Theoretical Simulation Of CH₄ Adsorption And Separation In Two Kinds Of MOFs

Porous materials have excellent properties in gas storage and separation,transmission performance,photoelectric properties,catalytic activity and selective permeability,and so on.It depends on the introduction of characteristic functional groups and unique characteristics including low density,porosity,the adjustable pore structure and large surface areas,etc.As a result,they were widely used in the production of aerospace materials,insulation materials,battery electrodes,optoelectronic components and efficient separation membrane,etc.Among them,the porous materials play an irreplaceable role in gas storage and separation.Therefore,it has great potential for the development of this area.Depletion of resources,environmental pollution problems have become increasingly prominent.Methane,as a new energy,has gradually attracted people's attention.In this paper,two kinds of new porous materials are designed by means of substitution and assembly,the gas adsorption and separation properties are investigated by means of computational simulations.This investigation provides theoretical guidance for the experimental synthesis.Specifically include:1.The gases adsorption and separation properties in the novel metal-organic frameworks(CAU-17-X)were investigated by combining Grand canonical Monte Carlo(GCMC)simulation and Dispersion Correction Density Functional Theory(DFT-D3).After comparing with the selectivities of 6 binary mixtures in several porous materials(including UMCM-1,Cu-BTC,CAU-17,ZIF-8,IRMOF-1 and COF-5),CAU-17 has a high CH4/H2 selectivity.Next,the functionalized CAU-17 were gained,in which halogen atom and hydroxyl group replaced the hydrogen atom on benzene ring.These materials also expressed the remarkable CH4/H2 selectivity.The next step is to explore the origin for high selectivity of methane in CAU-17 materials in depth.Firstly,under the same conditions,the CH4 uptakes of classic porous materials are lower than CAU-17 and functionalized CAU-17 materials,while the H2 adsorption capacities are in contrary to CH4.Secondly,the high selectivity was depended on the different isosteric heats of gases.Thirdly,the higher interaction energy was calculated by DFT-D3 between the CH4 and channels than H2.Moreover,CAU-17 has three channels.Rectangle channel was occupied by for mixed gases in the beginning!2.According to the topology analysis,a series of novel MOFs were designed based on the recently synthesized ST MOFs(including ST-1,ST-2 and ST-3)and the Zn-MOFs(including UMCM-1,MOF-205,MUF-7a).The adsorption properties of CH4 in the novel MOFs were investigated by GCMC simulation.MOF-P and MOF-N have ultrahigh methane capacities in high pressure,because they have the high porosity and pore volume.Moreover,the highest isosteric heat of CH4 was found in MOF-J,in other word,the small pore materials have the stronger interaction energy with CH4.However,the lower interaction energies were found in MOF-P or MOF-N,in which have the higher adsorption capacities.This investigation provides theoretical guidance for the directed synthesis of new porous materials suitable for gas adsorption.