Anion Valence Research Articles

The Influence of Salt Anions on Heavy Metal Ion Adsorption on the Example of Nickel.

The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.

New insight into the preferred valency of interlayer anions in hydrotalcite-like compounds: The effect of Mg/Al ratio

Abstract Magnesium-aluminum hydrotalcite-like compounds with molar ratios of Mg/Al ranging from 1.93 to 6.63 were synthesized and characterized with elemental analysis, XRD, SEM, TG/MS, XPS, 27Al solid state MAS NMR, 13C solid state CP MAS NMR, and vibrational spectroscopy (FTIR and Raman). The results of physico-chemical studies show that the materials are free of impurities and consistently point to the steady evolution of the interlayer anion composition upon increase of Mg/Al ratio. In particular, it is observed that the growing content of magnesium within the hydrotalcite layer is accompanied by the gradual substitution of dinegative interlayer carbonate anions with mononegative bicarbonates and/or nitrates. The observation contradicts the generally accepted view that the hydrotalcite-like structures have greater affinities for multivalent anions compared with monovalent ones. It is argued that in materials with low degree of Al for Mg substitution, hence larger distance between the charge generating sites, compensation by monovalent anions enhances Coulombic interactions within the hydrotalcite-like structure.

Anion-responsive carbon nanosystem for controlling selenium fertilizer release and improving selenium utilization efficiency in vegetables

The application of Se fertilizers could promote plant growth and enhance Se contents of crops. However, traditional Se fertilizer tended to be lost with rainwater and caused Se pollution. Thus, it was necessary to develop a smart nanosystem to control Se fertilizer release. In this work, an anion-responsive nanosystem was prepared using polyethylenimine modified hollow/mesoporous carbon nanoparticles (PHMCN), and selenate could be effectively loaded into PHMCN (the highest loading capacity: 389 mg/g) by electrostatic attraction. The release of Se from this nanosystem could be sensitively triggered using PO43−, CO32−, and OH− as the model anions by ion exchange, and the release amount of Se was dependent on the concentration and valence of anions, so that the Se loss could be significantly reduced and the yield and Se content of vegetables increased. This work provides a promising strategy for obtaining Se-enriched vegetables and reducing Se pollution.

Anomalous flatband voltage shift of AlFxOy/Al2O3 MOS capacitors: A consideration on dipole layer formation at dielectric interfaces with different anions

We experimentally investigated the dipole layer formation at Al2O3/AlFxOy (x:y = 1:1 and 1:2.5) interfaces, which would be explicable by considering the anion density difference as the key parameter to determine the dipole direction at the dielectric interface with different anions. Molecular dynamics (MD) simulation of Al2O3/AlF3 demonstrates a preferential migration of O from Al2O3 to AlF3 compared with F to the opposite direction which suggests that anion migration due to the density difference could determine the direction of the dipole layer formed at this interface. In addition, charge separation due to the difference in the anion valences could have certain effect simultaneously.

Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe application of nanoparticles. In this study, dispersion and aggregation of nano-TiO2 in aqueous solutions containing various anions were investigated. The influences of anion concentration and valence on the aggregation size, zeta potential and aggregation kinetics were individually investigated. Results showed that the zeta potential decreased from 19.8 to −41.4mV when PO43− concentration was increased from 0 to 50mg/L, while the corresponding average size of nano-TiO2 particles decreased from 613.2 to 540.3nm. Both SO42− and NO3− enhanced aggregation of nano-TiO2 in solution. As SO42− concentration was increased from 0 to 500mg/L, the zeta potential decreased from 19.8 to 1.4mV, and aggregate sizes increased from 613.2 to 961.3nm. The trend for NO3− fluctuation was similar to that for SO42− although the range of variation for NO3− was relatively narrow. SO42− and NO3− accelerated the aggregation rapidly, while PO43− did so slowly. These findings facilitate the understanding of aggregation and dispersion mechanisms of nano-TiO2 in aqueous solutions in the presence of anions of interest.

