On the potential auxeticity of Covalent Organic Frameworks Muscat G. A. 1 , Grima, J.N. 1,2 , Farrugia P. S. 1 , Cardona M. A. 1 , Gatt R. 1 1 Metamaterials Unit, Faculty of Science, University of Malta, Malta, 2 Department of Chemistry, Faculty of Science, University of Malta, Malta Covalent Organic Frameworks (COFs) are crystalline, porous, organic molecules, composed of light elements (H, B, C, N and O) linked together through covalent bonds. 1 These compounds are characterised by a large surface area, tuneable pore size and structure, low density and structure customisation. 2 Due to such properties, COFs have versatile applications such as adsorbents, for the removal of organic pollutants, 3 & metal ionsfrom aqueous solutions 4 and the capturing of gas molecules. 5 To date, researchers have successfully synthesised several two- and three dimensional (2D and 3D) COFs. 2D COFs such as COFs- 1 and 5 exhibit a sheet-like structure analogous to the packing of graphite. 1 Conversely, 3D COFs, such as COF 320 possess an interwoven diamond-like structure. 6 To date, comprehensive investigations into the mechanical properties of COFs are limited to 2D COFs, particularly TP-COF and COFs-1 & 5. 7 These COFs have displayed an auxetic behaviour reaching a Poisson's ratio of approximately -1.5. 7 Conversely, no prior literature on the mechanical properties of 3D COFs has been published. In view of this, a cohort of 3D COFs were studied, and COF 320 was identified as a potentially auxetic 3D COF using molecular simulations in Materials Studio 6.1. 6 A method to study the effect of guest molecules was developed to mimic the effect of air on caged systems, thereby better predicting the potential auxetic properties of experimental structures. This study offers insight into the potential auxeticity of existing 3D COFs, paving the way for the design of other inherently auxetic 3D COFs. References 1. Cote, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. 2005 , 310 . 2. Ding, S.-Y.; Wang, W. Covalent Organic Frameworks (COFs): From Design to Applications. Chem. Soc. Rev. 2013 , 42 (2), 548–568. https://doi.org/10.1039/C2CS35072F. 3. Wang, W.; Deng, S.; Ren, L.; Li, D.; Wang, W.; Vakili, M.; Wang, B.; Huang, J.; Wang, Y.; Yu, G. Stable Covalent Organic Frameworks as Efficient Adsorbents for High and Selective Removal of an Aryl-Organophosphorus Flame Retardant from Water. ACS Appl. Mater. Interfaces 2018 , 10 (36), 30265–30272. https://doi.org/10.1021/acsami.8b06229. 4. Merí-Bofí, L.; Royuela, S.; Zamora, F.; Ruiz-González, M. L.; Segura, J. L.; Muñoz-Olivas, R.; Mancheño, M. J. Thiol Grafted Imine-Based Covalent Organic Frameworks for Water Remediation through Selective Removal of Hg(Ii). J. Mater. Chem. A 2017 , 5 (34), 17973–17981. https://doi.org/10.1039/C7TA05588A. 5. Zeng, Y.; Zou, R.; Zhao, Y. Covalent Organic Frameworks for CO 2 Capture. Adv. Mater. 2016 , 28 (15), 2855–2873. https:// doi.org/10.1002/adma.201505004. 6. Zhang, Y.-B.; Su, J.; Furukawa, H.; Yun, Y.; Gándara, F.; Duong, A.; Zou, X.; Yaghi, O. M. Single-Crystal Structure of a Covalent Organic Framework. J. Am. Chem. Soc. 2013 , 135 (44), 16336–16339. https://doi.org/10.1021/ja409033p.
P15
© The Author(s), 2023
Made with FlippingBook Learn more on our blog