Dynamic Metal-Organic Frameworks For Adsorptive Gas Separation

Dynamic metal-organic frameworks?MOFs?can selectively respond to various physical or chemical stimuli,leading to the structural transformation,which does not exist for other known solid-state materials.Such smart materials have important research value and application prospects in gas storage,adsorptive separation,molecular recognition,heterogeneous catalysis,chemical sensing and drug loading.Although a few studies have shown that dynamic MOFs can perform well in gas storage and separation,however,there are still some problems such as that structure design needs to be strengthened and solve the degradation of gas separation performance caused by the co-adsorption of mixed gases due to structural changes.In this paper,six ZIFs with GME topology:Zn?nim??bim?,Zn?nim??nbim?,Zn?nim??mbim?,Co?nim??bim?,Co?nim??nbim?and Co?nim??mbim?,as well as an ionic MOF:Me₂NH₂[In?atp?₂]were chosen for further research.It shows that the introduction of guest molecules induces dynamic structural changes.The mechanism of structural change and the gas separation performance of activated samples were deeply studied.The main results of the research are as follows:?1?Co?nim??nbim?and Co?nim??mbim?were firstly made by solvothermal synthesis,and four other GME-ZIFs with the same topology were investigated together.The effect of metals?Zn or Co?,functional groups and solvent molecules?N,N-dimethylformamide or ethanol?on the structural dynamic behavior of GME-ZIF and the resulting changes in adsorption behavior were further studied.In addition,the effects of metals,functional groups and pore volume on the actual CO₂/CH₄ separation performance were explored by analyzing the fixed-bed gas breakthrough measurement.?2?Three isomers with identical chemical composition but different structures were successfully obtained by activating an ionic MOF:Me₂NH₂[In?atp?₂]after exchanging with three different solvents:N,N-dimethylformamide,methanol and isopropanol.It is found that the reason of isomerism is the allocation of counter ions in the pore.The activated samples were tested for fixed-bed gas breakthrough measurement.It was proved that during the separation of C₃H₈/CH₄ and C₂H₆/CH₄,the high energy barrier is beneficial to the stability of the structure during the adsorption process,leading to optimized gas separation performance without co-adsorption,efficient purification of methane was successfully achieved.In this work,we have implemented Me₂NH₂[In?atp?₂]to add a new dimension in the energy landscape for gas separation performance.In this paper,the roles of solvents and activation methods in dynamic control of MOFs and the effects of their flexibility on gas separation were discussed.All the samples chosen have the ability to effectively separate gases,finding a new direction for design control of dynamic MOFs and the development of more efficient adsorbents in future.