Study on Structure and Electrochemical Properties of Zn-Sulfolane Based Electrolyte Solution

Ionic liquids (ILs) are organic salts with a melting temperature lower than the boiling point of water, while deep eutectic solvents (DESs) are usually composed of two or more components that can associate with each other through hydrogen bonds, and the resulting melting point of the mixture is lower than each of the components. These two classes of solvents share many remarkable properties, such as low volatility, non- flammability, wide liquidous range, and tunability; moreover, DESs are more inexpensive and environmentally friendlier. In addition to the fundamental scientific interest in these types of materials, our modeled systems are relevant to practical applications such as dye- sensitized solar cells and gas separations, as well as developing nanomaterials based on ILs. We first performed molecular dynamics (MD) simulations to study the structure and dynamics of DESs and ILs confined inside slit-like graphite and titania [rutile (110)] nanopores. Our results show that hydrogen bond donor (HBD) molecules of modeled DESs can form long-lived hydrogen bonds with the oxygen atoms in the rutile walls, consequently the rutile walls are coated by HBD layers that are almost depleted of ions, which exhibiting a liquid structure that departs from that of the bulk DES and with very slow dynamics. In contrast, for DESs inside graphitic pores, all species are present in the fluid layers near the carbon walls, the local liquid structure everywhere is similar to that of a bulk DES, and the overall dynamics are faster than those observed inside rutile pores of the same pore size. When the pore size is reduced, in general the hydrogen bonds formed can exist for longer time, a larger proportion of the hydrogen bonds involve the walls (in the case of a rutile pore), and the overall dynamics of the confined DES become slower. We then performed MD simulations of confined DESs or ILs in contact with gas phases containing CO2, and later a binary mixture of CO2 and CH4. When the amount of DES in the pore is varied, in the absence of DES, CO2 adsorbs to the pore walls, but increasing amounts of DES inside the pores quickly displace carbon dioxide into the gas/liquid interfaces, and into dissolution within the confined DES. As the amount of DES inside the pores increases, the diffusivity of CO2 reaches a maximum in partially filled pores and decays to the values observed in pores filled with DES, which are similar to the diffusion coefficients of CO2 in the bulk DES. The average number densities of CO2 near the confined DES (i.e., dissolved in the DES, and adsorbed at the pore walls and at the gas/liquid interface) are significantly larger than the corresponding value observed in the bulk DES. Furthermore, the solubility selectivity, diffusion selectivity and permselectivity of CO2 over CH4 inside the pore will alter with different pore materials, the properties of confined DESs or ILs, the loadings of solvents in the nanopores. Additionally, biased MD simulations have been performed to model the heterogeneous nucleation of IL [dmim+][Cl-] near a graphitic surface from its supercooled liquid phase. As nucleation is a rare event, a combination of techniques (i.e. the string method in collective variables and Markovian milestoning with Voronoi tessellations) has been used to obtain a minimum free energy path connecting the supercooled liquid and crystal phases, and determine the free energy and the rates involved in the nucleation process. It is found that when the subcooled liquid phase is in contact with a graphitic disk, the free energy barrier becomes about 42% smaller (~49 kcal/mol), and the critical nucleus formed is about 17% smaller (~3.0 nm) than the one observed for homogeneous nucleation.

The effects of a hydrogen bond acceptor and hydrogen bond donor on carbon dioxide absorption via natural deep eutectic solvents were studied in this work. Naturally occurring non-toxic deep eutectic solvent constituents were considered; choline chloride, b-alanine, and betaine were selected as hydrogen bond acceptors; lactic acid, malic acid, and fructose were selected as hydrogen bond donors. Experimental gas absorption data were collected via experimental methods that uses gravimetric principles. Carbon dioxide capture data for an isolated hydrogen bond donor and hydrogen bond acceptor, as well as natural deep eutectic solvents, were collected. In addition to experimental data, a theoretical study using Density Functional Theory was carried out to analyze the properties of these fluids from the nanoscopic viewpoint and their relationship with the macroscopic behavior of the system, and its ability for carbon dioxide absorption. The combined experimental and theoretical reported approach work leads to valuable discussions on what is the effect of each hydrogen bond donor or acceptor, as well as how they influence the strength and stability of the carbon dioxide absorption in deep eutectic solvents. Theoretical calculations explained the experimental findings, and combined results showed the superiority of the hydrogen bond acceptor role in the gas absorption process, with deep eutectic solvents. Specifically, the cases in which choline chloride was used as hydrogen bond acceptor showed the highest absorption performance. Furthermore, it was observed that when malic acid was used as a hydrogen bond donor, it led to low carbon dioxide solubility performance in comparison to other studied deep eutectic solvents. The cases in which lactic acid was used as a hydrogen bond donor showed great absorption performance. In light of this work, more targeted, specific, deep eutectic solvents can be designed for effective and alternative carbon dioxide capture and management.

