Molecular Structure Of Ionic Liquids Research Articles

Synthetization and Characterization of Zinc Oxide Nanoparticles by X- Ray Diffractometry (XRD), Fourier Transforms, Infra-Red Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Antibacterial Activity Test

Purpose: Nanomaterials with their derivable potentials offer wide obtain ability and have recently aroused much attention for biomedical applications. Nowadays, nanomaterials-based colorimetric sensing is a quickly emerging field of sensing applications. Nanomaterials are considered as the main component of colorimetric determination of hydrogen peroxide to replace the natural enzyme-based sensors because of some associated intrinsic drawbacks. Considering the advantageous properties of ionic liquid (IL) for various applications, significant attention has been made to the use of ionic liquid stabilized metal NPs which may serve as a regulator to enhance the catalytic performance of the metal nanoparticles in the different IL reaction medium. 
 Methodology: The peroxidase-like activity of IL coated metal NPs (IL-MNPs) have been considered for the catalytic oxidation reaction of chromogenic substrate 3,3,5,5- tetramethylbenzidine (TMB) in the presence of H2O2 at an estimated wavelength of 652 nm.
 Results: The synthesized metal nanoparticles (Ag) were produced using a chemical reduction method. Various characterization techniques like FTIR, UV-Visible spread Reflectance Spectroscopy [UV-VIS DRS], were employed, which verified the structure, nano-size and successful combination of metal dopant ion into the samples. The molecular structure of ionic liquid with varying cations was produced and confirmed by 1H-NMR spectroscopy. The ionic liquid was coated on metal nanoparticles to enhance their conductivity. 
 Unique Contribution to Theory, Practice and Policy: Optimized reaction conditions like pH, temperature and catalyst dosage affect catalytic activity and color sensing properties. The coating of [Min] Ac on Ag achieved low detection limits and colorimetric detection of [Pyr] based Ag.

Achieving Greener, Super-Robust Performance Water-Based Lubrication: Obtained by a Multifunctional Ionic Liquid Aqueous System and Formation of Unique Interfacial Interactions

Owing to the green, high-performance, and application-specific work conditions, water-based lubricating systems show unlimited potential for chemical engineering development. The interfacial behavior of functional additives in aqueous systems is complex and variable due to polarity and interfacial activity, thus showing important research significance. Herein, five novel ionic liquids were synthesized; their unique interfacial behavior in the polar water system contributes a lot to the advanced corrosion resistance and the improved extreme pressure-bearing capacity. The polar groups in the molecular structure of ionic liquids can adsorb preferentially in competition with water molecules, resulting in the formation of an adsorption layer with a high elastic modulus on the metal surface. Benefiting from the tribochemical reaction and the strong polar adsorption effect, the tribofilm at the sliding asperity exhibited effective antiscuffing and antiwear performance. Moreover, their characteristic cationic groups enrich the driving force of the molecular self-assembly process and enhance the ability to form ordered molecular aggregates, whose behavior in an aqueous system facilitates super-robust lubricity. This work can promote the in-depth understanding, future design, and optimization of the aqueous lubricating system, providing content enrichment and expansion for the lubrication technology for harsh service conditions.

Molecular Dynamics of Ionic Liquids from Fast-Field Cycling NMR and Molecular Dynamics Simulations.

Understanding the connection between the molecular structure of ionic liquids and their properties is of paramount importance for practical applications. However, this connection can only be established if a broad range of physicochemical properties on different length and time scales is already available. Even then, the interpretation of the results often remains ambiguous due to the natural limits of experimental approaches. Here we use fast-field cycling (FFC) to access both translational and rotational dynamics of ionic liquids. These combined with a comprehensive physicochemical characterization and MD simulations provide a toolkit to give insight into the mechanisms of molecular mechanics. The FFC results are consistent with the computer simulation and conventional physicochemical approaches. We show that curling of the side chains around the positively charged cationic core is essential for the properties of ether-functionalized ionic liquids, and we demonstrate that neither geometry nor polarity alone are sufficient to explain the macroscopic properties.

