Modification Of Metal-organic Frameworks For CO₂ Capture Using Modeling Approach

CO₂ is a major component of greenhouse gases and plays a significant role in global warming.Established as a new class of crystalline porous materials,metal organic frameworks?MOFs?have been considered as an ideal platform for CO₂ capture due to their large surface area,tremendous structures and tunable functionality.To design MOFs that meet the actual requirements,it is essential to explore new modification method for enhancing CO₂ capture performance,to develop new force field for describing the interaction between gas molecules and strong binding groups,to investigate the effects of gas impurities on CO₂ capture in MOFs.In this work,the multiscale simulation method,which combines the first principles calculation and grand canonical Monte Carlo simulation,were performed to design a series of new MOFs and to construct the structure–property relationships of MOFs for carbon dioxide capture;The force field parameters of GCMC simulations were derived from first principle calculations to guarantee the accuracy of the computations;the metal alkoxide functionalized,chelation of transition metals and heteroatoms incorporation were proposed as a promising method for enhancing CO₂ adsorption in MOFs,the adsorption mechanism were investigated and the CO₂ adsorption performance of these functionalized MOFs were calculated.The effect of functionalization on the capture of CO₂ in ZIFs with the presence of water vapor and other trace gas impurities.This work would be helpful for the development of new MOFs with high CO₂ capture efficiency for industrial application.MOFs with unsaturated metal sites exhibit remarkable CO₂ capture capacity.Metal alkoxide functionalization is a method for more stably incorporating metal cations into MOF linkers.In this work,metal alkoxide functionalization in MOFs was extend to three groups of alkali?Li,Na,and K?,alkaline-earth?Be,Mg,and Ca?,and first-row transition?Sc to Cu?metals in order to enhance CO₂ capture.The high interactions of CO₂ with metal alkoxide linkers can attribute to the strong effect of metal cations on polarizing the CO₂molecule.Li,Be,Ca,Ti,V,Mn,and Fe metals were selected as the idea modifier of MOFs among all the metals studied for capturing CO₂ effectively.The developed force field parameters along with GCMC simulations were used to calculate the isotherm for all the metal alkoxide-functionalized MOFs,and found that Ti functionalized MOFs exhibits the highest uptake amount of CO₂ among the these metals.Ti atoms were incorporated into six MOFs with various topology,pore volume,and pore size by metal alkoxide functionalized,and the results shown that the CO₂ uptake amounts in Ti functionalized MOFs at low pressure were depent on the pore size of MOFs,while the high pressure adsorption performances were related to the pore volumes.The MOFs with large pore size are more suitable for incorporating metal alkoxide groups.The incorporation of metal cations into MOFs with large pore size can significantly enhance both adsorption amounts and delivery amounts.The chelation of transition metals was proposed as a new method for enhancing CO₂capture in MOFs.The first row transition metals,from Sc to Zn,were chelated into two Zr-based MOFs containing 2,2?-Bipyridine?bpy?groups:UiO?bpydc?and BPV-MOF.The adsorption mechanisms of CO₂ on the chelated linkers were explored by using quantum mechanical calculation.Among the first row transition metals,the chelation of Mn?II?,Fe?II?,Co?II?,Ni?II?,Cu?II?,and Zn?II?gives higher binding energies than other transition metals.The adsorption capacities of CO₂ in metal chelated MOFs at room temperature were determined by GCMC simulation with force field parameters derived by first principle calculations.The results show that the chelation of Mn?II?into MOFs shows the highest uptake amount at low pressure.The CO₂ uptake amounts in UiO?bpydc?-MnCl₂ and BPV-MOF-MnCl₂ are about six times higher than the original counterparts at 298 K and100 kPa.Incorporation of heteroatoms on the ligand can incorporate strong binding sites into MOFs.The adsorption mechanisms of CO₂ on heterocyclic ligands were investigated by density functionalized theory calculations.The incorporation of heteroatoms alters the distribution of charge in the system,introducing regions of negative charge around heteroatoms,leading to enhanced interactions between framework atoms and CO₂molecules.The CO₂ adsorption and separation performance of four UiO-templated MOFs?UiO-67,UiO?BPYDC?,Zr-BTDC,and Zr-BFDC?comprising N,S,and O heterocyclic ligand were studied by grand canonical Monte Carlo simulations.The MOFs comprising O-heterocyclic ligand?Zr-BFDC?shows the highest CO₂ adsorption amount and the highest selectivity for CO₂/N₂ and CO₂/CH₄.The incorporation of heteroatoms into MOF linkers for enhancing CO₂ selectivity of MOFs is more effective under low temperature conditions.In addition,by changing the heteroatoms on the ligands,the CO₂ working capacity can be precisely tuned.Finally,the effect of functionalization on the capture of CO₂ in ZIFs with the presence of water vapor and other trace gas impurities were explored by investigated the effects of water vapor and trace gas impurities?SO₂ and O₂?on CO₂ capture in series of isoreticular ZIFs?ZIF-8,ZIF-90,ZIF-Cl,ZIF-NO₂,and SALEM-2?using grand canonic Monte Carlo simulations.The presence of O₂ was found to have almost no effect on CO₂ adsorption and CO₂/N₂ separation in all five ZIFs.In ZIF-8,ZIF-Cl,and SALEM-2,the presence of H₂O or SO₂ has negligible effect on CO₂ adsorption and CO₂/N₂ separation in the three ZIFs.In ZIF-90 and ZIF-NO₂,H₂O and SO₂ shows a cooperative effect on CO₂ adsorption.The presence of H₂O or SO₂ can enhance the adsorption heat of CO₂ in ZIF-90 and ZIF-NO₂.Particularly,in ZIF-NO₂,the CO₂ adsorption amounts and the CO₂/N₂ selectivity increased with the increasing of H₂O concentration.Our results indicate that the functional group play significant role on the CO₂ capture in ZIFs from actual flue gas.By changing the functionalities of ZIF materials,H₂O and SO₂ may play a positive role during CO₂adsorption and separation process.