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Acid Exfoliation of Imine-linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

preprint
submitted on 20.08.2019 and posted on 21.08.2019 by David Burke, Chao Sun, Ioannina Castano, Nathan C. Flanders, Austin Evans, Edon Vitaku, David McLeod, Robert H. Lambeth, Lin Chen, Nathan Gianneschi, William Dichtel
Covalent organic frameworks (COFs) are highly modular, porous, crystalline polymers of interest for charge storage devices, nanofiltration membranes, optoelectronic devices, and more. COFs are typically synthesized as microcrystalline powders, a morphology that limits their performance in these applications, and their limited solubility precludes large-scale processing into more useful morphologies and devices. Here, we report a general, scalable method to exfoliate two-dimensional imine-linked COF powders by temporarily protonating their linkages. The resulting suspensions were cast into continuous, crystalline COF films up to 10 cm in diameter. This strategy was successfully applied to three different COF structures, and excellent film thickness control (50 nm to 20 µm) was achieved by modifying the suspension composition, concentration, and casting protocol. Acid-mediated exfoliation is a promising strategy for solution processing readily accessible imine-linked COF powders into functional devices.

Funding

NSF CBET-1706219

NSF DMR-1720139

NSF DGE-1842165

NSF DGE-1324585

DOE DE-AC02-06CH11357

NSF ECCS-1542205

History

Email Address of Submitting Author

wdichtel@northwestern.edu

Institution

Northwestern University

Country

United States

ORCID For Submitting Author

0000-0002-3635-6119

Declaration of Conflict of Interest

The authors declare no conflict of interest.

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