Supramolecular Interaction-Mediated Surface Engineering Of Metal-Organic Framework Nanoparticle And The Application In Preparing Crack-Free Porous Coatings

Metal-Organic Framework（MOF）material is a two-dimensional or three-dimensional crystalline coordination polymer material formed by metal nodes（metal ions or metal clusters）and multidentate organic ligands.Due to the highly tunable crystal structures and functions,high porosity and stable chemical properties of MOF materials,MOF materials have been applied in many research fields,such as catalysis,gas adsorption,separation,storage,and drug delivery.Compared with macro-sized bulk MOF materials,MOF nanoparticles show improved physicochemical properties in some aspects due to their high specific surface area and improved solvent dispersity.Previous literatures have demonstrated self-assembly of MOF nanoparticles through bottom-up approach can overcome some of the shortcomings of macroscopic MOF bulk materials.To date,the common methods for preparing MOF nanoparticle assemblies are:（1）assemble unmodified MOF nanoparticles via van der Waals forces at the interface;（2）assemble MOF nanoparticles via hydrophobic-hydrophobic interaction and electrostatic interaction by introducing surfactants on the outer surface of MOF nanoparticles;（3）assemble MOF nanoparticles via polymer polymerization reaction at the interface of MOF nanoparticles.These MOF assemblies formed by above-methods are often low in MOF content,and it is difficult to achieve dynamic and reversible regulation of the assembly.To meet these challenges of the assembly of MOF nanoparticles,this thesis reports a highly controllable method for the assembly of MOF nanoparticles based on crown ether-bisecondary ammonium salt interaction by using supramolecular host-guest interaction.By using this method crack-free,high-load MOF coatings was realized.（1）UiO-66 was selected as the model system,due to the presence of unsaturated metal sites on the surface of MOF nanoparticles.The carboxylated 21-crown-7 was introduced onto the surface of UiO-66 nanoparticles through the coordination surface modification.The surface of UiO-66 was further modified with bisecondary ammonium salts（Bisas）based on supramolecular host-guest interaction.The UiO-66 nanoparticles before and after modification were characterized using XRD,SEM and TEM.The results showed that the three types of UiO-66 nanoparticles（B21C7-modified,Bisas-modified,and unmodified UiO-66）all maintained their original properties,including crystallinity,size and morphology.By using characterizations such as DLS,¹H NMR,XPS and N₂ isothermal adsorption,we demonstrated that ligands were successfully introduced onto the surface of the UiO-66 nanoparticles.The introduction of B21C7and Bisas modifications on the surface of UiO-66 nanoparticles significantly improved the colloidal stability of UiO-66 nanoparticles.（2）By interfacing UiO-66 nanoparticles using supramolecular host-guest interaction between 21-crown-7 amd bisecondary ammonium salts,the formation of micro-scale UiO-66 nanoparticle assembly can be realized.The UiO-66 nanoparticle assembly was systematically characterized by SEM and confocal fluorescence microscopy.The assembly kinetics of UiO-66 nanoparticles mediated by supramolecular host-guest interaction was systematically studied using the turbidity change.By using KPF₆/18-crown-6 and triethylamine/trifluoroacetic acid,reversible regulation of the self-assembly process of UiO-66 nanoparticles can be achieved.（3）By using supramolecular host-guest interaction,UiO-66 nanoparticles modified with B21C7 and Bisas can be used to prepare crack-free porous MOF coatings by drop coating,spin coating,and suction filtration methods.By using SEM and metallographic microscope characterization,we demonstrated that coating materials prepared by modified UiO-66 nanoparticles show fewer cracks compared with the ones prepared by unmodified UiO-66 nanoparticles.The dye adsorption experiments further proved that the crack-free MOF coating prepared by host-guest interaction significantly improved adsorption ability compared with the unmodified MOF coating.（4）The supramolecular assembly method based on the supramolecular host-guest interaction is universal.This method was further applied for surface modification of four distinct MOF nanoparticles with different metal clusters and organic ligands,namely MIL-53-（Fe）,MIL-101-（Cr）,PCN-222 and NU-1000.The four MOF nanoparticles before and after modification were systematically characterized by XRD,DLS and SEM,showing B21C7 and Bisas were successfully modified on the surface of MOF nanoparticles.All MOF nanoparticles can assemble into micro-scale assemblies through supramolecular host-guest interaction.In summary,this thesis developed a general method based on the supramolecular host-guest interaction between 21-crown-7-bi-secondary ammonium salts to prepare microscale assembly of MOF nanoparticles.This method can be applied to a variety of MOF nanoparticles,showing interactions between MOF nanoparticles can be enhanced to prepare micro-scale MOF assemblies.Compared with previously reported method,the B21C7-Bisas supramolecular host-guest interaction reported in this paper can realize the reversible regulation of MOF assembly,significantly improving the content of MOF in the assembled materials such as MOF coating.The prepared crack-free potous MOF coating is expected to be useful in adsorption,separation,antifouling,antibacterial,and other applications in the future.