Thermal Stability Of Ionic Liquids Research Articles

Thermal stabilities and decomposition mechanisms under oxygen and nitrogen atmospheres for imidazolium ionic liquids with different cations

Ionic liquids (ILs) are room temperature molten salts, have received extensive attention from the academic community due to their excellent characteristics. In the context of global warming, more and more scholars are looking forward to using ILs as a gas adsorbents, especially ILs containing bis(trifluoromethylsulfonyl)imine (Tf2N). It is well known that the thermal stabilities of ILs are affected by many factors, and the cation type is one of them. In this paper, five imidazole ILs with different functional groups on the side chains of the imidazole rings were selected as the research objects, and their anions were all Tf2N. The thermal decomposition characteristics and thermal effects of the selected samples were determined by thermal gravimetric analyzer (TGA) and differential scanning calorimetry (DSC). The experimental data showed that the most stable ionic liquid was that with the simplest side chain, and the more complex the side chain was, the lower the thermal stability of the sample. In addition, some of their decomposition products were studied with thermogravimetric analyzer coupled with Fourier-transform infrared spectrometry (TG–FTIR). The decomposition mechanisms of the samples did not change under different atmospheres.

Quality conversion of H2S into β-mercaptopropionic acid by CETSA-based ionic liquid

With respect to the detrimental hydrogen sulfide (H2S), a whole new range of hydrophilic ionic liquids (ILs) could conveniently catalyze into more widely needed chemical reagents. ILs could be beneficial to increase the solubility and ionization of H2S, resulting in the Michael addition reaction with acrylic acid to produce β-mercaptopropionic acid. In this study, four kinds of hydrophilic ILs were synthesized by using carboxyethiosuccinic acid (CETSA), which contains three carboxyl groups with different chemical properties, as anions and combined with basic cations. The effect of the structure and reaction conditions of ILs on the catalytic activity of the system was studied. The result showed that the CETSA-based ILs with N, N, N′, N' -tetramethyl-1, 6-hexamethylenediamine (TMHDA) as cation had the best catalytic effect. ILs catalyst can greatly improve the selectivity and yield of the target product in addition reaction, which could be used for eight times at least without a noticeable decrease in its activity and conversion. In the absence of H2S cylinders, the conversion of acrylic acid can reach 99.21%, and the selectivity and yield of mercaptopropionic acid can reach 92.57% and 91.84% with [TMHDAH]CETSA. The ILs was characterized by FTIR, 1H NMR, 13C NMR and MS in order to determine the structure of the ILs. The thermal stability of ILs in the reaction system was observed by TG and DSC, and the ionization of ILs in solvent was measured by pH meter.

Thermal stability and flammability of several quaternary ammonium ionic liquids

With the development of potential large-scale industrial application of quaternary ammonium ionic liquids in the fields of gas separation, high-temperature lubricants and even rocket propellants, deep investigations are required to reveal the possible hazards of thermal decomposition, the flammability and the hazardous gaseous products. In this study, the thermal stability of five typical quaternary ammonium ionic liquids, [N2222][NTF2], [N2222][PF6], [N2222]Br, [N4444]Br and [N4444][PF6], were studied using thermogravimetric analyser (TGA). The results show that the thermal stability of ionic liquids follows an order of [N2222][NTF2] > [N2222][PF6] > [N4444][PF6] > [N2222]Br > [N4444]Br, indicating that the thermal stability is obviously affected by the anion, with an order of [NTF2]− > [PF6]− > Br−. Besides, increasing the alkyl chain length in the cation will reduce the thermal stability. In addition, Fire Testing Technology (FTT) cone calorimeter was used to investigate the flammability and found that the longer alkyl chains of quaternary ammonium ionic liquids make great contribution on larger the total heat release, the peak value of heat releasing rate and shorter ignition time. Moreover, with the same cation, [N2222]Br and [N4444]Br were shortened the ignition time and produced larger amount of heat than [N2222][PF6] and [N4444][PF6], respectively. It clearly shows that the risk of fire is also affected by the anion, with an order of Br− > [PF6]− > [NTF2]−. Finally, the decomposition products were measured by thermogravimetry coupled with Fourier-transform infrared spectroscopy (TG-FTIR), and it is deduced that the nucleophilic Br− from [Nmmmm]Br (m = 2,4) and F− from the [NTF2]− and [PF6]− during decomposition will attack the alkyl chain of the cation, which generated gaseous products such as fluoroalkanes, bromoalkanes, olefins, etc.

