Imidazolium-based Room Temperature Ionic Liquids Research Articles

Flipping Water Orientation at the Surface of Water-in-Salt and Salt-in-Water Solutions.

Salt-in-water and water-in-salt mixtures are promising for battery applications and fine-tuning of room-temperature ionic liquid (RTIL) properties. Although critical processes take place at interfaces of these systems, including charge transfer and heterogeneous catalytic reactions, the microscopic interfacial structures remain unclear. Here, we apply heterodyne-detected sum-frequency generation spectroscopy to aqueous solutions of imidazolium-based RTILs to unveil the microscopic structure of the interfaces of these solutions with air. Our results show that, under salt-in-water conditions, the orientation of the OH group hydrogen-bonded to the other water molecules flips from the OH group pointing down into the liquid for pure water to up due to the accumulation of anions in the cation-rich interfacial region. However, under the water-in-salt condition, the interfacial water molecules are confined by RTIL, and their orientation is down. Details of the water organization depend critically on the alkyl chain length of the imidazolium cation. Our results demonstrate that the surface structure can be tuned by altering the molecular structure and concentration of the RTIL.

Transport properties of imidazolium-based room temperature ionic liquids in confinement of slit charged carbon nanopores: New insights from molecular simulations

The paper presents a study of the behavior of room-temperature ionic liquids with different alkyl chain lengths and anion types in slit negatively charged carbon nanopores of various widths (1–15 nm) using all-atom molecular dynamics simulations. The structure of the confined ionic liquids is investigated using number, mass, and charge density profiles and radial distribution functions. The paper also discusses such characteristics as mean squared displacement of ions in all directions, self-diffusion coefficients of cations and anions in the bulk, their temperature dependences, electrical conductivity. Some energy characteristics are obtained by quantum chemical calculations. It is established that there is a bulk region in the pore center for all the confined ionic liquids, starting from the pore width of 7 nm. The sums of the cationic and anionic self-diffusion coefficients of different ionic liquids can be arranged as follows: D[OMIM][BF4] < D[EMIM][BF4] < D[OMIM][NTf2] < D[EMIM][NTf2]. Due to layering structure inside the pore, the dynamics of the ions is heterogeneous. It is shown that the RTILs with longer alkyl chains have lower electrical conductivities regardless of temperature. The opposite effect associated with the species size is observed for RTILs with different anions.

Effects of Methylating Imidazolium-Based Ionic Liquids on Viscosity: New Insights from the Compensated Arrhenius Formalism.

Methylation of the C(2) carbon on imidazolium-based room temperature ionic liquids (RTILs) causes an unexpected increase in viscosity when paired with the anion bis(trifluoromethylsulfonamide) [Tf2N]-, but the viscosity decreases when the methylated imidazolium is paired with a tetracyanoborate [B(CN)4]- anion. This paper investigates these different observations in viscosity using the compensated Arrhenius formalism (CAF) for fluidity (inverse viscosity), which assumes fluidity to be a thermally activated process. CAF activation energies are determined for imidazolium [Tf2N]- and methylated imidazolium [Tf2N]- and compared to imidazolium [B(CN)4]- and methylated imidazolium [B(CN)4]-. The results show that the activation energy increases with methylation for [Tf2N]-, but it decreases with methylation for [B(CN)4]-. The CAF results also yield information concerning the entropy of activation, which are compared for the two systems.

Dynamic molecular ordering in multiphasic nanoconfined ionic liquids detected with time-resolved diffusion NMR

Molecular motion in nanosized channels can be highly complicated. For example, water molecules in ultranarrow hydrophobic nanopores move rapidly and coherently in a single file, whereas by increasing the pore size they organize into coaxial tubes, displaying stratified diffusion. Interestingly, an analogous complex motion is predicted in viscous charged fluids, such as room temperature ionic liquids (RTILs) confined in nanoporous carbon or silica; however, experimental evidence is still pending. Here, by combining 1H NMR diffusion experiments in different relaxation windows with molecular dynamics simulations, we show that the imidazolium-based RTIL [BMIM]+[TCM]−, entrapped in the MCM-41 silica nanopores, exhibits an intricate dynamic molecular ordering; adsorbed RTIL molecules form a fluctuating charged layer near the pore walls, while in the bulk pore space they diffuse discretely in coaxial tubular shells, with molecular mean square displacement following a nearly ∼τ0.5 time dependence, characteristic of single file diffusion.

