Constructing Mechanical Shuttles in a Three-dimensional (3D) Porous Architecture for Selective Transport of Lithium...

Lithium (Li) extraction from brines is a major barrier to the sustainable development of batteries and alloys; however, current separation technology suffers from a trade-off between ion selectivity and permeability. Herein, a crown ether mechanically interlocked 3D porous organic framework (Crown-POF) was prepared as the porous filler of thin-film nanocomposite membranes. Crown-POF with penta-coordinated (four O_crown atoms and one N_tert-amine atom) adsorption sites enables a special recognition for Li⁺ ion. Moreover, the four N_tert-amine atoms on each POF branch facilitate the flipping motion of Li⁺ ion along the skeletal thread, while retaining the specified binding pattern. Accordingly, the crown ether interlocked POF network displays an ultrafast ion transfer rate, over 10 times that of the conventional porous materials. Notably, the nanocomposite membrane gives high speed and selectivity for Li⁺ ion transport as compared with other porous solid-based mixed-matrix membranes.