Unraveling the coordination approach of Eu(iii) in cyphos nitrate ionic liquid – a comprehensive luminescence spectroscopy study

Abstract

In consideration of the mounting attention drawn by the ionic liquid cyphos 101 (trihexyl(tetradecyl)phosphonium chloride: [P₆₆₆₁₄][Cl]) in the recovery of rare earth metals and other valuable species from their waste matrices, an effort was made using luminescence spectroscopy to study the detailed liquid–liquid extraction and coordination behavior of Eu(III) using the nitrate form of cyphos 101 (cyphos nitrate: [P₆₆₆₁₄][NO₃]) in its undiluted form. Eu(III) complexation with [P₆₆₆₁₄][NO₃] at each stage of the extraction process was investigated using the luminescence spectroscopy technique. Various extraction parameters such as aqueous phase acidity, concentrations of ionic liquid extractant and initial Eu(III) ion, extraction time, experimental temperature, etc. were tuned to discover their impact on the complexation process. The uniqueness of the nitrate ion in ionic liquid was explored by comparing the emission patterns of Eu(III) with [P₆₆₆₁₄]-based ionic liquids containing different anions. In addition, the affirmative effect of increasing the initial aqueous phase nitrate ion concentration in the coordination process was underscored by comparing the emission patterns in the chloride medium. The luminescence results of the Eu(III)– [P₆₆₆₁₄][NO₃] complex were compared both in unirradiated and irradiated ionic liquid phases. Asymmetry ratio (AR) and lifetime data under each experimental condition were ascertained, thereby revealing the precise nature of complex formation and strength of the metal–solvate species (metal–ligand complex formation) formed. The stripping of the loaded Eu(III) from the [P₆₆₆₁₄][NO₃] phase was established and the results were presented in the form of the emission patterns of Eu(III) in both phases.