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Excess thermodynamic properties of a wide variety of aqueous electrolyte solutions at elevated temperatures have been determined with the ORNL high-temperature isopiestic facility. This unique experimental apparatus provides very precise results over the useful temperature range of 110 to 250 C. The isopiestic method is a comparative technique which, in the present case, uses the Pitzer-Peiper-Busey formulation for NaCl(aq) as the reference electrolyte. At elevated temperatures the ion-interaction model of Pitzer continues to be the most useful description of the experimental results. The authors experimental program has included the alkali metal chlorides, sulfates, hydroxides, bromides, and bisulfates, the alkaline earth metal chlorides, and several specific compounds of scientific and practical interest. Numerous common-ion mixed electrolyte solutions have also been investigated in this program. In general, the activity coefficients of all the studied electrolytes decrease with increasing temperature. However, prominent differences between members of the same family remain, particularly when considered as the excess Gibbs free energy. The tendency for ion association increases with increasing temperature and becomes a factor at the higher temperatures. Trends and specific effects are illustrated with examples taken from the database generated in their high-temperature thermodynamic program.

Amelioration and remediation technology was developed for phosphogypsum utilization in Haplic Chernozem of South-European facies (Rostov Region). The technology comprises phosphogypsum dispersed application into the soil layer of 20–45 cm during intra-soil milling. In the model experiment, the phosphogypsum doses 0 (control), 10, 20, and 40 t ha−1 were studied. The Cd thermodynamic forms in soil solution were calculated via the developed mathematical chemical-thermodynamic model and program ION–3. The form of ion in soil solution (or water extract) was considered accounting the calcium-carbonate equilibrium (CCE) and association of ion pairs CaCO30; CaSO40, MgCO30, MgSO40, CaHCO3+, MgHCO3+, NaCO3−, NaSO4−, CaOH+, MgOH+. For calculation of the equilibrium of microelements concentration in soil solution ion including heavy metals (HMs), the coefficient of microelement association kas was proposed. According to calculations, Cd2+ ion in soil solution was mostly bounded to associates CdOH+, partly to associates CdCO30 and CdHCO3+. The calculated kas of Cd was 1.24 units in the control option of experiment and decreased to 0.95 units at phosphogypsum dose 40 t ha−1. The ratio of “active [Cd2+] to total Cd” reduced from 33.5% in control option to 28.0% in the option of phosphogypsum dose 40 t ha−1. The biogeochemical barrier for penetration of HMs from soil to plant roots was high after application of phosphogypsum. According to calculation by ION–3, the standard soil environmental limitations overestimate the toxicity of Cd in soil solution. New decision for intra-soil milling and simultaneous application of phosphogypsum was developed to provide the environmentally safe waste recycling.

Activity coefficients in aqueous solutions of alkali metal nitrates at 298 K have been calculated by the generalized Debye–Huckel theory using experimental values of the static dielectric constant of solutions. It has been shown that calculation without optimization of model parameters in a number of systems reproduces the dependence of activity coefficients on cation radius and the levelling of potassium, rubidium, and cesium cations influence on activity coefficients in the presence of nitrate ions. The effect of hydration and ion association on the thermodynamic properties in the series of studied systems has been considered.

Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed were comprehensively investigated. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate ([A336][Cyanex272]) could selectively extract W over Mo at an initial pH value of 5.5; the best separation factor βW/Mo of 25.61 was obtained for a solution with low metal concentrations (WO3: 2.49 g/L, Mo: 1.04 g/L). The [A336][Cyanex272] system performed effectively for solutions of different W/Mo molar ratios and different metal ion concentrations in the feed. The chemical reaction between [A336][Cyanex272] and W followed the ion association mechanism, which was further proved by the Fourier-transform infrared (FTIR) spectra of loaded [A336][Cyanex272] and the free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped using a 0.20 mol/L sodium hydroxide solution. Finally, the selective extractions of W and Mo from two synthetic solutions of different high metal concentrations were obtained; the separation factor βW/Mo reached 23.24 and 17.59 for the first and second solutions, respectively. The results suggest the feasibility of [A336][Cyanex272] as an extractant for the separation of tungsten and molybdenum.

During lithium-ion battery charging and discharging, carbonate electrolytes degrade from redox side reactions to produce electrode surface films. The composition of these films depends on the compo...

A study is performed of the electrical conductivity of a number of ionic liquids based on 1-alkyl-3-methylimidazolium quaternary salts with inorganic anions in acetonitrile. The Lee–Wheaton approach is used to calculate the ion association constants Ka, limiting molar electrical conductivity (λ0), and the Gibbs energy of association (ΔG) in solutions. It is shown that the nature and size of the anion has a decisive influence on the association of the studied ionic liquids. It is found that the limiting molar electrical conductivity of bromides is lower than that of hexafluorophosphates and tetrafluoroborates.

Sodium citrate (Na3Cit) has a crucial role in many biological and industrial processes. Yet, quantitative information on its hydration and the ion association between Na+ and Cit3– ions in a broad ...

The review generalizes and analyzes published data on different methods of studying structural characteristics of the solvation environment of alkali metal ions (except for Li+) in various electron-donor oxygen-containing solvents. Coordination numbers of alkali metal ions, interspecies distances, and types of ion association are discussed. The solvation structures of alkali metal cations in water and some nonaqueous systems are compared. The number of solvent molecules and the distance between the cation and oxygen atom of solvent molecule in the first coordination sphere are independent of physicochemical properties of the solvent.

The activity coefficients in aqueous solutions of lithium and sodium sulfates at 298 K were calculated by the generalized Debye–Huckel theory using the experimental values of the static permittivity of the solutions. The effect of the hydration and ion association on the dielectric and thermodynamic properties of the electrolyte solutions was considered.