Adsorption of reactive dyes from aqueous solution by dirty bentonite

The preparation of magnesium hydroxide coated bentonite, B–Mg(OH)2 composite, and its capacity to remove anionic reactive dyes; Procion blue HP (PB) and Remazol brilliant blue R (RB) from aqueous solution were reported in this study. The adsorbent was characterized by X-ray fluorescence analysis, X-ray powder diffraction, thermal gravimetric analysis, Brunauer Emmett Teller surface area analysis; scanning electron microscopy, and Fourier transform infrared spectroscopy. The effectiveness of B–Mg(OH)2 composite to remove dyes was examined at different initial concentrations, pH, temperature and ionic strengths. At pH=2, the maximum dye adsorption was found as 98.2% for RB and 87.8% for PB. Kinetic studies revealed that adsorption follows a pseudo-second-order model, and rate constants were evaluated. The Langmuir monolayer adsorption capacities of PB and RB in aqueous solution were estimated at 298K as 40.22 and 66.90mg/g, respectively. A temperature uptake from 278K to 313K induced an increase of adsorption for both dyes and the process was found to be physiosorptive, endothermic and spontaneous. Higher concentration or more valence of anions of electrolytes in dye solution caused decreasing dye adsorption efficiency of B–Mg(OH)2 composite.

The origin of electronic band structure anomaly in topological crystalline insulator group-IV tellurides

AbstractGroup-IV tellurides have exhibited exotic band structures. Specifically, despite the fact that Sn sits between Ge and Pb in the same column of the periodic table, cubic SnTe is a topological crystalline insulator with band inversion, but both isovalent GeTe and PbTe are trivial semiconductors with normal band order. By performing first-principles band structure calculations, we unravel the origin of this abnormal behaviour by using symmetry analysis and the atomic orbital energy levels and atomic sizes of these elements. In group-IV tellurides, the s lone pair band of the group-IV element is allowed by symmetry to couple with the anion valence p band at the L-point, and such s–p coupling leads to the occurrence of bandgap at the L-point. We find that such s–p coupling is so strong in SnTe that it inverts the band order near the bandgap; however, it is not strong enough in both GeTe and PbTe, so they remain normal semiconductors. The reason for this is the incomplete screening of the core of the relatively tight-binding Ge 4s orbital by its 3d orbitals and the large atomic size and strong relativistic effect in Pb, respectively. Interestingly, we also find that the rhombohedral distortion removes the inversion symmetry and the reduced s–p coupling transforms the α-SnTe back to a normal semiconductor. Our study demonstrates that, in addition to spin–orbital coupling, strain and interface dipole fields, inter-orbital coupling is another effective way to engineer the topological insulators.

Method for estimating ionicities of oxides using O1s photoelectron spectra

The average valence, ValO, of the oxygen anions in the perovskite oxide BaTiO3, was found using O1s photoelectron spectra to be −1.55. This experimental result is close to the theoretical value for BaTiO3 (−1.63) calculated by Cohen [Nature 358, 136 (1992)] using density functional theory. Using the same approach, we obtained values of ValO for several monoxides, and investigated the dependence of ValO and the ionicity on the second ionization energy, V(M2+), of the metal cation. We found that the dependence of the ionicity on V(M2+) in this work is close to that reported by Phillips [Rev. Mod. Phys. 42, 317 (1970)]. We therefore suggest that O1s photoelectron spectrum measurements should be accepted as a general experimental method for estimating the ionicity and average valence of oxygen anions.

Effect of Electrolytes and Correlations for Salinities at the Optimum Formulation of Sodium Dodecyl Benzene Sulfonate Microemulsions

AbstractThe influences of different kinds of electrolytes on sodium dodecyl benzene sulfonate microemulsions were investigated in this work. Electrolyte cations had a strong influence on the microemulsion phase behavior. The higher the valence of the cation was, the stronger the influence of the electrolyte on the microemulsion phase inversion and the higher the optimum solubilization parameters, ordered as AlCl3 > MgCl2 > NH4Cl > KCl > NaCl. The anion in electrolytes showed a relatively weak influence. The influences of anions with equal valence are almost the same for sodium salts, and a lower valence had a stronger impact on microemulsion phase inversion, ordered as Cl− > CO32− = SO42− > PO43−. The change of anions in sodium salts had little influence on the optimum solubilization parameters , all in the range of 5.301 ± 0.105 goil/gsurfactant. The efficiency ratio of electrolytes was defined based on the cationic charge concentration in mol/l. The efficiency ratios for electrolytes with monovalent cations were inversely proportional to (1 + Zi), where Zi is the anion valence, but this was not true for electrolytes with higher valence cations. For a microemulsion using electrolyte mixtures, the efficiency ratio shows a linear relationship with that of the component salts and the composition of the mixture.

