Supramolecular membrane channels for highly selective lanthanide separations

Supramolecular membrane channels built from pillar[5]arene scaffolds with specialized ligands selectively transport middle lanthanide ions like europium and terbium, enabling efficient, eco-friendly separation and recycling of rare-earth metals.

Background

Lanthanide elements are vital components in modern clean energy and electronics, finding applications in batteries, permanent magnets, lighting, catalysts, and medical imaging. Global demand for these metals has surged alongside the expansion of electric vehicles, wind turbines, portable devices, and advanced defense systems.

Despite their importance, natural ores contain closely related mixtures of lanthanides that show minimal differences in ionic radius and chemical behavior, making isolation of individual elements a formidable challenge. The growing push for renewable energy technologies and the need to recycle lanthanides from end-of-life products have intensified calls for more efficient, cost-effective, and environmentally benign separation methods.

Most industrial separation processes rely on solvent extraction and ion exchange, which typically require multiple stages and prolonged contact times to distinguish elements with nearly identical properties. These methods consume large volumes of organic solvents and strong acids, generate hazardous waste, and demand significant energy input for heating and recycling. The low intrinsic selectivity of existing resins and extractants often leads to lengthy, multistage workflows, high operational costs, and environmental burdens that hinder scalable, sustainable lanthanide purification.

Technology description

Supramolecular membrane channel nanopores built on a pillar[5]arene scaffold appended with diphenylphosphine oxide ligands enable highly selective lanthanide ion transport across lipid membranes. Two primary variants, featuring six- or ten-carbon alkyl tails, form artificial channels that facilitate rapid passage of middle lanthanides such as Eu³⁺ and Tb³⁺ while excluding monovalent and divalent ions (K⁺, Na⁺, Ca²⁺, Mg²⁺) and protons.

Control channels lacking the DPP ligand show minimal transport, demonstrating the critical role of the phosphine oxide moiety. Ion transport kinetics, patch-clamp measurements, stopped-flow fluorescence assays, and molecular dynamics simulations confirm the channels’ high selectivity performance and elucidate water-mediated interactions governing ion permeation. Compared to conventional solvent extraction, these channels achieve order-of-magnitude improvements in lanthanide–lanthanide discrimination, with Eu³⁺/La³⁺ selectivity exceeding 40 and Tb³⁺/La³⁺ selectivity over 140.

Chain length variation and ligand chemistry enable tunable pore architecture, while proton exclusion results from water dipole reorientation within the pore. Molecular dynamics and potential of mean force calculations reveal that specific hydration shell interactions drive exceptional selectivity, far surpassing traditional methods.

This modular, membrane-embedded architecture offers an energy-efficient, environmentally benign strategy for ore purification and recycling of end-of-life electronics, promising scalable solutions for critical rare earth separations.

Benefits

High transport selectivity for middle lanthanides over common mono‐ and divalent ions, enabling efficient purification
Exceptional lanthanide‐lanthanide discrimination (e.g., Eu³⁺/La³⁺ >40, Tb³⁺/La³⁺ >140) for high‐purity separations
Proton exclusion minimizes interference and stabilizes ion transport performance
Modular design (ligand chemistry and alkyl chain length) allows tunable selectivity
Eco-friendly alternative to solvent extraction, reducing cost and environmental impact
Direct applicability to ore beneficiation and recycling of end-of-life consumer materials

Commercial applications

High-purity lanthanide extraction
E-waste rare earth recovery
Permanent magnet purification
LED phosphor material purification
Automotive catalyst recycling

Additional information

Pillar[5]arene-based channels bearing diphenylphosphine oxide ligands via alkyl tails form membrane-embedded nanopores that transport Eu³⁺ and Tb³⁺ with >18:1 selectivity over K⁺, Na⁺, Ca²⁺, Mg²⁺. Variants with 6- or 10-carbon chains yield Eu³⁺/La³⁺ selectivity >40 and Eu³⁺/Yb³⁺ ~30. Proton exclusion arises from central water dipole reorientation. MD simulations and PMF analysis attribute selectivity to water-mediated ion–ligand interactions.