The correlations present in the ionic liquids (ILs) are essential to interpret the ion association and dynamics processes. The correlated and uncorrelated ionic conductivities reported from two different types of experiments were calculated employing molecular dynamics methods by exercising appropriate care to obtain the diffusive regions. The ionic conductivity is found to be correlated with lifetimes of the ion-pair and ion-cage formation. In this study, the structure and dynamic properties of five cyclic ammonium-based ILs were investigated by comparing the experimental results with the calculated transport properties: (1) 1-allyl-1-methylpyrrolidinium, (2) 1-propyl-1-methylpyrrolidinum, (3) 1-methyl-1-allylpiperidinium, (4) 4-allyl-4-methylmorpholin-4-ium, and (5) 4-allyl-4-ethylmorpholin-4-ium with bis(trifluoromethanesulfonyl)imide anion as the common anion. We observed the linear relationship between the inverse of ion-pair lifetimes and ionic conductivities. The diffusion coefficients obtained from velocity autocorrelation functions follow a trend similar to that of the experiment as compared to mean square displacements (MSDs). The ionic conductivities from correlated MSD and current autocorrelation functions are compared to the ionic conductivities from the conductometer experiment. The time correlation functions of the ion-pair and ion-cage dynamics were calculated. The correlation functions were used to obtain the lifetimes. Pyrrolidinium-based ILs show lower lifetimes than other ILs, which correlates with the conductivity. Morpholinium-based ILs show higher interaction between ions than other ILs. This result supports the slower dynamics present in morpholinium-based ILs than in other ILs. In this work, our objective is to give atomic insight into the dynamics of IL, which could not be extracted from the experiment, and relate microscopic properties with macroscopic properties.

A simple, sensitive and selective spectrofluorometric method has been developed for the determination of enoxaparin sodium in bulk and dosage forms (injection). The method was based on the quantitative quenching effect of enoxaparin on the native fluorescence of acriflavine due to the formation of nonfluorescent supramolecular ion issociation complex between the studied drug and acriflavine dye in aqueous solution. The decrease of acriflavine fluorescence was observed at 506 nm after excitation at 402 nm. The relationship between quenching fluorescence intensity and concentration of enoxaparin sodium was linear in the range 0.05-20 µg/ml and with correlation coefficient 0.9990 and with LOD and LOQ 0.011 and 0.035 µg/ml respectively. The average recovery was 100.51% and RSD is less than 3.23%. The stoichiometry of enoxaparin to acriflavine was calculated a 1:4. The method was applied successfully to the determination of enoxaparin form injection samples and the results were in a good agreement with certified value and standard addition procedure.

Electrolyte additives play an important role in suppressing lithium dendrites through tailoring the composition/property of the SEI, however lacking of additives can achieve high performances both in ether and carbonate electrolytes hinders further enhancement of the high voltage lithium-metal batteries. Here, lithium perchlorate (LiClO4) has been presented as an excellent additive to meet the above requirements. An optimized chemical composition of SEI can be achieved through the formation of ionic association. Our results indicate that the LiClO4 behaves like a catalyst, which promotes LiTFSI to form a better SEI to inhibit further reaction. Superior coulombic efficiencies and cycling performances were obtained both in ether and carbonate electrolytes. This study paves a new pathway for designing bi-soluble additives for safe lithium metal batteries.

The NaCl–H2O binary is a first approximation to fluids in the deep crust and upper mantle. Such fluids are fundamental to understanding geophysical properties, metal transport, and ore genesis within the Earth. Consequently, recent experimental studies have sought to determine the equation of state of the NaCl–H2O binary as a function of composition. However, experimental characterization is not straightforward at extreme conditions and there is so far little understanding of the molecular nature of associated fluids. Variations in the structure of water, ion solvation, and ion association affect properties such as ionic strength and electrical conductivity. These properties in turn influence geophysical signatures and metal solubilities at high pressure and temperature (P,T). We performed a series of NPT ab initio molecular dynamics simulations as a function of pressure (0.5–4.5 GPa), temperature (20–800 °C), and composition (1–14 m NaCl) to develop a molecular-level understanding of high P,T NaCl brines. Comparison of simulation results with experimental and theoretical densities provides a foundation for testing current levels of theory. The simulations have allowed us to determine the nature of ion solvation, ion association, and the effect of solutes on the solvent at high P,T. The PBE functional used here is known to over-structure water and overestimate the density of aqueous fluids at ambient conditions. This is due to an inadequate treatment of hydrogen bonding and dispersion. However, we find excellent agreement between theory and experimental densities at elevated P,T. Accordingly, we have extrapolated the existing equation of state to regions that have not been measured experimentally. From the O–O pair distribution functions, we interpret the improved agreement as resulting from the breakdown of hydrogen bonding at high P,T. At ambient conditions, the presence of Na and Cl has a strong effect on the structure of water. However, at high P,T, even 14 m NaCl has no effect on water structure. Nevertheless, Na and Cl are highly associated. We propose that NaCl brines at high P,T are best described as hydrous melts rather than as aqueous electrolytes.

Solid polymer electrolytes are key components in many electrochemical devices. For an in-depth study of the basic parameters of such electrolytes, we developed a previously proposed method in order to determine the charge carrier density (n), mobility (μ), and diffusion coefficient (D) of ionic conductors using electrochemical impedance analysis. This reinforced method was tested with a composite solid electrolyte based on polyethylene oxide, ethylene carbonate, LiCF3SO3, and alumina filler by analyzing DC conductivity, frequency dependence of AC conductivity, and the complex dielectric function. The results show a clear picture of the temperature dependence of the parameters n, μ, and D; for example, at 20 °C, more than 15% of the total number of ions available in the electrolyte are mobile, and this value decreases with increasing temperature, most probably due to increased ion association in agreement with measurements using other techniques. The increase in ionic conductivity with increasing temperature is thus due to an increased mobility of the ionic species.

Calorimeter with an isothermal shell was used at a temperature of 298.15 K to measure the following parameters: enthalpy of NiSO4(k) dissolution in water followed by generation of two molar concentration solutions; enthalpy of four NiSO4 aqueous solutions dilution having various molar concentrations followed by generation of solutions with approximately the same concentration values. Based on the data obtained, enthalpy and ion association constant in the NiSO4 aqueous solution, as well as standard enthalpy of the aqueous solution formation, were determined for the indicated compound. The latter value made it possible to establish a more accurate value of standard enthalpy in the Ni2+ cation formation in an aqueous solution, which turned out to be equal to --52.3 ± 0.5 kJ/mol.