Ionic liquids for electrochemical applications: Correlation between molecular structure and electrochemical stability window

Ionic gating has emerged as an effective and versatile tool to tune the charge-carrier density of a material and control its electronic ground state, as well as to develop low-temperature devices such as electrochemical transistors. Ionic liquids are a promising gating agent due to their high thermal- and electrochemical stability for both fundamental and applied research. However, the understanding of the correlation between the molecular structure of ionic liquids and their electrochemical stability is quite limited. For this reason, this study aims at determining the guidelines for synthesizing ionic liquids suitable for their use as electrolytes at low temperatures. A series of twenty-three ionic liquids having various ammonium cations, composed of three ''short chains'' and one ''long chain'', and Tf2N as the anion, were synthesized. Afterwards, their thermal behavior was determined to identify those ionic liquids exhibiting Tg < −50 °C. The anodic and cathodic limits of the selected ionic liquids were measured via linear-sweep voltammetry using an electrochemical transistor configuration, working at −33 °C. Electrochemical windows having absolute values from 2.9 to 5.7 V were measured. Overall, five guidelines were determined from the experimental results: first, the cations influence both cathodic and anodic limits; second, the asymmetric ammonium cations show larger electrochemical stability than symmetric ones; third, the electrochemical stability decreases at the increase of the length of the ''long chain''; fourth, alkyl long chains show a larger anodic limit, but smaller cathodic limit than ether long chains having the same length; fifth, the ether chain with largest electrochemical stability comprises three carbon atoms and one oxygen.

Study of quantitative structure-property relationship for density of ionic liquids based on Monte Carlo optimization

Ionic liquids (ILs) have attracted increasing interests and applications due to its unique physiochemical properties. Density is a vital physical property of ILs. In this work, a comprehensive collection of density data is conducted on 184 variable ILs. The study of quantitative structure-property relationship (QSPR) is carried out for the selected density data of ILs using simplified molecular input line entry specification (SMILES) as the representation of the molecular structure of ILs by means of CORAL software. QSPR relationships were constructed with the balance of correlations (BC) and the classic scheme. Results from three random splits displayed desirable models for predicting the external test set with the correlation coefficient (R2) and cross validated correlation coefficient (Q2) in ranges of 0.8234–0.9770 and 0.7599–0.9745, respectively. The best predictions obtained by the balance of correlations along with the global SMILES descriptors are included in the modeling process. The average statistical characteristics of the external test set are the following: n =36, R2 =0.9770, Q2= 0.9745, standard error of estimation (s)=0.023, mean absolute error (MAE) =0.018 and Fischer F-ratio (F)=1443

Effect of Solid Substrates on the Molecular Structure of Ionic Liquid Nanofilms.

Fundamental understandings of the interfacial molecular structure of solid-confined ionic liquids (ILs) have significant impacts on the development of many cutting-edge applications. Among the extensive studies on the molecular structure at the IL/solid interface, direct observation of a double-layering quantized growth of [Cnmim][FAP] on mica was recently reported. In the current work, the atomic force microscopy (AFM) results directly show that the growths of [Bmim][FAP] nanofilms on silica and amorphous carbon are different from the double-layering growth on mica. The growth of [Bmim][FAP] nanofilms on silica is dominated by the aggregation of the IL molecules, which can be attributed to the inadequate negative charging of the silica surface resulting in a weak electrostatic interaction between silica and the IL cation. [Bmim][FAP] on amorphous carbon shows a fairly smooth film for the thinner nanofilms, which can be attributed to the π-π+ parallel stacking between the cation imidazolium ring and the randomly distributed sp2 carbon on the amorphous carbon surface. Our findings highlight the effect of different IL/solid interactions, among the several competing interactions at the interface, on the resulting molecular arrangements of various IL.

Cost-Effective Processing of Carbon-Rich Materials in Ionic Liquids: An Expeditious Approach to Biofuels.

