Molecular insight into the separation mechanism of crown Ether-Based channels for lithium Extraction

The shortage of lithium resources can be effectively improved by using membrane separation technology to extract lithium from salt lake brines that contain rich Li. In this study, GO modified with functionalized crown ether group (2)-hydroxymethyl-15-crown-5,15C) was used as a separation membrane for Li+/Mg2+. The effect of 15C and its content on the separation mechanism of Li+/Mg2+ in membrane was designed and studied by molecular dynamics simulation. Improving water permeability of the membrane can be achieved with the appropriate amount of 15Cs, but an excessive amount of 15C will result in channel obstruction, which is not conducive to the transport of water molecules. In addition, the special recognition of Li+ by 15Cs enhances the transmission of Li+ within the channel. Finally, it is found that the dehydration behavior of Li+ is facilitated by the interaction between 15Cs and Li+. As the diameter of Li+ is smaller than the diameter of the 15C cavity, dehydrated Li+ passes through the 15C cavity with ease under pressure. This means that during the separation process, Li+ enters a "dual transport" mode. The membrane gains higher permeability for Li+ while blocking Mg2+. This study clarifies the rapid transport mechanism of Li+ in GO-15C,which provides a feasible strategy for designing highly selective Li+/Mg2+ separation membranes.