Applications of ionic liquids in electrochemical sensors

Ionic liquids (ILs) are molten salts with the melting point close to or below room temperature. They are composed of two asymmetrical ions of opposite charges that only loosely fit together (usually bulky organic cations and smaller anions). The good solvating properties, high conductivity, non-volatility, low toxicity, large electrochemical window (i.e. the electrochemical potential range over which the electrolyte is neither reduced nor oxidized on electrodes) and good electrochemical stability, make ILs suitable for many applications. Recently, novel ion selective sensors, gas sensors and biosensors based on ILs have been developed. IL gels were found to have good biocompatibility with enzymes, proteins and even living cells. Besides a brief discussion of the properties of ILs and their general applications based on these properties, this review focuses on the application of ILs in electroanalytical sensors.     

Melting properties of molten salts and ionic liquids. Chemical homology,correlation, and prediction

The application of the concept of chemical homology to describe melting properties of molten salts and ionic liquids (ILs) is analyzed. This concept was used several years ago to correlate and predict properties of solids and more recently to correlate melting temperatures of ILs. To analyze the characteristics of the extended method, this is first applied to melting properties of organic substances for which abundant data are available. The method is extended to analyze its applicability for properties of molten salts and ILs such as glass transition temperature, heat of melting, and entropy of melting. The foundation of the chemical homology concept is revised, and the difficulties for extending the method to correlate and predict melting properties of ILs are presented. Despite the difficulties, the homology concept can still be used with some conditions and limitations that are analyzed in this article. Several correlations are proposed.     

Ionic liquids in separation techniques

The growing interest in ionic liquids (ILs) has resulted in an exponentially increasing production of analytical applications. The potential of ILs in chemistry is related to their unique properties as non-molecular solvents: a negligible vapor pressure associated to a high thermal stability. ILs found uses in different sub-disciplines of analytical chemistry. After drawing a rapid picture of the physicochemical properties of selected ILs, this review focuses on their use in separation techniques: gas chromatography (GC), liquid chromatography (LC) and electrophoretic methods (CE). In LC and CE, ILs are not used as pure solvents, but rather diluted in aqueous solutions. In this situation ILs are just salts. They are dual in nature. Too often the properties of the cations are taken as the properties of the IL itself. The lyotropic theory is recalled and the effects of a chaotropic anion are pointed out. Many results can be explained considering all ions present in the solution. Ion-pairing and ion-exchange mechanisms are always present, associated with hydrophobic interactions, when dealing with IL in diluted solutions. Chromatographic and electrophoretic methods are also mainly employed for the control and monitoring of ILs. These methods are also considered. ILs will soon be produced on an industrial scale and it will be necessary to develop reliable analytical procedures for their analysis and control.     

A mini review on synthesis,properties and applications of deep eutectic solvents

Organic solvents have been of great importance for many chemical synthesis, storage and separation processes. The industries and research laboratories are heavily dependent on organic solvents in bulk; are highly volatile, lipophilic, toxic and causes a number of issues to the human health and the environmental fitness. Neoteric solvents have been proposed as a better substitute to these harmful organic solvents, and scientists have come up with several neoteric solvents in the last three decades, to name a few: ionic liquids (ILs), switchable solvents, bio-based solvents and deep eutectic solvents (DESs). These neoteric solvents attract a great deal of interest from the scientific community due to plenty of possibilities, therefore, they have huge impact and novel studies are reported quite frequently on the same. In this review, we intend to focus to brief on deep eutectic solvents, about their properties, synthesis, promising applications, and how they gradually emerged from ILs and later stood out as a different class of neoteric solvent, which overcomes many shortcomings of ILs. DESs are possibly receptive synthetic compounds and their relationship based on the hydrogen bond donor or acceptor restricts their reactivity and allow to explore in different disciplines of science.     

Retention characteristics of organic compounds on molten salt and ionic liquid-based gas chromatography stationary phases

The interest of using ionic liquids (ILs) as stationary phases in gas chromatography (GC) has increased in recent years. This is largely due to the fact that new classes of ILs are being developed that are capable of satisfying many of the requirements of GC stationary phases. This review highlights the major requirements of GC stationary phases and describes how molten salts/ILs can be designed to largely meet these needs. The retention characteristics of organic solutes will be discussed for ammonium, pyridinium, and phosphonium-based molten salts followed by imidazolium, pyridinium, pyrollidinium, and phosphonium-based IL stationary phases. The versatility of ILs allows for the development of stationary phases based on dicationic ILs, polymeric ILs, and IL mixtures. To aid in choosing the appropriate IL stationary phase for a particular separation, the reader is guided through the different types of stationary phases available to identify those capable of providing the desired separation selectivity of organic solutes while allowing for flexibility in ranges of temperature used throughout the separation.     

