Conversion of uranium hexafluoride and recovery of uranium from ionic liquids
Described are methods for the recovery of uranium from uranium hexafluoride dissolved directly into ionic liquids.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
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Conversion of uranium hexafluoride and recovery of uranium from ionic liquids
Described are methods for the recovery of uranium from uranium hexafluoride dissolved directly into ionic liquids.
Hatchett, David W.↗
Tuning the dynamics of imidazolium-based ionic liquids via hydrogen bonding. I. The viscous regime
Combining results from impedance spectroscopy and oscillatory shear rheology, this study focuses on the relation between the mass and charge flows and on how these are affected by the H-bonding in viscous ionic liquids (ILs). In particular, we compare the relaxational behaviors of the paradigmatic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and its OH-functionalized counterpart 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OHEMIM-TFSI). Our results and their analysis demonstrate that the presence of cationic OH-groups bears a strong impact on the overall dynamics of OHEMIM-TFSI, although no signatures of suprastructural relaxation modes could be identified in their dielectric and mechanical responses. To check whether at the origin of this strong variation is the H-bonding or merely the difference between the corresponding cation sizes (controlling both the hydrodynamic volume and the inter-charge distance), the present study includes 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PMIM-TFSI), mixtures of EMIM-TFSI and PMIM-TFSI with lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI), and mixtures of OHEMIM-TFSI with PMIM-TFSI. Their investigation clearly reveals that the dynamical changes induced by H-bonding are significantly larger than those that can be attributed to the change in the ion size. Moreover, in the mixtures of OHEMIM-TFSI with PMIM-TFSI, a dilution of the OH-groups leads to strong deviations from ideal mixing behavior, thus highlighting the common phenomenological ground of hydroxy-functionalized ILs and other H-bonded liquids.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Characterization of the acoustic cavitation in ionic liquids in a horn-type ultrasound reactor
Most ultrasound-based processes root in empirical approaches. Because nearly all advances have been conducted in aqueous systems, there exists a paucity of information on sonoprocessing in other solvents, particularly ionic liquids (ILs). In this work, we modelled an ultrasonic horn-type sonoreactor and investigated the effects of ultrasound power, sonotrode immersion depth, and solvent’s thermodynamic properties on acoustic cavitation in nine imidazolium-based and three pyrrolidinium-based ILs. The model accounts for bubbles, acoustic impedance mismatch at interfaces, and treats the ILs as incompressible, Newtonian, and saturated with argon. Following a statistical analysis of the simulation results, we determined that viscosity and ultrasound input power are the most significant variables affecting the intensity of the acoustic pressure field (P), the volume of cavitation zones (V), and the magnitude of the maximum acoustic streaming surface velocity (u). V and u increase with the increase of ultrasound input power and the decrease in viscosity, whereas the magnitude of negative P decreases as ultrasound power and viscosity increase. Probe immersion depth positively correlates with V, but its impact on P and u is insignificant. 1-alkyl-3-methylimidazolium-based ILs yielded the largest V and the fastest acoustic jets – 0.77cm 3 and 24.4ms -1 for 1-ethyl-3-methylimidazolium chloride at 60W. 1-methyl-3-(3-sulfopropyl)-imidazolium-based ILs generated the smallest V and lowest u – 0.17cm 3 and 1.7ms -1 for 1-methyl-3-(3-sulfopropyl)-imidazolium p-toluene sulfonate at 20W. Sonochemiluminescence experiments validated the model.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Structure of Novel Phosphonium-Based Ionic Liquids with S and O Substitutions from Experiments and a Mixed Quantum-Classical Approach
This article presents experimental characterization information and synchrotron X-ray scattering measurements on a set of novel O- and S-substituted phosphonium-based ionic liquids (ILs) all coupled with the bis(fluorosulfonyl)imide (FSI-) anion. The ILs include the ethoxyethyltriethylphosphonium (P 222(2O2) + ) and triethyl[2-(ethylthio)ethyl]phosphonium (P 222(2S2) + ) cations, and we contrast results on these with those for unsubstituted triethylpentylphosphonium (P 2225 + ). The article also introduces a physics-based protocol that combines classical force field studies on larger simulation boxes with classical and first-principles studies on smaller boxes. The method produces significantly improved S(q) functions in the regime which in prior publications we have associated with inter- and intraionic adjacency correlations. By understanding which shorter-range structural changes improve S(q) in the q-regime of interest, we are also able to pinpoint specific deficiencies in the classical force field model. The approach we take should be quite general and could help study other complex liquids on different length scales.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids
Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this paper, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the duration of charging. Finally and furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Understanding the Molecular‐level Interactions Between Ionic Liquids and Molecular Species to Design and Develop Novel Solvent Systems for Environmental and Energy Applications (DOE-EPSCoR – DE‐SC0020282 Final Technical Report)
The central theme of the work is to develop an understanding of the molecular-level interactions between ionic liquids and molecular species that govern a specific set of separations (aliphatic/aromatic, Topic I), reactions (SNAr, high-temp reactions, Topic II) and polymer (ultrahigh performance polymers, Topic III) synthesis processes through the synergistic application of synthesis, characterization and simulation. Understanding these interactions will provide significant insight into how to optimize these and other processes that are influenced by these interactions. An important additional goal is to build the collaborative infrastructure to enable the cluster researchers to develop professional relationships to enhance this and future research endeavors. This collaboration, the Alabama Advanced Solvents Cluster (AASC) is on ongoing collaborative effort between many of the investigators.
