Valence Of Ions Research Articles

Mechanism of ionic polarizability, bond valence, and crystal structure on the microwave dielectric properties of disordered Li10MTi13O32 (M = Zn, Mg) spinels

The influence mechanism of the microwave dielectric properties of disordered spinels Li10MTi13O32 (M = Zn, Mg) was investigated via structural refinement, ionic polarizability, bond valence, P–V–L theory, Raman spectroscopy, and DC conductivity.

Significantly enhanced mechanoluminescence from Nb5+ co-doped ZrO2:Sm3+via a high valence ion doping strategy

The mechanoluminescence and afterglow properties of ZrO2:Sm3+ were significantly improved by introducing Nb5+ into the phosphor. Combined with the trap state analysis, a probable luminescence mechanism model was produced.

Valence fluctuation in Yb3Si5 probed by synchrotron X-ray photoemission spectroscopy

We report the direct evidence of valence fluctuation in the thermoelectric material Yb3Si5 by using synchrotron X-ray photoemission spectroscopy. The Yb 3d core level photoemission spectrum of a Yb3Si5 single crystal shows clear separation of the Yb2+ peak and Yb3+ multiplet peaks. From the spectral weight of each component, the mean valence of Yb ions is estimated to be +2.67 at 20 K. Furthermore, a Kondo resonance peak just below the Fermi energy is also observed by high-resolution soft X-ray photoemission spectroscopy, suggesting the valence fluctuating state in Yb3Si5.

Cation valence dependence of hydrogen bond and stacking potentials in DNA mesoscopic models

Monovalent and divalent cations play a crucial role in living cells and for molecular techniques such as PCR. Here we evaluate DNA melting temperatures in magnesium (Mg2+) and magnesium‑potassium (Mg2++ K+) buffers with a mesoscopic model that allows us to estimate hydrogen bonds and stacking interaction potentials. The Mg2+ and Mg2++ K+ results are compared to previous calculations for sodium ions (Na+), in terms of equivalent sodium concentration and ionic strength. Morse potentials, related to hydrogen bonding, were found to be essentially constant and unaffected by cation conditions. However, for stacking interactions we find a clear dependence with ionic strength and cation valence. The highest ionic strength variations, for both hydrogen bonds and stacking interactions, was found at the sequence terminals. This suggests that end-to-end interactions in DNA will be strongly dependent on cation valence and ionic strength.

Developing high-Q × f value MgNb2–xTaxO6(0≤x≤0.8) columbite ceramics and clarifying the impact mechanism of dielectric loss: Crystal structure, Raman vibrations, microstructure, lattice defects, chemical bond characteristics, structural parameters, and microwave dielectric properties in-depth studies

With the increasing frequency of wireless mobile communication, dielectric materials with higher Q × f are required to enhance the signal strength of microwave passive devices and thus compensate for the rapid attenuation of high-frequency signals during propagation. In order to improve the Q × f of the MgNb2O6 system and study the internal mechanism between the structure and microwave dielectric properties, Ta5+ ion is introduced to design and fabricate MgNb2−xTaxO6 (0 ≤ x ≤ 0.8) ceramics by the solid-state reaction method. The single columbite phase and dense structure are observed throughout the entire composition range. All elements (Mg, Nb, Ta, and O) can be detected by X-ray photoelectron spectroscopy. Insights from the Raman spectroscopy and group theoretical analysis reveal that the Ag(2) and Ag(3) modes located at ∼ 905 cm−1 dominate the Raman vibration. In addition, the ɛr depends on the polarizability reflected by the C–M equation and Raman shift. The τf closely relates to the bond energy of the Nb/Ta–O bond and restoring force characterized by average octahedral distortion of [Nb/TaO6]. Notably, the crucial factors for the huge improvement of Q × f are clarified deeply, in terms of the lower internal strain, the reduced ordering-induced domain size, and the chemical bond valence closer to the ionic valence state, which promotes the stability of crystal structure. Moreover, the introduction of lower electronegative ions enhances the ability of electrons to compensate for oxygen vacancies, thereby reducing the dielectric loss caused by the conductance. Excellent microwave properties (ɛr = 19.2, Q × f = 170,000 GHz, and τf = −55.6 ppm °C–1) are achieved in MgNb1.4Ta0.6O6 ceramic, specifically a nearly 40% increase in the Q × f. This work has enriched the theory associated with low dielectric loss and provided the MgNb1.4Ta0.6O6 ceramic with a pretty high-Q × f for the application in the design of the 5G/6G wireless communication devices.

