Ionic Liquids: Eco-friendly Substitutes for Surface and Interface Applications

The ionic liquids (ILs) have been recognized as the salts of differently made anions and cations, existing in liquid form at rt or below 100 °C. They have drawn their special attention as an alternative to toxic solvents, such in organic transformations along with several other fields such as wastewater management, organic transformations, chemical transformations, synthesis of heterocycles, sensing applications, etc. The present work shall describe the basis of ILs, their types, structural insights, and mechanistic overview along with a brief introductory account of ILs for the general benefit of the reader of the present works.

Ionic Liquids (ILs) are believed to be designer solvents, and their use has helped to speed up research in the field of chemistry properties like high viscosity and low vapor pressure. ILs are well-known for their physicochemical properties that can be modified to obtain desired functionality and improved efficiency, analyte extraction selectivity, and sensitivity. ILs have been studied through the methodologies for their synthesis, recyclability after use, reusability for different applications, toxicity against living organisms, and degradation with time. Usually, ILs have considerably better solvents than traditional solvents, but their synthesis involves harmful chemicals. ILs have also proved to be superior lubricants to other lubricants, which show high performance because friction in ILs may be regulated actively by using an external electric potential even when it is diluted in oil. ILs are proven appreciable electrolytes and have significant performance in the generation of energy. ILs are considered an alternative to the traditional solvents obtained from fossils. This chapter will concentrate on current advances in surface and interfacial applications.

Ionic liquids (IL) are biodegradable and green designer solvents for use in lots of vital applications i.e., catalysis, CO2 capture, green chemistry synthesis, energy storage, particle stabilization, self-assembly media and lubrication. ILs show many attractive properties in proximity to solid surfaces. ILs form well-defined interfacial layers that are tunable-electrically and thermally as well as stable- mechanically, electrically and thermally over a wide range. The structure of solid-ILs interfaces plays a basic role in these applications. In this book chapter, the recent literature is presented while future research information’s discussed. In the past decade, there has been rising interest in this topic, and significant progress has been made in understanding such interfaces. It has been known that electrostatic forces self-assembly of ILs and solid-IL interfaces are two key parameters. Moreover, how the structure of the IL-interface impacts the property, e.g., conductivity, viscosity and friction, has yet to be understood. Surface properties of ILs are explored with techniques that probe force, such as atomic force microscopy (AFM) and surface force apparatus (SFA), with scattering techniques such as neutron (NR) and X-ray reflectometry (XRR), sum frequency generation spectroscopy (SFGS) and other techniques, as well as with molecular dynamics (MD) simulations and theory.

The development of surface-active ionic liquids (SAILs) has gained significant interest in recent decades and has successfully replaced the currently utilized conventional surfactants. Due to the amphiphilic character of the SAILs, they have become remarkable surfactants and are particularly important for commercial and field usage. SAILs formed microemulsions and have shown potential in various sectors, including oil recovery and dispersion. The effectiveness of SAILs was measured by their capacity to develop microemulsions. Moreover, it was stated that efficient SAILs could develop a stable microemulsion throughout extended periods at low surfactant concentrations. Similarly, normal ionic liquids (ILs) gained significant attraction as a dispersion medium for colloidal systems as a potential alternative to volatile organic solvents. Colloidal stability is a crucial parameter for evaluating the characteristics and efficacy of colloidal systems. Therefore, the main emphasis is critically discussing the fundamental studies on colloidal stability. Considering the importance and significance of surfactant and colloidal behavior of ILs, this chapter describes these properties by employing recent relevant literature on the topic. The aggregation properties of SAILs alone and the mixed systems of SAILs and conventional surfactants are discussed with their usage in environmental clean-up. Moreover, the colloidal stability of SAILs, as well as the important factors that influence colloidal stability, are discussed in this chapter.

Today, Ionic liquids have been very well recognized in the field of corrosion as efficient inhibitors of various metals and alloys, owing to their environmentally friendly nature and strong adsorption properties. The alteration in the cationic part of the ionic liquids increases the electron donation capacity which makes their interaction feasible with the metal surface in the aggressive medium. This attraction leads to the protection of the metal surface from dissolution. The dissociation behavior of ionic liquid indicates the mode of adsorption on the surface of the metal. The adsorption of ionic liquid is also dependent on its chemical structure, the nature of a charge on the metal surface, and many other factors. This chapter gives an overview of factors governing the adsorption of inhibitors on the metal surface, mechanistic details, etc., with significant illustrations as documented in the literature.

The motivation behind recreating this chapter is to give a summary of the bibliographical insights expected to make the segment. In the first part, we examine the adsorption of ionic liquids (ILs) as efficient, effective and eco-friendly corrosion inhibitors for various alloys and metals surface in different corrosive media environments and the restraint and coordination chemistry of ionic liquids. The anticorrosive activity of different ILs has been examined with electrochemical techniques followed by weight-loss measurement. The impact of the ILs composition (polar and nonpolar substituents in anions & cations, and alkyl tail length), temperature, concentration, and nature of the medium, which influence the metal corrosion protection, was discussed. In the second part, we examine the interfacial structure and adsorption mechanism of different ILs on the Au (111) surface investigated via quantum chemical calculations.

