Molecular Simulation Study Of Novel Pore Materials For The Separation Of Toxic Gases

Air pollution is a critical issue that affects human health and the ecological environment.The air pollution caused by using enormous amounts of fossil fuels in China has severely affected people's quality of life.The small molecule gases in air pollution mainly include carbides,sulfides,and nitrides.Metal-organic framework materials?MOFs?and covalent organic framework materials?COFs?have attracted extensive attention due to their adjustable specific surface area,porosity,pore structure,and functional groups,and have used in the storage and separation of gases,catalysis,sensitization,and so on.In this dissertation,molecular simulations were used to study the separation of SO₂,NH₃,H₂S,NO₂,NO,and CO from the air by MOFs and COFs,and the structure-property relationship of the porous materials to remove these toxic gases was discussed.Firstly,Grand Canonical Monte Carlo?GCMC?simulations were conducted to study the adsorption performance of toxic gases in 89 MOFs and COFs,and top ten adsorbents for each toxic gas was screened.The structure-property relationship by analyzing the pore geometry and material composition of the MOFs and COFs was evaluated to optimize the adsorption conditions for toxic gases.From the metal cluster structure,MOFs with open-metal sites have a more significant influence on the adsorption of NH₃,H₂S,NO₂ and NO.Especially for the adsorption of NH₃,the influence of the open metal sites can reach over 90%,which shows that the electrostatic interaction plays an essential role in the adsorption process of NH₃.Moreover,the screening results show that ZnBDC and IRMOF-13 are ideal candidates for capturing both of NH₃,H₂S,NO₂,NO,and CO.Secondly,this article also used the above materials to study the separation of sulfides in the air.The mixed air system with a sulfide concentration of 100 ppm was used as the research object,in which the air was a simplified mixed model with a molar ratio of N₂ to O₂ of 79:21.Through the study of desulphurization process of pressure swing adsorption?PSA?and temperature swing adsorption?TSA?,selectivity,working ability and selection parameters of each material in the separation process of the mixed system was evaluated.Molecular dynamics?MD?simulations were used to investigate the effect of N₂concentration changes in some preferred materials on the diffusion behavior of various gases in the system.The results show that UiO-66,ZIF-71,ZIF-69,and ZIF-97 have satisfactory performance in the separation of hydrogen sulfide in the air.At normal temperature and pressure,their selectivity to H₂S is higher than 300 and adsorption capacity is higher than 0.01 mmol/g;their PSA capacity from 1 bar to 10 bar can reach0.06 mmol/g;their TSA capacity from 348 K to 298 K can reach 0.008 mmol/g.The study on the purification of SO₂ in air found that UiO-66,ZIF-71,ZIF-69,MIL-100,Zn-DOBDC,ZnBDC,IRMOF-11,and MIL-140B are ideal materials.At normal temperature and pressure,their selectivity to SO₂ is higher than 500 and adsorption capacity is higher than0.06 mmol/g;their PSA capacity from 1 bar to 10 bar can reach 0.2 mmol/g;their TSA capacity from 348 K to 298 K can reach 0.05 mmol/g.The diffusion rate of sulphide in the above-mentioned candidate materials is basically unchanged and is between the lower values of 2×10^-11 m²/s to 4×10^-10 m²/s.The comprehensive analysis found that ZIFs have satisfactory performance in the removal of sulfides.The adsorption density map shows that the nitrogen-containing heterocyclic groups in the pores of the ZIFs have a strong attraction to the sulfides.It is also found that MOFs with open Zn metal sites have better SO2 adsorption performance.The adsorption density map shows that O atoms in SO2 was preferably adsorbed around Zn atoms exposed on the inner walls of the pores.The effect of open metal sites on sulfide separation in the X-DOBDC?X=Zn,Mg,Ni,and Co?series was Zn>Mg>Ni>Co.