Rare earth elements (REEs) are essential for many modern technologies. Separating REEs is a challenging, resource-intensive process. We are working to separate REEs using molecularly specific membranes. Previous attempts to prepare hyper-selective molecular membranes via molecular engineering were unsuccessful because they failed to control this higher-order structure. Recently, we have combined synthetic design and interfacial preorganization to produce nanofilms with the structural regularity needed for high-performance filtration. Membranes produced through this method were found to be ultra-specific (Å-size resolution) with high fluxes and good long-term stabilities, which enabled their unrivaled performance in pharmaceutical purification. Now we are using these design principles to systematically explore nanofiltration membrane designs for REE refining. This study will answer fundamental questions regarding ion-selective membrane separations such as, what is the interaction between nanochannel geometry and pore chemistry in REE dehydration and transmembrane transport? We hypothesize that selective REE transport will be achieved only in size-matched channels with balanced REE desolvation interactions. More broadly, developing the design principles needed to purify REE could yield membranes specific for enriching other dissolved minerals such as lithium or transition metals, which are also national security priorities. This work is funded by the Defense Advanced Research Projects Agency.

Key Papers in Molecularly Precise Membranes

Aligned macrocycle pores in ultrathin films for accurate molecular sieving, Jiang et al., Nature, 2022, 609, 58-64