Bivalent Ions Research Articles

Simple pyrolysis of alginate-based hydrogel cross-linked by bivalent ions into highly porous carbons for energy storage

Searching for a sustainable precursor that is capable of absorbing microwave energy is crucial for its rapid conversion into porous carbon via microwave heating. Here, alginate-based hydrogel beads cross-linked by bivalent ions (Cu2+, Zn2+, and Ca2+) are converted into porous carbons (SPCs) in 10 min by applying simple microwave-assisted pyrolysis. Water wrapped in hydrogel beads and bivalent ions serve as initial microwave absorbers to convert alginate into char which acts as a good microwave absorber in the following stages. Additionally, bivalent ions also act as a gelling agent to generate hydrogel beads, as a porogen to obtain a highly porous structure, and as a metal donor to form the SPC/Cu composite. The resultant SPC has a high specific surface area of 1336 m2 g−1, a large total pore volume of 0.56 cm3 g−1, interconnected macropores, as well as a high oxygen content of up to 13.2%. These attractive characteristics give SPC a remarkable rate capability of 72% at 50 A g−1. Interestingly, the interconnected macropores in SPC offer sufficient space for Cu growth via the redox reactions of Cu2+; thus, the SPC/Cu composite without acid wash shows a specific capacitance as high as 804 F g−1 at 0.5 A g−1.

Aging indicators for stored carioca beans

High temperature, moisture content and radiation conditions, common in the tropics, accelerate the physiological post-harvest disorders in beans, affect integument color and bean hardness. This study explored the darkening and hardening mechanisms in carioca type beans during storage. The contrasting genotypes for bean darkening and hardening (BRS Estilo and BRS Pontal: rapid darkening and hardening; BRSMG Madrepérola and CNFC 10467: slow darkening and partially resistant to hardening; and a Canadian genotype of the Pinto Bean type resistant to darkening (negative control)) were evaluated right after harvest and after six months storage at 20.3 ± 0.2 °C and 78.9 ± 6.0% RH, with respect to their physicochemical, biochemical and morphological attributes. All the samples hardened with time, but the velocity of darkening did not always parallel the degree of hardening of the beans (that increase linearly with time), which indicates that the color of the bean integument was not a safe indicator to predict the culinary quality of carioca beans. During storage, the SOD (superoxide dismutase) activity and LP (lipid peroxidation) in the cotyledon increased, and the increase was more significant in the integument of the rapid-darkening genotypes. The oxidative stress detected in the beans apparently started in the green bean formation phase, continuing during post-harvest, especially for the rapid-darkening beans. Quantification of the bivalent ions in the bean fractions, together with the degree of membrane damage was positively associated with bean darkening, independent of the group. Thus, aging of the carioca beans could be triggered by a complex mechanism involving diverse intrinsic factors in different degrees according to the genotype and the post-harvest period, but some parameters could serve as indicators, as cooking time, hardness and color, to differentiate between rapid and slow darkening beans.

Structural phase transition, optical bandgap, interband electronic transition, and improved magnetism in bivalent Ca-, Sr-, Pb-, and Ba-doped BiFeO3 ceramics

Perovskite compounds Bi0.7A0.3FeO3−δ (BAFO) (A = Ca, Sr, Pb, and Ba) with improved optical and magnetic properties have been synthesized by solid-state method. The effect of bivalent ions substitution on the phase transition, microstructure, optical, and magnetic properties are investigated in detail. X-ray diffraction and Raman scattering spectra analyses indicate the phase transition from rhombohedral to cubic in doped samples and the coexistence of the two phases in BBFO, inducing strong lattice distortions. A blue shift observed in d–d transitions energies can reveal the decreased internal chemical pressure, thus leading to the slight increase in bandgaps of BSFO, BPFO, and BBFO. While, narrowed bandgap of 1.96 eV can be found in BCFO for the increased tailing of the conduction band edge into the gap. Besides, room-temperature ferromagnetism has been observed in Sr-, Pb-, and Ba-doped samples which can be resulted from the suppression of spiral structure of BFO. These results lay a solid foundation on further exploring the potential abilities of BFO ceramics as multiferroic photovoltaic materials.

