Aqueous Solutions Of Na Research Articles

Attosecond formation of charge-transfer-to-solvent states of aqueous ions probed using the core-hole-clock technique

Charge transfer between molecules lies at the heart of many chemical processes. Here, we focus on the ultrafast electron dynamics associated with the formation of charge-transfer-to-solvent (CTTS) states following X-ray absorption in aqueous solutions of Na+, Mg2+, and Al3+ ions. To explore the formation of such states in the aqueous phase, liquid-jet photoemission spectroscopy is employed. Using the core-hole-clock method, based on Auger–Meitner (AM) decay upon 1s excitation or ionization of the respective ions, upper limits are estimated for the metal-atom electron delocalization times to the neighboring water molecules. These delocalization processes represent the first steps in the formation of hydrated electrons, which are determined to take place on a timescale ranging from several hundred attoseconds (as) below the 1s ionization threshold to only 20 as far above the 1s ionization threshold. The decrease in the delocalization times as a function of the photon energy is continuous. This indicates that the excited electrons remain in the vicinity of the studied ions even above the ionization threshold, i.e., metal-ion electronic resonances associated with the CTTS state manifolds are formed. The three studied isoelectronic ions exhibit quantitative differences in their electron energetics and delocalization times, which are linked to the character of the respective excited states.

Nanoporosity and Isosteric Enthalpy of Adsorption of CH4, H2, and CO2 on Natural Chabazite and Exchanged

This paper describes the isosteric enthalpy through narrow pores at low levels of coverage through adsorption of CO2, CH4, and H2 on pores in natural chabazite exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, and with variable time and temperature of treatment. Experimental data of CO2, CH4, and H2 adsorption were treated by the Freundlich and Langmuir equations. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric enthalpy of adsorption. The exchange with Mg2+ and Na+ favors an increase in the adsorption capacity for CO2. while that of Ca2+ and Mg2+ favor adsorption through to H2 and CH4. These cations occupy sites in strategic positions S4 and S4’, which are located in the channels and nanocavities of these zeolites. The presence of Ca2+ and Mg2+ at S4 and S4′ sites causes increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. Depending on the conditions of the exchange treatment, Ca2+ and Mg2+, and Na+ were found to be most favorable, well distributed, and accessible for CO2, CH4, and H2 adsorption.

Performance modelling of zeolite-based potentiometric sensors

Developing simple and cost-effective electrochemical sensors for widespread on-site application is of considerable practical importance in agriculture, environmental monitoring and food science. Among multiple sensing platforms, potentiometry is particularly effective in terms of simplicity, low cost and mass-production. This work is focused on a systematic analysis of the structure – performance relationship using chemometric techniques, which can be applied to sensor arrays with varying response patterns. The potentiometric sensitivity of zeolite-modified electrodes, containing thirteen synthetic and three natural zeolites, in aqueous solutions of Na+, K+, NH4+, Ca2+ and Mg2+ has been correlated with a range of zeolite characteristics using PCA and PLS modelling, thus demonstrating how structural and physical properties impact the performance of zeolite-modified potentiometric sensors. In addition to steric factors, e.g. zeolite pore size, the important characteristics governing the sensor performance are the Si/Al ratio and the presence of specific extraframework cations. For instance, K+ and Na+ show a strong effect on the potentiometric sensitivity towards Ca2+. The level of precision achieved by the PLS models indicates that semi-quantitative predictions are feasible. To improve the computational models, larger sets of data with a wider range of zeolite-modified sensors are necessary. The constituent materials of such sensors should have a set of well-defined properties, which can be controlled and tuned for a particular application. It is anticipated that synthetic rather than natural zeolites would satisfy such requirements.

