Large Ion Concentrations Research Articles

Physical properties of Pr3+ substituted zinc spinel (ZnPrxFe2−xO4) nanoferrites synthesized via sol–gel auto-combustion route

Spinel ferrites, a group of metal oxides, have garnered significant attention in the recent decade due to their high demand for numerous applications, including data storage and microwave device applications. In this context, we studied the effect of different doping concentrations of large Pr ions on the physicochemical properties of spinel lattice, such as dielectric and magnetic properties. In this research, we successfully fabricated a series of praseodymium ion-doped zinc spinel ferrites ZnPrxFe2-xO4 nanoparticles 0.00≤x≤0.20 via a simple and economical sol–gel auto-combustion approach. XRD (X-ray Diffraction Analysis) and FTIR investigations validate the presence of a cubical phase, with the crystallite size varying between 11 nm to 19 nm depending on the amount of Pr present. The Scherrer method, Williamson-Hall analysis (WH), and size-strain plot method (SSP) were investigated the correlation of crystalize size. The SSP approach has a better correlation coefficient than the WH method. Transmission electron microscopy TEM shows that the prepared material possessed the cubic and spherical symmetry. The significant variation in electrical parameters was discussed at an applied frequency ranging from 1 MHz to 3 GHz. The dielectric constant is approximately constant in low-frequency regions then relaxation peaks were observed at nearly 1.4 GHz and 2.2 GHz. The dielectric constant and complex dielectric constant of these samples dropped as the praseodymium content increased. Investigations regarding the magnetic properties were carried out using a vibrating sample magnetometer (VSM) at −23 k Oe to +23 k Oe. Low coercivity and relaxation peaks at high frequencies suggest that this material may be suitable for core materials, microwave technologies and recording media.

The ion channels of endomembranes.

The endomembrane system consists of organellar membranes in the biosynthetic pathway [endoplasmic reticulum (ER), Golgi apparatus, and secretory vesicles] as well as those in the degradative pathway (early endosomes, macropinosomes, phagosomes, autophagosomes, late endosomes, and lysosomes). These endomembrane organelles/vesicles work together to synthesize, modify, package, transport, and degrade proteins, carbohydrates, and lipids, regulating the balance between cellular anabolism and catabolism. Large ion concentration gradients exist across endomembranes: Ca2+ gradients for most endomembrane organelles and H+ gradients for the acidic compartments. Ion (Na+, K+, H+, Ca2+, and Cl-) channels on the organellar membranes control ion flux in response to cellular cues, allowing rapid informational exchange between the cytosol and organelle lumen. Recent advances in organelle proteomics, organellar electrophysiology, and luminal and juxtaorganellar ion imaging have led to molecular identification and functional characterization of about two dozen endomembrane ion channels. For example, whereas IP3R1-3 channels mediate Ca2+ release from the ER in response to neurotransmitter and hormone stimulation, TRPML1-3 and TMEM175 channels mediate lysosomal Ca2+ and H+ release, respectively, in response to nutritional and trafficking cues. This review aims to summarize the current understanding of these endomembrane channels, with a focus on their subcellular localizations, ion permeation properties, gating mechanisms, cell biological functions, and disease relevance.

Metal–Organic Framework-Based Aerogel: A Novel Adsorbent for the Efficient Removal of Heavy Metal Ions and Selective Removal of a Cationic Dye from Aqueous Solution

