Probing the electronic environment of binary and ternary ionic liquid mixtures by X-ray photoelectron spectroscopy

Men, Shuang; Licence, Peter

doi:10.1016/j.cplett.2017.08.034

Cited by 8 publications

(5 citation statements)

References 24 publications

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“…These observations show that the XPS-derived anion-dependent interaction strength scale for ILs is a ground-state effect (in XPS language, an initial-state effect) and not a product of electron density redistribution after the core-hole is created in XPS (i.e., not an XPS final-state effect). This finding strongly backs the assumption used regularly in the IL XPS literature that initial-state effects dominate E B shifts for ILs. − ,− ,− Therefore, the effect of different anions on the cation can be related to ground-state differences.…”

Section: Resultssupporting

confidence: 81%

“…differences can be understood in terms of the ability of electrons surrounding the atom with the core-hole to react to the creation of that core-hole, akin to the polarizability of the neighboring atoms. Almost all experimental XPS studies of ILs have assumed that the initial-state interpretation holds. − ,− Calculated core binding energies, E B (core,calc. ), for a small number of IL ion pairs in the initial-state approximation (without a core-hole) and the final-state approximation (with a core-hole) , gave reasonable matches to experimental data, and comparisons of E B (core,exp.)…”

Section: Introductionmentioning

confidence: 99%

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Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Gousseva,

Towers Tompkins,

Seymour

et al. 2024

J. Phys. Chem. B

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Using a combination of experiments and calculations, we have gained new insights into the nature of anion−cation interactions in ionic liquids (ILs). An X-ray photoelectron spectroscopy (XPS)-derived anion-dependent electrostatic interaction strength scale, determined using XPS core-level binding energies for IL cations, is presented here for 39 different anions, with at least 18 new anions included. Linear correlations of experimental XPS core-level binding energies for IL cations with (a) calculated core binding energies (ab initio molecular dynamics (AIMD) simulations were used to generate high-quality model IL structures followed by single-point density functional theory (DFT) to obtain calculated core binding energies), (b) experimental XPS core-level binding energies for IL anions, and (c) other anion-dependent interaction strength scales led to three main conclusions. First, the effect of different anions on the cation can be related to ground-state interactions. Second, the variations of anion-dependent interactions with the identity of the anion are best rationalized in terms of electrostatic interactions and not occupied valence state/unoccupied valence state interactions or polarizability-driven interactions. Therefore, the XPS-derived anion-dependent interaction strength scale can be explained using a simple electrostatic model based on electrostatic site potentials. Third, anion−probe interactions, irrespective of the identity of the probe, are primarily electrostatic, meaning that our electrostatic interaction strength scale captures some inherent, intrinsic property of anions independent of the probe used to measure the interaction strength scale.

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Section: Resultssupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Gousseva,

Towers Tompkins,

Seymour

et al. 2024

J. Phys. Chem. B

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“…It is possible that the presence of such non-native structures is responsible for the experimental observation that CO 2 solubility is in excess of the ideal mixing predictions for the binary mixtures of [C 4 mim]Cl–[C 4 mim][NTf 2 ], [C 2 mim] ethylsulfate [C 2 H 5 SO 4 ]–[C 2 mim][NTf 2 ], and [C 4 mim][C 2 H 5 SO 4 ]–[C 2 mim][NTf 2 ] mixtures. , Welton and co-workers also concluded that nonideality in binary ionic liquid systems is likely to arise when there is a substantial difference in the hydrogen bonding ability of the anions, as this can result in preferential interaction at distinct cationic locations. Nonideality in terms of immiscibility of ionic liquids, , electronic environment of anions, − viscosity, , ionic conductivity, and CO 2 solubility have also been reported.…”

Section: Introductionmentioning

confidence: 95%

Thermophysical Properties of Imidazolium-Based Binary Ionic Liquid Mixtures Using Molecular Dynamics Simulations

