Enhancing the stability of covalent organic frameworks (COFs) is an interesting research target. The predominant approaches for increasing the stability of COFs has involved employing irreversible coupling reactions or increasing the steric hindrance of monomers.

Wei Zhang, University of Colorado, Boulder, USA, and colleagues have developed a strategy for increasing the stability of COFs by constructing double-walled structures. The team found that introducing a second linker, aligned parallel to the first (simplified structure pictured above in the bottom row), led to a remarkable boost in COF stability. They synthesized two double-walled covalent organic frameworks, called DW-COF-1 and DW-COF-2, via imine condensation. The team prepared a hexatopic amine via a condensation reaction of p-tolunitrile, followed by nitration and hydrazine reduction. The amine was reacted with linear dialdehydes to give the desired COFs.

The double-walled COFs showed significantly improved stability when exposed to basic solutions or hot water compared with the corresponding single-walled COFs. The frameworks also displayed excellent performance in gas separation. The strategy successfully maintained the porosity of the frameworks. Overall, the work could be useful for the development of new COFs for applications, e.g., in electronic devices, gas storage, or catalysis.

• Double‐Walled Covalent Organic Frameworks with High Stability,
  Yu Gong, Shaofeng Huang, Zepeng Lei, Lacey Wayment, Hongxuan Chen, Wei Zhang,
  Chem. Eur. J. 2023.
  https://doi.org/10.1002/chem.202302135