Design And Synthesis Of Polyazole-based Metal-organic Framework Materials And Research On Gas Adsorption And Separation Performance

As a new type of crystalline porous materials,metal-organic frameworks(MOFs)have received the attention of researchers owing to the structural designability,extra-large surface area and tunable pore size and are widely used in gas storage and separation,heterogeneous catalysis,and so on.Among various organic ligands,polyazolate ligands are of special interesting.The polyazole ligands usally have diversity coordination modes and the uncoordinated N atoms can act as Lewis base sites to bind gas molecules and thus promote the gas uptake performance of MOFs.In this thesis,we firstly summarized the recent developement of polyazolate MOFs.Further,1,2,4-triazole with different alkly substituents and cuprous halides were selected in the first section to prepare novel MOFs to investigate the effects of substituents and halogen atoms on the gas adsorption performance.Compounds 1-6,namely[Cu8X4(L)4](X=Cl,Br and 1)were obtained.Single crystal analysis showed that these MOFs are isostructures with[Cu4X4]cluster as inorganic building blocks.The gas adsorption results showed that a combination of alkly groups and halogen atoms effectilvely tuned the gas adsorption of these MOFs.When the substituent is the same,the gas adsorption amount is sequentially decreased in the order of Cl,Br,and I.Furthermore,with the the same[CU4X4]building blocks,the MOF decorated by ethyl groups clearly has higher gas uptake amounts than those with propyl groups.The isothermal adsorption enthalpy of these MOFs obtained by the virial equation suggest that all the gas uptake performance belongs to physical adsorption.At the same time,IAST theoretical calculation and breakthrough experiments show that the ethyl-decorated MOFs exhibit higher C2-hydrocarbon/CH4 and CO2/CH4 selectivity.Specially,the C2H2/CH4 separation time for compound 1 was up to 20 min.In the following section of this thesis,1,3,5-benzenetristetrazolate(BTT)ligand was selected to assemble with cadmium salts under the solvothennal conditions.A series of linear dicarboxylate linkers with different substituents were utilized as co-ligands.As a result,six Cd-BTT-dicarboxylate MOFs were successfully obtained.Compounds 7-11 are isomorphic,which are constructed from ID Cd-BTT chains.The flexible cyclohexanedicarboxylic acid led to compound 12,which is different of a skeleton.The adsorption performance of MOF materials for small molecules such as N2,CO2,CH4,C2H2 and C2H4 was studied by isothermal physical adsorption experiment.The results show that the surface areas of these MOF materials are mainly affected by the substituent goups and MOF with-OH substituent has the highest surface area.The dasorption for CO2,C2H2 and C2H4 was tuned by the synergistic effect of Lewis basicity and bulk of substituent groups.The adsorption performance of OH-decorated MOF is best.The isotherm adsorption enthalpy data show that compound 11 exhibits strongest interaction with C2H2,CO2 and C2H4 gas molecules,and the adsorption enthalpy is 52.6,44.0 and 44.5 kI/mol,respectively.The NH2-decorated compound showed a strong interaction with CH4,and the adsorption enthalpy reached 27.5 kJ/mol.Moreover,the separation performance of these MOF materials for two-component mixed gas was calculated by IAST method.All these MOFs exhibits high C2-hydrocarbon/CH4 separation performance and the C2H2/CH4 separation ratio is about 351 at 273 K and latm for compound 11.