Editorial pubs.acs.org/CR
Introduction: Ionic Liquids
I
ranging from the molecular level to the industrial level. The popular multiscale method originating from other disciplines was extended to IL systems. Furthermore, Izgorodina, Seeger, Scarborough, and Tan17 give an overview on how to predict the energetic, physical, and spectroscopic properties of ILs by means of quantum chemical methods and empirical approaches. Among others, the COSMO-RS (conductor-like screening model for real solvents) model, which is an a priori predictive model, is the most widely used in the IL community, enabling theoretical calculations to decrease the amount of required experimental work. Zhang, Zhang, Zhang, and Deng18 focus on the nanoconfined scale in ILs and the interactions between ILs and the pore walls inside porous materials; this brings to the ILs distinctly modified physicochemical properties when compared to the corresponding bulk liquid. The potential applications of nanoconfined ILs in catalysis, separation, ionogels, supercapacitors, carbonization, and lubrication are thoroughly reviewed. In many chemical reaction processes, ILs are suggested as solvents, catalysts, reagents, or combinations of these. Zhang, Song, and Han19 provide a comprehensive review on the catalytic conversion of cellulose, hemicellulose, lignin, and lignocellulosic biomass into value-added chemicals and fuel products, in which ILs act as the solvents or as IL-based catalysts. Various useful products can be obtained through lignocellulose valorization using ILs. Qiao, Ma, Theyssen, Chen, and Hou20 discuss an interesting family of ILs, i.e. temperature-responsive ILs, which are used for the thermoregulated catalytic systems, such as hydroformylation, reduction with H2 or CO, and coupling reactions. The working principle is that this type of IL can form a homogeneous mixture with the reactants and products, but be separated from them readily when the reaction conditions are changed. From the viewpoint of chemical engineering, the most important advantage is that the gas/liquid−solid mass transfer limitations, which may be the rate-determining step in many catalytic transformations, can be overcome. Dai, Zhang, Huang, and Lei21 provide a detailed review of ILs in several important and typical selective oxidation reactions. ILs are preferable in this context as highly efficient catalysts and innovative green solvents due to their unique physical properties, including their nonvolatility, reaction rate acceleration effects, and high thermal stability. In particular, their use as “biphasic catalysts”, or “immobilized catalysts” obtained by immobilizing metal- or nonmetalcontaining ILs onto mineral or polymer supports, is highlighted in detail. In separation processes, the selection of suitable solvents (or separating agents) is a key for targeted process intensification. Ventura, e Silva, Quental, Mondal, Freire, and Coutinho22 offer a detailed review on the use of ILs as solvents in the extraction and/or purification of bioactive compounds, ranging from small organic compounds to more complex molecules. Different IL-
onic liquids (ILs) are normally defined as compounds completely composed of ions with melting point below 100 °C. The first IL (ethylammonium nitrate) was reported by Paul Walden in 1914, who at that time never realized that ILs would become a major scientific area after almost one century. Actually, ILs as innovative fluids have received wide attention only during the past two decades. The number of SCI papers published on ILs has exponentially increased from a few in 1996 to >5000 in 2016, exceeding the annual growth rates of other popular scientific areas. This indicates that more and more researchers are engaged in studying this exciting area, with the outcomes being plentiful. A multidisciplinary study on ILs is emerging, including chemistry, materials science, chemical engineering, and environmental science. More specifically, some important fundamental viewpoints are now different from the original concepts, as insights into the nature of ILs become deeper. For example, the physicochemical properties of ILs are now recognized as ranging broadly from the oft quoted “nonvolatile, non-flammable, and air and water stable” to those that are distinctly volatile, flammable, and unstable. This is attributed to numerous combinations of cations and anions that meet the definition of ILs, leading to a diverse suite of behaviors. Regardless, ILs remain more desirable than conventional volatile solvents and/or catalysts in many physical and chemical processes, often exhibiting “green” and “designer” properties to a useful degree. As their chemical variety has grown, ILs have been further divided into many types, e.g., room-temperature ILs (RTILs),1−6 task-specific ILs (TSILs),7,8 polyionic liquids (PILs),9,10 and supported IL membranes (SILMs)11,12 that include composites of ILs supported on metal−organic frameworks (MOFs).13,14 The hybrid organic−ionic nature of ILs and the resulting intermolecular interactions give rise to a complex set of phenomena, creating an area of study that is both fascinating and challenging. Scientists and engineers are often required to screen for suitable ILs quickly for a specific process. For this purpose, the identification of structure− performance relationships disclosing the interplay among ILs, solutes, supports, and the components in mixtures becomes vital, requiring a close integration of experimental, theoretical, and computational methods. Thus, it is necessary to collect our recent findings in this area and summarize the governing rules behind these complex phenomena. This compelled us to invite a number of prestigious scientists to contribute to this thematic issue on ILs for Chemical Reviews. We should mention that deep eutectic solvents (DESs) are not highlighted in this thematic issue because DESs and ILs form two quite different solvent families. For more detail on DESs, please see the excellent review written by Smith, Abbott, and Ryder.15 This issue covers a range of different aspects of ILs, beginning with the multiscale science of ILs. It is evident that a better understanding of IL behavior at the microscopic scale will help to elucidate macroscopic fluid phenomena, and thus promote the industrial application of ILs. Dong, Liu, Dong, Zhang, and Zhang16 discuss the multiscale aspects of ILs, © 2017 American Chemical Society
Special Issue: Ionic Liquids Published: May 24, 2017 6633
DOI: 10.1021/acs.chemrev.7b00246 Chem. Rev. 2017, 117, 6633−6635
Chemical Reviews
Editorial
Douglas R. MacFarlane
based extraction processes are addressed, including liquid− liquid extraction, solid−liquid extraction, solid-phase extraction, and induced-precipitation techniques. The use of ILs can bring about higher extraction yields and purification factors when compared to conventional solvents and materials. The progress in IL science is closely related to the development of characterization techniques. Infrared (IR) and Raman spectroscopies have proven to provide exceptional fundamental insight into ionic interactions and the resulting liquid structure in ILs. Paschoal, Faria, and Ribeiro23 discuss the application of IR and Raman spectroscopies in the mid- and low-frequency range in the bulk liquid, as well as in understanding the structural modifications of ILs accompanying phase transitions induced by variable temperature or pressure. To the best of our knowledge, it is the first review on this topic, and we expect that many scientists and engineers will find it to be a useful resource. Are ILs chemically stable? This topic is very important to ensure that potential industrial application of ILs becomes a reality. The review by Wang, Qin, Mu, Xue, and Gao24 covers the chemical stability and reactivity of popular imidazoliumbased ILs, including thermal decomposition, hydrolysis, and nucleophilic reactions of anions under actual operating conditions (e.g., high temperature, and the presence of water, air, or other gases). Thus, this review will provide a guide for further industrial application of ILs. Two reviews in this issue deal with innovative applications of ILs in emerging areas. Egorova, Gordeev, and Ananikov25 discuss the biological activity of ILs and their applications in drug synthesis and drug delivery systems, with a particular emphasis on a novel active pharmaceutical ingredient−ionic liquid (APIL-IL) concept. In these cases, ILs are utilized as components of drug or drug delivery systems, and in the dual roles of reaction media and catalysts in drug synthesis. In an entirely different area, Watanabe, Thomas, Zhang, Ueno, Yasuda, and Dokko26 discuss the application of ILs in energy storage and conversion materials and devices. They review the use of ILs as electrolyte materials for Li/Na ion, Li/S, and Li/ O2 batteries, fuel cell electrolytes, and electrode materials, especially those including ionic-liquid-derived N-doped carbons. Some ILs can meet the stringent criteria imposed by various energy applications due to their unique properties, including nonflammability, high electrochemical stability, and high ionic conductivity. Finally, we would like to thank all the authors for their excellent contributions to this thematic issue. We also thank the editorial staff of Chemical Reviews for their valuable suggestions in initiating the thematic issue, as well as their hard work in handling the manuscripts. We hope that young scientists and students who are engaged in studying this exciting area can benefit significantly from the publication of this collection of reviews and thereby make further important progress in the field.
