Lanthanide-Dependent Self-Assembly of Ion-Extractant Complexes at Liquid Interfaces: Inversion or Exclusion?
- 1Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States.
- 2Ames National Laboratory, Iowa State University, Ames, Iowa50011, United States.
- 3NSF's ChemMatCARS, Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois60637, United States.
Abstract
The separation of lanthanide elements by solvent extraction is traditionally governed by differences in the thermodynamic stability of extracted complexes; however, ion-specific interfacial complexation can play an important role in determining selectivity in kinetic separations. Nevertheless, the structural and chemical origins of such interfacial selectivity remain poorly understood. In this work, we combine sum frequency generation (SFG) vibrational spectroscopy with X-ray scattering to resolve interfacial structures of extractant-ion complexes at liquid surfaces. Measurements across pH and lanthanide concentration regimes reveal how changes in aqueous conditions alter the molecular organization of interfacial bis(2-ethylhexyl) phosphoric acid (HDEHP)-lanthanide ion complexes. Across the lanthanide series, light lanthanide ions, e.g., those from La to Dy, tend to form relatively ordered monolayers with HDEHP as characterized by strong CH and weak OH vibrational signals with corresponding electron density profiles and surface ion concentrations. In contrast, heavy lanthanide ions, e.g., those from Er to Lu, tend to produce more disordered interfacial assemblies as reflected by weaker CH stretches, stronger OH signals that are accompanied by surprisingly low lanthanide ion surface densities. These systematic, structural, and chemical differences suggest that HDEHP-heavy lanthanide complexes are more readily organized into increasingly centrosymmetric structures that are poised for transport, explaining their apparent absence at liquid-liquid interfaces at equilibrium. These results establish interfacial organization as a key factor governing lanthanide extraction chemistry and point to kinetic handles to impart unconventional selectivity.
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BibTeX
@article{sun2026lanthanidedependent,
title = {{Lanthanide-Dependent Self-Assembly of Ion-Extractant Complexes at Liquid Interfaces: Inversion or Exclusion?}},
author = {Pan Sun and Uvinduni I Premadasa and David Walwark and Wei Bu and Benjamin Doughty},
journal = {The journal of physical chemistry. B},
year = {2026},
month = oct,
doi = {10.1021/acs.jpcb.6c03936},
url = {https://europepmc.org/article/MED/42917247},
note = {CC BY},
}
RIS
TY - JOUR
TI - Lanthanide-Dependent Self-Assembly of Ion-Extractant Complexes at Liquid Interfaces: Inversion or Exclusion?
AU - Pan Sun
AU - Uvinduni I Premadasa
AU - David Walwark
AU - Wei Bu
AU - Benjamin Doughty
PY - 2026
DA - 2026/10/01
JO - The journal of physical chemistry. B
DO - 10.1021/acs.jpcb.6c03936
UR - https://europepmc.org/article/MED/42917247
AB - The separation of lanthanide elements by solvent extraction is traditionally governed by differences in the thermodynamic stability of extracted complexes; however, ion-specific interfacial complexation can play an important role in determining selectivity in kinetic separations. Nevertheless, the structural and chemical origins of such interfacial selectivity remain poorly understood. In this work, we combine sum frequency generation (SFG) vibrational spectroscopy with X-ray scattering to resolve interfacial structures of extractant-ion complexes at liquid surfaces. Measurements across pH and lanthanide concentration regimes reveal how changes in aqueous conditions alter the molecular organization of interfacial bis(2-ethylhexyl) phosphoric acid (HDEHP)-lanthanide ion complexes. Across the lanthanide series, light lanthanide ions, e.g., those from La to Dy, tend to form relatively ordered monolayers with HDEHP as characterized by strong CH and weak OH vibrational signals with corresponding electron density profiles and surface ion concentrations. In contrast, heavy lanthanide ions, e.g., those from Er to Lu, tend to produce more disordered interfacial assemblies as reflected by weaker CH stretches, stronger OH signals that are accompanied by surprisingly low lanthanide ion surface densities. These systematic, structural, and chemical differences suggest that HDEHP-heavy lanthanide complexes are more readily organized into increasingly centrosymmetric structures that are poised for transport, explaining their apparent absence at liquid-liquid interfaces at equilibrium. These results establish interfacial organization as a key factor governing lanthanide extraction chemistry and point to kinetic handles to impart unconventional selectivity.
SN - 1520-6106
SN - 1520-5207
ER -