsequent experiments also found that compared with the original Zn-MOF,the doping of Cu（II）ions enhanced the detection sensitivity of Fe³⁺,NFT,NFZ,FZD and TC.Using the large conjugated ligands N,N-Di-（3-pyridyl）-1,4,5,8-naphthalene diimide（3-DPNDI）and Cu Cl₂ metal salts,three Cu-based MOFs（complexes 1–3）with one-dimensional（1D）,two-dimensional（2D）and three-dimensional（3D）structures were successfully prepared by introducing different uncoordinated ligands and adjusting the ligand:metal salt ratio.The results showed that 1D Cu-MOF had good Fenton-like catalytic activity,and the degradation efficiency of methylene blue（MB）was significantly higher than that of 2D and 3D Cu-MOF.The formation of J-type aggregation in 1 may be related to the linear coordination mode of Cu₂Cl₂ cluster.Compared with the hexagonal coordination pattern of the binuclear cluster in complex 2 and the cubic tetragonal coordination pattern of complex 3,the linear coordination pattern of the Cu₂Cl₂ cluster in complex 1 is more favorable for binding with the linear ligand into linear 1D structure.This 1D linear structure facilitates the formation of orderedπ-πstacking of large conjugated ligands.Underπ-πinteraction,1D chains are parallel-stacked by dislocation to form J-type aggregated 2D supramolecular layers.The ordered and energy-saving J-type aggregation conformation changes the interactions between molecules,reduces the band gap and expands the visible light absorption edge.It can also provide a fast channel for electron transport and effectively improve the utilization rate of photogenerated carrier.In addition,the Fenton-like reaction of complex 1 has a wider p H adaptability than the traditional Fenton reaction,and it also shows good mass transfer,recyclability and universality in the photocatalytic process.