Alkali Earth Cations Research Articles

Catalytic activities of zeolite compounds for decomposing aqueous ozone

The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone.

Quantitative reconstruction of early cretaceous paleoclimate using paleosol carbonates in China

In this study, an attempt to quantitatively rebuild the Early Cretaceous paleoclimate was executed by employing calcareous paleosols (fossil soils), which have a horizon of pedogenic carbonate accumulation within the profile, in the central Sichuan Basin of southwestern China and Jinlingshi-Yangshan Basin of northeastern China, using the relationships between the climate and geochemical proxies, depth to calcic horizon and oxygen stable composition of pedogenic carbonates in modern soils. During the early Valanginian and early-middle Berriasian ages in the central Sichuan Basin, the climate was dominantly cold and dry, with a mean annual temperature (MAT) within 5 and 9 °C (standard error (S.E.) = ±5.8 °C) and mean annual precipitation (MAP) within ~190 and ~320 mm. During the late Barremian age (~126 Ma), the MAP was within ~200 and ~380 mm, and MAT was between 9 and 13 °C (S.E. = ±5.8 °C) in the Jinlingsi-Yangshan Basin. Noticeably, for the paleosols which formed under the arid climate, alkali and alkaline earth cations were weakly leached from the soil profile, and even accumulated on the soil surface. Therefore, geochemical indices (such as the chemical index of alteration (K2O-free) and alkaline index) to evaluate the chemical weathering, including base cations (Ca2+, Mg2+, Na+ and K+), as the functions of precipitation and air temperature, are unsuitable for paleoclimate reconstruction of paleo-aridisols.

Lithium Plating in the Presence of Alkali and Alkaline Earth Cations

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Carbon nitride nanotube as a sensor for alkali and alkaline earth cations

Adsorption of several alkali (Li+, Na+, and K+) and alkaline earth (Be2+, Mg2+, and Ca2+) cations on the surface of a zigzag (9, 0) carbon nitride nanotube has been investigated using density functional theory. It has been found that almost all of the cations prefer to be strongly chemisorbed at the center of porous site of the tube surface. The adsorption of alkaline cations much more influences the electronic properties of the tube, in comparison with the alkali ones, so that it is transformed from an intrinsic semiconductor with HOMO/LUMO energy gap of 4.02eV to extrinsic p-type one with the gap of 0.54–1.94eV. The alkaline cation adsorption may significantly raise potential barrier of the electron emission from the tube surface, hence impeding the field emission. It has been also concluded that the electrical sensitivity of the tube toward the cations may be in the order: Be2+≫Mg2+≫Ca2+≫Li+∼Na+∼K+.

Boson peak of alkali and alkaline earth silicate glasses: Influence of the nature and size of the network-modifying cation

The influence of the size of the alkaline earth cation on the boson peak of binary metasilicate glasses, MSiO(3) (M = Mg, Ca, Sr, Ba), has been investigated from vibrational densities of states determined by inversion of low-temperature heat capacities. As given both by C(p)/T(3) and g(ω)/ω(2), the intensity of the boson peak undergoes a 7-fold increase from Mg to Ba, whereas its temperature and frequency correlatively decrease from 18 to 10 K and from 100 to 20 cm(-1), respectively. The boson peak results from a combination of librations of SiO(4) tetrahedra and localized vibrations of network-modifying cations with non-bridging oxygens whose contribution increases markedly with the ionic radius of the alkaline earth. As a function of ionic radii, the intensity for Sr and Ba varies in the same way as previously found for alkali metasilicate glasses. The localized vibrations involving alkali and heavy alkaline earth cations appear to be insensitive to the overall glass structure. Although the new data are coherent with an almost linear relationship between the temperature of the boson peak and transverse sound velocity, pure SiO(2) and SiO(2)-rich glasses make marked exceptions to this trend because of the weak transverse character of SiO(4) librations. Finally, the universality of the calorimetric boson peak is again borne out because all data for silicate glasses collapse on the same master curve when plotted in a reduced form (C(P)∕/T(3))/(C(P)/T(3))(b) vs. T/T(b).

Thermodynamic Properties of Uranyl Minerals: Constraints from Calorimetry and Solubility Measurements

More than 50 uranyl minerals, phases containing U6+ as the uranyl UO22+ cation, and hydroxide, carbonate, phosphate, and silicate anions, H2O, and alkali and alkaline earth cations, occur in nature and as corrosion products of spent nuclear fuel. Despite their importance and the need to understand their thermodynamics to predict uranium solubility, fate, and transport in the environment, reliable thermodynamic data have only been available recently. This paper summarizes recent studies of enthalpies of formation using high temperature oxide melt solution calorimetry and Gibbs free energies from solubility experiments. Standard state thermochemical parameters (at 25 °C and 1 bar) are tabulated and the stability and transformation sequences of these phases are discussed. The enthalpies of formation from oxides are discussed in terms of crystal structure and Lewis acid–base interactions.

