Syntheses,Structures And Gas Separation Properties Of MOFs With Mixed Pyrazole And Carboxylic Acid Ligands

Metal organic framework(MOFs)materials,also known as porous coordination polymers(PCPs),are a new class of organic-inorganic hybrid solid porous materials.The reticular chemistry of MOFs means that the structural and functional diversity of MOFs can be reasonably regulated by selecting different component modules(inorganic nodes and/or organic ligands).Among them,pyrazol-based MOFs are considered as a very potential porous material.The strong metal-N coordination bonds as well as the stable bidentate coordination of pyrazol ligands after deprotonation will lead to stable and diversified framework structures with interesting physical and chemical properties.These materials can be used in many applications including gas adsorption,fluorescence and catalytic studies.However,it has been found the deprotonation of pyrazol ligands is difficult to be achieved in many cases,leading to the formation of coordination compounds with low-dimensional structures rather than 3D MOF frameworks.This thesis proposes the mixed-ligands strategy to design and synthesize a series of stable pyrazolyl-based MOFs containing carboxylic acid ligands,in the consideration of the strong metal-carboxylic acid interactions and the unique coordination mode of metal-pyrazole.As a result,several new crystalline pyrazol-based MOFs materials were obtained by using rigid 2,7-bis,3,5-dimethypyrazol-1,4,5,8-naphthalene tetracylic anhydride(H₂NDI)and different carboxylic acid ligands(H₂NDC,DOBDC,H₂BDC).Their application in gas adsorption and separation properties were also investigated in detail.Firstly,a novel pyrazole-based Co-MOF material FJU-115 with paddle-wheel clusterd as nodes was synthesized by the hydrothermal reaction of cobalt nitrate and mixed ligands H₂NDI and H₂NDC,which is structurally characterized by a double-interpenetrated frameworks.Interestingly,the significant difference observed in the powder X-ray diffraction patterns of samples before and after activation of FJU-115suggested the formation of a new compound FJU-116,which has been further confirmed by the single-crystal X-ray diffraction.In addition,according to the adsorption data of single component gas,FJU-116 showed relatively high adsorption volumes of C₂H₂,which were 80.67 cm³ g^-1(273 K and 1 bar)and 46.59 cm³ g^-1(296K and 1 bar),respectively.The mixed gas dynamic column separation experiment showed that FJU-116 has a high separation performance for C₂H₂/CH₄ mixed gas(15.5).Secondly,a novel pyrazol-based Zn-MOF material FJU-117 was designed and synthesized by using mixed ligand H₂NDI and DOBDC.Interestingly,FJU-117 with mononuclear zinc node showed a highly thermal stability up to 375 ? due to the[2+2]quadruple interpenetrated frameworks.According to the one-component gas adsorption test,FJU-117a has a high adsorption capacity of CO₂,which is 74.89 cm³ g^-1(296 K and 1 bar)and 97.23 cm³ g^-1(273 K and 1 bar),respectively.Through the mixed gas dynamic column separation experiment,it is proved that FJU-117a shows an effective separation effect for CO₂/N₂ mixed gas.Finally,a novel pyrazole-based Zn-MOF FJU-59 with double-interpenetrated frameworks was designed and synthesized by using the mixed ligands H₂NDI and H₂BDC,which showed a highly thermal stability up to 420 ?.The maximum adsorption capacity of FJU-59a to C₂H₂ and CO₂ is 68 cm³ g^-1(C₂H₂)and 51.6 cm³ g^-1(CO₂)at 296 K and 1 bar,respectively.The calculation of ideal solution adsorption theory(IAST)showed that FJU-59a is a potential porous material for the separation of C₂H₂/CO₂ mixed gas,which has been verified by the mixed gas dynamic column separation test.It showed that FJU-59a has a higher separation effect on C₂H₂/CO₂mixed gas(4.6).