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Stoichiometry of Lanthanide–Phosphate Complexes at the Water Surface Studied Using Vibrational Sum Frequency Generation Spectroscopy and DFT Calculations

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journal contribution
posted on 14.06.2021, 14:10 authored by Ryoji Kusaka, Masayuki Watanabe
In the solvent extraction of metal ions, the transport mechanism of metal ions through the liquid–liquid organic/aqueous interface remains unclear. In this study, the adsorption process of trivalent lanthanide ions from the aqueous phase to the interface in the solvent extraction of lanthanides with di­(2-ethylhexyl)­phosphoric acid (HDEHP) extractant is investigated by using a model interfacewater surface covered with HDEHP (air/HDEHP/aqueous interface). As a result, symmetric POO stretch signals of HDEHP observed by vibrational sum frequency generation spectroscopy and density functional theory calculations show that the stoichiometric ratio of lanthanide–HDEHP complexes formed at the air/HDEHP/aqueous interface is 1:1. The formation of the interfacial 1:1 lanthanide–HDEHP complex could be an elementary chemical process occurring just before the transfer of lanthanide ions to the side of the organic phase.