Two-dimensional graphene oxide/MXene lamellar membrane cross-linked by urea with adjustable interlayer spacing for efficient dye rejection and ion sieving

Two-dimensional (2D) membranes demonstrate good performance in molecular and ion separation due to their unique layer structure. However, the sieving performance of 2D membranes is severely limited by drawbacks such as poor stability and low mass transfer rates. Here, we propose a design strategy using urea as a cross-linking agent to construct stable and regular nanochannels inside the graphene oxide/MXene (GO/MXene) composite membranes. More importantly, by changing the composition, the effective interlayer spacing of the membrane can be easily adjusted within 4.47-8.92 & Aring; with angstrom-level precision for tunable ion sieving. The composite membrane exhibits high water permeance (79.58 L m(-2) h(-1) bar(-1)) and excellent small molecule dye rejection (>99 %). Moreover, depending on the ionic valence state, the membrane exhibits significant ion sieving. The good Cl-/SO42- selectivity (11.64) makes it a promising alternative to conventional ion exchange membranes. This study demonstrates an innovative and facile way to construct 2D lamellar membranes with stable structures for efficient and precise separation.