In our work, thermal properties, phase transitions, and processes of molecular relaxation of nitrate and perchlorate ions in the lithium nitrate–potassium nitrate binary eutectic system doped with lithium perchlorate LiClO4 were studied by differential scanning calorimetry and Raman spectroscopy. The values of specific electrical conductivity of the LiNO3–KNO3 nitrate eutectic and the LiNO3–KNO3–LiClO4 ternary salt system were also obtained. The electrical conductivity was investigated up to melting temperatures and it was found that the addition of lithium perchlorate LiClO4 to the LiNO3–KNO3 binary eutectic leads to an increase in the specific ionic conductivity of the ternary salt system. Lithium perchlorate functions as an active additive that promotes the increase of ion mobility due to competing mechanisms of anion-cation interactions. The value of specific ionic conductivity reaches a maximum in the system when 0.2 mol of lithium perchlorate is added. It has been established that with the increasing addition of lithium perchlorate to the nitrate eutectic, the melting peak of the LiNO3–KNO3 eutectic decreases. For the composition with an initial content of 0.5LiClO4, a phase transition of the LiNO3–KNO3 eutectic is not registered. It is obvious that in the system take place an exchange reaction between potassium nitrate and lithium perchlorate with the formation of KClO4 and LiNO3. This conclusion is also confirmed by the data of Raman scattering spectra, which show that with increasing addition of LiClO4, the peak of fully symmetric stretching vibration ν1(KNO3) decreases and the peak of ν1(KClO4) is observed. The addition of 0.5 mol of LiClO4 leads to the total disappearance of the peak of ν1(KNO3). Interionic interactions in the salt systems, leading to changes in the local symmetry of the NO3ˉ-ion, are reflected in their transport and thermodynamic properties.

The difference of solvent properties can significantly affect the solvation phenomena in individual and, especially, in mixed solutions. In particular, it can be assumed that in mixed solvents, i.e. in systems with intermediate dielectric permittivity (mixtures of linear and cyclic carbonic acid esters), cations will bind molecules of linear esters more strongly and bind molecules of cyclic esters more weakly than it takes place in individual solvents. In the present work the Raman spectra of lithium perchlorate solvents in propylene carbonate (PC), dimethyl carbonate (DMC) and their mixture in a wide range of salt concentrations are studied. It is shown that the solvation effects of the cation are clearly traced in the region of symmetric ring vibrations (~690-730 cm-1) of propylene carbonate and in the region of deformation vibrations of CCA (~520 cm-1) of dimethyl carbonate. These effects are also evident in the mixed solvent. The so-called method of differential spectroscopy was used to judge the structural changes of mixed-solvent systems. It consisted in constructing spectra of lithium salt solutions in mixed solvents, additive sum of spectra of lithium salt solutions in PC and DMC, as well as their difference (differential spectra). The analysis of differential spectra allows us to conclude that in systems with mixed solvent there is a weakening of interaction of propylene carbonate molecules with ions, and there is a preferential solvation of cations and anions by dimethyl carbonate molecules. Also, unlike propylene carbonate, dimethyl carbonate solvates perchlorate ions, which follows from the line contour changes in the region of CH3-group vibrations (2970 cm-1) solvation of anions is also observed in the mixed solvent. For citation: Rabadanov K.Sh., Gafurov M.M., Akhmedov M.A., Rabadanova D.I., Magomedova A.G. Investigation of solvation in lithium perchlorate -propylene carbonate-dimethyl carbonate system by raman spectroscopy. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 36-42. DOI: 10.6060/ivkkt.20246705.6967.

In recent years, there has been a boom in the publication of research results on ionic (electrolyte) systems used in the creation of electrochemical energy systems (batteries, supercapacitors, etc.). One of the alternative ways to obtain dynamic information in ionic systems is spectroscopic experiments, and the most valuable information on the behavior of condensed systems at picosecond and adjacent time intervals is provided by vibrational spectroscopy. The source of this information is the analysis of the shape and width of the lines in the vibrational spectra of ion systems. This review aims to systematize the theoretical and methodological aspects of the study of the dynamics of ion systems by vibrational spectroscopy.

