Synthesis And Applications Of Hierarchically Structured Metal-Organic Frameworks Materials

Recent ten years, MOFs as new class of porous crystalline materials built from metal ions building units connected by organic linkers have attracted much more attentions owing to their large pore sizes, high apparent surface areas, low density, tunable pore metrics, flexible tailoring, various topologies, and promising applications in hydrogen storage, adsorption, molecular recognization, sensing, catalysts, and drug delivery.However, most of the reported microporous MOFs display some restrictions because narrow pores do not allow accessing of bulky molecules to their internal surface, thereby limiting their practical applications in heterogeneous catalysis, absorption and separation. In contrast, meso-and macropore MOFs may meet the demands for the growing applications emerging in processes involving large molecules due to large pore volumes and high surface areas. According to the principle of molecular engineering, and crystal engineering, rational design and synthesis of meso-and macropore MOFs crystalline materials by selecting special metal ions and functional organic ligands remains a great challenge. In many cases the framework itself often breakdown upon removal of the guest molecules. At the same time, much more attention has turned to preparation of nano-scale hierarchical structured MOFs with meso-and macropore using surfactants as structure directing agents (SDA) to reduce the diffusion path length to fit the potential applications in sensing, molecule separation, and heterogeneous catalysts. The main contents of this thesis are as follows:1. Hierarchically mesostructured MIL-101metal-organic frameworks (MOFs) were successfully synthesized under solvothermal synthesis conditions by using the cationic surfactant cetyltrimethylammonium bromide as a supramolecular template. The mesostructured MIL-101MOFs were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms at77K. The results suggest that the mesostructured MIL-101MOFs obtained are composed of numerous MOF nanocrystals. Pore size distribution analyses of the as-synthesized MOF samples reveal that such mesostructured MIL-101MOFs have well-defined trimodal pore size distributions showing simultaneous existence of meso-and macropore channel systems. Significantly, such hierarchically mesostructured MIL-101exhibits remarkably accelerated adsorption kinetics for dye removal in comparison with the bulk MIL-101crystals, which is due to unique hierarchically meso-and macropores created in the solid.2. Successfully synthesized hierarchically structured MIL-100(Fe)nanocrystalline MOFs using anionic surfactant sodium dodecyl benzene sulfonate (LAS) as structure-directing agent under solvothermal conditions. The structures were confirmed by PXRD, infrared spectrum (IR), SEM, TEM, and nitrogen adsorption-desorption isotherms at77K. The results show that the hierarchically structured MIL-100(Fe) MOFs size of nanocrystals can be tuned by varying dosage of LAS. Significantly, such hierarchically structured MIL-100(Fe) nanocrystalline exhibits remarkably photocatalytic decolorization of methylene blue (MB) dye in comparison with the bulk MIL-100(Fe) crystals, which is due to unique hierarchically meso-and macropores created in the solid. This may be helpful to design novel photocatalyst materials.3. Novel morphologies of MIL-101(Cr) were successfully synthesized via a novel polymer polyethylene alcohol (PVA) surfactant-assisted technique. The characterized by PXRD, SEM, and nitrogen adsorption-desorption isotherms at77K. The results indicated that size and shape of can be tuned by varying of dosage of PVA. The pore size distribution date show that as-synthesized MOF samples existence of meso-and macropore channel systems.