This work presents a cost-effective approach for processing of renewable carbon-rich biomass using pyridinium-based Lewis acidic ionic liquids (LAILs). Rice husk as carbon-rich lignocellulosic waste was pretreated with a series of neutral and Lewis acidic ionic liquids to yield valuable intermediate platform monosaccharides. Novelty in the work lies in direct conversion of lignocellulosic carbohydrates into reducing sugars without their further conversion into 5-hydroxymethylfurfural or any other platform chemicals that are fermentation inhibitors for bioethanol production. The unconverted cellulose-rich material (CRM) is regenerated as a delignified material by the simultaneous addition of antisolvents. CRM and recovered lignin obtained after pretreatment were analyzed via scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. The process was optimized with respect to a high yield of platform sugars and the quantity as well as quality of recovered CRM and lignin contents. Various reaction parameters involving the molecular structure of ionic liquids (ILs), Lewis acidic strength of ILs, biomass loading into IL, time, temperature, and biomass particle size were screened thoroughly. From all of the tested ILs, unsymmetrical 3-methylpyridinium IL having N-octyl substitution and chloroaluminate anion showed a greater conversion efficiency at 100 °C for 1.5 h. FTIR and SEM analyses of recovered CRM justify >90% lignin removal from rice husk. From all of the removed lignin, 60 wt % of original lignin content was recovered. The Lewis acidic system possessed recycling ability up to 3 times for subsequent treatment of rice husk without a significant loss of efficiency.

Effect of side chain modifications in imidazolium ionic liquids on the properties of the electrical double layer at a molybdenum disulfide electrode.

Knowledge of how the molecular structures of ionic liquids (ILs) affect their properties at electrified interfaces is key to the rational design of ILs for electric applications. Polarizable molecular dynamics simulations were performed to investigate the structural, electrical, and dynamic properties of electric double layers (EDLs) formed by imidazolium dicyanamide ([ImX1][DCA]) at the interface with the molybdenum disulfide electrode. The effect of side chain of imidazolium on the properties of EDLs was analyzed by using 1-ethyl-3-methylimidazolium ([Im21]), 1-octyl-3-methylimidazolium ([Im81]), 1-benzyl-3-methylimidazolium ([ImB1]), and 1-(2-hydroxyethyl)-3-methylimidazolium ([ImO1]) as cations. Using [Im21] as reference, we find that the introduction of octyl or benzyl groups significantly alters the interfacial structures near the cathode because of the reorientation of cations. For [Im81], the positive charge on the cathode induces pronounced polar and non-polar domain separation. In contrast, the hydroxyl group has a minor effect on the interfacial structures. [ImB1] is shown to deliver slightly larger capacitance than other ILs even though it has larger molecular volume than [Im21]. This is attributed to the limiting factor for capacitance being the strong association between counter-ions, instead of the free space available to ions at the interface. For [Im81], the charging mechanism is mainly the exchange between anions and octyl tails, while for the other ILs, the mechanism is mainly the exchange of counter-ions. Analysis on the charging process shows that the charging speed does not correlate strongly with macroscopic bulk dynamics like viscosity. Instead, it is dominated by local displacement and reorientation of ions.

Ionic liquids for high performance lithium metal batteries

The pursuit of high energy density has promoted the development of high-performance lithium metal batteries. However, it faces a serious security problem. Ionic liquids have attracted great attention due to their high ionic conductivity, non-flammability, and the properties of promoting the formation of stable SEI films. Deeply understanding the problems existing in lithium metal batteries and the role of ionic liquids in them is of great significance for improving the performance of lithium metal batteries. This article reviews the effects of the molecular structure of ionic liquids on ionic conductivity, Li+ ion transference number, electrochemical stability window, and lithium metal anode/electrolyte interface, as well as the application of ionic liquids in Li-high voltage cathode batteries, Li-O2 batteries and Li-S batteries. The molecular design, composition and polymerization will be the main strategies for the future development of ionic liquid-based electrolytes for high performance lithium metal battery.

