Basic ionic liquids promoted chemical transformation of CO<Subscript>2</Subscript> to organic carbonates

Ionic liquids (ILs), especially basic ILs with unique physicochemical properties, have wide application in catalysis. Using basic ILs as catalysts for the conversion of cheap, abundant, nontoxic, and renewable CO₂ into value-added organic carbonates is highly significant in view of environmental and economic issues. This review aims at giving a detailed overview on the recent advances on basic ILs promoted chemical transformation of CO₂ to cyclic and linear carbonates. The structures of various basic ILs, as well as the basic ILs promoted reactions for the transformation of CO₂ to organic carbonates are discussed in detail, including the reaction conditions, the yields of target products, the catalytic activities of basic ILs and the reaction mechanism.     

Imidazolium Ionic Liquids,Imidazolylidene Heterocyclic Carbenes,and Zeolitic Imidazolate Frameworks for CO2 Capture and Photochemical Reduction

Imidazolium ionic liquids (ILs), imidazolylidene N‐heterocyclic carbenes (NHCs), and zeolitic imidazolate frameworks (ZIFs) are imidazolate motifs which have been extensively investigated for CO₂ adsorption and conversion applications. Summarized in this minireview is the recent progress in the capture, activation, and photochemical reduction of CO₂ with these three imidazolate building blocks, from homogeneous molecular entities (ILs and NHCs) to heterogeneous crystalline scaffolds (ZIFs). The developments and existing shortcomings of the imidazolate motifs for their use in CO₂ utilizations is assessed, with more of focus on CO₂ photoredox catalysis. The opportunities and challenges of imidazolate scaffolds for future advancement of CO₂ photochemical conversion for artificial photosynthesis are discussed.     

Microstructures of Choline Amino Acid based Biocompatible Ionic Liquids

Bio-compatible ionic liquids (Bio-ILs) represent a class of solvents with peculiar properties and exhibit huge potential for their applications in different fields of chemistry. Ever since they were discovered, researchers have used bio-ILs in diverse fields such as biomass dissolution, CO₂ sequestration, and biodegradation of pesticides. This review highlights the ongoing research studies focused on elucidating the microscopic structure of bio-ILs based on cholinium cation ([Ch]⁺) and amino acid ([AA]⁻) anions using the state-of-the-art and classical molecular dynamics (MD) simulations. The microscopic structure associated with these green ILs guides their suitability for specific applications. ILs of this class differ in the side chain of the amino acid anions, and varying the side chain significantly affects the structure of these ILs and thus helps in tuning the efficiency of biomass dissolution. This review demonstrates the central role of the side chain on the morphology of choline amino acid ([Ch][AA]) bio-ILs. The seemingly matured field of bio-ILs and their employment in various applications still holds significant potential, and the insights on their microscopic structure would steer the field of target specific application of these green ILs.     

Polyoxometalate-Based Compounds for Photo- and Electrocatalytic Applications

Photo/electrocatalysis of water (H₂O) splitting and CO₂ reduction reactions is a promising strategy to alleviate the energy crisis and excessive CO₂ emissions. For the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO₂ reduction reaction (CO₂RR) involved, the development of effective photo/electrocatalysts is critical to reduce the activation energy and accelerate the sluggish dynamics. Polyoxometalate (POM)-based compounds with tunable compositions and diverse structures are emerging as unique photo/electrocatalysts for these reactions as they offer unparalleled advantages such as outstanding solution and redox stability, quasi-semiconductor behaviour, etc. This Minireview provides a basic introduction related to photo/electrocatalytic HER, OER and CO₂RR, followed by the classification of pristine POM-based compounds toward different catalytic reactions. Recent breakthroughs in engineering POM-based compounds as efficient photo/electrocatalysts are highlighted. Finally, the advantages, challenges, strategies and outlooks of POM-based compounds on improving photo/electrocatalytic performance are discussed.     