Thermal decomposition of phosphonium salicylate and phosphonium benzoate ionic liquids

The thermal stability of ionic liquids is important for their use in a variety of applications. Here, reactive molecular dynamics simulations and thermogravimetric analyses were used to explore the thermal decomposition mechanisms of phosphonium salicylate and phosphonium benzoate. Experiments performed at different heating rates indicated that the decomposition temperatures of phosphonium salicylate and phosphonium benzoate were comparable, but phosphonium benzoate was less stable than phosphonium salicylate under isothermal high temperature conditions. The lower thermal stability of the benzoate compared to the salicylate was reproduced in reactive molecular dynamics simulations. The simulations also showed that cation chain length had little effect on thermal stability. The simulations revealed that thermal decomposition for both phosphonium salicylate and phosphonium benzoate occurred through many different pathways that could be broadly categorized as proton-transfer, association, and dissociation reactions. The phosphonium benzoate underwent more of these reactions and exhibited a wide range of reaction pathways in each category than the phosphonium salicylate. Multiple possible mechanisms were explored to explain this difference and it was found that the dominant factor was the presence of the hydroxyl group in salicylate that affects the ability of oxygen atoms to take part in proton-transfer reactions that are the first step of all subsequent reactions. These findings demonstrate that even subtle differences in anion chemistry may significantly affect the thermal stability of ionic liquids, suggesting avenues for tuning these properties through molecular design.

Thermal Stability of Ionic Liquids: Effect of Metals

We investigated the thermal stability and corrosion effects of a promising ionic liquid (IL) to be employed as an advanced heat transfer fluid in solar thermal energy applications. Degradation tests were performed on IL samples kept in contact with various metals (steel, copper and brass) at 200 °C for different time lengths. Structural characterization of fresh and aged IL samples was carried out by high-resolution magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectroscopic analyses, while headspace gas chromatography–mass spectrometry was employed to evaluate the release of volatile organic compounds. The combination of the above-mentioned techniques effectively allowed the occurrence of degradation processes due to aging to be verified.

Four Phosphonium‐based Ionic Liquids. Synthesis, Characterization and Electrochemical Performance as Electrolytes for Silicon Anodes

AbstractHerein, we describe the synthesis, characterization and electrochemical performance of four phosphonium‐based ionic liquids (ILs) as electrolytes, Physicochemical properties such as viscosity, density, ionic conductivity, and thermal stability of ILs and conventional organic solvent ethylene carbonate (EC)/diethyl carbonate (DEC) were experimentally determined at different temperatures. All ILs showed thermal stability greater than 300 °C, surpassing the stability of the conventional organic solvent, whose flash points were 145 and 23 °C for EC and DEC, respectively. Nevertheless, at room temperature, all ILs are much more viscous than EC/DEC. The composite Si ‐[P2224][FSI] (triethyl‐n‐butylphosphonium bis(fluoromethylsulfonyl)imide) and Si‐EC/DEC anodes exhibit initial specific capacities at 0.15 A/g of 2409 and 2631 mAh/g, respectively. This demonstrates that despite the inferior transport properties of ILs, short alkyl‐substituted phosphonium ILs like [P2224][FSI] are potentially competitive for the new generation of electrolytes for LIBs. NMR, DSC, TGA, and galvanostatic discharged/charged were used as characterization techniques.

Thermal stability of ionic liquids in nitrogen and air environments

Ionic liquids (ILs) are being developed and studied for a variety of high-temperature applications, including as solvents for separations (where thermal regeneration is used) and as heat transfer fluids. Dynamic decomposition information has been reported for numerous ILs in the literature at various ramp rates. Although this information is useful for assessing how different characteristics, such as cation substituent groups or choice of anion, affect the decomposition of the ILs, dynamic decomposition temperature may overestimate the thermal stability of these compounds. Isothermal decomposition data is necessary when developing ILs in order to truly evaluate their thermal stability for high-temperature applications. However, this information is lacking for many ILs. In this study, we provide both fast (10 K/min) and slow (2 K/min) dynamic decomposition data, as well as isothermal decomposition data at five temperatures from 513.15 to 593.15 K for a selection of seventeen imidazolium, pyridinium, and tetraalkylammonium ILs and from 373.15 to 473.15 K for eight tetraalkylphosphonium ILs. There is significant mass loss after 16 h for most ILs even at 100 K below the decomposition temperature determined from dynamic measurements. Most ILs with the bis(trifluoromethylsulfonyl)imide anion ([Tf2N]−) show zero order mass loss, indicating that the mass loss is actually by evaporation rather than decomposition. Aminopyridinium ILs with [Tf2N]− are particularly thermally stable. We also compare isothermal decomposition rates for ILs under inert (N2) versus oxidative (air) gaseous environments. The mass loss activation energies are lower in air, suggesting more decomposition (vs. evaporation) in air. Mass spectrometry confirms that nucleophilic substitution is the main decomposition mechanism for most ILs in N2, but β-elimination also occurs for the tetra-alkylphosphonium ILs.

