Adsorptive Separation Of Gas With Anion Functional Ultramicroporous Materials By Responsive Recognition Mechanism

The separation of hydrocarbon or electronic gas mixtures is critical to the efficient utilization of high-purity chemicals,however,the process is always energy-intensive due to the complex components with similar properties.The current adsorption mechanisms based on the molecular difference along with the only one dimension fails to afford the separation with high capacity,high selectivity and easy regeneration,and novel separation mechanisms and efficient adsorbents are urgently needed.The article revealed the systematic study on the control of flexible framework and responsive molecular recognition mechanism of anion functional ultramicroprous materials based on its fine-tuning pore structure as well as the anion functional sites.Benefiting from the comprehensive understand about the molecular difference,the designed materials with tailor-made pore size and pore chemistry achieve the efficient separation of mixtures,like electronic gas,cracking gas and hydrocarbon isomers.The main contents are as follows:The deep insight into the control of flexible framework and the responsive molecular recognition is fundamental to the design of highly-efficient flexible materials.The systematic study is conducted to understand the modulation of the flexible structure and the molecule-based responsive behavior.The DFT-D calculation is used to demonstrate the influence of self-assembled building blocks on the flexibility of the frameworks,and the specific molecule diffusion behavior is well elucidated,revealing responsive molecular recognition separation mechanism based on the flexible framework.The rotation behavior of the building blocks has effect on the energy change of the whole system,and the modulation of the structure of the building blocks enables the accurate control of expressed structural flexibility of porous materials.The flexible behavior induced by the guest molecules is adaptive to the properties and size of molecules,which enabling the selective molecules recognition.The study provides the deep insight into the control of the structural flexibility,also the ideas for the design of responsive materials.Three different anion functional ultramicroporous materials ZrFSIX-2-Cu-i(ZU42),NbOFFIVE-2-Cu-i(ZU-62)and ZrFSIX-2-Zn-i(ZU-66)are designed towards the separation of Xe and Kr.The results of adsorption isotherms and the breakthrough experiments on the above three materials reveal that NbOFFIVE-2-Cu-i with suitable pore size and pore chemistry exhibits high Xe/Kr separation selectivity(43.29)and Kr productivity(206 mL g-1,>99.9%).The impressive Xe/Kr separation performance of NbOFFIVE-2-Cu-i is attributed to the "inverse size-sieving" effect,and the detailed separation mechanism is revealed by the single crystal X-ray diffraction and DFT-D calculations.In detail,though the larger molecular size of Xe than Kr,Xe with higher polarizability is easy to induce the deformation of the pore structure,which makes it easier to be adsorbed;In contrast,Kr is excluded due to the low affinity with the pore window,realizing the "inverse size-sieving" effect of smaller-size molecules.The one-step removal of trace alkyne and propadiene from cracking gas is regarded as the great challenge in chemical separations.Here,a multi-functional molecular separator GeFSIX-14-Cu-i(ZU-33)that is dual-response to both guest molecules and temperature stimuli is developed.Its efficient separation performance is well demonstrated by both the single-component adsorption isotherms as well as the dynamic breakthrough experiments.In addition,based on the single crystal X-ray diffraction and simulation studies,the microscopic adsorption behavior of alkynes and propadiene within the framework is revealed and the potential adaptive structural deformation mechanisms are demonstrated.The simulation studies clarify that the selective trace alkyne and propadiene capture ability from cracking gas of GeFSIX-14Cu-i is attributed to the different responsive behavior,such as the polar alkyne and propadiene are easy to be adsorbed due to the low energy barrier.Meanwhile,the intrinsic adaptive structural deformation enables the high binding affinity of the porous materials towards all acetylene,propyne and propadiene.Based on the molecular size and shape difference between the C6 alkane isomers,the anion functional ultramicroporous material SnFSIX-2-Cu-i(ZU-72)with suitable pore size and zigzag distributed functional sites is designed to solve the current dilemma of low selectivity and high energy consumption.The separation performance and regeneration ability of C6 alkane isomers are systematically measured,In addition,the internal thermal management process is revealed by the single-crystal X-ray diffraction and simulation studies,and the critical role in determining the regeneration ability of porous materials is elucidated.SnFSIX-2-Cu-i achieves the exclusion to the di-branched alkanes,as well as the benchmark mono-/di-branched alkanes separation selectivity(6.97).Meanwhile,the thermal management of the framework and the functional sites with appropriate strength enable the moderate regeneration of adsorbents.Moreover,SIFSIX-1-Cu and NbOFFIVE-bpy-Ni(ZU-61)with modulated building blocks realizes the efficient separation of 2,3-dimethylbutane and 2,2dimethylbutane,and gasoline with RON of 105 is obtained.The studies also find that the above porous materials also exhibit great performance for C5 and C7 alkane isomers separation.In summary,the rational control pore structure and pore chemistry of the targeted porous materials based on the comprehensive recognition of specific molecular difference show superiority in dealing with the complex systems.The efficient separation performance is attributed to the unique responsive behavior of the flexible framework,and the ideal also provides guidance towards the design of efficient adsorbents and the novel separation strategies.