Study On Design,Synthesis And Adsorption Properties Regulation Of 3d Metal-organic Framework Based On Nitrogen Heterocyclic Carboxylic Acid Ligands

Metal-Organic frameworks(MOFs)or porous coordination polymers(PCPs)have excellent surface area and topological structure,good thermal stability and chemical stability.Therefore,it has broad application potential in gas storage,gas separation,enantio-selective separation,heterogeneous catalysis,chemical sensing and drug delivery.In order to obtain more functional MOF materials,designing and synthesizing MOF materials that meet the needs of human production and life is one of the goals that researchers are trying to achieve,so it is a challenging and popular synthesis and design in the field of new materials.In this paper,based on the nitrogen heterocyclic carboxylic acid ligands and 3d transition metals,the metal organic frameworks of different structure types were successfully constructed,and their structures,adsorption,iodine loading and post-modification control were explored.The full text is divided into four chapters:The first chapter is the research background related to the preface and the topic.It mainly introduces some methods of designing and synthesizing MOFs and the MOFs in some fields(gas adsorption storage separation,fluorescence sensing,photoelectric organic catalysis,magnetism,etc.).The application explains the significance of the topic and the detailed description of the progress of the topics involved.In the second chapter,through the pillar-type construction strategy,In solvent thermal conditions,a case of three-dimensional luminescent microporous MOF[Zn(trz)(BTDB)_0.5]·2DMF(1)was obtained by using rigid luminescent organic ligands 4,4'-(1,2,5-4,7-diyl)-two benzoic acid with triazole and d¹⁰metal Zn²⁺ions.This compound has a pore size of 1.D channel(5.99×5.99(?),B=5.12×5.12(?))in the c-axis direction and has a hole ratio of 42.7%.It was found by thermogravimetric analysis that the main frame could be stably maintained to 348°C,and powder diffraction of the aqueous solution immersed in the p H range of 3-12 gave good stability of the complex.The fluorescence drop in the 0.01 M Fe³⁺aqueous solution was 0.93%of the original fluorescence intensity(the luminous intensity was reduced from 408100 to 3790),and it was found that the compound can be used as a fluorescent detection material for detecting metal Fe³⁺in an aqueous solution.The saturated adsorption amount of nitrogen to nitrogen at 77K is 214.28 cm³g^-1,and the S_BETis 585.95 m²/g and S_Langmuiris 755.11 m²/g by 77 K-N₂isothermal adsorption-desorption curve fitting.The saturated adsorption capacity of carbon dioxide gas at 195 K is 257.91 cm³g^-1,and the S_BETobtained by isothermal adsorption-desorption curve fitting of 195 K-CO₂is 647.26 m²/g,and S_Langmuiris 829.51 m²/g.The vacant sample was immersed in a saturated iodine solution in cyclohexane for seven days,and it was confirmed by thermogravimetric heating release that 1 g of Compound 1 can carry 0.366 g of iodine,and the release form of iodine molecule in Compound 1 in methanol is mainly I^-.This chapter shows that pre-synthetic construction strategies are one of the effective ways to synthesize specific functional complexes.The third chapter describes the similarity of 2-hydroxymethyl-5-carboxybenzimidazole and2-hydroxyethyl-5-carboxybenzimidazole on the basis of the privious work of this group under the conditions of solvothermal synthesis.The ligands were mixed in three different compounds(compound 2=hydroxymethyl:hydroxyethyl=2:1,compound 3=hydroxymethyl:hydroxyethyl=1:1,compound 4=hydroxymethyl:hydroxy Ethyl=1:2.Powder Diffraction Characterization Analysis of ligand doping does not affect the bulk structure of MOF.The analysis of mass spectrometry,nuclear magnetic and other means shows that the compound compound contains different ligand ratios consistent with the feed ratio.The ratio of compounded