The use of dielectric relaxation spectroscopy (DRS) for studying electrolyte solutions is reviewed, focussing on the authors’ investigations over the last three decades. It is shown that this often-overlooked technique provides powerful insights into the nature of ion-ion and ion-solvent interactions. DRS is revealed to be particularly useful for detection of weak ion association and, due to its unique ability to detect solvent-separated species, the quantitation of ion pairing. It is demonstrated that DRS correctly determines chemical speciation for ion-paired systems where major spectroscopic techniques (NMR, Raman, UV-vis) fail. DRS also provides important insights into ion solvation. In aqueous solutions, it has been used to build up a coherent set of ‘effective’ hydration numbers for ions based on the dynamics of proximate water molecules, and has a unique ability to detect ‘slow’ water resulting from hydrophilic and hydrophobic hydration of solutes. DRS has been especially useful for characterising the behaviour of ionic liquids (ILs), e.g. showing they possess rather low dielectric constants and, surprisingly, contain no significant concentrations of ion pairs. Neat ILs and their mixtures with molecular solvents are shown by ultra-broadband DRS to exhibit extremely complicated behaviour especially at frequencies in the THz region.

ChemPhysChem 10, (2021). doi:10.1002/cphc.202100602, Published by Wiley-VCH Verl., Weinheim

Ionic liquid (IL) materials are promising electrolytes with striking physicochemical properties for energy and environmental applications. Heterogeneous structures and transport quantities of monomeric and polymeric ILs are intrinsically intercorrelated and span multiple spatiotemporal scales, which is more feasible for coarse-grained (CG) simulations than atomistic modelling. Herein we constructed a novel CG model for ethyl-imidazolium tetrafluoroborate ILs with varied cation alkyl chains ranging from C2 to C20, and the interaction parameters were validated against representative static and dynamic properties that were obtained from atomistic reference simulations and experimental characterizations at relevant thermodynamic states. This CG model was extended to study thermotropic phase behaviors of monomeric ILs and to explore ion association structures and ion transport quantities in polymeric ILs with different architectures. A systematic analysis of structural and dynamical quantities identifies an evolution of liquid morphology from homogeneous to nanosegregated structures and then a smectic mesomorphism via a gradual lengthening of cation alkyl chains, and thereafter a distinct structural transition characterized by a monotonic decrease in orientational and translational order parameters in a sequential heating cascade. Backbone and pendant polymeric ILs exhibit evident anion association structures with cation monomers and polymer chains, and striking intra- and interchain coordinations between cation monomers owing to an intrinsic polymer architecture effect. Such a peculiar ion pairing association leads to a progressive increase in anion intrachain hopping probabilities, and a concomitant decrease in anion interchain hopping events with a gradual lengthening of polymeric ILs. The anion diffusivities in polymeric ILs are intrinsically correlated with ion pairing association lifetimes and ion structural relaxation times via a universal power law correlation D ∼ τ−1, irrespective of polymer architectures.

We report amplified near-IR (NIR) fluorescence in organic rhodamine dye nanoparticles, which can be synthesized on the basis of ion association between rhodamine-800 (Rho-800) cation and tetrakis(4...

The complex formation and the ion-association of the ion-pair formed between the anionic chelate of molybdenum(VI)‒3,5-dinitrocatechol (3,5-DNC) with the cation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) in the liquid–liquid extraction system Mo(VI)‒3,5-DNC‒MTT‒H2O‒CHCl3 was studied by spectrophotometry. The optimum conditions for the chelate formation and extraction of the ion-associated complex Mo(VI)‒3,5-DNC‒MTT were established. The molar ratio of the components in the ion-associated complex Mo(VI)–3,5-DNC–MTT was determined by independent methods. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. Based on this, a reaction scheme, a general formula and a structural formula of the complex were suggested.

Complex crystallization pathways are common in protein crystallization, tetrahedrally coordinated systems, and biomineralization, where single or multiple precursors temporarily appear before the formation of the crystal. The emergence of precursors is often explained by a unique property of the system, such as short-range attraction, directional bonding, or ion association. But, structural characteristics of the prenucleation phases found in multistep crystallization remain unclear, and models are needed for testing and expanding the understanding of fluid-to-solid ordering pathways. Here, we report 3 instances of 2-step crystallization of hard-particle fluids. Crystallization in these systems proceeds via a high-density precursor fluid phase with prenucleation motifs in the form of clusters, fibers and layers, and networks, respectively. The density and diffusivity change across the fluid-fluid phase transition increases with motif dimension. We observe crystal nucleation to be catalyzed by the interface between the 2 fluid phases. The crystals that form are complex, including, notably, a crystal with 432 particles in the cubic unit cell. Our results establish the existence of complex crystallization pathways in entropic systems and reveal prenucleation motifs of various dimensions.

We have developed a novel one-step method for photoreduction synthesis of morphology-controlled Ag nanoparticles (AgNPs) under the irradiation of narrow band blue light emitting diodes. The results showed that AgNPs with different morphologies can be prepared by controlling the irradiation time. More importantly, a new spectrophotometry based on the silver phenanthroline-eosin ion association system was established to detect the concentration of Ag+. In the presence of polyvinyl alcohol, Ag+ can combine with 2,4,5-7-tetrabromofluorescein disodium salt and 1,10-phenanthroline monohydrate forming red ternary complex in ammonium acetate buffer (pH 7.0). The new method was applied to determine the concentration of Ag+ during the formation of AgNPs. According to the changes of Ag+ concentration and morphologies, a potential mechanism for the structural transition of AgNPs was given.

Electrical conductances of solutions of tetraphenylphosphonium chloride, sodium tetraphenylborate, and sodium chloride in polyethylene glycol (PEG) + water mixed solvent systems having 0.200, 0.400, and 0.600 mass fractions of PEG are reported at 298.15 K. In this study three different average molar masses of PEG, e.g., 300 (designated as PEG 300), 400 (designated as PEG 400), and 600 (designated as PEG 600) g·mol−1 were employed. The conductance data have been analyzed using the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance, the association constant and the association diameter of the electrolytes. The ionic contributions to the limiting molar conductances have been estimated using tetraphenylphosphonium tetraphenylborate as the “reference electrolyte”, considering the similarity of the sizes and chemical characters of the tetraphenylphosphonium and tetraphenylborate ions possessing a quasi-spherical surface of the phenyl rings. Analyses of the results provided important information as to the ion-association and solvation behavior of the electrolytes/ions investigated in PEG + water mixed solvent media.

