Eutectics: formation, properties, and applications

Deep eutectic solvent assisted fabrication of zirconium phytate thin nanosheets for important biomass transformations

Utilization of naturally occurring resources to construct functional catalytic materials is significantly important, and facile and environmental-benign strategies are highly desired to afford the materials having a specific structure and good catalytic activity. Herein, we reported an innovative deep eutectic solvent (DES)-assisted strategy to synthesize zirconium phytate with a thin nanosheet structure (denoted as Zr-Phy-DES) using plant-originated phytic acid (PhyA) as the renewable building block. This strategy was eco-friendly and adjustable owing to the designability of DESs. The Zr-Phy-DES as an acidic catalyst showed high activity on two important biomass transformations, i.e., dehydration of carbohydrates and Meerwein-Ponndorf-Verley reduction of ethyl levulinate. Interestingly, Zr-Phy-DES showed higher catalytic performance than the zirconium phytates prepared in ethylene glycol and N,N-dimethylformamide, confirming the advantage of DESs for preparing functional materials. Notably, the unique feature of this proposed strategy is that renewable catalysts are prepared in an environmental-benign solvent for efficiently catalyzing biomass transformation.

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An eco-friendly strategy for preparing catalytic materials with a specific structure

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The catalytic activity of the prepared materials varied with the type of solvents

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The material prepared in deep eutectic solvent showed better performance

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Catalytic materials from natural resources and green solvents to convert biomass

Natural Deep Eutectic Solvents Based on Choline Chloride and Phenolic Compounds as Efficient Bioadhesives and Corrosion Protectors

Natural deep eutectics solvents (NADES), owing to their high solvation capacity and nontoxicity, are actively being sought for many technological applications. Herein, we report a series of novel NADES based on choline chloride and plant-derived polyphenols. Most of the obtained phenolic NADES have a wide liquid range and high thermal stability above 150 °C. Among them, small-sized polyphenols, like pyrogallol, vanillyl alcohol, or gentisic acid, lead to low-viscosity liquids with ionic conductivities in the order of 10^-3 S cm^-1 at room temperature. Interestingly, polyphenols possess valuable properties as therapeutic agents, antioxidants, adhesives, or redox-active compounds, among others. Thus, we evaluated the potential of these novel NADES for two applications: bioadhesives and corrosion protection. The mixture of choline chloride-vanillyl alcohol (2:3 mol ratio) and gelatin resulted in a highly adhesive viscoelastic liquid (adhesive stress ≈ 135 kPa), affording shear thinning behavior. Furthermore, choline chloride-tannic acid (20:1) showed an extraordinary ability to coordinate iron ions, reaching excellent corrosion inhibitive efficiencies in mild steel protection.

CO2 capture by 1,2,3-triazole-based deep eutectic solvents: the unexpected role of hydrogen bonds

Herein, tetraethylammonium 1,2,3-triazolide ([Et₄N][Tz]), 1,2,3-triazole (Tz), and ethylene glycol (EG) are used to form DESs for CO₂ capture. Surprisingly, [Et₄N][Tz]-EG DESs can react with CO₂, but [Et₄N][Tz]-Tz cannot react with CO₂, although both of the two systems contain the same anion [Tz]^-. Unexpectedly, with the addition of EG to [Et₄N][Tz]-Tz, the formed ternary DESs [Et₄N][Tz]-Tz-EG can react with CO₂, although neither EG nor [Et₄N][Tz]-Tz can react with CO₂ before the combination of them. NMR, FTIR and theoretical calculation results disclose that the surprise CO₂ absorption behavior mainly depends on the strength of hydrogen bonds (H-bonds) between the anion [Tz]^- and H-bond donors (EG or Tz). The strength of the H-bond between [Tz]^- and Tz is much stronger than that between [Tz]^- and EG. The strong H-bond between [Tz]^- and Tz in [Et₄N][Tz]-Tz greatly reduces the basicity of [Tz]^-, rendering the anion [Tz]^- unreactive to CO₂. In [Et₄N][Tz]-Tz-EG ternary DESs, EG competes with Tz to form a H-bond with [Tz]^-, which weakens the strength of the H-bond between [Tz]^- and Tz. Moreover, H-bonds also impact the desorption behavior. [Et₄N][Tz] : EG (1 : 2) is regenerated at 60 °C, whereas the chemisorbed CO₂ by [Et₄N][Tz] : Tz : EG (1 : 2 : 2) can be released even down to 30 °C.