Novel Horizon: Smart TiO2/Sn(IV)SbP Nanocomposite with Enhanced Electrochemical and Photocatalytic Properties

In the present research work, sol-gel derived smart nanocomposite of tin antimonophosphate mixed with different concentration of TiO2 (0–40%) has been synthesized and further characterized through XRD, SEM, EDS, and HRTEM. The aim of this study is to relate the electrical conductivity dependence behavior with the different doping concentration of TiO2 (0–40%) in the composite. For this, ion exchange capacity (IEC) has been selected as a preliminary criterion for the measurement of other electrochemical properties like; membrane potential, transport number and permselectivity. The composite with 20% TiO2 in tin antimonophosphate possesses a maximum value, i.e. 0.97 meq/g for IEC, and has been further studied as a case for the material characterisation. Membrane potential, transport number, permselectivity values for the nanocomposite membrane have been found to be better than pristine membrane, for both monovalent and bivalent ions. The composite with 20% TiO2 in tin antimonophosphate further used a photocatalyst for the degradation MB dye. It shows 97% removal efficiency with apparent rate constant of 0.01314 min–1. The photocatalytic degradation of MB follows pseudo-first order kinetics.

Nanocomposite membranes embedded with dopamine-melanin nanospheres for enhanced interfacial compatibility and nanofiltration performance

Nanomaterials incorporation in polymer membranes has been widely recognized as an effective strategy to improve membrane performance in filtration such as desalination. However, the poor compatibility between nanomaterials and polymer matrix restricts the enhancement of rejection because of unavoidable defects. In this work, we present a nanocomposite membrane by incorporating a kind of well-compatible polymeric nanomaterial, dopamine-melanin nanospheres with functional groups in cellulose triacetate (CTA) to improve the separation performance. The abundant amine and hydroxyl groups of dopamine-melanin nanospheres, not only contribute to the increase of membrane hydrophilicity for enhancing water flux, but also improve the interfacial compatibility between dopamine-melanin nanospheres and CTA matrix for maintaining excellent rejection. More significantly, the negative charges of dopamine-melanin nanospheres intensify the zeta potentials of membrane, which enhances the salt rejection by Donnan effect. The optimal NC-0.4 membrane yielded water flux of 22 L m−2 h−1 and high rejections to salts, MgSO4 (97.6%) > Na2SO4 (96.5%) > MgCl2 (91.8%) > NaCl (76.1%), owing to the synergistic effect of size exclusion and electrostatic repulsion. Moreover, the NC-0.4 membrane obtained excellent rejections to monovalent and bivalent ions. Therefore, blending well-compatible polymeric nanomaterials with polymer matrix could be an effective strategy to develop high-performance membrane for desalination.

Comparison of Inflammatory Effects in THP-1 Monocytes and Macrophages after Exposure to Metal Ions.

Monocytes and macrophages are the first barrier of the innate immune system, which interact with abrasion and corrosion products, leading to the release of proinflammatory mediators and free reactive molecules. The aim of this study was to understand inflammation-relevant changes in monocytes and macrophages after exposure to corrosion products. To do this, the THP-1 cell line was used to analyze the effects of metal ions simultaneously in monocytes and differentiated macrophages. Cells were stimulated with several concentrations of metal salts (CoCl2, NiCl2, CrCl3 × 6H2O) to analyze viability, gene expression, protein release and ROS production. Untreated cells served as negative controls. While exposure to Cr(3+) did not influence cell viability in both cell types, the highest concentration (500 µM) of Co(2+) and Ni(2+) showed cytotoxic effects mirrored by significantly reduced metabolism, cell number and a concomitant increase of ROS. The release of IL-1β, IL-8, MCP-1 and M-CSF proteins was mainly affected in macrophages after metal ion exposure (100 µM), indicating a higher impact on pro-inflammatory activity. Our results prove that monocytes and macrophages react very sensitively to corrosion products. High concentrations of bivalent ions lead to cell death, while lower concentrations trigger the release of inflammatory mediators, mainly in macrophages.