The Influence of Hydrogen Bond Donors on the CO2 Absorption Mechanism by the Bio-Phenol-Based Deep Eutectic Solvents

Recently, deep eutectic solvents (DESs), a new type of solvent, have been studied widely for CO₂ capture. In this work, the anion-functionalized deep eutectic solvents composed of phenol-based ionic liquids (ILs) and hydrogen bond donors (HBDs) ethylene glycol (EG) or 4-methylimidazole (4CH₃-Im) were synthesized for CO₂ capture. The phenol-based ILs used in this study were prepared from bio-derived phenols carvacrol (Car) and thymol (Thy). The CO₂ absorption capacities of the DESs were determined. The absorption mechanisms by the DESs were also studied using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and mass spectroscopy. Interestingly, the results indicated that CO₂ reacted with both the phenolic anions and EG, generating the phenol-based carbonates and the EG-based carbonates, when CO₂ interacted with the DESs formed by the ILs and EG. However, CO₂ only reacted with the phenolic anions when the DESs formed by the ILs and 4CH₃-Im. The results indicated that the HBDs impacted greatly on the CO₂ absorption mechanism, suggesting the mechanism can be tuned by changing the HBDs, and the different reaction pathways may be due to the steric hinderance differences of the functional groups of the HBDs.     

含CO2/离子液体系统相行为及其在反应与分离中的应用进展

目前已知的绿色溶剂主要包括超临界流体（Supercritical fluids,SCFs）、离子液体（Ionic liquids,ILs）、二氧化碳膨胀液体（CO₂ expanded liquids, CXLs）、水以及上述溶剂的混合物等。其中,由超临界CO₂（Supercritical CO₂,SCCO₂）与ILs混合而构成的新兴溶剂,因为化学热力学方面的特性,成为近年来研究的热点,未来很有发展前景。本文回顾了目前为止在该领域所开展的工作,总结了影响SCCO₂与IL相行为的主要因素。包括温度、压力、ILs的含水量、ILs的阴离子、ILs的阳离子、ILs的摩尔体积以及助溶剂等。同时分析了ILs/SCCO₂与溶质形成的多元混合物相行为的成因。介绍了ILs/CO₂在萃取、反萃取、膜分离、反胶束、萃取与反应耦合等分离方面的应用。由于传统的单元操作很难满足无污染和对过程集成的要求,因而含有ILs/ SCCO₂的分离反应耦合过程将是未来是实现清洁生产的发展方向。     

Elucidation of the Roles of Ionic Liquid in CO2 Electrochemical Reduction to Value-Added Chemicals and Fuels

The electrochemical reduction of carbon dioxide (CO₂ER) is amongst one the most promising technologies to reduce greenhouse gas emissions since carbon dioxide (CO₂) can be converted to value-added products. Moreover, the possibility of using a renewable source of energy makes this process environmentally compelling. CO₂ER in ionic liquids (ILs) has recently attracted attention due to its unique properties in reducing overpotential and raising faradaic efficiency. The current literature on CO₂ER mainly reports on the effect of structures, physical and chemical interactions, acidity, and the electrode–electrolyte interface region on the reaction mechanism. However, in this work, new insights are presented for the CO₂ER reaction mechanism that are based on the molecular interactions of the ILs and their physicochemical properties. This new insight will open possibilities for the utilization of new types of ionic liquids. Additionally, the roles of anions, cations, and the electrodes in the CO₂ER reactions are also reviewed.     

Computer‐Assisted Design of Imidazolate‐Based Ionic Liquids for Improving Sulfur Dioxide Capture,Carbon Dioxide Capture,and Sulfur Dioxide/Carbon Dioxide Selectivity

