Mixed matrix membranes based on two-dimensional materials for efficient CO2 separation: A comprehensive review

Nowadays, CO2 emission, the major factor in global warming, is alarmingly on the rise. Hence, the international demand for state-of-the-art technologies to separate and capture CO2 is growing. Accordingly, mixed matrix membranes (MMMs), a new class of materials formed by incorporating nanofillers into the polymer matrices, have been demonstrated to be a promising and versatile platform for CO2 separation by taking synergistic advantages of nanoparticles and polymers. In recent years, two-dimensional materials (2DMs) have drawn a great deal of attention as efficient fillers of MMMs due to their high surface area, lamellar structure, and nanometer thickness. Besides these characteristics, some 2DMs like GO and MOF enjoy selective pores on their surfaces that act as transportation channels, facilitating CO2 permeation through MMMs. In this work, the stability and gas separation properties of MMMs containing different types of 2D fillers (including GO, MOF, COF, MXene, g-C3N4, clay, MoS2, etc.) are critically reviewed. Moreover, some novel 2D-structure materials, such as antimonene, as potential fillers of MMMs for gas separation applications were proposed. The most common strategies for raising the efficiency of 2DMs, such as surface modification, adjusting sheet thickness, changing interlayer size, manipulation of the pore size, organization/alignment, and filler hybridization, are comprehensively investigated. Finally, some remaining challenges and thought-provoking ideas for further improving the stability and performance of 2DM-based MMMs for CO2 separation are outlined.