A novel synthesis offers unprecedented insight into the kinetic formation of COFs, whilst simultaneously providing a facile route to these important materials
A micelle-mediated synthesis of an important class of materials called covalent organic frameworks (COFs) has been developed by researchers from the deMello group. The work, led by Dr Josep Puigmartí-Luis in collaboration with The Universidad Autónoma de Madrid, enables the preparation of stable and monodisperse sub-20 nm COFs under aqueous conditions at room temperature and low pressure.
COFs are comprised of covalently-linked organic molecules, joined in such a way that they form highly organized crystalline 2D or 3D networks. Whilst COFs can be generated from a few relatively simple elements (B, C, H, N, O), the arrangement of these elements into tunable crystalline frameworks imparts significant functionality. Their porous structures and large surface areas make COFs excellent materials for gas storage, and as catalysts for chemical reactions. However, challenges remain in COF synthesis, which typically requires high temperatures and the use of undesirable hazardous solvents. Furthermore, the most common synthetic protocols yield COFs as unprocessable microcrystalline powders. All these factors have reduced the implementation of COFs in nano and biological devices.
To approach this problem, Dr Carlos Franco and Dr David Rogríguez-San-Miguel developed a method of forming COFs which involves first encapsulating the highly hydrophobic building blocks inside separate populations of hydrophilic micelles. In addition to solubilizing the hydrophobic components, the micelles act as a barrier to keep the two reactive species from rapidly combining in solution. By ensuring COF formation is dependent on the merging of the two micelle populations the team were able to gain unprecedented control over the process. These COFs were found to be monodisperse and highly stable, even over a six month period, and can be easily isolated as a bulk material through gentle dissolution of the micelles. Furthermore, the gentle and controlled nature of this approach enabled the researchers to study the process of COF formation using analytical tools not amenable to previous synthetic protocols. By coupling time-resolved light and X-ray scattering experiments with computational modelling the team were able to create a detailed model of the COF self-assembly. This work improves our understanding of COFs whilst simultaneously improving their synthesis, and will help to ensure wider adoption within the scientific community.
Written by Daniel Richards.
Read the full paper here.
The micelle-mediated formation of imine-linked COFs proceeds under ambient
conditions in an aqueous environment