Two-dimensional (2D) membranes have demonstrated potential for molecular separation; however, their applicability for Li/Mg ion separation has been restricted by their negatively-charged and easily-swellable properties in water. Moreover, their practical application has been hindered by the challenge of producing significant quantities of single-layer nanosheets. To overcome these challenges, we have developed a scalable method for synthesizing micro-sized nitrate ZnAl layered double hydroxide (LDH) and subsequent exfoliating to yield monolayer nanosheets for the construction of 2D membranes. The sub-nanometer channels of the LDH membrane is positively charged, which prevents the passage of magnesium ions. These channels also impede the flow of magnesium ions that are more difficult to dehydrate. As a result, the LDH membranes exhibit robust lithium-magnesium separation ability, with a separation ratio of 6 (Li/Mg). This work provides a method for producing high-quality LDH nanosheets and validates the enormous potential of LDH membranes in the field of lithium-magnesium separation.

Two-dimensional (2D) nanosheets with thickness of one to several atoms serve as ideal building units for separation membranes. Herein, we report the construction of ultrathin membranes with layered double hydroxides (LDHs) nanosheets, polyacrylic acid (PAA) and polyethyleneimine (PEI) alternately deposited on porous substrates. The chemical tuning of PEI leads to an accurate regulation of interlayer spacing in angstrom scale, resulting in selective nanochannels for CO2 permeation. The laminar membranes with CO2 transport-facilitated channels exhibit excellent gas separation performance and exceed the limit of the state-of-the-art membranes with CO2 permeance of 1068 GPU, CO2/N2 and CO2/CH4 selectivity of 126 and 330 respectively. A synergistic effect of solution-diffusion and molecular sieving was proposed for this prominent CO2 separation performance. The strategy demonstrated in this work would open up new avenues for effective CO2 separation and capture in recycling of carbon resources.

Stretchable gas barrier films achieved by hydrogen-bond self-assembly of nano-brick multilayers