Faraday effect and refractive index of some imidazolium-based room-temperature ionic liquids and magnetic ionic liquids

Knowledge of the Faraday effect (FE) is very important in fundamental research and applications. Here, we report FE and refractive index studies for two magnetic ionic liquids (MILs), namely 1-ethyl- and 1-butyl-3-methylimidazolium tetrachloroferrate. Similar studies are also conducted for ionic liquids (ILs) that have a diamagnetic counteranion in place of [FeCl4]. The magnitudes of the Verdet constants of MILs are comparable and exhibit a negative sign. Furthermore, they are about one order larger than those of ILs with a diamagnetic counteranion of a positive sign. The Verdet constant shows monotonic variations as a function of wavelength in the range from 450 to 650 nm and is mainly related to charge transfer transitions in [FeCl4], with bands located in the UV region, though the contribution of d-d transitions in Fe+3 is negligible. A model for describing the measured Verdet constant data as a function of wavelength and temperature is given with respective values of effective Faraday A-, B-, and d-terms. The introduction of an empirical rule allows the estimation of Verdet constants of iron and imidazolium derivative based MILs, which are in some cases very high, thus indicating their potential in photonics applications. Imidazole shows a positive and nearly-two orders lower magnitude of the Verdet constant. The mixture of an MIL and acetonitrile allows the tuning of both the Verdet constant and the refractive index. The refractive indices, thermo-optic coefficients, and electronic polarizabilities of MILs are higher than those of ILs with a diamagnetic counteranion.

CO2 solubility and diffusivity in 1-ethyl-3-methylimidazolium cation-based ionic liquids; isochoric pressure drop approach

In this study, an experimental approach based on the isochoric pressure drop principle was implemented to measure (at low equilibrium pressure, 1.3–3.6 bar) the solubility and binary diffusivity of CO2 (constant and variable) in four imidazolium-based room-temperature ionic liquids (RTILs), namely, 1-ethyl-3-methylimidazolium acetate ([emim][Ac]), 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]), 1-ethyl-3-methylimidazolium methyl sulfate ([emim][MeSO4]) and 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]). The molar fraction of the dissolved CO2 and Henry's law constant were measured from experimental data. Constant binary diffusion coefficients were measured from the transient thin-film and semi-infinite volume models. In the original approach, the variable diffusivity coefficient model was used to measure the concentration-based variable diffusion coefficient. Anion interaction of the RTILs was found to have a strong influence on the CO2 solubility, and Henry's law constant and the studied anions were ranked as [Ac]− >> [EtSO4]− > [DCA]− > [MeSO4]−. Increasing temperature is not likely for CO2 solubility while it favors CO2 diffusivity. Thin-film model diffusivity measurements were found to be more suitable for [emim][MeSO4] and [emim][EtSO4], while semi-infinite volume model was suitable for [emim][Ac] and [emim][DCA]. Variable diffusion coefficients were found not to be a monotonous function of time, which increased in early stages and decreased after a certain time. Gibbs free energy, enthalpy, and entropy values indicate the strength of the favorable interaction between CO2 and RTILs, mildly exothermic in nature and falling in the range of physisorption.

