Aqueous Salt Solutions Research Articles

Interplay of interactions in nanoparticle–surfactant complexes in aqueous salt solution

The evolution of phase behavior and interactions in anionic silica nanoparticles (Ludox HS40), surfactants [non-ionic decaethylene glycol mono-dodecyl ether (C12E10) and anionic sodium dodecyl sulfate (SDS)], and nanoparticle–surfactant solutions in the presence of salt (NaCl) has been studied using small-angle neutron scattering and dynamic light scattering. In an anionic silica nanoparticle solution (1 wt. %), the phase behavior is controlled by salt concentrations (0–1 M) through screening electrostatic interactions. In the case of 1 wt. % surfactant solutions, the anionic SDS surfactant micelles show significant growth upon adding salt, whereas non-ionic surfactant C12E10 micelles remain spherical until a high salt concentration (1 M). In the mixed system of HS40–C12E10, a transition from a highly stable transparent phase to a two-phase turbid system is observed with a small amount of salt addition CS* (∼0.06 M). The single transparent phase of this system corresponds to sterically stabilized micelles-decorated nanoparticles. For the turbid phase, the results are understood in terms of depletion attraction induced by non-adsorption of C12E10 micelles, which explains the appearance of turbidity at a much lower concentration of salt. In the mixed system of similarly charged nanoparticles and micelles (HS40-SDS), the phase behavior is governed by no physical interaction between the components, and salt screens the repulsive interaction among nanoparticles. These results are further utilized to tune multicomponent interactions and phase behavior of nanoparticles with a mixed C12E10-SDS surfactant system in the presence of salt. The mixed surfactants provide tuning of nanoparticle–micelle as well as micelle–micelle interactions to dictate the phase behavior of a nanoparticle–surfactant solution. In these systems, the effective potential can be described by double-Yukawa potential taking account of attractive and repulsive parts at low and intermediate salt concentrations (<CS*). At high salt concentrations (>CS*), the aggregation of nanoparticles is characterized by fractal aggregates.

Thermodynamic modeling of aqueous lithium salt solutions with association electrolyte nonrandom two-liquid activity coefficient model

The high charge density of lithium ion and the resulting strong association phenomena make thermodynamic modeling of aqueous lithium electrolyte solutions extremely challenging. In this study, the association electrolyte nonrandom two-liquid activity coefficient model of Lin et al. (AIChE J. 2022, 68(2), e17422) is utilized to correlate and predict thermodynamic properties and solubility behavior of aqueous single electrolyte solutions of LiCl, LiBr, LiI, and LiNO3, and their mixed electrolyte solutions. Capturing self-association of water, cross-association of ion and water for hydration, and cross-association of cation and anion for ion-pairing, the association model accurately represents the literature experimental data up to saturation concentrations and at the temperature ranging from 263 K to 523 K. This study further investigated the effect of anions of the lithium salts, and re-confirmed that the order of solution non-ideality as LiI > LiBr > LiCl > LiNO3 because the anions with stronger association strengths are more likely to form ion pairs and thus lower the mean ionic activity coefficients.

Three-electrode cell calorimeter for electrical double layer capacitors.

A calorimeter was built to measure the heat from a porous capacitive working electrode connected in a three-electrode configuration. This makes it possible to detect differences between cathodic and anodic heat production. The electrochemical cell contains a large electrolyte solution reservoir, ensuring a constant concentration of the salt solution probed by the reference electrode via a Luggin tube. A heat flux sensor is used to detect the heat, and its calibration as a gauge of the total amount of heat produced by the electrode is done based on the net electrical work performed on the working electrode during a full charging-discharging cycle. In principle, from the measured heat and the electrical work, the change in the internal energy of the working electrode can be determined as a function of the applied potential. Such measurements inform about the potential energy and average electric potential of ions inside the pores, giving insight into the electrical double layer inside electrode micropores. Example measurements of the heat are shown for porous carbon electrodes in an aqueous salt solution.

Investigation of Cu2+ Desorption from Phosphorylated Lignocellulosic Sorbent in Aqueous Solutions of Acids, Salts, and Complex Formation Agents

Investigation of Cu2+ Desorption from Phosphorylated Lignocellulosic Sorbent in Aqueous Solutions of Acids, Salts, and Complex Formation Agents

