Understanding the Role of Microstructure in Ti₃C₂T_<i>x</i> MXene Membrane Performance

Ti₃C₂T_<i>x</i> MXene membranes have attracted considerable interest for separation technologies owing to their well-defined and tunable interlayer channels. However, reported water permeability values vary widely, suggesting the presence of additional, unrecognized factors influencing water transport. In this study, we demonstrate that both the dynamic microstructure of MXene membranes under pressure and the flake size of Ti₃C₂T_<i>x</i>, used in fabrication play critical roles in determining water flux. We observed a substantial decline in water permeability, from tens of L/m²·bar·h to below 5 L/m²·bar·h, during filtration, attributed to compaction of the initially loose membrane structure. Notably, the change in the microstructure is reversible, with the disordered microstructure recovering after drying. Moreover, MXene flake size is found to impact the tortuosity of water pathways, where membranes constructed from smaller flakes exhibit higher permeability. For example, membranes fabricated with an average flake size of 4 μm achieved water permeabilities 2.15 times lower than those made with 0.17 μm flakes. These findings underscore the complex interplay between microstructure dynamics, flake size, and liquid transport, offering key insights for the rational design of high-performance MXene-based separation membranes.