New nanostructured apatite-type (Na+,Zn2+,CO32−)-doped calcium phosphates: Preparation, mechanical properties and antibacterial activity

Nanoparticles with the sizes in the range (20–30) nm of apatite-type Na+,Zn2+,CO32−-doped calcium phosphates were prepared from aqueous solution of Na+-Ca2+-Zn2+-NO3−-CO32−-PO43- system at molar ratios Ca2+/PO43- =1.67, CО32−/РО43- = 1, Zn2+:Ca2+ = 1:100 or 2:100. The elemental analysis showed growth of Zn2+ content in composition of samples from 0.61 to 1.95 wt% at increasing of Zn2+ amount in an initial solution. According to FTIR and Raman data, B-type substitution of PO43− by CO32− realized in apatite-type calcium phosphates. The mechanical properties study for prepared phases showed the dependence of Young's modulus and compressive strength on Zn2+ amount in their composition. Growth of S. epidermidis after the contact with synthesized apatite containing Na+ (0.25 wt%), Zn2+ (0.61 wt%) and CO32− (1.18 wt%) was significantly delayed with an extension of lag time from 1 to 13–14 h. The prepared sample can be considered as a new prospective biomaterial with antibacterial potential.

Critical Admission Temperature of H₂ and CH₄ in Nanopores of Exchanged ERI Zeolites.

Due to the nanoporous nature of zeolitic materials, they can be used as gas adsorbents. This paper describes the effect of critical admission temperature through narrow pores of natural ERI zeolites at low levels of coverage. This phenomenon occurs by adsorption of CH4 and H2 on pores in natural erionite. The zeolite was exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, times, and temperatures of treatment. Experimental data of CH4 and H2 adsorption were treated by the Langmuir equation. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric heats of adsorption. The Ca2+ and Mg2+ cations favor the adsorption phenomena of H2 and CH4. These cations occupy sites in strategic positions Ca1, Ca2, and Ca3, which are located in the nanocavities of erionite zeolites and K2 in the center of 8MR. Following the conditions of temperature and the exchange treatment, ERICa2 and ERINa3 samples showed the best behavior for CH4 and H2 adsorption.

Characterization of Nax(Ca/Sr)1-2xNdxWO4 complex tungstates fine-grained ceramics obtained by Spark Plasma Sintering

Mineral-like matrix Nax(Ca/Sr)1-2xNdxWO4 (x = 0, 0.1 and 0.2) for radwaste is proposed. Powder samples of complex tungstates have been synthesized by coprecipitation from aqueous solutions of Na, Ca, Sr, Nd salts. Crystallographic characteristics of compounds have been calculated and a monotonous change observed in them along with some x value changes. Monophasic ceramics with high relative density (97–100%) from these powders have been obtained through Spark Plasma Sintering (SPS). SPS of tungstates has been shown to occur in multiple stages, with the sintering kinetics at the final stage of sealing controlled by diffusion both in the crystal lattice and along grain boundaries. Activation energies have been determined for sintering of tungstates at different x values. The reduced activation energy of sintering at the third heating stage (at high temperatures) could be ascribed to the grain growth.

Fluorescent Ag nanoclusters prepared in aqueous poly(acrylic acid-co-maleic acid) solutions: a spectroscopic study of their excited state dynamics, size and local environment.

Stable, fluorescent Ag nanoclusters were prepared in aqueous solutions of Na(+) salt of the carboxylate-rich polymer poly(acrylic acid-co-maleic acid) under brief spells of UV irradiation. The nanoclusters were nearly spherical, with diameters within 1.90 ± 0.50 nm, but displayed a prominent red edge excitation shift (REES) of fluorescence upon exciting within the visible absorption band, indicating heterogeneity of energy level distributions. Spectroscopic studies revealed that irrespective of whether the nanoclusters are excited in their UV or visible absorption bands, their fluorescence always ensues from the same manifold of emissive states, with a broad range of fluorescence lifetimes from ∼150 fs to 1 ns.

Structural changes in water exposed to electric fields: A molecular dynamics study

The aim of this contribution is to study the changes of structural and dynamic properties of water molecules exposed to electric fields, external ones or generated by ions. For this purpose a set of molecular dynamics simulations has been performed for a series of systems modeling aqueous electrolyte solutions and pure water. Two aqueous solutions of Na+ and UO22+ ions were considered. The systems presenting pure water were exposed to external fields of a different strength in the range E=(0.25÷2.5)×109V/m. The external fields within the studied range are able to slow down water molecules and even crystallize the system. The fields generated by the ions act rather locally but can induce the reorientation and even the hydrolysis of neighboring water molecules.

