Organic-Acid-Mediated Growth of Oriented Membrane from 2D-Structured Zirconium MOF for CO₂ Separation

Two-dimensional structured metal-organic framework (2D-structured MOF) membranes with functionalized and ordered-direction pores hold significant promise for efficient CO₂ separation. However, the direct synthesis of such membranes remains a substantial challenge. Herein, we report a novel organic-acid-mediated conversion strategy for direct transformation of a preformed metal-organic gel (MOG) into an oriented membrane of 2D-structured MOF. The MOG is initially synthesized and subsequently dissociated to release Zr₆ clusters, which promotes the nucleation and growth of the MOF structure. Small organic molecules of formic acid are employed to modulate the coordination between Zr₆ clusters and 4,4',4″-tricarboxyltriphenylamine ligand (TCA^3-). By finely tuning the balance between crystallization and intergrowth kinetics, a highly oriented Zr-TCA membrane is fabricated, exhibiting excellent crystallinity and structural homogeneity. The resulting Zr-TCA membrane features nitrogen-functionalized, well-aligned pores oriented parallel to the direction of gas permeation; enabling outstanding CO₂/N₂ separation performance, with an exceptional CO₂ permeance of 1857.3 GPU and a high CO₂/N₂ selectivity of 39.2 at 0.12 MPa and 25 °C.