Syntheses,Structures And Properties Of Metal-Organic Frameworks Constructed By Tetrachloroterephthalic Or 4,4',4''-Nitrilotribenzoic Ligands

In recent years,with the social progress and the development of science and technology,the importance of gas is increasing both in industry and daily life.Therefore,the filed of storage and separation of gas is attracted by more and more researchers.The metal-organic framework(MOF)with novel structure and excellent performance has shown great potentials in gas adsorption and separation.Mixed gases can be separated by adjusting the pore size of MOF,or by introducing suitable functional groups to strengthen the interaction between MOF and gas.Thus the gas separation can be achieved by virtue of the unique pore structure of MOFs and distinct interaction between the gases and MOFs.In this thesis,tetrachloroterephthalic acid(abbreviated as H₂TCBDC)and 4,4',4''-nitrilotribenzoic acid(abbreviated as H₃NTB)were selected as organic ligands to construct MOF.The carboxylic oxygen of tetrachloroterephthalic ligand can coordinate with metal ions to form the main framework of MOF,while chlorine atoms can be served as functional groups in the pores of MOF and regulate the interactions between MOF and guest gas molecules.The presence of the chlorine atoms in the organic ligand also enhance the stability of MOFs.4,4',4''-nitrilotribenzoic ligand with flexible skeleton and various configurations enable the 4,4',4''-nitrilotribenzoic ligand with different configurations in different enviroments,resulting in MOFs with diverse structures.Here,eight MOFs were synthesized based on the these ligands and transition metal ions(zinc ions and cobalt ions).Firstly,five MOFs based on the tetrachloroterephthalic ligand and zinc ions are deascibed.In compound 1,zinc ions are bridged by 1,2,4-triazole ligands to form one-dimensional(1D)chains,which are further connected by tetrachlorotetracarboxylic ligands to form a three-dimensional(3D)structure with 1D square channels.Subsequently,the pore structure of compound 1 was characterized in detail.At 298 K,the adosption selectivity of compound 1 is 3.59 for acetylene/carbon dioxide mixture with a molar ratio of 50/50,and 6.18 for propyne/propylene mixture with a molar ratio of 1/99,and 4.66 for xenon/krypton mixture with a molar ratio of 20/80.Therefore,compound 1 shows good separation performance for these mixtures.The pore channles of compound 1 are filled with chlorine atoms.Since the hydrogen atoms of acetylene and propyne are the acidic hydrogen atoms.Therefore,acetylene and propyne gases can form hydrogen bonds with the chlorine atoms,leading to compound 1 adsorb acetylene or propyne gases selectively.Thus the separation of acetylene/carbon dioxide and propyne/propylene mixtures are achieved with compound 1.In addition,chlorine atom is easy to polarize,while xenon with large radius is a more polarizable atom.The strong electrostatic interaction can be formed due to the dipole interaction between chlorine atoms and xenon gases.Therefore,compound 1 has a good separation perfromance for xenon/krypton mixture.Compound 2 was obtained by replacing 1,2,4-triazole ligand with 3-amino-1,2,4-triazole.In compound 2,the zinc ion is bridged by 3-amino-1,2,4-triazole ligand to form a 1D chain,which is bridged by tetrachloroterephthalic ligands to form a 3D structure.The 3D structure is negatively charged and has 1D triangular channels and1D hexagonal channels.The counterions for the 3D structure is the zinc hexahydrate cations filled in the triangular channels.Compound 3 is constructed from zinc ions and tetrazole and tetrachloroterephthalic ligands.In compound 3,zinc ions were bridged by tetrazole ligands to form a 1D chain,which s bridged by tetrachloroterephthalic ligands to form a 3D structure,which was similar to that of compound 1.The gas adsorption of these two compounds was tested,but the test results are not good,which may be caused by the shrinkage of the pores resulted from the deformation of the 3D framework during the activated processes.Compounds 4 and 5 were synthesized by reaction of the tetrachloroterephthalic acid and triethylenediamine with zinc ion.In compound 4,each binuclear[Zn₂(COO)₄]unit is connected by two triethylenediamine ligands to form a 1D chain.Each 1D chain is bridged with four adjacent 1D chains through the tetrachloroterephthalic ligands to form a 3D structure with square channels.At 298 K and 1atm,the xenon adsorption uptake of compound 4 is 5.09 mmol/g.Compound 4 can maintain a good xenon adsorption performance after five cycles of adsorption.For compound 4,the adosption selectivity for the xenon/krypton mixture with a molar ratio of 20/80 is 9.39.The adsorption capacity of xenon and the separation coefficient of xenon/krypton for compound 4 are outperform the reported MOF materials.The binuclear[Zn₂(COO)₃]unit in compound 5 is different from the binuclear[Zn₂(COO)₄]unit in compound 4.The binuclear[Zn₂(COO)₃]units linked by the triethylenediamine and tetrachloroterephthalic ligands in compound 5 to forms a two-dimensional layered structure.The later part of this thesis describes three MOFs constructed by 4,4',4''-nitrilotribenzoic ligands and zinc ions and cobalt ions.In compound 6,two Co₈(?₃-OH)₄ clusters are bridged by four NTB^3-ligands,forming a caged structure with a diameter of about 10×6.3(?)².Adjacent cages share Co₈(?₃-OH)₄ clusters,forming a 1D columnar secondary structural unit(SBU).Each 1D columnar SBU connects four adjacent 1D columnar SBU through NTB^3-ligands to form a 3D framework.Compound6 has a large adsorption capacity for ethane at 298 K and 1 atm.After ten cycles of cyclic adsorption,it can still maintain good ethane adsorption performance,indicating it can be used as a good ethane storage material.The adsorption selectivity of equimolar ethane and ethylene at 1 atm is 1.7.Compound 6 has high ethane adsorption capacity,relatively low adsorption heat and moderate adsorption selectivity.Thus it is one of the excellent materials for separating ethane/ethylene mixture.The separation mechanism is the multiple interactions between ethane and pore wall mainly composed of benzene rings.In compound 7,each trinuclear[Zn₃(COO)₆]secondary building unit is connected by six NTB^3-ligands and two formic ligands to form a 3D structure,in which there are1D channels.In compound 8,each zinc ion is bridged by four NTB^3-ligands to form a3D structure.Two 3D structures are interpenetrated with each other to form a 2-folded interpenetrated 3D structure.The yield of compound 7 is extremely low,and the pore volume of compound 8 is too small,so the gas adsorption properties of these two compounds is not performed.