Heterostructured two-dimensional covalent organic framework membranes for enhanced ion separation

Linker Exchange as Facile Method for Post-Synthetic Modification of β-Ketoenamine-linked Covalent Organic Frameworks

Post-synthetic linker exchange performed on covalent organic frameworks (COFs) has become an important method to introduce functional building blocks into their backbone and thus to tune their chemical and physical properties. However, the linker exchange method has so far only been described for COFs with relatively weak linkages like imines. Herein, it is shown that this method can be also used for a post-synthetic linker exchange reaction on a β-ketoenamine linked COF. The time needed to achieve considerable linker exchange is much prolonged compared to other COFs with less stable linkages, however, this enables to achieve very good control on the ratio of the respective building blocks within the framework.

Aromatic Amine-Functionalized Covalent Organic Frameworks (COFs) for CO2/N2 Separation

CO₂ is a prominent example for an exhaust gas, and it is known for its high impact on global warming. Therefore, carbon capture from CO₂ emissions of industrial processes is increasingly important to halt and prevent the disruptive consequences of global warming. Covalent organic frameworks (COFs) as porous nanomaterials have been shown to selectively adsorb CO₂ in high quantities and with high CO₂/N₂ selectivity. Interactions with amines are recognized to selectively adsorb CO₂ and help capture it from exhaust emissions. Herein, a novel COF (Me₃TFB-(NH₂)₂BD), which was not accessible via a direct condensation reaction, was synthetized by dynamic linker exchange starting with Me₃TFB-BD. Despite the linker exchange, the porosity of the COF was largely maintained, resulting in a high BET surface area of 1624 ± 89 m²/g. The CO₂ and N₂ adsorption isotherms at 273 and 295 K were studied to determine the performance in carbon capture at flue gas conditions. Me₃TFB-(NH₂)₂BD adsorbs 1.12 ± 0.26 and 0.72 ± 0.07 mmol/g of CO₂ at 1 bar and 273 and 295 K, respectively. The COF shows a high CO₂/N₂ IAST selectivity under flue gas conditions (273 K:83 ± 11, 295 K: 47 ± 11). The interaction of the aromatic amine groups with CO₂ is based on physisorption, which is expected to make the regeneration of the material energy efficient.