Lipids extraction from wet Chlorella pyrenoidosa sludge using recycled [BMIM]Cl

In this study, experiments on pretreating one species of microalgae (Chlorella pyrenoidosa) using one kind of ionic liquid (IL) of [BMIM]Cl were conducted. The aim of this work is to evaluate the recycling efficacy of expensive IL solvent for effective cell disruption. It was indicated that the molecular structure of IL was stable during the recycling test. Five times antisolvent precipitation of microalgae debris after lipid extraction using methanol recovered 99.8% IL with the energy consumption of 4.46 MJ per kg dry Chlorella pyrenoidosa. The chromatography was used to separate IL and hydrolysates, resulting in the IL loss below 1.97 g per kg dry Chlorella pyrenoidosa.

Spreading of Nanodroplets of Ionic Liquids on the Mica Surface.

Previously, the molecular structure of ionic liquids (ILs) next to a solid surface has been extensively studied because the IL–solid interfaces are critical to many important applications. What is largely unknown is the mobility of ILs confined to a solid surface. The solid-like stable structure of ILs on the solid surfaces has been reported in previous research, which indicates that the mobility of ILs next to a solid surface is quite low and the structure of ILs will not change with time. However, here, we show that the nanodroplets of ILs flow on the mica surface, which suggest that, at a small scale, the solid-like stable structure of ILs on the solid surfaces indeed changes with time. Interestingly, although the IL nanodroplets show a layered structure, no terrace-like flow of the droplet has been observed, which has been attributed to the weak mica–IL interaction at low humidity.

In Situ Tracking of Organic Reactions at the Vapor/Liquid Interfaces of Ionic Liquids.

The molecular structures of ionic liquids at interfaces play a crucial role in determining their chemical activities in applications. In situ X-ray photoelectron spectroscopy (XPS) was used to track the evolution of X-ray irradiation-induced chemical reactions in a series of ionic liquids ([Cn mim][AuCl4 ]; n=4, 6, 8, 10) on the Si (111) single-crystal surface. Analyses of microstructure and chemical bonding based on the XPS results indicated that reactions occurred at the vapor/liquid interfaces of the ionic liquids. The time-resolved XPS spectra revealed that with increasing irradiation time, the intensity of the peak corresponding to trivalent Au anion decreased for the four ionic liquids as Au was continually reduced to a lower chemical state and finally converted to gold nanoparticles. The rate and conversion of the reaction were associated with the length of the alkyl chain of the ionic liquids cation. Molecular dynamics simulations further revealed that the alkyl chain of the cation in the ionic liquids was oriented towards the vacuum environment at the vapor/liquid interface. Our results provide a real-time atomic-scale experimental evidence of organic reactions at the vapor/liquid interfaces of ionic liquids. The findings are important for understanding the roles of ionic liquids in catalysis, separation, electrochemistry, functional materials, and so on.

A new FCCS-CFD coupled method for understanding the influence of molecular structure of ionic liquid on bubble behaviors

The complex interaction between cations and anions as well as the molecular structure makes the ionic liquids (ILs) different from organic solutions. Thus, the conventional hydrodynamic models, which are suitable for water and organic solutions, are not able to predict bubble behaviors in ILs accurately. In this work, a new FCCS (Fragment Contribution Corresponding State)-CFD(CFD) coupled method is proposed, so that the influence of molecular structure of ILs can be revealed. A source term which represents the electrostatic interaction between cations and anions of ILs is introduced into the momentum equation, which makes the model reflect strictly the inner feature of ionic liquids. The simulation results show that the relative error of aspect ratio is only 0.06%, much lower than 3.73% which is calculated by the conventional method, indicating the new method is more accurate. Furthermore, the bubble behaviors, i.e. the bubble shape and velocity, in 30 ILs are simulated. As a result, the relationship between molecular structures of ILs and bubble behaviors, as well as the bubble flow regime is obtained.

