Stoichiometry of lanthanide-phosphate complexes at the water surface studied using vibrational sum frequency generation spectroscopy and DFT calculations

日下 良二; 渡邉 雅之

Journal of Physical Chemistry B, 125(24), p.6727 - 6731, 2021/06

https://doi.org/10.1021/acs.jpcb.1c04583

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.