The work is aimed at studying the effect of mechanical activation on the structure and electrical conductivity of the NaClO4 – and KClO4 – basedcomposites. Based on the result of the analysis of the DSC curves of the (1–x) NaClO4 – x Al2O3 and (1–x) KClO4 – x Al2O3 composites measured while heating and cooling the samples, it was established that the enthalpy of phase transitions in them decreased with an increase in the concentration of the nanosized dopant. A complication of all active vibrational contours corresponding to internal vibrations of the molecular anion in the composites with increasing Al2O3 concentration and a shift of the band of the fully symmetric stretching vibration v1 (A) to a low-frequency region was revealed by Raman spectroscopy. Based on electrochemical impedance spectroscopy data, it was determined that for the 0.4NaClO4 – 0.6Al2O3 system subjected to mechanoactivation, the values of specific ionic conductivity increased by two orders of magnitude as compared to that of pure NaClO4, while for the 0.4KClO4 – 0.6Al2O3 system, the values of specific ionic conductivity increased by three orders of magnitude as compared to the initial salt at T = 320 °C.

The physicochemical properties of the eutectic system 78.2LiClO4–21.8NaClO4 and its heterogeneous composites with nanosized alumina are studied at different temperature, phase state, and Al2O3 concentration using the methods of Raman spectroscopy, differential scanning calorimetry (DSC), and impedance spectroscopy. The addition of Al2O3 increases the ionic conductivity and decreases the activation energy. The Raman spectroscopic studies have shown that the addition of alumina leads to the formation of the amorphous phase as a result of destruction of the crystalline phase of sodium perchlorate.

The effect of mechanical activation on the structure and conductivity of the KNO 3 –Al 2 O 3 composite is considered. The analysis of DSC curves measured in the course of heating of the 0.5KNO 3 –0.5Al 2 O 3 composite shows that the enthalpy of phase transitions decreases with the increase in the time of mechanical activation. Based on the X-ray diffraction analysis, it is shown that the mechanical activation reduces the grain size and makes the grains more defective. According to the data of electrochemical impedance spectroscopy, the ionic conductivity of the system KNO 3 –Al 2 O 3 obtained by mechanical activation is 3.8 × 10 –5 S/cm at T = 373 К and 2 × 10 –3 S/cm at T = 473 К and its activation energy is 0.19 eV, which is comparable with the parameters of composites with the same chemical composition obtained by the ceramic method. The Raman spectroscopic study reveals the formation of the metastable γ-KNO 3 phase in the system KNO 3 –Al 2 O 3 at the temperature above 397 К . The increase in conductivity of the KNO 3 –Al 2 O 3 composite at 373–403 К is associated with the presence of an additional metastable γ-KNO 3 phase.

Spectroscopic studies of molten electrolytes have been carried out for more than 50 years. The information available in the literature on the problems arising in high-temperature spectroscopic measurements of molten electrolytes, as well as methods and technical solutions to overcome them, and the design of optical heating cells used for these purposes is fragmentary. The purpose of this review is to summarize the information available in the literature on techniques and methods for high-temperature spectroscopic measurements of molten electrolytes. A description of various techniques used in spectroscopic studies of molten electrolytes, including IR transmission spectroscopy, reflection and emission spectroscopy, reflection-adsorption spectroscopy, spectroelectrochemical Raman and IR spectroscopy is presented. A description of the design of the corresponding optical heating cells is given, as well as examples of spectra obtained using them. The review is useful for researchers studying electrolyte melts and specialists developing medium-temperature chemical current sources based on them.

