Subnanometer-scale control of channel height in two-dimensional montmorillonite membrane for ion separation

Two-dimensional (2D) membranes with ordered interlayer channels have shown a huge potential in ion separation. However, the effective, arbitrary, and precise control of channel height is still challenging. Herein, the cetyltrimethylammonium chloride (CTAC) is proposed for the intercalation of montmorillonite with certain interlayer spacing, which enables the feasible preparation of a 2D membrane for efficient ion separation. The intercalated CTAC plays a significant role in stabilizing the ion transport channels because its hydrophobic end enhanced the swelling resistance of the membrane. In addition, the channel with any height from 0.40 nm to 0.52 nm can be precisely controlled by changing the CTAC dosage. When the channel height is controlled from 0.504 nm to 0.440 nm, the separation factor of Na+/Cs+ could be improved from 190.99 to 1039.79. This strategy realizing the precise and facile control over the channel height in the subnanometer scale provides a reference for efficient ion separation by using 2D membranes. [Display omitted] •CTAC-modified 2D MMT membrane with ordered interlayer channels is prepared.•CTAC significantly prolongs the stability of the membrane in water.•Channel with any height in 0.40–0.52 nm is controlled by changing CTAC dosage.•Na+ and Cs + can be effectively separated by controlling the channel height.