Ultrasonic‐Assisted Ionic Liquid Extraction of Four Biflavonoids from Ginkgo biloba L.

AbstractIn the study, four main biflavonoids (bilobetin (BIL), ginkgetin (GIN), isoginkgetin (IGIN) and sciadopitysin (SCI)) were extracted from Ginkgo biloba L. by ultrasonic‐assisted ionic liquid extraction (UAILE). The above four biflavonoids from Ginkgo biloba L. were simultaneously determined by the established high performance liquid chromatography (HPLC) approach. Next, three novel ionic liquids (ILs) were synthesized by one‐step method from benzoxazole and three acids or salts. The structure of ILs were characterized by elemental analysis, infrared spectroscopy and nuclear magnetic resonance. Moreover, the thermal stability of ILs was evaluated by thermogravimetric analysis. Through screening the extraction effect of 9 different ILs, [EPy]BF4 was screened as the optimal extraction agent. Through single factor and response surface analysis, the optimum extraction conditions of the four kinds of biflavonoids from Ginkgo biloba L. were further investigated. The optimum conditions were as follows: 0.148 mol/L IL concentration, 25 min extraction time, 1 : 14 g/ml solid‐liquid ratio, and 280 W ultrasonic power. The extraction rates of BIL, GIN, IGIN and SCI in Ginkgo biloba L. were 2.44 mg/g, 4.33 mg/g, 6.50 mg/g and 13.97 mg/g, respectively. Compared with ethanol‐UAE, infiltration extraction (IE) and percolation extraction (PE), UAILE not only could obtain more biflavonoids, but also could save the extraction time. In addition, the results of recovery test indicated that the recovered IL could be repeatedly extracted for 6 times. In general, three novel ILs were first synthesized in this study. The UAILE was first applied to extract the four biflavonoids in G. biloba L. This study provided a valuable reference for further investigation on G. biloba L.

Impacts of TGA furnace parameters for prediction of long-term thermal stability of ionic liquids

The concept of maximum operation temperature is established for the prediction of the time dependent thermal stability of ionic liquids based on kinetic evaluation of thermogravimetric analysis. The influence of the furnace control parameters on the maximum operation temperature (MOT) is shown using the example of 1-methyl-3-propylimidazolium iodide ([C3C1im]I) with respect to three different parameter sets of a programmed proportional integral derivative (PID) controller of the TGA. Kinetics of thermal decomposition of [C3C1im]I have been investigated with the implementation of an improved kinetic model. The activation energy obtained using the Kissinger-Akahira-Sunose equation showed variations apparently due to the decomposition degree. The model compound is decomposed by a one-step kinetics, which results from pseudo zero order relationship of the activation energy to the conversion rate. The activation energy, pre-exponential factor, and the activation energy are strongly dependent on the parameters of TGA furnace controller.

Thermal Stability of Ionic Liquids: Current Status and Prospects for Future Development

Ionic liquids (ILs) are the safest solvent in various high-temperature applications due to their non-flammable properties. In order to obtain their thermal stability properties, thermogravimetric analysis (TGA) is extensively used to analyze the kinetics of the thermal decomposition process. This review summarizes the different kinetics analysis methods and finds the isoconversional methods are superior to the Arrhenius methods in calculating the activation energy, and two tools—the compensation effect and master plots—are suggested for the calculation of the pre-exponential factor. With both parameters, the maximum operating temperature (MOT) can be calculated to predict the thermal stability in long-term runnings. The collection of thermal stability data of ILs with divergent cations and anions shows the structure of cations such as alkyl side chains, functional groups, and alkyl substituents will affect the thermal stability, but their influence is less than that of anions. To develop ILs with superior thermal stability, dicationic ILs (DILs) are recommended, and typically, [C4(MIM)2][NTf2]2 has a decomposition temperature as high as 468.1 °C. For the convenience of application, thermal stability on the decomposition temperature and thermal decomposition activation energy of 130 ILs are summarized at the end of this manuscript.