Metal organic framework-ionic liquid hybrid catalysts for the selective electrochemical reduction of CO2 to CH4

The electrochemical reduction of CO2 towards hydrocarbons is a promising technology that can utilize CO2 and prevent its atmospheric accumulation while simultaneously storing renewable energy. However, current CO2 electrolyzers remain impractical on a large scale due to the low current densities and faradaic efficiencies (FE) on various electrocatalysts. In this study, hybrid HKUST-1 metal-organic framework–fluorinated imidazolium-based room temperature ionic liquid (RTIL) electrocatalysts are designed to selectively reduce CO2 to CH4. An impressive FE of 65.5% towards CH4 at −1.13 V is achieved for the HKUST-1/[BMIM][PF6] hybrid, with a stable FE greater than 50% maintained for at least 9 h in an H-cell. The observed improvements are attributed to the increased local CO2 concentration and the improved CO2-to-CH4 thermodynamics in the presence of the RTIL molecules adsorbed on the HKUST-1-derived Cu clusters. These findings offer a novel approach of immobilizing RTIL co-catalysts within porous frameworks for CO2 electroreduction applications.

Influence of the Electric Charge of Spin Probes on Their Diffusion in Room-Temperature Ionic Liquids.

The rotational and translational diffusion of negatively charged and uncharged spin probes in five imidazolium-based room-temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium tetrafluoroborate, emimBF4, 1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4, 1-octyl-3-methylimidazolium tetrafluoroborate, omimBF4, 1-octyl-3-methylimidazolium hexafluorophosphate, omimPF6, and 1-octyl-3-methylimidazolium chloride, omimCl, has been studied by means of electron paramagnetic resonance spectroscopy. Detailed analyses of the spin-Hamiltonian parameters and spin exchange interactions have been carried out. The temperature dependences of the line broadening induced by the electronic dipole-dipole interaction and the electron spin exchange coupling are determined. The translational mobility of spin probes is semiquantitatively characterized and successfully explained in the framework of a hypothesis based on the assumption of polar and unpolar domains within the RTILs.

Ultrasonication-assisted chelating ligand-free extraction of Pb(II) from aqueous solution by using room temperature ionic liquids

This work aims to study the extraction of Pb(II) from contaminated aqueous solutions using imidazolium-based room temperature ionic liquids as sole extracting agent, i.e., without using any chelating agent and mixing agent. Secondly, ultrasonication technique is employed first time, to facilitate the swift contact of potentially toxic metal ions present in aqueous solution with ionic liquid. Furthermore, various salting-out agents were investigated to reduce the leaching of ionic liquid (IL) cations into aqueous phase upon extraction of toxic metal ion. > 90% of Pb(II) was removed from artificially contaminated aqueous solution using 100 mg of IL in 6 min sonication time. Moreover, the used ionic liquid was proved to be selective for Pb(II) in real water conditions. MgSO4 salt at 1.0 M concentration found to be superior salting-out agent without having any adverse effect on the extraction efficiency. Determination of total dissolved organic carbon in treated aqueous solution was used as potential tool to propose the mechanism of metal ions transfer to ionic liquid phase from aqueous solution. This study show that ultrasonication-assisted extraction of potentially toxic lead metal ion from aqueous system using imidazolium-based ionic liquids as sole extracting agent followed by the application of salting-out agents to reduce the release of IL cations in aqueous phase offers great potential for practical application.

Order-disorder in room-temperature ionic liquids probed via methyl quantum tunneling

Room-temperature ionic liquids are promising candidates for applications ranging from electrolytes for energy storage devices to lubricants for food and cellulose processing to compounds for pharmaceutics, biotransformation, and biopreservation. Due to the ion complexity, many room-temperature ionic liquids readily form amorphous phases upon cooling, even at modest rates. Here, we investigate two commonly studied imidazolium-based room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, as well as their mixtures, to demonstrate how the complex interplay between the crystalline and amorphous phases is affected by the processing conditions, such as thermal history, liquid mixing, and applied pressure. We show that quantum tunneling in the cation methyl groups, measured by high-resolution inelastic neutron scattering, can be used to probe the order-disorder in room-temperature ionic liquids (crystalline vs amorphous state) that develops as a result of variable processing conditions.

