Low Ionic Concentrations Research Articles

Double Unit-Cell Silicogermanate Nanosheets Developed by Salting-Out Mechanism for Biomass Conversion.

Zeolite nanosheets with an extremely thin thickness featuring both unique pore systems and low diffusion resistance have the potential to achieve enhanced catalytic performance in the conversion of bulky molecular biomass. The preparation of unit-cell level nanosheets generally requires complex and costly multifunctional surfactants or an organic structure-directing agent (OSDA). Commercially available and environmentally friendly ionic liquids can also direct the structure of zeolite nanosheets by π-π stacking when these kinds of OSDA are used in large amount. Herein, we first report unit-cell-sized silicogermanate nanosheets of NS-IM-20 (UWY topology), 5 nm in thickness, which were synthesized at a relatively low ionic liquid concentration with the assistance of halide ion (Cl-). The Pd-loaded NS-IM-20 nanosheets with a hierarchical porosity and moderate acidity act as promising bifunctional catalysts for selective biomass conversion.

Surface tension of aqueous electrolyte solutions. A thermomechanical approach.

We determine the surface tension of aqueous electrolyte solutions in contact with non-polar dielectric media using a thermomechanical approach, which involves deriving the stress tensor from the thermodynamic potential of an inhomogeneous fluid. To obtain the surface tension, we calculate both the normal and tangential pressures using the components of the stress tensor, recently derived by us [Y. A. Budkov and P. E. Brandyshev, J. Chem. Phys. 159, 174103 (2023)] within the framework of Wang's variational field theory. Using this approach, we derive an analytical expression for the surface tension in the linear approximation. At low ionic concentrations, this expression represents the classical Onsager-Samaras limiting law. By utilizing only one fitting parameter, which is related to the affinity of anions to the dielectric boundary, we successfully approximated experimental data on the surface tension of several aqueous electrolyte solutions. This approximation applies to both the solution-air and solution-dodecane interfaces, covering a wide range of electrolyte concentrations.

The effect of ions on liquid-solid interface investigated by charge sensitive direct current droplet-based electricity generator

The contact electrification (CE) between DI water and SiO2 or fluorinated polymer has been proven to be mainly due to electron transfer, which is significantly influenced by ions in solution. However, how these ions in water affect the charge transfer at the liquid-solid (L-S) interface is still unresolved, especially for the already charged friction layer. Here, a direct current droplet-based electricity generator (DC-DEG) which is sensitive to the change of charge transfer at the L-S interface is adopted to detect the effects of ions in the neutral salt solution on the charged PTFE surface. The distribution of ions on the charged L-S interface (the change of electric potential on the solid surface) and its effects on the output of DC-DEGs have been studied. The results indicate that the charge transfer of droplets and then the output of DC-DEGs are closely related to the concentrations of salt solutions. Anions can enhance the surface potential of PTFE due to their adsorptions on PFTE while cations can reduce it due to their screen effect. At low ionic concentrations, the surface potential enhancement caused by anion adsorption is larger than that surface potential reduction caused by screen effect from cations. At high ionic concentrations, the electrostatic screen effect of cations increases a lot to weaken the surface potential and reducing the charge separation of droplets induced by electrostatic induction (EI). This work explains the redistribution process of ions at the L-S interface and also provides a clever solution for improving the electrical output performance of DEGs.

Ion-Solvent Interactions under Confinement Hold the Key to Tuning the DNA Translocation Speeds in Polyelectrolyte-Functionalized Nanopores.

