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 (TCA3-). 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.