Purification of biodiesel prior to utilizing it as an alternative fuel is an essential industrial practice. Low glycerol content is one of the important pointers needed for passing the EN 14214 and ASTM D6751 international biodiesel standards. In this study, choline chloride (ChCl) as salt and ethylene glycol and 2,2,2-Trifluoroacetamide as hydrogen bond donors (HBDs) were employed to synthesize two ammonium salt-non glycerol based Deep Eutectic Solvents (DES). The physical properties of the synthesized DESs were measured and analyzed. These DESs were utilized to remove all the free glycerol from the palm oil-based biodiesel. The results indicated that all the tested DESs were able to remove all free glycerol successfully. The Central Composite Design (CCD) of the Response Surface Methodology (RSM) was used to to experiment design and optimization of total glycerol removal using ethylene glycol-based DESs and 2,2,2-Trifluoroacetamide-based DESs. The maximum total glycerol removal by ethylene glycol-based DESs was obtained at 0.66 ethylene glycol mole fraction and at DES/biodiesel molar ratio of 3 with removal efficiency of 23.85% as well as by 2,2,2-Trifluoroacetamide-based DESs at 0.60 2,2,2-Trifluoroacetamide mole fraction and at DES/biodiesel molar ratio of 2.93 with removal efficiency of 29.29%. The reusability of these DESs for removing free glycerol and total glycerol content from palm oil-based biodiesel was also investigated. This study proves that both ammonium salt-non glycerol based DESs can be successfully employed to remove the glycerol from palm oil-based biodiesel.

Study on separation of acetonitrile and methanol azeotropic system using tetraethylammonium chloride-based deep eutectic solvents

Understanding the speciation of metal ions in heterogeneous hydrogen-bonded deep eutectic solvents (DES) has immense importance for their wide range of applications in green technology, environmental remediation, and nuclear industry. Unfortunately, the fundamental nature of the interaction between DES and actinide ions is almost completely unknown. In the present work, we outline the speciation, solvation mechanism, and redox chemistry of uranyl ion (UO22+) in DES consisting of choline chloride (ChCl) and urea as the hydrogen-bond donor. Electrochemical and spectroscopic techniques along with molecular dynamics (MD) simulations have provided a microscopic insight into the solvation and speciation of the UO22+ ion in DES and also on associated changes in physical composition of the DES. The hydrogen-bonded structure of DES plays an important role in the redox behavior of the UO22+ ion because of its strong complexation with DES components. X-ray absorption spectroscopy and MD simulations showed strong covalent interactions of uranyl ions with the constituents of DES, which led to rearrangement of the hydrogen-bonding network in it without formation of any clusters or aggregations. This, in turn, stabilizes the most unstable pentavalent uranium (UO2+) in the DES. MD analysis also highlights the fact that the number of H-bonds is reduced in the presence of uranyl nitrate irrespective of the presence of water with respect to pristine reline, which suggests high stability of the formed complexed species. The effect of added water up to 20 v/v % on speciation is insignificant for DES, but the presence of water influences the redox chemistry of UO22+ ions considerably. The fundamental findings of the present work would have far reaching consequences on understanding DES, particularly for application in the field of nuclear fuel reprocessing.

