Study On The Synthesis And Adsorption Properties Of Flexible Metal-Organic Framework

Metal-organic frameworks?MOFs?material,constructed by the combination of organic building units and metal nodes through coordination bonds,is a crystalline porous material,possessing the characteristics of structural designability,pore environment controllability,and molecular precision,and which makes it having underlying applications in gas storage and separation,energy storage and conversion,catalysis and other aspects.Flexible metal-organic framework is an important type among the MOFs family,which can respond to various physical and chemical stimuli,and has unique features that are not available in other solid materials we are familiar with.This stimulus makes the local molecular conformation and/or unit cell size and its symmetry changes in the microstructure.Meanwhile the dynamic behavior of the flexible MOFs in the macroscopic properties is controllable.So that it has prominent advantages in gas storage and separation and attracts widespread attentions.In this paper,three different flexible structures of MOFs were synthesized,and their dynamic structures and gas adsorption properties were studied respectively.The main results are as follows:?1?We successfully synthesized two new flexible MOFs?Mn-MOF-a and Mn-MOF-b?which have same chemical composition and different structures,via the solid-phase synthesis method and by kinetic vacuum activation using the supramolecular[Mn?INA?₂?H₂O?₄]at different temperatures.Then,we performed a series of structural characterizations of these two MOFs,and explored their behavior to absorb CO₂,CH₄,C₂H₄,C₂H₆,C₃H₆ and C₃H₈.We found that neither of these two MOFs adsorbed CH₄,step-like adsorption is founded for CO₂,C₂H₄,C₂H₆,C₃H₆,and C₃H₈.We further found that the molecular size of these gases are larger than the pore size of MOFs,so it can be determined that both of these MOFs are flexible.It is interesting to show that,to the adsorption amount of different gases,the Mn-MOF-b is two to three times compared with that of Mn-MOF-a.?2?Based on the previous research of the synthesis of ST-631 by the research group,we changed the type of metal salt and extended the reaction time,the results showed that size of the ST-631 crystal particles increased and the purpose of separating impurities were achieved,and we found a method to expand the scale of synthesis ST-631.In the process of solvent exchange for ST-631,it was found that after using DCM for solvent exchange,the diffraction peak of ST-631 changed through performing PXRD test.After the ST-631 was activated,we found that the activated samples were amorphous,and then tested the adsorption and desorption of different gases and steam for the activated ST-631,and then found the adsorption of water vapor is the highest.ST-631 has a high adsorption capacity for water vapor,so it maybe can be used to capture and release water.