Non-Flammable Sodium Asymmetric Imide Salt-Based Deep Eutectic Solvent for Supercapacitor Applications

This study reports two deep eutectic solvents (DESs) based on alkaline imide salts with asymmetric anions as functional electrolytes for supercapacitor (SC) application. The eutectic mixture of sodium (fluorosulfonyl) (trifluoromethanesulfonyl) imide (NaFTFSI) or sodium cyano-trifluoromethanesulfonyl imide (NaTFSICN) with ethylene carbonate (EC) delivers a non-flammable and stable liquid. The eutectic diagrams of the electrolytes directed to an optimal composition ( w salt = 0.25), hinging to that of conventional carbonate-based electrolytes, i.e., 1 mol L -1 . The volumetric properties of the DESs revealed a "stacking" effect, reflecting a strong coordination bond between the imide and EC anions without solvating the Na + cations. The DES transport properties (i.e., viscosity, conductivity, and ionicity) and temperature variations designate a high organization, similar to ionic liquids. The DESs, when coupled with activated carbon electrodes in a two-electrode symmetric configuration, yield specific capacities of 150 F g -1 at a normalized current density of 0.5 A g -1 (and 120 F g -1 at 2 A g -1 ). The SC maintained 80% of its initial capacity beyond 100 h of floating at an operating voltage of 2.4 V and showed a 150 mV per hour potential loss under self-discharge. The devised eutectic mixtures offer a promising new pathway for simple, safe, and effective electrolytes for SC applications.

Low-molecular-weight supramolecular adhesives based on non-covalent self-assembly of a small molecular gelator

Currently developed adhesives are overwhelmingly polymeric in nature. Herein, we highlight for the first time the potential of supramolecular eutectogels assembled from small molecules as robust low-molecular-weight (LMW) supramolecular adhesives in air, water and organic solvents, and under low temperatures. These supramolecular eutectogels were produced from commercial alkyl trimethyl ammonium bromide (C_nTAB) in emerging deep eutectic solvents (DESs), which demonstrated rapid (∼2 min), robust, and tunable adhesion to both hydrophilic and hydrophobic surfaces at room temperature in air. Moreover, high adhesion performance was maintained even in liquid nitrogen (-196 °C), underwater, and in organic solvents. A study of the structure-property relationship of these adhesives and molecular dynamics (MD) simulations further clarified the assembly and adhesion mechanism of the C₁₂TAB molecules in DESs. Compared with traditional polymer adhesives and several existing examples of LMW supramolecular adhesives with solvent-free dry network structures, the spontaneous self-assembly of LMW gelators in versatile DESs provides a new strategy for the facile construction of high-strength supramolecular adhesives with gel network structures for a diverse range of harsh environments.

In situ activation of green sorbents for CO2 capture upon end group backbiting

Thermolysis of a urethane end group was observed as a first time phenomenon during activation. This unzipping mechanism revealed a new amine tethering point producing a diamine-terminated oligourea ([10]-OU), acting as a green sorbent for CO₂ capturing. The oligomer backbites its end group to form propylene carbonate (PC), as proved by in situ TGA-MS, which can reflect the polymer performance by maximizing its capturing capacity. Cross polarization magic angle spinning (CP-MAS) NMR spectroscopy verified the formation of the proven ionic carbamate (1:2 mechanism) with a chemical shift at 161.7 ppm due to activation desorption at higher temperatures, viz., 100 °C (in vacuo) accompanied with bicarbonate ions (1:1 mechanism) with a peak centered at 164.9 ppm. Fortunately, the amines formed from in situ thermolysis explain the abnormal behavior (carbamates versus bicarbonates) of the prepared sample. Finally, ex situ ATR-FTIR proved the decomposition of urethanes, which can be confirmed by the disappearance of the pre-assigned peak centered at 1691 cm^-1. DFT calculations supported the thermolysis of the urethane end group at elevated temperatures, and provided structural insights into the formed products.

Neoteric deep eutectic solvents: history, recent developments, and catalytic applications

Deep eutectic solvents (DESs) are modified versions of ionic liquids (ILs) and are formed by the fusion of polar components (liquids or solids) via hydrogen bonding interactions. DESs are prepared by the simple mixing of two or three cheap constituents (that are capable of self-association) with gentle heating, which leads to a drastic decrease in their melting points. The resultant clear homogeneous mixture consists of cations, anions, as well as neutral molecules; this will contribute both ionic and molecular solvent properties to the DESs. DESs have emerged as alternatives to conventional organic solvents and ILs, which meet different criteria such as availability, low cost, low toxicity, biodegradability, recyclability, ease of preparation method, tunable, and designer physiochemical properties. Many of them have attracted considerable attention and haave been applied in distinct fields of chemistry. To summarize the full-scale development of DESs, this review discusses the history, classifications, various methods of preparation, properties, and some major applications in catalysis in the last three years. This review is expected to be helpful for the further development of DESs based on a summary of the fundamental research in the field.