A new strategy involving the computer‐assisted design of substituted imidazolate‐based ionic liquids (ILs) through tuning the absorption enthalpy as well as the basicity of the ILs to improve SO₂ capture, CO₂ capture, and SO₂/CO₂ selectivity was explored. The best substituted imidazolate‐based ILs as absorbents for different applications were first predicted. During absorption, high SO₂ capacities up to ≈5.3 and 2.4 mol mol_IL⁻¹ could be achieved by ILs with the methylimidazolate anions under 1.0 and 0.1 bar (1 bar=0.1 MPa), respectively, through tuning multiple N ⋅⋅⋅ S interactions between SO₂ and the N atoms in the imidazolate anion with different substituents. In addition, CO₂ capture by the imidazolate‐based ILs could also be easily tuned through changing the substituents of the ILs, and 4‐bromoimidazolate IL showed a high CO₂ capacity but a low absorption enthalpy. Furthermore, a high selectivity for SO₂/CO₂ could be reached by IL with 4,5‐dicyanoimidazolate anion owing to its high SO₂ capacity but low CO₂ capacity. The results put forward in this work are in good agreement with the predictions. Quantum‐chemical calculations and FTIR and NMR spectroscopy analysis methods were used to discuss the SO₂ and CO₂ absorption mechanisms.     

Task-specific ionic liquids for carbon dioxide absorption and conversion into value-added products

Ionic liquids (ILs), by virtue of their special properties such as functional designability and high thermal stability, have been widely used as absorbent to CO₂ and catalyst for CO₂ conversion. This review summarizes the recent developments from 2019 to 2021 on task-specific ionic liquids (TSILs) with modulable properties by introducing specific functional groups to anions or/and cations for CO₂ absorption and conversion. The increase of basicity in TSILs by introducing amino/or amine groups or collaboration with multiple active sites of carboxyl, imidazolyl, pyridyl, and hydroxyl groups achieve high CO₂ affinity and absorption capacity. To solve the defects of high viscosity, ether groups are introduced to TSILs for CO₂ absorption. Besides, recent studies on CO₂ thermal catalytic conversion focused on the construction of C–O bonds and C–N bonds are also summarized. The catalytic activity of TSILs is enhanced by improving the synergy effect of different functional groups on anions and cations. It is expected that this minireview will provide the understanding of the current developments and perspective for practical CO₂ absorption and transformation by TSILs.     

Thermo- and Photocatalytic Activation of CO2 in Ionic Liquids Nanodomains

Ionic liquids (ILs) are considered to be potential material devices for CO₂ capturing and conversion to energy-adducts. They form a cage (confined-space) around the catalyst providing an ionic nano-container environment which serves as physical-chemical barrier that selectively controls the diffusion of reactants, intermediates, and products to the catalytic active sites via their hydrophobicity and contact ion pairs. Hence, the electronic properties of the catalysts in ILs can be tuned by the proper choice of the IL-cations and anions that strongly influence the residence time/diffusion of the reactants, intermediates, and products in the nano-environment. On the other hand, ILs provide driving force towards photocatalytic redox process to increase the CO₂ photoreduction. By combining ILs with the semiconductor, unique solid semiconductor-liquid commodities are generated that can lower the CO₂ activation energy barrier by modulating the electronic properties of the semiconductor surface. This mini-review provides a brief overview of the recent advances in IL assisted thermal conversion of CO₂ to hydrocarbons, formic acid, methanol, dimethyl carbonate, and cyclic carbonates as well as its photo-conversion to solar fuels.     

Computer‐Aided Design of Ionic Liquids as CO2 Absorbents

Ionic liquids (ILs), vary strongly in their interaction with CO₂. We suggest simple theoretical approach to predict the CO₂ absorption behavior of ILs. Strong interaction of the CO₂ with the IL anions corresponds to chemical absorption whereas weak interaction indicates physical absorption. A predictive estimate with a clear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of a solvation model instead of optimizing it only in gas phase as has been done to date. The resulting Gibbs free energies compare very well with experimental values and the energies were correlated with experimental capacities. Promising anions, for ionic liquids with reversible CO₂ absorption properties can be defined by a reaction Gibbs free energy of absorption in the range of ?30 to 16 kJ mol^?1.     