A comparative study on the effect of ionic liquid composition on the contributions of faradaic current in ionic liquid carbon paste electrodes by chemometrics method

The total current of electroanalytical data is assumed to be composed of three main constituents including faradaic current, step charging current and induced charging current. The contribution of each type of current in total current can be related to the structure and composition of the electrode as well as the nature of the analyte and supporting electrolyte. By using multivariate curve resolution-alternating least squares (MCR-ALS), as a powerful chemometrics technique, total current can be deconvoluted to its three components. In this study, the contribution of faradaic current in total current at carbon ionic liquid electrodes (CILEs) was investigated. The main focus was on the effect of the molecular structure of ionic liquid and it's weighting percent in the electrode. The studied ionic liquids were heptylpyridinium hexa-fluorophosphate, decylpyridinium hexa-fluorophosphate and dodecylpyridinium hexa-fluorophosphate at four different compositions. Results showed that structure of ionic liquid and it is weighting has a significant effect on faradaic current contribution. The contribution of the relative faradaic current varies in the range of 27% to 37% whereas the contribution of the charging current is much higher and that of induced charging current represents the least contribution.

Capacitive behavior of chestnut shell-based porous carbon electrode in ionic liquid electrolytes

This paper studies the electrochemical behaviors of symmetric supercapacitors with the porous carbon obtained from chestnut shells as active materials and ionic liquids as electrolytes, including 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]imide (EMImTF2N), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and 1-Butyl-3-methylimidazolium tetrafluoroborate (BMImBF4). Experimental data observed at a current density of 0.1 A/g showed that symmetric supercapacitor using EMImBF4 as the electrolyte had the maximum specific capacitance of 208.7F/g, while 180.8F/g for EMImTF2N and 134.6F/g for BMImBF4. However, specific capacitance of supercapacitors assembled with EMImBF4, EMImTF2N and BMImBF4 respectively retained 62.9%, 94.5% and 71.5% of the initial values after 2000 galvanostatic charge-discharge cycles. The relationship between the molecular structure of ionic liquids and electrochemical properties of the supercapacitors was discussed based on the experimental data.

Origin of heterogeneous dynamics in local molecular structures of ionic liquids.

Room-temperature ionic liquids (ILs) are generally considered as structurally heterogeneous with inherent polar/apolar phase separation. However, even after a decade of research, local dynamics in the heterogeneous structures of ILs remain neglected. Such local dynamics may influence the ion transport of electrolytes, as well as the reaction rate of solvents. In this study, we performed molecular dynamics simulation to analyze the local dynamics for the structural heterogeneity of ILs. Calculations of the diffusion, reorientation, and association dynamics showed a distinct heterogeneous dynamics between the polar and apolar regions of ILs. Further studies demonstrated that such local dynamic differences originate from local structural heterogeneity. Different energy barriers determine a predominant fast reorientation dynamics in apolar regions and a locally vibrating behavior in polar regions. Additionally, we suggested a new jumping mechanism to clarify the dynamic heterogeneity of ions in the polar regions. The results will help determine the origin of the heterogeneous dynamics in IL local structures and provide a theoretical basis for tuning the dynamic properties of ILs used as electrolytes or reaction solvents.

Corrigendum: From Molecular Structures of Ionic Liquids to Predicted Retention of Fatty Acid Methyl Esters in Comprehensive Two‐Dimensional Gas Chromatography

