Facile Preparation of Mixed-Matrix Membrane for Highly Selective Separation of CO2 via a Defected Zr-MOF Fluorination-Modified Strategy

Abstract

To address increasing climate deterioration, it is of great value to prepare highly permselective separation membranes for CO₂ enrichment and separation. In this study, zirconium-based metal-organic frameworks (Zr-MOFs) containing defective structures (defected-UiO-66-NH₂, D-UN) with a high volume yield (12 g L^–1 in a single batch) were prepared at room temperature for the first time using a simple green-synthesis strategy. After the modification with pentafluorobenzaldehyde, the fluorine-containing D-UN (named F-g-UN) nanoparticles showed the characteristics of local and dense distribution of fluorine elements. Due to the optimized CO₂ affinity and improved dispersion of fluorination modification, the prepared mixed-matrix membrane (MMM) F-g-UN@AO-PIM-1 achieved synergistic improvement in CO₂ permeability and selectivity, exceeding the 2008 Robeson upper bound (CO₂ 664.1 Barrer and CO₂/CH₄ 34.2) and the 2018 binary CO₂/CH₄ mixed-gas upper bound (CO₂/CH₄ 28.7). The substantial cause was the introduction of fluorine species, verified by relevant experiments and mechanism analyses such as CO₂ adsorption. This work proves the feasibility of using crystal defect engineering and post-treatment strategies to enhance separation functions and offers new insights into designing efficient and low-cost MMMs for gas separation, promoting their application in separation membranes including but not limited to gas separation.