Topological engineering of two-dimensional ionic liquid islands for high structural stability and CO2 adsorption selectivity

Ionic liquids (ILs) as green solvents and catalysts are highly attractive in the field of chemistry and chemical engineering. Their interfacial assembly structure and function are still far less well understood. Herein, we use coupling first-principles and molecular dynamics simulations to resolve the structure, properties, and function of ILs deposited on the graphite surface. Four different subunits driven by hydrogen bonds are identified first, and can assemble into close-packed and sparsely arranged annular 2D IL islands (2DIIs). Meanwhile, we found that the formation energy and HOMO–LUMO gap decrease exponentially as the island size increases via simulating a series of 2DIIs with different topological features. However, once the size is beyond the critical value, both the structural stability and electrical structure converge. Furthermore, the island edges are found to be dominant adsorption sites for CO₂ and better than other pure metal surfaces, showing an ultrahigh adsorption selectivity (up to 99.7%) for CO₂ compared with CH₄, CO, or N₂. Such quantitative structure–function relations of 2DIIs are meaningful for engineering ILs to efficiently promote their applications, such as the capture and conversion of CO₂.

Multi-scale simulations reveal the structure and properties of the two-dimensional ionic liquid islands supported by graphite, and the island edges show an ultrahigh adsorption selectivity for CO₂ compared with CH₄, CO, or N₂.     

Synthesis of crosslinked PEG/IL blend membrane via one-pot thiol–ene/epoxy chemistry

Poly(ethylene glycol) (PEG)-based membranes have obtained considerable attentions for CO₂ separation for their promising CO₂ separation performance and excellent thermal/chemical resistance. In this work, a one-pot thiol–ene/epoxy reaction was used to prepare crosslinked PEG-based and PEG/ionic liquids (ILs) blend membranes. Four ILs of the same cation [Bmim]⁺ with different anions ([BF₄]⁻, [PF₆]⁻, [NTf₂]⁻, and [TCM]⁻) were chosen as the additives. The chemical structure, thermal properties, hydrophilicity, and permeation performance of the resultant membranes were investigated to study the ILs' effects. An increment in CO₂ permeability (~34%) was obtained by optimizing monomer ratios and thus crosslinking network structures. Adding ILs into optimized PEG matrix shows distinct influences in CO₂ separation performance depending on the anions' types, due to the different CO₂ affinities and compatibilities with PEG matrix. Among these ILs, [Bmim][NTf₂] was found the most effective in enhancing CO₂ transport by simultaneously increasing the solubility and diffusivity of CO₂. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals LLC. J. Polym. Sci. 2020 , 58, 2575-2585     

Selection and design of ionic liquids as solvents in extractive distillation and extraction processes

Since the late 1990’s there has been a tremendous growth in literature on ionic liquids (ILs) for a broad range of applications, i.e. catalysis, electrolytes for batteries, in solvolysis of biomass, and also in separation technology. ILs can be applied as solvents for absorption (e.g. of CO₂), extractive distillation and extraction processes. That ILs are not magic solvents but have their limitations has also become evident during the past years. Especially the high costs associated with ILs and the lack of experience with these materials in the industrial practice are factors limiting industrial adoption of ILs. The often praised versatility of properties that can be achieved through combination of different cations and anions generates a huge amount of options and makes it difficult to decide where to start when selecting/designing a solvent. This paper focuses on solvent selection/design for applications in extractive distillations and liquid-liquid extractions; also, solvent performance in several specific case studies taken from the open literature is discussed. Important recommendations include: a) make a conceptual process design including the recovery step, regeneration of the IL may be a critical parameter; b) if extractions from aqueous streams are studied, the uptake of water by the IL is an important factor because such co-extracted water is evaporated during the regeneration; c) compare the process with conventional processes to check whether it performs better than the state-of-the-art in industry.     