Polyoxometalates in Imidazolim-based Ionic Liquids: Acceptor Number and Polarity Estimated from Their Voltammetric Behaviour.

The selection of an appropriate solvent is essential for achieving high yields and selectivity in chemical reactions. The chemical and physical parameters of organic solvents have been classified into several groups, and solvents can be compared with each other with respect to these properties. The acceptor number (AN), donor number (DN) and polarity (ETN) have been widely accepted and used for theoretically and quantitatively evaluating the properties of organic solvents. In a similar manner, the AN, DN and ETN of room temperature ionic liquids (RTILs) have been estimated from spectral changes in solvatochromic compounds. In this paper, the AN and ETN of eight types of imidazolium-based RTILs were estimated from the relationship between the AN and ETN values and the first redox potential obtained from the voltammograms of polyoxometalates (POMs) in various organic solvents. The obtained parameters were compared with those estimated by spectrophotometric methods reported previously by several groups. This new method for estimating the AN and ETN of RTILs using the voltammetric behaviour of POMs with low charge density and high symmetry could provide the other path to obtain more reliable AN and ETN of RTILs.

Improving the wettability of structural steels by employing ionic liquids

Surface wetting behavior is tied to different surface phenomena such as lubrication and corrosion resistance of steel surfaces. In this study, the surface wetting behavior of room-temperature ionic liquids (RTILs) treated steel surfaces is investigated. To this end, polished steel surfaces are individually surface-treated using seven imidazolium-based RTILs with varying alkyl chain lengths ([CnMIM], n = 2, 4, 6) and anion groups ([PF6], [NTf2], [Br], [BF4], [AlCl4]) for two different exposure durations (0.5 h and 4 h). The wetting behavior of RTIL-treated steel surfaces is quantified in terms of contact angles and surface energies corresponding to polar (water) and non-polar (diiodomethane) probing liquids. The RTIL surface treatment is observed to improve the surface wetting behavior of steel surfaces for both polar and non-polar probing liquids. The average initial water contact angle of steel surfaces decreased by 24−87% after RTIL surface treatment. Similarly, the average initial non-polar liquid contact angles of RTIL-treated steel surfaces decreased by 25−66% when compared to the untreated steel surface. The water contact angle decreased with an increase in the time elapsed after droplet impingement on the surface, whereas, for the non-polar liquid, the contact angle remained relatively unchanged during the elapsed duration adopted herein. The average surface free energy of RTIL-treated steel specimens increased by 49%−100%, which rendered the RTIL-treated steel surfaces more wettable. The increase in the RTIL treatment time only nominally improved the wetting of steel surfaces for both polar and non-polar probing liquids. The results reported herein can be used to prepare the surfaces of inaccessible structural steel components and bridge bearings for efficient water cleaning and lubrication.

Effect of supramolecular polymeric aggregation in room temperature ionic liquids (RTILs) on catalytic activity in the synthesis of 4H-chromene derivatives and Knoevenagel condensation

RTILs exhibit supramolecular self-assembled polymeric aggregation due to noncovalent interactions. The influence of the aggregation behaviour of RTILs on catalytic activity is evident but still poorly understood. The present work focuses on establishing a relationship between the role of supramolecular self-assembly of RTILs on catalysis in organic reactions. Herein, we report four unreported, air and water stable, halide free, C2-symmetrical, third generation, hydrophobic imidazolium-based room temperature ionic liquids (RTILs 1–4), their synthesis and function as catalysts for the synthesis of 4H-chromene derivatives (terahydrobenzo[b]pyran) and Knoevenagel condensation. The RTILs showed unprecedented solubility/miscibility behaviour. The RTILs showed that 1,3-dihexylimidazolium 2-aminobenzoate [hhim][OAB] (RTIL-3) performed better in terms of yield and reaction time. Supramolecular polymeric aggregation was explored by employing ESIMS, while the critical aggregation concentration (CAC) was calculated via recording electrical conductivity of RTILs in absolute ethanol. We have also used rheometry experiments to explore forces governing the occurrence of aggregates in the liquid phase of RTILs.

