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15 pages, 3337 KiB

Open AccessArticle

Effect of Thiouronium-Based Ionic Liquids on the Formation and Growth of CO₂ (sI) and THF (sII) Hydrates

by Mário R. C. Soromenho, Anastasiia Keba, José M. S. S. Esperança and Mohammad Tariq

Int. J. Mol. Sci. 2022, 23(6), 3292; https://doi.org/10.3390/ijms23063292 - 18 Mar 2022

Cited by 3 | Viewed by 1588

Abstract

In this manuscript, two thiouronium-based ionic liquids (ILs), namely 2-ethylthiouronium bromide [C₂th][Br] and 2-(hydroxyethyl)thiouronium bromide [C₂OHth][Br], were tested at different concentrations (1 and 10 wt%) for their ability to affect CO₂ (sI) and tetrahydrofuran (THF) (sII) hydrate formation [...] Read more.

In this manuscript, two thiouronium-based ionic liquids (ILs), namely 2-ethylthiouronium bromide [C₂th][Br] and 2-(hydroxyethyl)thiouronium bromide [C₂OHth][Br], were tested at different concentrations (1 and 10 wt%) for their ability to affect CO₂ (sI) and tetrahydrofuran (THF) (sII) hydrate formation and growth. Two different methods were selected to perform a thermodynamic and kinetic screening of the CO₂ hydrates using a rocking cell apparatus: (i) an isochoric pressure search method to map the hydrate phase behavior and (ii) a constant ramping method to obtain the hydrate formation and dissociation onset temperatures. A THF hydrate crystal growth method was also used to determine the effectiveness of the ILs in altering the growth of type sII hydrates at atmospheric pressure. Hydrate–liquid–vapor equilibrium measurements revealed that both ILs act as thermodynamic inhibitors at 10 wt% and suppress the CO₂ hydrate equilibria ~1.2 °C. The constant ramping methodology provides interesting results and reveals that [C₂OHth][Br] suppresses the nucleation onset temperature and delays the decomposition onset temperatures of CO₂ hydrates at 1 wt%, whereas suppression by [C₂th][Br] was not statistically significant. Normalized pressure plots indicate that the presence of the ILs slowed down the growth as well as the decomposition rates of CO₂ hydrates due to the lower quantity of hydrate formed in the presence of 1 wt% ILs. The ILs were also found to be effective in inhibiting the growth of type sII THF hydrates without affecting their morphology. Therefore, the studied thiouronium ILs can be used as potential dual-function hydrate inhibitors. This work also emphasizes the importance of the methods and conditions used to screen an additive for altering hydrate formation and growth. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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12 pages, 3313 KiB

Open AccessArticle

The Structure of the Electric Double Layer of the Protic Ionic Liquid [Dema][TfO] Analyzed by Atomic Force Spectroscopy

by Christian Rodenbücher, Yingzhen Chen, Klaus Wippermann, Piotr M. Kowalski, Margret Giesen, Dirk Mayer, Florian Hausen and Carsten Korte

Int. J. Mol. Sci. 2021, 22(23), 12653; https://doi.org/10.3390/ijms222312653 - 23 Nov 2021

Cited by 6 | Viewed by 2316

Abstract

Protic ionic liquids are promising electrolytes for fuel cell applications. They would allow for an increase in operation temperatures to more than 100 °C, facilitating water and heat management and, thus, increasing overall efficiency. As ionic liquids consist of bulky charged molecules, the [...] Read more.

Protic ionic liquids are promising electrolytes for fuel cell applications. They would allow for an increase in operation temperatures to more than 100 °C, facilitating water and heat management and, thus, increasing overall efficiency. As ionic liquids consist of bulky charged molecules, the structure of the electric double layer significantly differs from that of aqueous electrolytes. In order to elucidate the nanoscale structure of the electrolyte–electrode interface, we employ atomic force spectroscopy, in conjunction with theoretical modeling using molecular dynamics. Investigations of the low-acidic protic ionic liquid diethylmethylammonium triflate, in contact with a platinum (100) single crystal, reveal a layered structure consisting of alternating anion and cation layers at the interface, as already described for aprotic ionic liquids. The structured double layer depends on the applied electrode potential and extends several nanometers into the liquid, whereby the stiffness decreases with increasing distance from the interface. The presence of water distorts the layering, which, in turn, significantly changes the system’s electrochemical performance. Our results indicate that for low-acidic ionic liquids, a careful adjustment of the water content is needed in order to enhance the proton transport to and from the catalytic electrode. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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11 pages, 1403 KiB

Open AccessArticle

Bioderived Ionic Liquids and Salts with Various Cyano Anions as Precursors for Doped Carbon Materials

by Alina Brzęczek-Szafran, Bartłomiej Gaida, Agata Blacha-Grzechnik, Karolina Matuszek and Anna Chrobok

Int. J. Mol. Sci. 2021, 22(19), 10426; https://doi.org/10.3390/ijms221910426 - 27 Sep 2021

Cited by 11 | Viewed by 1844

Abstract

Carbohydrate moieties were combined with various cross-linkable anions (thiocyanate [SCN], tetracyanoborate [TCB], tricyanomethanide [TCM], and dicyanamide [DCA]) and investigated as precursors for the synthesis of nitrogen-doped and nitrogen-/sulfur-co-doped carbons. The influence of the molecular structures of the precursors on their thermophysical properties and [...] Read more.

