Improved Efficiency and Stability of MXene Membranes via Interlayer Space Tuning for Oily Water Separation

Surfactant-stabilized oil-in-water emulsions are a major environmental concern due to their severe consequences for aquatic organisms and humans. Two-dimensional materials, particularly MXenes, are widely used in various applications and could be used in designing advanced membranes. The narrow interlayer spacing and intrinsic oxidation severely limit mass diffusion and induce poor stability, respectively, of MXene-based separating layers on the membrane support, rendering it challenging to use for oil-water separation. Herein, a high-performing, minimally defective MXene membrane with large d-spacing was fabricated. The d-spacing of the MXene sheets was controlled using Si-based species as the intercalating agents. The modified MXene-based membrane (ultrasonication-assisted exfoliated MXene with Si pillars) (U-MX-Si) exhibited an enlarged interlayer spacing of 11 Å, increased surface energy of 41 mJ·m^-2, and less defective separating layer compared to that of pristine MXene, which was due to enhanced interlayer spacing. This phenomenon induced a higher degree of exfoliated sheets that facilitated better MXene sheet self-assembly on the membrane support, thereby resulting in high separation efficiency (99%). An increase in the surface energy of the U-MX-Si membrane caused a constant permeate flux during operation, which demonstrated their practical implications. This study presents an important pathway for designing MXene-based membranes for separation applications.