离子液体中的聚合反应研究进展

室温离子液体是一种新兴的可替代挥发性有机化合物（VOCs）的绿色溶剂和高效的反应介质，为减少或消除化学反应和过程工程中的环境问题提供了重要的途径。以离子液体为反应介质进行聚合反应，可消除或减小VOCs的危害，也可实现催化剂的有效回收利用和聚合物的纯化，更好地控制聚合反应及聚合产物的结构与性质、乃至直接用作高效的聚合催化剂。本文综述近年来离子液体中聚合反应的研究现状及最新进展，分析现存的问题，并展望今后的发展方向。     

离子液体参与构建的胶束

离子液体参与构建的有序组合体,以其独特的物理化学性质及在众多领域的应用潜能而引起广泛关注。本文结合我们的研究工作,对离子液体参与构建的胶束体系的主要研究成果进行了综述,重点介绍了传统表面活性剂在离子液体中胶束的形成、表面活性离子液体在水溶液中的聚集行为、离子液体作为添加剂对传统表面活性剂胶束的影响。在此基础上,归纳了部分体系胶束形成的机理和规律,并展望了离子液体构建的胶束体系研究和发展的方向。     

Temperature-responsive ionic liquid/water interfaces: relation between hydrophilicity of ions and dynamic phase change

Phase separation between ionic liquids (ILs) and molecular liquids is of interest physico-chemically, and also has industrial relevance. IL/water mixtures are of great interest in many fields. Unlike static phase separation between IL and water, dynamic shifts of IL/water mixtures between a homogeneous mixture and separate phases have a wide variety of applications. The miscibility of ILs with water generally increases upon heating, and a few ILs undergo a lower critical solution temperature (LCST)-type phase transition with water in which the separated biphases become miscible upon cooling. As the phase transition is controlled by changing the temperature by a few degrees, the LCST-type phase response of IL/water mixtures makes it possible to use ILs as solvents in various energy-saving processes. Since many hydrophilic ILs do not undergo phase separation with water, we aim to determine the necessary conditions under which hydrophobic ILs undergo the phase transition. Based on physico-chemical analysis of many hydrophobic ILs that undergo a phase separation after mixing with water, we find there is a particular range of "hydrophilicity" of these hydrophobic ILs within which the LCST-type phase transition is possible. Accordingly, a hydrophilicity index (HI) of ILs is proposed, in terms of the number of water molecules in the separated IL phase. The HI value proves to be a good indicator of the phase behaviour of IL/water mixtures, as well as their phase transition temperature. Potential application of the LCST-type phase change to the selective extraction of water-soluble proteins is also summarised.     

Ionogels, ionic liquid based hybrid materials

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).     

Interface properties of ionic liquids containing metal ions: features and potentialities

Interfaces and surfaces are the regions where important events happen: catalysis, molecular recognition, charge transfer, polymerization, and many other critical processes take place at the boundary between one medium and another. In this article we discuss the interface (liquid/air) properties of ionic liquids (ILs) containing dissolved metal ions with the aim to show the possibility to use metal salts to transform ILs and their surfaces into engineered liquid supports to apply in material sciences, separation procedures or to use as optical devices.     

离子液体谱学性质和热力学数据关联的新进展

离子液体的性质是其微观结构和相互作用的外在表现,与其应用密切相关.谱学手段能从分子水平上探测离子液体的微观环境和相互作用,近年来在定量关联或预测离子液体宏观性质方面发挥着越来越重要的作用.本文着重概述了红外光谱(IR)、拉曼光谱(Raman)、核磁共振波谱(NMR)和电子顺磁波谱(ESR)等常见谱学手段在定量关联离子液体及其溶液体系宏观性质方面的研究进展以及发展方向.     

