Construction And Property Studies Of Sc Metal-Organic Frameworks And Hierarchically Porous Metal-Organic Frameworks

Over the past two decades, Metal-Organic Frameworks(MOFs), constructed by organic ligands and metal ions or clusters, have attracted much attention due to their great potential applications in gas adsorption and separation, catalysis, enantioseparation, molecular sensing. The rapid development of MOFs leads to the gradually improvement of their natures and functions.In particular, MOFs can serve as catalyst owing to their unusual pore shapes and tunable pore sizes. Recently, great efforts have been devoted to the development of trivalent metal derivatives heterogeneous Lewis acid catalysts. Compared to traditional Lewis acid catalysts, these trivalent metal compound catalysts display outstanding catalytic activities in terms of carbon-carbon bond forming reactions and Friedel-Crafts reactions due to their high activity and selectivity. Sc(III) readily forms MOFs with variable pore size and high thermal stability, which leads to a high stereoselectivity of catalytic effect. Hence, we devote to constructing novel Sc-MOFs on the basis of the reported works and studying their catalytic and cyclic performance.Although MOFs have been studied for years and the researchers have achieved great achievements in recent years, the pores of a majority reported MOFs are micropores, which limits their further applications. In comparison to traditional porous materials, such as microporous zeolites and mesoporous materials, mesoporous MOFs(meso MOFs) may offer the advantages of both mesoporous materials and microporous MOFs simultaneously, yielding enormous scientific and technological interest. The ligand-extension method and template-direction strategy were proposed for the construction of meso MOF materials. However, the synthesis of extended organic ligands would be very complicated, and some meso MOF materials are not stable after the removal of the guest molecules or template. Thus the facile synthesis of stable meso MOFs remains a great challenge.Based on the above background, this thesis is committed to using simple and effective strategies to synthesize novel and unique micro- and mesoporous MOF materials. The formation mechanism, structural composition and properties have been investigated and major achievements have been made as follows:1. Three Sc-MOFs were successfully constructed from the assembly of 2,3-pyridine dicarboxylic acid(H2pydc) ligand and Sc(III) ions under hydrothermal conditions. The different coordination geometry of Sc ion and H2 pydc ligand leads to the structural variety of three compounds from 1D to 3D. Compound 1 is a T-shape chain, and constructed to a 3D supramolecular framework via hydrogen-bonding. Compound 2, a waved layer, interacts with water molecules via hydrogen-bonding to construct a 3D supramolecular structure. Compound 3 is a 3D framework with nbo-a topology. All the compounds based on the Sc2(pydc)2 building units exhibit high thermal and water stabilities, and can be used as effective heterogeneous lewis acid catalysts for the cyanosilylation of aldehyde.2. We described a simple, convenient temperature-controlled assembly of a series of Cu-BTC meso MOFs by using a template-free strategy. The Cu-BTC meso MOF materials have distinct characteristics of mesoporous materials and narrow pore size distributions. The mesopores, which are constructed by the stacking of microporous Cu-BTC nanoparticles, can be simply adjusted by varying the synthesis temperature. This template-free strategy could be applied to other organic solvents conditions. Moreover, Cu-BTC meso MOFs with large mesopores provide the possibility for potential application in oxygen reduction reaction(ORR).3. The immobilization of BSL2 on Cu-BTC hierarchically porous MOF material has been demonstrated for the first time. The Cu-BTC hierarchically porous material was facile fabricated via a template-free strategy. Moreover, the immobilized BSL2 was served as heterogeneous biocatalyst for esterification reaction. It is worth noting that the modification of lipase with surfactant prior to the experiment improved the immobilization efficiency and stability of BSL2. Noticeably, the immobilized BSL2 still exhibits 90.7% of its initial enzymatic activity even after 10 cycles. This study indicates that hierarchically porous MOF material might serve as a new type of host matrix material to immobilize enzymes for catalysis applications in organic solvents under mild conditions.4. Mesostructured ZIF-8 material has been prepared via a hard-template strategy. FDU-12, which has large mesopores, was selected as the template. SAXS and N2 sorption studies demonstrate that Zn O was effectively filled in the mesopores of FDU-12 through soak and calcination process. SEM and TEM characterization indicate that the as-synthesized ZIF-8 posses mesostructures. This work would make a foundation to create new and unique muti-functional porous materials with a wide range of practical applications.