Solvation shell resolved THz spectra of simple aqua ions - distinct distance- and frequency-dependent contributions of solvation shells.

Hydration of ions is a topic of broad relevance in chemistry and biology. Liquid-state terahertz spectroscopy has been demonstrated to be able to detect even small solute-induced changes in the hydrogen bond network dynamics at the solute-water interface. Here, we apply ab initio molecular dynamics simulations to study the solvation of Na(+) and Cl(-) in bulk water in the context of their far-infrared responses. Spatial decomposition schemes for infrared spectra down to the THz regime reveal the importance of both dipolar couplings and correlations in particle motion in these aqueous solutions. The explicit representation of the electronic structure properly captures the solute-solvent polarization effects that are crucial for the interpretation of recent experimental data. This demonstrates that theoretical spectroscopy significantly complements experimental measurements and provides most detailed insights by selectively monitoring the spectral activity due to distinct hydration spheres.

CO2 Sequestration by Natural Zeolite for Greenhouse Effect Control

This paper describes the adsorption of CO2 on pores in natural erionite exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, variable time and temperature of treatment. Experimental data of CO2 adsorption were treated by the Freundlich and Langmuir equations. Complementarily were evaluated standard adsorption energies and the degree of interaction of the gas with the zeolite; the evolution of isosteric heats of adsorption was analyzed. The exchange with Na+ favors the creation of emergent pores thus causing an increase of the adsorption capacity for CO2. The presence of Na+ at micropore entrances causes an increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. The development of nanopores in erionite was evaluated through the Barrett-Joyner-Halenda and NLDFT methods. Depending on the conditions of the exchange treatment, Na+ was found to be most favorable, well distributed, and accessible for N2 adsorption.

Photocatalytic hydrogen evolution from aqueous solutions of Na2S/Na2SO3 under visible light irradiation on CuS/Cd0.3Zn0.7S and Ni Cd0.3Zn0.7S1+

• Ni- and Cu-doped Cd 0.3 Zn 0.7 S photocatalysts were synthesized. • 1 wt% CuS/Cd 0.3 Zn 0.7 S was 2-folder active than Cd 0.3 Zn 0.7 S photocatalyst. • Photocatalytic activity 3520 μmol H 2 per gram per hour was achieved. • A model of the hydrogen production from Na 2 S/Na 2 SO 3 was proposed. Noble-metal-free photocatalysts CuS/Cd 0.3 Zn 0.7 S and Ni z Cd 0.3 Zn 0.7 S 1 + z were prepared by a two-step technique. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy, low-temperature N 2 adsorption/desorption, X-ray photoelectron spectroscopy, and UV–vis spectroscopy. The photocatalytic activity was tested in a batch reactor in the hydrogen evolution from aqueous solutions of Na 2 S/Na 2 SO 3 under visible light irradiation ( λ > 420 nm). The activity of CuS/Cd 0.3 Zn 0.7 S photocatalysts was shown to exceed that of Ni z Cd 0.3 Zn 0.7 S 1+ z photocatalysts likely because of the hetero-junctions between CuS and Cd 0.3 Zn 0.7 S nanoparticles. The highest photocatalytic activity (3520 μmol g −1 h −1 ) was possessed by 1 mol% CuS/Cd 0.3 Zn 0.7 S. A model of the photocatalytic hydrogen production from aqueous solutions of Na 2 S/Na 2 SO 3 was proposed on the basis of the Langmuir–Hinshelwood mechanism.