Osmotic dehydration of wild garlic in sucrose–salt solution

Abstract Due to its nutritional and nutraceutical qualities, wild garlic (Allium ursinum L.) has great potential for use in the food and pharmaceutical industries. The availability of this plant is limited to the spring season, and it is perishable immediately after harvest. Osmotic dehydration (OD) is verified as an effective pre-treatment to improve sustainability by reducing the water content of raw material with minimal negative effect on its nutritive and sensorial qualities. In this study, OD of wild garlic leaves in aqueous solution of sucrose and salt was analysed at three temperatures and after diverse immersion times. The effects of the processing time and temperature on the dry matter content, water loss, and solid gain were evaluated using response surface methodology and analysis of variance. Some components in the samples were determined before and after OD. The results showed that during OD, the dry matter content of wild garlic increased from 7.91 ± 1.08% to 51.51 ± 1.34%. The maximum achieved values for water loss (0.6189 ± 0.0146 g/g i.s.) and solid gain (0.2417 ± 0.0146 g/g i.s.) indicated a good dehydration level. In the osmotically dehydrated wild garlic, the amount of analysed minerals decreased, sodium and sugar increased, and the content of protein, cellulose, and fat did not change – compared to the fresh sample.

Continuous Flow Synthesis of Cd1-x Znx S and CdS/ZnS Core/Shell Semiconductor Nanoparticles by MicroJet Reactor Technology.

From aqueous precursor solutions of metal salts and sodium sulfide using MicroJet Reactor (MJR) technology Cd1-x Znx S and CdS/ZnS core/shell semiconductor nanoparticles were synthesized. The MJR approach represents an automated, continuous, flexible and scalable route for nanoparticle synthesis, providing a tight control over process parameters and thus simple size, shape and composition control. Since particle sizes below the excitonic Bohr radius were obtained by MJR, the nanoparticulate materials exhibit quantum confinement effects. By varying the precursor ratio the band gap of Cd1-x Znx S Quantum Dots (QDs) could be targeted from 3.1 to 3.6 eV. CdS/ZnS core/shell QDs were prepared by enclosing CdS particles from MJR with ZnS produced by thermal decomposition of a Zn-MPA complex. Adjustment of the shell thickness increased the photoluminescence intensity by 43 %. Synthesis of ternary sulfides in the form of core/shell particles broadens the spectrum of materials accessible by MJR and demonstrates the extraordinary flexibility of the technology.

Distinct behaviors of KNO3 and NaNO3 in specific heat enhancement of molten salt nanofluid

This study aims to examine the effects of the solvent of molten salt nanofluids on the specific heat capacity (SHC) and furthermore to understand the mechanism for enhanced SHC of the nanofluids. Moreover, the effects of the electrical double layer (EDL) on the SHC enhancement were quantitatively analyzed for a single salt and binary salt-based nanofluids. Two different nanoparticles, SiO2 and graphite, were dispersed in sodium nitrate (NaNO3), potassium nitrate (KNO3) and NaNO3-KNO3 mixtures. The SHC of the nanofluids was experimentally measured by a differential scanning calorimetry. The SHC of the NaNO3-SiO2 nanofluids was increased up to 17.2 % in liquid phase, whereas the SHC enhancements of the binary salt-SiO2 nanofluids were varied between-1.2 and 8.2 % in liquid phase. Additionally, the SHC enhancement was unfavorably proportional to the mass ratio of NaNO3 in the binary salt-SiO2 nanofluids. In graphite nanofluids, the SHC was enhanced up to 20.1 % and 7.1 % in KNO3 and NaNO3, respectively. However, the enhancement in the SHC was <7.8 % in the binary salt-graphite nanofluids. The zeta potentials of the SiO2 nanoparticle in the aqueous salt solution were linearly increased with the composition of NaNO3 which can be correlated with the salt solvent dependent SHC in the binary salt nanofluid. Finally, the EDL analysis indicates that SiO2 nanoparticles have stronger attractive force in ionic solutions than graphite. Furthermore, the EDL interactive forces demonstrate that the potential energy in the EDL adjacent to the nanoparticles determines the SHC enhancement of the molten salt nanofluids. KeywordsNanofluidSpecific heatMolten saltZeta potentialElectric double layerInteraction potential energy

Enhanced Acetaminophen Electrochemical Sensing Based on Nitrogen-Doped Graphene.

Because of the widespread acetaminophen usage and the danger of harmful overdosing effects, developing appropriate procedures for its quantitative and qualitative assay has always been an intriguing and fascinating problem. A quick, inexpensive, and environmentally friendly approach based on direct voltage anodic graphite rod exfoliation in the presence of inorganic salt aqueous solution ((NH4)2SO4-0.3 M) has been established for the preparation of nitrogen-doped graphene (exf-NGr). The XRD analysis shows that the working material appears as a mixture of few (76.43%) and multi-layers (23.57%) of N-doped graphenes. From XPS, the C/O ratio was calculated to be 0.39, indicating a significant number of structural defects and the existence of multiple oxygen-containing groups at the surface of graphene sheets caused by heteroatom doping. Furthermore, the electrochemical performances of glassy carbon electrodes (GCEs) modified with exf-NGr for acetaminophen (AMP) detection and quantification have been assessed. The exf-NGr/GCE-modified electrode shows excellent reproducibility, stability, and anti-interfering characteristics with improved electrocatalytic activity over a wide detection range (0.1-100 µM), with a low limit for AMP detection (LOD = 3.03 nM). In addition, the developed sensor has been successfully applied in real sample analysis for the AMP quantification from different commercially available pharmaceutical formulations.