Due to its sensitivity to molecular interactions between functional groups of molecules and ions, vibration spectroscopy is the most tool for studying speciation in nonaqueous solutions. In this paper, vibrational spectra of ionic solutions filled with nanosized oxides have been studied. Solvated cations, anions, SSIPs, and CIPs have been detected, and their concentrations have been determined with due regard for equilibria existing in the solvent. It has been established that all the particles that exist in the solutions of lithium perchlorate in dimethyl sulfoxide are also present in filled solutions, but their relative amount varies. The course of the revealed changes in the number of particles in the systems under study does not allow us to identify the character of the effect of the solid filler field on the particles in the solution. There is no evidence of adsorption of dimethyl sulfoxide or anions on aluminum oxide.

Structural and dynamic properties of the composites based on lithium perchlorate LiClO 4 at various temperatures, phase states, and concentrations of the inert fillers SiO 2 and Al 2 O 3 were studied by Raman scattering (RS) and differential thermal analysis (DTA). It was shown that an amorphous phase formed in the (1 – х )LiClO 4 + x SiO 2 and (1 – х )LiClO 4 + x Al 2 O 3 composites (for x ≥ 0.4), its thermal effect was recorded at 200°С. In the Raman spectrum of the heterogeneous system, in the frequency range corresponding to totally symmetric vibration of the perchlorate anion, an additional component with a Raman maximum at ν _1^c ∼ 954 cm –1 , which could be attributed to an amorphous phase, was also revealed. While the filler concentration increased, the values of enthalpies of phase transitions decreased monotonically, and at x = 0.8, both spectral and thermophysical manifestations of phase transitions completely disappeared. Doping of lithium perchlorate with silicon and aluminum oxides led to an increase in ionic conductivity. The maximum values of conductivity were observed for the 0.4LiClO 4 + 0.6SiO 2 and 0.5LiClO 4 + 0.5Al 2 O 3 composites.

In this paper, the effect of mechanical activation on the structure and electrical conductivity of the KNO3-Al2O3 composite was studied. Based on the analysis of DSC curves measured during heating and cooling of the sample, it was found that the enthalpy of phase transitions decreases with increasing time of mechanical activation of the 0.5KNO3-0.5Al2O3 composite. X-ray diffraction analysis shows that mechanical activation leads to a decrease in the grain dimension and an increase in the defectiveness. Based on the electrochemical impedance spectroscopy data, it was determined that for the KNO3-Al2O3 system subjected to mechanical activation, the values of specific ionic conductivity are 3.8×10-5 S/cm at T = 373 K and 2×10-3 S/cm at T = 473 K and the energy value activations of 0.19 eV are comparable with the parameters of a composite of the same chemical composition obtained by the ceramic technique. Raman spectroscopy revealed the formation of a metastable γ-phase KNO3during the mechanoactivation of the composite, which is stable at temperatures above 397 K. It is proposed that an increase in electrical conductivity in the KNO3-Al2O3 composite at 373-403 K is due to the presence in the composite of an additional metastable γ-phase KNO3.

Sorption properties of activated carbon prepared from peach wood by chemical activation with phosphoric acid toward copper ions were studied. The produced activated carbons were characterized by N2 adsorption, scanning electron microscopy, Boehm titration, potentiometric titration and Fourier transform infrared techniques. The highest surface area (588 m2/g) and total pore volume (0.19 cm3/g) were obtained at a carbonization temperature of 600 °C with an impregnation ratio of 1/1. We have found that the dependence of Cu2+ ions adsorption on their concentration in the solution on these carbons is adequately described by Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm equations. The analysis of kinetic data indicates that the adsorption process is described by equations of mixed diffusion kinetics (with some predominance of external diffusion) and equations of pseudo-first- and pseudo-second-order models. Sorption kinetics describe of the ions under study shows that the pseudo-second-order equation allows describing experimental data with higher correlation coefficients R2. Study of the effect of the concentration of phosphoric acid used for chemical activation on the texture and sorption properties of the resulting carbons showed that the optimal concentration of H3PO4 was 20%. In the present study the numerical value of adsorption of the mean free energy is 13.36 kJ mol −1 which corresponds to ion-exchange process. Quantum-chemical calculations show that oxygen-containing (carboxyl, phenolic, carbonyl) surface groups and various phosphorus-containing groups participate in adsorption of copper ions on the carbons under consideration.

