Study On Gas Chromatographic Separation Media For Guest Molecules Controlling The Stacking Of MOFs Nanosheets

Metal-organic frameworks(MOFs)are new porous materials with highly ordered framework structures formed by self-assembling coordination between organic linkers and inorganic metal ions.MOFs with tunable structures,high porosity and excellent chemical and thermal stabilities have been explored in the fields of separation,adsorption and catalysis.Recently,MOFs as stationary phases provide higher resolution,selectivity and reproducibility for isomer separation in gas chromatography(GC).Comparing with the traditional stationary phases,the separation performance of MOFs can be significantly improved through oriented design of changing the organic linkers or metal centers,which is favorable for optimizing the sensitivity and reliability for GC separation.We control the twisted or untwisted stacking of two-dimensional Zr-BTB(BTB=1,3,5-(4-carboxylphenyl)-benzene)nanosheets by a solvent-induced strategy,which are used as stationary phases to separate disubstituted benzene derivatives isomers.The detailed research contents and results as follows:1.The guest molecules control the stacking modes of metal-organic framework nanosheets for highly selective isomer separations.The guest molecule of methyl benzene(MB)and ethyl acetate(EA)induce twisted stacking of two-dimensional Zr-BTB nanosheets.Zr-BTB-MB and Zr-BTB-EA nanosheets showed the specific rotation angles of 12~o,18~o,24~o and 6~o,18~o,24~o,30~obetween adjacent nanosheets,respectively,which is in accordance with theoretical calculations.Meanwhile,the alkanes control untwisted stacking of two-dimensional Zr-BTB nanosheets,resulting in highly ordered nanochannels.The untwisted two-dimensional Zr-BTB nanosheets show the excellent gas chromatographic separations of benzene derivative isomers,which is better than twisted nanosheets stacking.2.Benzene and ester homologues control the stacking modes of metal-organic framework nanosheets for highly selective isomer separations.Different guest molecules induce twisted or untwisted stacking of nanosheets,which created porous materials with different pore environments.We control the stacking of two-dimensional Zr-BTB nanosheets through guest solvent molecules of benzene homologues and ester compounds,and further explore the effects of molecular functional groups on the stacking of the nanosheets.Comparing with ester compounds,interaction between benzene homologues and MOFs is stronger,which is conducive to the formation of multilayer stacking of nanosheets.Moreover,the length of the alkane chain for two sets of homologous molecules affects the stacking of the nanosheets.The solvent molecules of side-chain alkanes with 1-2 carbon atoms induce twisted stacking of nanosheets,which have no isomer separation ability.The side-chain alkanes with 3or more carbon atoms induce untwisted stacking of nanosheets because the hydrophobic interaction of the alkane chain plays a dominant role.With the increase of alkane chain length,the stacking nanosheets are more orderly and the ability of separation isomers is stronger.In this chapter,the guest molecules with different functional groups induce different stacking of nanosheets,which lays the foundation for the accurate regulation of the stacking of nanosheets on the molecular level.