Uranyl Ion Extraction with Conventional PUREX/TRUEX Ligands Assessed by Electroanalytical Chemistry at Micro Liquid/Liquid Interfaces

Stability Series for the Complexation of Six Key Siderophore Functional Groups with Uranyl Using Density Functional Theory

Determining stability constants of uranyl complexes with the principal functional groups in siderophores and identifying stability series is of great importance to predict which siderophore classes preferentially bind to U^VI and, hence, impact uranium speciation in the environment. It also helps to develop resins for scavenging U^VI from aqueous solutions. Here, we apply a recently developed computational approach to calculate log β values for a set of geochemically relevant uranium organometallic complexes using Density Functional Theory (DFT). We determined the stability series for catecholate, hydroxamate, α-hydroxycarboxylate, α-aminocarboxylate, hydroxy-phenyloxazolonate, and α-hydroxyimidazole with the uranyl cation. In this work, the stability constants (log β₁₁₀) of α-hydroxyimidazolate and hydroxy-phenyloxazolonate are calculated for the first time. Our approach employed the B3LYP density functional approximation, aug-cc-pVDZ basis set for ligand atoms, MDF60 ECP for U^VI, and the IEFPCM solvation model. DFT calculated log β₁₁₀ were corrected using a previously established fitting equation. We find that the siderophore functional groups stability decreases in the order: α-hydroxycarboxylate bound via the α-hydroxy and carboxylate groups (log β₁₁₀ = 17.08), α-hydroxyimidazolate (log β₁₁₀ = 16.55), catecholate (log β₁₁₀ = 16.43), hydroxamate (log β₁₁₀ = 9.00), hydroxy-phenyloxazolonate (log β₁₁₀ = 8.43), α-hydroxycarboxylate bound via the carboxylate group (log β₁₁₀ = 7.51) and α-aminocarboxylate (log β₁₁₀ = 4.73). We confirm that the stability for the binding mode of the functional groups decrease in the order: bidentate, monodentate via ligand O atoms, and monodentate via ligand N atoms. The stability series strongly suggests that α-hydroxyimidazolate is an important functional group that needs to be included when assessing uranyl mobility and removal from aqueous solutions.

Trapped in the coordination sphere: nitrate ion transfer driven by the cerium(iii/iv) redox couple

The electrochemical transfer of nitrate anions between oil and water phases—driven by the reduction and oxidation of cerium coordination complexes in oil phases—provides a new entry into chemical separations where an electrode potential tunes solute transfer between phases by ‘trapping’ the migrating anion on the cerium cation.

Amperometric Ion Sensing Approaches at Liquid/Liquid Interfaces for Inorganic, Organic and Biological Ions

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) has become an invaluable tool for the selective and sensitive detection of cationic and anionic species, including charged drug molecules and proteins. In addition, neutral molecules can also be detected at the ITIES via enzymatic reactions. This chapter highlights recent developments towards creating a wide spectrum of sensing platforms involving ion transfer across the ITIES. As well as outlining the basic principles needed for performing these sensing applications, the development of ITIES-based detection strategies for inorganic, organic, and biological ions is discussed.

Recent developments in electrochemistry at the interface between two immiscible electrolyte solutions for ion sensing

The most recent developments on electrochemical sensing of ions at the liquid–liquid interface are reviewed here.

Electrochemical behaviour of ferrocenes in tributylmethylphosphonium methyl sulfate mixtures with water and 1,2-dichloroethane

Electron transfer (ET) reactions in ionic liquid (IL)|organic solvent (1,2-dichloroethane, DCE) and IL|water mixtures were investigated using a Pt disk ultramicroelectrode (UME) along with ferrocene (Fc) and ferrocenemethanol (FcCH2OH) redox probes as electroactive species dissolved in the respective mixtures. The IL utilized was tributylmethylphosphonium methyl sulfate (P4441CH3SO4). The diffusion coefficient of each redox species was determined at each incremental increase of DCE or water to the IL using a chronoamperometric technique that is concentration independent. The IL|DCE mixture exhibited little change in the Fc diffusion coefficient, DFc, up to a DCE mole fraction (χDCE) of 0.5; the observed value, 2.0 × 10−8 cm2 s−1, agrees well with that typically reported for ILs in the literature. After which, the DFc quickly rose to a value commonly found in conventional molecular solvents, 1.3 × 10−5 cm2 s−1 (at χDCE = 0.8). An analogous result was not observed for IL|water mixtures using FcCH2OH, such that [Formula: see text] varied from 0.2 to 1.2 × 10−9 cm2·s−1 at a [Formula: see text] of 0 to 0.8. It was proposed that a large increase in the DFc in the IL|DCE mixture versus [Formula: see text] in the IL|water series was owing to P4441CH3SO4’s more hydrophobic character. Its hydrophobicity was quantified by measuring the formal ion transfer potentials of the IL component ions at a water|DCE immiscible interface.

Formal transfer potentials of strontium and uranyl ions at water|1,2-dichloroethane interfaces

The extraction of dioxouranium (UO22+), or uranyl, and strontium (Sr2+) ions from spent nuclear fuel (SNF), often through a biphasic (aqueous / organic solvent) ligand assisted process, is critical for the implementation of a closed-loop nuclear fuel cycle whereby SNF is diverted from permanent geological disposal and the life of the nuclear industry is extended. Deeper understanding of the biphasic extraction process can be achieved through facile electrochemical experiments at a liquid|liquid interface. Of primary importance to developing a quantitative analysis of the ligand assisted or facilitated ion transfer (FIT) (i.e., transfer through interfacial complexation) case is to first quantify the free or simple metal IT; that is the amount of applied potential required to “push” ions across the water|organic interface. This value is, in fact, a constant referred to as the formal transfer potential ([Formula: see text]), which is unique to each metal ion in the biphasic system. Because of their hydrophilicity they often limit the polarizable potential window. Values for [Formula: see text], for the most part, have only been estimated. With a microinterface housed at the tip of a 25 µm capillary it is possible to reduce the Faradaic current to observe their transfer. Herein is described the quantification of [Formula: see text] and [Formula: see text] or the formal transfer potentials for dioxouranium and strontium ions, respectively.