This paper presents the results of a differential scanning calorimetry study of phase transitions in (1 − x)MNO3–xAl2O3 (M = Li, Na, K, Rb) composites. It was found that an additional stable high-temperature ferroelectric phase of potassium nitrate (phase III) is formed in KNO3–Al2O3 nanocomposites. Sharp decrease in enthalpies of phase transitions of salts, including melting enthalpies, was observed in the nitrates doped with Al2O3 nanoparticles. For the first time, the concept of the specific enthalpy of phase transitions of a salt in a composite is introduced, which is normalized to the salt concentration and specific surface area of the oxide and depends only on the nature of the contacting substances. The regularities of the change in the enthalpy of melting of (1 − x)MNO3–xAl2O3 versus the radius of alkali metal cation have been established.

Thermal, structural and electrical properties of composite solid electrolytes (1-x)(C4H9)(4)NBF4-xAl(2)O(3) with nanocrystalline gamma-alumina were investigated by DSC, X-ray diffraction, IR spectroscopy, impedance and electrochemical measurements. It was found that the melting enthalpy of (C4H9)(4)NBF4 in the composites strongly decreases and its value approaches to zero in the composites with x >= 0.9, where x is the molar fraction of alumina, indicating the transformation of (C4H9)(4)NBF4 to an interface-stabilized amorphous state. This effect was quantitatively interpreted in terms of the brick-wall model assuming that a layer of amorphous phase of the ionic salt is formed at salt/oxide interfaces. At the alumina concentration of x = 0.9, corresponding to a volume fraction of alumina f = 0.53, almost all the ionic salt gets into the interface layer the thickness of the amorphous layer is nearly 3 nm. These results agree with the results of X-ray diffraction studies and IR spectroscopy. Introduction of nanocrystalline gamma-alumina into the (C4H9)(4)NBF4 matrix leads to a relative increase in conductivity by more than 2 orders of magnitude, conductivity goes through a maximum of 0.21 mS/cm at 130 degrees C for the composite with x = 0.9. This composite is characterized by a non-Arrhenius temperature dependence, typical for glassy electrolytes. It was shown that the electrochemical voltage for the composite 0.1(C4H9)(4)NBF4-0.9Al(2)O(3) is nearly 4 V.

Thermal, structural and electrical properties of composite solid electrolytes (1-x)(C4H9)4NBF4–xAl2O3 with nanocrystalline γ-alumina were investigated by DSC, X-ray diffraction, IR spectroscopy, impedance and electrochemical measurements. It was found that the melting enthalpy of (C4H9)4NBF4 in the composites strongly decreases and its value approaches to zero in the composites with x ≥ 0.9, where x is the molar fraction of alumina, indicating the transformation of (C4H9)4NBF4 to an interface-stabilized amorphous state. This effect was quantitatively interpreted in terms of the brick-wall model assuming that a layer of amorphous phase of the ionic salt is formed at salt/oxide interfaces. At the alumina concentration of x = 0.9, corresponding to a volume fraction of alumina f = 0.53, almost all the ionic salt gets into the interface layer the thickness of the amorphous layer is nearly 3 nm. These results agree with the results of X-ray diffraction studies and IR spectroscopy. Introduction of nanocrystalline γ-alumina into the (C4H9)4NBF4 matrix leads to a relative increase in conductivity by more than 2 orders of magnitude, conductivity goes through a maximum of 0.21 mS/cm at 130 °C for the composite with x = 0.9. This composite is characterized by a non-Arrhenius temperature dependence, typical for glassy electrolytes. It was shown that the electrochemical voltage for the composite 0.1(C4H9)4NBF4–0.9Al2O3 is nearly 4 V.

