Neat Room Temperature Ionic Liquid Research Articles

Photophysics and rotational dynamics of Nile red in room temperature ionic liquid (RTIL) and RTIL-cosolvents binary mixtures

The photophysics and rotational dynamics of nile red (NR) have been studied in neat room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl)imide ([emim]+[Tf2N]ˉ) and RTIL-cosolvents binary mixtures with the variation of temperature from 278K to 333K. We have used methanol, acetonitrile, and benzene as a cosolvents. The fluorescence lifetime values of the nile red in RTIL and RTIL-cosolvent binary mixtures are gradually decreased on increasing of temperature in a regular manner. The rotational dynamics of nile red in neat RTIL and RTIL-cosolvents binary mixtures were analyzed using Stokes-Einstein-Debye (SED) hydrodynamic theory and GW-quasihydrodynamic model. We observed that in all cases experimental values of rotational reorientation time exhibits sub-slip behaviour. We have also carried out fluorescence lifetime imaging microscopy (FLIM) study to observed the distribution of lifetime of nile red on the surface of RTIL and RTIL-cosolvents binary mixtures.

The Electrochemistry of Low-Temperature Molten Quinones for All-Organic Redox Flow Batteries

Grid-scale energy storage is perhaps the most important issue to overcome to pave the way for a 100% renewable grid. The lack of economically viable grid-scale energy storage precludes the use of renewable energy sources past a certain percentage of the load. Redox flow batteries (RFBs) are well suited for large scale storage, but suffer from some limitations. One of these is low density of the anolyte and catholyte, due to low solubility of the active species in the solvent.1 Density can be increased by designing an electrochemically active species to be an ionic constituent in a room-temperature ionic liquid (RTIL), generally defined as a salt that is molten below ~100°C. This allows the maximum concentration of the electrochemically active molecule in any liquid, by eliminating solvation entirely. Temperatures < 120°C will allow cell construction from relatively low-cost materials, allow compatibility with more conventional separators, and reduce the complications with system sealing found in high temperature systems. In this talk we present the electrochemistry of several quinone-based RTILs and their performance as RFB anolytes. Quinones are excellent active materials for molecular engineering, as they are organic, generally stable owing to their aromaticity, and can be modified at several sites with functional groups, to customize the molecule as an ionic liquid constituent. Aqueous RFBs with quinone active species have shown promise recently.2 The conductivity of the quinone-based RTIL [trihexyltetradecylphosphonium] [anthraquinone-2-sulfonate]3 or [P14666][AQS] is shown in Figure 1 at several temperatures and concentrations. The diluent was 1 M [tetrabutylammonium] [tetrafluoroborate] (TBATFB) in acetonitrile, and the highest concentration was neat RTIL with no diluent. Conductivity was reduced in the case of neat RTIL, but the RTIL displayed the characteristic quinone electrochemical reactions at all concentrations, including the neat material. The viscous nature of the neat RTIL was responsible for the drop in conductivity, and the size of the cation was responsible for the relatively low concentration of the neat RTIL. Molecular engineering of the RTIL structure can be used to decrease viscosity, increase conductivity, and increase concentration. The effects of the nature of constituents on the bulk ionic liquid properties have been examined, and the effects of constituent molecule symmetry, size, shape, and flexibility have informed the design of several ionic liquid candidates that can overcome the conductivity-viscosity challenge and provide a dense anolyte for high energy density electrical storage. References H. S. Chen, T. N. Cong, W. Yang, C. Q. Tan, Y. L. Li and Y. L. Ding, Prog Nat Sci, 19, 291 (2009).K. Lin, Q. Chen, M. R. Gerhardt, L. Tong, S. B. Kim, L. Eisenach, A. W. Valle, D. Hardee, R. G. Gordon and M. J. Aziz, Science, 349, 1529 (2015).A. Patrick Doherty, S. Patterson, L. Diaconu, L. Graham, R. Barhdadi, V. Puchelle, K. Wagner, J. Chen and G. G. Wallace, J Mex Chem Soc, 59, 263 (2015). Figure 1

Probing the phase transformation of Selenium nanoparticles synthesized in the host matrix of neat room temperature ionic liquid via radiation route