Selective monoalkylation of hydroquinone in the presence of SO3H-functionalized ionic liquids as catalysts

A process aiming at O-alkylation of hydroquinone (HQ), where ionic liquids (ILs) act as catalyst is objectively described. Five SO3H-functionalized ILs having different cations were prepared and characterized by NMR and FTIR techniques. The acidity and thermal stability of ILs were determined by Hammett function and thermogravimetric analysis (TGA), respectively. The catalytic activity of these ILs were tested for O-alkylation of HQ with methanol in 4-methoxyphenol (4MP) in the presence of small amount of benzoquinone (BQ). The effect of reaction parameters such as temperature, time, catalyst loading and substrate concentration on the conversion of HQ and product distribution was examined and optimized to maximize the yield of 4MP using 1,3-disulfonic acid imidazolium hydrogen sulfate (IL2) catalyst. Maximum yield of desired product 4MP 93.79% was obtained at 338 K temperature, 5.45 × 10–2 mol HQ, 8.33 × 10–3 mol BQ, and 10.37 mol% catalyst loading in 120 min reaction time. Single-product formation was observed up to 338 K temperature but higher temperature (above 338 K) and longer reaction time resulted in the formation of 2,4-dimethoxyphenol (24DMP) as a by-product. Catalyst recyclability was also established up to the fifth run which showed no declination in its activity.

The study of decomposition of 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide by using Termogravimetry: Dissecting vaporization and decomposition of ILs

The question of thermal stability of ionic liquids (ILs) is often raised in the scope of industrial application of ILs. The most widely used approach for this purpose is Thermo Gravimetric Analysis (TGA) with the determination of decomposition “Tonset” incorrectly called Decomposition Temperature. In the present study with the help of TGA study of 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide we have shown the Tonset or specified mass-loss rate cannot be applied as the innitial point of decomposition. We have proposed a new approach allowing dissecting the mass loss caused by vaporization of the sample and its thermal decomposition. The further analysis of the decomposition mass loss by using “isoconversional kinetics” allows to determine kinetic parameters of decomposition such as pre-exponential factor A and activation energy EA. The experimental activation energy EA = (250 ± 15) kJ·mol−1 agreed with the gas phase B3LYP calculated value by Kroon EA = 250 kJ·mol−1.

How thermal stability of ionic liquids leads to more efficient TiO2-based nanophotocatalysts: Theoretical and experimental studies

Ionic liquids (ILs) containing distinct nitrogen-bearing organic cations (pyridinium, pyrrolidinium, imidazolium, ammonium, morpholinium) were first used for the preparation of 23 IL-TiO2 types of composites by ionic liquid assisted solvothermal synthesis. These 23 optimal ILs structures (i.e. compounds exhibiting an optimal combination of specific properties, functionality, and safety) for synthesis and experimental validation were selected by computational high-throughput screening from a combinatorically created library containing 836 ILs theoretically designed and characterized candidates. Then, selected IL-TiO2 structures with potential photocatalytic activity were synthesized with the use of solvothermal reaction. Then, the decomposition level, the role of the individual IL cation structure on the morphology, thermal stability, surface and photocatalytic properties of the IL-TiO2 microparticles were determined experimentally. The chemoinformatic analysis of the relationship between the structure of the ionic liquid, its thermal stability under the conditions of synthesis and photocatalytic activity was applied for the first time. The results presented here are the first step in the development of methodology (combined experimental and theoretical) that may simplify the procedure of designing safer and more efficient TiO2-based photocatalyst. The developed computational methodology makes it possible to predict properties of newly synthesized IL-TiO2 materials before synthesis and identifies structural features of ILs that influence the efficiency of IL-TiO2 system. The presented approach reduces the number and cost of necessary experiments, as well as increases the success ratio of efficient TiO2-based photocatalyst design by a selection of optimal IL structures (i.e. ionic liquid characterized by a combination of most promising physicochemical features).