DNA sequencing and sensing using nanopore technology delves critically into the alterations in the measurable electrical signal as single-stranded DNA is drawn through a tiny passage. To make such precise measurements, however, slowing down the DNA in the tightly confined passage is a key requirement, which may be achieved by grafting the nanopore walls with a polyelectrolyte layer (PEL). This soft functional layer at the wall, under an off-design condition, however, may block the DNA passage completely, leading to the complete loss of output signal from the nanobio sensor. Whereas theoretical postulates have previously been put forward to explain the essential physics of DNA translocation in nanopores, these have turned out to be somewhat inadequate when confronted with the experimental findings on functionalized nanopores, including the prediction of the events of complete signal losses. Circumventing these constraints, herein we bring out a possible decisive role of the interplay between the inevitable variabilities in the ionic distribution along the nanopore axis due to its finite length as opposed to its idealized "infinite" limit as well as the differential permittivity of PEL and bulk solution that cannot be captured by the commonly used one-dimensional variant of the electrical double layer theory. Our analysis, for the first time, captures variations in the ionic concentration distribution across multidimensional physical space and delineates its impact on the DNA translocation characteristics that have hitherto remained unaddressed. Our results reveal possible complete blockages of DNA translocation as influenced by less-than-threshold permittivity values or greater-than-threshold grafting densities of the PEL. In addition, electrohydrodynamic blocking is witnessed due to the ion-selective nature of the nanopore at low ionic concentrations. Hence, our study establishes a functionally active regime over which the PEL layer in a finite-length nanopore facilitates controllable DNA translocation, enabling successful sequencing and sensing through the explicit modulation of translocation speed.

Electrokinetic Manipulation of Biological Cells towards Biotechnology Applications.

The presented study demonstrates the capability of the template-based electrokinetic assembly (TEA) and guidance to manipulate and capture individual biological cells within a microfluidic platform. Specifically, dielectrophoretic (DEP) focusing of K-562 cells towards lithographically-defined "wells" on the microelectrodes and positioning singles cells withing these "wells" was demonstrated. K-562 lymphoblast cells, are widely used in immunology research. The DEP guidance, particularly involving positive DEP (pDEP), enables the controlled guidance and positioning of conductive and dielectric particles, including biological cells, opening new directions for the accurate and efficient microassembly of biological entities, which is crucial for single cell analysis and other applications in biotechnology. The investigation explores the use of glassy carbon and gold as electrode materials. It was established previously that undiluted physiological buffer is unsuitable for inducing positive DEP (pDEP); therefore, the change of media into a lower ionic concentration is necessary. After pDEP was observed, the cells are resubmerged in the Iscove's modified Dulbecco's medium (IMEM), a cell culturing media, and incubated. A dead/alive staining assay was performed on the cells to determine their survival in the diluted buffer for the period required to capture them. The staining assay confirmed the cells' survival after being immersed in the diluted biological buffer necessary for electrokinetic handling. The results indicate the promise of the proposed electrokinetic bio-sorting technology for applications in tissue engineering, lab-on-a-chip devices, and organ-on-a-chip models, as well as contributing to the advancement of single cell analysis.

Surface addition of Ag on PbO2 to enable efficient oxygen evolution reaction in pH-neutral media

Electrocatalysts, particularly earth-abundant metal oxide ones, exhibit poor performance in catalyzing the oxygen evolution reaction (OER) under neutral conditions due to low ionic concentrations. This study introduces a novel strategy for fabricating a PbO2 + Ag composite electrode with significantly improved OER activity and stability in a pH-neutral environment. Our results suggest that incorporating Ag as a surface additive improves the efficiency of utilizing adsorbed oxygenated species via the bridge-site-top-site pathway. Moreover, the surface decoration of Ag resulted in enhanced electrocatalytic stability by diverting the attack of oxygenated species to Pb thereby effectively preventing Pb dissolution. The results not only establish a method for utilizing PbO2 in pH-neutral OER applications, but also propose a potential strategy for employing less noble catalysts in cost-effective electrochemical energy conversions.