On the permselectivity of cation-exchange membranes bearing an ion selective coating

Monovalent ion selective membranes are permeable for monovalent ions while rejecting divalent ions to some extent. Different processes and applications like electrodialysis, microbial fuel cells, and flow batteries utilize such selective properties. Industrial membranes have a specific coating of equal charge to reject the bivalent counter ions. It has been suggested in the past that the current density regime at which such composite ion exchange membranes are operated can strongly influence their ion selectivity towards monovalent ions. Here, we now confirm this observation for a commercial CMS membrane as well as for a novel microgel modified membrane. The higher the applied current density is, the more acute the drop in selectivity becomes as opposed to the unmodified reference membrane where bivalent ions are transported preferentially. This work focuses on the relationship between selectivity and current density regime using (1) a conventional commercial membrane, (2) a commercial monovalent ion selective membranes as well as (3) a tailor-made selective membrane, the latter being surface-modified with quaternized Poly (2-vinylpyridine) (qP2VP) microgels. Experimental electrodialysis results in combination with (a) direct numerical simulations of mixed ion transport through the composite architecture and (b) a swelling analysis of the microgels by ellipsometry reveal that layer responsiveness and structural change of the modification layer is responsible for the decrease in permselectictivity upon an increased current density. The swelling reduces the charge density of the modification and therewith the rejection of divalent ions. It would be highly desirable to synthesize modification layers that have a low ion transport resistance while maintaining its volumetric charge density independent of the current density applied.

Synthesis and characterization of novel thin films derived from pyrazole-3-one and its metal complex with bivalent nickel ion to improve solar cell efficiency

In this work, an organic ligand and its metal complex with Ni (II) ion was synthesized and used to improve solar cell efficiency. The organic Schiff base ligand, 4-(1, 3-benzodioxol-5-ylmethylideneamino)-1, 5-dimethyl-2-phenylpyrazole-3-one [L], was produced by condensation reaction of 4-aminoantipyrine with piperonaldehyde in absolute ethanol. The synthesized organic ligand [L] was characterized using 1H and 13C NMR, FT-IR, UV–Vis, elemental analysis (C.H.N), X-ray diffraction (XRD), mass spectrum, and atomic force microscope (AFM). The Ni (II) complex [M] was obtained in a molar ratio (2:1) (L:M). The prepared complex was characterized using X-ray diffraction (XRD), magnetic susceptibility measurement, elemental analysis (C.H.N), electrical molar conductivity, Fourier-transform infrared FT-IR, UV–Vis spectroscopy, atomic force microscope (AFM) and flame atomic absorption technique. Results suggested an octahedral geometry around the bivalent Ni (II) ion. Drop casting method was employed to prepare thin films of nanoparticles of the synthesized compounds. The optical, morphological, and structural properties for those particles were also studied and they were used to improve the silicon solar cell after the depositing on the silicon slides. The efficiency of the resulted inorganic solar cell was higher than the organic solar cell.

Synthesis and electrochemical behaviour of GO doped ZrP nanocomposite membranes

In this study, new nanocomposite ion-exchange membranes were prepared by incorporating graphene oxide (GO) in the inorganic matrix of zirconium phosphate (ZrP) by sol-gel method. The synthesized GO-ZrP membranes were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Water content and ion exchange capacity were found to increase initially with increase in concentration of GO up to 0.2 wt% and then decreased with further increase in concentration of GO. The electrochemical properties of prepared membranes like membrane potential, transport number, fixed charge density, permeability and ionic flux were explored. The fabricated membranes exhibited higher membrane potential, transport number and fixed charge density for monovalent ions (NaCl) than those for bivalent ions (BaCl2). These membranes exhibited lower permeability and ionic flux for bivalent ions as compared to those for monovalent ions. The conductivity measurements for both monovalent and bivalent ions were performed on the nanocomposite membranes, and it was noticed that the conductivity of the membranes was higher for monovalent ions.

