UiO-Based Mixed Matrix Membranes for Efficient CO₂ Separations

Mixed matrix membranes (MMMs) containing UiO-type metal-organic frameworks (MOFs) have shown excellent potential for CO₂ separation processes due to their unique permeability and selectivity properties. However, while the performance of MOF-based MMMs has been widely studied, the effect of structural defects and polymer-filler compatibility are not yet fully understood. In this work, the CO₂ separation performance of Pebax MH1657-based MMMs is systematically evaluated incorporating 5-20 wt% of Zr-based MOF, including UiO-66, UiO-67, and two defect-engineered UiO-66 analogues, featuring extended linker (UiO-66_A) or cluster (UiO-66_F) vacancies. The structural, morphological, and thermal properties of the membranes are thoroughly characterized, with emphasis on correlating these features with gas transport performance. Single-gas permeation experiments (CO₂, CH₄, H₂) reveal that incorporating UiO nanoparticles within the matrix consistently enhanced CO₂ permeability, reaching 145 Barrer for the 20 wt% UiO-66_F MMM, a 216.4% increase over the neat membrane. CO₂/CH₄ and CO₂/H₂ selectivities also improve upon increasing MOF loadings, with UiO-66_F achieving values of 25 and 18, respectively. This study provides insights for designing high-performance MMMs for CO₂ separation applications, such as biogas upgrading and hydrogen purification.