ABSTRACT
Several mixtures of butyl acetate (BA) and an ionic liquid (1-methyl-3-octylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C1C8Pyrro][NTf2], 1-octyl-pyridinium bis(trifluoromethylsulfonyl)imide, [C8Pyr][NTf2], 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C1C4Im][NTf2] or 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C1C8Im][NTf2]) have been characterized by measuring density, viscosity and conductivity, from pure BA to pure ILs at 298.15 K. The ionicity of these mixtures has been determined on the basis of electrical conductivity and NMR spectroscopy. IR spectra of these mixtures were used to examine the interactions between ions. In parallel, Pt(iv) was extracted from the acidic aqueous phase towards mixtures of BA and [C1C8Im][NTf2] over the entire composition range. A drastic modification in the distribution coefficient of Pt(iv) was observed at ca xAB = 0.8. A drop was also observed in the ionicity of the extracting phase (IL + BA) at a similar composition. The variation of the distribution coefficient is ascribed to changes in the interactions in the mixtures, which in turn could induce changes in the extraction mechanism.
ABSTRACT
A thorough investigation of the reference electrodes for electrochemical measurements is presented in three ionic liquids (ILs), namely 1-butyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide [BMIM][Tf2N], 1-octyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide [OMIM][Tf2N] and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide [BMPyrr][Tf2N]. The influence of technical aspects such as internal resistance, scan rate and concentration of the active species on cyclic voltammetry has been investigated using three quasi-reference electrodes (QREs) (AgCl, Pt, and Pd) and three reference electrodes (REs) (Fc(+)/Fc/Pt, Ag(+)/Ag, and Cl(-)/AgCl/Ag). The results show that the internal resistance has to be taken dynamically into account during any cyclic voltammetry experiment. Quasi-reference electrodes can be used only for qualitative electrochemical studies. Reference electrodes based on Ag(+)/Ag or Fc(+)/Fc dissolved in an IL have a stable potential over 15 h and thus can be used to perform reliable electrochemical experiments in ionic liquids and to get quantitative information such as potentials.
ABSTRACT
We have studied the extraction of four HA acids (HNO(3), HReO(4), HClO(4), HCl) to a hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)amide (BMI(+) Tf(2)N(-)) at room temperature, in a wide range of acidic concentrations in water. The effect of tributylphosphate (TBP) as co-solvent is investigated. According to experimental observations, water dragging to the IL phase increases with added TBP and/or acids. Acid extraction is found to be weak, however, for the four acids except for concentrated HNO(3) (>3 M). Molecular dynamics simulations on model biphasic systems show that TBP is not surface active, but well dissolved in the IL. They also reveal the importance of HA acid model (either totally or half dissociated) and of the TBP content on acid extraction to the IL. Furthermore, they show that "the proton" can be extracted by TBP (H(3)O(+)(TBP)(3)"complex") without its A(-) conjugated base, via a cation transfer mechanism (BMI(+) transfer to water). Experiments and simulations show that TBP plays an important role in the mutual solubility between water and ionic liquid, by different amounts, depending on the HA acid. On the other hand, both approaches indicate that a HTf(2)N containing aqueous solution completely mixes with the [BMI][Tf(2)N] IL that contains the same Tf(2)N(-) anion.
ABSTRACT
This work is devoted to establishing a quantitative structure-property relationship (QSPR) between the chemical structure of ionic liquids (ILs) and their viscosity followed by computer-aided design of new ILs possessing desirable viscosity. The modeling was performed using back-propagation artificial neural networks on a set of 99 ILs at 25 °C, covering a large viscosity range from 3 to 800 cP. The ISIDA fragment descriptors were used to encode molecular structures of ILs. These models were first validated on 23 new ILs from Solvionic company and then used to predict the viscosity of three new ILs which then have been synthesized and tested. The models display high predictive performance in external 5-fold cross validation: determination coefficients R(2) > 0.73 and absolute mean root mean square error < 70 cP. For three ILs synthesized and tested in this work, predicted viscosities are in good qualitative agreement with the experimentally measured ones.