Improving osteogenesis of calcium phosphate bone cement by incorporating with manganese doped β-tricalcium phosphate.

Lack of osteogenic capacity limits the bone repair effect of calcium phosphate cement (CPC). In present work, bivalent manganese ion (Mn2+) doped β-tricalcium phosphate (Mn-TCP) was incorporated into CPC to enhance its osteogenic ability. The incorporation of Mn-TCP promoted the hydration reaction of CPC. The presence of Mn2+ made the hydration products finer. When adding 10wt% Mn-TCP in CPC (Mn-CPC-1), the setting time of CPC was shortened, whereas the strength and injectability were not changed. Mouse Bone marrow mesenchymal stem cells (mBMSCs) on Mn-CPC-1 and CPC with 20wt% Mn-TCP (Mn-CPC-2) presented better adhesion and spreading behaviors. Besides, Mn-CPC-1 promoted the gene levels of ALP, Col-I and OC while Mn-CPC-2 promoted the gene levels of Runx2 and OC. Cellular behaviors were related to two points: one was the increase of adsorption capacity of proteins (e.g. BSA) after changing the surface properties of bone cements; and the other was the biological role of Mn2+ released from CPC in osteogenesis. All the results indicated that CPC incorporated with 10wt% Mn-TCP has good osteogenesis and proper physicochemical properties, which will be a prospective biomaterial applying in the area of bone regeneration.

Influence of process parameters on separation performance of strategic elements by polymeric nanofiltration membranes

Employing nanofiltration, a separation of uncharged solutes, monovalent, and bivalent ions from multicomponent aqueous solutions is potentially feasible. Separation is strongly influenced by process parameters as well as the feed properties and membrane characteristics. The aqueous solution in this study includes strategic elements (Ge, Co, Mo, Re) in a wide range of concentrations and varying ionic species. The feed composition mirrors a bioleachate of a German flue dust resulting from copper ore smelting. In a number of cross-flow experiments, the separation performance of eight commercial polymeric nanofiltration membranes was evaluated and the influence of transmembrane pressure, flow velocity, flow regime, recovery, and ionic strength was investigated. It was observed that a high ionic strength (evoked by a high Zn concentration) affects Re retention negatively and decreases permeability. By increasing the transmembrane pressure, the separation selectivity towards Re is enhanced. An almost quantitative Re separation is realized with a cut-off below 200 Da (RO90, NE-90). The utilized NF99HF membrane shows the best results regarding permeability and separation selectivity towards Re, Ge, and Mo.

Against Expectations: Unassisted RNA Adsorption onto Negatively Charged Lipid Bilayers.

The composition and physicochemical properties of biological membranes can be altered by diverse membrane integral and peripheral proteins as well as by small molecules, natural and synthetic. Diverse oligonucleotides have been shown to electrostatically interact with cationic and bivalent ion loaded zwitterionic liposomes, leading to the formation of oligonucleotide-liposome aggregates. However, interaction of RNAs with other membrane surfaces remains ill understood. We used the nonnatural RNA10 to investigate RNA binding to anionic and net-uncharged membrane surfaces. RNA10 had initially been selected in a screen for nonnatural RNA motives that bind to phosphatidylcholine liposomes in the presence of Mg2+. Here we show that interaction of defined RNA molecules with membrane surfaces crucially depends on electrostatic surface properties. Furthermore, RNA10 electrostatically binds to anionic lipid bilayers in the absence of Mg2+ or other bivalent cations, and this interaction leads to measurably changed physicochemical properties of the bilayer and the oligonucleotide. Thus, the structure of polyanionic RNA can be modulated via contact with negatively charged membrane surfaces and vice versa.

