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ChemEngineering
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Advanced Ionic Liquid-Based Mixed Solvent Systems
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Advanced Ionic Liquid-Based Mixed Solvent Systems

A special issue of ChemEngineering (ISSN 2305-7084).

Deadline for manuscript submissions: closed (28 October 2019) | Viewed by 27429

Special Issue Editor

Prof. Dr. Mark P. Heitz

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Guest Editor
Department of Chemistry and Biochemistry, SUNY Brockport, 228 Smith Hall, 350 New Campus Drive, Brockport, NY 14420, USA
Interests: ionic liquids (ILs); deep eutectic solvents (DESs); cosolvent solutions with ILs and DESs; supercritical fluid solvation; proteins; microheterogeneous media; molecular solvation dynamics; laser-based spectroscopy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Over the past few decades, there has been a dramatic surge in the number of articles published in the literature that focus on (room-temperature) ionic liquids.  Interest in these salts has caused research to soar past the point of being just a curiosity to one of extensive efforts aimed at understanding these materials.  As a result, ionic liquids are arguably among the most studied materials in the physical sciences. The tremendous amount of work by researchers across many disciplines arises from the ever-growing number of applications of ionic liquids in areas such as chemical synthesis, engineering, and fabrication of electrochemical devices, among many others.

It is often the case that applications of ‘new’ materials frequently outpace the development of a detailed, molecular-level understanding.  Therefore, the importance of building a predictive capability becomes necessarily and progressively more important. Appropriately, much of the research published to date (both theoretical and experimental) has focused on neat ionic liquids.  However, as the diversity of applications continues to expand, ionic liquids are being combined with molecular cosolvents to further enhance their utility.

While a significant amount of effort has been made to study molecular-level details concerning the structure, dynamics, and interactions in neat ionic liquids, there is much work to do on cosolvent-modified ionic liquid systems. The chemistry, physics, and engineering of ionic liquid systems requires both experimental and theoretical approaches to achieve the desired understanding of the underpinnings that drive the widening array of ionic liquid-based materials.  To this end, a complete picture will only be achieved when a concerted effort involving all available tools is applied. This Special Issue seeks to highlight new results that discuss the properties and applications of multicomponent ionic liquid-cosolvent systems toward the advancement of a more complete understanding of ionic liquid chemistry and engineering.

Prof. Mark P. Heitz
Guest Editor

Manuscript Submission Information

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Keywords

  • ionic liquids
  • multicomponent ionic liquid solvent systems
  • molecular dynamics
  • thermodynamics
  • solution structure
  • physical and applied chemistry of ionic liquid solutions

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Published Papers (5 papers)