School of Chemistry, Monash University, Australia
AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. ORCID
Zhigang Lei: 0000-0001-7838-7207 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS. Biographies Zhigang Lei is a professor at the State Key Laboratory of Chemical Resource Engineering at Beijing University of Chemical Technology, China. He received his B.S. degree in 1995 from Wuhan Institute of Technology, and his Ph.D. degree in 2000 from Tsinghua University. Then, he became a postdoctoral researcher at Beijing University of Chemical Technology, working with Professor Chengyue Li. In 2003− 2005, he worked as a researcher at the Research Center of Supercritical Fluid Technology (Tohoku University, Sendai, Japan). In 2005−2006, he received the world-famous Humboldt Fellowship and carried out his research as Chair of Separation Science and Technology (Universität Erlange-Nürnberg, Erlangen, Germany). In 2006, he came back to Beijing University of Chemical Technology. His current research interests include chemical process intensification and predictive molecular thermodynamics. He has contributed to about 120 papers in international journals and one book entitled Special Distillation Processes, published by Elsevier B.V. (2005). Biaohua Chen is a professor at the State Key Laboratory of Chemical Resource Engineering at Beijing University of Chemical Technology, China. He received his Ph.D. degree in 1996 from China University of Petroleum (Beijing). In 2000, he was a visiting scholar at Washington University in St. Louis and the University of Washington. He has received two National Science and Technology Progress Prizes (second class), two provincial or ministerial level Science and Technology Progress Prizes (first class), and one Natural Science Progress Prize. Now he is a member of the Standing Committee of the Beijing Chemical Industry Association and a member of the Editorial Board of the Journal of Petrochemical Universities (China). His main research interests are green chemistry and environmental catalysis. He has contributed to more than 150 papers in international journals. Yoon-Mo Koo is a Professor at the Department of Biological Engineering at Inha University, Korea. He received a B.S. degree (Seoul National University, Korea), an M.S. degree (KAIST, Korea) and a Ph.D. degree (Purdue University, USA), all in Chemical Engineering. He served as the Dean of College of Engineering, Inha University, and as the President of Korean Society of Biotechnology and Bioengineering, and he is currently a Member of the National Academy of Engineering, Korea. His research interests include biological separation and purification, microbial mixed culture, and ionic liquids. He has contributed to more than 140 papers in international journals. He was the organizing committee chairman of the 6th International Congress on Ionic Liquids (COIL-6), held on June 16−20, 2015, in Jeju, Korea.
Zhigang Lei*
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, China
Biaohua Chen
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, China
Douglas R. MacFarlane is an Australian Laureate Fellow at Monash University. He is also the program leader of the Energy Program at the Australian Centre for Electromaterials Science. His research interests focus on a broad range of ionic liquid properties and applications. He was a Ph.D. graduate from Austen Angell’s group at Purdue and after
Yoon-Mo Koo
Department of Biological Engineering, Inha University, Korea 6634
DOI: 10.1021/acs.chemrev.7b00246 Chem. Rev. 2017, 117, 6633−6635
Chemical Reviews
Editorial
(20) Qiao, Y.; Ma, W.; Theyssen, N.; Chen, C.; Hou, Z. Temperature-Responsive Ionic Liquids: Fundamental Behaviors and Catalytic Applications. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00652. (21) Dai, C.; Zhang, J.; Huang, C.; Lei, Z. Ionic Liquids in Selective Oxidation: Catalysts and Solvents. Chem. Rev. 2017, DOI: 10.1021/ acs.chemrev.7b00030. (22) Ventura, S. P. M.; e Silva, F. A.; Quental, M. V.; Mondal, D.; Freire, M. G.; Coutinho, J. A. P. Ionic-Liquid-Mediated Extraction and Separation Processes for Bioactive Compounds: Past, Present, and Future Trends. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00550. (23) Paschoal, V. H.; Faria, L. F. O.; Ribeiro, M. C. C. Vibrational Spectroscopy of Ionic Liquids. Chem. Rev. 2017, DOI: 10.1021/ acs.chemrev.6b00461. (24) Wang, B.; Qin, L.; Mu, T.; Xue, Z.; Gao, G. Are Ionic Liquids Chemically Stable? Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00594. (25) Egorova, K. S.; Gordeev, E. G.; Ananikov, V. P. Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00562. (26) Watanabe, M.; Thomas, M. L.; Zhang, S.; Ueno, K.; Yasuda, T.; Dokko, K. Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices. Chem. Rev. 2017, DOI: 10.1021/ acs.chemrev.6b00504.
postdoctoral fellowships in France and New Zealand took up an academic position at Monash in 1983. He has published more than 600 papers and 30 patents. He was elected to the Australian Academy of Sciences in 2007 and to the Australian Academy of Technological Sciences and Engineering in 2009.
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DOI: 10.1021/acs.chemrev.7b00246 Chem. Rev. 2017, 117, 6633−6635
