Fabrication of polymer-supported ZIF-8 membranes via interfacial-epitaxial coupled growth for C₃H₆/C₃H₈ separation

The fabrication of polymer-supported metal-organic framework (MOF) membranes is a promising approach for efficient C₃H₆/C₃H₈ separation. However, the main obstacles to construct MOF layers are low nucleation density at substrate interface and uncontrolled crystal growth, which hinders the concurrent attainment of a defect-free structure and an ultrathin separation layer. Herein, we report a synergistic strategy combining coordination anchoring with interfacial-epitaxial coupled (IEC) growth. Initially, a polyacrylic acid (PAA) functional layer was introduced onto the substrate surface to achieve coordination anchoring of Zn²⁺ ions. Subsequently, an asymmetric concentration gradient of reactants was established at the surface of substrate through contra-diffusion growth, confining the nucleation of ZIF-8 crystals strictly to the interfacial region. This process culminated in in-situ growth in a high-concentration ligand environment, promoting epitaxial crystal growth and repairing intercrystalline microdefects, thereby enhancing the crystallinity and structural order of the MOF layer. The optimized membrane achieved a high C₃H₆ permeance of 417.1 GPU with a C₃H₆/C₃H₈ selectivity of 36.3 for equimolar C₃H₆/C₃H₈ mixtures, along with excellent thermal stability, pressure resistance, and long-term operational stability. This work highlights the synergistic regulation of MOF growth via confined nucleation and interfacial engineering and develops a novel strategy for the controlled fabrication of defect-free MOF membranes on flexible substrates.