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Research

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19 pages, 2914 KiB  
Article
Spectroscopic Studies of a Phosphonium Ionic Liquid in Supercritical CO2
by Mark P. Heitz, Zackary C. Putney and Joel Campaign
ChemEngineering 2020, 4(2), 20; https://doi.org/10.3390/chemengineering4020020 - 27 Mar 2020
Viewed by 3114
Abstract
Fluorescence spectroscopy was used to study a solution comprised of coumarin 153 (C153)+ trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14]+ [Tf2N]−)+ supercritical CO2 (scCO2). We compare the spectroscopy of C153 in neat scCO2 to that of [...] Read more.
Fluorescence spectroscopy was used to study a solution comprised of coumarin 153 (C153)+ trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14]+ [Tf2N]−)+ supercritical CO2 (scCO2). We compare the spectroscopy of C153 in neat scCO2 to that of C153/scCO2 with the addition of ionic liquid (IL). Excitation and emission peak frequencies of C153 in scCO2 and in IL/scCO2 diverged at reduced densities (ρr = ρ/ρc) below the CO2 critical density. At low fluid density, spectral changes in the IL/scCO2 solutions showed evidence that C153 experiences a very different microenvironment—one that is unlike neat scCO2. The data show that the presence of IL clearly influences the C153 excitation and emission profiles. Excitation was broadened and red shifted by >2000 cm−1 and the presence of an additional low-energy emission component that was red shifted by ~3000 cm−1 was clearly visible and not observed in neat scCO2. The solution heterogeneity was controlled by changing the scCO2 density and at high fluid density, both the excitation and emission spectra were more similar to those in neat scCO2. Steady-state anisotropy also showed that at low fluid density, the C153 emission was significantly polarized. Aggregation of C153 has been reported in the literature and this led us to hypothesize the possibility that C153 dimer (aggregation) formation may be occurring in scCO2. Another possible explanation is that dye–IL aggregates may dissolve into the scCO2 phase due to C153 acting as a “co-solvent” for the IL. Time-resolved intensity decay measurements yielded only slightly non-exponential decays with accompanying time constants of ~3–4 ns that were significantly shorter than the 5–6 ns time constants in neat scCO2, which are suggestive of C153–IL interactions. However, these data did not conclusively support dimer formation. Pre-exponential factors of the time constants showed that almost all of the emission was due to monomeric C153. Full article
(This article belongs to the Special Issue Advanced Ionic Liquid-Based Mixed Solvent Systems)
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9 pages, 1255 KiB  
Article
Dissolution of Chitin in Deep Eutectic Solvents Composed of Imidazolium Ionic Liquids and Thiourea
by Satoshi Idenoue, Kazuya Yamamoto and Jun-ichi Kadokawa
ChemEngineering 2019, 3(4), 90; https://doi.org/10.3390/chemengineering3040090 - 2 Dec 2019
Cited by 25 | Viewed by 4996
Abstract
Chitin is an abundant organic resource but shows poor solubility, leading to difficulty in utilization as materials. We have already reported that an ionic liquid (IL), 1-allyl-3-methylimidazolium bromide, dissolves chitin at concentrations up to ca. 5 wt %. However, the color of the [...] Read more.
Chitin is an abundant organic resource but shows poor solubility, leading to difficulty in utilization as materials. We have already reported that an ionic liquid (IL), 1-allyl-3-methylimidazolium bromide, dissolves chitin at concentrations up to ca. 5 wt %. However, the color of the resulting solution is blackened, mainly owing to the presence of bromide. On the other hand, some deep eutectic solvents (DESs) have been already reported to dissolve chitin. In this study, we found that DESs composed of imidazolium ILs and thiourea dissolved chitin without obvious coloring. DESs are systems formed from eutectic mixtures of hydrogen bond accepters and donors. We first prepared DESs by heating mixtures of imidazolium ILs with thiourea at 100 °C for 30 min with stirring. Predetermined amounts of chitin were then added to the DESs, and for the dissolution, the mixtures were left standing at room temperature for 24 h, followed by heating at 100 °C for 24 h with stirring. The dissolution processes were evaluated by CCD camera views, which revealed in most cases the dissolution of chitin at 2–5 wt % concentrations with the present DESs. Full article
(This article belongs to the Special Issue Advanced Ionic Liquid-Based Mixed Solvent Systems)
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14 pages, 2668 KiB  
Article
Conductivity, Viscosity, Spectroscopic Properties of Organic Sulfonic Acid solutions in Ionic Liquids
by Anh T. Tran, Jay Tomlin, Phuoc H. Lam, Brittany L. Stinger, Alexandra D. Miller, Dustin J. Walczyk, Omar Cruz, Timothy D. Vaden and Lei Yu
ChemEngineering 2019, 3(4), 81; https://doi.org/10.3390/chemengineering3040081 - 1 Oct 2019
Cited by 8 | Viewed by 5887
Abstract
Sulfonic acids in ionic liquids (ILs) are used as catalysts, electrolytes, and solutions for metal extraction. The sulfonic acid ionization states and the solution acid/base properties are critical for these applications. Methane sulfonic acid (MSA) and camphor sulfonic acid (CSA) are dissolved in [...] Read more.
Sulfonic acids in ionic liquids (ILs) are used as catalysts, electrolytes, and solutions for metal extraction. The sulfonic acid ionization states and the solution acid/base properties are critical for these applications. Methane sulfonic acid (MSA) and camphor sulfonic acid (CSA) are dissolved in several IL solutions with and without bis(trifluoromethanesulfonyl)imine (HTFSI). The solutions demonstrated higher conductivities and lower viscosities. Through calorimetry and temperature-dependent conductivity analysis, we found that adding MSA to the IL solution may change both the ion migration activation energy and the number of “free” charge carriers. However, no significant acid ionization or proton transfer was observed in the IL solutions. Raman and IR spectroscopy with computational simulations suggest that the HTFSI forms dimers in the solutions with an N-H-N “bridged” structure, while MSA does not perturb this hydrogen ion solvation structure in the IL solutions. CSA has a lower solubility in the ILs and reduced the IL solution conductivity. However, in IL solutions containing 0.4 M or higher concentration of HTFSI, CSA addition increased the conductivity at low CSA concentrations and reduced it at high concentrations, which may indicate a synergistic effect. Full article
(This article belongs to the Special Issue Advanced Ionic Liquid-Based Mixed Solvent Systems)
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12 pages, 3019 KiB  
Article
Vapor Pressure Mapping of Ionic Liquids and Low-Volatility Fluids Using Graded Isothermal Thermogravimetric Analysis
by Sudhir Ravula, Nathaniel E. Larm, Mohammad A. Mottaleb, Mark P. Heitz and Gary A. Baker
ChemEngineering 2019, 3(2), 42; https://doi.org/10.3390/chemengineering3020042 - 20 Apr 2019
Cited by 70 | Viewed by 8166
Abstract
One of the hallmarks of ionic liquids (ILs) and a critical part of their sustainable implementation is their low volatility, although statements in this regard are frequently made in the absence of a critical evaluation. Although it is generally accepted that conventional ILs [...] Read more.
One of the hallmarks of ionic liquids (ILs) and a critical part of their sustainable implementation is their low volatility, although statements in this regard are frequently made in the absence of a critical evaluation. Although it is generally accepted that conventional ILs exhibit significantly reduced vapor pressures relative to common organic solvents, glib statements about ILs having zero volatility can no longer be abided, even if a concrete temperature-dependent vapor pressure, Pvap(T), framework for placement of IL performance has not yet been established. In this communication, Pvap(T) values of 30 illustrative low-volatility fluids—including representative imidazolium-, ammonium-, and pyrrolidinium-based aprotic ILs; examples of protic, polymeric, and di-cationic ILs; as well as deep eutectic solvents (DESs) and glycols—were determined using a simple, convenient, and reproducible isothermal thermogravimetric method. Guided by this “vapor pressure map”, observed trends can be discussed in terms of anion basicity, cation geometry, alkane chain length, hydrogen bonding strength, and van der Waals forces, providing a context for the placement of theoretical and experimental vapor pressures gleaned in future IL and DES studies. Full article
(This article belongs to the Special Issue Advanced Ionic Liquid-Based Mixed Solvent Systems)
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Review