A Molecular Theory of Polypeptide Adsorption at Inorganic Surfaces

A faithful description of polypeptide adsorption at ionizable surfaces remains a theoretical challenge from a molecular perspective due to the strong coupling of local thermodynamic nonideality and ionizations of both the adsorbate and substrate that are sensitive to the solution condition such as pH, ion valence, and salt concentration. Building upon a recently developed coarse-grained model for natural amino acids in bulk electrolyte solutions, here we report a molecular theory applicable to polypeptide adsorption on ionizable inorganic surfaces over a broad range of inhomogeneous conditions. Our thermodynamic model is able to account for diverse solution effects as well as the amino-acid sequence on polypeptide adsorption and surface association such as hydrogen bonding or bidentate coordination. The theoretical predictions have been validated by extensive comparison with experimental data for the adsorption isotherms of three representative polypeptides at a titanium surface.

SYNTHESIS AND LUMINESCENCE OF CERIUM DOPED KSrY(BO3)2

The rare-earth borate compounds are widely used in various fields of science and technology as solid-state lasers, LEDs, and plasma panels. Development of blue emitting phosphors typically involves doping with cerium ions various matrices, exhibiting high photoluminescence quantum yields for LEDs. However, the main problem of such compounds, in addition to the concentration quenching, is the presence in the matrix of both the trivalent Ce3+ and tetravalent Ce4+ states of cerium ions. The goal. Study of the luminescent properties of the new KSrY0.95(BO3)2:0.05Ce3+ compound. Experimental. New phosphors based on complex borate KSrY(BO3)2 doped with cerium ions have been obtained by the solid-phase synthesis. The mixture of the starting materials after grinding in an agate mortar has been calcined at 700°C in a platinum crucible for 12 hours. The calcination temperature has been increased in steps of 50°C with re-ground of the mixture at each stage. The KSrY0.95(BO3)2:0.05Ce3+sample has been annealed in hydrogen at 900°C for 8 hours. Results and discussion. The X-ray phase analysis has shown that the new compound crystallizes in the monoclinic space group P21/m. The calculated unit cell parameters for KSrY0.95(BO3)2:0.05Ce3+are: a = 9.2861(23) Å, b = 5.3654(6) Å, c = 6.5854(14) Å, V = 289.7(1) Å3. In the crystal structure of KSrY(BO3)2, each B atom is connected to three O atoms, forming a BO3 triangle. The planar groups (BO3)3 are distributed layer by layer in the plane. The Y atoms are surrounded by six oxygen atoms, forming an octahedral structure and occupying interlayer positions.Ce3+ ions in the crystal lattice mainly replace the Y+3positions based on the similarity of the ionic radius and valency of Y+3 (r = 0.90 Å, CN = VI), Ce3+ (r = 1.01 Å, CN = VI). Conclusion. At a wavelength of 440 nm, the excitation spectrum exhibits one absorption band with the 2F7/2 → 5D1 energy transition, which corresponds to the excitation of the cerium ion from the ground state to the excited state. A decrease in the luminescence intensity of the KSrY0.95(BO3)2:0.05Ce3+ sample has been found for 3 hours after its annealing.

Experimental study on the effects of salt solution pH on the performance of reverse electrodialysis stack

Reverse electrodialysis (RED) is a promising way of harvesting salinity gradient energy (SGE). The seawater or industrial wastewater may have various pHs. Here the RED performance involving sodium salt solutions with different ion valence ratios including anions of Cl-, SO42-, and PO43- is experimentally investigated in symmetric and asymmetric pH configurations. In the symmetrical pH configuration, increasing the solution pH significantly weakens the energy conversion performance for the 1:1 and 1:3 salts; for the 1:2 salt, the power density and energy conversion efficiency increase and then decrease with increasing pH due to the coupling effects of OH- on the ion transportation through AEMs and CEMs. In the asymmetric pH configuration, increasing the pH of the low concentration solution decreases the power density and energy conversion efficiency. As the pH of the high concentration solution increases, the output power and energy conversion efficiency decrease and then increase for the 1:1 salt due to the coupling effects of the ion transmembrane concentration difference and OH- on the ion migration of IEMs; for the 1:2 salt, the output power and energy conversion efficiency increase and then decrease; for the 1:3 salt, OH- inhibits the hydrolysis of Na3PO4 and anion migration, leading to the lowered output power density and energy efficiency.

The Application of the Nanofiltration Membrane NF270 for Separation of Fermentation Broths.

