Theoretical Study On The Electronic Structure And Adsorption Property Of MOFs Supported Ionic Liquids

Metal-Organic Frameworks?MOFs?is one kind of porous crystalline materials,which are composed of metal cations or clusters and organic ligands by coordination bonds.MOFs materials have been flourishing applications because of their controlled pore testures and large surface areas,and can apply to catalysis,hydrogen storage,gas sorption and separation,chemical sensing,and magnetism.In recent years,researchers have devoted themselves to studying the loading of other molecules in the pore of MOFs,and then affecting or improving the performance of MOFs.Ionic liquids?ILs?are widely used as a new green solvent,however,their actual applications are limited due to high viscosity.Taking porous material MOFs as supports in ILs can prospectively reduce the high viscosity of ILs and contribute to improve the adsorption and separation capacity of material.In this paper,ILs are loaded on the pore of different MOFs,and the mechanism between MOFs and ILs was studied.It will provides a theoretical basis for the future selection of appropriate MOFs supported ILs.The major taget of this thesis is to study the different types of MOFs supported IL by using the first principle calculation based on density functional theory?DFT?,and analyse the changes of electronic structure,adsorption capacity for CO₂.Specific research content includes:?1?Based on the DFT method,Zn-MOF-74@[Emim][BF₄]has been explored.The stability of the complex system,the changes of electronic structure and the adsorption capacity of Zn-MOF-74@[Emim][BF₄]on CO₂ were analysed.There are strong interaction generates between the Zn atom and anion of[Emim][BF₄],and the Coulomb forces caused the change of Zn-MOF-74 coordination configuration.The loading of IL disrupts the symmetry of Zn-MOF-74 structure and enhances the interionic interactions.After deformation,the charge transfers between Zn-MOF-74and[Emim][BF₄].The chemical adsorption between MOF and IL is verified.CO₂was adsorbed on the Zn-MOF-74 system.The adsorption property was analyzed based on the Bader charge,electron density difference?EDD?and interaction diagrams.At this time,the adsorption energy of CO₂ was explored.The mechanism of Zn-MOF-74 and Zn-MOF-74@[Emim][BF₄]complexes for CO₂ absorption was compared and the adsorption energy of complex was calculated.?2?In combination with the VASP program and Gaussian 09 calculations,the electronic structure and stable configuration characteristics of the open-organic ligands MOF-253 supported[Emim][BF₄]were studied.In addition,the mechanism of the CO₂ adsorption on MOF-253@[Emim][BF₄]was also analyzed.The calculated MOF-253@[Emim][BF₄]was stable.Bonding energy between the MOF-253 and[Emim][BF₄]is mainly due to the van der Waals force generated by electron polarization.And no significant electron transfer occurred between the complexes.The results clearly indicated that the supported IL is physically adsorbed on the MOF-253 system.The open organic ligands of MOF-253 adsorbs CO₂ as an effective adsorption sites.From the calculation result,it was found that the adsorption energy is weak.The mechanism of CO₂ adsorption by MOF-253@[Emim][BF₄]was analyzed and its adsorption energy was calculated.