Ion-Exchange Properties of Alkali-Metal Redox-Intercalated Vanadyl Phosphate

Ion exchange of alkali metals in M_xVOPO₄·yH₂O (M=H, Na, K, Rb, Cs) is reported. The role of valence, size, and affinity of the cations in the exchange process is discussed. The interlayer distance in the H_1-xK_xVOPO₄·yH₂O system is discussed in terms of finite layer rigidity theory. Different behavior is observed for K_xNa_1-xVOPO₄·yH₂O dependening on the starting compound used. When potassium in KVOPO₄·H₂O is exchanged for Na⁺, one phase compound is formed. In contrast, K_xNa_1-xVOPO₄·yH₂O formed from NaVOPO₄·H₂O and K⁺ is a multiphase system. Ion exchange does not proceed when exchanging ions differ distinctly from each other in size, e.g., sodium and cesium.     

Dissolution of uranium oxides under alkaline oxidizing conditions

Bench scale experiments were conducted to determine the dissolution characteristics of UO₂, U₃O₈, and UO₃ in aqueous peroxide-containing carbonate solutions. The experimental parameters investigated included carbonate countercation (NH₄ ⁺, Na⁺, K⁺, and Rb⁺) and H₂O₂ concentration. The carbonate countercation had a dramatic influence on the dissolution behavior of UO₂ in 1 M carbonate solutions containing 0.1 M H₂O₂, with the most rapid dissolution occurring in (NH₄)₂CO₃ solution. The initial dissolution rate (y) of UO₂ in 1 M (NH₄)₂CO₃ increased linearly with peroxide concentration (x) ranging from 0.05 to 2 M according to: y = 2.41x + 1.14. The trend in initial dissolution rates for the three U oxides under study was UO₃ ≫ U₃O₈ > UO₂.     

Sorption of cesium from water solutions on potassium nickel hexacyanoferrate-modified <Emphasis Type="Italic">Agaricus bisporus</Emphasis> mushroom biomass

In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using ¹³⁷Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within 1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm³ g⁻¹. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH₀ 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K⁺, Na⁺, NH₄ ⁺) and divalent (Ca²⁺, Mg²⁺) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved.     

Studies on the exchange characteristics of [Co(NH3)6]3+ in amberlite IRC-50

Summary The exchange of Co(NH₃)₆]³⁺-ions on amberlite IRC-50 resin has been studied at room temperature. For this exchange process the cations are effective in the order: Cs⁺<Rb⁺<K⁺<Na⁺<Li⁺<NH₄ ⁺<Mg²⁺ <Ca²⁺<H⁺ and (C₂H₅)₄N<(CH₃)₄N⁺ ≪Cetyltrimethylammonium-ion <Cetylpyridinium-ion. The logarithm of the selectivity coefficient gives linear graphs when plotted against the radius of the hydrated ions or the reciprocals of theDebye-Hückel parameter?.     

Sorption of uranyl ion on hydrous silica: Effects of ionic strength and ethylenediaminetetraacetic acid (EDTA)

The effects of ionic strength and of ethylenediamin et etraacetic acid (EDTA) on the sorption of uranyl ion, UO₂ ²⁺, to SiO₂·xH₂O (silica gel) were investigated. It was observed that pH and the ions present in the supporting electrolytes influence the ionic strength effects. The presence of different sodium salts in the concentration range (0.20 to 1.40M) suppressed the sorption of UO₂ ²⁺ in the order: NaNO₃ < NaClO₄ < NaCl < NaOCOCH₃ < Na₂SO₄ [pH 2.75(±0.05)], while the presence of perchlorate salts of Li⁺, Na⁺ and Ca²⁺ (0.20 to 1.40M) promoted the sorption of UO₂ ²⁺ on silica gel in the order: LiClO₄∼NaClO₄<Ca(ClO₄)₂ at pH 2.80(±0.05). The ionic strength effect on UO₂ ²⁺ sorption was studied in presence of EDTA (0–1.00·10⁻³M) in the pH range 2.90 to 5.57. The sorption data and speciation calculation suggest negligible complexation of UO₂ ²⁺ with EDTA at I≥1.00M NaClO₄. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.     