Ameliorating the existing purification methods with more affordable, efficient, and industrially adoptable methods that remove heavy metal ions from contaminated drinking water constitutes a persistent technological challenge. Metal–organic framework (MOF)-based materials with their excellent adsorption performance are recently explored as an alternative method to the traditional methods. Here, we report a MOF/biopolymer composite-based aerogel that is a cost-effective, highly efficient, and environmentally sustainable material for the removal of large concentrations of heavy metal ions (1277 mg of Pb2+, 466 mg of Cd2+, and 706 mg of Cr6+ per gram of the aerogel) and the selective removal of the cationic dye crystal violet (310 mg/g) from its mixture with (anionic) methyl orange from contaminated water samples. The MOF used herein is 2-methylimidazole zinc complex (ZIF-8), whereas the biopolymer is the nontoxic and biodegradable Iota-Carrageenan (iCG), a sulfated polysaccharide extracted from red seaweeds. We have transformed the ZIF-8 powder into a moldable, load-bearable, flexible, and eco-friendly ZIF-8@iCG aerogel. SEM images confirmed that ZIF-8 is physically embedded in Iota-Carrageenan, forming a honeycomb structure. The ZIF-8 is located onto the fibers of iCG, forming a thermally stable, flame-retardant ZIF-8@iCG hydrogel, with high mechanical strength and intrinsic porosity. The aerogel removes 92.03% of Pb2+ ions from an intentionally spiked Pb2+ solution (1 ppm), making this water sample drinkable upon three successive filtrations. The thermodynamics of metal ion adsorption suggest that the adsorption kinetics follow the Langmuir adsorption isotherm model and the adsorption process is endothermic. Ion leaching experiments suggest that leaching of zinc ions from the aerogel is negligible. Thus, the newly designed ZIF-8@iCG aerogel is a potentially effective adsorbent for the removal of heavy metal ions and organic dyes from drinking water and is intended for industrial use.

Superconductivity in magnetically doped SrTiO3

Doped SrTiO3 is a superconductor whose pairing mechanism is still not fully understood. The response of a superconductor to impurities has long been used to obtain insights into the nature of the superconducting state. Here, the superconductivity of SrTiO3 films that are doped or alloyed with different rare earth ions, which carry a magnetic moment, is investigated. It is shown that large concentrations (up to a few percent) of rare earth ions with unpaired f-electrons, such as Sm and Eu, do not reduce the superconducting critical temperature and critical fields. The finding is independent of whether the rare earth ion acts as a dopant or is an isovalent impurity. The interactions between the superconducting condensate and the magnetic dopants that could result in the observed insensitivity to magnetic impurities are discussed.

Particle-in-cell simulations of the Cassini spacecraft’s interaction with Saturn’s ionosphere during the Grand Finale

ABSTRACT A surprising and unexpected phenomenon observed during Cassini’s Grand Finale was the spacecraft charging to positive potentials in Saturn’s ionosphere. Here, the ionospheric plasma was depleted of free electrons with negatively charged ions and dust accumulating up to over 95 per cent of the negative charge density. To further understand the spacecraft–plasma interaction, we perform a three-dimensional Particle-In-Cell study of a model Cassini spacecraft immersed in plasma representative of Saturn’s ionosphere. The simulations reveal complex interaction features such as electron wings and a highly structured wake containing spacecraft-scale vortices. The results show how a large negative ion concentration combined with a large negative to positive ion mass ratio is able to drive the spacecraft to the observed positive potentials. Despite the high electron depletions, the electron properties are found as a significant controlling factor for the spacecraft potential together with the magnetic field orientation which induces a potential gradient directed across Cassini’s asymmetric body. This study reveals the global spacecraft interaction experienced by Cassini during the Grand Finale and how this is influenced by the unexpected negative ion and dust populations.

Surface Charge Modulation and Reduction of Non-Linear Electrolytic Screening in FET-Based Biosensing

We experimentally investigate the influence of non-linear electrolytic screening by the electric double layer (EDL) and its impact on the field-effect transistor (FET) sensitivity to charged (bio)molecules. We use DNA hybridization to a PNA capture probe layer as model system. By co-depositing positively or negatively charged blocker molecules together with the PNA capture probes on the negatively charged SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surface of the FET, we control the overall surface charge and modulate the strength of local ion concentration within the EDL. We observe a FET signal enhancement of up to 51% when the overall charge including the captured analyte itself swings roughly symmetrically around zero during capture, as confirmed by zeta potential measurements. Surface plasmon resonance measurements rule out a change in captured analyte density as the origin of the enhancement in sensitivity. This confirms that excess screening caused by the large local ion concentration, which increases non-linearly with potential in the EDL, is responsible for a loss in sensitivity in bioFETs with a charged surface. These experimental findings agree with the early theoretical works that find a low surface potential to be desirable for the best bioFET performance.

