Synthesis, Structure And Gas Adsorption Properties Of Metal-organic Frameworks Based On Linear Carboxylic Acid Ligands

During the past decades,metal-organic frameworks(MOFs)as new type of crystalline porous materials have been extensively researched for their structural diversities and potential applications in gas storage and separation,magnetism,luminescence and electrocatalysis.In particular the gas adsorption and separation properties of MOFs have attracted great attention due to the multiple binding sites,high porosities,outstanding specific surface area and diverse structural models.Gas separation is a critical industrial and energy intensive process for separating components of chemical mixtures in many fields.Particularly,due to high cost,inactivation of the catalysts,and similar gas mixtures are difficult to be well separated,although much progress has been made,the development of high-performance gas separation materials is highly desired to achieve high separation efficiency and low cost.For microporous inorganic materials(e.g.,carbon molecular sieves,zeolites,etc.),it is difficult to simultaneously realize high adsorption capacity and high selectivity,greatly restricting their separation efficiency.This requires us to find a new type of adsorption and separation material instead of microporous inorganic material.For the properties of MOFs,it was used as selective molecular sieves for gas separation by regulating the properties of pores.For example,the introduction of specific functional groups,decoration of organic ligands or tuning pore matrices are able to improve,optimize or diversify adsorption capacities and selectivity.Hence,the rational design of MOFs structures with predictable pore characteristics is highly critical for the functional realization of desired properties.However,employing a rational design strategy to construct porous MOFs with predictable structures for specific applications still remains one of the most challenging tasks.Altering the organic ligands is one of the most effective and easily strategies to change the topology of the three-dimensional porous frameworks.The effective approach to design the structure and function is using different organic ligands to change the size and shape of the pore systematically.In this paper,a series of MOFs with high performance were synthesis from the perspective of structure,and demonstrated MOFs as an emerging porous material.The following results were obtained:(1)A series of MOS-free MOFs[M₃(OH)]L(INA)₃](M=Co,Zn,Fe;L=TDC,FDC,EDOTDC)based on novel 8-connected trimeric SBU were synthesis by choosing the ligands and changing the bond angle of the ligands.Specifically,linear dicarboxylates,commonly observed in 9-connected trimers,are replaced by bent ones,which create a steric effect to squeeze out one of six regularly present-COOR groups around trimers,leading to an unusual trimer configuration with five-COOR groups and three pyridyl group.We have also shown the feasibility of modulating adsorption properties by regulating the pore features using ligands of different bending angles and steric hindrance.Based on this particular structural model,compounds exhibit excellent C₂H₆storage capacities as well as high ethane-selective C₂H₆/CH₄separation selectivities at room temperature.The synthetic strategy may facilitate new research on the pore design of new highly-connected trimer-based MOFs for high ethane adsorption and separation of ethane toward ethylene.These properties enable them as promising candidates for light hydrocarbon storage and purifications.(2)By liquid phase synthesis,a piddle-layer Co-MOF was synthesized based on sole bifunctional organic ligand 1-H-indazole-5-carboxylic acid(IDCA).The adsorption performance,pore structure and the crystal structure were studied.By the analysis of the adsorption performance,it was proved that it has a good adsorption performance for CO₂and C2 hydrocarbon gas.Furthermore,through of CO₂/CH₄separation ratio of 17.94(298 K)by IAST simulation calculation which is higher than many compounds.The structurally activity relationship was deeply discussed,to explore its potential application in gas separation field.(3)By liquid phase synthesis,a piddle-layer Zn-MOF was synthesized based on a bifunctional organic ligand which have fluorescence characteristics and adsorption activity.Through the analysis of the pore size of crystal structure,this structure has well gas adsorption properties.In addition,the compound has excellent fluorescence properties,under the excitation of UV light,compound showed bright bluish light.Through the aqueous solution of different ion detection,this compound not only show the excellent water stability,and show the specificity of Fe³⁺ion recognition.It provides a simple way for pore control and the application of MOFs in fluorescence sensors.