Rationally Designed Biomolecules for the Interfacial Separation of Rare Earth Elements

Currently, solvent extraction is commonly used for separation of rare earth elements, transferring the trivalent cations (REEs) from an aqueous phase into an organic solvent. This process is energy intensive and environmentally unfriendly, requiring large volume of organic solvents and organo-phosphate-based surfactants. The talk will describe our efforts to exploit the high affinity of a surface-active Lanthanide Binding Tag (LBT) peptide that coordinates selectively with REE ions for its use in bioinspired/eco-friendly extraction processes. Additionally, to enhance the surface activity and identify the bound cationic species at the air-aqueous interface, we redesigned the LBT peptide adding a short hydrophobic tri-amino acid sequence. X-ray reflectivity and x-ray fluorescence near total reflection measurements on the adsorbed layer were used to compute the surface concentration of the peptide, the surface concentration of the Ln³⁺ cation, and electron density profile of the interfacial layers. We demonstrate that we can capture the selectivity of LBT peptides, and we can enhance the surface activity of the peptides through the rational design of both hydrophobicity and net charge. The ability to tune the amino acid sequence of these surface-active molecules to either improve their surface adsorption and/or selectivity with REEs could be advantageous for an eco-friendly, selective separation method of REEs.