Static SIMS analysis of carbonate on basic alkali‐bearing surfaces

Carbonate is a somewhat enigmatic anion in static secondary ion mass spectrometry (SIMS) because abundant ions containing intact CO₃^2? are not detected when analyzing alkaline‐earth carbonate minerals common to the geochemical environment. In contrast, carbonate can be observed as an adduct ion when it is bound with alkali cations. In this study, carbonate was detected as the adduct Na₂CO₃·Na⁺ in the spectra of sodium carbonate, bicarbonate, hydroxide, oxalate, formate and nitrite and to a lesser extent nitrate. The appearance of the adduct Na₂CO₃·Na⁺ on hydroxide, oxalate, formate and nitrite surfaces was interpreted in terms of these basic surfaces fixing CO₂ from the ambient atmosphere. The low abundance of Na₂CO₃·Na⁺ in the static SIMS spectrum of sodium nitrate, compared with a significantly higher abundance in salts having stronger conjugate bases, suggested that the basicity of the conjugate anions correlated with aggressive CO₂ fixation; however, the appearance of Na₂CO₃·Na⁺ could not be explained simply in terms of solution basicity constants. The oxide molecular ion Na₂O⁺ and adducts NaOH·Na⁺ and Na₂O·Na⁺ also constituted part of the carbonate spectral signature, and were observed in spectra from all the salts studied. In addition to the carbonate and oxide ions, a low‐abundance oxalate ion series was observed that had the general formula Na_2?xH_xC₂O₄·Na⁺, where 0 < x < 2. Oxalate adsorption from the laboratory atmosphere was demonstrated but the oxalate ion series also was likely to be formed from reductive coupling occurring during the static SIMS bombardment event. The remarkable spectral similarity observed when comparing the sodium salts indicated that their surfaces shared common chemical speciation and that the chemistry of the surfaces was very different from the bulk of the particle. Copyright © 2003 John Wiley & Sons, Ltd.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.     

Sequential bond energies of water to sodium glycine cation

Absolute bond dissociation energies of water to sodium glycine cations and glycine to hydrated sodium cations are determined experimentally by competitive collision-induced dissociation (CID) of Na⁺Gly(H₂O)_x, x = 1–4, with xenon in a guided ion beam tandem mass spectrometer. The cross sections for CID are analyzed to account for unimolecular decay rates, internal energy of reactant ions, multiple ion–molecule collisions, and competition between reaction channels. Experimental results show that the binding energies of water and glycine to the complexes decrease monotonically with increasing number of water molecules. Ab initio calculations at four different levels show good agreement with the experimental bond energies of water to Na⁺Gly(H₂O)_x, x = 0–3, and glycine to Na⁺(H₂O), whereas the bond energies of glycine to Na⁺(H₂O)_x, x = 2–4, are systematically higher than the experimental values. These discrepancies may provide some evidence that these Na⁺Gly(H₂O)_x complexes are trapped in excited state conformers. Both experimental and theoretical results indicate that the sodiated glycine complexes are in their nonzwitterionic forms when solvated by up to four water molecules. The primary binding site for Na⁺ changes from chelation at the amino nitrogen and carbonyl oxygen of glycine for x = 0 and 1 to binding at the C terminus of glycine for x = 2–4. The present characterization of the structures upon sequential hydration indicates that the stability of the zwitterionic form of amino acids in solution is a consequence of being able to solvate all charge centers.     