Experimental results of the osmotic coefficients of aqueous solutions of 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4], 1-ethyl-3-methylimidazolium methylsulfate [EMIM][MeSO4], 1-ethyl-3-methylimidazolium tosylate [EMIM][Tos], 1,3-dimethylimidazolium methylsulfate [MMIM][MeSO4], tributylmethylphosphonium methylsulfate [TBMP][MeSO4] and triisobutylmethylphosphonium tosylate [(iBu)3MP][Tos] obtained by vapor pressure osmometry (VPO) at 298.15 K and at atmospheric pressure are reported in this work. From this data water activity (aw), vapor pressure (p), mean molal activity coefficients (γ±), Gibbs free energy due to mixing (ΔGmix) and excess Gibbs free energy change (ΔGE) are calculated. The activity coefficient data obtained are correlated with McMillan-Mayer theory and Pitzer model. The results obtained are elucidated in terms of ion association and structural characteristics of ILs.

Glyme solvents are a promising avenue of research in novel electrolytes, due to their thermal and chemical stability, large electrochemical window, and tunable properties. This work investigates the transport properties of LiPF6 and NaPF6 salts in Monoglyme (G1), Diglyme (G2), and Tetraglyme (G4). Self-Diffusion coefficients, and degrees of ion association were found through spectroscopic techniques. Raman and Fourier-Transform Infrared (FTIR) spectroscopy exhibited an absorbance peak at 740 cm−1, corresponding to the a1g mode; known to signify the presence of solvent-separated and contact ion pairs. The increased intensity of this peak for G1 compared to G4 suggests that the electrolyte exhibits stronger association with decreasing solvent size. Nuclear Magnetic Resonance Diffusometry measurements yield self-diffusion coefficients for 7Li, 23Na, and 19F across all samples to be on the order of 10−9 m2s−1 in G1, to 10−11 m2s−1 in G4. Comparison of conductivities calculated from the measured diffusivities and the Nernst-Einstein equation with conductivity measurements deduced from Electrochemical Impedance Spectroscopy (EIS) determined the ion association degree; the electrolytes were shown to exhibit stronger ion pairing with increased temperature which is attributed to a decrease in the dielectric constant of the solvents with increasing temperature. Additionally, the ion association was shown to decrease with increasing solvent molecular size, consistent with FTIR findings.

Label-free biosensing based on the nanoporous anodic alumina (NAA) membrane emerged as a versatile biosensing platform in the recent decade. In the present work, we developed a new immunosensing strategy based on the nanochannels of NAA and the ion pair interaction mediated by electrochemistry of C60. The NAA served as the matrix for the immobilization of the capture antibodies. The incubation of target antigens resulted in the formation of the immunocomplexes and thus an increase of the steric hindrance of the nanochannels. Therefore, the concentration of the redox probe transported through the nanochannels decreases, which can be detected at the working electrode modified with C60. Herein, we initially found that the cathodic peak ascribed to the reduction of C60 to C60– was obviously enhanced by the presence of the redox probe K3[Fe(CN)6] and which was contributed to the formation of a ternary ion association complex among C60, tetraoctylammonium bromide, and K3[Fe(CN)6]. Therefore, the transportation ...

The effect of 1‑octyl‑3‑methylimidazolium salicylate, [OMIm][Sal] and 1‑octyl‑3‑methylimidazolium ibuprofenate, [OMIm][Ibu] as active pharmaceutical ingredient ionic liquids (API-ILs) on the solvation properties of l -alanine in aqueous media have been investigated by thermophysical properties determination. The partial molar volume of transfer (ΔtraVϕ0), partial molar isentropic compressibility of transfer (Δtraκϕ0), viscosity B-coefficient of transfer (∆traB), ion association constant (KA) and molar refraction (RD) quantities have been calculated using the measured density, speed of sound, viscosity, electrical conductance and refractive index data. The results showed that the ion-polar and polar-polar interactions between API-ILs and l -alanine are dominant.

In this study, the ion association characteristics and the hydration dynamics of Mg2+ ions in MgSO4 aqueous solution at various concentrations were systematically investigated using density functional theory and classical molecular dynamics simulations. The results show that contact associated (CA) and solvent separated (SS) structures of Mg2+ and SO42− ions are the dominant species and play different roles in the crystallization and gelation processes of MgSO4 aqueous solution due to their distinctive association trend and the distinctive dynamics of their second hydration shells. The CA structures are more stable and the further aggregation of these clusters is sluggish in MgSO4 aqueous solution. The supersaturation or the formation of gel state can be partially attributed to the abundance of CA structures in supersaturated MgSO4 aqueous solution. In contrast, although the ion exchange in SS structures occurs frequently, the aggregation of SS structures is active and can be greatly promoted by increasing of the concentration. The dynamics of the second hydration shells around Mg2+ ions of SS structures also becomes more active as the concentration increases. The dynamic evolution characteristics of SS structures demonstrate their aggregation tendency for nucleation in the oversaturated MgSO4 aqueous solution, which helps to understand the nucleation mechanism in MgSO4 aqueous solution and the role of ion hydration dynamics in the nucleation process.

The extraction behavior and mechanism of uranium(VI) from aqueous solution with the multidentate ligand N,N,N″′,N″′-tetraoctyl-N″,N″-ethidene diglycolamide (TOE-BisDGA) as extractant were investigated. The extraction percentages of uranium(VI) were found to increase with increasing aqueous nitric acid solution. The extraction process was deduced to proceed by neutral extraction mechanism or ion association extraction mechanism, and the TOE-BisDGA extractant formed a major 1:1 complex with uranium(VI) in xylene system. The possible molecular structure of extracted pieces were presumed to be [UO2(NO3)2(TOE-BisDGA)] or [UO2(TOE-BisDGA)](NO3)2 or [UO2(NO3)TOE-BisDGA)](NO3) by ESI–MS and extraction mechanism.