ABSTRACT
By coupling EXAFS, UV-vis spectroscopy, and molecular dynamics and quantum mechanical calculations, we studied the competitive complexation of uranyl cations with nitrate and chloride ions in a water immiscible ionic liquid (IL), C(4)mimTf(2)N (C(4)mim(+): 1-butyl-3-methyl-imidazolium; Tf(2)N(-) = (CF(3)SO(2))(2)N)(-): bis(trifluoromethylsulfonyl)imide). Both nitrate and chloride are stronger ligands for uranyl than the IL Tf(2)N(-) or triflate anions and when those anions are simultaneously present, neither the limiting complex UO(2)(NO(3))(3)(-) nor UO(2)Cl(4)(2-) alone could be observed. At a U/NO(3)/Cl ratio of 1/2/2, the dominant species is likely UO(2)Cl(NO(3))(2)(-). When chloride is in excess over uranyl with different nitrate concentrations (U/NO(3)/Cl ratio of 1/2/6, 1/4/4, and 1/12/4) the solution contains a mixture of UO(2)Cl(4)(2-) and UO(2)Cl(3)(NO(3))(2-) species. Furthermore, it is shown that the experimental protocol for introducing these anions to the solution (either as uranyl counterion, as added salt, or as IL component) influences the UV-vis spectra, pointing to the formation of different kinetically equilibrated complexes in the IL.
ABSTRACT
The complexation of the lanthanide Eu(III) and the actinides Cm(III) and Am(III) by N3- was investigated by application of time-resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (XAFS) in the ionic liquid solution of C4mimTf2N (1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide). TRLFS measurements show that the interaction of azide with Eu(CF3SO3)3 and Eu(ClO4)3 results in both dynamic luminescence quenching by collisional encounters of N3- with Eu(III) and static luminescence quenching by inner-sphere complexation of Eu(III) by N3-. Hereby, the complexation of Eu-triflate by azide starts at a lower N3- concentration as compared to the perchlorate salt. The authors ascribe this phenomenon to a stronger bonding of ClO4- toward the metal ion than triflate, as well as to a stronger electrostatic repulsion of N3- by the perchlorate ligand. In both actinide samples (Cm(ClO4)3, Am(ClO4)3), the complexation with azide exhibits a clear kinetic hindrance. Nevertheless, mixed actinide-perchlorate-azide complexes are formed after several days in C4mimTf2N. The different reaction kinetics for the Ln- and An-complexation by azide may provide the opportunity for an effective separation of lanthanides from actinides in the nuclear fuel cycle by the use of N-based extractants in ionic liquid solution.
ABSTRACT
The first coordination sphere of the uranyl cation in room-temperature ionic liquids (ILs) results from the competition between its initially bound counterions, the IL anions, and other anions (e.g., present as impurities or added to the solution). We present a joined spectroscopic (UV-visible and extended X-ray absorption fine structure)-simulation study of the coordination of uranyl initially introduced either as UO2X2 salts (X-=nitrate NO3-, triflate TfO-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium-based ILs (C4mimA, A-=PF6-, Tf2N-, BF4- and C4mim=1-methyl-3-butyl-imidazolium) as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. The addition of Cl- anions promotes the solubilization of the nitrate and triflate salts in the C4mimPF6 and the C4mimBF4 ILs via the formation of chloro complexes, also formed with other salts. The first coordination sphere of uranyl is further investigated by molecular dynamics (MD) simulations on associated versus dissociated forms of UO2X2 salts in C4mimA ILs as a function of A- and X- anions. Furthermore, the comparison of UO2Cl(4)2-, 2 X- complexes with dissociated X- anions, to the UO2X2, 4 Cl- complexes with dissociated chlorides, shows that the former is more stable. The case of fluoro complexes is also considered, as a possible result of fluorinated IL anion's degradation, showing that UO2F42- should be most stable in solution. In all cases, uranyl is found to be solvated as formally anionic UO2XnAmClp2-n-m-p complexes, embedded in a cage of stabilizing IL imidazolium or ammonium cations.
ABSTRACT
Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium LIII -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechanical calculations of gas-phase model complexes. EXAFS spectra were measured in aqueous solutions of up to 10 M triflic and 11.5 M perchloric acid, as well as mixtures of perchloric acid and sodium perchlorate. In no case is the perchlorate anion coordinated to UO2(2+). The number of equatorial water molecules bound to UO2(2+) is always about five. In the case of the 10 M CF3SO3H solution, an inner-sphere complexation of the triflate is observed with a U-S radial distance of 3.62 Å. These results are in qualitative agreement with quantum mechanical calculations of model uranyl complexes, according to which the interaction energies of anions follow the order perchlorate