Room temperature ionic liquid assisted rapid synthesis of amorphous Se nanoparticles: Their prolonged stabilization and antioxidant studies

Considering the meticulous synthetic procedures as well as rapid phase transformation of amorphous-Selenium (α-Se) nanoparticles, herein, an attempt has been made by employing a highly facile and rapid approach to sort out such issues. An imidazolium-based room temperature ionic liquid (RTIL) was used in the synthetic protocol, wherein it played the role of a solvent, a reducing agent as well as a stabilizing agent. The synthesis was carried out in purely ambient conditions, while Se nanoparticles formation was over within 10 min of the reaction. The appearance of brick-red color indicated the formation of α-Se nanoparticles, which was further confirmed by various techniques such as XRD, Raman mapping and TEM. The electron based microscopic studies revealed the average size of the nanoparticles as 34 ± 5 nm with globular morphology. An important aspect of this work is that the α-Se nanoparticles were stable for more than 1 month, as compared to a few minutes-to-days, known hitherto. The phase stability of the nanoparticles has been explained taking into account of the structural and the fluidic aspects of the RTIL. Besides, these nanoparticles exhibited fairly good antioxidant properties, which have been discussed by comparing with standard antioxidant.

Expanding the Solubility Parameter Method MOSCED to Pyridinium-, Quinolinium-, Pyrrolidinium-, Piperidinium-, Bicyclic-, Morpholinium-, Ammonium-, Phosphonium-, and Sulfonium-Based Ionic Liquids.

MOSCED (modified separation of cohesive energy density) is a solubility parameter method that offers an improved treatment of association interactions. Solubility parameter methods are well known for their ability to both make quantitative predictions and offer a qualitative description of the underlying molecular-level driving forces, lending themselves to intuitive solvent selection and design. Currently, MOSCED parameters are available for 130 organic solvents, water, and 33 imidazolium-based room temperature ionic liquids (ILs). In this work, we expand MOSCED to cover 66 additional ILs containing the pyridinium, quinolinium, pyrrolidinium, piperidinium, bicyclic, morpholinium, ammonium, phosphonium, and sulfonium cations using 10,052 experimental limiting activity coefficients. The resulting parameters may readily be used to predict the phase behavior in mixtures involving ILs.

Cation Molecular Structure Affects Mobility and Transport of Electrolytes in Porous Carbons

We examined the electrosorption and ion dynamics of imidazolium-based room temperature ionic liquids (RTILs) having short (3-carbon, C3mim+) and long (12-carbon, C12mim+) cations, that is, 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C3mimTFSI) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C12mimTFSI), confined in ordered mesoporous carbon (OMC) and analyzed the influence of the cation alkyl chain length on the ion dynamics and the capacitive behavior using electrochemical measurements together with quasi-elastic neutron scattering (QENS) observations and classical density functional theory (cDFT) computations. Electrochemical tests highlighted the significant influence of specific applied potentials on accumulated charge storage densities and on the limits of saturation of larger electrolytes in the pores. Computational analyses corroborated these findings and predicted a 16% increase in the capacitance of the smaller-cation electrolyte under high applied potentials. However, QENS experiments revealed a behavior of decoupling of alkyl chain dynamics from the ring in electrolytes with larger ions. cDFT calculations identified density spikes for C12mim+ away from the pore walls to further corroborate this unique behavior. Our insights into chain length-dependent dynamics and electrosorption in complex electrolyte-electrode systems deepen fundamental understanding of confined RTIL electrolyte behavior in the porous carbon electrodes.