Kapoor

Shah

2018

J. Chem. Eng. Data

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Until very recently, task-specific ionic liquids have been designed by altering the chemistry of either the cation, anion, or both. An alternative approach, that is gaining considerable momentum, is to consider ionic liquids that are derived from mixing two different ionic liquids and varying the molar composition of such blends to exert precise control over the desired physicochemical and biological properties. As the number of ionic liquids that result from mixing is projected to be close to a billion, it is highly desirable to predict a priori whether ionic liquid mixtures can be considered as ideal solutions of their pure analogues. Toward this end, we employ molecular dynamics simulations to predict the density, molar volumes, excess molar volumes, self-diffusion coefficients, and ionic conductivities for 11 ionic liquid mixture systems as a function of mole fractions spanning the entire range of compositions of the constituent ionic liquids. The ionic liquid mixtures investigated here are 1-n-butyl-3-methylimidazolium [C4mim]+ chloride Cl– paired with [C4mim]+ acetate [CH3COO]−/[OAC]−, [C4mim]+ trifluoroacetate [CF3COO]−/[TFA]− and [C4mim]+ trifluoromethanesulfonate [CF3SO3]−/[TFS]−, and [C4mim][OAC] combined with [C4mim][TFA] and [C4mim][TFS]. The effect of change in the alkyl chain length on the thermophysical properties of ionic liquid mixtures containing anions as Cl––methylsulfate [MeSO4]−, and Cl––bis(trifluoromethanesulfonyl)imide [NTf2]− is evaluated by coupling with 1-ethyl-3-methylimidazolium [C2mim]+, 1-n-hexyl-3-methylimidazolium [C6mim]+, and 1-n-octyl-3-methylimidazolium [C8mim]+ cations. The deviation of the property trend from the linear mixing rule is discussed in terms of the difference in the properties of pure ionic liquid analogues.

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“…Experimental techniques utilized to study the IL–vacuum interface of IL mixtures include high-resolution Rutherford backscattering (HRBS), − low-energy ion scattering (LEIS), reactive atom scattering (RAS), , small-angle X-ray scattering, neutron scattering, time of flight secondary ion mass spectrometry (ToF-SIMS) , and X-ray photoelectron spectroscopy (XPS) ,,− The aforementioned scattering ,− and mass spectrometry , techniques, some of which are highly surface sensitive, have allowed for the examination of interfacial composition. Examination of the IL–vacuum interface with electron photoemission (XPS) has allowed for the elucidation of changes in electronic properties ,,− and angle-resolved XPS (AR-XPS) to probe interfacial composition. , Herein, we utilize AR-XPS to examine interfacial composition.…”

Section: Introductionmentioning

confidence: 99%

Anion Enhancement at the Liquid–Vacuum Interface of an Ionic Liquid Mixture

et al. 2018

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The liquid−vacuum interface was investigated for a ionic liquid (IL) mixture containing 1-ethyl-3-methylimidazolium acetate, [C 2 MIM][OAc], and 1ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C 2 MIM][TFSI]. Herein, we detail a quantitative connection between molecular simulations and angle-resolved X-ray photoemission spectroscopy for an IL−vacuum interface. Results show that for a mixture with a low concentration of [TFSI] − , the anion [OAc] − is slightly depleted from the interface, whereas the [TFSI] − anion is significantly enhanced relative to the bulk. Both experiments and simulations reveal that the mole fraction of [TFSI] − increases significantly from the bulk value in the top 17 Å. Furthermore, simulations show that [TFSI] − has a preferred orientation at the liquid−vacuum interface.

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Probing the electronic environment of binary and ternary ionic liquid mixtures by X-ray photoelectron spectroscopy

Cited by 8 publications

References 24 publications

Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Thermophysical Properties of Imidazolium-Based Binary Ionic Liquid Mixtures Using Molecular Dynamics Simulations

Anion Enhancement at the Liquid–Vacuum Interface of an Ionic Liquid Mixture

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