Lanthanide-Selective Artificial Channels.

Abstract

Lanthanides serve as essential elements for modern technology, playing critical roles in batteries, wind turbines, portable electronics, and energy-efficient lighting. Purifying lanthanides from ores and recycling them from end-of-life consumer materials are costly and damaging to the environment due to inefficient separation technologies. In this study, we present a new approach for lanthanide separations using supramolecular membrane channel nanopores based on a pillar[5]arene scaffold with appended diphenylphosphine oxide (DPP) ligands. These channels show high transport selectivity (>18:1) of the middle lanthanides, europium (Eu³⁺) and terbium (Tb³⁺) ions, over monovalent K⁺ ions and also excluded other common mono- and divalent metal ions (Na⁺, Ca²⁺, and Mg²⁺) including protons. These membrane channels also have high lanthanide-lanthanide transport selectivity with Eu³⁺/La³⁺ selectivity of >40 and Eu³⁺/Yb³⁺ selectivity of ∼30. Additionally, they demonstrated significantly higher selectivities between middle lanthanides and both light and heavy lanthanides: Tb³⁺/La³⁺ (∼140), Tb³⁺/Yb³⁺ (∼72), Tb³⁺/Nd³⁺ (∼58), and Eu³⁺/Nd³⁺ (∼17), which are considerably higher than selectivities reported in studies using traditional solvent extraction methods. Molecular dynamics simulations indicate that the high selectivity observed is due to specific water-mediated interactions between the hydrated ions and the channel. Our findings could contribute to ongoing efforts to improve lanthanide separation efficiency and reduce the environmental impact associated with current methods.