Ultra-Low Density Covalent Organic Framework Sponges with Exceptional Compression and Functional Performance.

The emergence of covalent organic frameworks (COFs) macroscopic objects with hierarchical porous structures addresses the limitations of traditional COF powders, which are challenging to process, thus bringing them closer to practical applications. However, the brittleness of the parent COF powder results in poor mechanical stability of these COF macroscopic objects, presenting a significant challenge that must be overcome for their continued development. In this work, we successfully obtained a continuous, hierarchically porous, and interconnected open-cell COF structure made up of hollow sponge walls of thickness 100-250 nm through a template-assisted framework process. This unique structure endows the COF sponge with a high surface area (1655 m g), ultralow density (2.2 mg cm), and exceptional mechanical stability. Even after 300 000 compressions at a 50% compression rate, its stress and height decreased by only 7.9% and 7.1%, respectively. These properties grant the COF sponge excellent solvent absorption capacity, catalytic performance, and reusability. Therefore, this work broadens the development pathway for COF macroscopic objects and is expected to further unlock the potential of COFs in practical applications.