The current study assembles liquid-microextraction, surface enhanced Raman spectroscopy (SERS) and chemometric algorithms in one platform for chromium speciation using octahedral Cu2O@Ag nanocomposites (Cu2O@AgNCs) as a SERS substrate. The reaction between cationic dye rhodamine 6G (RG+) and the chlorochromate anion (CrO3Cl−) at pH < 1.0 has been exploited for chromium determination by the phenomenon of ion association. The conditions of microextraction were carefully established, followed by depositing the sediment organic phase on the ethanolic octahedral Cu2O@AgNCs suspension. The SERS intensity was recorded for the complex ion associate (RG+·CrO3Cl−) versus a reagent blank. Chemometric algorithms such as partial least squares (PLS) and variable selection competitive adaptive reweighted sampling (CARS)-PLS were applied for masking redundancy in the SERS spectra of the complex ion associate (RG+·CrO3Cl−) formed in the sediment phase extract. Substrate characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), stoichiometry, analytical applications, selectivity and standard method validation was performed. The designed octahedral Cu2O@AgNCs/RG+/HCl probe displayed a detection limit of 0.028 μg L−1 for chromium(VI) under optimized chemometric modeling and microextraction conditions.

Structure of alkaline aqueous NaBH4 solutions at NaBH4 concentrations of 1.0 to 9.1 mol·dm−3 (almost saturated) as well as a 1.3 mol·dm−3 NaOH solution was studied by X-ray diffraction and Empirical Potential Structure Refinement (EPSR) modelling. In the 1.0 mol dm−3 alkaline NaBH4 solution, Na+ is surrounded by around six water molecules with octahedral geometry. With an increase in NaBH4 concentration, the hydration number of Na+ decreases from 4.8 ± 1.1 at 2.25 mol·dm−3 solution to 2.9 ± 1.3 at 9.1 mol·dm−3 with an almost constant Na+-O (W: H2O) distance of 2.34 A. The decrease in hydration number for Na+ is compensated by the formation of ion pairs between Na+ and BH4− to ensure an octahedral hydrated geometry for Na+. About 6.0 ± 1.6 water molecules are likely to bond to BH4− via tetrahedral edges or tetrahedral corners without a very specific hydration geometry, giving rise to each hydrogen atom of BH4− bound to 2.3 ± 1.0 water molecules through dihydrogen bonds. The hydration number around BH4− decreases with increasing concentration. BH4− tends to form contact ion pairs with Na+ at the Na-B distances of 3.24 A and 2.82 A in tetrahedral-corner-shared and tetrahedral-edge-shared fashions, respectively; the number of Na-B interactions increases from 0.3 ± 0.5 in 1.0 mol·dm−3 (almost negligible) to 2.1 ± 0.9 in 9.0 mol·dm−3. Tetrahedral-edge-shared bidentate ion pair is likely to be the preferred and dominant ion cluster over the wide concentration range. Ion association between the Na+ and BH4− was crosschecked by density function theory (DFT) calculations on [NaBH4(H2O)6] clusters.

The choline ion (Ch+) is ubiquitous in nature and also its synthetic homologue, chlorocholine (ClCh+), is widely used. Nevertheless, surprisingly little information on the hydration and counter-ion binding of these cations can be found in the literature. In this contribution we report effective hydration numbers, determined by dielectric relaxation spectroscopy, and ion-pair association constants with Cl-, determined by dilute-solution conductivity measurements. In combination with RISM calculations the obtained data suggest that for Ch+ water is bound to the hydroxy group via hydrogen bonds whereas for ClCh+ a rather stiff clathrate-like shell around the chlorine atom seems to be formed. With Cl- both cations form contact ion pairs with association constants of only ∼2 to 3 M-1.

The hydrolysis of Ba2+and Ra2+was studied at 25 °C in aqueous mixtures of NaOH and NaClO4using an ion exchange method and radiotracer and batch techniques. The distribution of133Ba and226Ra between solid (ion exchange resin) and aqueous (mixture of NaOH and NaClO4) phases was measured via gamma spectrometry and liquid scintillation counting. The total ionic strength was kept constant and the concentration of NaOH in the aqueous phase was varied from 0 (pure NaClO4) to pure NaOH from sample to sample. It was shown that an increase of the Ba2+or Ra2+concentration in the aqueous phase with an increase of the NaOH concentration cannot be explained solely by Ba2+or Ra2+activity coefficient differences in the NaOH and NaClO4media (salting out) and that weak BaOH+and RaOH+ion pairing occurs in the systems studied. A model for weak ion association was developed and apparent BaOH+and RaOH+stability constants were derived assuming the formation of weak aqueous NaOH(aq) ion pairs via non-linear curve fitting. It was demonstrated that systematic uncertainties have a much greater contribution to the NaOH(aq), BaOH+and RaOH+stability constant uncertainty budget compared to stochastic uncertainties and a method for estimation of the systematic uncertainties was proposed. The method combines fitting, restricted primitive model computations with surveyed literature data that resulted in a stability constant for NaOH(aq) that ranged from 0 to 1 at ionic strengths below 5 mol·kg−1(i.e. KNaOH= 0.5 ± 0.5, where the uncertainty is a systematic 95% confidence interval). The variation of KNaOHallowed the estimation of the systematic 95% confidence interval in the apparent stability constants of BaOH+and RaOH+. The specific ion interaction theory was used to extrapolate the derived logarithms of the BaOH+and RaOH+apparent stability constants to zero ionic strength (log10K = 0.7 ± 0.2 for both ion pairs) and obtain the relevant ion interaction parameters. It was shown that both the Ba2+and Ra2+ions have similar activity coefficients and undergo similar short-range interactions in aqueous NaOH-NaClO4media.

Recently, an aqueous glycine solution has been proposed as a non-toxic environmentally friendly lixiviant to leach precious metals such as gold. In confined spaces, gold can be leached effectively using cyanide as a lixiviant. However, in unconfined applications, cyanide poses detrimental environmental effects due to its high level of toxicity. In order to investigate the effectiveness of lixiviant systems containing glycine and examine their potential, it is essential to identify the thermodynamic properties and stability domains of metal-glycinate complexes. Numerous studies have been conducted on the thermodynamic equilibrium of divalent metal-glycinate formations but those of monovalent metal-glycinate are scarce in general and inexistent for most precious metals including gold. In this study, we use data analysis to relate the standard partial molal properties of metal-glycinate complexes to the standard partial molal properties of various metals and estimate the equilibrium constants of monovalent metal-glycinate formation at ambient conditions. Finally, the standard partial molal properties of the metal-glycinate complexes and their revised Helgeson-Kirkham-Flowers (HKF) equations of state have been estimated and used to deduce the equilibrium constants of metal-glycine systems at different temperatures. The proposed method has been tested using existing experimental data and showed excellent consistency.