Prediction of glycerol removal from biodiesel using ammonium and phosphunium based deep eutectic solvents using artificial intelligence techniques

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, high viscosity while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen box acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBD, the DES forms a eutectic mixture resulting in a large melting point depression due to extensive hydrogen bonding between the components.Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of two DESs: glyceline (glycerol + choline chloride) and ethaline (ethylene glycol + choline chloride). Fast-field cycling 1H relaxometry, pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), 13C NMR relaxation, and pressure-dependent NMR experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from 13C relaxation indicate slow local motion of glycerol at low choline chloride (ChCl) content. We show how the additional hydroxyl group present in glycerol contributes to not only higher viscosities, but a larger perturbation of the hydrogen bonding network by the addition of ChCl.Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiPF6, LiBF4, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. We observe that due to anion effects, the heterogeneities present in DES result in differential solvation for some species where there is a distinction of lithium salts co-existing in these holes as well as the bulk. The large changes in the structural organization of DESs that result from the presence of lithium salts will serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

This study investigates the effect of using water as a low-viscosity component in ternary amine-based deep eutectic solvents (DESs) on the physicochemical properties, thermal stability, and CO2 absorption capacity of the resulting DESs. It should be emphasized that water is a component of the ternary DES. The effect of water content in the DES, type of hydrogen bond acceptors (HBAs), hydrogen bond donors (HBDs), and HBA:HBD ratio on the above parameters was investigated. Moreover, the effect of temperature and pressure on the CO2 absorption capacity of DESs was predicted using the predictive model COSMO-RS. This model was also used to predict the CO2 solubility in the DESs and the results were compared with the experimental values. The results showed that the addition of small amounts of water, e.g., 5 and 10 wt% during preparation, can significantly decrease the viscosity of the resulting DESs, up to 25% at room temperature, while maintaining the high CO2 absorption capacity and high thermal stability. The ternary DESs based on MEA exhibited a high CO2 absorption capacity of 0.155–0.170 g CO2 / g DES. The ternary DESs were found to be thermally stable with a decomposition temperature of 125°C, which promotes the use of such solvents in post-combustion capture processes. Finally, COSMO-RS proved to be a suitable tool for qualitative prediction of CO2 solubility in DESs and demonstration of trends related to the effects of temperature, pressure, molar ratio, water content, HBD and HBA on CO2 solubility.

Insights into the enhanced thermal stability of lysozyme with altered structure and activity induced by choline chloride-based deep eutectic solvents containing polyols and sugars

The liquid–liquid extraction of a nitrogen-containing aromatic “pyridine” and nitrogen/sulfur-containing aromatic “benzothiazole” from n-hexane and n-heptane using deep eutectic solvents (DESs) was studied in this work. A DES composed of methyltriphenylphosphonium bromide as hydrogen bond acceptor and ethylene glycol as hydrogen bond donor was selected for this separation. The main objective of this work was to assess whether the same DES can be applied for the denitrogenation “extraction of pyridine” and desulfurization “extraction of benzothiazole” of fuels. Moreover, the influence of n-alkane chain length on the extraction performance was studied. First, the solubilities of the pyridine, benzothiazole, n-hexane, and n-heptane in the DES were determined at 298.2 K and 1.01 bar. Thereafter, the pseudoternary liquid–liquid equilibrium (LLE) data for the four systems {n-hexane + pyridine + DES}, {n-heptane + pyridine + DES}, {n-hexane + benzothiazole + DES}, and {n-heptane + benzothiazole + DES} were determined at a temperature of 298.2 K and a pressure of 1.01 bar. The assumption of a pseudoternary system was validated showing that none of the DES’ constituents appears in the raffinate phase. From the LLE data the distribution ratios and selectivites of pyridine and benzothiazole were calculated. Both pyridine and benzothiazole were successfully extracted from their mixtures with n-hexane and n-heptane, with pyridine showing higher selectivity than benzothiazole and almost similar distribution ratios. Finally, The LLE data were correlated with the nonrandom two-liquid model using ASPEN PLUS. The modeled results showed a strong correlation with the experimental results (relative mean standard deviation (%)) = 0.04–0.36).