Atmospheric Pressure Plasma-Treated Polyurethane Foam as Reusable Absorbent for Removal of Oils and Organic Solvents from Water.

This paper reports the optimization of a two-step atmospheric pressure plasma process to modify the surface properties of a polyurethane (PU) foam and, specifically, to prepare a superhydrophobic/superoleophilic absorbent for the removal of oils and nonpolar organic solvents from water. In particular, in the first step, an oxygen-containing dielectric barrier discharge (DBD) is used to induce the etching/nanotexturing of the foam surfaces; in the second step, an ethylene-containing DBD enables uniform overcoating with a low-surface-energy hydrocarbon polymer film. The combination of surface nanostructuring and low surface energy ultimately leads to simultaneous superhydrophobic and superoleophilic wetting properties. X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurements are used for the characterization of the samples. The plasma-treated PU foam selectively absorbs various kinds of hydrocarbon-based liquids (i.e., hydrocarbon solvents, mineral oils, motor oil, diesel and gasoline) up to 23 times its own weight, while it completely repels water. These absorption performances are maintained even after 50 absorption/desorption cycles and after immersion in hot water as well as acidic, basic and salt aqueous solutions. The plasma-treated foam can remove mineral oil while floating on the surface of mineral oil/water mixtures with a separation efficiency greater than 99%, which remains unaltered after 20 separation cycles.

Ultrasonic Investigation of Thermodynamic and Electrochemical Properties of Aqueous Solutions of Ammonium Salts and Comparative Study Among the Chosen Salts

Ultrasonic Investigation of Thermodynamic and Electrochemical Properties of Aqueous Solutions of Ammonium Salts and Comparative Study Among the Chosen Salts

Conductometric and Fluorescence Probe Analysis to Investigate the Interaction between Bioactive Peptide and Bile Salts: A Micellar State Study.

The present work deals with the micellar state study of sodium cholate and sodium deoxycholate in the aqueous solution of a bioactive peptide, namely glycyl dipeptide, having different concentrations through conductivity and fluorescence methods at different temperatures. The data obtained from conductivity is plotted against the concentration of Bile salts, and CMC (critical micelle concentration) values are calculated. The results realized have been elucidated with reference to Glycyl dipeptide-bile salts hydrophobic/hydrophilic interactions existing in solution. In addition, the CMC values converted to mole fraction (Xcmc) values have been used to evaluate the standard thermodynamic factors of micellization viz., enthalpy H, free energy ΔGm0, and entropy (ΔSm0) which extract information regarding thermodynamic feasibility of micellar state, energy alteration, and the assorted interactions established in the existing (bile salts-water-glycyl dipeptide) system. Furthermore, the pyrene fluorescence spectrum has also been utilized to study the change in micro polarity induced by the interactions of bile salts with glycyl dipeptide and the aggregation action of bile salts. The decrease in modification in the ratio of intensities of first and third peaks i.e., (I1/I3) for the pyrene molecules in aqueous bile salts solution by the addition of dipeptide, demonstrates that the micelle polarity is affected by glycyl dipeptide. This ratio has also been utilized to determine CMC values for the studied system, and the results have been found to be in good correlation with observations made in conductivity studies.

Palladium Nanoparticles Entrapped In a Hydrogen Bonded Crystalline Organic Salt Matrix as a Selective Heterogeneous Reduction Catalyst

Hydrogen bonded crystalline organic salt matrix encapsulates Pd nanoparticles and makes them selective non-pyrophoric catalysts towards reduction of carbon – carbon triple bonds, inhibiting simultaneous C=O reduction. The comparison of the catalytic performance with Pd/C was carried out to show similar catalytic activity of both catalysts towards C=C bonds.

Electric Potential of Ions in Electrode Micropores Deduced from Calorimetry.

The internal energy of capacitive porous carbon electrodes was determined experimentally as a function of applied potential in aqueous salt solutions. Both the electrical work and produced heat were measured. The potential dependence of the internal energy is explained in terms of two contributions, namely the field energy of a dielectric layer of water molecules at the surface and the potential energy of ions in the pores. The average electric potential of the ions is deduced, and its dependence on the type of salt suggests that the hydration strength limits how closely ions can approach the surface.

