Binary-filler engineering of ZIF-8 and mesoporous silica in PEBAX mixed-matrix membranes toward enhanced CO2 separation performance

Abstract

Mixed-matrix membranes (MMMs) incorporating porous fillers provide an effective strategy to overcome the permeability–selectivity trade-off in polymeric membranes for CO₂ separation. However, single-filler systems often exhibit intrinsic limitations, where microporous fillers tend to enhance selectivity at the expense of permeability, while mesoporous fillers generally improve permeability but provide limited selectivity enhancement. In this study, a binary-filler system consisting of microporous ZIF-8 (1.5 wt%) and mesoporous silica (0–0.5 wt%) was introduced into a Pebax-1657 matrix to investigate their distinct and cooperative roles in regulating gas transport behavior and mechanical properties. Structural characterization confirmed uniform filler dispersion and modulation of segmental packing without altering the intrinsic polymer framework. ZIF-8 enhanced CO₂/N₂ selectivity through preferential CO₂ adsorption, while mesoporous silica introduced additional diffusion pathways that improved gas permeability. The silica loading significantly influenced both permeability and selectivity, and an optimal silica content of 0.25 wt% yielded a CO₂ permeability of 136 Barrer with a CO₂/N₂ selectivity of 73.4, approaching the 2008 Robeson upper bound. In addition, the binary-filler membrane exhibited improved mechanical flexibility and stable separation performance over 7 days of continuous operation. These results demonstrate that binary-filler engineering provides an effective strategy for developing high-performance Pebax-based MMMs for carbon capture applications.