Terms Of Ion Concentrations Research Articles

Reformulating the permselectivity‐conductivity tradeoff relation in ion‐exchange membranes

AbstractPolymer membranes used in separation applications exhibit a tradeoff between permeability and selectivity. That is, membranes that are highly permeable tend to have low selectivity and vice versa. For ion‐exchange membranes used in applications such as electrodialysis and reverse electrodialysis, this tradeoff is expressed in terms of membrane permselectivity (i.e., ability to selectively permeate counter‐ions over co‐ions) and ionic conductivity (i.e., ability to transport ions in the presence of an electric field). The use of membrane permselectivity and ionic conductivity to illustrate a tradeoff between counter‐ion throughput and counter‐ion/co‐ion selectivity in ion‐exchange membranes complicates the analysis since permselectivity depends on the properties of the external solution and ionic conductivity depends on the transport of all mobile ions within a membrane. Furthermore, the use of these parameters restricts the analysis to ion‐exchange membranes used in applications in which counter‐ion/co‐ion selectivity is required. In this study, the permselectivity‐conductivity tradeoff relation for ion‐exchange membranes is reformulated in terms of ion concentrations and diffusion coefficients in the membrane. The reformulated framework enables a direct comparison between counter‐ion throughput and counter‐ion/co‐ion selectivity and is general. The generalizability of the reformulated tradeoff relation is demonstrated for cation‐exchange membranes used in vanadium redox flow batteries.

Mechanistic insight into electricity generation from moving ionic droplets on graphene

Recent experiments have demonstrated that moving water droplets on polymer-supported graphene can generate electric voltages in graphene. Here, we perform a multi-scale analysis on the mechanism of the generated voltages on the basis of an interplay among the substrate, graphene and ionic water. We find that the attraction of ions in water by substrate dipoles drives charge redistribution in graphene, forming an electric triple layer (ETL) at the water/graphene/substrate interface, made of an ion layer fixed on graphene, an image charge layer in graphene and a counterion layer in water. As a droplet moves on graphene, dynamic formation of the ETL at its front end drives a flow of charge in graphene. Using Langmuir adsorption theory combined with ab initio calculations, we determine the ion concentration in the ETL and estimate the amount of charge that each ion can draw in graphene. Then, the electric current in graphene is formulated in terms of ion concentration, droplet velocity, graphene thickness and density of substrate dipoles, which well reproduces experimentally measured currents in graphene. These results underscore the importance of tailoring substrate dipoles in optimizing the performance of devices for water energy harvesting and promoting practical applications.

Broadband mid-infrared amplified spontaneous emission from Er/Dy co-doped fluoride fiber with a simple diode-pumped configuration

Er3+/Dy3+ co-doped double-clad ZBLAN optical fiber has been used to obtain amplified spontaneous emission (ASE) broadband light sources cladding-pumped by 980-nm multimode laser diode (LD) sources. It has been demonstrated that mid-infrared broadband emission extending from 2515 to 3735 nm was obtained by energy transfer between Er3+ and Dy3+. We experimentally investigated the optimum design of Er3+/Dy3+ co-doped ZBLAN fiber in terms of ion concentration, fiber length, pumping configuration, and pumping power. The ASE output power was more than 2.5 mW when the LD pump power was set at 5 W. To assess its potential for gas sensing applications, the fabricated ASE light source was used to successfully detect methane gas with concentrations at 1% and 5%. The simple and stable construction of our ASE light source is suitable for practical purposes.

Degradation of groundwater quality in the coastal aquifers of the USA

The objective of this study is to analyze groundwater types and the extent of seawater intrusion in terms of ion concentrations in groundwater sample using USGS monitoring wells. Groundwater quality indices [fsea, GQI (dom), GQI (mix), GQI (swi)] were used to estimate the spatial distributions of groundwater types in the US coastal aquifers. Results showed that the dominating groundwater chemistry in the study area was Na+ and Cl−. Results also indicated that seawater intrusion of groundwater occurred in the US coastal aquifers. Based on the results of GQI (mix) and GQI (dom), most of the wells fell under domain II in the Piper diagram, indicating that they were of the Na–Cl water type. Na–Cl and mixed Ca–Mg–Cl were determined to be the two dominant groundwater types in the coastal aquifers of the US seawater intrusion evident in the Palm Beach and Miami-Dade counties of Florida, the San Diego and Santa Barbara areas of California, and within Virginia and New Jersey on the east coast. As the sea level continues to rise further inland, Na–Cl concentration in groundwater will increase, particularly in aquifers along low-lying coasts.