In this study, molecular dynamics simulations were used to investigate the role of hydration shells on the stabilization of ion clusters. The stabilization of [CaClx]2−x (x = 4–6) species can be enhanced by their hydration shells. The shrinkage of the third hydration shell can be observed for the [CaClx]2−x complex while not for the [CuCl]+ or [CaCl2]0 species in an aqueous solution. The shrinking third shell together with the second shell of Ca2+ form a compact inner hydration shell around those clusters promoting their existence in an aqueous solution. Their inner hydration shells, forming a distinctive hydrogen bond network around the ion cluster, act as a “cage” structure, confining multi-Cl− ions around Ca2+, and promote the occurrence of [CaClx]2−x species in the aqueous solution. Our results demonstrate that the structural characteristics of some ion clusters combined with their distinctive hydration characteristics have a huge impact on ion association in an aqueous phase.

The effect of 1-hexyl-3-methylimidazolium salicylate, [HMIm][Sal] as an ionic liquid form of active pharmaceutical ingredient (API-IL) on the thermodynamic behavior of two simple amino acids, glycine and l-alanine have been investigated. The densities, speeds of sound, viscosities, and refractive indices of the amino acids in the mixtures of ([HMIm][Sal] + water) have been determined at T = 298.15 K. Moreover, the electrical conductivities of the studied API-IL in water and aqueous mixtures of the amino acids have been calculated using the measured specific conductivities. The measured data were utilized to compute the partial molar volume of transfer (ΔtraVϕ0), partial molar isentropic compressibility of transfer (Δtraκϕ0), viscosity B-coefficient of transfer (ΔtraB), ion association constant (KA), and molar refraction (RD) quantities. The increase in the positive values of ΔtraVϕ0, Δtraκϕ0 and ΔtraB with an increase in the API-IL concentration indicates that the ion–polar and polar–polar interactions be...

Anionic surfactant as sodium dodecyl sulfate (SDS) can be assayed by using methylene blue (MB). The ion-association of SDS-MB can be extracted solventless but sorbed on a specified polyurethane foam (PUF) monolithic rod, prepared in the lab by mixing polyether with methylene diphenyl diisocyanate (MDI). The blue product (the ion-association of SDS-MB) on the rod can be followed by a smartphone (iPhone 6S). With a set of conditions, a single standard calibration can be applied. The proposed green analytical procedure can be employed for on-site assay. Application to real water samples was demonstrated.

In this paper, we investigate the consequences of ion association, coupled with the considerations of finite size effects and orientational ordering of Bjerrum pairs as well as ions and water molecules, on electric double layer near charged surfaces. Based on the lattice statistical mechanics accounting for finite sizes and dipole moments of ions, Bjerrum pairs and solvent molecules, we consider the formation of Bjerrum pairs and derive the mathematical expressions for Bjerrum pair number density as well as cation/anion number density and water molecule number density. We reveal the several significant phenomena. Firstly, it is shown that our approach naturally yields the equilibrium constant for dissociation-association equilibrium between Bjerrum pairs and ions. Secondly, at low surface charge densities, an increase in the bulk concentration of Bjerrum pairs enhances the permittivity and decreases the differential capacitance. Next, for cases where Bjerrum pairs in an alcohol electrolyte solution have a high value of dipole moment, Bjerrum pair number density increases with decreasing distance from the charged surface, and differential capacitance and permittivity is high compared to ones for the cases with lower values of Bjerrum-pair dipole moments. Finally, we show that the difference in concentration and dipole moment of Bjerrum pairs can lead to some variation in osmotic pressure between two similarly charged surfaces., Comment: 28pages, 13 figures

Electro-chemical sensors response characteristics of three different electrodes modified with carbon paste (CP), screen printed (SC) and Poly-vinyl chloride(PVC) were fabricated to verify the credibility of drug “AVELOX”, whose generic name is “Moxifloxacin HCl” (AV-MOXH) are traced and calculated. The sensing membranes contain AVELOX (Moxifloxacin HCL) ion association complexes with “sodium tetraphenyl borate” (NaTPB), “Phosphomolybdic acid” (PMA), and “Phosphotungstic acid” (PTA) and “Ammonium Reineckate” (RN) as electro-active materials. All the three electrodes (ICPE, IPVC and ISPE) are subjected to underneath study displays fast, viable and near-Nernstian linear responses above a relative wide-ranging concentration which varies from (1.0×10-6)molL-1 to (1.0×10-2)molL-1 of AV-MOXH at 25°C along with a mono-valent cationic slope. On the basis of calculations and presented data in the paper shows that that the IPVCs modified electrodes, have slope values measured with 7.5mg are (53.2 ± 1.5),(58.2 ± 3.9) and (51.6 ± 2.0) mV decade -1 for NaTPB, PMA and PTA ion pairing reagents respectively. For ISPE modified electrode, the observed slope values are (59.7 ± 2.0) mV decade -1 with 22mg for NaTPB ion pair, (60.1 ± 2.0)mV decade -1 with 16mg for RN ion pair and (58.9 ± 3.2)mV decade -1 with 30 mg for PTA ion pair. Whereas, the obtained value of ICPE electrode altered with 7.5mg NaTPB shows slope calculated at (58.0 ± 2.0)mV decade -1 . The sensors demonstrate good discernment of Av-MOXH from numerous inorganic and organic compounds such as glucose, sucrose, Na+, Ca+,etc. Additionally, the isothermal coefficients along by selectivity coefficients is diagnosed. The modified Screen Printed Electrode sensor appears to be highly sensitive for determination of AV-MOXH. Electrode response was set up to observe their pH dependence range (2-6) for ISPEs and IPVC electrodes and (3-7) pH range for ICPE electrode with varied range of temperature. The short response time, life time validity, recovery and all the method of validation such limit of detection and limit of quantification are estimated. This potentiometric method is suitable for determining AV-MOXH in pharmacological formulations, and the findings obtained are comparable to the “HPLC official method” in terms of agreement. As a result, the postulated potentiometric approach was verified in accordance with IUPAC guidelines.

