National Renewable Energy Laboratory,
Keywords: rare earth separations, photochemical, light-driven, ligands, extractants
Summary:Industrial separations of critical lanthanide elements, or rare earths (REs), based on cation-size are not sustainable and create large amounts of solvent, energy, and time waste. We have developed an innovative approach that aims to use light to drive photophysical and photochemical reactions that could ultimately be used for the separations of similarly sized RE ions, exploiting the unique optoelectronic properties of REs. This strategy taps into the distinctive and discontinuous electronic structures of well-shielded 4f orbitals of the individual RE ions, via dynamic and element specific photo-induced modifications of the chemical environment surrounding the metal ions. We have synthesized ligands with tailored chemical and physical motifs that will enable demonstration of efficient modulation of excited-state photochemical reactions via control of (i) large, dynamic excited-state perturbations of the photophysical properties of the complexes or (ii) sensitization of ligand-centered photochemical reactions. Our work will expand our understanding and manipulation of excited-state energy flow in lanthanide complexes, to permit control of solubility and separability, ultimately opening up the possibility of a new paradigm for energy, time, and resource-efficient separations of critical rare earth elements.