Molecular Design of Polyoxometalate-Based Compounds for Environmentally-Friendly Functional Group Transformations: From Molecular Catalysts to Heterogeneous Catalysts

This review article summarizes our recent researches for molecular design of polyoxometalates (POMs) and their related compounds for environmentally-friendly functional group transformations. The divacant POM [γ-SiW₁₀O₃₄(H₂O)₂]⁴⁻ exhibits high catalytic performance for mono-oxygenation-type reactions including epoxidation of olefins and allylic alcohols, sulfoxidation, and hydroxylation of organosilanes with H₂O₂. We have successfully synthesized several POM-based molecular catalysts (metal-substituted POMs) with controlled active sites by the introduction of metal species into the divacant POM as a “structural motif”. These molecular catalysts can efficiently activate H₂O₂ (vanadium-substituted POM for epoxidation) and alkynes (copper-substituted POM for click reaction and oxidative homocoupling of alkynes). The aluminum-substituted POM exhibits Lewis acidic catalysis for diastereoselective cyclization of (+)-citronellal to (−)-isopulegol. In addition, we have developed POM-based “molecular heterogeneous catalysts” by the “solidification” and “immobilization” of catalytically active POMs.     

Ionic liquids as novel solvents and catalysts for the direct polycondensation of N,N′‐(4,4′‐oxydiphthaloyl)‐bis‐L‐phenylalanine diacid with various aromatic diamines

Ionic liquids (ILs) are often considered green solvents capable of replacing traditional organic solvents and have been extensively studied in materials chemistry and catalysis. In this study, the direct polycondensation of N,N′‐(4,4′‐oxydiphthaloyl)‐bis‐L ‐phenylalanine diacid with various aromatic diamines was performed in IL media. The influence of various reaction parameters, including the nature of the IL cations and anions, the monomer structures, the reaction temperature, and the reaction time, on the yields and inherent viscosities of the resulting optically active poly(amide imide)s (PAIs) were investigated. Direct polycondensation successfully preceded in ILs and triphenyl phosphite (a condensing agent) without any additional extra components, such as LiCl and pyridine, which are used in similar reactions in ordinary molecular solvents. Therefore, ILs can act as both solvents and catalysts. Various high‐molecular‐weight, optically active PAIs were obtained in high yields with inherent viscosities ranging from 0.54 to 0.88 dL/g. This method was also compared with three other classical methods for the polycondensation of the aforementioned monomers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6545–6553, 2005     

Application of a group contribution equation of state for the thermodynamic modeling of binary systems (gas + ionic liquids) with bis[(trifluoromethyl)sulfonyl]imide anion

The properties of ionic liquids (ILs) can be modified by appropriate selection of cations and anions. Even if an infinite number of ionic liquids can be generated, only a limited number of families of anions and cations are used. The group contribution equation of state (GC-EoS) is a promising method for calculating the phase behavior of systems with ILs. If the parameters of the characteristic functional group of a IL family are fitted by using data of a reduced number of ILs of the family, then the phase behavior of all the ILs of the same family can be predicted using exclusively the data of the pure components. Previously, the parameters of the IL families with an imidazolium-based cation and the anions PF₆, BF₄NO₃, and Tf₂N were fitted to experimental data [19], and some ternary systems (CO₂ + organics + ionic liquid [bmim][BF₄]) were also modeled [22]. In this work, the GC-EoS was used to calculate phase behavior of gases {(CO₂, O₂, or SO₂) + ionic liquids} with Tf₂N anion and cations of the families 2,3-dimethyl-imidazolium, 1-alkyl-1-methyl-pyrrolidinium, and 1-alkyl-3-methyl-pyridinium. The GC-EoS was able to reproduce experimental data with deviations of the same order of experimental uncertainty. With the correlated parameters it will be possible to predict the phase behavior of systems with ILs of the families considered in this work.     