36 MATERIALS SCIENCE↗
Clean surface processing of rubrene single crystal immersed in ionic liquid by using frequency modulation atomic force microscopy
Surface processing of a rubrene single crystal immersed in ionic liquids is valuable for further development of low voltage transistors operated by an electric double layer. We performed a precise and clean surface processing based on the tip-induced dissolution of rubrene molecules at the ionic liquid/rubrene single crystal interfaces by using frequency modulation atomic force microscopy. Molecular resolution imaging revealed that the tip-induced dissolution proceeded via metastable low density states derived from the anisotropic intermolecular interactions within the crystal structure.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Life-Cycle Greenhouse Gas and Water Intensity of Cellulosic Biofuel Production Using Cholinium Lysinate Ionic Liquid Pretreatment
Cellulosic biofuels present an opportunity to meet a significant fraction of liquid transportation fuel demand with renewable, low-carbon alternatives. Certain ionic liquids (ILs) have proven effective at facilitating hydrolysis of lignocellulose to produce fermentable sugars with high yields. Although their negligible vapor pressure and low flammability make ILs attractive solvents at the point of use, their life-cycle environmental impacts have not been investigated in the context of cellulosic biorefineries. This study provides the first life-cycle greenhouse gas (GHG) and water use inventory for biofuels produced using IL pretreatment. We explore two corn stover-to-ethanol process configurations: the conventional water-wash (WW) route and the more recently developed integrated high gravity (iHG) route, which eliminates washing steps after pretreatment. Our results are based on the use of a representative IL, cholinium lysinate ([Ch][Lys]). We find that the WW process results in unacceptably high GHG emissions. The iHG process has the potential to reduce GHG emissions per megajoule of fuel by ~45% relative to gasoline if [Ch][Lys] is used. Use of a protic IL with comparable performance to [Ch][Lys] could achieve GHG reductions up to 70-85%. The water intensities of the WW and iHG processes are both comparable to those of other cellulosic biofuel technologies.
09 BIOMASS FUELS↗
Cross-Linked Poly(ethylene oxide) Ion Gels Containing Functionalized Imidazolium Ionic Liquids as Carbon Dioxide Separation Membranes
1,3-Substituted imidazolium bis(trifluoromethylsulfonyl)imide (Tf 2 N) ionic liquids (ILs) were incorporated at 40 and 60 vol % loading into a cross-linked poly(ethylene oxide) polymer network to create ion gels for carbon dioxide (CO 2 )-selective gas separation membranes. The ILs plasticize the poly(ethylene oxide)-based polymer to increase its gas permeability. Compared to the base polymer, with a CO 2 permeability of 145 barrer and a CO 2 against nitrogen (N 2 ) selectivity of 47, the highest CO 2 permeability achieved was 530 barrer coupled with a CO 2 /N 2 selectivity of 31 by having 60 vol % [1-ethyl-3-methylimidazolium][Tf 2 N]. The extent of gas permeability improvement depends on the cation’s terminal substituent. Substituents that promote additional noncovalent intermolecular interactions, such as hydroxyl, benzyl, and nitrile, can reduce the gas diffusivity by reducing the polymer chain mobility. Here, while n -alkyl, branched alkyl, and oligo(ethylene glycol) substituents can significantly increase the gas permeability, the shortest substituents (such as ethyl) were the most effective because they promote high ionic charge density.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Sn-Based Alloys Synthesized in an Ionic Liquid at Room Temperature: Cu6Sn5 as a Case Study
Sn-based alloys are increasingly investigated owing to possible electronic/structural modulations of interest for electrocatalysis and energy storage applications. Here, we report on the use of a chemical system consisting of an ionic liquid (1-ethyl-3- methylimidazolium bis(trifluoromethanesulfonyl)imide: [EMIm(+)][TFSI-]) and Sn-based precursor Sn(TFSI)(2) both featuring similar anionic groups. This strategy increases the solubility of the cationic precursor in the IL and avoids the formation of side-products during the precipitation of Sn-nanoparticles formed upon reaction with a reducing agent (NaBH4). Using NMR relaxometry, we further established that these nanoparticles are stabilized by specific interactions with the cationic group of the IL. Targeting the composition Cu6Sn5, we further demonstrated that this approach can be used to prepare Sn-based alloys which could not be prepared using conventional chloride-based precursors.