Thermal analysis and mechanical methods applied to studying properties of SBR compounds containing ionic liquids

The goal of this work was to study new systems for activating sulphur vulcanisation of butadiene-styrene elastomer (SBR) using thermal analysis techniques complementarily with rheological and mechanical properties measurements. New activating systems consist of nanosized zinc oxide and ionic liquids (ILs) – benzalkonium or alkylammonium salts. In this article, we discuss the effect of zinc oxide and ILs on the cure characteristics, vulcanisation kinetics, crosslink density, mechanical properties, damping behaviour and thermal stability as well as resistance to thermooxidative and UV ageing of SBR.Nanosized zinc oxide with ILs reduced the vulcanisation time and temperature of rubber compounds. Their application results in increased vulcanisate crosslink density as well as the improvement of mechanical properties such as tensile strength and vibration damping ability. The influence of ionic liquids on SBR properties depends mainly on the anion present in the molecule. The most active ILs seem to be those with the lactate anion.     

Organometallic Ionic Liquids Containing Sandwich Complexes: Molecular Design,Physical Properties,and Chemical Reactivities

Ionic liquids (ILs) are salts with low melting points and are useful as electrolytes and solvents. We have developed ILs containing cationic metal complexes, which form a family of functional liquids that exhibit unique physical properties and chemical reactivities originating from metal complexes. Our study explores the liquid chemistry in the field of coordination chemistry, where solid-state chemistry is currently the main focus. This review describes the molecular design, physical properties, and reactivities of organometallic ILs containing sandwich or half-sandwich complexes. This paper mainly covers stimuli-responsive ILs, whose magnetic properties, solvent polarities, colors, or structures change by the application of external fields, such as light, heat, and magnetic fields, or by reaction with coordinating molecules.     

Metal-containing ionic liquids and ionic liquid crystals based on imidazolium moiety

Ionic liquids and ionic liquid crystals of imidazolium salts composed of various transition and main group metals have been reviewed. Ionic metal complexes of imidazoles and N-heterocyclic carbenes possess the similar properties were also included. These types of ILs and ILCs have been realized as potential solvents, catalysts, catalyst precursors and reagents for many organic transformations and provide ecofriendly protocols. They have also been found to play key roles in material science. Many of these IL systems are air- and moisture stable and are considered as alternatives for air- and moisture sensitive chloroaluminate-based ILs.     

New task-specific ionic liquids as bifunctional organocatalysts; Synthesis,characterization, and computational insights

A new class of functionalized imidazolium-based Task-Specific Ionic Liquids (TSILs) is designed as low-cost bifunctional organocatalyst. New alkoxymethylimidazolium ILs are efficiently synthesized under solvent free conditions and extensively characterized by physical and spectral studies. The newly synthesized ILs demonstrate excellent catalytic potential in condensation reactions of high importance, such as the Biginelli reaction for the synthesis of medicinally important dihydropyrimidiones. The effect of the alkoxy group and counter-ions in the imidazolium salts were evaluated in detail. Moreover, computational studies were employed to explore the structural dynamics and physicochemical properties of the prepared ionic liquids. 3-(iso-butoxymethyl)-1-methyl-1H-imidazol-3-ium tetrafluoroborate (ⁱBOMMIMBF₄ 7) exhibited the highest catalytic ability due to the combined influence of the alkoxy group structure, counterion nature, high electrophilicity index, and availability of the reactive C2-H. Some notable advantages of the new TSILs include efficient catalyst preparation, simple work-up procedure, recyclability, short reaction times, and excellent yields.     

NMR studies of ionic liquids: Structure and dynamics

The past two decades have seen the advent of a new class of solvents with unique properties, referred to as “Ionic Liquids”. This term describes low-melting organic salts, which open a window for chemical processes in ionic environments near room temperature. A molecular-based understanding of their properties is crucial for a rational design for applications. An important prerequisite is the characterization and understanding of their structure and dynamics. Application of NMR techniques to characterize ionic liquids has rendered many unique and valuable insights on these subjects. Here, recent highlights and typical applications are elucidated along with the advantages and limitations of the various techniques.     

