Ultra-impregnable MXene/ChNC@TiO₂ Membrane for Oil/Water Microemulsion Separation and Photocatalytic Degradation of Dyes

TiO₂-coated chitin nanocrystals (TiO₂@ChNCs) inserted between two-dimensional (2D) nanosheets of MXene, and composite membranes with both oil/water emulsion separation and visible photocatalytic degradation of dyes, were prepared. TiO₂ was generated <i>in situ</i> on the surface of chitin nanocrystals (ChNCs) to obtain ChNC@TiO₂. Subsequently, polydopamine (PDA) was used as an adhesive to insert ChNC@TiO₂ into MXene nanosheets, followed by vacuum filtration to obtain the ChNC@TiO₂ membranes. With the addition of ChNC@TiO₂, the hydrophilicity and water permeance of the membrane were significantly improved. Due to the unique water channel structure formed by the insertion of the ChNC@TiO₂, the pure water permeance of the MXene/ChNC@TiO₂ composite membrane increased from 2450 L m^-2 h^-1 bar^-1 of the MXene membrane to 4480 L m^-2 h^-1 bar^-1. Oil/water separation experiments showed that the composite membrane could effectively separate various oil/water emulsions containing surfactants while maintaining excellent stability (with 1 M HCl and 1 M NaOH) and recyclability. In addition, due to the synergistic effect of MXene nanosheets and TiO₂ nanoparticles, MXene/ChNC@TiO₂ membranes exhibited excellent photocatalytic degradation properties under visible light for Congo Red (CR), Crystal Violet (CV), and Methylene Blue (MeB) trapped on the membrane. Our work provides new insights into the design of MXene-based separation membranes with self-cleaning capabilities for the separation of oil/water microemulsions and the photocatalytic degradation of organic dyes.