Effects of monovalent and multivalent ions on the stability of a polyelectrolyte complex with entrapped surfactants

In this article, we report the effects of nine different monovalent and multivalent salts on the particle size and stability of refined, positively charged polyelectrolyte complexes (PECs) with entrapped surfactant. Dynamic light scattering and ζ potential measurements of these polymeric particles as a function of various salt concentrations showed that both counter ions and co-ions induced a concentration-dependent increase in the particle size and a decrease in the ζ potential. We found that the anion concentration where the particle size doubled and the maximum anion concentration beyond which particle precipitation occurred (Ca,max) demonstrated a power law dependence on the anion valence. Moreover, for anions of the same valence but different hydration radio, Ca,max decreased in the following order: NO3 → Cl → HPO42− > SO42− > PO43−. However, unlike the case of hard colloids where co-ions have relatively little effect on particle interactions, the co-ions also increased the hydrodynamic radii of our PECs in the following order: K+ ≈ Na+ > Ca2+ > Mg2+ > Al3+. Furthermore, we found that the entrapped surfactants were shielded from the adverse effect of multivalent ions; this established that the monovalent and multivalent ions interacted with the polyelectrolyte shells of the PEC. This behavior was in contrast with the effect of salts on mixtures containing the polyelectrolyte and surfactant components, where the addition of salts typically causes an interaction with the individual components. Because several biomedical and technological applications involving PECs require saline environments, our studies provide insight into how small ions influence the PEC stability in applications involving varying salinities. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42099.

Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Cetyl Ether and Potassium Salt at Different Temperatures

The aqueous two-phase system (ATPS) containing the polyoxyethylene(20) cetyl ether (C56H114O21, POELE20) and three potassium salts (KOH, K2CO3, and K3PO4) at the three temperatures (288.15, 298.15, and 308.15) K were designed. The binodal data of the studied systems were determined and correlated with three experience equations, and a satisfactory correlation effect was gained. The effect of the type of salt on the phase-forming ability of the system was discussed in the study of effective excluded volume (EEV), phase diagram, and Gibbs free energy of ionic hydration. It was found that the phase-forming ability of the system was enhanced with the increase in system EEV and anion valence, and it also increased with an increase in the absolute value of Gibbs free energy of ionic hydration. The binodal curves are influenced by the system temperature, and it was found that, with the increase in temperature, the binodal curves moved to the left and the two-phase areas expanded. Moreover, the effect of temperature on the slope of the tie line was studied, and we have drawn a conclusion that the value of the slope of the tie line increased with rising temperature.

Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Lauryl Ether and Sulfate Salt at Different Temperatures

The aqueous two-phase system (ATPS) containing the polyoxyethylene(20) cetyl ether (C56H114O21, POELE20) and three potassium salts (KOH, K2CO3, and K3PO4) at the three temperatures (288.15, 298.15, and 308.15) K were designed. The binodal data of the studied systems were determined and correlated with three experience equations, and a satisfactory correlation effect was gained. The effect of the type of salt on the phase-forming ability of the system was discussed in the study of effective excluded volume (EEV), phase diagram, and Gibbs free energy of ionic hydration. It was found that the phase-forming ability of the system was enhanced with the increase in system EEV and anion valence, and it also increased with an increase in the absolute value of Gibbs free energy of ionic hydration. The binodal curves are influenced by the system temperature, and it was found that, with the increase in temperature, the binodal curves moved to the left and the two-phase areas expanded. Moreover, the effect of temperat...