Herein, Selenium (Se) nanoparticles (NPs) have been synthesized in the host matrix of a neat room temperature ionic liquid (RTIL) via rapid, one-pot electron beam (EB) mediated approach. A dark red coloured solution was obtained, which exhibited absorption bands at 520, 620 and 730 nm. The Se NPs were predominantly amorphous, as was indicated from the XRD and TEM studies. This was further evident from the Raman mapping of the NPs. The NPs extracted from the RTIL showed assembling of the primary units (flake and spherical shaped) into an interconnected porous nanostructure. Interestingly, the well-known amorphous to crystalline phase transformation of Se NPs was found to be much slower (>2 months) in RTIL compared to few minutes-to-days as reported in earlier studies. Further, the interplay of dose rate was found to have significant impact on the morphology of the Se NPs. An equivalent dose of γ-ray irradiation (low dose rate) produces largely globular and less interconnected NPs. Based on the results obtained, it can be inferred that the RTIL simultaneously played the role of a solvent, a stabilizer and an in-situ source of radicals for the reduction of precursors. The underlying mechanism for the formation and subsequent morphological evolution of Se nanostructures in the two methods (EB and γ-irradiation) has been proposed, and was rationalized in the viewpoint of dose rate difference in addition to the existence of innate structural and fluidic aspects of the RTIL.

SEM Observation of Hydrous Superabsorbent Polymer Pretreated with Room-Temperature Ionic Liquids

Room-temperature ionic liquid (RTIL), which is a liquid salt at or below room temperature, shows peculiar physicochemical properties such as negligible vapor pressure and relatively-high ionic conductivity. In this investigation, we used six types of RTILs as a liquid material in the pretreatment process for scanning electron microscope (SEM) observation of hydrous superabsorbent polymer (SAP) particles. Very clear SEM images of the hydrous SAP particles were obtained if the neat RTILs were used for the pretreatment process. Of them, tri-n-butylmethylphosphonium dimethylphosphate ([P4, 4, 4, 1][DMP]) provided the best result. On the other hand, the surface morphology of the hydrous SAP particles pretreated with 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) was damaged. The results of SEM observation and thermogravimetry analysis of the hydrous SAP pretreated with the RTILs strongly suggested that most water in the SAP particles are replaced with RTIL during the pretreatment process.

Diffusion of Organic Dyes in Ionic Liquid and Giant Micron Sized Ionic Liquid Mixed Micelle: Fluorescence Correlation Spectroscopy

Diffusion of organic dyes in neat room temperature ionic liquid (RTIL) and RTIL-mixed micelle has been studied by fluorescence correlation spectroscopy (FCS). We have selected two RTILs, 3-pentyl-1-methyl imidazolium bromide ([C5C1Im][Br]) and the corresponding tetra-fluoroborate ([C5C1Im][BF(4)]). Diffusion coefficients (D(t)) of three organic dyes--DCM (neutral), C480 (neutral), and C343 (anionic)--in these RTILs are ∼100 times slower compared to water. This indicates very high viscosity of the RTILs. In contrast to water, the D(t) in RTIL exhibits a wide distribution which suggests the presence of heterogeneity (nanoscale organization). The presence of ions in the RTILs markedly affects diffusion in the RTILs. D(t)'s of C480 (neutral) and C343 (anionic) are very similar in water but in RTILs the ionic dye C343 diffuses 1.7 times slower than neutral C480. This is attributed to the electrostatic force exerted by the ions in the RTILs. In the giant (∼2-4 μm) [C5C1Im][Br]-triblock copolymer (P123) mixed micelle D(t) of DCM, C480, and C343 are found to be 7, 15, and 7 μm(2) s(-1), respectively. The results are compared with those in P123 micelle and gel.

Simple and low temperature preparation and characterization of CdS nanoparticles as a highly efficient photocatalyst in presence of a low-cost ionic liquid

A simple and low temperature method is proposed for preparation of CdS nanoparticles in presence of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM] [EtSO4], a room-temperature ionic liquid (RTIL). The powder X-ray diffraction (XRD) studies display that the products are excellently crystallized in the form of cubic structure and size of the nanparticles prepared in presence of the RTIL is smaller than that prepared in water. Energy dispersive X-ray spectroscopy (EDX) investigations reveal that the products are very pure and nearly stoichiometric. The results obtained by scanning electron microscopy (SEM) demonstrate that the CdS nanoparticles prepared in presence of the RTIL have lower tendency for aggregation relative to the prepared sample in water. Diffuse reflectance spectra (DRS) of the product prepared in the neat RTIL, shows 1.52 eV blue shift relative to bulk CdS, which can be attributed to quantum confinement effect of the CdS nanoparticles. A possible formation mechanism for CdS nanoparticles in presence of the RTIL is presented. Photocatalytic activity of the CdS nanoparticles towards photodegradation of methylene blue (MB) using UV and visible lights was performed. The results demonstrate that observed firstorder rate constant for photodegradation of MB on CdS nanoparticles prepared in the neat RTIL are about 20 and 6 times greater than the prepared sample in water using visible and UV lights, respectively.