Reaction parameters dependence of the CO2/epoxide coupling reaction catalyzed by tunable ionic liquids, optimization of comonomer-alternating enhancement pathway

Glycerol based symmetrical cations with different anions accommodated ionic liquids (ILs) was found to be the most prominent catalyst system to produce cyclic carbonate (CC) from carbon dioxide (CO2) and propylene oxide (PO) for the first time. The synthesized ILs was analyzed by different spectroscopic technique, the thermal stability of ILs was analyzed by TGA, DSC. The mole ratio of IL/DBU gives a positive effect towards the product yield and selectivity. The best catalytic activity and long-term durability of ILs could be due to the synergistic combination of cation and anion makes an ideal catalyst for title reaction. The effect of ILs loading, temperature, pressure, and time on the production of cyclic carbonate was also investigated to determine the best reaction conditions (final 2 MPa CO2 pressure, 4 h, and 110 °C) the propylene carbonate (PC) selectivity and yield was 98.2 and 91.9%. Moreover, based on TGA and FT-IR analysis the catalyst system could be reusable up to four times (16 h) with no change in catalyst performance and product selectivity. In addition, the probable mechanism of this reaction was also proposed with the help of 13C NMR analysis.

Nafion/Protic Ionic Liquid Blends: Nanoscale Organization and Transport Properties

© 2019 American Chemical Society. In this work, the possibility of using the protic ionic liquids N-ethylimidazolium trifluoromethylsulfonate, [EIm][TfO], and N-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [EIm][TFSI], as charge carriers in appropriately modified Nafion membranes has been investigated. The superior thermal stability of ionic liquids, as compared to that of water-based electrolytes, hypothetically offers a wider temperature range of fuel cell operation as well as an increased electrochemical performance even at low-humidity conditions. The nano- and microstructure of Nafion membranes swollen with these protic ionic liquids has been studied in detail, with focus on the correlation with the observed ionic conductivity. Although the presence of the ionic liquid within the hydrophilic domains of Nafion suppresses the thermomechanical properties of the polymer, satisfactory conductivities are achieved between 90 and 150 °C, namely, in the range 0.2-1.2 × 10-3 S/cm.

Thermophysical properties of dicationic imidazolium-based ionic compounds for thermal storage

In order to improve the thermal stability of ionic liquids and enhance the thermal storage density, a series of dicationic ionic compounds containing incorporated Br−, BF4−, PF6−, NTf2− anions were synthesized. The structures of these dicationic ionic compounds were confirmed by 1H NMR, 13C NMR and FT-IR. The dicationic ionic compounds' thermo-physical properties were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of molecular configuration on the heat of fusion was studied by changes alkyl side-chain, linkage chain, molecular structure symmetry, and anions. The quantum calculation was carried to validate the number of hydrogen bonds for the dicationic ionic compounds. The results showed that hydrogen bonds significantly increased compared to that of the monocationic ionic liquids (MILs). The thermal analysis results indicate that dicationic ionic compounds exhibit excellent thermal stability; the decomposition temperatures higher than 560 K; the melting points and heat of fusion value reached 481 K and 116.26 kJ·kg−1, respectively. These values are higher than those of the MILs.

Insights for Designing the Hydrocarbon Recovery from Ionic Liquids by Distillation in the Aliphatic/aromatic Separation by Liquid-liquid Extraction

Nowadays the aliphatic/aromatic separation by liquid-liquid extraction using ionic liquids (ILs) is an interesting topic in the search of a new class of separation processes for the oil industry. The wide majority of papers published until now has focused in maximizing the IL extractive properties as can be found in a recent review by Canales and Brennecke (2016); in addition, in the recent past, this search was also oriented to find a commitment election between IL extractive and physical properties, with especial focus on reducing the viscosity to limit its impact on mass transfer and pumping (Larriba et al., 2013a). However, the challenge in the development of this new liquid-liquid extraction technology based on ILs is the selective recovery of aromatics from the solvent. Although IL non-volatile character is suggested as a clear advantage for separation purposes, this is truly a limitation in the vapor-liquid separation as was reported in last papers dealing with the vapor-liquid equilibria involving aliphatics, aromatics, and ILs due to the pretty low equilibrium pressures (Navarro et al., 2015). In addition, the thermal stability of ILs is another drawback since scarce species could be used at industrial scale over 473 K (Navarro et al., 2013). Finally, extracted aromatics have not commercial purity and further purification is mandatory before the aromatic/IL separation (Larriba et al., 2013a). In this work, the simulation of three different recovery sections based on vapor-liquid separations was performed to give some remarks that can help to design distillation processes involving large amounts of ionic liquids. Seven ionic liquids among the most promising species proved so far were selected to completely cover the transferability between liquid-liquid and vapor-liquid equilibria (LLE and VLE, respectively). Aspen Plus commercial simulator was used implementing the Non-Random Two Liquids (NRTL) models from the experimental data regressions for the corresponding n-heptane + toluene + ionic liquid ternary systems. Aromatic recoveries and purities for three different process configurations were analysed in order to stablish the impact of the ionic liquid extractive and thermal properties on the design of a suitable recovery section from an industrial point of view.

