Covalent Organic Framework–Covalent Organic Framework Bilayer Membranes for Highly Selective Gas Separation

Abstract

Covalent organic frameworks (COFs) have been proposed as alternative candidates for molecular sieving membranes due to their chemical stability. However, developing COF membranes with narrowed apertures close to the size of common gas molecules is a crucial task for selective gas separation. Herein, we demonstrate a new type of a two-dimensional layered-stacking COF-COF composite membrane in bilayer geometry synthesized on a porous support by successively regulating the growth of imine-based COF-LZU1 and azine-based ACOF-1 layers via a temperature-swing solvothermal approach. The resultant COF-LZU1-ACOF-1 bilayer membrane has much higher separation selectivity for H/CO, H/N, and H/CH gas mixtures than the individual COF-LZU1 and ACOF-1 membranes due to the formation of interlaced pore networks, and the overall performance surpasses the Robeson upper bounds. The COF-LZU1-ACOF-1 bilayer membrane also shows high thermal and long-time stabilities.

Fabrication of a Hydrogen‐Bonded Organic Framework Membrane through Solution Processing for Pressure‐Regulated Gas Separation

“…[3] During the last several decades, ordered porous materials such as zeolite, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs) have been successfully prepared into membranes for efficient gas separation, which can exhibit superior gas permeability and selectivity simultaneously. [4][5][6][7][8][9] However, this type of polycrystalline membranes are usually prepared via hydrothermal or solvothermal methods, which are challenging for scale-up, compared to the solution processing of polymer. Mixed-matrix membranes composed of polymers and inorganic microporous fillers are therefore under intensive study today, [10] while the issues of interfacial gaps and inhomogeneous dispersion still needs to be solved.…”

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built‐In Functions

“…This linkage yields another type of π‐conjugated COFs that contain integrated zwitterion units in the pore walls. We have explored azine linkages by the condensation of aldehydes and hydrazines for the designed synthesis of COFs (Figure ), which are promising for CO 2 capture, fluorescence, and photoinduced hydrogen evolution …”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…Diese Verknüpfung liefert einen weiteren Typ von π‐konjugierten COFs mit an den Porenwänden integrierten Zwitterioneneinheiten. Ferner untersuchten wir die Azinverknüpfung durch Kondensation von Aldehyd und Hydrazin für die spezifische Synthese von COFs (Abbildung ), die vielversprechend für die CO 2 ‐Abscheidung, Fluoreszenz und photoinduzierte Wasserstoffentwicklung sind …”

“…Ferner untersuchten wir die Azinverknüpfung durch Kondensation von Aldehyd und Hydrazin fürdie spezifische Synthese von COFs (Abbildung 10), [78] die vielversprechend fürd ie CO 2 -Abscheidung,F luoreszenz und photoinduzierte Wasserstoffentwicklung sind. [95][96][97] Vork urzem ist uns die Entwicklung einer C = C-Verknüpfung fürd ie Synthese von COFs gelungen (Abbildung 10). [85] Die sp 2 c-COFs sind vollständig p-konjugiert, und ihre Gerüste bestehen ausschließlich aus sp 2 -Kohlenstoffatomen, womit sie eine Plattform fürd as Design von photoelektrischen Materialien und Spinsystemen bieten.…”