Ionic conductivity of multicomponent fluorite-structured fluorides

Influence of mixing of homovalent cations on the fast anionic conductivity, static permittivity, and thermal diffusivity is investigated in multicomponent fluorite-structured concentrated solid solutions of alkali earth and rare earth fluorides. Influence of mixing of alkali earth cations on electrical properties of fluoride superionics is studied in Ba0.7 − x Sr x La0.3F2.3 single crystals and Ca0.85 − x Sr x Nd0.15F2.15 transparent polycrystals. Influence of mixing of rare earth cations on electrical properties of fluoride superionics is studied in Ba0.75La0.25 − x Nd x F2.25 and Ba0.35Sr0.35(R 1, ..., R i )0.3F2.3 (i = 1–6; R i stands for rare earth elements) single crystals. It is shown that the ionic conductivity decreases with increasing difference between mean ionic radii of rare earth and alkali earth cations. Up to 350°C, the fastest ionic conductivity is found in Ba0.35Sr0.35La0.3F2.3 single crystals.

Electrochemical and spectrophotometric study on trivalent neodymium ion in molten binary mixtures of LiCl and alkali earth chlorides

The thermodynamic stability of Nd(III) complexes was studied by electrochemical techniques for molten binary mixtures composed of LiCl and an alkali earth chloride, CaCl 2, SrCl 2, or BaCl 2 at 923 K. The Gibbs free energy change of formation of Nd(III) in the melts was determined. The obtained values showed a good correlation with the polarizing power of solvent cations. The Nd(III) complex was more stable in the melts with low polarizing power. The electronic absorption spectrum of the hypersensitive f– f transition of Nd 3+ was investigated to obtain information about the structural change of the NdCl 6 3 - complex. The estimated oscillator strength of the 4 G 5/2, 2 G 7/2 ← 4 I 9/2 transition and the degree of the energy splitting in electronic energy levels showed different trends upon the polarizing power for each of added alkali earth chloride. This indicates that the coordination environments further from second neighbors could have significant impact on the electronic energy levels of Nd(III) in the mixtures including alkali earth cations.

Synthesis and complexive abilities in cone conformation of upper rim functionalized of calix[4]arene with alkali and alkali earth cations

The synthesis and complexive abilities of 5-mono­[(tert-butoxycarbonyl)-amino]-11,17,23-triamino-25,26,27,28-tetrabutoxycalix[4]arene (L1) and 5,11,17,23-tetrakis[(tert-butoxycarbonyl)-amino]-25,26,27,28-tetrabutoxycalix[4]arene (L2) towards the alkali cations Li+, Na+, K+, Rb+, Cs+ and the alkali earth cations Mg+2, Ca+2, Sr+2 and Ba+2in methanol-chloroform mixture have been evaluated at 25°C using UV-Vis spectrophotometric techniques. The results show that the ligands are capable of complexing with all the cations by 1:1 metal to ligand ratios. Molecular mechanics calculations have been used to model the geometries of the alkali and alkali earth cations with the ligands using the Hyperchem 7 computational package. The selectivity is presented considering that the calculated formation constants are in the order Li+>>Na+>K+>Rb+>Cs+and Mg+2>Ca+2>Sr+2>Ba+2with the ligands. Also, L1 shows more attraction towards the smaller alkali and alkali earth metal ions than L2.

Cd1−xBix(Cd1+xIn1−x)VO6 (0 ≤ x ≤ 0.14): A New Polar Oxide with Second-Harmonic Generation

The structure of the new polar oxide, Cd2InVO6, was determined by powder X-ray diffraction. Cd2InVO6 crystallizes in space group P31 with the unit cell parameters: a = 12.218 96(4), c = 9.256 75(4) A. The Cd2+ and In3+ ions are statistically disordered in nine independent positions (M1−M9) with a certain level of site preference. M1−M3 form highly asymmetric oxygen-coordination polyhedra, which are similar to those formed by alkali or alkali-earth cations. M4−M9 are in distorted octahedral cavities. It is shown that M1−M3 are likely occupied mostly by Cd2+ while M4−M9 are extensively mixed by Cd2+ and In3+. The structure is best described as a framework of interconnected M4−M9 distorted octahedra with the M1−M3 polyhedra off-framework and the three independent VO4 tetrahedra filling the channels of the framework structure by corner-sharing with the MO6 octahedra. The polar framework is composed of M4O6∼M9O6 octahedra in a five-connected net with the topology nomination (33, 63, 94). The Bi3+-substituted c...