Effects of electrical image forces on salt dissolved in water.

It will be shown that for a solution of salt dissolved in water in contact with a metallic or dielectric wall, the concentration of salt ions (both positive and negative) near the wall can be large enough to exceed the salt's solubility limit, as a result of electrical image charge forces. In addition, since the dielectric constant of water increases from 2.1 at the wall to 81 at about 1 nm from a solid wall, there will be an attractive image potential near the plane on which this increase of the dielectric constant occurs. Such large ion concentrations could possibly be used in water desalination.

Transverse migration and microfluidic concentration of DNA using Newtonian buffers.

We present experimental evidence that DNA can be concentrated due to an electrohydrodynamic coupling between a pressure-driven flow and a parallel electric field. The effects of buffer properties on the process were measured in a microfluidic channel. The concentration rates and the efficiency of trapping DNA were quantified as functions of the ion and polymer concentrations of the buffer solution. Buffers with large ion concentrations hindered the ability to trap DNA, reducing the short-time efficiency of the concentration process from nearly 100% to zero. Importantly, DNA was trapped in the microfluidic channel even when the buffer solution lacked any measurable viscoelastic response. These observations indicate that electrohydrodynamic migration drives the concentration of DNA. We found no evidence of viscoelastic migration in these experiments.

Complex formation between copper(II) and arginine in two ionic media and in a large range of reagent concentration

Arginine and copper(II) play an important role in human physiology. Arginine is a precursor of NO which is a vasodilator and the right quantity of copper(II), bound to several amino acids, is necessary for the human body. The complex formation between copper(II) and arginine is studied at 25 °C and in two different ionic media: 1.00 mol dm−3 NaClO4 and 1.00 mol dm−3 NaCl. The investigation is carried out potentiometrically, by employing in 1.00 mol dm−3 NaClO4 cells involving glass and copper amalgam electrodes. In 1.00 mol dm−3 NaCl, only the glass electrode can be used. In both ionic media, the adoption of the constant ionic medium allows to extend the investigation to a large range of reagent concentration. Experimental data can be explained by assuming the formation of mononuclear complexes in copper(II). In 1.00 mol dm−3 NaClO4, complexes with the participation of hydrogen ions are assumed. The presence of the main complex in a large hydrogen ion concentration is supported also by spectrophotometric measurements.

Solvation and Entropic Regimes in Ion-Containing Block Copolymers

The phase behavior of ion-containing block copolymers is studied using a field-theoretic model consisting of fully mobile ions immersed in a heterogeneous dielectric medium. Two distinct thermodynamic regimes are found to emerge, resulting from the competition between ion translational entropy and solvation free energy. In the regime dominated by entropy, the disordered phase is stabilized by the addition of ions. In the regime dominated by solvation free energy, the disordered phase is destabilized, leading to a “chimney”-like channel of stable ordered phases at sufficiently large ion concentrations. The two regimes are demarcated by the parameter λB, which quantifies the variation in solvation energy upon transferring ions between different dielectric domains. Estimates of λB for experimental systems suggest that the majority of block copolymer electrolytes fall within the solvation regime.