cyclic voltammetry↗
Stabilized Electrode/Electrolyte Interphase by a Saturated Ionic Liquid Electrolyte for High-Voltage NMC532/Si-Graphite Cells
Nonaqueous electrolyte has become one of the technical barriers in enabling Li-ion battery comprising of a high voltage cathode and high capacity anode. Here, we demonstrate a saturated piperidinum bis(fluorosulfonyl)imide ionic liquid (IL) with a LiFSI salt not only supports the redox reaction on the cathode at high voltages, but also shows exceptional kinetic stability on the lithiated anode as evidenced by its improved cycling performance in a NMC532/Si-graphite full cells cycled between 4.6 and 3.0 V. On the basis of the spectroscopic/microscopic analysis and molecular dynamics (MD) simulations, the superior performance of the cells is attributed to the formation of solid-electrolyte-interphase on both electrode as well as unique solvation structure where a deadlocked coordination network is established at the saturated state, which prevents transition metal dissolution into the electrolyte via a solvation process.
25 ENERGY STORAGE↗
Polycation ionic liquid tailored PEO-based solid polymer electrolytes for high temperature lithium metal batteries
Poly(ethylene oxide) (PEO)-based polymer electrolytes are promising candidates for solid-state electrolytes in safer, next generation lithium metal batteries. Despite their benefits however, PEO-based electrolyte exhibits highly crystalline ethylene oxide chains that provide poor ionic conductivity and, thus severely limit its practical application. Here, we report the use of hydroxypropyl trimethylammonium bis(trifluoromethane) sulfonimide chitosan salt (HACC-TFSI), which is an amorphous poly(ionic liquid) based biomass chitosan derivative, as a modifier for PEO-based solid polymer electrolytes (SPEs) to address these deficiencies. Hybrid SPEs with HACC-TFSI display enlarged amorphous regions with enhanced ionic conductivity. Interactions between quaternary ammonium cations and TFSI-anions in hybrid SPEs are also found to promote dissociation between Li + and TFSI - , which further increases ionic mobility. Moreover, the electrochemical stability, mechanical strength, and thermal stability of hybrid SPEs are collectively superior to blank SPEs without HACC-TFSI. LiFePO 4 /SPEs/Li full-cells assembled using 10wt% HACC-TFSI in PEO (10%HACC-TFSI/SPEs) electrolyte provide a capacity of 161.3 mAh g -1 and operate with excellent cycle performances at 0.2 C and 60 C. Finally, even when the temperature is increased to 150 C, LiFePO 4 /SPEs/Li cells with 10%HACC-TFSI/SPEs still display remarkable cycle performance with 73% capacity retention after 100 cycles at 1 C rate.
25 ENERGY STORAGE↗
Ionic-Liquid-Assisted Microwave Synthesis of Solid Solutions of Sr 1– x Ba x SnO 3 Perovskite for Photocatalytic Applications
Nanocrystalline Sr 1–x Ba x SnO 3 (x = 0, 0.2, 0.4, 0.8, 1) perovskite photocatalysts were prepared by microwave synthesis in an ionic liquid (IL) and subsequent heat-treatment. The influence of the Sr/Ba substitution on the structure, crystallization, morphology, and photocatalytic efficiency was investigated and the samples were fully characterized. On the basis of X-ray diffraction results, as the Ba content in the SrSnO 3 lattice increases, a symmetry increase was observed from the orthorhombic perovskite structure for SrSnO 3 to the cubic BaSnO 3 structure. The analysis of the sample morphology by SEM reveals that the Sr 1–x Ba x SnO 3 samples favor the formation of nanorods (500 nm–5 μm in diameter and several micrometers long). The photophysical properties were examined by UV/Vis diffuse reflectance spectroscopy. The band gap decreases from 3.85 to 3.19 eV with increasing Ba 2+ content. Furthermore, the photocatalytic properties were evaluated for the hydroxylation of terephthalic acid (TA). The order of the activities for TA hydroxylation was Sr 0.8 Ba 0.2 SnO 3 > SrSnO 3 > BaSnO 3 > Sr 0.6 Ba 0.4 SnO 3 > Sr 0.2 Ba 0.8 SnO 3 . Here, the highest photocatalytic activity was observed for Sr 0.8 Ba 0.2 SnO 3 , and this can be attributed to the synergistic impacts of the modification of the crystal structure and morphology, the relatively large surface area associated with the small crystallite size, and the suitable band gap and band-edge position.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Minimal implicit-solvent coarse-grained simulation of Pluronic block copolymers with ionic liquids
Pluronic block copolymers, composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) in a triblock structure (PEO–PPO–PEO), are well known for their amphiphilic character and ability to self‐assemble into micelles in aqueous solution. The addition of ionic liquids (ILs) can further modulate the core–shell structures of these copolymers, influencing their stability, critical micellization temperature, and size. However, fully atomistic simulations often become prohibitively expensive due to the size and complexity of these systems. In this work, coarse‐grained simulations using a minimal implicit‐solvent model were performed to examine how two classes of ILs, namely, 1‐alkyl‐3‐methylimidazolium ([C n C 1 im]) and 1‐alkyl‐3‐methylpyrrolidinium ([C n C 1 pyrr]), change the micellization