Prediction of single salt rejection in PES/CMS based membranes

This study explains the modeling of synthesized membranes using the Donnan Steric Pore model (DSPM) based on the Extended Nernst Planck Equation (ENP). Conventionally, structural parameters required to predict the performance of the membranes were determined through tedious experimentation, which in this study are found using a new MATLAB technique. A MATLAB program is used to determine the unknown structural parameters such as effective charge density (Xd), effective pore radius (rp), and effective membrane thickness to porosity ratio (Δx/Ak) by using the single solute rejection and permeation data. It was found that the model predicted the rejection of studied membranes accurately, with the E5C1 membrane exceeding the others (E5, E5C5) for rejection of single and divalent salt's aqueous solutions. The rejection of 100 ppm aqueous solution of NaCl for E5C1 was around 60%, whereas, for an aqueous solution of 100 ppm, CaCl2 rejection reached up to 80% at 10 bar feed pressure. The trend of salt rejection for all three membranes was found to be in the following order: E5C1 > E5C5 > E5, confirming that their structural parameters-controlled ion transport in these membranes. The structural parameters, such as effective pore radius, effective membrane thickness to porosity ratio, and effective charge density for the best performing membrane, i.e., E5C1, were determined to be 0.5 nm, 16 μm, and −6.04 mol/m3,respectively. Finally, it can be asserted that this method can be used to predict the real performance of membranes by significantly reducing the number of experiments previously required for the predictive modeling of nanofiltration-type membranes.

Effect of dry salt versus brine injection plus dry salt on the physicochemical characteristics of smoked salmon after filleting

Smoked fish fillets are pre-salted as a food conservation and quality preservation measure. Here we investigated biochemical and sensory aspects of smoked salmon fillets. Left-side salmon fillets were dry-salted while the right-side fillets underwent a mixed salting method consisting of an injection of saturated brine followed by surface application of dry salt. After 6 h of salting, all the fillets were smoked. At each step of the process, quality was evaluated using instrumental measurements (pH, color, texture, water content, salt content, aw), and lipid distribution was visualized by MRI. Mixed-salted fillets had a higher salt content than dry-salted fillets and variability in salt distribution was dependent on the salting process. However, these variations had no effect on pH, color or texture, which showed similar values regardless of salting method. Fatty areas had a lower salt content due to slower diffusion of aqueous salt solutions through them. Mixed salting speeds up the salting of the muscle without significantly affecting the quality traits of the salmon fillet.

Impact of Ion-Ion Correlated Motion on Salt Transport in Solvated Ion Exchange Membranes.

The influence of dynamical ion-ion correlations and ion pairing on salt transport in ion exchange membranes remain poorly understood. In this study, we use the framework of Onsager transport coefficients within atomistic molecular dynamics simulations to study the impact of ion-ion correlated motion on salt transport in hydrated polystyrene sulfonate membranes and compare with the results from aqueous salt solutions. At sufficiently high salt concentrations, cation-anion dynamical correlations exert a significant influence on both salt diffusivities and conductivities. Anion-anion distinct correlations, arising from the imbalance between the concentration of free (mobile) cations and anions, and the retarding effect of the fixed charge groups on cations, proves to be an additional important feature for polymer membranes. Our results demonstrate that dynamical correlations should become an important consideration in experimental measurements of salt diffusivities and conductivities for non-dilute salt solutions in polymer membranes.

Water Desalination Using Polyelectrolyte Hydrogel: Gibbs Ensemble Modeling.

Polyelectrolyte hydrogels can absorb a large amount of water across an osmotic membrane as a result of their swelling pressure. On the other hand, the insoluble cross-linked hydrogel network enables dewatering under the influence of external (thermal and/or mechanical) stimuli. Moreover, from a thermodynamic perspective, a polyelectrolyte hydrogel is already an osmotic membrane. These properties designate hydrogels as excellent candidates for use in desalination, at the same time avoiding the use of expensive membranes. In this article, we present our recent theoretical study of polyelectrolyte hydrogel usage for water desalination. Employing a coarse-grained model and the Gibbs ensemble, we modeled the thermodynamic equilibrium between the coexisting gel phase and the supernate aqueous salt solution phase. We performed a sequence of step-by-step hydrogel swellings and compressions in open and closed systems, i.e., in equilibrium with a large and with a comparably small reservoir of aqueous solution. The swelling in an open system removes ions from the large reservoir, whereas the compression in a closed system decreases the salt concentration in the small reservoir. We modeled this stepwise process of continuous decrease of water salinity from seawater up to freshwater concentrations and estimated the energy cost of the process to be comparable to that of reverse osmosis.