Although there are no mistakes in the calculations reported, the authors regret that three typographical errors in Equations (2), (8) and (9) were not identified during the proof stage. The discussions and conclusions are unaffected by this Corrigendum. Corrected Equation (2) requires the addition of “log” in front of “ECL” on the left hand side of this equation. This equation now becomes: (2) Corrected Equations (8) and (9) require replacement of “L” with “1” on the right hand sides of the equations. These equations now become: (8) (9) Furthermore, the word “ab initio” mentioned throughout the manuscript, is more correctly called “density functional theory (DFT)”. There is an additional source of support that was inadvertently omitted in the Acknowledgements. In particular, the valuable provision of chemical standards and all the GC columns for this study received from Supelco was not mentioned. Therefore, the Acknowledgements text should have read as follows: C.K., Y.N. and A.X.Z. acknowledge the provision of Monash Graduate Scholarships (MGS) from Monash University Institute of Graduate Research (MIGR), Monash International Postgraduate Research Scholarship (MIPRS) and Dean’s scholarships from the School of Chemistry and Faculty of Science, Monash University. We acknowledge funding from the ARC under Discovery Program grants DP130100217 and DP01095335. P.J.M. acknowledges the Australian Research Council (ARC) for a DORA fellowship. We also gratefully acknowledge Supelco for provision of chemical standards and the GC columns for this study.

Gas–liquid mass‐transfer properties in CO2 absorption system with ionic liquids

The deficiency of mass‐transfer properties in ionic liquids (ILs) has become a bottleneck in developing the novel IL‐based CO2 capture processes. In this study, the liquid‐side mass‐transfer coefficients (kL) were measured systematically in a stirred cell reactor by the decreasing pressure method at temperatures ranging from 303 to 323 K and over a wide range of IL concentrations from 0 to 100 wt %. Based on the data of kL, the kinetics of chemical absorption of CO2 with mixed solvents containing 30 wt % monoethanolamine (MEA) and 0–70 wt % ILs were investigated. The kL in IL systems is influenced not only by the viscosity but also the molecular structures of ILs. The enhancement factors and the reaction activation energy were quantified. Considering both the mass‐transfer rates and the stability of IL in CO2 absorption system, the new IL‐based system MEA + [bmim][NO3] + H2O is recommended. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2929–2939, 2014

From Molecular Structures of Ionic Liquids to Predicted Retention of Fatty Acid Methyl Esters in Comprehensive Two‐Dimensional Gas Chromatography

AbstractIonic liquids (ILs) are attractive stationary phases to broaden selectivity in gas chromatography (GC). The rational design, selection and application of ILs in comprehensive two‐dimensional GC is a desirable goal. In this study, methods to predict two‐dimensional chromatograms of fatty acid methyl esters (FAMEs) starting from given structures of IL stationary phases and their interactions with FAME solutes are described. Molecular parameters of the dipole moment, lowest unoccupied molecular orbital energy and molar volume of different ILs were calculated by using Gaussian 09. With established correlations between molecular simulation and linear solvation energy relationships, molecular parameters were converted to s, e and l values for stationary phase descriptors. This allowed reliable prediction of the equivalent chain length of FAMEs on each IL column (with the correlation R2=0.98). Isovolatility curves in GC×GC space of reference saturated FAMEs were then determined for each IL column to take into account the dependence of retention time on temperature in temperature‐programmed separation. The resulting predicted GC×GC chromatograms were compared with previously reported experimental results. Correlations with R2 values of 0.99 and 0.98 were achieved for the first‐ and second‐dimension retention times, respectively.

A priori prediction of the octanol–water partition coefficient (Kow) of ionic liquids

The octanol–water partition coefficient (Kow) of ionic liquids (ILs) is an important indicator for its toxicity and environment impact. In this work, the Kow is determined from the ratio of infinite dilution activity coefficient of IL in the water-rich and octanol-rich phases. In particular, the Pitzer-Debye−Hückel (PDH) model combined with the predictive COSMO-SAC model is used for calculating the activity coefficients. A root-mean square deviation of 0.75 is achieved for log Kow, or a factor of 4 in Kow, for a total of 67 ILs at ambient condition. The long-range coulomb interactions (from the DH model) contribute an almost constant value of −1.35 to log Kow, regardless of the type of IL. The change of log Kow with the molecular structure of IL is found to be dominated by the short-range attractive interactions between the IL and the solvents, including the hydrogen bonding and nonhydrogen bonding surface interactions. The combination of PDH and COSMO-SAC models provides not only the quantitative predictions of Kow of ILs and but also physical insights to the relations between Kow and the molecular structure of ILs.