Nuclear magnetic resonance, fluorescence correlation spectroscopy and time-resolved fluorescence anisotropy studies of intermolecular interactions in bis(1-methyl-1H-imidazol-3-ium-3-yl)dihydroborate bis(trifluoromethylsulfonyl)amide and its mixtures with various cosolvents

Temperature-Dependent Constrained Diffusion of Micro-Confined Alkylimidazolium Chloride Ionic Liquids

Alkylimidazolium chloride ionic liquids (ILs) have many uses in a variety of separation systems, including micro-confined separation systems. To understand the separation mechanism in these systems, the diffusion properties of analytes in ILs under relevant operating conditions, including micro-confinement dimension and temperature, should be known. For example, separation efficiencies for various IL-based microextraction techniques are dependent on the sample volume and temperature. Temperature-dependent (20-100 °C) fluorescence recovery after photobleaching (FRAP) was utilized to determine the diffusion properties of a zwitterionic, hydrophilic dye, ATTO 647, in alkylimidazolium chloride ILs in micro-confined geometries. These micro-confined geometries were generated by sandwiching the IL between glass substrates that were separated by ∼1 to 100 μm. From the measured temperature-dependent FRAP data, we note alkyl chain length-, thickness-, and temperature-dependent diffusion coefficients, with values ranging from 0.021 to 46 μm2/s. Deviations from Brownian diffusion are observed at lower temperatures and increasingly less so at elevated temperatures; the differences are attributed to alterations in intermolecular interactions that reduce temperature-dependent nanoscale structural heterogeneities. The temperature- and thickness-dependent data provide a useful foundation for efficient design of micro-confined IL separation systems.

Ionic liquids and deep eutectic solvents for the recovery of phenolic compounds: effect of ionic liquids structure and process parameters

Water pollution is a severe and challenging issue threatening the sustainable development of human civilization. Besides other pollutants, waste fluid streams contain phenolic compounds. These have an adverse effect on the human health and marine ecosystem due to their toxic, mutagenic, and carcinogenic nature. Therefore, it is necessary to remove such phenolic pollutants from waste stream fluids prior to discharging to the environment. Different methods have been proposed to remove phenolic compounds from wastewater, including extraction using ionic liquids (ILs) and deep eutectic solvent (DES), a class of organic salts having melting point below 100 °C and tunable physicochemical properties. The purpose of this review is to present the progress in utilizing ILs and DES for phenolic compound extraction from waste fluid streams. The effects of IL structural characteristics, such as anion type, cation type, alkyl chain length, and functional groups will be discussed. In addition, the impact of key process parameters such as pH, phenol concentration, phase ratio, and temperature will be also described. More importantly, several ideas for addressing the limitations of the treatment process and improving its efficiency and industrial viability will be presented. These ideas may form the basis for future studies on developing more effective IL-based processes for treating wastewaters contaminated with phenolic pollutants, to address a growing worldwide environmental problem.

Microheterogeneity in imidazolium and piperidinium cation-based ionic liquids: 1D and 2D NMR studies

Existence of microheterogeneity of imidazolium and piperidinium cation-based ionic liquids (ILs) containing PF₆ and NTf₂ anions has been investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6- and NTf2-) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6- and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state. We have also observed existence of heterogeneous environment for piperidinium cation-based ILs which is different from imidazolium ILs. It appears that existence of microheterogeneity in IL is ubiquitous and therefore open up the ILs field to revisit. Copyright © 2017 John Wiley & Sons, Ltd.

A review of NMR methods used in the study of the structure and dynamics of ionic liquids

Recently, NMR spectroscopy has been emerging out as a powerful tool to study the structure and dynamics of ionic liquids (ILs) and ILs-Li⁺ salt mixtures. This mini-review primarily focuses on the applications of various NMR spectroscopic techniques such as self-diffusion measurements, NMR relaxometry, two-dimensional NMR, and other novel NMR approaches to study the structure and dynamics of ILs and its mixtures with lithium salts. Copyright © 2017 John Wiley & Sons, Ltd.

Ion pair and solvation dynamics of [Bmim][BF4 ] + water system

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate/water mixtures were analysed over the whole water composition (x_w ) in order to study the rotational and translational behaviour of the ions. We employed a multinuclear NMR approach to determine anion/cation/water diffusion coefficients and longitudinal relaxation rates at different water content. In neat ionic liquids (IL), the cation diffuses faster than the anion, and at low x_w , anions and cations share almost the same diffusion coefficient, but above a critical water concentration, the anion begins to diffuse faster than the cation. We identified this composition as approximately 10% x_w where the ions share the same diffusion coefficient. We found that the water at this composition seems to have a much more dramatic effect in the rotational diffusion of the anion that decreases substantially and approaches that of the anion in the diluted IL. Translational and rotational dynamics of the ions suggest that water is first incorporated in pockets in the nanostructure of the IL allowing the ions to maintain most of the cation/anion interactions present in neat IL but already disrupting some anion/cation interactions due to preferential interaction with the anion. HOESY and NOESY data show that water displays contacts both with the cation and the anion in a positive NOE regime in contrary to the negative regime found for the cation/anion and cation/cation cross-relaxation. This is in accordance with the high relative diffusion coefficient of water and suggests that water molecules can exchange between preferential location sites that allow water to maintain contacts both with the anion and cation.