The Organic Phase Drives Metal Complex Dehydration at Liquid–Liquid Interfaces through Hydrophobic Interactions in Solvent Extraction

High Resolution Image Download MS PowerPoint Slide Dehydration is a critical step in transferring hydrated metal ions from the aqueous phase to the organic phase, typically facilitated by complexation with amphiphilic extractants. Here we reveal a distinct, hydrophobically driven dehydration mechanism at the liquid–liquid interface, in which the organic (oil) phase promotes metal complex dehydration through molecular interactions between extractant alkyl chains and the alkane solvent. In a representative Eu 3+ –di(2-ethylhexyl)phosphoric acid (HDEHP) extraction system, vibrational sum-frequency generation (VSFG) spectroscopy demonstrates that Eu in interfacial complexes becomes less hydrated in the presence of n -dodecane, correlating with enhanced ordering of the interfacial alkyl chains. These results establish that hydrophobic interactions organize the interfacial environment to drive metal dehydration, providing new mechanistic insight into the molecular origins of liquid–liquid extraction.