Spectroscopic and electrochemical studies on the complexes of urea ligands with uranyl (VI) and europium (III) in ionic
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Spectroscopic and electrochemical studies on the complexes of urea ligands with uranyl (VI) and europium (III) in ionic liquid Zong Guo1 · Xin Wu1 · Yupeng Liu1 · Shaowen Hu1 · Taiwei Chu1 Received: 29 June 2020 / Accepted: 2 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The spectroscopic and electrochemical behavior of the complex of tetraalkylurea ligands with uranyl(VI) and europium(III) in ionic liquid 1-butyl-3-methylimidazolium bis(tri-fluoromethylsulfonyl)imide ([Bmim][NTf2]) was studied. As the steric hindrance of the substituent increases, the number of ligands in the [UO2(L)n]2+ complex decreases, however, Eu(III) maintains 8-coordinated complexes [Eu(L)8]3+. The effect of urea ligands on the redox potential of Eu(III) is significantly greater than that of UO22+. Tetrabutylurea can better stabilize the low-valence Eu(II) and improve the redox reversibility of UO22+. Keywords Uranyl(VI) · Europium(III) · Tetraalkylurea ligands · Ionic liquid · Spectroscopy · Electrochemistry
Introduction In aqueous solution, uranium mostly exists in the form of hexavalent uranyl, and lanthanide (Ln) mostly exists in the form of trivalent lanthanide ions [1]. However, in crystals and non-aqueous solvents, uranium and lanthanide can also exhibit other valence states [2]. Ionic liquids [3] are a type of molten salts with melting points below 100 °C. Compared with traditional organic solvents, ionic liquids (IL) have wider electrochemical windows, so that different valence states of uranium and lanthanide can remain stable in ionic liquid [4]. The study of the electrochemical behavior of different valence uranium species in ionic liquids is one of the important concerns of applying ionic liquids in nuclear fuel cycling. Early research [5] showed that in the alkaline ionic liquid [BuPy][Cl/AlCl3], UO3 was easily dissolved in form Zong Guo and Xin Wu have contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10967-020-07441-w) contains supplementary material, which is available to authorized users. * Taiwei Chu [email protected] 1
Radiochemistry and Radiation Chemistry Key Laboratory of Fundamental Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
of [UO2Cl4]2− and underwent an irreversible two-electron reduction process. Ikeda et al. [6, 7] and Vasudeva et al. [8, 9] have studied the electrochemistry of [ UO2Cl4]2− in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), and found that [ UO2Cl4]2− exhibited a quasi-reversible redox process in [Bmim]Cl. The stable reduction product [UVO2Cl4]3− was confirmed by electrochemical and UV–visNIR spectroscopic methods in mixed [Emim]Cl/[Emim] [BF4] (Emim is 1-ethyl-3-methylimidazolium) ionic liquid system [10]. Studies have shown [11] that acidic aluminum chloride ionic liquid could stabilize divalent lanthanide metal ions, for instance, Sm(II), Eu(II), Tm(II) and Yb(II) could be obtained in A lCl3-[Bupy]Cl ionic liquid by electr
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