Synthesis of Hierarchically Porous UiO-66 MOF Materials and Their Applications in Catalysis and Water Purification

Zhang, Furui

doi:https://doi.org/10.21985/n2-6150-h403

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Synthesis of Hierarchically Porous UiO-66 MOF Materials and Their Applications in Catalysis and Water Purification

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In the first two decades of the 21st century, metal organic frameworks (MOFs) have attracted much attention in both fundamental-research and-industrial application areas. Derived from a vast library of both inorganic metal nodes and organic linker bridges, MOFs are crystalline materials whose structures and chemical environments can both be tuned in a facile manner. The molecular nature of the building blocks normally engender MOFs with small micropores (< 2 nm) and very high surface areas, but they also limit the diffusivity of guest molecules inside its porous matrix and restrict the entrance of species larger than the aperture size. This could greatly slow down their performance in applications that requires fast molecular transport, such as sorption and catalysis. Designing and synthesizing MOF materials with both micropores (< 2 nm) and large mesopores (2-50 nm) or even macropores (>50 nm), namely hierarchically porous MOF materials, can overcome these limitations, achieve efficient mass transport, and enhanced performances, thus broaden applications of the MOF materials. To implement this approach, this thesis focuses on the development of meso-/microporous and macro-/microporous MOF-based materials and corroborate their applications in catalysis and water purifications.Specifically, a class of removable block-copolymer templates were used to engender mesopores into a Zr-based MOF during its growth, seeded by pre-synthesized MOF nanoparticles. Such a seed-mediated, template-assisted growth could be iteratively repeated to increase the proportion of mesopore in the resulted materials. With a thrice-grown material, significant enhancements in adsorption capacity and catalytic activity were observed, comparing to its micropore-only counterpart. Further studies of the templating effect by Pluronic polymers led us to a new 2D Zr-based MOF structure, proposed to arise from the coordination hindrance brought by the polymers on the metal nodes during MOF growth. A commercially available water-purification polymer membrane was then combined with the seeded strategy to grow microporous Zr-based MOFs inside its macropores, resulting in a macro-/microporous membrane material, which were shown to be highly efficient and selective in removing phosphate from groundwater with the presence of other anions. A unique electro-assisted technique was additionally applied on this composite membrane to further improve the adsorption and desorption kinetics. This strategy, when combined with the template-assisted strategy described above can form a general approach for fabricating the next generation of hierarchically porous MOF materials.

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