The article presents the results of the preparation and study of a gel-polymer electrolyte based on lignin obtained from Pinus sylvestris. Sulfonation and subsequent chlorination of lignin make possible implementation of the principle of mono-ionic conductivity in a natural biopolymer matrix, which provides predominantly cationic conductivity of the electrolyte. Based on the results of the qualitative and quantitative analysis of the synthesized samples, the mechanisms of the chemical conversion of the biopolymer, the structure models of the converted fragments of macromolecules, as well as the quantum-chemical calculation of their electronic and geometric parameters are presented. The key electronic characteristics of the gel polymer electrolytes (GPE) based on a composite of lignins with 20 wt.% polyvinyl alcohol are determined by impedance spectroscopy. The maximum value of the specific volume conductivity is 2.48 × 10−4 S cm−1, which is comparable with most commercial electrolytes of this type, but at the same time, record values are reached in the number of lithium cation transfer tLi+ of 0.89. The studies allow to identify the basic laws of the effect of chemical modification on the structure of GPE and describe the mechanism of ionic conductivity.

The paper presents a comprehensive study of the Li0.42K0.58NO3- R (R = alpha-Al2O3, gamma-Al2O3, SiO2) and (LiNO3 - LiClO4) - gamma- Al2O3 composite salt systems by vibrational spectroscopy, X-ray diffractometry, and differential scanning calorimetry. According to the results of Raman spectra and XRD analysis, it has been found that in the case of a sufficiently small filler (15 nm-gamma-Al(2)O(3 )and SiO2), an amorphous phase appears, both for systems based on Li0.42K0.58NO3 and for the nanocomposite based on (LiNO3)(0.5)-(LiClO4)(0.5). In the case of nanocomposites based on the Li0.42K0.58NO3 system, this additionally leads to the formation of the metastable KNO3 (R3m) phase. The temperature changes in the half-widths of the corresponding bands of the Raman spectrum during the transition from a solid-phase to a molten state become less significant as the concentration of the oxide filler increases. At x >= 0.7, on the temperature dependences of the half-width of the v1 (A) band in the vicinity of the melting point, only a small kink characteristic of amorphous systems is noticed. This is confirmed by the results of thermal analysis. It has been found that the solid filler has a different effect on the processes of orientational and vibrational relaxation in the molten phases of the studied NIS, namely, the orientational mobility of NO3- decreases, while the relaxation rate of its vibrational excitation increases. (C) 2021 Elsevier B.V. All rights reserved.

The thermal effects and dielectric properties of a lithium-ion polymer electrolyte, namely, polyethylene glycol (PEG 1500)–lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), are studied for different molar fractions of salt in polymer by the methods of electrochemical impedance spectroscopy and differential thermal analysis. The complicated form of the “final” diffusion impedance of the PEG 1500‑LiTFSI electrolyte system may be associated with superposition of two processes that occur simultaneously in the solid electrolyte interphase (SEI) layer and at the boundary of the electric double layer (EDL) It is found that the obtained diffusion coefficients do not fit the Arrhenius model in describing the mechanism of transfer of lithium ions in the PEG polymer matrix. It is shown that as the concentration of LiTFSI in PEG 1500 increases, the time of dielectric relaxation decreases. It is assumed that in the PEG 1500–LiTFSI system, the increase in the ionic conductivity with the increase in the temperature up to 343 K proceeds due to wave fluctuations of the lithium ion and the movements of the PEG 1500 matrix.

The reasons leading to the asymmetry of the shape of the ν1(А1) contour of the nitrate ion in the spectra of lithium nitrate melts were analyzed. It was shown that the application of the Rothschild–Yao theory gives the best agreement between the calculated and experimental spectra. However, the physical meaning of some of parameters given in this theory is not clear. The asymmetry of shape of the vibration contour ν1(A1) of the nitrate ion for a lithium nitrate melt, can be caused by the inhomogeneity of local structure caused by different rates of dynamic interactions between the particles of system.