The potential for nanofiltration (NF) in removing both relatively low molecular weight (MW) organic species and charged solutes from complex media is noteworthy. The main aim of the current work was to improve understanding of the separation mechanisms of fermentation broths components in the NF process. For this purpose, the experimental investigations were performed using the commercial polyamide NF270 membrane. The feed solution was ultrafiltered 1,3-propanediol (1,3-PD) broths. The separation results were analyzed and discussed in light of the detailed characteristics of both the membrane and the broth components. It has been noted that the membrane ensured the complete 1,3-PD permeability and significant rejection of some feed components. A thorough analysis showed that the retention of carboxylic acids was based on both the Donnan effect and sieve mechanism, according to the following order: succinic acid > lactic acid > acetic acid > formic acid. Indeed, acids retention increased with increasing charged acids ions valency, Stokes radius (rS) as well as MW, and decreasing diffusion coefficient (D). In turn, for ions, the following orders retention was determined: SO42− = PO43− > Cl− and Ca2+ > Na+ > NH4+ ~ K+. It indicated that the ions retention increased with increasing ions charge density, hydrated radius (rH), and hydration energy (Eh). It showed that the separation of the ions was based on the Donnan exclusion, sieving effect, and dielectric exclusion.

In situ XPS and impedance spectroscopy studies of (1 − x)Ba0.5Bi0.5FeO3 − xGd2O3 ceramics with negative temperature coefficient

Perovskite-phase (1 − x)Ba0.5Bi0.5FeO3 − xGd2O3 ceramics with negative temperature coefficient (NTC) were synthesized by solid-state reaction. X-ray diffraction (XRD) measurements showed that all samples exhibited a tetragonal perovskite structure. In addition, all samples showed a typical NTC effect; their room resistivity ρ25 and thermal constant B25/75 were regulated by the Gd2O3 doping content, and varied in the 4.70 × 105–4.72 × 106 Ω cm and 5573–6697 K ranges, respectively. In situ X-ray photoelectron spectroscopy (XPS) elucidated the conduction mechanism of Ba0.5Bi0.5FeO3-based ceramics was the electron hopping type, and the source of NTC effect was the change in the content of different valence ion pairs and the increase in electronic mobility with increasing temperature. Impedance analysis showed that the samples were electrically inhomogeneous, and their grain boundary resistance was higher than the grain resistance. The corresponding relaxation process might originate from the release of space charge and the ionization of oxygen vacancies.

Framework Dimensional Control Boosting Charge Storage in Conjugated Coordination Polymers

Conjugated coordination polymers (CCPs) with extended π-d conjugation, which can effectively promote long-range delocalization of electrons and enhance conductivity, are superior to traditional metal-organic frameworks (MOFs) and attracted great attention for potential applications in chemical sensors, electronics, energy conversion/storage devices, etc. However, the precise construction of CCPs is still challenging due to the complex and uncontrollable reactions of CCPs. Herein, two different framework dimensions of CCPs are controllably realized by employing the same ligand (2,3,5,6-tetraaminobenzoquinone (TABQ)) and the same metal (copper) as center ions. The manipulation of reaction leads to different valences of ligands and metal ions, different coordination geometries, and thereby 1D-CuTABQ and 2D-CuTABQ frameworks, respectively. High performance of charge storage is hence achieved involving the storage of both cations and anions, and therein, 2D-CuTABQ shows a high reversible capacity of ≈305mAhg-1 , good rate capability and high capacity retention (≈170mAhg-1 after 2000 cycles at 5Ag-1 with 0.01% decay per cycle), which outperforms 1D-CuTABQ and almost all of the reported MOFs as cathodes for batteries. These results highlight the delicate structural control of CCPs for high-performance batteries and other various applications.

Ion dehydration using magnetic fields and impacts on permeability across RO membranes

Magnetic fields have been used as a mitigation process for controlling mineral scaling in diverse applications, including membrane systems. Changes in scale formation have been attributed, in part, to changes in ion hydration. The objective of this study was to evaluate how passage through a multi-directional magnetic field affected the permeability of relevant cations and anions through a seawater reverse osmosis membrane (SW30HR). Changes in ion permeability were evaluated as a function of flow velocity through the magnetic system and described in terms of changes in the ion hydration and in turn changes in the energy penalty that a given ion must incur to permeate across the RO membrane. Ion permeability across the SW30HR membrane increased after having passed through the magnetic system. Increases in ion permeability became most pronounced once a flow velocity through the magnetic system was ≥35 cm/s and were a function of the ion charge density for ions of the same valence. Increases in ion permeability were attributed to dehydration of the ions by the magnetic system resulting in a reduction in the energy penalty required for the relevant ions to transport across the membrane barrier.

