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.

Keywords: ion channels; lanthanide–lanthanide separations; nanopores; pillar[5]arene; rare earth elements.