Solutions Of Alkali Metal Salts Research Articles

Neodymium sorption on the Na-form of Transcarpathian clinoptilolite

The sorption properties of Na-modified Ukrainian Transcarpathian clinoptilolite towards neodymium aqueous solutions under dynamic conditions have been investigated. The sorption capacity of the Na-from of Transcarpathian clinoptilolite towards Nd(III) significantly depends on the concentration of neodymium salt, the pH of the solution, and the heat treatment temperature of the sorbent. Nd(III) is most efficiently sorbed from slightly alkaline solutions (pH 8.5), mainly by adsorption of neutral hydrolyzed forms of Nd(OH)3 on the surface of Na-clinoptilolite samples preheated at 75 °C. During the passage of an Nd(III) solution with a concentration of 1 μg mL−1 through the sorbent at a rate of 3 mL min−1 under optimal conditions, the sorption capacity of Na-clinoptilolite is 7.2 mg g−1, which is in 4 and 2.3 times higher than that of natural and acid-modified forms of this zeolite. It is shown that under the experimental conditions with an increase in the flow rate, the thickness of the stationary surface layer decreases, which leads to a decrease in the sorption capacity of Na-clinoptilolite. The best Nd(III) desorbents are solutions of mineral acids and acidified solutions of alkali metal salts (except NaCl), which provide 93–98 % extraction of lanthanide from the zeolite matrix. The method for neodymium trace amounts preconcentration from aqueous solutions in a solid-phase extraction mode with a further determination of this rare earth element by a spectrophotometric method was developed. The detection limit of this method is 0.75 ng mL−1 and the linearity was evaluated in the range of 2.5–500 ng mL−1.

Expansion of Ion Effects on Water Induced by a High Hydrophilic Surface of a Polymer Network.

The spatial extent and anion-cation cooperativity of the ion effect on the structure and dynamics of water have long been debated but are still controversial. Previously, we experimentally demonstrated the extensive and cooperative effect of ions on water in a polyamide network by measuring the reflection wavelength (λ) on the ion sensor of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel-immobilized photonic crystals. In the present study, we investigated the influence of the polymer surface on the ion effect by adopting a highly hydrophilic poly(N-isopropylacrylamide-co-N-acryloylaza-18-crown-6) hydrogel as a sensor matrix. In alkaline earth metal salt solutions, the copolymer hydrogel membrane sensor showed the redshift of λ for the specific combination of cations and anions, that is, Ca2+/Cl- and Sr2+/NO3-, which resulted from the concerted binding of ion pairs to the copolymer receptor. In alkali metal salt solutions, the ion sensor showed the blueshift of λ originating from the osmotic dehydration suppressed by the salts. The strength of the ion effect was evaluated by the average osmotic pressure (ΠA) required for the salt-inhibited dehydration in the early stage of hydrogel contraction. From the calculation results of ΠA for the copolymer and PNIPAAm hydrogels, it was found that the high hydrophilic copolymer surface more significantly enhanced the ion effect of structure-making cations (i.e., Li+) compared with borderline (Na+) and structure-breaking (K+ and Cs+) cations. Furthermore, the ion effect exhibited the higher ion cooperativity in combination with chloride anions than with nitrate anions. The enhancement of the long-range cooperative ion effect is derived from the expansion of the interactions between ions, water molecules, and the hydrophilic polymer network.

Origins of Superlubricity Promoted by Hydrated Multivalent Ions.

Strong hydration repulsion exists between two negatively charged surfaces in the alkali metal salt solutions, together with the fluid response to the shear of hydration layers, leading to superlubricity. However, whether the multivalent ions can obtain superlubricity has not been revealed yet. Here, we evaluate the lubrication and adsorption properties of multivalent ions at different concentrations between Si3N4 and sapphire surfaces. The divalent and trivalent ions exhibit extremely low friction coefficients of 0.005-0.006 and 0.002-0.004, respectively, under contact pressures above 0.25 GPa, and three trivalent ions can achieve superlubricity at quite low sliding speeds (3.1 mm/s), which is a significant breakthrough for superlubricity under boundary lubrication. Moreover, compared with monovalent ions, divalent ions can reduce surface potential and lower surface charge density even further, and trivalent ions can neutralize the negatively charged ceramic surfaces and even lead to charge inversion due to excess adsorption of the cations, which ensures strong adsorption of hydrated multivalent ions on friction surfaces.