Rapid sample clean-up procedure for aminophosphonate determination by LC/MS analysis

Aminophosphonates are commonly utilised for complexing bivalent ions such as calcium and magnesium. With regard to environmental samples, the analysis of these highly polar compounds is still challenging due to matrix effects and lacking analytical standard methods. We have recently developed a LC/MS method for common aminophosphonates without derivatisation. This LC/MS method delivers precise and accurate measurement for standard samples with very low concentration of cations disturbing the analysis. However, due to matrix effects this LC/MS method requires a sample clean-up being also applicable to natural water or wastewater samples. We developed and optimised a sample clean-up procedure applying strong cation exchange resin Dowex 50WX8. This clean-up allows a single LC/MS analysis of hydroxyethelidene(diphosphonic acid) (HEDP), aminotris(methylenephosphonic acid) (ATMP), ethylenediaminetetra(methyloenephosphonic acid) (EDTMP), diethylenetriaminepenta(methylenephosphonic acid) (DTPMP) and its major intermediates amino(methylphosphonic acid) (AMPA) and iminodi(methylenephosphonic acid) (IDMP). We compared different test conditions with six aminophosphonates in either ultra pure water or tap water. The latter was used to simulate cation concentrations typical for natural waters. To elute all aminophosphonate including AMPA, ammonium acetate addition was necessary. The addition of ammonium acetate was combinable with all tested aminophosphonates and provides high sample quality for LC/MS analysis. For acceptable recovery, the smallest aminophosphonate AMPA required the highest addition of ammonium acetate (1000 mg L-1) during the sample clean-up. Finally, the optimised clean-up procedure was successfully applied to identify and quantify phosphonates from an industrial wastewater sample. The sample clean-up procedure is simple, cheap, rapid and precise and can be further combined with solid phase extraction and more sensitive LC/MS methods.

Spatial charge relaxation in glasses poled in the air and argon atmospheres

Thermal poling of a multicomponent silicate glass was performed in air and in argon atmospheres at various voltages, and the temperature dependences of the depolarization currents (TSDC) in the poled glasses were studied. In addition, the concentration profiles of univalent and bivalent cations in subanodic regions of the poled glasses were measured with EDS and SIMS techniques. The difference in the displacements of bivalent ions at poling of the glasses in closed and open anode configurations allowed us to identify “frozen” spatial charge relaxation peaks observed in the TSDC measurements and to relate these peaks to hydrogen and bivalent metal ions relaxation.

Assembly of MIL-101(Cr)-sulphonated poly(ether sulfone) membrane matrix for selective electrodialytic separation of Pb2+ from mono-/bi-valent ions

Acidic functionalized polymer-MIL-101 composite membrane were considered as a promising material for the electrodialytic separation of targeted bi-valent metal ion from industrial waste water. Architectural strategy for these specific selective membrane was based on the presence of acidic functional groups (–SO3H) and coordinately unsaturated metal sites. In general, scalability and mechanical stability were the key limitations for MOF based membranes. But we report a simple preparation of flexible and mechanical stable MIL-101(Cr) composite membrane. In this method, MIL-101 was entrapped within hydrophilic pore/ion conducting channels of the sulphonated poly(ether sulfone) (SPES) matrix by hydrophilic-hydrophilic interactions. Further, incorporation of MIL-101(Cr) within SPES matrix significantly improved the membrane’s properties. We adopted a simple approach enabling fine distribution of hydrophilic material within the pore of acidic functionalized polymer containing hydrophilic and hydrophobic segments. MIL-101 is expected to be confined responsible for the pore modification. Well optimized MIL-10 membrane showed good permselectivity for mono-valent (Na+) and bi-valent (Zn2+, and Ni2+) ions, while impervious nature for Pb2+. Further, simple preparation and cost-effective nature of SPES@MIL-101 membranes are the attractive feature for fabricating Pb2+ impervious membrane for its selective separation. Reported new class of membrane preparation protocols open a window for fabricating nano-channels for selective ion transport.