Raman spectroscopy study of water confinement in ionic liquid 1-butyl-3-methylimidzolium nitrate

Clusterization process of water molecules called “water pockets” in the imidazolium-based room temperature ionic liquid (RTIL) 1‑butyl‑3‑methylimidazolium nitrate ([C4mim][NO3]) was investigated using Raman spectroscopy. Changes of Raman spectra were observed in four different spectral regions when the content of heavy water (D2O) in the RTIL-D2O system was continuously increased. It was found that different parameters of the Raman bands were sensitive to the added content of D2O. Discontinuous distribution in the concentration dependencies of those parameters was registered. The extent of “water pockets” formation process was determined from discontinuities in the concentration dependencies of monitored shifts and integral intensities of the Raman bands. The blue shift of symmetric NO3− stretching mode at 1041 cm−1 and the stretching mode at 2nd carbon position C(2)–H at 3100 cm−1 of imidazolium ring was noticed in the spectra even after adding of infinitesimal content of water to the mixture. The identical behavior analyzing the Raman band at 706 cm−1 assigned to NO3− bending mode was discovered. Moreover, the ratio of integral intensities of two Raman bands at 600 and 625 cm−1 assigned to GT and TT forms of butyl chain was also found to be dependent on the content of D2O in the mixture. The distribution among relative integral intensities of Raman bands assigned to vibrations of different water clusters was sensitive to the content of D2O in the mixture too. Overall, the lower boarder of “water pockets” formation process (X = 0.6 molar D2O ratio) in [C4mim][NO3] came up with the discontinuous spectral changes observed for NO3− stretching mode, and vibrational modes of different water clusters. The upper boarder of “water pockets” formation process (X = 0.86 M D2O ratio) was found out from discontinuities in concentration dependencies of imidazolium ring stretching mode, and vibrational modes of different water clusters. The conformational changes of [C4mim]+ cation at the same D2O concentration corresponding to the upper boarder of “water pockets” formation were observed.

The Influence of Water on the Double-Layer Capacitance of an Ionic Liquid

Solvent-free electrolytes, room temperature ionic liquids (RTILs) have properties in between solid electrolytes and electrolyte solutions with a number of potential applications in electrochemical systems. One of their main advantages is their large potential window, in some cases 4.5-6V 1,2. The presence of impurities, water in particular, may reduce the width of this potential window. The adsorption of water at electrodes has only recently been investigated theoretically3 and experimentally2,4. Feng et al. studied humid imidazolium-based ionic liquids and the adsorption of water at a carbon-like electrode using molecular dynamics simulations3. They found that the adsorption of water increases with potential and that the electrosorption effect is stronger at potentials positive of the potential of zero charge (p.z.c.), due to the stronger interaction of water with the anions. Motobayahsi and Osawa used Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS) as a tool to detect the presence of water in the electrochemical double layer (ECDL) of a humid imidazolium-based RTIL at an Au electrode 4. They confirmed that water accumulates at the electrode even at low concentrations and that the adsorption is more pronounced at potentials positive of the p.z.c.. In this study we employ electrochemical impedance spectroscopy to determine the electrochemical double layer capacity CDL of 1-butyl-1-methy-pyrrolidinium bis[(trifluoromethyl)sulfonyl]imide (PyrTFSI) in contact with an Au(111) electrode. The water content of PyrTFSI is carefully adjusted and monitored from very dry (from 1.4 water molecules for 1000 RTIL anions (1000 : 1.4) to 1000 : 87.4). Recorded Nyquist spectra are fitted to three equivalent circuits and we give a detailed physical explanation for the single circuit elements. Electrochemical Scanning Tunnelling Microscopy is used to monitor the Au(111) surface to ensure that the electrode does not change during the electrochemical measurements. Our experimentally obtained CDL vs. potential curves are compared to curves calculated by mean-field theory (Fig. 1). Together, experiment and theory yield a conclusive understanding of the influence of water on the electrode-RTIL interface: 1.Our results show potential-dependent agglomeration of water in the ECDL, as found by AFM 4; 2.Theoretical predictions regarding the sensitivity of CDL of RTILs towards water are confirmed 3; 3.Theoretical tools such as mean-field theory calculations with the compacity parameter γ of RTILs 5 are shown to be able to reproduce experimental data. From the parameters used in the calculation properties of RTILs, like the preferred interaction of water with anions, can be deducted. (1) Buzzeo, M. C.; Hardacre, C.; Compton, R. G. ChemPhysChem 2006, 7 (1), 176–180. (2) Friedl, J.; Markovits, I. I. E.; Herpich, M.; Feng, G.; Kornyshev, A. A.; Stimming, U. ChemElectroChem 2016, 71 (111), 311–315. (3) Feng, G.; Jiang, X.; Qiao, R.; Kornyshev, A. A. ACS Nano 2014, 8 (11), 11685–11694. (4) Motobayashi, K.; Osawa, M. Electrochem. commun. 2016, 65, 14–17. (5) Kornyshev, A. A. J. Phys. Chem. B 2007, 111 (20), 5545–5557. Figure 1: (left) Normalized double layer capacitance over potential of 1-butyl-1- methyl-pyrrolidinium bis[(trifluoromethyl)sulfonyl]imide with various contents of water obtained from electrochemical impedance spectroscopy. (right) Double layer capacitance over potential calculated from mean field theory with the driest ionic liquid in red and the wettest in teal. with Graph adapted from 2 . Figure 1