Experimental and mechanism study on the separation of isobutyl alcohol and water azeotrope using hydrophobic deep eutectic solvents

Deep eutectic solvents-based adsorbents in environmental analysis

Novel chemistry of Deep Eutectic Solvents (DES) is a matter of current interest as the unusual properties of these solvents make them a versatile medium for a variety of reactions. In particular, they provide media with a wide potential window and high ionic strength for the redox chemistry of metals. A wide range of type II DES (Metal halide (MX) + Hydrogen Bond Donor (HBD)) with AlCl3 (MX) have been synthesised, where hydrogen bond donors (HBD) included acetamide, methyl-, dimethyl-, trimehylacetamide, urea, di- and tetramethylurea. The ratio of AlCl3 - HBD was maintained at 1.5:1 throughout. Viscosity and conductivity of these novel DES, have been related to the melting point of HBD as well as to the availability of proton exchanging groups. Mechanisms of aluminium deposition/dissolution from room temperature chloroaluminate melts were studied in order to elucidate the effects of amines type on the properties of these novel electrolytes. Mass transport and speciation were investigated by means of Electrochemical Quartz Crystal Microbalance (in dispersive mode), UV-Vis and NMR. It was found that although the higher deposition rate was proportional to the higher conductivity of the respective DES, the rate of the stripping process was related to the type of HBD used. Creation of an aluminium based battery requires a balance between current efficiency and deposition rate and this can be achieved by a choice of suitable HBD. The influence of surface tension of DES on their electrochemical properties, and ultimately availability of proton exchanging groups to participate in liquid formation is currently under investigation. Figure 1

The pretreatment or disruption of a cellulose I \(\beta \) crystallite by four deep eutectic solvents (DES): choline-chloride ethylene glycol, choline-chloride oxalic acid, choline-chloride urea, and choline-chloride levulinic acid, was described from the atomistic interactions observed in molecular dynamics and ab-initio (NCI-AIM) studies. The cellulose I \(\beta \) disruption was studied considering plausible correlations between the Kamlet-Taft (α and β) solvent parameters, and a series of thermodynamic, structural, and energetic properties. It was found that the Kamlet-Taft parameters correlated with the thermodynamic properties of the DES, as well as their variations after the addition of the cellulose crystallite. Structural analysis revealed that the weaker the interactions within the molecules of the solvent, the stronger the interactions between the hydroxyl group from cellulose with the chloride anion and with the hydrogen bond donor. Further analysis indicated that the \(R-CO-R\) moieties in the hydrogen bond donor within the solvent, displayed best interplaying with the cellulose. The hydrogen bond occupancies within the cellulose crystallite, evidenced that the main \(O6-H6\cdots O2/O3\) and \(O2-H2\cdots O6\) interchain hydrogen bonds in the glucan located at the edge of the solute, were replaced by weak \(O6-H6\cdots O4\) hydrogen bonds in all solvents. This effect was related to the \({O/Cl}_{DES}\cdots H-donor\) and \({O}_{DES}-{H}_{DES}\cdots acceptor\) HBs between cellulose and DES molecules, and it was confirmed by the non-covalent interactions obtained through DFT calculations. The energetic interactions and the atomistic degree of disruption of the cellulose crystallite, were not completely described by the Kamlet-Taft β or α parameters when considered separately. Surprisingly, by using the net basicity (\(\beta -\alpha \)) definition such correlations were improved, suggesting that both parameters must be considered together to develop new, green, and sustainable solvents for cellulose pretreatment process.Graphic abstract

Gallic acid (GA) (3,4,5-trihydroxybenzoic acid), which is a natural secondary metabolite and widely isolated from various plants, is for the first time employed as a hydrogen bond donor (HBD) for preparing a deep eutectic solvent (DES) with choline chloride (ChCl) as a hydrogen bond acceptor (HBA). This DES has been applied as an extractant to separate gycerol from biodiesel. The finding indicates that a DES could be formed at a molar ratio of ChCl to GA of 5 : 1, 6 : 1, and 7 : 1. The characterization of the synthesized DES shows its acidic polar property with a pH of lower than its constituents, density of lower than biodiesel, and the viscosity within the range reported for previously prepared DES. Functional groups analysis using FTIR indicated the presence of all functional groups from GA and ChCl in the DES structure, along with the absence of any new spectral peaks, suggesting that there was no chemical reaction involved in the DES formation. Its ability to reduce the glycerol concentration in the biodiesel in the range of 74.6 to 99.8 % denotes its capability as a potential extractant for separation of glycerol from biodiesel.