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Abstract
Crystalline framework materials, such as metal-organic frameworks (MOFs) and covalent framework materials (COFs), exhibit outstanding porosity, tunability and stability. These advantages make this emerging class of materials a promising and versatile platform for the construction of heterogeneous catalysts with high reactivity, durability and recyclability. My PhD research aims to rationally design crystalline framework materials as sustainable catalysts through a dual molecular and material approach, by establishing novel synthetic protocols, employing rigorous characterization techniques, and developing more efficient and synthetically useful catalytic processes. Chapter 1 of this dissertation aims to introduce basic concepts of crystalline framework materials, including their design principles, synthetic strategies and applications. Because they simultaneously possess well-defined molecular structures and intrinsic material properties, these crystalline framework materials can combine the high reactivity and tunability of homogeneous with the stability and recyclability of heterogeneous catalysts. The first part of the dissertation, including Chapters 2 and 3, focuses on using MOFs as a platform to develop bimetallic systems for sustainable catalysis. These chapters describe post-synthetic strategies for the construction of dual catalytic centers, either homobimetallic or heterobimetallic, that can work synergistically to activate small molecules such as O2 and CO2. These systems demonstrated how synergy between two metal sites can lead to superior reactivity compared to their mononuclear analogs or a simple mixture of two monofunctional catalysts. Moreover, these highly reactive catalytic sites are site-isolated in the framework, inhibiting undesired deactivation processes such as aggregation or nanoparticle formation, which significantly increases the durability and recyclability of these MOF-based catalysts. The second part, including Chapters 4, 5 and 6, presents strategies to design COFs for sustainable photocatalysis. Photosensitizing motifs can be introduced into COF backbones with rational design of structures. Furthermore, a second catalytic site can be installed via post-synthetic linkage modification or metalation to construct bifunctional catalysts. The proximity between the photosensitizing motif and the catalytic site drastically accelerates electron transfer during photocatalysis, and the site-isolation effect prevents catalyst deactivation, improving the sustainability of these catalysts.