Ionic liquids (ILs) have shown immense potential as suitable alternatives to environmentally damaging volatile organic solvents (VOS). These unique materials possess very unusual physicochemical properties, such as low melting point, high boiling point, excellent thermal and chemical stability, large electrochemical window, very low volatility and high conductivity. One of the most important features associated with ILs is that their physicochemical properties, like viscosity, density, hydrophobicity, solubility, polarity, etc., can be effectively tuned for desired applications just by tuning the structures of cations and/or anions. Further, these designer solvents show dual behavior, i.e., electrolytes and solvents. In the last two decades, these unique materials have shown tremendous application potential in various interdisciplinary research areas, such as synthesis, catalysis, separation, extraction, nanoscience, and pharmaceutics, among many others. Further, the formation of surfactant self-assembled nanostructures (micelles and microemulsions (ME)) within ionic liquid-based systems of immense importance due to the vast utility of these nanostructures well as ILs in various fields of science and technology. These microheterogeneous systems can be effectively used as greener alternatives to those environmentally harmful volatile organic solvents which are largely used for academic and industrial research purposes.atile organic solvents which are largely used for academic and industrial research purposes. The IL-based self-assembled nanostructures show major advantages due to their affinity to solubilize many chemical and biochemical solutes (both hydrophilic as well as hydrophobic), thereby expanding their potential application as solubilizing media, media for synthesis, catalysis and biocatalysis, separation and extraction, drug delivery vehicles, and media for biochemical stability (e.g., protein and enzyme stability). This book chapter will highlight the formation and utility of various types of self-assembled nanostructures formed by surfactants, polymers, etc., within Ils-based media.

The use of ionic liquids as solvents or catalysts has a notable impact. As a result, there is increasing interest in developing applications for them in a variety of synthetic reactions. The purpose of this chapter was not to be entirely complete, but rather to summarise some of the most recent advances in the use of ionic liquids in organic synthesis as a catalyst. The present chapter focuses on a general introduction to green and sustainable chemistry, as well as how it relates to homogeneous catalysis. A brief history of ILs as homogeneous catalysts is presented, various along with preparative routes and applications. Starting with their application, ILs have been used as catalysts in a variety of organic reactions. This focuses on the synthesis, significance, and applications of ILs. Although they are not particularly useful as solvents, they are now being used as catalysts in organic chemistry catalytic reactions.

The scarcity of water has motivated diverse research efforts toward developing efficient techniques for the treatment of wastewater for its reuse. The applications of conventional wastewater treatment technologies, such as chemical precipitation, ion exchange, flotation, flocculation and coagulation, membrane filtration, etc., have been identified with diverse limitations. The commonest of them include high investment and operational costs, the formation of toxic by-products and sludge generation. Ionic liquids (ILs) have been used in numerous analytical and industrial extraction processes; however, their potential in the treatment of wastewater is yet to be fully exploited. This chapter, therefore, explores the applications of various ILs in wastewater treatment and proposes their versatility in the deployment of effective, selective, and rapid extraction processes for the removal of diverse water pollutants. However, the application of technologies based on the use of ILs possesses various challenges, which include a choice of an appropriate ionic liquid, high testing requirement for private applications, disposal, the regeneration process of ILs, scalingup of the whole removal of pollutants, and technological applications.

The wide use of noxious and non-degradable metals due to industrialization has become a major factor in rising health concerns. Diseases associated may involve cardiovascular disorders, brain damage, cancer, etc., and this leads to the development of certain methods for the sole purpose of cleaning water, soil, air, etc., to remove metals categorized as toxic ones. Ionic liquids with remarkable thermal stability, association ability, exhibiting low vapour emission, etc., are considered eco-friendly for the decontamination of toxic metal impurities. These ionic liquids involve certain modes of interactions like an electrostatic, dipole, van der Waals, etc., for the effective separation and extraction of metals. Also, the property of reusability associated with ionic liquids makes them be used on a wide scale.

The utilization of metals and alloys has been on the increase due to rapid technological advancement and industrialization. Nevertheless, these widely used metallic materials are subject to degradation due to exposure to the environment. Several methods have been applied by scientists to address the problem of corrosion. One of the most successful methods to control metallic degradation remains the application of chemical inhibitors. Ionic liquids are renowned organic compounds with high adsorption abilities and exceptional properties which have drawn attention to their use as corrosion inhibitors. In contemporary years, different types of ionic liquids have been reported to showcase their effectiveness in protecting metallic surfaces from corrosive ions. This chapter discusses recent advancements in the utilization of highperformance ionic liquids as eco-friendly inhibitors in different corrosive environments, as documented in literature over the last three years.