Solubility of TINOPAL CBS-X fluorescent dye at different EDTA concentrations and pH values: Implications regarding its applicability in field tracer tests

TINOPAL CBS-X has been described in published literature as a fluorescent dye that is suitable for use as a tracer in groundwater investigations. However, several of these field tests have yielded unexpected results. In this study the influence that the complexation agent EDTA (ethylenediaminetetraacetate) and pH have on the solubility of TINOPAL CBS-X have been systematically investigated in the laboratory and the results obtained validated with thermodynamic calculations using the PhreeqC software. Modeling indicated that the amount of EDTA required for complete TINOPAL CBS-X dissolution is, in many aquifers, so great that its use is no longer feasible. However, softening the water by adding NaOH appears to be a promising way to increase TINOPAL CBS-X solubility. Water with a low availability of bivalent and/or trivalent ions yielded solubilities up to two orders of magnitude higher than waters from limestone aquifers with a high Ca2+ ion content. Results revealed that the spectrum of TINOPAL CBS-X applicability as a conservative tracer in aquatic environments is limited to a limited range of specific water chemistries. The long tailing in the breakthrough curve and the retarded breakthrough of TINOPAL CBS-X in a previously reported carbonate karst aquifer field tracer test was accurately reproduced by a transport model with a modified input function based on solubility modeling. Travel times and attenuation by incompletely dissolved tracers are tend to be overestimated, which can be problematic with regard to predictions of contaminant transport, or the delineation of water protection zones. The use of TINOPAL CBS-X as a conservative tracer and the concentrations required needs therefore to be carefully evaluated with respect to water-hardness, pH, alkalinity, and dilution rates. An input script for PhreeqC is provided to help estimate appropriate concentrations of TINOPAL CBS-X, thus enhancing its potential and reliability for future groundwater research.

Bioprinting of a Cell-Laden Conductive Hydrogel Composite.

Bioprinting has gained significant attention for creating biomimetic tissue constructs with potential to be used in biomedical applications such as drug screening or regenerative medicine. Ideally, biomaterials used for three-dimensional (3D) bioprinting should match the mechanical, hydrostatic, bioelectric, and physicochemical properties of the native tissues. However, many materials with these tissue-like properties are not compatible with printing techniques without modifying their compositions. In addition, integration of cell-laden biomaterials with bioprinting methodologies that preserve their physicochemical properties remains a challenge. In this work, a biocompatible conductive hydrogel composed of gelatin methacryloyl (GelMA) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was synthesized and bioprinted to form complex, 3D cell-laden structures. The biofabricated conductive hydrogels were formed by an initial cross-linking step of the PEDOT:PSS with bivalent calcium ions and a secondary photopolymerization step with visible light to cross-link the GelMA component. These modifications enabled tuning the mechanical properties of the hydrogels, with Young's moduli ranging from ∼40-150 kPa, as well as tunable conductivity by varying the concentration of PEDOT:PSS. In addition, the hydrogels degraded in vivo with no substantial inflammatory responses as demonstrated by haematoxylin and eosin (H&E) and immunofluorescent staining of subcutaneously implanted samples in Wistar rats. The parameters for forming a slurry of microgel particles to support 3D bioprinting of the engineered cell-laden hydrogel were optimized to form constructs with improved resolution. High cytocompatibility and cell spreading were demonstrated in both wet-spinning and 3D bioprinting of cell-laden hydrogels with the new conductive hydrogel-based bioink and printing methodology. The synergy of an advanced fabrication method and conductive hydrogel presented here is promising for engineering complex conductive and cell-laden structures.

Adsorption of bivalent lead ions from an aqueous phase system: Equilibrium, thermodynamic, kinetics, and optimization studies.