Calculation of Electrical Double Layer Potential Profiles in Nanopores from Grand Canonical Monte Carlo Simulations

The electrical double layer (EDL) profiles of electrical potential within charged slit-type pores is calculated in this work via a combination of grand canonical Monte Carlo (GCMC) simulations and electrodynamics concepts. The electrical potential distribution inside the pore is calculated with respect to field-free virtual bulk electrolyte solution implicit in the grand canonical ensemble. The GCMC simulations for slit-type pores performed in this work show that entropy effects lead to the exclusion of co-ions from the pore to allow densely packed counterions to efficiently neutralize surface charge. This phenomenon, in conjunction with the fact that electrical effects are long range with respect to the source charge, leads to a semioscillatory behavior of the potential profiles not predicted by classical theory. While bulk conditions in terms of ion concentrations are achieved in the center of the pore for most pore sizes studied in this work, electrical bulk conditions are not achieved except for the l...

How does an animal behave like a plant? Physiological and molecular adaptations of zooxanthellae and their hosts to symbiosis

Cnidarians (corals and sea anemones) harbouring photosynthetic microalgae derive several benefits from their association. To allow this association, numerous symbiotic-dependent adaptations in both partners, resulting from evolutionary pressures, have been selected. The dinoflagellate symbionts (zooxanthellae) are located inside a vesicle in the cnidarian host cell and are therefore exposed to a very different environment compared to the free-living state of these microalgae in terms of ion concentration and carbon content and speciation. In addition, this intracellular localization imposes that they rely completely upon the host for their nutrient supply (nitrogen, CO2). Symbiotic-dependent adaptations imposed to the animal host by phototrophic symbiosis are more relevant to photosynthetic organisms than to metazoans: indeed, the cnidarian host often harbours diurnal changes of morphology to adapt itself to the amount of light and possesses carbon-concentrating mechanisms, antioxidative defences and UV sunscreens similar to that present in phototrophs. These adaptations and the contrasting fragility of the association are discussed from both ecological and evolutionary points of view.

Reliability of Constant Charge Method for Molecular Dynamics Simulations on EDLCs in Nanometer and Sub‐Nanometer Spaces

AbstractThe constant charge method (CCM) and constant potential method (CPM) are two major techniques to apply electric charges on electrodes for molecular dynamics (MD) simulations on electric double‐layer capacitors (EDLCs). Compared with CCM, CPM is more realistic since the influence of electrode polarization is taken into account, although computationally more expensive. In this work, the reliability of CCM for MD simulations on EDLCs in nanometer and sub‐nanometer spaces is investigated. Particular attention is paid to the comparison of CCM and CPM for modeling EDLCs in terms of ion concentration and EDL structures in such nano/sub‐nano confined spaces, which are widely found in graphene‐based materials. The deviation for ion concentration calculated from CCM and CPM was found to be significant in both neutral and charged confined spaces (e. g., deviation ratio of 40.27 % and 11.18 % for Cl− ions in neutral and charged 9 Å space, respectively), which is different from previous observations in bulk solutions. This result could be attributed to the strong electrode polarization in nano/sub‐nano confined spaces. Although CCM and CPM yielded essentially similar EDL structures, the time evolution of electrode charge with a potential difference could be conducted only with CPM. The findings of the current work could provide useful insights for choosing appropriate methods for MD simulation on EDLCs in nano/sub‐nano confined spaces.

Two-Step Salt Stress Acclimatization Confers Marked Salt Tolerance Improvement in Four Rice Genotypes Differing in Salt Tolerance

In this study, four rice genotypes were evaluated for their salt tolerance characteristics in terms of ion concentrations and expression levels of OsHAK1, a gene that is involved in the regulation of K ion uptake. Salt tolerance profiles were assessed at 0, 0.5, 1.0, 1.5 and 2.0% NaCl. It was observed that the growth of salt-sensitive (RD6 and Sakon Nakhon) and moderately salt-tolerant (Niaw Ubon 2) cultivars were completely inhibited at 1.5% NaCl, with satisfactory growth observed for salt-tolerant (Pokkali) cultivar. One- and two-step treatments were compared for their efficacy in inducing salt tolerance in rice plants. One-step treatment was ineffective for producing rice plants with improved salt tolerance, while two-step treatment was a promising approach, producing salt-tolerant rice plants growing vigorously at 1.5% NaCl. Inductively coupled plasma–optical emission spectrometry indicated that salt-sensitive cultivars produced from two-step treatment showed improvements in their abilities to maintain \(\hbox {Na}^{+}/\hbox {K}^{+}\) ratios. Real-time qRT-PCR revealed that a remarkable increase in the OsHAK1 transcript level was not observed in plants grown at 1.5% NaCl. Besides, the OsHAK1 transcript level was not related to Na and/or K concentrations, and \(\hbox {Na}^{+}/\hbox {K}^{+}\) ratios, suggesting that other genes involved in \(\hbox {K}^{+}\) uptake regulation may express at higher levels and therefore, OsHAK1 expressed at low levels.