Electrodeposition in Ionic Liquids

Due to their attractive physico‐chemical properties, ionic liquids (ILs) are increasingly used as deposition electrolytes. This review summarizes recent advances in electrodeposition in ILs and focuses on its similarities and differences with that in aqueous solutions. The electrodeposition in ILs is divided into direct and template‐assisted deposition. We detail the direct deposition of metals, alloys and semiconductors in five types of ILs, including halometallate ILs, air‐ and water‐stable ILs, deep eutectic solvents (DESs), ILs with metal‐containing cations, and protic ILs. Template‐assisted deposition of nanostructures and macroporous structures in ILs is also presented. The effects of modulating factors such as deposition conditions (current density, current density mode, deposition time, temperature) and electrolyte components (cation, anion, metal salts, additives, water content) on the morphology, compositions, microstructures and properties of the prepared materials are highlighted.     

Hydrogen bonds: a structural insight into ionic liquids

Ionic liquids (ILs) have attracted intensive attention in academia and industry due to their unique properties and potential applications. Nowadays, much interest is focused on finding out what is the main force that determines the properties of ionic liquids. Intuitively like NaCl, in high-temperature molten salt (HTMS) the electrostatic Coulomb force is regarded as the dominant factor that determines the behaviors of ILs. However, a large amount of evidence indicates that such a molten-salt-based simplified explanation is not consistent with the corresponding experimental results. Besides the Coulomb force, the hydrogen bond is another important noncovalent interaction in the IL and is closely related to some important properties and applications, as suggested in some new research results. Therefore in this review, we present results concerning the hydrogen bond in ILs, from the perspective of experiment and calculation, to shed light on its effects and roles. The deep insights into structure, in particular the hydrogen bonds, can provide us with a rational design for the new ILs to fulfill the demands in some complicated chemical processes.     

Biocatalysis and Biomass Conversion in Alternative Reaction Media

In this Minireview, the state of the art in the use of ionic liquids (ILs) and deep eutectic solvents (DESs) as alternative reaction media for biocatalytic processes and biomass conversion is presented. Initial, proof‐of‐concept studies, more than a decade ago, involved first‐generation ILs based on dialkylimidazolium cations and non‐coordinating anions, such as tetrafluoroborate and hexafluorophosphate. More recently, emphasis has switched to more environmentally acceptable second‐generation ILs comprising cations, which are designed to be compatible with enzymes and, in many cases are derived from readily available, renewable resources, such as cholinium salts. Protic ionic liquids (PILs), prepared simply by mixing inexpensive amines and acids, are particularly attractive from both an environmental and economic viewpoint. DESs, prepared by mixing inexpensive salts with, preferably renewable, hydrogen‐bond donors such as glycerol and amino acids, have also proved suitable reaction media for biocatalytic conversions. A broad range of enzymes can be used in ILs, PILs and DESs, for example lipases in biodiesel production. These neoteric solvents are of particular interest, however, as reaction media for biocatalytic conversions of substrates that have limited solubility in common organic solvents, such as carbohydrates, nucleosides, steroids and polysaccharides. This has culminated in the recent focus of attention on their use as (co)solvents in the pretreatment and saccharification of lignocellulose as the initial steps in the conversion of second‐generation renewable biomass into biofuels and chemicals. They can similarly be used as reaction media in subsequent conversions of hexoses and pentoses into platform chemicals.     

Sugar-Based Ionic Liquids: Multifaceted Challenges and Intriguing Potential

Carbohydrates represent a promising option in transitioning from oil-based chemical resources to renewable ones, with the goal of developing chemistries for a sustainable future. Cellulose, hemicellulose, and largely available monosaccharides already provide useful chemical building blocks, so-called platform chemicals, such as levulinic acid and hydroxymethyl furfural, as well as solvents like cyrene or gamma-valerolactone. Therefore, there is great anticipation for novel applications involving materials and chemicals derived from sugars. In the field of ionic liquids (ILs), sugar-based ILs have been overlooked for a long time, mainly on account of their multistep demanding preparation. However, exploring new strategies for accessing sugar-based ILs, their study, and their exploitation, are attracting increasing interest. This is due to the growing concerns about the negative (eco)toxicity profile of most ILs in conjunction with their non-sustainable nature. In the present review, a literature survey concerning the development of sugar-based ILs since 2011 is presented. Their preparation strategies and thermal behavior analyses, sorted by sugar type, make up the first two sections with the intention to provide the reader with a useful guide. A final overview of the potential applications of sugar-based ILs and their future perspectives complement the present analysis.