About changes in the physicochemical properties of aqueous solutions used as a liquid electrolyte cathode

The gas discharge between liquid electrolyte cathode and metal anode was experimentally investigated. Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, sodium hydroxide, and potassium hydroxide were used as the electrolyte cathode. Decrease aqueous solution was compensated by adding distilled water (solvent) in a continuous mode in the discharge burning process. It was found that, despite the significant dilution with a solvent, the specific electrical conductivity of aqueous solutions of alkali metal salts and alkalis varies slightly.

Numerical simulation of mixed lubrication considering surface forces

Abstract Mixed lubrication describes a lubrication regime where elastohydrodynamic lubrication and asperity contact coexist. Surface spacing is expected to be small during the interaction between nano-scale smooth surfaces. When alkali metal salt solution is applied as lubricant, short-range surface forces are incorporated into an existing model to simulate mixed lubricated non-conformal sliding contact. The new model is examined in a wide range of sliding velocities to demonstrate the effect of surface forces at different lubrication regime, from boundary lubrication to full film hydrodynamic lubrication. It is revealed that surface forces reduce friction coefficient particularly at mixed lubrication regime. Reduction of surface roughness improves contribution of surface forces and makes it easier to achieve superlubricity at low speed.

Evolution of Current–Voltage Characteristics and Surface Morphology of Homogeneous Anion-Exchange Membranes during the Electrodialysis Desalination of Alkali Metal Salt Solutions

Evolution of Current–Voltage Characteristics and Surface Morphology of Homogeneous Anion-Exchange Membranes during the Electrodialysis Desalination of Alkali Metal Salt Solutions

SOLUBILITY IN ALCOHOLS AND ALCOHOLYSIS REACTIONS OF CARBONATES, SULFIDES, CYANIDES, AND PHOSPHATES OF ALKALI METALS

The published data on the solubilities of lithium, sodium, potassium, rubidium and cesium carbonates; sodium bicarbonate; sodium sulphide; potassium and sodium cyanides; orthophosphates, hydro- and dihydroorthophosphates of potassium and sodium, as well as sodium pyrophosphate in methanol, ethanol, 2-propanol, 2-methyl-1-propanol, benzyl alcohol, ethylene glycol, methyl cellosolve and glycerol have been considered and collected. A little bit information for salts has been taken from the most common solubility handbooks, but most of data was selected from scientific articles. There is an acid-base equilibrium with the formation of the corresponding alcoholates in the systems "potassium or sodium carbonate/methanol, ethanol, ethylene glycol, ethylene glycol monomethyl ether", "sodium sulphide/methanol, ethanol, 2-propanol, 2-methyl-1-pro-panol, benzyl alcohol", "potassium cyanide/methanol, ethylene glycol, glycerol", "potassium or sodium orthophosphate/ethylene glycol", and "sodium pyrophosphate/ethylene glycol". The mechanism of the reaction of alcoholysis and the formation of alcoholates from the alkali metal salts and alcohols is based on the distribution of the components in phases. Analysis of all phases in the alcohol solutions of alkali metal salts proved the presence of an alcoholysis reaction in some salt/alcohol systems. The concentrations of dissolved salts in alcoholate-generating systems are significantly lower than those determined by the gravimetric method without taking into account the alcoholysis reaction and are considered in the common handbooks "solubilities of the corresponding salts in alcohols". A classification of inorganic alkali metal salts reacting with alcohols in the alcoholysis reaction has been proposed. The analysis of literature data showed that along hydroxides and alkali metal salts, the hydrides, organometallic compounds, acetylenides, nitrides, amides (including alkyl amides) as well as azides can react with alcohols to form alkoxides by alcoholysis reaction. Alcoholysis of salts can be considered as a promising method for the production of alkali metal alkoxides in which the salt is used instead of metal or hydroxide.

Quartz/Aqueous Electrolyte Solution Interface: Molecular Dynamic Simulation and Interfacial Potential Measurements

In this complementary experimental and theoretical study, we employ surface and electrokinetic potential measurements and equilibrium molecular dynamics (MD) techniques to study the electrical interfacial layer between aqueous solutions of electrolytes and an oxide solid surface. More specifically, we investigate the behavior of a prototypical model system consisting of the (0001) quartz surface in contact with aqueous solutions of alkali metal salts under different conditions. The inner surface potential and electrokinetic ζ-potential were measured by means of single crystal electrodes and via streaming current measurements, respectively. Calculated ζ-potentials allowed us to benchmark MD simulations against experiments, thereby, on the one hand, verifying the validity of our strategy and, on the other hand, enabling a detailed molecular picture of the investigated phenomena and elucidating the role of both water and ions in the formation of the multilayered quartz/aqueous electrolyte interface.