How a Transition‐Metal(II) Chloride Interacts with a Eutectic AlCl3‐Based Ionic Liquid: Insights into the Speciation of the Electrolyte and Electrodeposition of Magnetic Materials

Electrostatic interactions are characteristic of ionic liquids (ILs) and play a pivotal role in determining the formation of species when solutes are dissolved in them. The formation of new species/complexes has been investigated for certain ILs. However, such investigations have not yet focused on eutectic liquids, which are a promising class of ILs. These liquids (or liquid coordination complexes, LCCs) are rather new and are composed of cationic and anionic chloro complexes of metals. To date, these liquids have been employed as electrolytes to deposit metals and as solvents for catalysis. The present study deals with a liquid that is prepared by mixing a 1.2:1 mol ratio of AlCl₃ and 1‐butylpyrrolidine. An attempt has been made to understand the interactions of FeCl₂ with the organic molecule using spectroscopy. It was found that dissolved Fe(II) species interact mainly with the IL anion and such interactions can lead to changes in the cation of the electrolyte. Furthermore, the viability of depositing thick magnetic films of Fe and Fe–Al has been explored.     

Atomistic modeling toward high‐efficiency carbon capture: A brief survey with a few illustrative examples

With the negative environmental implications of the anthropogenic emission of greenhouse gases like CO₂ having been scientifically established, emphasis is being placed on a concerted global effort to prevent such gases from reaching the atmosphere. Especially important are capture efforts at large point emission sources like fossil fuel power generation, natural gas processing, and various industrial plants. Given the importance and scale of such activities, it is a significant priority to optimize the capture process in terms of speed, energy requirements, and cost efficiency. For CO₂ capture, in particular, multiple systems are being pursued both with near‐term retrofitting and medium‐ to long‐term designs in mind, including: (1) liquid solvents like amines, carbonates, and ionic liquids (ILs); (2) microporous sorbents like zeolites, activated carbon, and metal‐organic frameworks; (3) solid sorbents like metal‐oxides and ionic clays; and (4) polymeric and inorganic membrane separators. Each system is unique in its molecular‐level guest–host interactions, chemistry, heats of adsorption/desorption, and equilibrium thermodynamic and transport properties as a function of loading, temperature, and pressure. This opens up exciting opportunities for molecular modeling in the design and optimization of materials systems. Here, we offer a brief survey of molecular modeling applications in the field of carbon capture, with a few illustrative examples from our own work primarily involving amine solutions and ILs. Important molecular dynamics, Monte Carlo, and correlations‐based work in the literature relevant to CO₂ capture in other systems are also discussed. © 2013 Wiley Periodicals, Inc.     

An efficient model for the prediction of CO2 hydrate phase stability conditions in the presence of inhibitors and their mixtures

A thermodynamic model for the prediction of CO₂ hydrate phase stability conditions in the presence of pure and mixed salts solutions and various ionic liquids (ILs) is developed. In the proposed model van der Waals and Platteeuw model is used to compute the hydrate phase, Peng–Robinson equation of state (PR-EoS) for the gas phase and the Pitzer–Mayorga–Zavitsas-Hydration model is employed to calculate the water activity in the liquid water phase. This model is an extension of the model developed by Tumba et al. (2011) for the prediction of methane and CO₂ hydrate phase stability conditions in the presence of tributylmethylphosphonium methylsulfate IL solution. Shabani et al. (2011) mixing rule is modified by incorporating the water–inhibitor (salt/IL) interaction parameter to calculate the water activity in mixed salt solutions. The model predictions are also calculated using the Pitzer–Mayorga model separately and compared with predictions of the developed model. The model predictions are compared with experimental results on the phase stability of CO₂ hydrate in the presence of ILs, pure and mixed salts as reported in literatures. The ILs are chosen from imidazolium cationic family with various anion groups such as bromide (Br), tetrafluoroborate (BF₄), trifluoromethanesulfonate (TfO), and nitrate (NO₃) and the common salts such as NaCl, KCl and CaCl₂. Good agreement between the developed model predictions and the literature data is observed. The overall average absolute deviation (AARD%) with Pitzer–Mayorga–Zavitsas-Hydration model is observed to be within ±1.36% while Pitzer–Mayorga model accuracy were about ±1.44 %. Further, the model is extended to calculate the inhibition effect of selected inhibitors (ILs and salts) on CO₂ hydrate formation.