Comparing solution-gate and bottom-gate nanowire field-effect transistors on pH sensing with different salt concentrations and surface modifications

Field-effect transistors (FETs) have been developed as pH sensors by using various device structures, fabrication technologies, and sensing film materials. Different transistor structures, like extended-gate (EG) FETs, floating-gate FET sensors, and dual-gate (DG) FETs, can enhance the sensor performance. In this article, we report the effects of using solution-gate and bottom-gate FET configurations on pH sensing and investigate the influence of different ionic concentrations of buffers in the measured signals. The surface charge of hafnium dioxide (HfO2) affected by the buffer pH, with/without the modification of polyethylene glycol (PEG) terminated with hydroxyl groups, and the location of applied gate voltage are vital factors to the sensor performance in pH sensing. Based on the results, the solution-gate FET exhibits good pH sensitivity even in the high ionic strength solutions of bis-tris propane (BTP), and these values of pH sensitivity are close to the Nernst limit (59.2 mV/pH). In general, silane-PEG-OH modification can reduce the deviations of measured signals in pH sensing. The performance of bottom-gate FET is inferior in the BTP buffers with high ionic solutions but suitable to be operated in low ionic concentrations, such as 0.1, 1, and 10 mM BTP buffers. The size of the ions was also studied and discussed. The solution-gate FET demonstrates excellent performance under high ionic strengths, meaning a more significant potential for detecting biological molecules under physiological conditions.

Water quality impact on flotation Response: A focus on specific ions and temperature

Plant water recycling causes an accumulation of ions in the process water which may affect plant processes since processing routes are water intensive. Seasonal temperature differences affect the water quality through variation of the available recycled water within the plant between the summer and winter seasons. The objective of this study was therefore to investigate the effect of specific ions and temperature, relevant to onsite process water recycling and temperature variations brought about by seasonal changes, on the separation of gangue from valuable minerals in batch flotation of a low-grade Cu-Ni-PGE ore. Water and solids recoveries were impacted by Ca2+ and SO42-. At high SO42- concentrations, an increase in Ca2+ increased the mass of water and solids recovered. An increase in SO42- alone caused an increase in copper recovery whilst decreasing the copper grade. S2O32- alone affected the nickel recovery. An increase in S2O32- caused an increase in nickel recovery whilst the nickel grade was affected by the interaction of S2O32- and temperature. Furthermore, copper showed similar trends as those observed for nickel in the responses for the mineral grade. At high S2O32- concentration there was no observable change in the nickel and copper grades when temperature increased. At low S2O32- concentrations, an increase in temperature decreased the nickel and copper grades. In addition to the interactive effect of temperature and S2O32-, nickel was more temperature sensitive in comparison to copper. The study demonstrated that there are specific ion concentration ranges beyond which flotation performance was adversely affected and other ranges beyond which no observable effect on flotation was visible. Based on this understanding, it may be possible to predict the ideal operating conditions for the number of water recycles in a plant. The higher ionic concentrations and their corresponding ionic strengths resulted in a more stable froth in comparison to lower ionic concentrations and consequently an improvement in the recoveries.

Faster bipolar capacitive deionization with flow-through electrodes

Capacitive deionization (CDI) is an emerging technology in water cleaning applications. Bipolar electrode modules are promising for upscaling CDI systems by applying a high voltage over a stack of cells. Previous experiments indicate around 3 times faster removal rate can be achieved with a 5-cell stack of flow-between electrodes. In this work, we present the first flow-through bipolar CDI design. Surprisingly, the effective average salt adsorption rate (ASAR) of a 5-cell stack was around 10 times higher per electrode mass. The flow-through design allows for faster ion transport to match the higher charging rate. Also, the floating electrodes discharge near-instantaneous by internal short-circuit upon the removal of potential, leaving almost twice as much time for charging in a cycle. Resistance is lowered due to the removal of internal compartments in the design, and the benefits of flow-through devices outweigh any potential higher energy cost of mass transport. The high voltage at the extreme electrodes poses a risk of electrode oxidation but optimized device operation controls this risk by constraining the voltage locally. For the same reason, the device is best adapted for the deionization of moderate to low ionic concentrations, such as river water, well water, or municipal water. In summary, this work provides a simpler yet highly effective way of scaling up CDI for water-cleaning applications.

Finding Infinities in Nanoconfined Geothermal Electrolyte Static Dielectric Properties and Implications on Ion Adsorption/Pairing.