Classification of the new particle formation events observed at a tropical site, Pune, India

A total number of 109 new particle formation events identified in the ion-mobility spectra measured with a Neutral Cluster and Air Ion Spectrometer in the mobility range of 3.16–0.00133 cm2 V−1s−1 (Diameter* range 0.36–47.1 nm) at a tropical site at Pune, (18.53 °N, 73.85 °E, 573 m amsl) India from March 08, 2010–December 31, 2012 are classified based on their shape characteristics under four categories. Most of these events occurred in the morning hours of the pre-monsoon season during the hottest months (April and May) of the year. The meteorological conditions and the changes in ion characteristics associated with some typical events are examined. Average ion-mobility spectrum for the event days shows a minimum in the negative big cluster ion (diameter, 0.85–1.6 nm) concentration and two maxima in the positive intermediate (diameter, 1.6–7.4 nm) and large ion (diameter, 7.4–47.1 nm) concentrations as compared to the average spectrum for all days. Analysis of 7-days airmass back trajectories shows that since the only source of big cluster ions is through the growth of small cluster ions (diameter, 0.36–0.85 nm) the growth of small to big cluster ions is faster when the airmass approaches our site from the land. Further, the concentrations of positive intermediate and light large (diameter, 7.4–22 nm) ions is more when the airmass approaches from the Arabian Sea.

Styrenic block copolymer/sulfonated graphene oxide composite membranes for highly bendable ionic polymer actuators with large ion concentration gradient

In this study, sulfonated graphene oxide (sGO) with a large enhanced sulfonation degree of 1.65 mmol g−1 was simultaneously introduced as a highly ion conduction-activating carbonaceous filler for ionic polymer–metal composite (IPMC) actuator. The nanostructured styrenic block copolymer/sGO/ionic liquid (IL) composite membrane actuators revealed much larger actuation performance than top-ranked polyelectrolyte/IL actuators ever reported so far in terms of bending strain (0.88% under 2 V dc), initial strain rate (0.312% min−1), and charge-specific displacement (276.4 mm C−1). Moreover, SSPB/sGO/IL actuators exhibited excellent actuation performance without drawbacks of conventional IPMCs, such as back-relaxation and early loss of inner solvent. In addition, via tracking the movement of the IL's anion through energy-dispersive X-ray spectroscopy (EDS) analysis, not only the transporting behaviour of IL but also the pumping effect with solvated ion complexes inside the actuator are confirmed for the first time.

Ion diffusion may introduce spurious current sources in current-source density (CSD) analysis

Current-source density (CSD) analysis is a well-established method for analyzing recorded local field potentials (LFPs), that is, the low-frequency part of extracellular potentials. Standard CSD theory is based on the assumption that all extracellular currents are purely ohmic, and thus neglects the possible impact from ionic diffusion on recorded potentials. However, it has previously been shown that in physiological conditions with large ion-concentration gradients, diffusive currents can evoke slow shifts in extracellular potentials. Using computer simulations, we here show that diffusion-evoked potential shifts can introduce errors in standard CSD analysis, and can lead to prediction of spurious current sources. Further, we here show that the diffusion-evoked prediction errors can be removed by using an improved CSD estimator which accounts for concentration-dependent effects.NEW & NOTEWORTHY Standard CSD analysis does not account for ionic diffusion. Using biophysically realistic computer simulations, we show that unaccounted-for diffusive currents can lead to the prediction of spurious current sources. This finding may be of strong interest for in vivo electrophysiologists doing extracellular recordings in general, and CSD analysis in particular.

Modes of electrokinetic instability for imperfect electric membranes.

The direct transition to overlimiting current bypassing the stage of limiting currents is considered for imperfect membranes. Instability of the quiescent steady-state one-dimensional solution, which is the result of a balance of diffusion and electromigration, is investigated on the basis of the full Nernst-Planck-Poisson-Stokes system and a simplified quasielectroneutral system. A three-layer geometry, electrolyte-porous membrane-electrolyte, is considered. The usual assumption of a constant electrochemical potential along the membrane surface is removed from consideration. The effect of bulk and surface effects on the instability and transition to the overlimiting currents is evaluated for a different membrane selectivity. It becomes clear that for sufficiently small fixed charge concentration (large ion concentration in the electrolyte), the monotonic instability is replaced by an oscillatory one. The dependence of instability on the membrane porosity is found to be weak.