Effects of different B-site ions on the catalytic performance of 3DOM LaBO3 for the simultaneous elimination of NOx and soot particulates from diesel engines

Compared with gasoline engines, diesel engines play an irreplaceable role, but we must also pay attention to the adverse effects of exhaust emissions. The simultaneous elimination NOx and soot particles is an effective way of diesel exhaust abatement. The preparation of catalyst is the core of simultaneous elimination reaction. In this work, three-dimensionally ordered macroporous (3DOM) LaBO3 perovskite catalysts were successfully prepared by colloidal crystal templates method. The as-prepared catalysts were characterized by XRD, SEM, N2 adsorption–desorption, XPS, H2-TPR, NH3-TPD, NO-TPD and NO-TPO. We compared the effects of different B site ions on the catalytic activity through the above characterization methods and 3DOM LaMnO3 shows the best performance with the lowest CO2 peak temperature and the highest NO conversion. The reasons of high performance for desoot are associated with the amount of peroxide species, and de-NOx related to surface acidity and high valence ions.

Water oxidation in oxygenic photosynthesis studied by magnetic resonance techniques.

The understanding of light-induced biological water oxidation in oxygenic photosynthesis is of great importance both for biology and (bio)technological applications. The chemically difficult multistep reaction takes place at a unique protein-bound tetra-manganese/calcium cluster in photosystem II whose structure has been elucidated by X-ray crystallography (Umena etal. Nature 2011, 473, 55). The cluster moves through several intermediate states in the catalytic cycle. A detailed understanding of these intermediates requires information about the spatial and electronic structure of the Mn4 Ca complex; the latter is only available from spectroscopic techniques. Here, the important role of Electron Paramagnetic Resonance (EPR) and related double resonance techniques (ENDOR, EDNMR), complemented by quantum chemical calculations, is described. This has led to the elucidation of the cluster's redox and protonation states, the valence and spin states of the manganese ions and the interactions between them, and contributed substantially to the understanding of the role of the protein surrounding, as well as the binding and processing of the substrate water molecules, the O-O bond formation and dioxygen release. Based on these data, models for the water oxidation cycle are developed.

Effects of Mg-doping on distorted structure and enhanced electrochemical performance of V1-Mg O2 nanorods

In this work, a series of V1-xMgxO2 samples (x = 0–0.030) were synthesized by hydrothermal method. The corresponding laws of Mg2+ doping concentration on the microstructures and electrochemical performance of V1-xMgxO2 were studied in detail. The XRD results indicated that the prepared V1-xMgxO2 samples showed monoclinic crystal phase and Mg2+ doping caused lattice distortion in the experimental doping range. The SEM and TEM results showed that all the V1-xMgxO2 samples were nanorods and well-crystallized. The positron lifetime spectra showed that the main defects in the V1-xMgxO2 samples were vacancy clusters. The concentration and size of the defects were affected by the combined action of ion radius and valence state of doped Mg2+. The electrochemical results revealed that the samples showed better electrochemical properties when the Mg2+ doping concentration x is 0.015. The high discharge capacitance of the x = 0.015 sample reached 140.6 F/g and the capacitor retention of this sample was still about 90 % after 1000 cycles.

Research progress of manganese-based layered oxides as cathode materials for potassium-ion batteries

In this paper, the research progress of K x MnO 2 as cathode material for potassium-ion batteries is reviewed, and a series of doping modification (low valence substitution) of this material is summarized. Finally, the future optimization measures of K x MnO 2 are proposed. • The research progress and challenges of monobasic K x MnO 2 as cathode materials for potassium-ion batteries are summarized. • The advantages of doped binary ferromanganese-based and manganese-magnesium-based materials as cathode materials for potassium-ion batteries are summarized. • The future improvement measures of K x MnO 2 material are proposed. Potassium is inexpensive, abundant, and evenly distributed in the Earth’s crust. It has similar physical and chemical properties to those of lithium. Therefore, the use of potassium-ion batteries is expected to be realized. Cathode materials are important components of potassium-ion batteries. In addition to potassium-containing compounds, other cathode materials should be actively explored. Manganese-based oxides are widely used as cathode materials in various batteries because of their multiple ion valence states, abundant mineral reserves, low cost, and convenient synthesis methods. Among these various cathode materials manganese dioxide with a layered structure has a large interlayer spacing, which can be used for the insertion and extraction of potassium ions with a large ionic radius between the layers. Therefore, layered K x MnO 2 (KMO) cathode materials have significant potential for development. This paper reviews the research status of manganese-, ferromanganese-, manganese magnesium-, nickel manganese-, nickel cobalt manganese-, and iron titanium manganese-based metal oxides as cathode materials for potassium-ion batteries. Additionally, the obstacles and opportunities faced by KMO materials as cathode materials for potassium-ion batteries are comprehensively discussed.

