Target Recognition And Chromatographic Separation Based On Regulation Of Metal-organic Frameworks

Metal-organic frameworks(MOFs)with tunable pores,high specific surface areas and diverse functionalities have been explored extensively for gas adsorption and separation,photodynamic therapy,catalyst and sensing.MOFs are formed with inorganic metal centers and organic ligands.Through controlling the ratio of these secondary building blocks(SBU)and the amount of different modulators,it is possible to regulate the morphologies and the microstructure of MOFs.With the modulation of MOFs'morphologies and microstructure,the amount and structure of exposed active sites as well as the pore sizes and pore shapes of MOFs can be well-tuned.Thus,the performance of MOFs in different applications can be well controlled correspondingly.In this dissertation,several methods were employed to modulate the dimension,size,stacking mode and defects of MOFs based on MOF structure.Through these methods,the performance of MOFs was impoved in target molecule recognition and chromatographic separation.The detailed research contents and main results in this dissertation are as follows:(1)Metal-organic framework with tunable exposed facets as a high-affinity artificial receptor for enzyme inhibition.The copper-based HKUST-1 with tunable exposed facets was utilized as artificial receptors to recognize a serine protease,?-chymotrypsin(Ch T),leading to different recognition abilities.High-energy facet{100}facets had been successfully introduced into the traditional HKUST-1 which had only{111}facets.The different exposed facets of HKUST-1 had different arrangements of metal centers and organic linkers,and the different SBU of this material could recognize the enzyme through diverse driving forces.The HKUST-1 with more{111}facets showed higher ability to recognize?-chymotrypsin.The reason was that on the{111}facets,the three coplanar copper clusters shared one BTC(BTC=1,3,5-benzenetricarbocylic acid)linker which made the copper centers more accessible for the enzyme to approach,leading to the higher recognition ability.(2)Two-dimensional metal-organic framework nanosheets as a high-affinity artificial receptor:modulation of the Ch T activity.Two-dimensional MOF nanosheets was utilized as artificial receptors to recognize Ch T with high-affinity.Two layered MOFs were chosen here,Cu-MOF and Zn₂(bim)₄.Dispersing the original MOFs into different solvents accompanied by stirring or sonicating for different time,the MOFs nanosheets with a few or even single layer could be obtained.The Cu-MOF nanosheets with negative surface and unsaturated copper center could recognize Ch T through electrostatic and coordination interactions.While,the Zn₂(bim)₄ nanosheets with positive surface could hardly recognize the target enzyme.The further experiments proved that the Cu-MOF showed higher affinity towards Ch T than HKUST-1 because of the large surface area and the more accessible active sites.(3)Discovering the precise p H-controlled biomimetic catalysts:defective zirconium metal-organic frameworks as alkaline phosphatase.The pre-incubation p H of Zr-MOFs and the reaction p H were regulated to modulate the their recognization abilities towards the substrate of alkaline phosphatase(ALP).Zr-MOFs,Ui O-66,Ui O-67,PCN-700,PCN-701 and PCN-703,with mimic ALP activity were chosen here.Monotopic acids were chosen as the modulators to restrict the growth of these Zr-MOFs.Buffers with different p H were utilized to remove these monotopic acid and created more exposed active sites,enhancing the recognition abilities of these MOFs.Through precisely modulating the reaction p H(<0.01),the defects structure could be well-tuned,and the recognition abilities of MOFs could be controlled.The defects structure with optimized recognition abilities is H₂O-Zr₆-OH which is highly p H sensitive.(4)Modulating stacking modes of nanosized metal-organic frameworks by morphology engineering for isomer separation.The nano-NU-901 with different morphologies formed different stacking modes and pore size distributions,leading to diverse chromatographic separation abilities towards isomers.Nano-NU-901 with different morphologies had been successfully synthesized via adding different modulators.The NU-901 nanosheets would form relatively aligned stacking,accompany with relative uniformed pore size distribution.The NU-901 interpenetrated nanosheets would form random stacking,accompany with random pore size distribution.The NU-901 nanoparticles would form close packing,leading to a uniformed pore size distribution with only micropores.The unique pore environment of stacked NU-901 nanoparticles resulted in the best separation ability compared with NU-901 nanosheets and interpenetrated nanosheets.Besides,when NU-901 with three morphologies were utilized to separate disubstituted benzene,it was found that the para-isomer showed longest elution time compared with their ortho-and meta-isomers.The reason was that the micropores of NU-901 was so small that only para-isomer with the smallest minimum cross diameter could get into these pores,leading to stronger interactions with NU-901.