Charging State of Aerosols during Particle Formation Events in an Urban Environment and Its Implications for Ion-Induced Nucleation

The aim of this study was to investigate the charging state of atmospheric ions during particle formation (PF) events in an urban environment. We measured small ion (charged cluster) and large ion (charged particle) concentrations over a period of 13 months in Brisbane, Australia, using a neutral cluster and air ion spectrometer (NAIS) and obtained 245 complete days of data. PF events were observed on 110 days which count as 45% of the total. On the average, the positive small ion concentration was 40% higher than the negative. The positive large ion concentration was 20% higher than the negative. Generally, small ion concentrations peaked during the night, while large ion concentrations were a maximum during the day. Next, we classified the results into days on which there was a PF event and when there was not. We showed that PF events have a profound effect on small and large ion concentrations in the environment; the small ion concentrations decreased by about 30% while large ion concentrations increased by up to 100%. We identified two phenomena that have a bearing on ion-induced nucleation. Firstly, the fraction of particles that were charged consistently decreased during PF events and rarely exceeded the equilibrium value, suggesting that the formation process was not significantly influenced by an ion-induced mechanism. Secondly, small ion concentrations were higher in the pre-dawn hours of PF event days than on other days, while the fraction of clusters that were charged often showed an increase immediately prior to a PF event, both observations supporting an ion-induced mechanism of PF. This study serves as basis for future work explaining these observations.

Variability of air ion concentrations in urban Paris

Abstract. Air ion concentrations influence new particle formation and consequently the global aerosol as potential cloud condensation nuclei. We aimed to evaluate air ion concentrations and characteristics of new particle formation events (NPF) in the megacity of Paris, France, within the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric Pollution and climate effects, and Integrated tools for assessment and mitigation) project. We measured air ion number size distributions (0.8–42 nm) with an air ion spectrometer and fine particle number concentrations (&gt; 6 nm) with a twin differential mobility particle sizer in an urban site of Paris between 26 June 2009 and 4 October 2010. Air ions were size classified as small (0.8–2 nm), intermediate (2–7 nm), and large (7–20 nm). The median concentrations of small and large ions were 670 and 680 cm−3, respectively, (sum of positive and negative polarities), whereas the median concentration of intermediate ions was only 20 cm−3, as these ions were mostly present during new particle formation bursts, i.e. when gas-to-particle conversion produced fresh aerosol particles from gas phase precursors. During peaks in traffic-related particle number, the concentrations of small and intermediate ions decreased, whereas the concentrations of large ions increased. Seasonal variations affected the ion population differently, with respect to their size and polarity. NPF was observed in 13 % of the days, being most frequent in spring and late summer (April, May, July, and August). The results also suggest that NPF was favoured on the weekends in comparison to workdays, likely due to the lower levels of condensation sinks in the mornings of weekends (CS weekdays 09:00: 18 × 10−3 s−1; CS weekend 09:00: 8 × 10−3 s−1). The median growth rates (GR) of ions during the NPF events varied between 3 and 7 nm h−1, increasing with the ion size and being higher on workdays than on weekends for intermediate and large ions. The median GR of small ions on the other hand were rather similar on workdays and weekends. In general, NPF bursts changed the diurnal cycle of particle number as well as intermediate and large ions by causing an extra peak between 09:00 and 14:00. On average, during the NPF bursts the concentrations of intermediate ions were 8.5–10 times higher than on NPF non-event days, depending on the polarity, and the concentrations of large ions and particles were 1.5–1.8 and 1.2 times higher, respectively. Because the median concentrations of intermediate ions were considerably higher on NPF event days in comparison to NPF non-event days, the results indicate that intermediate ion concentrations could be used as an indication for NPF in Paris. The results suggest that NPF was a source of ions and aerosol particles in Paris and therefore contributed to both air quality degradation and climatic effects, especially in the spring and summer.

