An azine-linked covalent organic framework ACOF-1 membrane for highly selective CO2/CH4 separation

Abstract

Covalent organic frameworks (COFs) are promising for constructing gas-separation membranes due to their versatile architectures, customizable functionalities and chemical stabilities. However, synthesis of continuous COF membranes still remains a challenge and rather underexplored. Herein, we present a two-dimensional (2D) azine-linked ACOF-1 membrane synthesized on a porous support by a solvothermal approach. The ACOF-1 membrane with a thickness of 8 μm shows a high selectivity of 86.3 in CO₂/CH₄ mixed gas separation with a favorable CO₂ permeance of about 9.9 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹, and the overall performance exceeds the Robeson upper bound (2008). This surprising molecular sieving effect is attributed to an effective narrowing of the pore diameter (0.94 nm) owing to crystal intergrowth. A long-term test of gas permeation demonstrates the outstanding stability of the ACOF-1 membrane. These properties recommend the ACOF-1 membrane for CO₂ capture and other gas separations.