Formation of hydrogen from oxidation of Mg, Mg alloys and mixture with Ni, Co, Cu and Fe in aqueous salt solutions

We have investigated the oxidation processes of Mg, Mg alloys with Ni, Co, Cu and powdered mixtures of these metals obtained from mechanical treatment of individual components in orbital mill, in aqueous solutions of alkali and alkaline earth metals. It was demonstrated that nearly stoichiometric amount of hydrogen in respect to Mg can be obtained at production rates of up to 640 mL/g min by oxidation of Mg–Co alloy or mechanically processed Mg–Co powder (“mechanical alloy”) in aqueous solutions of Na or K chlorides. Activator metals are not oxidized during this reaction. It is assumed that Mg oxidation is similar to the electrochemical corrosion process.

Transformations of [Au(CN)2]− at the contact with activated carbon surface

We have studied the processes occurring when alkaline aqueous solution of Na[Au(CN)2] is brought in contact with activated carbon surface. It has been shown that the adsorption of the gold cyanide complex occurs via several independent routes, one of them being accompanied with the partial breakdown of the inner sphere of the compound and free cyanide ions release into the solution. The latter process decreases the gold recovery by aqueous NaOH during the high-temperature (150°C) desorption. A prolonged storage of the adsorbent saturated with [Au(CN)2]− in air produces a similar result. The reasons of the observed phenomena have been discussed.

The thermal behavior of Na[Au(CN)2] and the gold(I) dicyanaurate complex adsorbed on the activated carbon surface

The thermal behavior of crystalline Na[Au(CN)2] and the gold(I) cyanide complex adsorbed from neutral aqueous solution of Na[Au(CN)2] by the WSC-207C GR charcoal pre-washed from inorganic impurities was studied. The adsorption was established to lead to a significant decrease in the thermal stability of dicyanoaurate(I) anion. Using electron microscopy it was established that at the heating the adsorbent with the adsorbed [Au(CN)2]-anions up to 300°C labile metallic gold nanoparticles were formed. Chemisorption nature of adsorption of the [Au(CN)2]-anion by the activated carbon was assumed, and the nature of sorption sites involved in the formation of the primary bonds of gold(I) with the surface of the sorbent was considered.

The carbonatation of gypsum: Pathways and pseudomorph formation

In this paper, we present an experimental study of the interaction between gypsum (010) surfaces and aqueous solutions of Na 2 CO 3 with different concentrations. This interaction leads to the carbonatation (i.e., the transformation into carbonate minerals) of gypsum crystals, which under ambient conditions shows the characteristics of a mineral replacement and leads to the formation of pseudomorphs consisting of an aggregate of calcite crystals. Carbonatation progress was monitored by scanning electron microscopy (SEM) and glancing incidence X-ray diffraction (GIXRD). The carbonatation advances from outside to inside the gypsum crystal and occurs through a sequence of reactions, which involves the dissolution of gypsum and the simultaneous crystallization of different polymorphs of CaCO 3 [amorphous calcium carbonate (ACC), vaterite, aragonite, and calcite], as well as several solvent-mediated transformations between these polymorphs. The sequence in which CaCO 3 phases form is interpreted taking into consideration nucleation kinetics and the qualitative evolution of several chemical parameters in the aqueous solution. The textural characteristics of the transformed regions are described. The degree of faithfulness of the pseudomorphs obtained is related to the kinetics of the carbonatation process, which in turn depends on the initial concentration of carbonate in the aqueous solutions. Finally, changes in the rate at which the transformation front advances are discussed on the basis of both textural and physicochemical considerations.

Colloid-chemical properties of sodium and calcium salts of α-alkyl-substituted dicarboxylic acids

Surface activity and micelle formation ability in aqueous solutions of Na and Ca salts of α-alkyl-substituted dicarboxylic acids was studied in relation to the length of the hydrocarbon radical, total length of the hydrocarbon chain of the molecule, and mutual position of carboxy groups. The results obtained are compared with properties of saturated monocarboxylic and unsaturated oleic acids.