Ternary Deep Eutectic Solvent (DES) with a Regulated Rate-Determining Step for Efficient Recycling of Lithium Cobalt Oxide

Deep eutectic solvents (DESs) have attracted extensive research for their potential applications as leaching solvent to recycle valuable metal elements from spent lithium ion batteries (LIBs). Despite various advantages like being economical and green, the full potential of conventional binary DES has not yet been harnessed because of the kinetics during leaching. Herein, we consider the fundamental rate-determining-step (RDS) in conventional binary DES and attempt to design ternary DES, within which the chemical reaction kinetics and diffusion kinetics can be regulated to maximize the overall leaching rate. As a proof of concept, we show that the ternary choline chloride/succinic acid/ethylene glycol (ChCl/SA/EG) type ternary DES can completely dissolve LCO powder at 140 °C in 16 h. By systematically studying the leaching process at various conditions, the energy barrier during leaching can be calculated to be 11.77 kJ/mol. Furthermore, we demonstrate that the extraction of the cobalt ions from the leaching solution can be directly achieved by adding oxalic ions without neutralizing the solution. The precipitate can be used to regenerate LCO with high purity. The recycled materials show comparable electrochemical performance with commercial LCO. Our design strategy of ternary DES with regulated RDS is expected to have both scientific and technological significance in the field of hydrometallurgical recycling of LIBs.

Diels-Alder Cycloaddition Reactions in Sustainable Media

Diels-Alder cycloaddition reaction is one of the most powerful strategies for the construction of six-membered carbocyclic and heterocyclic systems, in most cases with high regio- and stereoselectivity. In this review, an insight into the most relevant advances on sustainable Diels-Alder reactions since 2010 is provided. Various environmentally benign solvent systems are discussed, namely bio-based derived solvents (such as glycerol and gluconic acid), polyethylene glycol, deep eutectic solvents, supercritical carbon dioxide, water and water-based aqueous systems. Issues such as method's scope, efficiency, selectivity and reaction mechanism, as well as sustainability, advantages and limitations of these reaction media, are addressed.

Deep eutectic solvents composed of bio-phenol-derived superbase ionic liquids and ethylene glycol for CO2 capture

Deep eutectic solvents (DESs) formed by bio-phenol-derived superbase ionic liquids (ILs) and ethylene glycol (EG) exhibit a high CO₂ capacity, up to 1.0 mol CO₂/mol DESs, which is much better than those of the parent ILs. Surprisingly, mechanism results indicate that CO₂ reacts with EG, but doesn't react with phenolic anions in the solvent, which is different from other DESs formed by superbase ILs and EG. The reaction pathway between CO₂ and DESs used in this work may include two steps. The first step is the acid-base reaction between the phenolic anion and EG, which forms HO-CH₂-CH₂-O^-, and then CO₂ is attached to the anion HO-CH₂-CH₂-O^- to form a carbonate species.

CO2 Absorption Mechanism by the Deep Eutectic Solvents Formed by Monoethanolamine-Based Protic Ionic Liquid and Ethylene Glycol

Deep eutectic solvents (DESs) have been widely used to capture CO₂ in recent years. Understanding CO₂ mechanisms by DESs is crucial to the design of efficient DESs for carbon capture. In this work, we studied the CO₂ absorption mechanism by DESs based on ethylene glycol (EG) and protic ionic liquid ([MEAH][Im]), formed by monoethanolamine (MEA) with imidazole (Im). The interactions between CO₂ and DESs [MEAH][Im]-EG (1:3) are investigated thoroughly by applying ¹H and ¹³ C nuclear magnetic resonance (NMR), 2-D NMR, and Fourier-transform infrared (FTIR) techniques. Surprisingly, the results indicate that CO₂ not only binds to the amine group of MEA but also reacts with the deprotonated EG, yielding carbamate and carbonate species, respectively. The reaction mechanism between CO₂ and DESs is proposed, which includes two pathways. One pathway is the deprotonation of the [MEAH]⁺ cation by the [Im]^- anion, resulting in the formation of neutral molecule MEA, which then reacts with CO₂ to form a carbamate species. In the other pathway, EG is deprotonated by the [Im]^-, and then the deprotonated EG, HO-CH₂-CH₂-O^-, binds with CO₂ to form a carbonate species. The absorption mechanism found by this work is different from those of other DESs formed by protic ionic liquids and EG, and we believe the new insights into the interactions between CO₂ and DESs will be beneficial to the design and applications of DESs for carbon capture in the future.