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25 pages, 9122 KiB  
Review
Specifically Designed Ionic Liquids—Formulations, Physicochemical Properties, and Electrochemical Double Layer Storage Behavior
by Zheng Yue, Qiang Ma, Xinyi Mei, Abigail Schulz, Hamza Dunya, Dana Alramahi, Christopher McGarry, Jim Tufts, Amartya Chakrabarti, Rituparna Saha and Braja K. Mandal
ChemEngineering 2019, 3(2), 58; https://doi.org/10.3390/chemengineering3020058 - 3 Jun 2019
Cited by 1 | Viewed by 4406
Abstract
Two key features—non-volatility and non-flammability—make ionic liquids (ILs) very attractive for use as electrolyte solvents in advanced energy storage systems, such as supercapacitors and Li-ion batteries. Since most ILs possess high viscosity and are less prone to dissolving common electrolytic salts when compared [...] Read more.
Two key features—non-volatility and non-flammability—make ionic liquids (ILs) very attractive for use as electrolyte solvents in advanced energy storage systems, such as supercapacitors and Li-ion batteries. Since most ILs possess high viscosity and are less prone to dissolving common electrolytic salts when compared to traditional electrolytic solvents, they must be formulated with low viscosity thinner solvents to achieve desired ionic conductivity and dissolution of electrolyte salts in excess of 0.5 M concentration. In the past few years, our research group has synthesized several specifically designed ILs (mono-cationic, di-cationic, and zwitterionic) with bis(trifluoromethylsulfonyl)imide (TFSI) and dicyanamide (DCA) as counter anions. This article describes several electrolyte formulations to achieve superior electrolytic properties. The performance of a few representative IL-based electrolytes in supercapacitor coin cells is presented. Full article
(This article belongs to the Special Issue Advanced Ionic Liquid-Based Mixed Solvent Systems)
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