To Freeze or Not to Freeze: Questioning the Origin of the Deep Eutectic in the Zinc Chloride Hydrate System

Zinc chloride is one of the most soluble salts in aqueous solutions, with an ambient temperature solubility of over 430 g per 100 g of water (ZnCl2·R H2O, R = 1.8). It also exhibits a deep eutectic, at R = 7.25 and -60 °C between pure water and the most water-rich crystalline hydrate, R = 4.5 (see Figure). We previously demonstrated that the molecular ions of the crystalline R = 3 hydrate persist into the melt (Tm = 5 °C) resulting in the ionic liquid [Zn(OH2)6][ZnCl4]. Results from an extensive series of Raman spectroscopy and synchrotron diffraction measurements will be shown to demonstrate that the [ZnCl4]2- anion persists to high dilution. These data further provide evidence for a complex hydration structure beyond the first neighbor water of the hexaaquo zinc cation. Notably the complex speciation/hydration structure directly correlates with the concentration-dependent differential scanning calorimetry of this system and will be shown to be the origin of the system’s deep eutectic. Evaluating the concentration dependence of the temperature and heat of the liquidus reveals that this salt solution exists as an ionic liquid up to a concentration of about 98 mole percent water, beyond which it follows more traditional electrolyte descriptions. The principles derived from this structural and spectroscopic analysis can be applied to more generally explain the freezing point depression in diverse systems. In particular, this analysis demonstrates how the phase diagrams and liquidus heat and temperature can reveal the nature of speciation within aqueous salt solutions. Figure 1

Differentiating the Structure and Dynamics of Solute-Bound Vs. Bulk Water in Deep-Eutectic Aqueous AlCl3 Solutions

Aqueous solutions of aluminum chloride exhibit a deep eutectic (-52˚C) that is likely due to solute-directed formation of complex network structures in the solvent. It is well known that the solute-bound solvent must have a distinct chemical environment from that of the bulk solvent. Commonly used vibrational spectroscopic measurements of aqueous salt solutions are not selective enough to directly identify distinct water environments in solution. However, variable-temperature 1H-NMR spectroscopy of aqueous solutions, specifically those with high charge density salts, can distinguish water directly bound to the cation from water of the bulk solution. This unique ability to resolve characteristic water peaks by NMR spectroscopy affords the opportunity to explore the hydration structure and dynamics of deep-eutectic aqueous solutions. The aqueous AlCl3 system is an excellent model to study solution structure since we can exploit the high charge density of the ions for which strong ion-dipole interactions are structure-directing to the solvent waters, allowing resolution of distinct water chemical environments. We conducted a thorough investigation of the composition- and temperature-dependent solution structure of the AlCl3 : water system using 1H-NMR spectroscopy, and X-ray and neutron diffraction. The room-temperature proton chemical shift of water proceeds downfield with increasing salt concentration until AlCl3•22H2O, the eutectic composition, after which further increasing concentration results in an upfield chemical shift (see Figure.) Using VT-NMR, we can resolve the first-nearest neighbor water signals from the bulk signal upon cooling. 1H-NMR T1 and T2 relaxation measurement of the distinct water environments reveal stark differences in proton mobility for compositions on the water-rich versus AlCl3-rich sides of the eutectic, implying significant changes in hydration structure. To evaluate the extent to which these changes are structural, a parallel set of composition- and temperature-dependent neutron and X-ray diffraction experiments demonstrate that both cations and anions exhibit significant structure-directing influences on the solution, which we hypothesize underlies deep eutectic behavior in aqueous solutions. Figure 1

Highly sensitive detection of broadband terahertz waves using aqueous salt solutions.

Water-based coherent detection of broadband terahertz (THz) wave has been recently proposed with superior performances, which can alleviate the limited detection bandwidth and high probe laser energy requirement in the solid- and air-based detection schemes, respectively. Here, we demonstrate that the water-based detection method can be extended to the aqueous salt solutions and the sensitivity can be significantly enhanced. The THz coherent detection signal intensity scales linearly with the third-order nonlinear susceptibility χ(3) or quadratically with the linear refractive index η0 of the aqueous salt solutions, while the incoherent detection signal intensity scales quadratically with χ(3) or quartically with η0, proving the underlying mechanism is the four-wave mixing. Both the coherent and incoherent detection signal intensities appear positive correlation with the solution concentration. These results imply that the liquid-based THz detection scheme could provide a new technique to measure χ(3) and further investigate the physicochemical properties in the THz band for various liquids.