In this study, a trioctylmethylammonium chloride (N263)- tributyl phosphate (TBP)-n-octanol-sulfonated kerosene (N263-T) synergistic extraction system and an N263-n-octanol-sulfonated kerosene (N263–O) system were used to treat cyanide (CN)-bearing wastewater. The extraction saturation capacity of the two systems was measured. The influences of the initial pH and phase ratio (O/A) of the two systems on extraction were compared and analyzed. Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and slope methods were used to analyze the characteristic functional groups in the loaded organic phase, the compositions of the extracted compounds in the extraction reactions and the reaction mechanism. The results indicated that the saturated extraction capacity of the N263-T system, which was much larger than that of the N263–O system, for metal CN complex ions was 4354.31 mg/L. In addition, the N263-T system operated over a wider pH range. The extraction rates of copper (Cu), zinc (Zn), and iron (Fe) ions at pH 14 were 97.4%, 99.1%, and 87.2%, respectively. There was a strong compatibilization effect of TBP on the extraction system. The extraction efficiency of the N263-T system for metal CN complex ions was higher than that of the N263–O system when O/A = 0.4. The saturated loaded N263-T and N263–O systems were stripped by 1 mol/L NaOH +2 mol/L NaSCN solution at O/A = 3. The metal ion concentration in the stripping solution could be enriched to 11996.6 and 8913.3 mg/L for the N263-T and N263–O systems, respectively. During the extraction process, the binding ratios of N263 cations to Cu(CN)32−, Zn(CN)42−, and Fe(CN)63− were 2:1, 2:1, and 3:1, respectively. The binding ratios of TBP to Cu(CN)32−, Zn(CN)42−, and Fe(CN)63− in wastewater were 3:1, 4:1, and 6:1, respectively. The P O group in TBP was linked to the C N group of the metal CN complex ion by hydrogen bonds using the water molecule as a bridge to form a supramolecular anion group, which entered into the organic phase and combined with the N263 cation under the action of ion association.

A simple, rapid, highly sensitive and selective non-extraction spectrophotometric and sequential injection analysis with lab-at-valve (SIA-LAV) methods for the determination of bismuth(III) have been developed based on the formation of a specific ion association complex (IA) between tetraiodobismuthate(III) anion and the polymethine dye Astra Phloxine (AP). The changes in the absorption spectra resulting from the formation of the IA are explained in the framework of the exciton theory by the aggregation of dye ions. The analytical wavelength was chosen in the region of an intense narrow bathochromically shifted band with maximum at 600 nm related to the band of the aggregated dye in a specific IA. It was shown that any cationic dye, including representatives of triphenylmethane, rhodamine and polymethine dyes, is capable of forming specific IAs. One of the most important prerequisites for the formation of a specific IA is its relatively low solubility. The UV-visible spectrum of the AP cation was calculated using the time-dependent density functional theory (TD-DFT). Superiority of the TD-DFT with the Franck-Condon approximation, which takes into account vibronic effects, was shown over the traditional non-vibrationally resolved TD-DFT calculations. The PBE1PBE functional is the most suitable in comparison with the used M06, CAM-B3LYP, WB97XD and M11 functionals. Carrying out the chemical reaction and mixing in an external mixing chamber allowed the mixing conditions to be adapted to the requirements necessary for the complete formation of the specific IA. Thus, the maximum possible sensitivity was achieved, which was about an order of magnitude higher than when using the classical SIA approach. Calibration ranges and detection limits (indicated in parentheses) for the developed spectrophotometric and SIA-LAV procedures were 0.04-0.5 (0.01) and 0.1-1.7 (0.03) µg L−1, respectively. The molar absorptivity and Sandell's sensitivity were found to be 6.6 × 104 mol−1 L cm−1 and 3.16 × 10−3 μg cm−2, respectively. The proposed methods were successfully applied for the determination of bismuth content in pharmaceutical compositions and alloys.

Herein, a novel validated potentiometric method is presented for the first time for citicoline determination. The method is based on measuring the potential using new constructed citicoline electrodes. The electrodes are based on the use of citicolinium/phosphomolybdate [Cit]2[PM] (sensor I) and citicolinium/tetraphenylborate [Cit][TPB] (sensor II) ion association complexes. These sensory materials were dispersed in plasticized polyvinyl chloride (PVC) polymeric membranes. The sensors revealed a Nernstian response with the slopes 55.9 &plusmn, 1.8(r2 = 0.9994) and 51.8 &plusmn, 0.9 (r2 = 0.9991) mV/decade over a linearity range of 6.3 &times, 10&minus, 6&ndash, 1.0 &times, 3 and 1.0 &times, 5&ndash, 3 M and detection limits of 3.16 &times, 6 and 7.1 &times, 6 M for sensors I and II, respectively. To ensure the existence of monovalent citicoline, all measurements were performed in 50 mM acetate buffer at pH 3.5. All presented electrodes showed good performance characteristics such as rapid response, good selectivity, high potential-stability and long life-span. Method verification and validation in terms of response linearity, quantification limit, accuracy, bias, trueness, robustness, within-day variability and between-days variability were evaluated. The method was introduced for citicoline determination in different pharmaceutical formulations and compared with the standard high performance liquid chromatography (HPLC) method.

Polymerized ionic liquids (polyILs) combine the unique properties of ionic liquids (ILs) with macromolecular polymers. But anion diffusivities in polyILs can be three orders of magnitude lower than that in ILs. Endeavors to improve ion transport in polyILs urgently need in-depth insights of ion transport in polyILs. As such in the work we compared ion transport in poly (1-butyl-3-vinylimidazolium-tetrafluoroborate) (poly ([BVIM]-[BF4])) polyIL and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]-[BF4]) IL. The diffusivities of ions in the polyIL and IL were measured and computed. According to the results of the molecular dynamics simulations performed, in the IL the coupling motion between an anion and the ions around determines the ion diffusivities, and the ion association lifetime gives the time scale of ion transport. But in the polyIL, the hopping of an anion among cages composed of cationic branch chains determines the diffusivity, and the associated anion transport time scale is the trap time, which is the time when an anion is caught inside a cage, not the ion association lifetime, as Mogurampelly et al. regarded. The calculation results of average displacements (ADs) of the polyIL chains show that, besides free volume fraction, average amplitudes of the oscillation of chains and chain translation speed lead to various diffusivities at various temperatures.

