Nanophase separation in aqueous dilutions of a ternary DES as revealed by Brillouin and NMR spectroscopy

Recyclable water-modified deep eutectic solvents for removal of multiple heavy metals from soil

Removing heavy metals from soil has always been a challenge in terms of safety and effectiveness. Deep eutectic solvents (DESs) are recognized as environmentally friendly reagents with great potential in the removal of heavy metals from soil. In this study, water was introduced as a third component to form new ternary deep eutectic water solvents (DEWSs) to improve their performance. The removal capacity, applicable conditions and mechanisms of sixteen DEWSs for heavy metals were systematically investigated. Experimental results showed that the presence of water significantly enhanced the removal efficiency of three DESs (Choline chloride plus Urea, DEU; Choline chloride plus l-lactic acid, DELA; and Choline chloride plus Ethylene glycol, DEEG) for heavy metals. However, as the molar ratio of water increased, the eutectic systems in the DEWSs weakened and eventually disappeared. Under optimum conditions, DEWLA7 (DELA : H2O = 2 : 8) showed the highest removal rate for cadmium, lead, copper and zinc, which were 43.42%, 94.73%, 90.72% and 96.44%, respectively. Hydrogen bonding, adsorption of oxygen functional groups, exchangeable hydrogen substitution, changes in viscosity properties and co-precipitation all contributed to the removal of heavy metals by DEWLA7. Notably, DEWLA7 had no significant effect on the content of major minerals and nutrients in the soil. Furthermore, DEWLA7 proved to be reusable for soil washing, and still retains a high removal rate of 37.32%-83.66% after multi-stage filtration treatment. Therefore, DEWLA7 was an unexplored and excellent soil washing agent with great potential in economic and social benefits.

Liquid structure and dynamics in the choline acetate:urea 1:2 deep eutectic solvent

We report on the thermodynamic, structural, and dynamic properties of a recently proposed deep eutectic solvent, formed by choline acetate (ChAc) and urea (U) at the stoichiometric ratio 1:2, hereinafter indicated as ChAc:U. Although the crystalline phase melts at 36-38 °C depending on the heating rate, ChAc:U can be easily supercooled at sub-ambient conditions, thus maintaining at the liquid state, with a glass-liquid transition at about -50 °C. Synchrotron high energy x-ray scattering experiments provide the experimental data for supporting a reverse Monte Carlo analysis to extract structural information at the atomistic level. This exploration of the liquid structure of ChAc:U reveals the major role played by hydrogen bonding in determining interspecies correlations: both acetate and urea are strong hydrogen bond acceptor sites, while both choline hydroxyl and urea act as HB donors. All ChAc:U moieties are involved in mutual interactions, with acetate and urea strongly interacting through hydrogen bonding, while choline being mostly involved in van der Waals mediated interactions. Such a structural situation is mirrored by the dynamic evidences obtained by means of ¹H nuclear magnetic resonance techniques, which show how urea and acetate species experience higher translational activation energy than choline, fingerprinting their stronger commitments into the extended hydrogen bonding network established in ChAc:U.

Should deep eutectic solvents be treated as a mixture of two components or as a pseudo-component?

Deep eutectic solvents (DESs) and dilutions thereof (mainly in H₂O but also in many other non-aqueous solvents and co-solvent mixtures) have recently attracted great attention. It is well known that DES dilutions exhibit deviations from ideality. Interestingly, the treatment of DES as a mixture of two components or a pseudo-component is by no means trivial when determining deviations in density and, mainly, in viscosity. Herein, we studied aqueous dilutions of one of the most widely studied DES, this is, that composed of choline chloride and urea in a 1:2 molar ratio (e.g., ChCl2U). Using density and viscosity data reported in previous works, we calculated the excess molar volumes (V^E) and excess viscosities (ln η^E) considering ChCl2U as either a mixture of two components or a pseudo-component, that is, taking the DES molecular weight as M_ChCl2U = f_ChClM_ChCl + f_UM_U = 86.58 g mol^-1 (with f_ChCl = 1/3 and f_U = 2/3) or as M^* _ChCl2U = M_ChCl + 2 M_U = 259.74 g mol^-1. We found that neither the sign of V^E and V^E* nor their evolution with temperature was influenced by the use of either M_ChCl2U or M^* _ChCl2U, and only the absolute magnitude of the deviation and the DES content (in wt. %) at which the minimum appears exhibited some differences. However, ln η^E and ln η^E* exhibited opposite signs, negative and positive, respectively. The odd achievement of negative ln η^E in aqueous dilutions of ChCl2U characterized by the formation of HB networks suggest the treatment of ChCl2U as a pseudo-component as more appropriate. Moreover, the role played by the presence of U in the evolution of ln η^E* with temperature was also discussed.