Infinities should naturally occur in the dielectric responses of ionic solutions relevant to many geochemical, energy storage, and electrochemical applications at a strictly zero frequency. Using molecular dynamics simulations cross-referenced with coarse-grained Monte Carlo models, using nanoslit pore models at hydrothermal conditions, and treating confined mobile charges as polarization, we demonstrate the far reaching consequences. The dielectric permittivity profile perpendicular to the slit (ϵ⊥(z)) increases, not decreases, with ionic concentration, unlike in the more widely studied megahertz-to-gigahertz frequency range. In confined electrolytes, the divergences in ϵ⊥(z) correctly describe crossovers between bulk- and surface-dominated dielectric behavior. Nanoconfinement at low ionic concentrations changes monovalent ion energetics by 1-2 kJ/mol, but no dielectric property studied so far is universally correlated to ion adsorption or ion-ion interactions. We caution that infinities signal violation of the "electrical insulator" dielectric assumption.

Improved Performance of Cation Exchange Membranes Coated with Chitosan

Desalination with electrodialysis is used to obtain fresh water from saltwater brines. However, removal of the salt can be inefficient at low ionic concentrations because of the drastic increase of voltage required under those conditions, leading to limited adoption of this process. In this study, a commercially available cation exchange membrane was successfully coated with chitosan with different degrees of deacetylation. Higher degrees of deacetylation led to increased hydrophilicity of the membrane surfaces and possibly improved the wetting of the surface with the salt solutions. The base membrane and membranes coated with varying degrees of deacetylation were tested to determine how standard electrodialysis metrics such as limiting current density (LCD), ionic flux, and current utilization were affected to evaluate the effects of membrane hydrophilicity. Higher hydrophilicity improved the NaCl flux, current efficiency, and voltage requirements at low NaCl concentrations. Our strategy provides a simple method to control the membrane hydrophilicity, leading to improved performance.

Hydrochemistry of surface waters in a permafrost headwater catchment in the Northeastern Tibetan Plateau

The permafrost headwater catchments in the Tibetan Plateau (TP) have experienced extensive permafrost degradation, which may cause major changes in riverine solutes. However, surface water hydrochemistry and its influencing factors in such catchments are poorly understood. Hydrochemistry data for different surface waters were obtained for the Yakou catchment in the Northeastern TP. The results indicate that the ionic and organic concentrations of frozen soil seeps (FSS) were higher on the north-facing slope compared to the south-facing slope, and that FSS may be involved in streamflow generation processes and in determining the spatial pattern of riverine solutes. The north-facing slope of the catchment has a thin active layer and wet moisture conditions compared to the south-facing slope; hence supra-permafrost water, with high ionic concentrations, can drain to the ground surface as FSS in the riparian zone and then recharge the surface ponding water and the main stream water. The high ionic concentrations of the supra-permafrost water and FSS can be attributed to intense rock weathering and evaporative effect, together with the high mobility of elements and the transport of organic matter. The tributaries, with low ionic concentrations, comprise a mixture of infiltrating precipitation and diluted supra-permafrost water. Carbonate weathering is the dominant weathering type within the catchment, but the weathering of evaporite and silicate is more important on the north-facing and south-facing slopes, respectively, and chemical weathering on the north-facing slope may be enhanced by strong physical erosion during repeated freeze–thaw cycles due to the wet conditions. The results indicate that the surface water hydrochemistry is heterogeneous on the different hillslope units, and that a thicker active layer under climate change may lead to a shift of hydrological and hydrochemical pathways, and thus a decrease in water and solute flux from the hillslopes, with underlying permafrost, to the river channel.

Post-thyroidectomy hypocalcemia and related complications

The incidence of post-thyroidectomy hypocalcemia is high while the factors involved include age (> 50 years), type of operation, operative time, neck dissection, histology of the surgical specimen and vocal fold paralysis. Low ionic calcium concentrations are indicative of the presence of symptoms of hypocalcemia and the need for oral calcium. Progression to definitive hypoparathyroidism occurs only in patients with clinical manifestations of post-thyroidectomy hypocalcemia. In general, the problem with post-surgical hypoparathyroidism resides in the surgical procedure itself. The most common are related to neuronal hyperexcitability, which explains the paresthesias, cramps and numbness, which usually start in the perioral region and on the fingertips. Muscle spasms and muscle stiffness are also common. When severe, hypocalcemia can lead to life-threatening spastic tetany, laryngospasm, and seizures. The current manuscript aimed to present a review of the bibliography on thyroidectomy and negative impact of its complications on human health, mainly because of a higher risk for developing hypocalcemia. To achieve the study goal, this review covered most recent published articles from 2017 onward.

