Hollow molecular structures known as COFs (covalent organic frameworks), which could serve as selective filters or containers for other substances and have many other potential uses, also tend to suffer from an inherent problem: It's difficult to keep a network of COFs connected in harsh chemical environments.
The conventional chemistry for linking building blocks into 2D COF sheets or 3D COF frameworks is reversible. This reversibility makes the connections within COFs weak and unstable in some chemical environments, limiting the practical applications of these COF materials.
Now, a team of Foundry staff and users has used a chemical process discovered decades ago to make the linkages between COFs much more sturdy, and to give the COFs new characteristics that could expand their applications.
This one simple chemical approach targets a chemical reaction to the area of these weak links, forming resilient bonds that were shown to hold up – like a strong weld – to harsh chemical environments during experiments.
COFs have been heavily studied because they are highly tunable and can be composed entirely of light elements like carbon, hydrogen, nitrogen, and oxygen – unlike structures known as MOFs (metal-organic frameworks) that contain heavier elements. Scientists can make COFs with different pore sizes that can impact their function, changing what can pass through them or what can be contained within these pores.
This could make the COF-based materials useful in systems that filter unwanted chemicals from water, for example, reduce carbon dioxide into other value-added chemical forms, or serve as highly efficient facilitators for other types of chemical processes.
An important aspect of the study was the use of advanced imaging techniques, such as high-resolution transmission electron microscopy (HRTEM) at the Molecular Foundry to see the structure of the bound COFs.
The images obtained, which clearly show the honeycomb-like lattice of 2D COFs, are among the best images yet of COFs, confirming the chemical changes in the COFs down to a fraction of a nanometer.