Prospects for practical use of kaminskii thermovoltaic effect

The effect discovered by Kaminskii V. V. in 1999 represents one of the new principles of transformation of thermal energy into electrical energy. It was observed in samarium monosulfide, the results of investigation of the tensorresistive effect in which were presented at the 1st CP-CPLP. The tensorresistive sensitivity was maximum among all semiconductors. Qualitative theoretical analysis of the formidable properties of SmS is made from the relations between ionization energy of impurities and ionization potentials and ionic radii, which are more favorable in rare earth elements. This is explained by the presence in the atoms of the 4-f electronic layers, which have the maximum electron density. This exclusivity determines the most rational area of practical applications of rare-earth semiconductors in quality of sensitive elements of transducers of physical quantities of resistive type. In the thermovoltaic effect, the samples located in the temperature field without gradient generate the electromotive force. The nature of the effect is related to the variation of the valence of Sm ions and the gradient of the concentration of impurities in the samples. The comparison of the parameters of Kaminskii's effect and Seebek's classical thermoelectric effect is given. Between them, the maximum values of the thermoelectric yield are 36% and 10%, respectively. The thermovoltaic effect, by virtue of its energy efficiency, absence of the need for the creation of the temperature gradient in the working element of the transducer, ecological purity and the possibility of the use of the unspecialized secondary thermal energy sources, has high prospects for practical use. The obtained results are explained by the fundamental causes related to the position of rare earth elements in Mendeleev's periodic table of elements.

Iron/manganese binary metal oxide-biochar nano-composites with high adsorption capacities of Cd2+: Preparation and adsorption mechanisms

Biochar has been widely used as an adsorbent to remove cadmium (Cd) from polluted waters because of its high specific surface area and rich functional groups. Efforts have been made to modify biochar to further improve its metal adsorption capacity. In this work, biochars prepared using cotton straw, corn straw, and rice husk, were first modified with ball-milling and iron/manganese (Fe/Mn) oxides to prepare Fe/Mn binary metal oxide-ball milled biochar (Fe/Mn-BMBCs). Compared with pristine biochars, Fe/Mn-BMBCs had rough surface with deposits of Fe/Mn oxide nanoparticles, larger specific surface areas (226.50–331.50 m2 g−1), and more oxygen-containing functional groups. The adsorption kinetics and isotherm of Cd2+ on both the pristine biochars and Fe/Mn-BMBCs were best described by the pseudo-second-order model and the Langmuir model, respectively, indicating that the adsorption of Cd2+ was primarily monolayer chemisorption. The adsorption capacities of Fe/Mn-BMBCs were 4.8–6.1 times higher than those of pristine biochars, respectively. When the solution ionic strength and valence of coexisting cation increased, the adsorption capacities of Fe/Mn-BMBCs decreased because of cation competition. In contrast, the adsorption capacities of Fe/Mn-BMBCs increased with the increasing solution pH value. Complexation with oxygen-bearing functional groups, ion exchange, Cd2+-π interaction and chemical precipitation were the main mechanisms of Cd2+ adsorption on Fe/Mn-BMBCs. Therefore, Fe/Mn-BMBCs prepared with different agricultural wastes have different Cd2+ adsorption capacities and can be used as environmentally friendly and effective adsorbents for Cd2+ removal from aqueous media.

Effects of Ion Valency on Polyelectrolyte Brushes: A Unified Theory

Effects of Ion Valency on Polyelectrolyte Brushes: A Unified Theory

Valence-skipping and quasi-two-dimensionality of superconductivity in a van der Waals insulator

Valence fluctuation of interacting electrons plays a crucial role in emergent quantum phenomena in correlated electron systems. The theoretical rationale is that this effect can drive a band insulator into a superconductor through charge redistribution around the Fermi level. However, the root cause of such a fluctuating leap in the ionic valency remains elusive. Here, we demonstrate a valence-skipping-driven insulator-to-superconductor transition and realize quasi-two-dimensional superconductivity in a van der Waals insulator GeP under pressure. This is shown to result from valence skipping of the Ge cation, altering its average valency from 3+ to 4+, turning GeP from a layered compound to a three-dimensional covalent system with superconducting critical temperature reaching its maximum of 10 K. Such a valence-skipping-induced superconductivity with a quasi-two-dimensional nature in thin samples, showing a Berezinskii-Kosterlitz-Thouless-like character, is further confirmed by angle-dependent upper-critical-field measurements. These findings provide a model system to examine competing order parameters in valence-skipping systems.