Validation of the flux number as scaling parameter for top-spray fluidised bed systems

Top-spray fluidised bed coating scale-up experiments have been performed in three scales in order to test and validate the Akkermans flux number as possible scale-up parameter. Coating operations were performed on low porosity sodium sulphate cores ( 180 – 350 μ m ) coated with aqueous solutions of Na 2 SO 4 using Dextrin as binder in three top-spray fluidised bed scales, i.e. a small-scale (type: GEA Aeromatic-Fielder Strea-1), medium-scale (type: Niro MP-1) and large-scale (type: GEA MP-2/3). Following the parameter guidelines adapted from the original patent description, the flux number was tested in the preferred range of 3.5–4.5 as well as with a value of 4.7 in a total of 24 experiments. The agglomeration tendency was observed to decrease with increasing flux number on an overall basis, but coating conditions with flux number values below 4.5 resulted in a complete collapse of the bed. Coating conditions with flux number values of 4.5 and 4.7 were however successful in terms of agglomeration tendency and match of particle size fractions, but indicated in addition a strong influence of nozzle pressure. The present paper suggests even narrower boundaries for the flux number compared to the patent descriptions, and adds further new guidelines for the successful scale-up of top-spray fluidised bed coating systems in terms of the flux number.

Conversion of Azobenzenes into N,N′-Diarylhydrazines by Sodium Dithionite

A number of chloro-, methyl- and methoxy-substituted azobenzenes have been reduced to the corresponding hydrazines by using an aqueous solution of Na 2 S 2 O 4 . The yield is generally excellent, but two compounds, viz. 4,4-dimethoxyazobenzene and 2,2,4,4,6,6-hexamethylazobenzene, gave no hydrazine at all.

Hard-to-cook defect in trifoliate yam Dioscorea dumetorum tubers after harvest

In an attempt to study the hard-to-cook defect in Dioscorea dumetorum tubers after harvest, yellow cultivars of trifoliate yam tubers were stored under range of temperatures (15, 30, 45 °C ) and relative humidity (59%, 75%, 86% RH), and then soaked and cooked in distilled water or 5% (w/v) aqueous solution of Na 2 EDTA. The hard-to-cook defect was separated into reversible and irreversible components. Results of phytate and lignin analysis led to the conclusion that these components reflect the pectin-phytate mechanism or reversible hardening and the lignification mechanism or irreversible hardening. Modeling of the hardening process indicated that the rate of reversible and irreversible reaction was dependent on storage conditions, however, irreversible hardening rate was generally faster than reversible hardening and then represented the major component of D. dumetorum tubers hardening.

Disodium Guanosine 5‘-Monophosphate Self-Associates into Nanoscale Cylinders at pH 8: A Combined Diffusion NMR Spectroscopy and Dynamic Light Scattering Study

We report a combined NMR and dynamic light scattering (DLS) study on the size of supramolecular structures formed by disodium guanosine 5'-monophosphate, Na(2)(5'-GMP), at pH 8. In general, two distinct types of aggregate species are present in an aqueous solution of Na(2)(5'-GMP). One type consists of stacking 5'-GMP monomers, and the other contains stacking G-quartets. Both types of aggregates can be modeled as rodlike cylinders. The cylinder diameter is 10 and 26 A for monomer aggregates and quartet aggregates, respectively. For Na(2)(5'-GMP) concentrations between 18 and 34 wt %, the cylinders formed by stacking G-quartets have an average length between 8 and 30 nm, corresponding to a stack of approximately 24-87 G-quartets. These nanoscale aggregates are significantly larger than what had previously been believed for Na(2)(5'-GMP) self-association at pH 8. The length of both types of 5'-GMP aggregates was found to increase with Na(2)(5'-GMP) concentration but was insensitive to the added NaCl in solution. While the aggregate size for monomer aggregates increases with a decrease in temperature, the size of G-quartet aggregates is essentially independent of temperature. We found that the size of G-quartet aggregates is slightly larger in D(2)O than in H(2)O, whereas the size of monomer aggregates remains the same in D(2)O and in H(2)O. We observed a linear relationship between the axial ratio of the 5'-GMP cylinders and the Na(2)(5'-GMP) concentration for both types of 5'-GMP aggregates, which suggests a common stacking mechanism for monomers and G-quartets.