High-Surface-Area ZIF-67 Nanoflowers: Synthesis and Application Toward Enhanced CH4/N2 Separation in Mixed Matrix Membranes

Abstract

Under elevated loading conditions, the aggregation of fillers emerges as a pivotal factor driving the degradation of separation performance in mixed matrix membranes. The two-dimensional (2D) modification of fillers, aimed at enhancing interfacial contact with polymers, has been recognized as an effective strategy to improve interphase compatibility and increase filler loading capacity. However, it is worth noting that the BET surface area of 2D fillers is typically relatively low. In this study, a two-step approach was developed. First, a “diffusion-mediated” process was combined with a solvent optimization strategy based on first-principles (DFT) calculations, achieving a 20-fold suppression in ZIF-67 nucleation-crystallization rate. This enabled the successful synthesis of a 2D amorphous nanoflower structure. Subsequently, the processing parameters were fine-tuned to enhance the specific surface area of ZIF-67 to 403 m2/g while preserving its 2D structural integrity. Ultimately, the as-prepared 2D ZIF-67 was incorporated into a hydrogenated styrene-butadiene block copolymer (SEBS) matrix to fabricate a mixed matrix membrane. Remarkably, at a filler loading of 20 wt%, the CH4 permeability coefficient increased significantly from 11.7 barrer to 35.3 barrer, while the CH4/N2 selectivity was maintained at 3.21, indicating minimal interfacial defects and demonstrating the feasibility and effectiveness of the proposed methodology.