Design and Synthesis of Imine-Linked Two-Dimensional Covalent Organic Frameworks

Ji, Woojung

doi:https://doi.org/10.21985/n2-02xw-4976

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Design and Synthesis of Imine-Linked Two-Dimensional Covalent Organic Frameworks

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Two-dimensional (2D) covalent organic frameworks (COFs) are a class of crystalline polymer networks that polymerize and crystallize into layered structures, characterized by their atomically precise structure, permanent porosity and high modularity. Imine-linked COFs are one of the most important and promising classes of macromolecular sheets, which form by the condensation of polyfunctional amines with aldehydes. These materials exhibit one of the broadest structural diversity of 2D networks and are attractive partly because of their enhanced hydrolytic and oxidative stability compared to their boron-linked counterparts. This stability coupled with their immense structural versatility has led to their development with desirable properties for various applications. As such, the field has currently explored these stable frameworks by probing many testable properties of the polycrystalline COF powders. Major developments, however, are still needed. A key, currently unmet need that will provide morphological control as well as improved materials quality is better mechanistic understanding of the COF formation and growth. In this dissertation, I will discuss the design and synthesis, formation mechanisms, different morphologies, as well as molecular adsorption and separation applications of 2D imine-linked COFs. In chapter 1 I will discuss a broad overview of imine linkage chemistries and the 2D COFs generated by these strategies. This chapter will start with the outline of contemporary strategies used to successfully polymerize imine-linked macromolecular sheets and the exploration of the chemical and structural COF variants produced through each of these methods. Next, the chapter discusses the nano- and macroscale morphologies of COFs and molecular adsorption and separation applications using imine COFs. Finally, Chapter 1 will end by highlighting additional insight needed to address some of the major challenges in the field and identify opportunities for continued study. Chapter 2 focuses on the design and synthesis of the amine-functionalized, 2D imine-linked COFs for perfluorinated alkyl substances (PFAS) removal from water. Chapter 3 is about thermal depolymerization and recrystallization of 2D imine-linked COFs, a novel phenomenon which can be used to improve and assess COF materials quality. Finally, Chapter 4 discusses a novel synthetic strategy for preparing imine-linked 2D COF single crystals of four different architectures.

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