Role of alkyl substituent in room temperature ionic liquid on the electrochemical behavior of uranium ion and its local environment

Experimental and Theoretical Insight into the Ionic Liquid-Mediated Complexation of Trivalent Lanthanides with β-Diketone and Its Fluorinated Analogue

A multitechnique approach with theoretical insights has been employed to understand the complexation of trivalent lanthanides with two β-diketones, viz. 1-phenyl-1,3-butanedione (L1) and 4,4,4-trifluoro-1-phenyl-1,3-butanedione (L2), in an ionic liquid (C6mim·NTf2). UV-vis spectral analysis of complexation using Nd3+ revealed the predominance of ML2+ and ML4- species. The stability constants for the PB complexes were higher (β2 ∼ 10.45 ± 0.05, β4 ∼ 15.51 ± 0.05) than those for the TPB (β2 ∼ 7.56 ± 0.05, β4 ∼ 13.19 ± 0.06). The photoluminescence titration using Eu3+ corroborated the same observations with slightly higher stability constants, probably due to the higher ionic potential of Eu3+. The more asymmetric (AL2ML4 ∼ 5.2) Eu-L2 complex was found to contain one water molecule in the primary coordination sphere of Eu3+ with more covalency of the Eu3+-O bond (Ω2L1 = 8.5 × 10-20, Ω4L1 = 1.3 × 10-20) compared to the less asymmetric Eu-L1 complex (AL1ML4 ∼ 3.5) with two water molecules having less Eu-O covalency (Judd-Offelt parameters: Ω2L1 = 7.3 × 10-20, Ω4L1 = 1.0 × 10-20). Liquid-liquid extraction studies involving Nd3+ and Eu3+ revealed the formation of the ML4- complex following an 'anion exchange' mechanism. The shift of the enol peak from 1176 to 1138 cm-1 on the complexation of the β-diketones with Eu3+ was confirmed from the FTIR spectra. 1H NMR titration of the β-diketones with La(NTf2)3 evidenced the participation of α-H of the β-diketones and protons at C2, C4, and C5 positions of the methylimidazolium ring. For the ML2 complex, 4 donor O atoms are suggested to coordinate to the trivalent lanthanides with bond distances of 2.3297-2.411 Å for La-O, 2.206-2.236 Å for Eu-O, and 2.217-2.268 Å for Nd-O, respectively, while for the ML4 complex, 8 donor O atoms were coordinated with bond lengths of 2.506-2.559 Å for La-O, 2.367-2.447 Å for Eu-O, and 2.408-2.476 Å for Nd-O. The Nd3+ ion was higher by 9.7 kcal·mol-1 than that of the La3+ ion for the 1:4 complex. The complexation energy with L1 was quite higher than that with L2 for both 1:2 and 1:4 complexes. Using cyclic voltammetry, the redox behavior of trivalent lanthanides Eu and Gd with β-diketonate in ionic liquid medium was probed and their redox energetic and kinetic parameters were determined.

Electrochemical reduction of uranium and rhenium in hydrochloric acid system

The electrochemical reduction of U(VI) and Re(VII) ions on Pt and Mo metals are discussed. The electrochemical behavior of U(VI) and Re(VII) in hydrochloric acid media was investigated using various electrochemical techniques. By analyzing the cyclic voltammogram of U(VI) and Re(VII) recorded on Pt electrode, a series of electrochemical reactions associated with uranium and rhenium were recognized, indicating that U(VI) and Re(VII) undergoes a single-step electron and multistep electron process under experimental conditions, respectively. The reduction of U(VI) and Re(VII) was found to be controlled by charge transfer and diffusion in hydrochloric acid media. The diffusion coefficient of U(VI) and Re(VII)was determined to be 4.22–5.99 × 10−6 cm2 s−1 and 1.50–2.90 × 10−5 cm2 s−1, respectively, and the activation energy for the diffusion are calculated to be 18.12 kJ mol−1 and 14.52 kJ mol−1 by cyclic voltammetry at different temperatures. The reduction process of U(VI) and Re(VII) at hydrochloric acid is further studied by potentiostatic electrolysis. It is feasible to realize the reduction of uranium and rhenium from aqueous solution by electrolysis.

Thermal, electrochemical and radiolytic stabilities of ionic liquids

Ionic liquids show instability when exposed to high temperature, to high voltage as electrolytes, or under irradiation.

Toward a Greenish Nuclear Fuel Cycle: Ionic Liquids as Solvents for Spent Nuclear Fuel Reprocessing and Other Decontamination Processes for Contaminated Metal Waste

The final disposition of spent nuclear fuel (SNF) is an area that requires innovative solutions. The use of ionic liquids (ILs) has been examined as one means to remediate SNF in a variety of different chemical environments and with different chemical starting materials. The effectiveness of various ILs for SNF reprocessing, as well as the reaction chemistry that occurs in them, is discussed.

A trialkyl phosphine oxide functionalized task specific ionic liquid for actinide ion complexation: extraction and spectroscopic studies

A trialkylphosphine oxide functionalized task specific ionic liquid (PO-TSIL) with a NTf₂⁻ counter anion was synthesized and evaluated for the extraction of actinide ions such as UO₂²⁺ and Pu⁴⁺ from acidic feed solutions.