Electronic Effect Related to the Nonuniform Distribution of Ionic Charges in Metal‐Cluster Chalcogenide Halides

Recently, it was shown that the bond valence model is a unique tool to describe the lattice strains in (TM)6 chalcogenide halides (TM = transition metal). Three different phenomena that result in valence violations were identified: (1) a steric conflict between countercations and the cluster–ligand framework, (2) a steric conflict between small (TM)6 clusters and large coordination polyhedra around the cluster or the so-called matrix effect, and (3) nonuniform distribution of the anion valences (bond valence sums) around the clusters. This paper shows that the model is valid for a wide family of cluster compounds with different nuclearities. On the basis of the separation of the steric and electronic effects in the calculation procedure, the unusual distribution of the anion valences in the cluster compounds was assigned to the nonuniform spreading of ionic charges. Thus, stabilization mechanisms in cluster compounds were explained by simple electrostatic interactions.

Bond-valence model for metal cluster compounds. II. Matrix effect

The bond-valence model was commonly considered as inappropriate to metal cluster compounds, but recently it was shown that the model provides unique information on the lattice strains and stabilization mechanisms in (TM)6-chalcohalides, Mx(TM)6Ly (TM = transition metal, L = the chalcogen and/or halogen ligands; M = counter-cation). The previous study was mainly devoted to the non-uniform distribution of the anion valences (bond-valence sums) around clusters. This and the previous paper are focused on two additional phenomena: (i) a steric conflict between counter-cations and the cluster-ligand framework resulting in `common' lattice strains [previous paper: Levi et al. (2013). Acta Cryst. B69, 419-425], and (ii) steric conflict between the small (TM)6-cluster and the large coordination polyhedron around the cluster or so-called matrix effect (this paper). It was shown that both phenomena can be well described by changes in the bond-valence parameters. This paper demonstrates that the matrix effect results in high strains in the TM-L bonds in most of the (TM)6-chalcohalides (TM = Nb, Mo, W and Re). In spite of this, the violations for the total TM valence are minimal, because the cluster stretching is fully or partially compensated by compression of the TM-L bonds. As a result, the influence of the matrix effect on the material stability is rather positive: it decreases the volume of the structural units and in many cases ensures a more favorable distribution of the bond valences around TM atoms, stabilizing the cluster compound.

Bond-valence model for metal cluster compounds. I. Common lattice strains

The bond-valence model was commonly considered as inappropriate to metal cluster compounds, but recently it was shown that the model provides unique information on the lattice strains and stabilization mechanisms in (TM)6-chalcohalides (TM = transition metal in the cluster). The previous study was mainly devoted to the non-uniform distribution of the anion valences (bond-valence sums) around clusters. This and the following paper focuses on two additional phenomena: (i) a steric conflict between counter-cations and the cluster-ligand framework resulting in `common' lattice strains (this paper), and (ii) steric conflict between the small (TM)6-cluster and the large coordination polyhedron around the cluster or so-called matrix effect [the next paper; Levi et al. (2013), Acta Cryst. B69, 426-438]. It was shown that both phenomena can be well described by changes in the bond-valence parameters. The calculations were based on the structural data known to date for a variety of (TM)6-cluster compounds, Mx(TM)6Ly (TM = Nb, Mo, W and Re; M = various additional cations, L = the chalcogen and/or halogen ligands). The results were used to explain the structural peculiarities of these compounds with remarkable physical properties and the mechanisms of their stabilization.

Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Lauryl Ether and Three Kinds of Potassium Salts at Different Temperatures

The binodal curves of the aqueous two-phase system (ATPS) containing the polyoxyethylene (10) lauryl ether (POELE10, C32H66O11) and three potassium salts (KOH/K2CO3/K3PO4) were determined at the temperatures (288.15, 293.15, 303.15, and 308.15) K. The three experience equations were used to fit the binodal data for the studied systems, and a satisfactory correlation effect was obtained. The effect of salts on the binodal curves for the investigated systems was discussed by the effective excluded volume (EEV), and we found that the salting-out effect is mainly influenced by valence of anion of salts. The salt containing the higher valence of anion has a stronger phase-forming ability than that with a lower charge of anion. The liquid–liquid equilibrium (LLE) data for the investigated systems were determined and correlated by the Othmer–Tobias and Bancroft equations. The effect of the change of temperature on the binodal curves and tie-lines was also studied through the analysis of the EEV values and cloud point (CP) figure. The increase in temperature leads to the strengthening hydrophobicity of POELE10 that drive more water transferring from the top phase to the bottom phase, which means the phase-forming ability of the whole systems was strengthened. Thus, the critical concentration of POELE10 and salts for forming ATPS decreases with the rising temperature.

