Modifying polysulfone dual-layer hollow fiber membrane with amine-functionalized bimetallic MOF (PEI@HKUST-1(Cu, Mg)) for improved mechanical stability and CO2/CH4 separation performance

Abstract

As the demand for cleaner energy sources and carbon dioxide (CO₂) capture technologies increases, membrane-based separation is increasingly seen as a viable, scalable, and eco-friendly option. However, fabricating mechanically stable membranes with high permeance and selectivity remains a significant challenge, owing to the limited CO₂ affinity sites and transport channels inside the membrane. This study investigates integrating the unique properties of metal-organic frameworks (MOFs) with the structural benefits of dual-layer hollow fiber (DLHF) membranes. Herein, a polyethyleneimine (PEI) functionalized bimetallic MOF (PEI@HKUST-1(Cu, Mg)) as filler was blended to polysulfone(PSf) matrix to fabricate MOF/PSf mixed matrix membrane (MMM) through co-extrusion and dry-jet wetting spinning process. The open metal sites (Cu²⁺ and Mg²⁺), high porosity, and the CO₂-philicity of the amine groups of the PEI-functionalized MOF could create additional CO₂ binding sites and transport channels, thus promoting the rapid permeation of CO₂ molecules through the membrane. The improved affinity among the organic linker, amines group, and polymer chains facilitated the formation of defect-free hollow fibers. Notably, the tensile strength increases from 4.51 MPa to 8.78 MPa for pure membranes to 10 wt% MOF-loaded membranes, showing a direct correlation between fiber strength and MOF loadings. The optimized membrane containing 5 wt% PEI@HKUST-1(Cu, Mg) exhibited a CO₂ permeance of 28 GPU and a CO₂/CH₄ selectivity of 51, displaying an increase of 75 % and 85.45 %, respectively, over the pure PSf membrane. These findings suggest that incorporating amine-functionalized MOFs can enhance the CO₂ separation performance and mechanical stability of hollow fiber membranes used in natural gas purification.