Deep eutectic solvents-based adsorbents in environmental analysis

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.

Investigating the effect of systematically modifying the molar ratio of hydrogen bond donor and acceptor on solvation characteristics of deep eutectic solvents formed using choline chloride salt and polyalcohols

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.

Insight into the experiment and extraction mechanism for separating carbazole from anthracene oil with quaternary ammonium-based deep eutectic solvents

The zinc secondary batteries (ZIBs) are promoting as one of the next-generation batteries using zinc with a high theoretical capacity as a negative electrode. However, the dendrite growth due to repeated charging and discharging are disadvantages. Deep eutectic solvents (DESs), which are obtained by mixing two or more compounds consisting of a hydrogen bond acceptor and a hydrogen bond donor, have suppressed dendrite growth.[1] Mixing Zn (ClO4)2・6H2O (solid) and sulfolane (SL, melting point 27.5 ℃) yields a DES and the DES prevents dendrite growth. However, the whisker-like Zn deposition is observed at high current density, suggesting that the DES cannot inherently prevent dendrite growth.[2] On the other hand, Dokko et al. have reported that the Li+ hopping conduction occurs in SL based super-concentrated electrolyte solution, suppressing concentration polarization.[3] Liquid structure plays a crucial role in the Li+ hopping conduction. In this work, to develop a DES that prevents dendrite growth by suppressing the concentration polarization, we prepared the SL based DESs consisting of various anions.Zn(ClO4) DES was prepared by mixing Zn (ClO4)2・6H2O and SL. We also prepared the DES with the anion changed to Zn (TfO)2. The liquid structures of Zn-SL DES were observed using a laser Raman spectrophotometer NRS-4500. The chronoamperometry of the Zn-symmetric cell was measured at room temperature. An electrochemical measurement system (SP-150, Bio-logic) was used for the electrochemical measurement.In the Raman spectrum of neat SL, a Raman band assigned to the scissoring vibration of SO2 is observed at 567 cm-1. This Raman bands appears at 571 cm-1 and 574 cm-1 in the Raman spectrum for Zn (ClO4)2 DES and Zn (TfO)2 DES, respectively. In addition, the FWHM of the band of Zn (TfO)2 DES is larger than that of Zn (ClO4)2 DES. In high concentration Li-SL electrolyte, Li+ interacts not only with SL but also with anions to form the contact ion pairs (CIP) and aggregates (AGG) in which the anion cross-links Li+. As these liquid structure form, the Raman band shifts to the high wavenumber and broadens. Therefore, the CIP and AGG may be easily formed in Zn (TfO)2 DES. This is expected to suppress concentration polarization and dendrite growth. In the case of migration-controlled Zn2+ transport, the current should increase with increasing the applied voltage. For the Zn (ClO4)2 DES, there was no increase in current density of the symmetric cell with increasing applied voltage. In contrast, for the Zn (TfO)2 DES, the current value increased continuously with increasing applied voltage, reaching a high value of 10.8 mA cm-2 at 600 mV. In addition, despite the low conductivity of Zn (TfO)2 DES, the high current density was observed upon polarization. We believe that this is due to the rapid transport of zinc by forming CIP and AGG. However, for Zn (TfO)2 DES, the current decay due to concentration polarization is observed at large polarization. To suppress the concentration polarization, Zn2+ concentration was increased and then the chronoamperometry measurements was conducted again. In the Zn (TfO)2 DES, there was no increase in the current density of the symmetric cell with increasing the applied voltage. On the other hand, the current density of the symmetric cell with Zn (ClO4)2 DES suddenly increased from 300 mV. This may be due to a change in electrode area caused by the formation of dendrites.４．References[1] Funian Mo, Guojin Liang, Qiangqiang Meng, et. al. Energy Environ. Sci., 706-715 (2019)[2] Xidong Lin, Guodong Zhou, Matthew J. Robson, et. al. Adv.Funct.Mater. 2109322 (2021)[3] Kaoru Dokko, Daiki Watanabe, et. al. J.Phys.Chem. B, 122, 10736–10745, (2018)

New chloroacetic acid-based deep eutectic solvents for solubilizing metal oxides

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

Redox and emission characteristics of Eu3+ in deep eutectic solvent: Unraveling the hidden potential of DES as luminescent media

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).