Spectrophotometric studies of alkali and alkali earth metal ions complexes of mono amino derivative of calix[4]arene

The synthesis and complexive abilities of 5,11,17-tris(tert-butyl)-23 amino-25,26,27,28-tetra-propoxycalix[4]arene towards alkali cations Li+, Na+, K+, Rb+, Cs+ and alkali earth cations Mg2+, Ca2+, Sr2+ and Ba2+ in methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex with all the cations by 1: 1 metal to ligand ratios. The selectivity presented considering the calculated formation constants are in the order Li+ > Na+ > K+ > Rb+ > Cs+ and Mg2+ > Ca2+ > Sr2+ > Ba2+ with the ligand.

Mixed-valence manganites

Mixed-valence manganese oxides (R1-χAχ)MnO3 (R=rare-earth cation, A=alkali or alkaline earth cation), with a structure similar to that of perovskite CaTiO3, exhibit a rich variety of crystallographic, electronic and magnetic phases. Historically they led to the formulation of new physical concepts such as double exchange and the Jahn-Teller polaron. More recent work on thin films has revealed new phenomena, including colossal magnetoresistance near the Curie temperature, dense granular magnetoresistance and optically-induced magnetic phase transitions. This review gives an account of the literature on mixed-valence manganites, placing new results in the context of established knowledge of these materials, and other magnetic semiconductors. Issues addressed include the nature of the electronic ground states, the metal-insulator transition as a function of temperature, pressure and applied magnetic field, the electronic transport mechanisms, dielectric and magnetic polaron formation, magnetic localization, ...

Natural zeolites as effective adsorbents in water and wastewater treatment

Natural zeolites are abundant and low cost resources, which are crystalline hydrated aluminosilicates with a framework structure containing pores occupied by water, alkali and alkaline earth cations. Due to their high cation-exchange ability as well as to the molecular sieve properties, natural zeolites have been widely used as adsorbents in separation and purification processes in the past decades. In this paper, we review the recent development of natural zeolites as adsorbents in water and wastewater treatment. The properties and modification of natural zeolite are discussed. Various natural zeolites around the world have shown varying ion-exchange capacity for cations such as ammonium and heavy metal ions. Some zeolites also show adsorption of anions and organics from aqueous solution. Modification of natural zeolites can be done in several methods such as acid treatment, ion exchange, and surfactant functionalisation, making the modified zeolites achieving higher adsorption capacity for organics and anions.

Diamagnetic probe atoms of Tin-119 in magnetically ordered ferrites with a brownmillerite-type structure

The method of Mossbauer probe spectroscopy on 119Sn nuclei was used applied to study the influence of the nature of the alkali-earth cation A2+ = (Ca, Sr) in A2Fe2O5 ferrites with an ordered brownmillerite-type structure on the formation of the local environment and magnetic hyperfine interactions of probe tin atoms.

The electrokinetic properties of carbonates in aqueous media revisited

The electrokinetic properties of model carbonate particles in aqueous media have been investigated with respect to their dependence on pH (ranging from 6 to 11) at 25 °C as a function of their structural and chemical diversities and of their biomimetical or inorganic precipitation modes. The model carbonates used were the calcium carbonate polymorphs—calcite, aragonite, and vaterite (CaCO 3) and the alkali-earth metal carbonate isomorphs—strontianite (SrCO 3) and witherite (BaCO 3). The results obtained in this study show that the most important potential-determining ions (pdi) are the alkali-earth cations (Me 2+), and confirm the previous findings which showed that H + and OH − are of secondary influence for the electrical surface properties. The differences in the electrophoretic mobility (EPM) and, consequently, the electrokinetic potential (the zeta-potential) of the investigated carbonate solids are governed by dissolution–precipitation processes at the mineral/solution interfaces, depending on the solubility product and on the concentration of Me 2+ that dominates in solution. The biomimetical precipitation route yielded solids that were, in terms of their electrokinetic properties, similar to those obtained by the inorganic process route.

Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid–solid interface

AbstractHydrothermal water–(pyroclastic) rock interactions were examined using flow‐through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75–250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature.Based on the chemistry of analysed solutions, the water–rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock–fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ‘surface layer’ comprised a 0.5–1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al‐rich cation‐leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10−4 to 10−7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively.

