Simulation Study On Gas Adsorption And Separation Performance Of Covalent Organic Framework Materials

Covalent Organic Frameworks（COFs）are composed of light elements through covalent bonds and have the characteristics of low density,high specific surface area,good stability,and easy regulation of structure and pore size.agent,has been used in the field of adsorption.In this thesis,the method of computational simulation is used to study the adsorption and separation of COFs in different gas systems,and by establishing the material structure-activity relationship,exploring the mechanism,and modifying the properties of the material,in order to play a role in the later screening and rational design of COFs.guiding role.The main work is as follows:1.Create data with 470 COF materials and investigate their separation performance for HCHO/N₂+O₂under vacuum adsorption（VSA）conditions.By establishing a structure-activity relationship,it can be found that when COF materials have moderate structural characteristics（such as maximum cavity diameter,accessible specific surface area,pore volume,and porosity）,their selectivity to HCHO/N₂+O₂is strong.At the same time,it was also found that in the 2D-COF of hcb topology type,its adsorption capacity for HCHO was excellent,far exceeding that of activated carbon,zeolite and some MOFs.After screening,it is determined that COF-LZU8 is the best separation material,and its microscopic adsorption and separation mechanism is explored.It can be found that there are two pore sizes of different sizes in the pores of the material,and there are multiple strong interaction sites in the small pore size,so high performance for HCHO/N₂+O₂separation can be achieved.By introducing functional groups to chemically modify COF-LZU8,it is obvious that the introduction of polar groups-OH can significantly improve the separation performance of the material,which provides a guiding direction for the design of functional materials in the future.2.Based on the established database,the adsorption and separation performance of clean flue gas（CO₂/N₂）under VSA conditions was explored.By establishing the structure-activity relationship,it was found that the structural characteristics of COF materials play an important role in the gas adsorption separation,because the adsorbate-adsorbent force is stronger than the large pore environment in a suitable material structure.Most COFs have good selectivity for cleaning flue gas,and the 2D-COFs with the top ten hcb topology types in the adsorption capacity have moderate pore environment and pore interlayer spacing,which makes them have the"sieving effect"of molecular sieves.CO₂has good selectivity and adsorption capacity.After screening,the best material was obtained:Si COF-Li,and the microscopic mechanism of separation performance was explored.It was found that the material has a counter cation Li+in the framework,and has a strong Coulomb electrostatic force with CO₂molecules whose quadrupole moment is greater than N₂.At the same time,after functional modification,it was found that the introduction of-F group can effectively improve the separation performance of the material,which is due to the Lewis acid-base interaction between F and CO₂and the synergy with other forces.3.The adsorption capacity of the single component gases NO and NO₂in the NO_xsystem is simulated by computational chemistry.The maximum cavity diameter,the accessible specific surface area and the pore volume can be known from the structure-activity relationship between the adsorption capacity and the structural characteristics.The impact of quantity is profound.However,COF-367-Co with larger structural features has a higher adsorption capacity,which is due to its suitable pore interlayer spacing and the Co sites on the porphyrin ring,which generate strong NO_xsystem gases.of the force.The structure analysis of the top ten COFs in adsorption capacity shows that the COFs of the dia topology type 3D-NPN series have excellent adsorption capacity for NO_x,which is caused by the moderate structural environment and interspersed structure of the series.