The main focal point of this chapter is to divulge the tribological properties and best application of ionic liquids (ILs). Specifically in the petroleum-based lubrication industry and energy transfiguration process, oil add-ons have been reporting the best applicability of ionic liquids (ILs). The much-influenced counterparts of ILs have been extremely reported to design efficient lubricating oil with the use of ILs. The specific type of ILs which are halogenated and non-halogenated synthesized was ethyl ammonium nitra is also revealing themselves as the best corrosion inhibitors for studying the tribology on different metal surfaces. In addition, the performance of ILs as oil-additive has been giving good results in terms of tribological performance. The main feature which has to mold the performance of the tribological property, is the modification of anion in ILs. This all enhances the effectiveness of lubricant and oiladditive properties. The main reason behind the corrosion and formation of thin films over metal surfaces is also discussed in detail using different types of ILs and metal surfaces.

Ionic liquids (ILs) are environmentally friendly solvents and catalysts that are made up of ions that melt at temperatures below 100 degrees Celsius. Due to their favorable features, they were used in a broad range of reactions. A phase-transfer catalyst (PTC) is a type of heterogeneous catalysis that involves chemical reactions that occur when a reactant migrates from one phase to another where a reaction can proceed. High reaction specificity and transformations can be made easier with PTC reactions. PTC has been used in oxidations, alkylation, nucleophilic replacements, polymerizations, reductions, and other processes. In recent years, scientists have become more interested in employing ILs instead of traditional PTCs in biphasic reactions. Their cation architecture and chain length changes have been shown to have a substantial impact on their performance as PTCs. This chapter aims to discuss the role of ILs as phase transfer catalysis in organic synthesis.

In this chapter, a series of asymmetric and symmetric ionic liquids (ILs) and IL-modified materials were considered for their versatile application as electrolytes and redox mediators in Photoelectrochemical (PEC) cells. Dye-sensitized solar cells (DSSCs) are PEC cells and third-generation photovoltaic (PV) cells that convert solar PV energy into electrical energy. They have piqued the interest of researchers worldwide due to their simple cell fabrication methods under ambient conditions, as well as their enormous commercialization potential due to their low cost; additionally, the benefits of colorfulness, probable plasticity and high power conversion efficiency (PCE) under indoor irradiation make PEC cells appealing. To attain a high PCE of cells, an organic solvent has to be included with the formulation of the redox mediator in the electrolyte. However, organic solvents are prone to evaporation and leakage. Consequently, PEC cells’ durability is reduced because of the chemical and thermal instability of the redox mediator in the electrolyte. The purpose of including ionic liquids into the redox mediator in the electrolyte was to solve the above-mentioned issue and to allow the PEC cells to act as sustainable energy cells. The chapter describes the integration of ionic liquids into the redox mediator in the electrolyte formulation and evaluates the impact of ionic liquids on the PCE of the cell in various electrolyte conditions.

Ionic liquids (ILs) attracted global attention owing to their superior functional properties, making them useful for many applications. Low volatility, wide liquidity range, better miscibility with organic and inorganic materials, better electrochemical stability, and negligible toxicity earn them a green solvent status. ILs are suitable alternatives to many volatile and flammable organic solvents that chokes our environment. The presence of asymmetric organic/inorganic ions gave them unique characteristics similar to biomolecules. They could interact with the cell membranes and penetrate the lipid bilayers to destroy bacterial cell membranes. They can selfassemble at the interfaces of polar and non-polar media. The nature of substrates, concentration, counter-ions, and polarity of the medium influence the extent and stability of the self-assembly. The self-assembled monolayers (SAMs) and multilayers of ILs impart intriguing properties to the surfaces. Surface modification with ILs is preferred over other methods considering their eco-friendly nature. The IL-mediated surface modification would help to improve the surface properties of polymers, metals, nanoparticles, ceramics, stones, medical devices, etc. The modified surfaces would have improved wettability, biocompatibility, and antimicrobial or antiviral properties. IL-modified surfaces could anchor enzymes to generate sustainable biocatalysts for a wide range of reactions. The inherent affinity of ILs towards gases like CO2 makes them suitable for generating gas-adsorbing surfaces. Assembled charge carriers in ILs are helpful in energy storage and electrochemical sensing applications. Poly(ionic liquids) (PILs) are also receiving much attention recently since they display synergistic properties of polymers and ILs to be employed in divergent fields. PILs are also suitable for the surface modification of different substrates. This chapter reviews the surface modification of materials using ILs and PILs and their biomedical applications.

The Molten salts having melting points near to or less than room temperature is termed ionic liquids (ILs). A full IL unit generally comprises two oppositely charged ions with a remarkable size difference, i.e., bulky cation and comparatively small anion. The ILs are also labelled as future solvents due to their design flexibility and greener approach. Owing to their large number of favourable characteristics, such as less toxicity, good solvating capacity, high conductivity, nonvolatility, super sensitivity, selectivity and electrochemical stability, these ILs have provided a broader range of applicability in the field of sensing. ILs are proven to be of good use in the area of sensors as well as biosensors, i.e., optical sensing, thermometric sensing, electrochemical sensing and fluorescent sensing, etc. The ILs can be tailored by changing cations and anions as per the demand of the applications. In the present chapter, various aspects of ILs, including the use of these ILs in various sensing applications, have been explored and summed up to present an organized view for the researcher community as well as general readers.