Dual optical detection of a novel selective mercury sensor based on 7-nitrobenzo-2-oxa-1,3-diazolyl subunits

A novel macromolecule based on 2-[3-(2-aminoethylthio)propylthio]ethanamine covalently bound to two 7-nitrobenzo-2-oxa-1,3-diazolyl moieties was prepared as a fluoroionophore and a chromophore for the selective optical detection of Hg 2+. The sensor was prepared in two steps and its fluoroionophoric and chromophoric properties toward various transition metal, alkali, and alkali earth cations were investigated. Compound 4 selectively binds Hg 2+, and the binding is indicated by both fluorescence quenching and a chromogenic change which can be detected by the naked eye. In an 80:20 acetonitrile/water solvent mixture, 4 acts as an ON–OFF fluorescence switch upon Hg 2+ binding, exhibiting efficient quenching and a detection limit of 10 −7 M or 20 ppb.

Adsorption of small molecules on alkali-earth modified titanosilicates

Removal of nitrogen from methane-rich streams is one of the most energy-intensive gas separations. Nitrogen rejection units are very expensive units and in streams with small and intermediate flowrates, adsorption technologies proved to be an economic alternative, if N 2 is selectively adsorbed in the adsorbent. In this work we have synthesized sodium titanosilicate (Na-ETS-4) and study the effect of exchanging Na with different alkali-earth cations in the structure, namely Sr and Ca. Adsorption equilibrium of CH 4 and N 2 and CO 2 were measured at 323 K in all the samples. The effect of different activation temperatures was studied in the modified samples. It was observed that activating the adsorbent at high temperatures prior to adsorption tests, the capacity of methane can be reduced. In the Ca-ETS-4 a shift in selectivity was observed: activating the adsorbent at higher temperatures result in an adsorbent with higher selectivity towards nitrogen. In all the samples tested, the loading of carbon dioxide is much higher than the loading of other gases indicating that this gas should be removed from the stream before nitrogen rejection.

Effect of composition and promoters in Au/TS-1 catalysts for direct propylene epoxidation using H2 and O2

A series of Au/titanium silicalite-1 (TS-1) catalysts with different Si/Ti ratios and promoted with alkali and alkaline earth cations were prepared by deposition–precipitation (DP) and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity was highly dependent on the pH of the DP synthesis solution and the final composition of the catalyst. Addition of Group 1 metals such as K or Cs had little effect on the gold content, but increased activity, while Group 2 metals such as Mg, Ca, Sr, and Ba increased both the gold content and the catalytic activity. The highest improvement was provided by a Mg promoted catalyst, which at 443K and 0.1MPa with a H2/O2/C3H6/Ar=1/1/1/7 feed mixture gave a propylene oxide (PO) formation rate of 88gPOh−1kgcat−1, compared to 57gPOh−1kgcat−1 for an unpromoted catalyst, corresponding to a 50% enhancement of activity. Ammonia temperature-programmed desorption (NH3-TPD) measurements indicated little change in adsorption amount with promotion indicating that the yield increase was not due to the elimination of acidic sites on the catalyst. Instead, the improved catalytic performance was ascribed to increased Au capture efficiency and dispersion by the catalyst. The effect of Si/Ti ratio, pH of synthesis, and the promoter ions on the gold content could be understood from their effect on the surface charge of the support.

Magnetic Properties and Negative Colossal Magnetoresistance of the Rare Earth Zintl phase EuIn2As2

Large, high quality single crystals of a new Zintl phase, EuIn(2)As(2), have been synthesized from a reactive indium flux. EuIn(2)As(2) is isostructural to the recently reported phase EuIn(2)P(2), and it is only the second reported member of the group of compounds with formula AM(2)X(2) (A = alkali, alkaline earth, or rare earth cation; M = transition or post-transition metal; and X = Group 14 or 15 element) that crystallizes in the hexagonal space group P6(3)/mmc (a = 4.2067(3) A, c = 17.889(2) A and Z = 2). The structure type contains layers of A(2+) cations separated by [M(2)X(2)](2-) layers along the crystallographic c-axis. Crystals of the title compound were mounted for magnetic measurements, with the crystallographic c-axis oriented either parallel or perpendicular to the direction of the applied field. The collective magnetization versus temperature and field data indicate two magnetic exchange interactions near 16 K, one involving Eu(2+)...Eu(2+) intralayer coupling and the other involving Eu(2+)...Eu(2+) coupling between layers. EuIn(2)As(2) is metallic and magnetoresistive, as is the isostructural phosphide, and both compounds have coincident resistivity and magnetic ordering transitions, consistent with the observation of colossal magnetoresistance. Negative colossal magnetoresistance (MR = {[rho(H) - rho(0)]/rho(H)} x 100%) of up to -143% (at T = 17.5 K, H = 5 T) is observed for EuIn(2)As(2), approximately half of that observed for the more resistive phosphide, which has a higher magnetic ordering temperature and local moment coupling strength.