Dielectric spectroscopy of nanocomposites based on iPP and aPS treated in the water solutions of alkali metal salts

In this paper, a new simple and environmentally friendly treatment technique for obtaining polymer nanocomposites with appropriate dielectric properties has been presented. Sheets of isotactic polypropylene and atactic polystyrene were immersed in 3 saturated water solutions of alkali metal salts (LiCl, NaCl, and KCl) at 2 fixed temperatures (23°C and 90°C), and 3 DC electrical potentials (+4 kV, −4 kV, and ground potential) were applied. A quantification of alkali metals in the polymer sheets was conducted by inductively coupled plasma optic emission spectrometry. The obtained concentration values were from 7.38·10−9 mol/cm3 to 1.25·10−7 mol/cm3. The qualitative analysis of potassium distribution in the polymer matrix was conducted by time‐of‐flight secondary ion mass spectrometry cross‐sectional record. The relative dielectric constant (ε′) of samples was investigated in the frequency range from 20 Hz to 9 MHz at the constant temperature of 22°C. Stable values of ε′ in fully measured frequency range were observed for both pure and treated samples. Next, the results of the dielectric spectroscopy measurements were compared and established the kind of treatment that provided the highest value of ε′. The relationship between the concentrations of alkali metals and the values of relative dielectric constant was determined for the samples obtained by a treatment at 90°C and +4 kV.

Superheated solutions in dual-temperature ion exchange separations

The problem of experimental determination of the differential enthalpy of ion exchange is considered. The determination of the enthalpy from experimental equilibrium coefficients is characterized by a high degree of error. A considerably more accurate method of determination of the differential enthalpy of ion exchange on selective ion exchangers is proposed. The method is based on the analysis only of the composition of the solution in the equilibrium system at two temperatures. The influence of temperature on the exchange of mono- and divalent ions on polyacrylic and polymethacrylic cation exchangers within the range from 273K to 400K is studied. It is shown than for all exchangers under study the differential enthalpy linearly increases with temperature. The role of the increase of ΔHn¯ with temperature in the process of a single-step dual-temperature separation is estimated. It is found that the increase of the upper temperature boundary leads to a very sharp increase of the degree of dual-temperature separation. This effect is most pronounced in superheated solutions. It is shown that when predicting changes in selectivity with temperature and the extent of purification of solutions of alkali metal salts from admixtures of divalent ions, it is necessary to take the temperature dependence of the ion exchange enthalpy into account.

Association of bromate ion in nonaqueous solutions of alkali metal salts

Manifestations of ion association of lithium cation with BrO3 - ion in the vibrational spectrum have been studied by IR spectroscopy. The microstructure of the bromate ion with lithium cation in a contact ion pair in an aprotic solvent has been determined by the density functional theory method in the B3LYP/cc-pVTZ approximation, and the vibrational spectrum of coordinated bromate ion has been calculated.

Supramolecular Isoguanosine Assemblies Form Hydrogels with Excellent Long-Term Stability.

Supramolecular nucleoside-based hydrogels have the potential to be utilized in drug delivery, regenerative medicine and for the construction of nanoscopic devices. Isoguanosine, its 2'-deoxyribonucleoside and the 2'-deoxy-2'-fluororibonucleoside form hydrogels in alkali metal salt solutions. Gel stability depends on the metal ions used (Li+ , Na+ , K+ , Rb+ , Cs+ ). All isoguanosine gels show long-term stability of several months, whereas guanosine gels collapse within minutes or hours. Rheological data confirm a 15 times higher hydrogel stability for isoguanosine compared to guanosine. Isoguanosine gel stability covers a broad pH range (pH 3-10), and the stability at physiological Na+ ion concentration is striking. SEM images reveal that isoguanosine self-assembles into helical stacked fibers that are interconnected whereas guanosine forms discrete ribbons. Moreover, isoguanosine gels display excellent loading and release ability for small molecules.

