| The solvothermal reaction of linear nitrogen-containing heterocyclic ligands and organic carboxylic acid ligands with transition metal ions was studied to prepare new metal-organic frameworks and analyze their crystal structures.By adjusting the number and position of nitrogen atoms of nitrogen heterocyclic ligands,the type of carboxylic acid ligands,the type of metal salt,solvent and reaction temperature,the self-assembly can control the structure,dimension,pore shape and size of metal organic frameworks.MOFs with novel structures were prepared.Through infrared spectroscopy,ultraviolet-visible absorption spectroscopy,thermogravimetric analysis,powder X-ray diffraction,magnetic susceptibility of variable temperature,fluorescence spectrum analyzed the obtained MOFs materials,focusing on the potential applications of these MOFs materials in the fields of dye adsorption and fluorescence sensing,and further studied the selective response of MOFs to organic dyes and nitro-containing explosives with their structure and coordination modes.The fluorescence quenching mechanism caused by the interaction of these small organic molecules with MOFs and the corresponding dye adsorption mechanism of MOFs were discussed.Specific research work:1.Based on 2,5-bis(1-imidazolium)pyridine(2,5-bipi)as the main ligand,with 5-hydroxym-phthalic acid(5-hip),m-phthalic acid(1,3-bdc)and V-type aromatic carboxylic acid ligand 4,4'-diphenyl ether dicarboxylic acid(H2oba)as the auxiliary ligand,Four new metal-organic frameworks[Cd(2,5-bipi)(5-hip)]n(1),[Mn(2,5-bipi)(1,3-bdc)]n(2),[Co(2,5-bipi)(1,3-bdc)(DMF)]n(3),[Cd(2,5-bipi)(oba)]n(4)were successfully constructed with transition metal ions Cd(II),Mn(II),Co(II).The solid-state photoluminescence properties of MOFs 1 and 3 were investigated,and the results indicated that MOFs 1 and 3 had potential applications in this regard.In addition,the dye adsorption properties of MOFs 1 and 3 were also explored.Six organic dye molecules of different sizes and charges were selected as the adsorption objects,and MOFs 1 and 3showed remarkable selective separation of Congo red(CR)dye according to the observation with naked eyes and the measurement results of UV-Vis spectrum.The total adsorption of CR on MOFs 1 and 3 was calculated to be43.02 and 44.75 mg/g,respectively.Magnetic studies were carried out on MOF 3,showing the transfer of antiferromagnetic interactions between metal ions.2.Based on 2,5-bis(1-imidazolium)pyrazine(2,5-bipa)as the main ligand,with succinic acid(H2suc)and 5-hydroxyphthalic acid(5-hip)as the auxiliary ligand,Three new metal-organic frameworks[Zn(2,5-bipa)(suc)]n(5),[Ni(2,5-bipa)(suc)(H2O)2]n(6),[Co(2,5-bipa)1.5(5-hip)(H2O)]n(7)were successfully constructed with transition metal ions Zn(II),Ni(II)and Co(II).Analyzing the crystal structure,MOFs 5 and 7 are both 3D structures.MOF6 firstly forms a 2D layered structure through ligand connection,and then accumulates into a 3D supramolecular structure through hydrogen bonding(O2-H3B...O3)between layers.Both ligands and MOF 5 were tested for fluorescence,and it was found that MOF 5 is a fluorescent sensing material with excellent performance(quantitative,high sensitivity,low detection limit,and good selectivity).It has been found that it has a unique recognition effect on Fe3+,Cu2+ions and 2-NT.3.A novel metal-organic framework was successfully constructed based on 1,4-bis(1-imidazole)benzene(1,4-bib)as the main ligand and5-aminoisophthalic acid(5-aip)as the auxiliary ligand[Co(1,4-bib)(5-aip)(DMF)]n(8).MOF 8 is a 2D structure,the asymmetric unit generates an infinite 1D chain along the a axis,and the bib ligands connect the 1D to form a 2D layered structure.Adjacent 2D layers are stacked into a 3D supramolecular network through hydrogen bonding(N5-H5A...O1).Magnetic studies were carried out on MOF 8,and the antiferromagnetic interaction between the metal ions of MOF 8 was carried out. |
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