(568e) Acid-Catalyzed Esterification Governs the Chain Elongation and the Oriented Attachment in Cof-5 Synthesis

Covalent-Organic Frameworks (COFs) have found application in a wide range of fields such as catalysis, membrane separations, adsorption, and drug delivery due to their high symmetry, porosity, crystallinity, and large surface area. However, long timescales of the synthesis, difficulties in characterization, formation of amorphous intermediate, and the limited understanding of the underlying reaction network have prevented the controlled synthesis of COF crystals. Furthermore, the existing solvothermal synthesis techniques are difficult to reproduce. To overcome these limitations, improve reproducibility, and obtain quantitative rate contributions of different polymerization phases, we employ experimental studies of a wide range of operating conditions to synthesize COF-5 crystals. The yield and grain sizes of the COF crystals were characterized using reliable and reproducible ex-situ techniques such as Fourier Transformed Infrared Spectroscopy (FTIR) and powdered X-ray diffraction (P-XRD). Optimization of the temperature, reactant concentrations, type of solvents, and catalysts have provided significant mechanistic and resulted in low reaction times, high yields, and larger particle sizes. The insights gained from the comprehensive experimental studies allowed the development of a microkinetic model which simulates millions of nodes in the COF reaction network. The error-minimized parameters in the microkinetic models reproduce the experimental results of COF-5 yield and grain sizes in a predictive manner. Furthermore, the microkinetic approach also validates the proposed reaction mechanism obtained from the experimental studies. Results suggest that the acid-catalyzed esterification governs the chain elongation and the oriented attachment of COF-5 crystals.