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.

Comprehensive exploration of the adsorption capacity of innovative betaine-based deep eutectic solvents for carbon dioxide capture

Deep eutectic solvents (DES) are an emerging type of green solvents that have been used in aqueous two-phase systems (ATPS). However, its application in ATPS can present some limitations, due to the nonstoichiometric partition between the two aqueous phases of the hydrogen-bond acceptor (HBA) and the hydrogen-bond donor (HBD) that compose the DES. In this context, pseudoternary DES-based ATPS, in which DES' components stoichiometry is maintained, appear as potential liquid–liquid systems to the extraction and separation of biomolecules. Here the pH influence on the phase equilibrium and DES' components partition on ATPS composed of DES, constituted by tetrabutylammonium chloride + ethanol/ n-propanol, and potassium citrate/citrate buffer was evaluated at 298 K and pH 9, 7, and 5. In addition the partition coefficients of gallic acid, caffeine, and L-tryptophan were also determined, allowing inferences to be made on the potential application of these systems. The results suggest that the change on the pH impacts the chemical speciation of the potassium citrate salt, and consequently its ability to form an ATPS, allowing the stoichiometric partition of DES' components and the formation of a pseudoternary system and the tuning of biomolecules partition behavior to be controled.

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

Deep eutectic solvents (DES), a class of novel green solvents, offer a promising alternative for the extraction of bioactive compounds from traditional Chinese medicinal herbs, addressing both environmental and efficiency limitations associated with conventional organic solvents. Their advantages include straightforward synthesis, low toxicity, biodegradability, and tunable physicochemical properties. This article systematically summarizes recent advances in the application of DES for extracting various active ingredients of traditional Chinese medicine, including flavonoids, saponins, alkaloids, polysaccharides, polyphenols, and volatile oils. It focuses on analyzing the structural characteristics of these compound classes and the underlying principles guiding DES selection, categorizes DES systems suitable for each class of active ingredient, and outlines the corresponding optimized process conditions. Building upon this foundation, the extraction mechanisms—particularly hydrogen bonding interactions and polarity matching between DES and target components—were investigated, and the influencing factors and underlying patterns governing DES extraction efficiency were systematically summarized. In response to current research challenges—including high viscosity, difficult separation and recovery, and the absence of a targeted design theory—future research directions were proposed to support the continued advancement of green extraction processes for traditional Chinese medicine.

Green fractionation and a comprehensive overview of lignin molecular structures during the DES (deep eutectic solvent) pretreatment are very important for lignin valorization and the whole biorefinery process. Herein, intractable woody biomass (poplar wood) was pretreated with five types of carboxylic-acid-based DESs (acetamide served as an HBA (hydrogen bond acceptor), propanedioic acid, tartaric acid, malic acid, glutaric acid, and succinic acid served as HBDs (hydrogen bond donors)) under the optimized pretreatment conditions. Results showed that the optimal delignification ratio was achieved for tartaric-acid-based DES at 140 °C for 20 min under microwave-assisted heating. Two-dimensional HSQC NMR data demonstrated that the isolated poplar DES lignin consisted mainly of β-β, β-O-4 (normal and acylated forms), β-5, and esterified p-hydroxybenzoates (PBs) in different contents. Especially, the contents of β-O-4 in the isolated DES lignin fractions varied based on the pretreatment temperature and different chemical compositions of the DES. The antioxidant activity (2,2-diphenyl-1-picrylhydrazyl, DPPH analysis), microstructure (scanning electron microscope, SEM), and molecular weights (gel permeation chromatography, GPC) of the DES lignin fractions demonstrated that the DES delignification promoted the rapid assembly of lignin nanoparticles (LNPs) and could yield homogeneous lignin (1.23 < PDI < 1.58) with controlled nanometer size (30–170 nm) and good antioxidant activity. This study will improve the knowledge of structural changes of lignin during the different carboxylic-acid-based DES pretreatments and maximize the lignin valorization.