Covalent organic frameworks for photocatalysis

The global energy crisis and environmental concerns are driving research into renewable energy and sustainable energy conversion and storage technologies. Solar energy, as an ideal sustainable resource, has significant potential to contribute to the goal of net-zero carbon emissions if effectively harnessed and converted into a reliable and storable form of energy. Photocatalysts have the potential to convert sunlight into chemical energy carriers. In this respect, covalent organic frameworks (COFs) have shown great promise due to their tunable structure on different length scales, high surface areas, and beneficial optical properties such as broad visible light absorption. This review offers a comprehensive overview of the key developments in COF-based photocatalysts for various applications, including water splitting, hydrogen peroxide generation, organic transformations, and carbon dioxide and nitrogen reduction. The underlying mechanisms, essential principles for material design, and structure-function relationships of COFs in various photocatalytic applications are discussed. The challenges faced by COF-based photocatalysts are also summarized and various strategies to enhance their performance are explained, such as improving crystallinity, regulating molecular structures, tailoring linkages, and incorporating cocatalysts. Finally, critical strategies are proposed for the utilization of photocatalytically generated chemicals into value-added products.