Single-Crystalline Imine-Linked Two-Dimensional Covalent Organic Frameworks Separate Benzene and Cyclohexane
Anusree Natraj1, Woojung Ji1, Junjie Xin2
1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Journal of the American Chemical Society
|October 20, 2022
Summary
Researchers synthesized high-quality, single-crystal two-dimensional covalent organic frameworks (2D COFs) rapidly under ambient conditions. These advanced 2D COFs demonstrate superior performance in molecular separations, highlighting the importance of crystalline structure.
Area of Science:
- Materials Science
- Nanotechnology
- Chemical Engineering
Background:
- Two-dimensional covalent organic frameworks (2D COFs) are layered, porous materials typically synthesized as polycrystalline solids with small crystalline domains.
- Existing synthesis methods often require harsh conditions and result in materials with limited crystalline perfection, hindering their application potential.
- The precise control over structure and crystallinity is crucial for unlocking the unique properties of 2D COFs.
Purpose of the Study:
- To develop a rapid and scalable method for synthesizing single crystals of imine-linked 2D COFs.
- To investigate the structural characteristics of these synthesized 2D COF single crystals.
- To evaluate the performance of 2D COF single crystals in molecular separation applications.
Main Methods:
- Polymerization of imine-linked 2D COFs in suspension to yield faceted single crystals.
- Characterization using high-resolution transmission electron microscopy (HRTEM) and continuous rotation electron diffraction (cRED).
- Incorporation of COF single crystals into gas chromatography (GC) columns for separation studies.
Main Results:
- Successful synthesis of single crystals of rhombic (TAPPy-PDA) and hexagonal (TAPB-DMPDA) imine-linked 2D COFs in minutes at ambient conditions.
- HRTEM and cRED confirmed the layered, single-crystalline nature of the COF crystals in the ab-plane.
- Single-crystalline 2D COFs exhibited selective retention of cyclohexane over benzene in GC separations, with TAPPy-PDA outperforming TAPB-DMPDA; polycrystalline counterparts showed poor or no separation.
Conclusions:
- This study presents the first ambient-pressure, rapid synthesis of imine-linked 2D COF single crystals.
- The superior performance of single-crystalline COFs in molecular separations underscores the critical role of material quality and crystalline perfection.
- High-quality 2D COFs hold significant promise for advanced separation technologies.
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