Nucleation and Growth of Covalent Organic Frameworks from Solution: The Example of COF-5
KAUST DepartmentLaboratory for Computational and Theoretical Chemistry of Advanced Materials
Physical Sciences and Engineering (PSE) Division
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AbstractThe preparation of two-dimensional covalent organic frameworks (2D COFs) with large crystalline domains and controlled morphology is necessary for realizing the full potential of their atomically precise structures and uniform, tailorable porosity. Currently 2D COF syntheses are developed empirically, and most materials are isolated as insoluble and unprocessable powders with typical crystalline domain sizes smaller than 50 nm. Little is known about their nucleation and growth processes, which involve a combination of covalent bond formation, degenerate exchange, and non-covalent stacking processes. A deeper understanding of the chemical processes that lead to COF polymerization and crystallization is key to achieving improved materials quality and control. Here, we report a kinetic Monte Carlo (KMC) model that describes the formation of a prototypical boronate-ester linked 2D COF known as COF-5 from its 2,3,6,7,10,11-hexahydroxytriphenylene and 1,4-phenylene bis(boronic acid) monomers in solution. The key rate parameters for the KMC model were derived from experimental measurements when possible and complemented with reaction pathway analyses, molecular dynamics simulations, and binding free-energy calculations. The essential features of experimentally measured COF-5 growth kinetics are reproduced well by the KMC simulations. In particular, the simulations successfully captured a nucleation process followed by a subsequent growth process. The nucleating species are found to be multi-layer structures that form through multiple pathways. During the growth of COF-5, extensions in the lateral (in-plane) and vertical (stacking) directions are both seen to be linear with respect to time and are dominated by monomer addition and oligomer association, respectively. Finally, we show that the experimental observations of increased average crystallite size with the addition of water are modeled accurately by the simulations. These results will inform the rational development of 2D COF polymerizations to control the rate of nucleation, thereby increasing their materials quality.
CitationLi H, Chavez AD, Li H, Li H, Dichtel WR, et al. (2017) Nucleation and Growth of Covalent Organic Frameworks from Solution: The Example of COF-5. Journal of the American Chemical Society. Available: http://dx.doi.org/10.1021/jacs.7b09169.
SponsorsWe would like to thank Dr. Brian J. Smith (Cornell) and Dr. Zhen Cao (KAUST) for helpful discussions. The work at KAUST was supported by internal funding from King Abdullah University of Science and Technology; we are grateful to the KAUST IT Research Computing Team and Supercomputing Laboratory for providing outstanding assistance as well as computational and storage resources. A.D.C. was supported by a National Defense Science and Engineering Graduate Fellowship. This work made use of the IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205), the State of Illinois, and International Institute for Nanotechnology (IIN). The collaborative work at Northwestern and Georgia Tech was supported by the Army Research Office under the MURI Center for Advanced Two-dimensional Organic Networks, CATON, under Award No. W911NF-15-1-0447, and under Award No. W911NF-17-1-0339 to Georgia Tech.
PublisherAmerican Chemical Society (ACS)
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