Theoretical Simulation On The Performance Of Metal-Organic Frameworks And Single-Layer Porous Materials For Gas Adsorption And Separation

The growing energy crisis and environmental problem along with the rapid development of modern society urge the exploitation of abundant and new-type environmental-friendly energy source.As a promising new-type energy source,the key challenges for the application of hydrogen energy are the adsorption and separation of hydrogen(H2).As for carbon dioxide(CO2),its adsorption and separation concern the mitigation of greenhouse effect without affecting the industrial development.Before the new-type energy source comes into service,the adsorption and separation of methane(CH4)are important for the realistic usage of natural gas.In addition,the separation of oxygen(O2)is of great importance in medical treatment,industry and daily life.This dissertation theoretically studies the adsorption and separation performance of H2,CO2,CH4 and O2 with metal-organic frameworks(MOFs)and single-layer porous materials.In chapter one,the critical role of the adsorption and separation performance of H2,CO2 and CH4,as well as the importance of O2 separation,are discussed.Moreover,the research progress in the fields of gas adsorption and separation using MOFs and single-layer porous materials are reviewed in this chapter.In chapter two,the theoretical basis and software applied in this dissertation are introduced.The Schrodinger equation for a polyatomic system can be solved approximately by selecting reasonable exchange-correlation functional and system's related properties are then obtained.For a system with a large number of particles,molecular dynamics method and Monte Carlo method are introduced to describe the motion trajectory and the average of physical quantities.In chapter three,the separation and storage performance of H2 in isoreticular MOFs(IRMOFs)are explored.Firstly,the force field parameters are verified and after that,IRMOF-10,-12,-14 and corresponding catenated structures,IRMOF-9,-11,-13,are simulated for the gas adsorption.The simulation results show that the selectivities for separating H2 from mixtures are much enhanced in the catenated structures,especially for IRMOF-11 and IRMOF-13.Meanwhile,H2 adsorption in lithium-doped IRMOFs is remarkably improved,especially for IRMOF-9-Li,in which the gravimetric and volumetric uptake reach4.91 wt%and 36.6g L-1 respectively at 243 K and 100bar.In chapter four,the properties of H2 separation,CO2 separation and CH4 separation with fluorinated and chlorinated metal-free fused-ring polyphthalocyanine(F-H2PPc and Cl-H2PPc)are studied.Feasible synthetic method of H2PPc and its halogenated structures are proposed,and structural and mechanical stabilities of H2PPc membranes are theoretically confirmed.By exploring the energy profiles for gas molecules passing through these membranes,we find that fluorination and chlorination can fine tune the permeable pores of H2PPc.In a wide temperature range,the calculated results demonstrate that F-H2PPc is a fascinating membrane for H2 separation,CO2 separation and CH4 separation.The other halogenated membrane,Cl-H2PPc is promising merely for the application in H2 separation/purification above 400K.In chapter five,the performance of O2 separation from harmful gases through porous graphene(PG)and graphdiyne(GDY)are dicussed.The PG pore is slightly larger in size than graphene and impermeable for O2 molecule.Although N-doped PG structure(1N-PG)barely changes the pore size,it effectively changes the electron density at the rim of pores and hence much enhances the permeance of O2,which makes 1N-PG an appropriate O2 separation membrane from harmful gases.Comparatively speaking,GDY has pores suitably larger in size than PG so that GDY is a candidate for O2 separation from harmful gases.Furthermore,we theoretically inspect the stability of GDY under O2-rich environment and demonstrate that GDY is a potential separation membrane for O2 from harmful gases.