Carbohydrate moieties were combined with various cross-linkable anions (thiocyanate [SCN], tetracyanoborate [TCB], tricyanomethanide [TCM], and dicyanamide [DCA]) and investigated as precursors for the synthesis of nitrogen-doped and nitrogen-/sulfur-co-doped carbons. The influence of the molecular structures of the precursors on their thermophysical properties and the properties of the derived carbon materials was elucidated and compared to petroleum-derived analogs. A carbohydrate-based ionic liquid featuring an [SCN] anion yielded more carbon residues upon carbonization than its 1-ethyl-3-methylimidazolium analog, and the resulting dual-doping of the derived carbon material translated to enhanced catalytic activity in the oxygen reduction reaction. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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21 pages, 5817 KiB

Open AccessArticle

Bis(trifluoromethylsulfonyl)imide Ionic Liquids Applied for Fine-Tuning the Cure Characteristics and Performance of Natural Rubber Composites

by Anna Sowińska, Magdalena Maciejewska and Anna Grajewska

Int. J. Mol. Sci. 2021, 22(7), 3678; https://doi.org/10.3390/ijms22073678 - 01 Apr 2021

Cited by 15 | Viewed by 2883

Abstract

The goal of this work was to apply ionic liquids (ILs) with bis(trifluoromethylsulfonyl)imide anion (TFSI) for fine-tuning the cure characteristics and physico-chemical properties of elastomer composites based on a biodegradable natural rubber (NR) matrix. ILs with TFSI anion and different cations, such as [...] Read more.

The goal of this work was to apply ionic liquids (ILs) with bis(trifluoromethylsulfonyl)imide anion (TFSI) for fine-tuning the cure characteristics and physico-chemical properties of elastomer composites based on a biodegradable natural rubber (NR) matrix. ILs with TFSI anion and different cations, such as alkylpyrrolidinium, alkylammonium, and alkylsulfonium cations, were applied to increase the efficiency of sulfur vulcanization and to improve the performance of NR composites. Thus, the influence of ILs on the vulcanization of NR compounds, as well as crosslink density and physical properties of NR vulcanizates, including tensile properties, thermal stability, and resistance to thermo-oxidative aging was explored. The activity of ILs seems to be strongly dependent on their cation. Pyrrolidinium and ammonium ILs effectively supported the vulcanization, reducing the optimal vulcanization time and temperature of NR compounds and increasing the crosslink density of the vulcanizates. Consequently, vulcanizates with these ILs exhibited higher tensile strength than the benchmark without IL. On the other hand, sulfonium ILs reduced the torque increment owing to the lower crosslinking degree of elastomer but significantly improved the resistance of NR composites to thermo-oxidation. Thus, TFSI ILs can be used to align the curing behavior and performance of NR composites for particular applications. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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16 pages, 5767 KiB

Open AccessArticle

Structural Reorganization of Imidazolium Ionic Liquids Induced by Pressure-Enhanced Ionic Liquid—Polyethylene Oxide Interactions

by Teng-Hui Wang, Li-Wen Hsu and Hai-Chou Chang

Int. J. Mol. Sci. 2021, 22(2), 981; https://doi.org/10.3390/ijms22020981 - 19 Jan 2021

Cited by 5 | Viewed by 3106

Abstract

Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C–H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM] [...] Read more.

Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C–H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM]⁺ and [HMIM]⁺. The pressure-induced phase transition of pure 1-butyl-3-methylimidazolium bromide ([BMIM]Br) is observed at a pressure of 0.4 GPa. Pressure-enhanced [BMIM]Br-PEO interactions may assist PEO in dividing [BMIM]Br clusters to hinder the aggregation of [BMIM]Br under high pressures. The C–H absorptions of pure 1-hexyl-3-methylimidazolium bromide [HMIM]Br do not show band narrowing under high pressures, as observed for pure [BMIM]Br. The band narrowing of C–H peaks is observed at 1.5 GPa for the [HMIM]Br-PEO mixture containing 80 wt% of [HMIM]Br. The presence of PEO may reorganize [HMIM]Br clusters into a semi-crystalline network under high pressures. The differences in aggregation states for ambient-pressure phase and high-pressure phase may suggest the potential of [HMIM]Br-PEO (M.W.~900,000) for serving as optical or electronic switches. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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16 pages, 3247 KiB

Open AccessArticle

Optimization for Liquid-Liquid Extraction of Cd(II) over Cu(II) Ions from Aqueous Solutions Using Ionic Liquid Aliquat 336 with Tributyl Phosphate

by Lai Yee Lee, Norhashimah Morad, Norli Ismail, Amir Talebi and Mohd Rafatullah

Int. J. Mol. Sci. 2020, 21(18), 6860; https://doi.org/10.3390/ijms21186860 - 18 Sep 2020

Cited by 17 | Viewed by 2757

Abstract

This study investigates the separation of two heavy metals, Cd(II) and Cu(II), from the mixed synthetic feed using a liquid-liquid extraction. The current study uses tri-octyl methylammonium chloride (Aliquat 336) as the extractant (with tributyl phosphate (TBP) as a phase modifier), diluted in [...] Read more.

