Tunable Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks Triggered by CO2 Sorption.
Chengjun Kang1, Zhaoqiang Zhang1, Adam K Usadi2
1Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117585, Singapore.
Journal of the American Chemical Society
|October 31, 2022
Summary
Two-dimensional covalent organic frameworks (2D COFs) exhibit unexpected hysteresis in CO2 adsorption due to interlayer shifting. This discovery reveals 2D COFs can behave as "soft" materials, opening new avenues for gas storage and separation technologies.
Area of Science:
- Materials Science
- Chemistry
- Nanotechnology
Background:
- Two-dimensional covalent organic frameworks (2D COFs) are typically considered rigid porous materials.
- Their gas sorption isotherms are generally smooth and reversible.
Purpose of the Study:
- To investigate an unusual hysteresis step observed in the CO2 adsorption isotherm of a 2D COF, TAPB-OMeTA.
- To understand the structural dynamics of 2D COFs during gas adsorption.
Main Methods:
- In situ powder X-ray diffraction (PXRD) measurements.
- Computational modeling and Pawley refinement.
- Density functional theory (DFT) calculations.
- Surface-initiated atom transfer radical polymerization (SI-ATRP) for functionalization.
Main Results:
- TAPB-OMeTA exhibits a hysteresis step in its CO2 adsorption isotherm, attributed to interlayer shifting.
- A quasi-AA stacking structure is formed during CO2 adsorption due to weakened interlayer attraction and repulsion from methoxy groups.
- Functionalization with poly(N-isopropylacrylamide) oligomers induced a second interlayer shifting and two adsorption steps, demonstrating tunability.
- DFT calculations confirmed the energetic preference for the quasi-AA stacking structure under a CO2 atmosphere.
Conclusions:
- 2D COFs can exhibit "soft" porous behavior when interacting with gases, challenging the traditional view of their rigidity.
- Interlayer shifting, influenced by gas interactions and functional group repulsion, is a key mechanism for this behavior.
- The tunability of interlayer shifting offers new possibilities for designing 2D COFs for advanced gas storage and separation applications.
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