Cytotoxicity of modified glass ionomer cement on odontoblast cells.

Recently a modified glass ionomer cement (GIC) with enhanced bioactivity due to the incorporation of wollastonite or mineral trioxide aggregate (MTA) has been reported. The aim of this study was to evaluate the cytotoxic effect of the modified GIC on odontoblast-like cells. The cytotoxicity of a conventional GIC, wollastonite modified GIC (W-mGIC), MTA modified GIC (M-mGIC) and MTA cement has been evaluated using cement extracts, a culture media modified by the cement. Ion concentration and pH of each material in the culture media were measured and correlated to the results of the cytotoxicity study. Among the four groups, conventional GIC showed the most cytotoxicity effect, followed by W-mGIC and M-mGIC. MTA showed the least toxic effect. GIC showed the lowest pH (6.36) while MTA showed the highest (8.62). In terms of ion concentration, MTA showed the largest Ca(2+) concentration (467.3mg/L) while GIC showed the highest concentration of Si(4+) (19.9mg/L), Al(3+) (7.2mg/L) and Sr(2+) (100.3mg/L). Concentration of F(-) was under the detection limit (0.02mg/L) for all samples. However the concentrations of these ions are considered too low to be toxic. Our study showed that the cytotoxicity of conventional GIC can be moderated by incorporating calcium silicate based ceramics. The modified GIC might be promising as novel dental restorative cements.

A closer look at the internal corrosion test for automotive heat exchangers: the OY water test

AbstractNowadays, automotive heat exchangers are mainly made from aluminum. Over the last few decades, the development of aluminum brazing sheet has been mainly focused on the improvement of the external corrosion resistance. Recently, the interest of the heat exchanger manufacturers has also moved toward the assessment of the internal corrosion resistance. Accelerated tests are used to simulate in‐service conditions. These tests are crucial as they provide information to predict the material and product performance. Various internal corrosion tests have been developed, the so‐called ‘OY water tests’. Among all companies, the testing parameters can be varied in terms of ion concentrations or pH. Although the OY water tests are constantly being improved, there is so far no common internal corrosion standard as existing for external corrosion assessment. The present work aims at providing better understanding corrosion mechanisms encountered in the OY water media. The role of various elements present in the solution, cupric, chloride, sulfate ions, has been determined. These parameters were assessed via immersion testing. In order to get better understanding of the corrosion mechanism, electrochemical analysis combined with SEM characterization was carried out. The electrochemical analysis enables the understanding of the thermodynamics and kinetics of the corrosion process while immersion tests are performed to quantify the level of corrosion and follow the surface evolution over time. Copyright © 2010 John Wiley & Sons, Ltd.

Thermal aggregation and ion-induced cold-gelation of bovine serum albumin

Protein cold-gelation has recently received particular attention for its relevance in bio and food technology. In this work, we report a study on bovine serum albumin cold-gelation induced by copper or zinc ions. Metal-induced cold-gelation of proteins requires two steps: during the first one, the heat treatment causes protein partial unfolding and aggregation; then, after cooling the solution to room temperature, gels are formed upon the addition of metal ions. The thermally induced behaviour has been mainly investigated through different techniques: Fourier transform infrared (FTIR) spectroscopy, circular dichroism, dynamic light scattering (DLS) and rheology. Data have shown that the aggregation process is mainly due to protein conformational changes--alpha-helices into beta-aggregates-forming small aggregated structures with a mean diameter of about 20 nm a few minutes after heating. After metal ion addition, the viscoelastic properties of the gels have been investigated by rheological measurements. The behaviour of the elastic and viscous moduli as a function of time is discussed in terms of ion concentration and type. Our results show that: (1) the elastic behaviour depends on ion concentration and (2) at a given ion concentration, gels obtained in the presence of zinc exhibit an elastic value larger than that observed in the Cu(2+) case. Data suggest that cold-gelation is the result of different mechanisms: the ion-mediated protein-protein interaction and the bridging effect due to the presence of divalent ions in solution.

Assessment of the availability of ions to plant roots from the determination of their chemical activity in nutrient solutions

Abstract In soilless culture, the chemical composition of the nutrient solutions is usually expressed in terms of ion concentrations which do not reflect their actual availability to plant roots : even in aqueous media, the ions supplied as salts can give rise to complexes ; furthermore, other kinds of ion interactions can be involved. The VEGACT model, developed from thermodynamic concepts used in geochemistry, affords a more reliable assessment of the energy level of the ions. Using a particular example, at equal concentrations, the roots are shown to take up potassium or nitrate ions more readily than calcium or phosphate ions. This model also affords the prediction of the possible occurrence of phosphate precipitation within nutrient solutions of a given composition.