This study investigates the separation of two heavy metals, Cd(II) and Cu(II), from the mixed synthetic feed using a liquid-liquid extraction. The current study uses tri-octyl methylammonium chloride (Aliquat 336) as the extractant (with tributyl phosphate (TBP) as a phase modifier), diluted in toluene, in order to investigate the selective extraction of Cd(II) over Cu(II) ions. We investigate the use of ethylenediaminetetraacetic acid (EDTA) as a masking agent for Cu(II), when added in aqueous feed, for the selective extraction of Cd(II). Five factors that influence the selective extraction of Cd(II) over Cu(II) (the equilibrium pH (pH_eq), Aliquat 336 concentration (Aliquat 336), TBP concentration (TBP), EDTA concentration (EDTA), and organic to aqueous ratio (O:A)) were analyzed. Results from a 2^5–1 fractional factorial design show that Aliquat 336 significantly influenced Cd(II) extraction, whereas EDTA was statistically significant for the antagonistic effect on the E% of Cu(II) in the same system. Moreover, results from optimization experiment showed that the optimum conditions are Aliquat 336 concentration of 99.64 mM and EDTA concentration of 48.86 mM—where 95.89% of Cd(II) was extracted with the least extracted Cu(II) of 0.59%. A second-order model was fitted for optimization of Cd(II) extraction with a R² value of 0.998, and ANOVA results revealed that the model adequately fitted the data at a 5% significance level. Interaction between Aliquat 336 and Cd(II) has been proven via FTIR qualitative analysis, whereas the addition of TBP does not affect the extraction mechanism. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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Review

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31 pages, 1630 KiB

Open AccessReview

A Review on Ionic Liquids-Based Membranes for Middle and High Temperature Polymer Electrolyte Membrane Fuel Cells (PEM FCs)

by Mohammad Ebrahimi, Wojciech Kujawski, Kateryna Fatyeyeva and Joanna Kujawa

Int. J. Mol. Sci. 2021, 22(11), 5430; https://doi.org/10.3390/ijms22115430 - 21 May 2021

Cited by 34 | Viewed by 4732

Abstract

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than [...] Read more.

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than 100 °C with high conductivity and thermal stability. The membranes containing ILs can conduct protons through the PEMs at elevated temperatures (more than 80 °C), unlike the Nafion-based membranes. A wide range of ILs have been identified, including chiral ILs, bio-ILs, basic ILs, energetic ILs, metallic ILs, and neutral ILs, that, from among them, functionalized ionic liquids (FILs) include a lot of ion exchange groups in their structure that improve and accelerate proton conduction through the polymeric membrane. In spite of positive features of using ILs, the leaching of ILs from the membranes during the operation of fuel cell is the main downside of these organic salts, which leads to reducing the performance of the membranes; however, there are some ways to diminish leaching from the membranes. The aim of this review is to provide an overview of these issues by evaluating key studies that have been undertaken in the last years in order to present objective and comprehensive updated information that presents the progress that has been made in this field. Significant information regarding the utilization of ILs in MT-PEMFCs and HT-PEMFCs, ILs structure, properties, and synthesis is given. Moreover, leaching of ILs as a challenging demerit and the possible methods to tackle this problem are approached in this paper. The present review will be of interest to chemists, electrochemists, environmentalists, and any other researchers working on sustainable energy production field. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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37 pages, 9839 KiB

Open AccessReview

Revisiting Ionic Liquid Structure-Property Relationship: A Critical Analysis

by Wagner Silva, Marcileia Zanatta, Ana Sofia Ferreira, Marta C. Corvo and Eurico J. Cabrita

Int. J. Mol. Sci. 2020, 21(20), 7745; https://doi.org/10.3390/ijms21207745 - 19 Oct 2020

Cited by 83 | Viewed by 7766

Abstract

In the last few years, ionic liquids (ILs) have been the focus of extensive studies concerning the relationship between structure and properties and how this impacts their application. Despite a large number of studies, several topics remain controversial or not fully answered, such [...] Read more.

In the last few years, ionic liquids (ILs) have been the focus of extensive studies concerning the relationship between structure and properties and how this impacts their application. Despite a large number of studies, several topics remain controversial or not fully answered, such as: the existence of ion pairs, the concept of free volume and the effect of water and its implications in the modulation of ILs physicochemical properties. In this paper, we present a critical review of state-of-the-art literature regarding structure–property relationship of ILs, we re-examine analytical theories on the structure–property correlations and present new perspectives based on the existing data. The interrelation between transport properties (viscosity, diffusion, conductivity) of IL structure and free volume are analysed and discussed at a molecular level. In addition, we demonstrate how the analysis of microscopic features (particularly using NMR-derived data) can be used to explain and predict macroscopic properties, reaching new perspectives on the properties and application of ILs. Full article

(This article belongs to the Special Issue Ionic Liquids: Applications in Energy and Environment)

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