Detailed speciation of electrolytes as a function of chemical system and concentration provides the foundation for understanding bulk transport as well as possible decomposition mechanisms. In particular, multivalent electrolytes have shown a strong coupling between anodic stability and solvation structure. Furthermore, solvents that are found to exhibit reasonable stability against alkaline-earth metals generally exhibit low permittivity, which typically increases the complexity of the electrolyte species. To improve our understanding of ionic population and associated transport in these important classes of electrolytes, the speciation of Mg(TFSI)2 in monoglyme and diglyme systems is studied via a multiscale thermodynamic model using first-principles calculations for ion association and molecular dynamics simulations for dielectric properties. The results are then compared to Raman and dielectric relaxation spectroscopies, which independently confirm the modeling insights. We find that the significant presence of free ions in the low-permittivity glymes in the concentration range from 0.02 to 0.6 M is well-explained by the low-permittivity redissociation hypothesis. Here, salt speciation is largely dictated by long-range electrostatics, which includes permittivity increases due to polar contact ion pairs. The present results suggest that other low-permittivity multivalent electrolytes may also reach high conductivities as a result of redissociation.

The micro-structure of hydration shell of solute in water is significant for understanding the properties of aqueous solutions. Raman spectroscopy has been employed for studying the hydration shell structure of the solute for decades, however, Raman imaging data is still seriously overlapped, making it challenging to obtain information on the spectrum of hydrated water molecules. In this paper, Raman spectroscopy was employed to study the O-H vibration peaks of LiCl aqueous solution and LiCl-MgCl2-H2O mixed aqueous solution. The changes of stretching vibration peak of 2800∼3800 cm-1 O-H and hydrogen bond network structure in aqueous solution were analyzed at room temperature and ion association. With the increase of magnesium salt ratio, the damage of solute to the bulk water gradually decreases in the mixed solution, which indicated that LiCl has a more significant influence on the bulk water molecules. It is mainly due to the intense hydration of Li+, which can not only affect the water molecules in the first hydration shell but also affect the water molecules in the second hydration shell. The number of water molecules in the first hydration shell were obtained by extracting the spectra of different solute first hydration shells from the solution spectra. Those spectra of the hydration shell were employed to study the micro-structures of the first hydration shells of anions, and the aggregation behavior of ions in the the mixed solution.

In this paper, the influence of the side chain length of five ionic liquids (ILs): 1-methylimidazolium chloride ([C0mim][Cl]), 1,3-dimethylimidazolium chloride (([C1mim][Cl]), 1-ethyl-3-methylimidazolium chloride (([C2mim][Cl]), 1-butyl-3-methylimidazolium chloride (([C4mim][Cl]) and 1-hexyl-3-methylimidazolium chloride (([C6mim][Cl]) on the interactions with ethylene glycol (EG) was studied. Based on the measurement of density and electrical conductivity of the ionic liquid + EG mixture in the temperature range (278.15–313.15) K, the values of apparent molar volume, standard partial molar volumes, apparent molar volume at infinite dilution, Masson's interaction coefficient, thermal expansion coefficient, limiting apparent molar expansibilities, Heppler's coefficient, ion association constants, thermodynamic parameters of ion-pair formation as well as diffusion coefficient was calculated. Experimental results were supported by molecular dynamic simulations. With the increase of the side chain length, from C0mim+ to C6mim+ cation, ion–dipole interactions on the solvation process decrease, and the influence of solvophobic solvation increases. Ionic liquids [C0mim][Cl] and [C1mim][Cl] show structure-breaker properties, [C4mim][Cl] and [C6mim][Cl] structure-making properties in EG solutions, while [C2mim][Cl] is borderline. The values of ion association constants in EG are higher than in water. The ion association process is spontaneous for all ionic liquids and entropy-driven. © 2021 Elsevier B.V.

The conductivity of polymerized ionic liquid graft copolymers (PILGCs) is usually three orders of magnitude lower than ionic liquids (ILs); researches are being performed actively to improve ion transport in PILGCs. In the research, the composite membrane of poly(1-butyl-3-vinylimidazolium-acetate) (poly([BVIM]-[OAc])) PILGC and NPs filled with 1-butyl-3-methylimidazolium acetate ([BMIM]-[OAc]) IL was developed. Ion transport in the composite is a combination of that in PILGC and IL and mechanisms underlying anion transport in the PILGC and the IL should both be explored in order to obtain profound knowledge of ion transport (mechanism) in the composite. Researchers still have discrepancy in the mechanisms of ion transport in PILGCs. We explored the mechanisms and time scales of ion transport in the PILGC and compared the differences in ion transport phenomena and mechanisms in the PILGC and the IL. 2D-IR experiments were performed and the results show that the peak-shape of the spectra of SCN− in the PILGC changes on a much slower time scale than that in the IL, indicating that the IL completes structure decay in a way significantly faster than the PILGC. Anion diffusivities in the composite, PILGC and IL at various temperatures were measured and calculated. Subdiffusion phenomena are caused by hindrance influence of surrounding units on anion motion. Therefore exploring subdiffusive regime gives mechanisms underlying ion transport: the subdiffusion phenomena of anion transport in the IL are caused by the coupling between anion motion and the motion of ions around, while that in the PILGC are caused by the trap of anions in cages composed of the PILGC chains before they get the opportunities to hop to cages nearby. According to our analysis, van der Waals (VDW) interactions play a more significant role than electrostatic interactions, including ion association interactions, in influencing the magnitude of anion diffusivities in the PILGC. It is wrong to explore ion transport mechanism via only analyzing electrostatic interactions between ions; anion transport is along PILGC chains most probably in successive steps and between PILGC chains most probably in separate steps, depending on jumping between neighboring cages. The trap time of an anion inside a cage, instead of ion association time, gives the time scale that associates with anion transport. The anion transport mechanism in the composite is a combination of fast structural relaxation in the IL and slow hopping between cages in the PILGC.