Extraction of $$ {\text{Np}}^{4+} $$ Np 4 + and $$ {\text{NpO}}_{2}^{2+} $$ NpO 2 2 + from Nitric Acid Medium Using TODGA in Room Temperature Ionic Liquids

Extraction of Np4+ and $$ {\text{NpO}}_{2}^{2 + } $$ was carried out from nitric acid feeds using solutions of N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) in two imidazolium-based room temperature ionic liquids, viz., 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C4mim][NTf2]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C8mim][NTf2]). The extraction equilibrium was attained within 2 h for both the metal ions in both the ionic liquids. While a cation exchange mechanism is proposed for the extraction of $$ {\text{NpO}}_{2}^{2 + } , $$ an ion-pair mechanism of extraction is proposed for the Np4+ ion. The nature of the extracted species was determined by carrying out experiments at varying concentrations of TODGA, and species of the type Np(L)2(NO3)4 and NpO2(L)2+ were found to be extracted in 3 mol·dm−3 HNO3. The identification of these extracted species was also supported from the variable nitrate and C4mim+ ion concentration experiments.

The influence of mesoscopic confinement on the dynamics of imidazolium-based room temperature ionic liquids in polyether sulfone membranes.

The structural dynamics of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (CnmimNTf2, n = 2, 4, 6, 10: ethyl-Emim; butyl-Bmim; hexyl-Hmim; decyl-Dmim) room temperature ionic liquids confined in the pores of polyether sulfone (PES 200) membranes with an average pore size of ∼350 nm and in the bulk liquids were studied. Time correlated single photon counting measurements of the fluorescence of the fluorophore coumarin 153 (C153) were used to observe the time-dependent Stokes shift (solvation dynamics). The solvation dynamics of C153 in the ionic liquids are multiexponential decays. The multiexponential functional form of the decays was confirmed as the slowest decay component of each bulk liquid matches the slowest component of the liquid dynamics measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments, which is single exponential. The fact that the slowest component of the Stokes shift matches the OHD-OKE data in all four liquids identifies this component of the solvation dynamics as arising from the complete structural randomization of the liquids. Although the pores in the PES membranes are large, confinement on the mesoscopic length scale results in substantial slowing of the dynamics, a factor of ∼4, for EmimNTf2, with the effect decreasing as the chain length increases. By DmimNTf2, the dynamics are virtually indistinguishable from those in the bulk liquid. The rotation relaxation of C153 in the four bulk liquids was also measured and showed strong coupling between the C153 probe and its environment.