Ionic diffusion and proton transfer in aqueous solutions of alkali metal salts

We report on a series of ab initio molecular dynamics investigations on LiCl, NaCl, and KCl aqueous solutions under the effect of static electric fields. We have found that although in low-to-moderate field intensity regimes the well-known sequence of cationic mobilities μ(K+) > μ(Na+) > μ(Li+) (i.e., the bigger the cation the higher the mobility) is recovered, from intense field strengths this intuitive rule is no longer verified. In fact, field-induced water molecular dissociations lead to more complex phenomena regulating the standard migration properties of the simplest monovalent cations. The water dissociation threshold is lowered from 0.35 V Å-1 to 0.25 V Å-1 by the presence of charged species in all samples. However, notwithstanding a one-stage process of water ionization and proton conduction takes place at 0.25 V Å-1 in the electrolyte solutions where "structure maker" cations are present (i.e., LiCl and NaCl), the KCl aqueous solution shows some hindrance in establishing a proton conductive regime, which is characterized by the same proton conduction threshold of neat water (i.e., 0.35 V Å-1). In addition, it turns out that protons flow easily in the LiCl (σp = 3.0 S cm-1) solution and then - in descending order - in the NaCl (σp = 2.5 S cm-1) and KCl (σp = 2.3 S cm-1) electrolyte solutions. The protonic conduction efficiency is thus inversely proportional to the ionic radii of the cations present in the samples. Moreover, Cl- anions act as a sort of "protonic well" for high field intensities, further lowering the overall proton transfer efficiency of the aqueous solutions. As a consequence, all the recorded protonic conductivities are lower than that for neat water (σp = 7.8 S cm-1), which strongly indicates that devices exploiting the proton transfer ability should be designed so as to minimize the presence of ionic impurities.

Chemical-spectroscopic determination of impurity elements in concentrated salt products from pyrochemical reprocessing of spent nuclear fuel

A procedure was developed for separating fission products and impurity elements from concentrated solutions of alkali metal salts by precipitation of carbonates for their subsequent determination by atomic emission spectroscopy. Coprecipitation of Cr, Al, Pb, Fe, Ni, Mo, Cu, Ca, Mg, Eu, Sm, and Gd with various collectors (Zn, Ga, Bi, In, Sc, Sr, Y, Cd) on introducing potassium carbonate into aqueous solutions of potassium sulfate, hydrosulfate, chloride, and nitrate with the salt concentration of 25 to 250 g dm–3 was studied. The optimum composition of the coprecipitants and the precipitation conditions were determined by methods of mathematical experiment design. The procedure developed is applicable to solutions of alkali metal sulfates, chlorides, and nitrates.

Transport properties and ion binding in aqueous solutions of alkali metal salts of poly(thiophen-3-ylacetic acid)

Aqueous solutions of poly(thiophen-3-ylacetic acid) neutralized with LiOH, NaOH, and CsOH were for the first time investigated using conductivity measurements (in concentrations, c, ranging from 2·10−5 to 8·10−2mol/dm3 and temperatures from 278.15 to 313.15K), transport number measurements (at 298.15K) and osmotic coefficient measurements using vapor pressure osmometry (at 313.15K) and cryoscopy, in order to identify essential electrochemical characteristics of this conjugated polyelectrolyte. The measurements of the polyion constituent transport number data suggested that a fraction of counterions traveled associated with polyions. The fraction of “free” counterions, determined from the transport measurements by the association theory of Huizenga, Grieger, and Wall was around 0.5, which is in good agreement with the osmotic coefficient data. Neither the fraction of “free” counterions, nor the osmotic coefficient significantly depends on the nature of the counterion species. The results obtained were analyzed in terms of the Poisson–Boltzmann theory, Manning's condensation approach, and modern scaling theory. Good agreement between the theoretical results and the fraction of “free” counterions, determined from the combination of the transport number and conductivity measurements, was obtained. The osmotic coefficients were well reproduced by the Poisson–Boltzmann cell model theory.

Catalytic decomposition of N2O over potassium-modified Cu-Co spinel oxides

Cu-Co spinel oxides with different compositions were prepared for N2O catalytic decomposition in the presence of oxygen. The active catalyst of Cu0.8Co0.2Co2O4 was incipiently impregnated by alkali metal salt solutions to prepare the modified catalysts. These catalysts were characterized by BET, XRD, SEM and XPS techniques, and their catalytic activity for N2O decomposition was tested. The effect of alkali metal species, potassium precursors and potassium loadings on catalytic activity was investigated. It was found that the catalytic activity of Cu0.8Co0.2Co2O4 modified by K2CO3 was much higher than that of bare oxide, while Cs/Cu0.8Co0.2Co2O4 was inferior to Cu0.8Co0.2Co2O4 for N2O decomposition. In the case of K/Cu0.8Co0.2Co2O4 with different potassium precursors, the catalyst activity was largely enhanced by the addition of K2CO3, while the doping of KNO3 and CH3COOK notably depressed the catalytic activity. Over the optimal catalyst of 0.05K/Cu0.8Co0.2Co2O4, 100% and 87.6% conversion of N2O was reached at 400 °C under the atmosphere of oxygen only and oxygen-steam together, respectively. In addition, K2CO3-modified catalyst in both reaction atmospheres showed higher stability than un-modified catalyst.