Calorimetric effect and thermokinetics in the formation process of a deep eutectic solvent

For the first time, we report the calorimetric effect and thermokinetics in the formation process of a model deep eutectic solvent (DES), ChCl:urea. Mixing of a 1-to-2 molar ratio of choline chloride and urea shows a rapid endothermic process under stirring. The rate constants and reaction orders are determined by analyzing the thermokinetic curves at several constant temperatures. Low activation energy and activation parameters demonstrate that the formation of this DES is a rapid process. Other thermodynamic parameters are also estimated.

Design and thermophysical characterization of betaine hydrochloride-based deep eutectic solvents as a new platform for CO2 capture

A schematic representation depicting the preparation and thermophysical insight into new deep eutectic solvents (DESs) and their utilization for CO2 capture.

Understanding of Bulk and Interfacial Structures Ternary and Binary Deep Eutectic Solvents with a Constant Potential Method: A Molecular Dynamics Study

In the last decade, deep eutectic solvents (DESs) emerge as promising electrolytes in supercapacitors and rechargeable batteries due to their unique properties, wide electrochemical window, low viscosity, and high ionic...

Room-temperature conversion of CO2 into quinazoline-2,4(1H,3H)-dione using deep eutectic solvents at atmospheric pressure with high efficiency

Deep eutectic solvents are found to catalyze CO2 conversion to quinazoline-2,4(1H,3H)-dione at room temperature and atmospheric pressure with nearly 100% yields for the first time.

Acidity Scales of Deep Eutectic Solvents based on IR and NMR

Acidic deep eutectic solvents (ADESs) have been utilized in various applications. Clearly, it is crucial to obtain acidity information that could reveal the relationship with performance. However, appropriate methods of...

Ionothermal synthesis of calcium-based metal–organic frameworks in a deep eutectic solvent

The ionothermal synthesis of Ca-MOFs has been performed using the 1 : 2 choline chloride : e-urea deep eutectic solvent, allowing the preparation of water sensitive materials.

Thermal, chemical, electrochemical, radiolytic and biological stability of ionic liquids and deep eutectic solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) are regarded as two kinds of novel solvents with high tunability and they exist in liquid-state for a wide range of temperature....

Room-temperature dissolution of PbI2 by a PEGylated deep eutectic solvent with high efficiency

PEGylated deep eutectic solvents could dissolve toxic PbI2 efficiently at room temperature.

Magnetic deep eutectic solvents: formation and properties

Deep eutectic solvents (DESs) have been well-known as novel solvents due to their unique properties, which are dispensable for the development of green chemistry in future. The CoCl2·6H2O and NiCl2·6H2O-based...

2D amorphous bi-metallic NiFe nitrides for a high-efficiency oxygen evolution reaction

Two-dimensional bi-metallic NiFe nitrides (2D NiFe-N) are successfully synthesized in the designed ternary deep eutectic solvents under the guidance of DFT calculations. Taking advantage of the unique properties of large-size, ultrathin amorphous 2D structure and modulable electronic structure, the NiFe_0.05-N exhibits extraordinary OER performance with relatively low overpotential of 238 mV at 10 mA cm^-2 and durable stability.

Eutectic-based liposome as a potential delivery system of paeonol

Deep eutectic solvents (DESs), as a new type of green solvent, show great advantages of easy preparation and no need of purification after synthesis and have great potential applications in various fields. Moreover, when combining active pharmaceutical ingredients (APIs) with DESs, a new type of drug delivery system called a therapeutic deep eutectic solvent (THEDES) can be developed to increase the solubility of the APIs and/or their permeation ability as well as bioactivity. Herein, we have designed a new THEDES based on paeonol and lauric acid with a molar ratio of 1 : 1. The physicochemical properties as well as the bioactivity were investigated by a series of techniques. The THEDES showed better solubility in water and similar bioactivities as compared to the pure APIs. Besides, we further prepared a THEDES liposome, which possessed an average size of about 120 nm with an encapsulation efficiency of 84%. The obtained liposome showed good stability during the experimental period, which indicated a potential application for the delivery of paeonol. The results presented herein suggested that THEDES may be regarded as a new strategy for the effective delivery of APIs.

