In situ Raman spectroscopy provides insights into the crystallization kinetics of 2D covalent organic frameworks

Covalent organic frameworks (COFs) are porous, crystalline materials built from organic aromatic subunits covalently bonded by reticular chemistry into two or three-dimensional networks. Like zeolites and metal organic frameworks (MOFs), COFs possess ordered structures with high surface areas and tunable pore sizes. These properties can be leveraged to design high-performance materials with applications including nanofiltration, gas separation, drug delivery, and catalysis. The implementation of 2D COF films as molecular sieves for nanofiltration, as an example, requires a keen understanding of the material’s crystallinity and subsequent pore structure. Raman spectroscopy has shown great sensitivity to the crystallinity of 2D COFs and has been established herein as a tool to probe the kinetics of crystallization during solvothermal synthesis. Raman spectroscopy allows for in situ monitoring of crystallinity with enhanced sensitivity and spatial resolution compared to methods based on diffraction. This technique can be extended to study the crystallization kinetics for other useful COF morphologies including thin films, mixed-matrix membranes, and nanoparticles. The insights gained from Raman spectroscopy may fill gaps in the understanding of fundamental phenomena including diffusion, reaction kinetics, and solvent interactions which govern the formation and crystallization of COFs.