Stable Metal-Organic Frameworks:Design And Functionalization

Metal-organic framework is a class of porous materials with the feature of high porosity,structural plasticity and specific surface area,which are composed by organic ligands and metal salts through self-assembly of coordination bond.In the past several decades,metal-organic frameworks have been studied for gas separation and storage,fluorescence,chemical sensing,catalysis,and drug delivery.However,due to the existence of coordination bonds,metal-organic frameworks have the disadvantages of low stability compared with other porous materials,such as zeolite,molecular sieves and covalent organic frameworks?COFs?.This thesis provides some strategies to synthesize and functionalize stable metal-organic frameworks on the basis of previous studies about the design and synthesis principle of stable organic metal frameworks.It has been proved for the first time that electric interaction can greatly enhance the stability of materials.At the same time,due to the presence of counterion in a stable framework,the material can be easily functionalized by guest molecule.This paper mainly introduces two kinds of stable metal-organic framework materials,and the materials can be utilized in catalysis,fluorescence and drug delivery through modification and utilization of the active sites in MOFs.Electrostatic interactions have been confirmed as one of the dominant factors for the stability of many materials in nature,which would be a valuable lesson we can learn from when we confront the stability issue for metal-organic frameworks?MOFs?.By engineering electrostatic interaction in MOFs,we demonstrated in this work that both the stability and functionality of MOFs can be effective regulated.Experimental and modeling suggest that the electrostatic interaction existed in cationic MOF?PFC-8?causes repulsive force toward the positive guest species in microenvironments and therefore protect the most vulnerable coordination bonds in structure from the attacking of reagent.As a consequence,PFC-8 can survive extremely acidic,oxidized,and high ionic strength condition,for example,12 M HCl?at least 301 days?,regia aqua?at least 86 days?,H₂O₂?at least 30 days?,as well as seawater?at least 30 days?.Diverse functionality can be simultaneously bestowed by substitution of the counterions of PFC-8 with exogenous functional species,expanding our ability to design MOFs adapt to demanding environment and functionality.A stable hierarchical porous metal organic framework PCN-56 with abundant Lewis acid sites?denoted as Defective-PCN-56?was synthesized by the low-temperature synthesis-induced defect formation method.The existence of mesopore in structure was confirmed by N₂ sorption isotherm and the successful encapsulation of large dye molecules.The Defective-PCN-56 has higher loading capacity toward anti-cancer drug Doxo compared with that of“nearly ideal-crystal”?denoted as Ideal-PCN-56?synthesized at high temperature,showing potential application as drug carrier.The low-temperature synthesis-induced defect formation strategy presented here provides a new and facile way to synthesize stable MOFs with the combination of intrinsic micropore and additional mesopore as well as abundant Lewis acid sites.