Conductance of concentrated electrolytes: Multivalency and the Wien effect.

The electric conductivity of ionic solutions is well understood at low ionic concentrations of up to a few millimolar but becomes difficult to unravel at higher concentrations that are still common in nature and technological applications. A model for the conductivity at high concentrations was recently put forth for monovalent electrolytes at low electric fields. The model relies on applying a stochastic density-functional theory and using a modified electrostatic pair-potential that suppresses unphysical, short-range electrostatic interactions. Here, we extend the theory to multivalent ions as well as to high electric fields where a deviation from Ohm's law known as the Wien effect occurs. Our results are in good agreement with experiments and recent simulations.

Ion transport to temperature and gate in organic electrochemical transistors with anti-freezing hydrogel

Organic electrochemical transistors (OECTs) are useful for biochemical sensors, logic circuits, and artificial neuromorphic systems and call for insights into operation mechanisms to allow constructing complicated digital systems of high qualities. Here, we fabricate anti-freezing hydrogel based, dual-channel OECTs to probe the temperature-dependence and distance-dependence of current to investigate the ion transport. In the temperature-dependence measurement down to −30 °C, a threshold gate voltage is observed as V th , E = 0.5 V , above which the electrochemical doping mode dominates. By tuning the gate voltage above V th , E , the activation energy for hole transport is dramatically raised from 0.2 to 245.2 meV. Via the in-situ multi-point measurement, the transient response potential in neighboring channels are found not synchronous but limited by the ion transport when the ion concentration is low. The results are compared with those of OECTs based on aqueous electrolyte and reveal the operational mechanisms of OECT based on anti-freezing hydrogel. • The anti-freezing hydrogel based OECTs were fabricated to temperature-dependence measurement. • The in-situ multi-point measurement of dual-channel OECT was implemented to reveal ion transport. • The operation mode switching of OECTs was determined by the threshold gate voltage ( V th , E ). • Distance-dependence effect of ion transport was exhibited in low ionic concentration.

Effective Ion Mobility and Long‐Term Dark Current of Metal Halide Perovskites with Different Crystallinities and Compositions

Ion transport properties in metal halide perovskite still constitute a subject of intense research because of the evident connection between mobile defects and device performance and operation degradation. In the case of X‐ray detectors, dark current level and instability are regarded to be connected to the ion migration upon bias application. Two compositions (MAPbBr3 and MAPbI3) and structures (single‐ and microcrystalline) are checked by the analysis of long‐term dark current evolution. Electronic current increases with time before reaching a steady‐state value within a response time (from 104 down to 10 s) that strongly depends on the applied bias. A coupling between electronic transport and ion kinetics exists that ultimately establishes the time scale of electronic current. Effective ion mobility is extracted for a range of applied electric field ξ. While ion mobility results field‐independent in the case of MAPbI3, a clear field enhancement is observed for MAPbBr3 (), irrespective of the crystallinity. Both perovskite compounds present effective ion mobility in the range of ≈ 10−7–10−6 cm−2 V−1 s−1, in accordance with previous analyses. The ξ‐dependence of the ion mobility is related to the lower ionic concentration of the bromide compound. Slower migrating defect drift is suppressed in the case of MAPbBr3, in opposition to that observed here for MAPbI3.

Wettability and Its Influencing Factors of Tight Sandstones in Coal Measures in Ordos Basin, China.