Functional groups in geminal imidazolium ionic compounds and their influence on thermo-physical properties

To enhance the thermal stability of ionic liquids (ILs) and increase the latent heat, the effect of functional groups for geminal dicationic ionic compounds were investigated and compared to that of monocationic ionic liquids (MILs) analogues. A series of new functionalized ionic compounds were synthesized by introducing vinyl group, cyanomethyl group, hydroxyl group, and carboxyl group to the imidazolium cation. The structures of these ionic compounds were confirmed by 1H NMR, 13C NMR and FT-IR. The thermal stability was determined by TGA; the melting temperature, heat of fusion and heat capacity were investigated by DSC for the synthetic ionic compounds. The thermal analysis results indicate that the functionalized ionic compounds show excellent thermal stability. The decomposition temperature and melting temperature can be up to 593.17 K and 484.99 K, respectively, and the latent heat can reach 64.40 KJ·mol−1. It's increased on average by 6.30%, 34.0% and 93.93%, respectively, as compared to alkyl chain ionic liquid (C2mim)Br. In addition, the heat capacity and thermal storage density of the functionalized ionic compounds are higher than those of the MILs. These superior properties are attributed to the additional hydrogen bonds and electrostatic energy in the functionalized ionic compounds.

Electrodeposition of Indium from a Phosphonium-Based Ionic Liquid

Electrochemical deposition of indium metal from aqueous electrolytes is challenging as it occurs simultaneously with hydrogen evolution. The evolution of hydrogen can compromise cathodic current efficiency and can cause porosity of the deposited metal, but it can be avoided by using ionic liquid electrolytes. The high thermal stability of ionic liquids allows for high-temperature electrodeposition on a liquid cathode, offering several advantages over a solid electrode, such as easier separation of electrolysis products and the possibility to design a continuous electrowinning process. In this paper, the electrochemical behavior of indium in the ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied at 120 °C and 180 °C. Indium metal was electrodeposited on platinum and molybdenum substrates and on a liquid indium cathode at 180 °C. Impurities present in commercial Cyphos IL 101 interfered with the measurement of the electrochemical window, so that it had to be carefully purified. The electrochemistry of indium in Cyphos IL 101 was studied by cyclic voltammetry, QMCB, rotating disk and rotating ring disk voltammetry. InCl3 concentration between 10 and 400 mM in Cyphos IL 101 were used in this study. Therefore, the major indium(III) species in solution corresponds to the [InCl6]3– complex. Using the Levich equation, a diffusion coefficient of (7.5 ± 0.1) 10–12 m2 s–1 at 120 °C was calculated for [InCl6]3–. It was found that indium(III) is the most stable oxidation state in the ionic liquid. This ion is reduced via a two-step process, going from indium(III) to indium(I) and subsequently to indium(0). The disproportionation of indium(I) to indium(III) and indium(0) was clearly illustrated. During cyclic voltammograms, the anodic and cathodic peak potentials was found to depend on the scan rate. As the scan rate increases, the separation between the anodic and cathodic peaks becomes greater, indicating that the deposition of indium is irreversible or quasi-reversible. The indium electrodeposits were characterized by SEM-EDS. When depositing indium on molybdenum substrates, the deposition of spherical indium droplets was observed, even at temperatures substantially below the melting point of indium (see figure). The probable mechanism behind this deposition morphology will be explained. Figure 1

A novel and simple approach for predicting activation energy of thermolysis of some selected ionic liquids

The knowledge of thermal stability of ionic liquids (ILs) is a key property for industrial applications because low thermal stability of ILs may limit and decrease their performance in high-temperature industrial application. Activation energy of thermolysis is one of the best choices for kinetic study of the degradation process of ILs. A novel and simple model has been introduced for the prediction of activation energy of thermolysis of imidazolium-, pyridinium-, and phosphonium-based ILs through the structure of their anions and cations. Experimental data of 73 ILs corresponding to 82 data points were used to derive the new correlation. The values of coefficient of determination (R2) and root-mean-squared error (RMSE) of the new model are 0.8904 and 22.5 kJ mol−1, respectively. For seven ILs corresponding to 13 measured data, the reliability of the new model has been tested and compared with complex quantum mechanical methods, where the outputs quantum mechanical methods were available. The values of RMSE are 17.2 and 80.9 kJ mol−1 for the new model and quantum mechanical approaches, respectively, which confirm high reliability of the new model.