(539b) A Click Chemistry-Based Membrane Platform for Selective Separations

Critical minerals like rare earth elements (REEs) are crucial for many modern applications and clean energy technologies. The current state-of-the-art for obtaining these minerals is solvent extraction. This separation technique is costly and has environmental drawbacks as it produces mixed, organic waste and leaves a large carbon dioxide footprint. Solid-phase separation, i.e. adsorptive or chromatographic columns are an alternative to solvent extraction. Recently, Lanmodulin protein (12,000 Da), a REE-binding protein with high affinity, has been studied on a resin support. An alternative approach to achieve still higher throughput and higher capacity per mass of adsorber is to covalently tether lanmodulin peptides (1,600 Da) on membrane scaffolds.

In this work, two approaches were taken for installing the peptide functionality on the membrane. First, allyl methacrylate (AMA) brushes were grafted from electrospun poly(vinylbenzyl) chloride (PVBC) membranes via controlled polymerization, AGET-ATRP. Once poly(AMA) was grafted, cysteine was attached to the brushes via thiol-ene click reaction using a UV initiator. Cysteine is used as a model ligand because it is the terminal end group of the engineered lanmodulin peptide. In a second approach, model cysteine was clicked to an allyl-containing aromatic polymer synthesized by collaborators at Arizona State University. Membranes were characterized by ATR-FTIR, Raman spectroscopy, and XPS to observe changes in surface chemistry as a result of functionalization reactions. NMR and XPS provided quantitative evidence for the yield of the thiol-ene click reactions. Specifically, XPS shows definitive peaks for S-C bond formation confirming the click reaction. The synthetic protocols established for cysteine were extended to the lanmodulin peptide. Equilibrium adsorption experiments are underway to quantify the adsorption capacity and affinity of the membrane-bound lanmodulin peptide. These synthetic strategies are laying the groundwork for bio-inspired membrane adsorbers designed for REE purification and other applications that require covalently tethered selective ligands.