NMR and Quantum Chemistry Study of Mesoscopic Effects in Ionic Liquids

(1)H, (13)C, and (81)Br NMR spectra of the neat room-temperature ionic liquid (RTIL), namely, 1-decyl-3-methyl-imidazolium bromide ([C(10)mim][Br]) as well as its solutions in acetonitrile, dichloromethane, methanol, and water have been investigated. The most important observation of the present work is the significant broadening of (81)Br NMR signal in the solutions of [C(10)mim][Br] in organic solvents, which molecules tend to associate into hydrogen bond networks and the appearance of the complex contour of (81)Br NMR signal in the neat RTIL as well as in the liquid crystalline (LC) ionogel formed in RTIL/water solution. The complex structure of (81)Br signal changes upon heating and dilution in water. It disappears at ca. 353 K and in the aqueous solution below ca. 0.1 mol fraction of RTIL. Several new (1)H NMR signals appear at the [C(10)mim][Br]/water compositions just before the solidification of the sample (approximately 0.3 mol fraction of [C(10)mim][Br]). These additional peaks can be attributed to the H(2)O protons placed in inhomogeneous regions of the sample or due to the appearance of nonequivalent water sites in LC ionogel, the exchange between which is highly restricted or even frozen. The complex shape of (81)Br NMR signal can originate from the presence of supra-molecular structures (mesoscopic domains) that live over the period of the NMR time-scale due to a very high viscosity of [C(10)mim][Br]. These domains exhibit some features of partially disordered solids (liquid- or plastic crystals). To evaluate the static and dynamic contributions into the relaxation rate of (81)Br nuclei, the quantum chemistry calculations of the electronic structure, magnetic shielding, and electric field gradient (EFG) tensors of [C(10)mim][Br] and related model systems (Br(-).6H(2)O cluster, with addition of the dipoles (hydrogen fluoride) and charged particles - cations: H(+) or C(1)mim(+)) were performed.

Dynamics of Solvent and Rotational Relaxation of Coumarin-153 in Room-Temperature Ionic Liquid 1-Butyl-3-methyl Imidazolium Tetrafluoroborate Confined in Poly(oxyethylene glycol) Ethers Containing Micelles

We have investigated solvent and rotational relaxation of coumarin 153 (C-153) in room-temperature ionic liquid (RTILs) 1-butyl-3-methyl-imidazolium tetrafluoroborate ([bmim][BF(4)]) and the ionic liquid confined in alkyl poly(oxyethylene glycol) ethers containing micelles. We have used octaethylene glycol monotetradecyl ether (C(14)E(8)) and octaethylene glycol monododecyl ether (C(12)E(8)) as surfactants. In the [bmim][BF(4)]-C(14)E(8) micelle, we have observed only a 22% increase in solvation time compared to neat [bmim][BF(4)], whereas in the [bmim][BF(4)]-C(12)E(8) system, we have observed approximately 57% increase in average solvation time due to micelle formation. However, the slowing down in solvation time on going from neat RTIL to RTIL-confined micelles is much smaller compared to that on going from water to water confined micellar aggregates. The 22-57% increase in solvation time is attributed to the slowing down of collective motions of cations and anions in micelles. The rotational relaxation times become faster in both the micelles compare to neat [bmim][BF(4)].

Additivity in the Optical Kerr Effect Spectra of Binary Ionic Liquid Mixtures: Implications for Nanostructural Organization

Low-frequency spectra of binary room-temperature ionic liquid (RTIL) mixtures of 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-pentyl-3-methylimidazolium bromide in the 0-250 cm(-1) region were studied as a function of mole fraction at 295 K. The spectra were obtained by use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The spectra of these binary mixtures are well described by the weighted sums of the spectra for the neat RTILs. This surprising result implies that the intermolecular modes giving rise to the spectra of the neat liquids must also produce the spectra of the mixtures. Additivity of the OKE spectra can be explained by a model in which locally ordered domains are assumed to exist in the neat liquid with the structures of these locally ordered domains preserved upon mixing. Recently published molecular dynamics simulations show that RTILs are nanostructurally organized with ionic networks and nonpolar regions. If ionic networks also exist in the mixture, the additivity of the OKE spectra implies that there are "blocks" along the network of the mixture that are ordered in the same way as in the neat liquids. These "block co-networks" would have a nanostructural organization resembling that of a block copolymer.