Punica granatum carpellary membrane powder (PGCM) and its surface modified form (MPGCM) with 2,4-dinitrophenylhydrazine (2,4-DNP) were used as adsorbents for removal of bivalent lead ions from aqueous phase system. Batch mode experiments using various parameters were carried out to assess the adsorption isotherms and dynamics of the process. Langmuir isotherm was well-fitted model for experimental data. Langmuir adsorption capacity using PGCM and MPGCM at pH of 7 was found to be 169.49 and 196.07mg/g, respectively. Rate constant and thermodynamic parameters were calculated to evaluate the kinetic model and temperature dependence nature of adsorption. Box-Behnken design was applied to optimize the adsorption process of bivalent lead ions for PGCM and MPGCM using pH (3.0-9.0), initial bivalent lead ions concentration (20-100mg/L), contact time (20-180min), and temperature (20-60°C) parameters. The optimum conditions for maximum removal of bivalent lead ions on PGCM were found to be at pH of 6.99, initial bivalent lead ions concentration of 98.95, contact time of 176.05, and temperature of 21.20°C and on MPGCM at pH of 6.51, initial bivalent lead ions concentration of 99.99, contact time of 177.89, and temperature of 20.02°C, respectively. PRACTITIONER POINTS: Adsorption of bivalent lead from water using Punica granatum carpellary membrane powder and its modified form MPGCM is discussed. Batch mode experiments using various parameters were carried out to assess the adsorption isotherms and dynamics of the process. Langmuir adsorption capacity using PGCM and MPGCM at pH of 7 was found to be 169.49 and 196.07mg/g, respectively. Box-Behnken design was applied to optimize the adsorption process of bivalent lead ions.

"Ion Solvation Spectra": Free Energy Analysis of Solvation Structures of Multivalent Cations in Aprotic Solvents.

Using advanced molecular dynamics free energy sampling techniques-both classical and ab initio-we analyze the solvation structures of multivalent cations in aprotic solvents. In contrast to previous studies of mono- and bivalent ions in organic solvents, mainly performed using hybrid cluster-continuum quantum chemistry calculations that rely on the assumption of uniqueness of ion solvation free energies, here we find that monatomic bivalent cations may have multiple well-defined minima, as previously reported only for water, or plateaus of free energy with respect to the ion-solvent coordination. These observations are generalized in the concept of the "ion solvation spectrum" to highlight the rich phenomenology related to ion solvation as opposed to the normally expected free energy profiles with a single coordination minimum. Specifically, we show that a single chemical species may exhibit a multiplicity of distinctly different electrochemical properties. Using one- and two-dimensional projections of the free energy landscape, we analyze the stability of ion solvation structures and reveal minimum free energy pathways for ion (de-)solvation with low-dimensional approximations to associated kinetic barriers. Unexpectedly, we show that in some cases the process of opening the first ion solvation shell, by removing a solvent molecule, may actually drive the ion into a free energy basin with a higher coordination number. Our study highlights some deficiencies of conventional methodologies for studying ion solvation as a path to determine redox potentials and provides experimentally testable predictions.

Fabrication of mixed matrix anion exchange membrane decorated with polyaniline nanoparticles to chloride and sulfate ions removal from water

A heterogeneous anion exchange membrane was modified by introducing polyaniline nanoparticles, in order to enhance its electrochemical properties in view of chloride and sulfate ion removal from water. Polyaniline nanoparticles were synthesized by facile chemical polymerization technique. Nanoparticles were characterized by FTIR, FESEM, and XRD. In addition, SOM images showed a uniform surface for membranes. Utilizing PANI nanoparticles in membrane body led to increase of water content, ion exchange capacity, surface hydrophilicity, and electrical conductivity. Membrane transport number and permselectivity were improved in NaCl solution by incorporating PANI nanoparticles; in Na2SO4 solution, they showed an opposite trend. The chloride and sulfate flux were enhanced by a low PANI concentration and declined at higher concentration. Modified PANI membranes showed a lower selectivity and flux for bivalent ions compared to monovalent ions. Membrane mechanical resistance was increased by using PANI in concentrations up to 2 wt% and decreased at higher PANI ratios.