With the recent development in exploration technology, extensive attention has been given to the tight sandstone gas reservoirs in coal measures. As a surface property of tight sandstone, wettability is a very important factor that controls the distribution and transport of gas and water inside the sandstone; thus, it plays a vital role in the sandstone gas-recovery process. In this study, a series of tests, namely, the Amott–Harvey wettability test, contact angle test, ζ-potential test, X-ray diffraction, thin-section analysis, scanning electron microscopy, and mercury intrusion porosimetry, were conducted to investigate the basic features of tight sandstones in coal measures and the effects of petrological characteristics, fluid properties, the underground environment, sedimentation, and diagenesis on the wetting behavior of sandstone. The impacts of three major forces, namely, the structural, electrostatic, and dispersion forces, on sandstone wettability were also discussed. The results showed that high surface roughness, high textural and compositional maturity, low organic matter content, a strong hydrodynamic sedimentary environment, weak compaction and cementation, high temperature, and high solution pH, as well as a low ionic concentration, enhance the hydrophilicity of the sandstone.

The effect of chitosan nanoparticles on the rheo-viscoelastic properties and lipid digestibility of oil/vinegar mixtures (vinaigrettes)

The role of chitosan nanoparticles on the rheological behaviour, antioxidant properties and lipid digestibility of vinaigrettes was investigated in comparison with a protonated chitosan polymer. Nanoparticles were produced using different concentrations of tripolyphosphate (TPP) and acetic acid. The lower ionic concentrations were used to encapsulate a fish protein hydrolysate. Rotatory tests produced shear-thinning behaviour in the different nanoparticle suspensions. The vinaigrettes with addition of both chitosan and nanoparticles exhibited a stationary shear-thinning flow with viscoelastic characteristics of weak gels. The presence of chitosan nanoparticles in the emulsified oil phase produced a three-dimensional network with higher energy stability in the case of hydrolysate-loaded nanoparticles. Both chitosan and chitosan nanoparticles increased the radical scavenging capacity of vinaigrettes, but not the ferric ion reducing power. Addition of empty or hydrolysate-loaded nanoparticles reduced lipid digestion in vinaigrettes to a greater extent than chitosan (≈45% with nanoparticles; 33% with chitosan).

Conductivity of Concentrated Electrolytes.

The conductivity of ionic solutions is arguably their most important trait, being widely used in electrochemical, biochemical, and environmental applications. The Debye-Hückel-Onsager theory successfully predicts the conductivity at very low ionic concentrations of up to a few millimolars, but there is no well-established theory applicable at higher concentrations. We study the conductivity of ionic solutions using a stochastic density functional theory, paired with a modified Coulomb interaction that accounts for the hard-core repulsion between the ions. The modified potential suppresses unphysical, short-range electrostatic interactions, which are present in the Debye-Hückel-Onsager theory. Our results for the conductivity show very good agreement with experimental data up to 3molars, without any fit parameters. We provide a compact expression for the conductivity, accompanied by a simple analytical approximation.

Thermodiffusive effect on the local Debye-length in an electroosmotic flow of a viscoelastic fluid in a slit microchannel

This work theoretically studies the influence of the thermodiffusive effect on the local Debye length thickness in a purely electroosmotic flow in a parallel flat plate microchannel. An imposed electric field between the ends of the microchannel interacts with an ionized viscoelastic fluid causing Joule heating, which induces a temperature gradients along the microchannel, affecting the fluid’s physical properties, and in a notable manner, the ionic distribution into the electric double layer (EDL), resulting in thermodiffusion. Consequently, an induced pressure field counterbalances the axial variation of the plug-like electroosmotic velocity to maintain the fluid mass continuity. Also, the ionic distribution and electrical potential based on the non-isothermal Poisson-Boltzmann equation are modified. To estimate the local Debye length thickness, the coupled set of the Poisson-Boltzmann, momentum, and energy equations are solved numerically in the limit of the lubrication approximation theory (LAT). Our results indicate that the thermodiffusion has an important effect on the thickness of the local Debye-length, particularly in the warm zone of the fluid. Besides, the ionic response to thermal fields is given by a positive Soret coefficient, which indicates that the ionic particles move from warm to cold regions in the fluid, giving place to a thinner Debye length and lower ionic concentration around the warming zone; this migration of ions confirms that the dimensionless mass-flow rate is affected with the Soret coefficient compared with the non-thermodiffusion case.