Molecular Simulation Of Porous Organic Framework Materials For Gas Adsorption And Separation

Adsorption separation technology is widely used in chemical,petroleum,environmental protection,and other fields due to its advantages of low cost,simple operation,and low energy consumption.The efficiency of adsorption and separation largely depends on the choice of adsorbent.Metal organic frameworks（MOFs）and covalent organic frameworks（COFs）,as new porous organic framework materials,have the advantages of large specific surface area,high porosity,low density,adjustable structure,and easy functionalization,which have been widely used in gas adsorption and separation.However,due to the diverse and large quantities of MOFs and COFs materials,it is not easy to find materials that have significant adsorption and separation effects on specific gases only through experimental means,and it is also difficult to systematically study the relationship between the structure and performance of materials.With the development of computer technology,computational chemistry can not only efficiently simulate the adsorption and separation behavior of gases in MOFs and COFs,quickly screen out porous organic framework materials,but also effectively explore their adsorption and separation mechanisms,to provide theoretical guidance for experimental researches.Based on this,a series of studies on materials in Zr-MOFs and COFs databases were carried out in this paper by using a multi-scale simulation method combining grand canonical Monte Carlo simulation method（GCMC）and density functional theory（DFT）.The main research contents are as follows:（1）The high-throughput computational screening method was used to study the adsorption and separation performance of 163 zirconium-based metal-organic frameworks in the Zr-MOFs database at room temperature and pressure for Rn/N₂and Rn/O₂mixed gases.The research results showed that the material exhibited better adsorption and separation ability,when the pore sizes of materials are between 5.6 and 8（?）（1（?）=0.1 nm）and the accessible surface areas are between 140 and 870 m²/g.Meanwhile,the introduction of strong polar functional groups such as carboxyl group（-COOH）and sulfonic group （-SO₃H）is beneficial to enhance the adsorption and separation ability of the material for Rn.These results can provide some theoretical guidance for the future design and synthesis of MOFs for Rn adsorption and separation.（2）The high-throughput computational screening method was used to systematically study the adsorption and separation performance of the Co RE COFs database containing 382 COFs structures for CH₄-CO₂-H₂S（0.70/0.298/0.002）mixed gas at 303 K,1 bar（0.1 bar）.The structural performance analysis shows that COFs with pore size of about 12.5（?）and porosity of about 0.65 are more suitable for simultaneous desulfurization and decarburization from dry biogas.By using adsorbent performance factor（APS）and the adsorbent selectivity parameter(S_sp)as evaluation metrics,the material Si COF-Li with the best adsorption and separation performance was identified.In addition,through the modification of 16 different functional groups and further analysis of the adsorption mechanisms,the results show that the existence of-F functional group and counter-ions is conducive to the adsorption of H₂S and CO₂.The results can provide theoretical guidance for the design and synthesis of novel COFs materials for acid gas adsorption and separation.（3）The ability of 435 COFs to adsorb and separate O₂/N₂（0.2/0.8）in air at room temperature was investigated by high-throughput computational screening.The ideal structural parameters of COFs material with O₂selectivity were determined by establishing the relationship of structural properties.At the same time,taking regenerability as an evaluation index,most of the materials have regenerability greater than 90%,and could be recycled.Using ILs to improve the pore environment of COFs is an effective way to improve the performance of COFs materials.Based on the configuration-dependent Monte Carlo method（CBMC）,different ionic liquids（ILs）with different loading capacity were loaded into the pores of COFs materials to form a series of ILs/COFs composites.The O₂/N₂mixtures were adsorbed by ILs/COFs composites at 298 K and 140 bar.The results show that the O_2/N₂separation ability of the modified composite have obviously improved.The results can provide theoretical guidance for the design of ILs/COFs composite materials.