Design and Synthesis of Porous Covalent Organic Frameworks

Abstract

Covalent Organic Frameworks (COFs) represent a dynamic class of materials characterized by the precise assembly of organic subunits into porous crystalline structures through strong covalent bonds. Originating from groundbreaking discovery of a two-dimensional COF in 2005, the field has rapidly evolved to include one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) COFs. Chapter 1 showcases diverse building blocks and topological structures. Additionally, innovative synthesis strategies have emerged, aligning with environmentally friendly and energy-saving principles. COFs, with their exceptional physical and chemical attributes, diverse design concepts, and innovative synthesis techniques, hold significant promise across various applications. Notably, they have gained substantial attention in energy conversion and storage due to their outstanding performance. Tailored modifications allow for fine adjustments in photon-absorption capacity, band structures, and electron-hole separation efficiency, crucial for achieving remarkable photocatalytic performance. Additionally, the inherent porous and highly conjugated structures of COFs offer abundant charge storage sites and accelerated electron conductivity, driving their exceptional performance in supercapacitors and metal-ion batteries. In chapter 2, the rational design of organic subunits to yield crystalline COFs as efficient photocatalysts is explored. Phenanthroimidazole-based COFs, namely PIm-COF1 and PIm-COF2, demonstrated substantial optical properties. PIm-COF2 exhibited a hydrogen evolution rate 14 times higher than PIm-COF1, attributed to the strong donor-acceptor effect and continuous separation and transfer of the photoexcited electron-hole pair. In chapter 3, a novel approach involving self-exfoliation during synthesis resulted in the creation of covalent organic nanosheets, denoted as PS-CON, featuring pyridinium sulfobetaine groups. PS-CON demonstrated impressive ionic conductivity, two orders of magnitude higher than its parent electrolyte, attributed to well-distributed cation and anion sites promoting lithium-ion dissociation. The organized pore channels and chain-like sulfonate structure facilitated efficient lithium-ion transport. PS-CON presents a high-performance organic electrolyte with a low activation energy and a wide electrochemical stabilization window, highlighting its tremendous potential. This research collectively contributes to the evolving landscape of COFs, demonstrating that a rational design allows COFs to contribute positively to energy conversion and storage.