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.