crystals showed that the adsorption amount of compound 2 was the largest and the relative specific surface area was the largest.The saturated adsorption capacity of compounds 2,3 and 4 corresponding to N₂adsorption was 171.45 cm³g^-1,162.42 cm³g^-1,150.58 cm³g^-1,respectively.650.1 cm³g^-1,537.8 cm³g^-1,535.7 cm³g^-1,S_BETwere 603.0 cm³g^-1,571.9 cm³g^-1,499.3 cm³g^-1,respectively.The saturated adsorption capacity of compounds 2,3 and 4 for CO₂adsorption was 140.76 cm³g^-1,135.40 cm³g^-1,117.86 cm³g^-1,S_BETare 603.0 cm³g^-1,571.9 cm³g^-1,499.3 cm³g^-1,respectively.The loadings of iodine molecules of compounds 2,3 and 4 were0.502 mol,0.474 mol and 0.460 mol.The gas adsorption change after heat elimination reaction was investigated by using compound 3 as an example.The heat treatment was determined by thermogravimetry and DSC characterization.The temperature at which the reaction was eliminated was 285°C.It took 12 h after the reaction was followed by the fluorescence of the reaction conversion process.The powder diffraction tracking followed by time and the nuclear magnetic resonance analysis before and after the thermal elimination reaction showed post-modification.The front and rear frame structure is unchanged.Gas adsorption experiments showed that the N₂and CO₂saturated adsorbents of compound 3'were 85.9 cm³g^-1,81.31cm³g^-1,respectively.The comparison between the series of compounds highlights the interaction between the host and the guest,providing more possibilities for gas adsorption and separation.In the fourth chapter,based on the reaction of 4-(4-pyridyl)-benzoic acid ligand and Fe²⁺metal salt under solvothermal conditions,a kind of iron-based microporous column chain MOFs[Fe₂(pybz)₄]·8Me CN(5)with poor chemical stability was obtained.The compound 6 was got by compound 5,which was oxidized at 150°C for 4 h.The?_mT value of 6 at 300 K is 4.3071cm³mol^-1K,and the spin value of the high spin state of Fe²⁺ion is S=4/2,3.00 cm³mol^-1K higher than that of Fe³⁺ion.It was S=5/2,and 3.75 cm³mol^-1K was low,demonstrating that the iron ion moiety in compound 5 was oxidized.The Mossbauer spectroscopy analysis shows that the content of iron in different valence states after oxidation is about n(Fe²⁺):n(Fe³⁺)=1:2,using the characteristic peaks of 651 cm^-1and 755 cm^-1of Raman spectroscopy.Infrared spectra of 1188,559 and 536 cm^-1characteristic peaks showed that the counter ion after oxidation was O₂^2-,and the molecular formula of compound 6 was:Fe ^IIFe ₂^III(pybz)₆(O₂).Since the oxidation requires150°C,the single crystal structure can only play the role of auxiliary analysis.The single crystal result analysis shows that the compound maintains the same framework before and after oxidation(the coordination mode of the metal,the coordination mode of the ligand and the three-dimensional framework are consistent)However,the smallest unit is different,the diamond window size is reduced(12.4×12.4(?)²becomes 9.6×9.6(?)²),and the porosity is reduced from45.2%to 39.6%(the removal of the counter ion is smaller than when the solvent is removed).The strategy of PSM enhanced its stability while maintaining the integrity of the frame structure,and powder diffraction confirmed that the originally extremely unstable compound remained stable in air and water.Due to the increase of the valence state of the metal after oxidation and the presence of counter ions,the gas adsorption type changed.The saturated adsorption amount of nitrogen gas decreased from 210.51 cm³g^-1to 75.38 cm³g^-1,and the saturated carbon dioxide adsorption capacity decreased from 230.51 cm³g^-1to 106.74.cm³g^-1.It is further shown by the iodine loading property that although the pores become smaller after the oxidation,the iodine molecules can be supported,and the loading amount is 0.425 g of iodine molecules per gram of the compound 6,and the action of the framework on the iodine molecules becomes stronger after the oxidation.