Concentrated solutions of individualized single walled carbon nanotubes

Solutions of alkali metal salts of single-walled carbon nanotubes (SWNTs) show individualization of the nanotubes without sonication-induced shortening. Bundles are fully exfoliated and length measurements show mean length over one micron, a rare case for liquid formulation of SWNTs. These concentrated solutions of individualized nanotubes in organic solvents can be freeze dried leading to ultralight, highly porous, conducting and mechanically stable carbon nanotube cryogels.

Potential for Using Simple 1,2,4-Triazole Salt Solutions as Highly Efficient CO2 Absorbents with Low Reaction Enthalpies

Simple solutions of alkali metal salts of 1,2,4-triazole (TrizM) in polyethyelene glycol (PEG) and dimethylsulfoxide (DMSO) were prepared and assessed for CO2 capture. These aprotic heterocyclic anions (AHAs) containing solutions exhibit excellent CO2 capture performances. The TrizM salts absorb CO2 chemically in a 1:1 stoichiometry. What is more attractive is that the CO2 chemical absorption enthalpies are as low as −33 ∼ −21 kJ mol–1, close to that of physical absorption by traditional ionic liquids (ILs). This makes regeneration of the absorbents highly energy-saving. The TrizM-PEG solution has a steady CO2 capture performance due to the nonvolatility of PEG, and therefore, it is durable for CO2 capture. In comparison, the TrizM-DMSO solution has a higher absorption capacity (120 mg/g solution) because of the higher solubility of TrizM. Such simple and inexpensive solutions show new potential as promising candidates for highly efficient, energy-saving, and economical CO2 catchers.

Effect of Alkali Metal Ions on the Dissociation of Glycine Pentapeptide in the Gas Phase

To obtain more structural information of polypeptides,glycine pentapeptide(simplified as GGGGG or G5)was chosen as a model to investigate the impact of alkali metal ions on the dissociation of GGGGG in the gas phase.Stoichiometric G5 and alkali metal salt solutions,including Li+ ,Na+ ,K+ ,Rb+ , were mixed,respectively,and then the solutions were left to stand at room temperature for 10 h to reach equilibrium.The mass spectrometric results indicated that the alkali metal ions and G5 could form 1:1 or 2: 1 non-covalent complexes in solution.The energy of the collision induced dissociation(CID)was 25 eV. The gas phase CID results demonstrate that in the 1:1 complexes,the extent of fragmentation decreases according to the order:Li+ ,Na+ ,K+ ,Rb+ .Moreover,the unusual c,z ions were observed in the Rb + complex. In the 2:1 non-covalent complexes,the extent of fragmentation increases according to the order:Li+ ,Na+ , K+ ,Rb+ .The gas phase dissociation of the Na+ ,K+ ,Rb+ 2:1 complexes are easier than their 1:1 complexes. Except for Li+ ,the activation abilities of the double metal ions to G5 are stronger than that of the single metal ion to G5,which can induce more dissection sites in the glycine pentapeptide and lead to the formation of more kinds of fragment ions.

Reversible Insertion of a Trivalent Cation onto MnO2 Leading to Enhanced Capacitance

Supercapacitor properties of MnO2 are studied generally in aqueous alkali metal salt solutions, often in a Na salt solution. During electrochemical discharge-charge processes, Na+ ions from the electrolyte get reversibly inserted/deinserted on the surface of MnO2 particles, which leads to redox reaction between MnOONa and MnO2. In the present study, it has been shown that MnO2 exhibits enhanced capacitance behaviour in a rare earth metal salt solution, namely, La(NO3)3 solution in comparison with NaNO3 and Mg(NO3)2 aqueous solutions. The specific capacitance increases with an increase in charge on the solution cation (Na+, Mg2+ and La3+). It is proposed that the number of surface sites for adsorption of cations remains unaltered in all solutions. The surface insertion of cation facilitates the reduction of Mn4+ in MnO2 to Mn3+ equivalent to the charge present on the cation. As the specific capacitance is related to the quantity of charge that is exchanged between the solid MnO2 and the aqueous solution, the trivalent cation (La3+) provides greater specific capacitance than in Mg(NO3)2 and NaNO3 electrolytes. Accordingly, the number of Mn(IV)/Mn(III) redox pairs involved in the neighbourhood of the adsorption site is one, two and three when Na+, Mg2+ and La3+ ions, respectively, are adsorbed.