Liquid−Liquid Equilibria of UCON + (Sodium or Potassium) Phosphate Salt Aqueous Two-Phase Systems at 23 °C

Six phase diagrams for UCON−phosphate salt aqueous two-phase systems (ATPSs), at 23 °C, are presented. The ATPSs were obtained combining UCON (a random copolymer of 50 % ethylene oxide and 50 % propylene oxide) and a phosphate salt (KH2PO4, K2HPO4, potassium phosphate buffer pH = 7, NaH2PO4, Na2HPO4, and sodium phosphate buffer pH = 7). Among the salts used, Na2HPO4 proved to be the most effective in ATPS formation, providing the greatest heterogeneous region in the phase diagram. The previous established relation between the anion valence and the concentration needed to form a biphasic system was confirmed: higher valence requires lower concentration. Na+ salts require, in all cases, lower concentration to form ATPSs than the corresponding K+ salts. The size of the heterogeneous region in the phase diagrams increases with an increase of the pH value of the salt used in ATPS preparation.

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

AbstractHydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SRK2SO4 > SRKCl and SRNa2SO4 > SRNaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Cationic and anionic daughters of AlOH and GaOH. An ab initio study

Neutral, cationic, and anionic AlOH, HAlO, GaOH, and HGaO species were studied using QCISD method with the aug-cc-pVTZ+5s4p3d basis sets. The kinetic barriers for the isomerization processes leading from MOH to HMO (M = Al,Ga) were also estimated for the neutral and ionic systems. It was found that AlOH and GaOH neutral molecules correspond to the global minima while their isomers are higher in energy by ca. 1.8–1.9 eV. The most stable neutral isomers (AlOH and GaOH) do not form stable anionic states while their tautomers (HAlO and HGaO) bind an excess electron forming stable valence (ground) and dipole-bound (excited) states of anions.

Rheological properties of reversible thermo-setting in situ gelling solutions with the methylcellulose–polyethylene glycol–citric acid ternary system (2): Effects of various water-soluble polymers and salts on the gelling temperature

The influences of various salts and water-soluble polymers on the phase transition temperature of thermo-setting gels prepared by combining methylcellulose (MC)–sodium citrate (SC)–polyethylene glycol (PEG) at appropriate ratios (the MC–SC–PEG system) were investigated. Concerning cations, comparison of the phase transition temperature between SC and tripotassium citrate (PC) showed a rapid increase in the viscosity of SC between 20 °C and 25 °C and an increase in the viscosity of PC between 30 °C and 35 °C. Concerning the valency of anions, comparisons among SC, disodium tartrate dihydrate (ST), disodium maleate hemihydrates (SM), and sodium sulfate (SS) showed a rapid increase in the viscosity of trivalent SC between 20 °C and 25 °C and changes in the viscosity of the three bivalent sodium salts (ST, SM, and SS) at ≥30 °C. Thus the phase transition temperature decreased with an increase in the valency of anions. Subsequently, the influences of various water-soluble polymers on the gelling temperature were compared. Using polyvinylpyrrolidone (PVP) instead of PEG, the gelling temperature decreased with an increase in the PVP concentration even without the addition of SC. Unlike PVP, the addition of xanthan gum as a viscosity-increasing polysaccharide did not reduce the gelling temperature irrespective of its concentration. Temperature-associated changes in viscosity were observed at a fixed SC concentration with changes in the concentration of PVP or PEG. The gel phase transition temperature increased from 46 °C to 50 °C in gels not containing PVP or PEG. The viscosity did not differ between the addition of PVP or PEG at a low concentration and its absence. However, the viscosity clearly changed after the addition of each agent at a high concentration.