of Pluronic block copolymers in aqueous solution. The effects of IL concentration and alkyl group length were investigated, and the model greatly improved the efficiency of simulating large‐scale micelle systems. Furthermore, the numerical simulations are qualitatively compared with experimental investigations. Our results show that adding ILs expands the micelle core by embedding IL tails among the PPO blocks, thereby increasing overall micelle size. Less polar ILs generally induce more pronounced micellar growth. However, the effect of IL tail length on conformation and micellar packing is non‐monotonic. Up to moderate chain lengths (around C8–C10), the IL tails can extend sufficiently to increase local separation within the micelle; at longer tail lengths, enhanced hydrophobic clustering and steric hindrance cause the tails to bend or fold, capping further expansion. In addition, although block copolymer chains tend to pack more closely in the presence of longer‐tailed ILs, the random coil size of an individual polymer chain does not necessarily shrink. Meanwhile, these insights provide a deeper understanding of how Pluronic/IL systems interact, informing applications in drug delivery, cosmetics, food, and environmental engineering. Finally, our minimal implicit‐solvent model can be applied to larger systems and longer timescales, substantially reducing computational cost while reproducing key structural trends observed experimentally.
Atomistic simulations↗
Interfacial Water Manipulation with Ionic Liquids for the Oxygen Reduction Reaction
The role that interfacial water plays in both promoting and inhibiting the electrochemical oxygen reduction reaction (ORR) remains somewhat unclear and controversial. Here, we use electroanalytical chemistry, spectroscopy, and microkinetic modeling to probe the impact of hydrophobic ionic liquid (IL) thin films on interfacial water structure and its role in promoting or inhibiting the ORR. Through the use of in situ ATR-SEIRAS, we find that the IL thin films limit the content of water at the interface and prevent the formation of hydrogen bond stabilized water organization. The impact of this exclusion of water on the promotion of the ORR is through the reduced coverage of OH ad spectator species. The decreased solvation of “active” OH ad species weakens its interaction with the catalyst surface, lowering the barrier to the last step in the ORR mechanism. This “destabilized” OH ad impact on ORR kinetics is confirmed through a microkinetic model. Furthermore, the results presented here highlight the mechanistic pathway through which hydrophobic ILs enhance ORR kinetics and point to pathways to both further improve this performance enhancement and the potential for integration of hydrophobic ILs into other technologically relevant elementary electrochemical reactions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of Charge Scaling on the Solvation Properties of Ionic Liquid Solutions
Scaled-charge force fields (FFs) are widely employed in the simulation of neat ionic liquids (ILs), where the charges on the ions are empirically scaled to approximately account for electronic polarization and/or charge transfer. Such charge scaling has been found to yield significant improvement in liquid-state thermodynamic and dynamic properties (when compared to experiment). However, the mean field approximation inherent in charge scaling becomes suspect when applied to IL mixtures or solutions. In this work, we simulate solutions of IL with various nonpolar and polar gas solutes and compare results of charge-scaled and polarizable FFs to experiment. Our results demonstrate that scaling of the Coulomb interaction inherent in scaled-charge FFs leads to an underestimation of the solute–solvent electrostatic interaction and thus also the enthalpy and free energy of solvation; this effect is particularly pronounced for polar solutes. In some cases, we find that this artificial reduction in the solute–solvent interaction can also alter the apparent phase behavior of the resulting solution. Altogether, the totality of our results suggests that explicit polarization (rather than charge scaling) is likely necessary to provide high transferability to both neat IL and IL mixtures and solutions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ionic Liquid Mixture Expands the Potential Window and Capacitance of a Supercapacitor in Tandem
Mixing room temperature ionic liquids (RTIL) may optimize electrolyte properties for the better performance of electrical double layer capacitors (EDLCs). To understand the composition effects, we theoretically investigate the potential window, interfacial structure, capacitance, and energy density of RTIL mixtures consisting of one common cation and two anions of different sizes. A combination of quantum density functional theory (QDFT) and classical density functional theory (CDFT) calculations indicates that the electrolyte composition has significant effects on the EDL structure and potential of zero charge, thereby altering the integral capacitance and electrochemical potential window. The two quantities can be optimized together to achieve the best EDLC performance.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