Covalent Organic Frameworks: A State-of-the-Art from Design, Synthesis to Gas Sensing Application with the Prospect of Ammonia Gas Detection

The rapid growth of human society and the necessity of protecting human health and security underscore the importance of identifying the toxic gases emitted by industrial sectors. Ammonia (NH₃) is a widely produced industrial colorless toxic gas with a strong odor, coupled with its harmful environmental and health impacts, such as contributing to air pollution (PM 2.5 formation) and severe impact on the respiratory system of the human body, even at low concentrations. Covalent Organic Frameworks (COFs) have emerged as revolutionary materials to address these current issues. The crystalline porous network through the dynamic covalent chemistry of COFs possesses versatile structural and chemical properties that make them ideal for gas sensing. This review provides a comprehensive overview of the latest advancements in COF-based gas sensors with a focus on ammonia sensing. Moreover, the detailed discussion about the structural design and synthesis methods of COFs and their important characterization techniques is presented. It concludes by providing a future outlook for developing advanced COF materials in gas sensing applications.