Efficient and ultrafast separation of Li+ and Mg2+ by the porous two-dimensional nanochannel of perm-selective montmorillonite membrane

Abstract

Recent innovations have created various two-dimensional membranes to break the Li+/Mg2+ selectivity limit of traditional separation membranes. However, the simultaneous achievement of ultrafast transport and high selectivity is still below the theoretical prediction. Herein, for overcoming these shortcomings, the two-dimensional montmorillonite membrane (2D MMT membrane) consisting of sulfonated polyvinyl alcohol (SPVA), ethylene glycol (EG), and polyacrylamide (PAM) is proposed based on the design of porous 2D nanochannels. It is found that the SPVA can effectively improve the membrane stability, but will densify the channel, and prevent ion transport. When the appropriate EG is included in the membrane component, the transport rate of Li+ can be increased from 0.29 mol h−1 m−2 to 0.56 mol h−1 m−2. However, because the transport of Mg2+ needs to overcome the high dehydration energy barrier, the JMg2+ changes little, hence increases in SMg2+Li+ from 4.1 to 7.3. In addition, the selectivity regulation of PAM can be further integrated, and the permselectivity of the membrane is improved to 9.2 due to the strong selective coordination of amide groups to Mg2+. This novel strategy provides a valuable reference for developing high-performance 2D MMT membranes, which can also promote the application of 2D membranes in the Li+/Mg2+ separation.