Fabricating lignin-containing cellulose nanofibrils with unique properties from agricultural residues with assistance of deep eutectic solvents

Lignocellulosic biomass-derived nanocellulose has been attracting more and more attentions due to its distinguished advantages and various applications, but its development has been restricted by the preparation especially with environmental friendly approach. Herein, lignin-containing cellulose nanofibrils (LCNF) was prepared from corncob via the combined pretreatment of choline chloride-based DES (ChCl-DES) and enzymatic hydrolysis followed by high-pressure homogenization. The effects of different types of ChCl-DES on the properties of LCNF were investigated and compared. The results showed that LCNF can be successfully fabricated through the combined pretreatments; the LCNF had an average diameter of 60-90 nm, exhibited good fluorescence, high thermal stability (up to 353 °C of T_max), hydrophobicity, stability, and redispersibility in organic solvent; AC-LCNF showed well oriented arrangement, the highest hydrophobicity and fluorescence, and distinguished redispersibility especially in DMSO. ChCl-DES as one green and sustainable approach would realize efficient separation and high value-added utilization of agricultural residues.

Paper-based aptamer-antibody biosensor for gluten detection in a deep eutectic solvent (DES)

Paper has been widely employed as cheap material for the development of a great number of sensors such as pregnancy tests, strips to measure blood sugar, and COVID-19 rapid tests. The need for new low-cost analytical devices is growing, and consequently the use of these platforms will be extended to different assays, both for the final consumer and within laboratories. This work describes a paper-based electrochemical sensing platform that uses a paper disc conveniently modified with recognition molecules and a screen-printed carbon electrode (SPCE) to achieve the detection of gluten in a deep eutectic solvent (DES). This is the first method coupling a paper biosensor based on aptamers and antibodies with the DES ethaline. Ethaline proved to be an excellent extraction medium allowing the determination of very low gluten concentrations. The biosensor is appropriate for the determination of gluten with a limit of detection (LOD) of 0.2 mg L⁻¹ of sample; it can detect gluten extracted in DES with a dynamic range between 0.2 and 20 mg L⁻¹ and an intra-assay coefficient of 10.69%. This approach can be of great interest for highly gluten-sensitive people, who suffer from ingestion of gluten quantities well below the legal limit, which is 20 parts per million in foods labeled gluten-free and for which highly sensitive devices are essential.

Viscosity Investigations on the Binary Systems of (1 ChCl:2 Ethylene Glycol) DES and Methanol or Ethanol

In this study, the viscosity behavior of two mixtures of Ethaline (1 ChCl:2 ethylene glycol) with either methanol or ethanol were investigated over the temperature range of 283.15–333.15 K at atmospheric pressure. The measured viscosities of neat Ethaline, methanol, and ethanol showed reliable agreement with the corresponding reported literature values. The mixture viscosities were modeled by an Arrhenius-like model to determine the behavior of viscosity with respect to temperature. The data were also modeled by the four well-known mixture viscosity models of Grunberg–Nissan, Jouyban–Acree, McAllister, and Preferential Solvation. All of the model results were reliable, with the Jouyban–Acree and Preferential Solvation models showing the most accurate agreement with the experimental measurements. The Jones–Dole viscosity model was also investigated for the measured viscosities, and by analyzing the results of this model, strong interactions among Ethaline and the alcohol molecules were proposed for both systems. As a final analysis, viscosity deviations of the investigated systems were calculated to study the deviations of the viscosity behaviors with respect to ideal behavior. Both systems showed negative viscosity deviations at all of the investigated temperatures, with the negative values tending towards zero, and hence more ideal behavior, with increasing temperatures. Moreover, in order to correlate the calculated viscosity deviations, the Redlich–Kister model was successfully used for both systems and at each investigated temperature.

Time-dependent air quality and pollutant concentration in the Jingjinji region: future gas capture by green solvents

Time-dependent air quality, pollutant concentration, major pollutants and pollution level in Jingjinji (around Beijing) from 2016 to 2020 are analyzed.

Deep eutectic solvents for the preparation and post-synthetic modification of metal- and covalent organic frameworks

The use of deep eutectic solvents (DES) as media for the preparation of metal- and covalent organic frameworks (MOFs and COFs) and their post-synthetic modification towards composites is reviewed.