# Effect of ligand alkyl chain length on lanthanide extraction using liposomes incorporating diglycolamic acid

## TL;DR

This paper introduces a new solvent-free method using liposomes to extract lanthanides efficiently and selectively.

## Contribution

The study demonstrates a solvent-free liposome-based system for lanthanide extraction with tunable stability via ligand alkyl chain length.

## Key findings

- Europium adsorption equilibrium occurs rapidly due to DGAA ligand head groups.
- Adsorption efficiency increases with DGAA concentration, requiring about three DGAA ligands per Eu(III) ion.
- Ligand incorporation stability depends on alkyl chain length, with longer chains providing better stability.

## Abstract

This study introduces an environmentally benign liposome-based extraction system that selectively separates and recovers lanthanides (Ln) without requiring an organic solvent. Recovery of Ln, particularly from high-level radioactive liquid waste streams, is critical for resource utilization and reducing long-term radiotoxicity. The proposed system incorporates highly Ln-selective diglycolamic acid (DGAA) ligands into phospholipid liposomes. Fluorescence spectroscopy demonstrated that europium (Eu) adsorption, mediated by the hydrophilic head group of the incorporated DGAA ligands, reached equilibrium almost immediately upon mixing. Inductively coupled plasma–mass spectrometry revealed that the adsorption efficiency increased with increasing concentration of incorporated DGAA. Approximately three DGAA ligands are required to adsorb one Eu(III) ion. The selectivity for heavy Ln was comparable to that of conventional DGAA-based solvent-extraction systems and was found to be independent of DGAA alkyl chain length. In contrast, the incorporation stability depended on alkyl chain length; for example, liposomes containing N,N-didodecyldiglycolamic acid retained the ligand without significant precipitation or fluorescence decrease for 7 days at concentrations up to 237 µM/g-egg lecithin. These findings establish liposome-based extraction as a flexible platform in which the ligand head group governs the adsorption characteristics while the alkyl chain length dictates the incorporation stability, providing a quantitative foundation for future solvent-free separation technologies.

The online version contains supplementary material available at 10.1007/s44211-026-00889-y.