Thermal effects of asymmetric electrolytes in electric double layer capacitors

This study presents a thermal model, derived from first principles, for electric double layer capacitors (EDLCs) with multiple ion species and/or asymmetric electrolytes. It accounts for both irreversible and reversible heat generation rates resulting from the transient electrodiffusion of ions within the electrolyte. Detailed numerical simulations of EDLCs with planar electrodes and binary and asymmetric electrolytes were performed under galvanostatic cycling. The irreversible Joule heating decreased with increasing valency and/or diffusion coefficient of either ion. The local reversible heat generation rate near a given electrode was determined by the properties of the counterion. It increased with increasing counterion valency and/or decreasing counterion diameter. As a result, the electrode with the counterion of smaller diameter and/or larger valency experienced significantly larger temperature oscillations during galvanostatic cycling than the opposite electrode. In general, EDLC electrolytes featuring ions with large valency and/or small diameter produce large capacitance but also large reversible heating. The present study suggests that EDLC electrolytes should feature large bulk ion concentrations and at least one ion with a large diffusion coefficient to minimize both irreversible and reversible heating.

Observations on the formation, growth and chemical composition of aerosols in an urban environment.

The charge and chemical composition of ambient particles in an urban environment were determined using a neutral particle and air ion spectrometer and an aerodyne compact time-of-flight aerosol mass spectrometer. Particle formation and growth events were observed on 20 of the 36 days of sampling, with eight of these events classified as strong. During these events, peaks in the concentration of intermediate and large ions were followed by peaks in the concentration of ammonium and sulfate, which were not observed in the organic fraction. Comparison of days with and without particle formation events revealed that ammonium and sulfate were the dominant species on particle formation days while high concentrations of biomass burning OA inhibited particle growth. Analyses of the degree of particle neutralization lead us to conclude that an excess of ammonium enabled particle formation and growth. In addition, the large ion concentration increased sharply during particle growth, suggesting that during nucleation the neutral gaseous species ammonia and sulfuric acid react to form ammonium and sulfate ions. Overall, we conclude that the mechanism of particle formation and growth involved ammonia and sulfuric acid, with limited input from organics.

Erbium‐Ion‐Doped Tellurite Glasss Fibers and Waveguides — Devices and Future Prospective: PART I

This review article focuses on the suitability of Er3+‐doped tellurium oxide glass for optical amplification in fiber, waveguides and as a component for optical integration to meet the emerging demand for broadband and fiber‐to‐home networks. The importance of the glass structure, in the context of Er3+‐ion spectroscopy, is emphasized for dissolving large concentrations of dopant ions. The spectroscopic methodologies involved in maximizing the gain per unit length of Er3+‐doped fiber is explained. In Part II of this study, a review of how the fiber gain data was then employed to engineer amplification in waveguides, which can be integrated with semiconductor pump sources, is presented.

Asymptotic and numerical analysis of electrohydrodynamic flows of dielectric liquid

We perform an asymptotic analysis of electrohydrodynamic (EHD) flow of nonpolar liquid subjected to an external, nonuniform electric field. The domain of interest covers the bulk as well as the thin dissociation layers (DSLs) near the electrodes. Outer (i.e., bulk) equations for the ion transport in hierarchical order of perturbation parameters can be expressed in linear form, whereas the inner (i.e., DSL) equations take a nonlinear form. We derive a simple formula in terms of various parameters which can be used to estimate the relative importance of the DSL-driven flow compared with the bulk-driven flow. EHD flow over a pair of cylindrical electrodes is then solved asymptotically and numerically. It is found that in large geometric scale and high ion concentration the EHD flow is dominated by the bulk-charge-induced flow. As the scale and concentration are decreased, the DSL-driven slip velocity increases and the resultant flow tends to dominate the domain and finally leads to flow reversal. We also conduct a flow-visualization experiment to verify the analysis and attain good agreement between the two results with parameter tuning. We finally show, based on the comparison of experimental and numerical solutions, that the rate of free-ion generation (dissociation) should be less than the one predicted from the existing formula.