On the coupling between ionic conduction and dipolar relaxation in deep eutectic solvents: Influence of hydration and glassy dynamics

We have studied the ionic conductivity and the dipolar reorientational dynamics of aqueous solutions of a prototypical deep eutectic solvent (DES), ethaline, by dielectric spectroscopy in a broad range of frequencies (MHz-Hz) and for temperatures ranging from 128 to 283 K. The fraction of water in the DES was varied systematically to cover different regimes, starting from the pure DES and its water-in-DES mixtures to the diluted electrolyte solutions. Depending on these parameters, different physical states were examined, including low viscosity liquid, supercooled viscous liquid, amorphous solid, and freeze-concentrated solution. Both the ionic conductivity and the reorientational relaxation exhibited characteristic features of glassy dynamics that could be quantified from the deviation from the Arrhenius temperature dependence and non-exponential decay of the relaxation function. A transition occurred between the water-in-DES regime (<40 wt. %), where the dipolar relaxation and ionic conductivity remained inversely proportional to each other, and the DES-in-water regime (>40 wt. %), where a clear rotation-translation decoupling was observed. This suggests that for a low water content, on the timescale covered by this study (∼10^-6 to 1 s), the rotational and transport properties of ethaline aqueous solutions obey classical hydrodynamic scaling despite these systems being presumably spatially microheterogeneous. A fractional scaling is observed in the DES-in-water regime due to the formation of a maximally freeze-concentrated DES aqueous solution coexisting with frozen water domains at sub-ambient temperature.

Connecting chloride solvation with hydration in deep eutectic systems

The Deep Eutectic Solvents (DESs) choline chloride:urea (x_ChCl = 0.33) and choline chloride:glycolic acid (x_ChCl = 0.5) were studied using viscosity-corrected ³⁵Cl NMR and MD simulations to probe the role of chloride as a function of water content.

Aqueous-Eutectic-in-Salt Electrolytes for High-Energy-Density Supercapacitors with an Operational Temperature Window of 100 °C, from -35 to +65 °C

Water-in-salt (WIS) electrolytes are gaining increased interest as an alternative to conventional aqueous or organic ones. WIS electrolytes offer an interesting combination of safety, thanks to their aqueous character, and extended electrochemical stability window, thanks to the strong coordination between water molecules and ion salt. Nonetheless, cost, the tendency of salt precipitation, and sluggish ionic transfer leading to poor rate performance of devices are some intrinsic drawbacks of WIS electrolytes that yet need to be addressed for their technological implementation. It is worth noting that the absence of "free'' water molecules could also be achieved via the addition of a certain cosolvent capable of coordinating with water. This is the case of the eutectic mixture formed between DMSO and H₂O with a molar ratio of 1:2 and a melting point as low as -140 °C. Interestingly, addition of salts at near-saturation conditions also resulted in an increase of the boiling point of the resulting solution. Herein, we used a eutectic mixture of DMSO and H₂O for dissolution of LiTFSI in the 1.1-8.8 molality range. The resulting electrolyte (e.g., the so-called aqueous-eutectic-in-salt) exhibited excellent energy and power densities when operating in a supercapacitor cell over a wide range of extreme ambient temperatures, from as low as -35 °C to as high as +65 °C.

Brillouin Spectroscopy as a Suitable Technique for the Determination of the Eutectic Composition in Mixtures of Choline Chloride and Water

Deep eutectic solvents (DESs) resulting from the right combination between a hydrogen-bond donor (HBD) and a hydrogen-bond acceptor (HBA) are becoming quite popular in number of applications. More recently, natural DESs (NADESs) containing sugars, natural organic acids, and amino acids as HBDs and ChCl as HBA have received great attention because of their further environmental sustainability as compared to regular DESs. Within this context, mixing water in controlled amounts has been widely accepted as a simple and practical way of altering DES chemical and thermodynamic properties, with viscosity and conductivity experiencing the most significant changes. However, the number of papers describing eutectic mixtures with water as the only HBD is scarce and basically none has been done in fundamental terms. Herein, we investigated mixtures composed of water as the only HBD and ChCl as the HBA using differential scanning calorimetry (DSC) as well as ¹H nuclear magnetic resonance (NMR) and Brillouin spectroscopies. We found the aqueous dilution of ChCl/2H₂O with a ChCl/2H₂O content of ca. 80 wt % was an eutectic. Interestingly, this mixture could be considered a NADES according to its eutectic distance (ΔT_me), in range to eutectics obtained in aqueous dilutions of salt hydrates.

Carbon and carbon composites obtained using deep eutectic solvents and aqueous dilutions thereof

Extending the “all-in-one” features of DESs to DES/H₂O binary mixtures.

Impact of optical tissue clearing on the Brillouin signal from biological tissue samples

Brillouin spectroscopy is a well-established technology in condensed matter physics to characterize the mechanical properties of inert materials, and it has been extended very recently to the study of biological samples. Transparency is beneficial for samples to be properly analyzed by Brillouin spectroscopy. Here, we explored the efficacy of optical tissue clearing techniques to improve the acquisition of Brillouin spectra from biological tissues in order to analyze their biomechanical properties. We describe the first application of Brillouin scattering to optically cleared biological tissues with CUBIC protocol. We conclude that, within the range of error, tissue clearing does not modify the mechanical properties of the studied biological tissues.