Nonlinear modeling of equilibrium sorption of selected anionic adsorbates from aqueous solutions on cellulosic substrates. Part 1: model development

A new nonlinear isothermal sorption model, incorporating Donnan equilibrium and electrical neutrality in the classical sorption model of direct dyes onto cellulosic substrates, as model adsorbates, is proposed. The nonlinear isothermal model was used to simulate equilibrium sorption of adsorbates containing ionic charges (z) of −2 to −4 on cellulose adsorbents at various temperature (T) and sodium chloride concentrations ([NaCl]). A detailed analysis of simulation results demonstrates that results based on the nonlinear sorption model highly agree with those based on the log-linear sorption model when the deviation in the concentration of sodium ions in the aqueous solution ([Na⁺] _S ) relative to [NaCl] used in the sorption system is restricted to <5.0%. Compared to the log-linear model, the nonlinear model avoids using graphical techniques that are relatively insensitive for determining important sorption parameters such as the internal accessible volume (V) and the standard affinity associated with sorption (−Δμ°). The nonlinear sorption model was used to examine the correlation of fit for previously reported sorption data. The model parameters V and −Δμ° based on curve fits were used to estimate V for cellulose as well as −Δμ°. The values were found to match those based on the conventional log-linear model when deviations of [Na⁺] _S relative to [`([\textNa ⁺ ]_S )] \overline{{[{\text{Na}}^{ + } ]_{S} }} were below 5%. The nonlinear model therefore provides a convenient and accurate technique to interpret the sorption of a range of anionic adsorbates on cellulosic substrates.     

Structure and Reactivity of Gas‐Phase Molybdenum Oxide Cluster Ions

Combining the ion cyclotron resonance method and a Knudsen effusion source, we obtained a series of Mo_xO_y ⁺ (x = 1 – 5, y = 1 – 15) molybdenum oxide cluster ions. We studied the dependence of the concentrations of these ions on the trapping time and their reactions with carbon monoxide. It is shown that Mo_xO_y ⁺ ions with x > 3 contain a cyclic Mo₃O₉ fragment in their structure. The oxygen bond energies in Mo_xO_y ⁺ ionic clusters are estimated.     

Effect of pH, ionic strength, foreign ions, fulvic acid and temperature on 109Cd(II) sorption to γ-Al2O3

The sorption of Cd(II) from aqueous solution on γ-Al₂O₃ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on γ-Al₂O₃ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on γ-Al₂O₃ was an spontaneous and endothermic process.     

Investigation of commercial sodium cacodylate trihydrate: penta‐μ‐aqua‐disodium(I) bis(dimethylarsenate) and di‐μ‐aqua‐bis[triaquasodium(I)] bis(dimethylarsenate)

Crystals from commercial samples of sodium cacodylate trihydrate, NaO₂As(CH₃)₂·3H₂O, were analyzed by single‐crystal X‐ray diffraction and two phases were identified, viz. penta‐μ‐aqua‐disodium(I) bis(dimethylarsenate), {[Na₂(H₂O)₅](C₂H₆AsO₂)₂}_n, (I), and di‐μ‐aqua‐bis[triaquasodium(I)] bis(dimethylarsenate), [Na₂(H₂O)₈](C₂H₆AsO₂)₂, (II). Both (I) and (II) form layered structures in which hydrated Na⁺ ions form layers in the ab plane, the cacodylate ions being located in between the layers. In (I), the two non‐equivalent Na⁺ ions (located at twofold axes) and the three non‐equivalent aqua ligands (one of which also lies on a twofold axis) form infinite polymeric layers, but in (II), layers of discrete centrosymmetric [Na₂(H₂O)₈]²⁺ ions are present. One of the commercial samples analyzed contained almost exclusively crystals of the tetrahydrate (II), while another sample consisted of a mixture of the two phases.     

Thermodynamic Properties of Quaternary Aqueous Solutions of Chlorides Charge-type 1-1*1-1*2-1: NH4Cl + NaCl + YCl2 + H2O with Y ≡ Mg2+, Ca2+, and Ba2+

Thermodynamic properties of quaternary aqueous solutions of mixed chlorides of 1-1*1-1*2-1 charge type with the cations (Na⁺, NH₄ ⁺; Mg²⁺, Ca²⁺, Ba²⁺) were determined using the hygrometric method. The quaternary systems NH₄Cl + NaCl + MgCl₂ + H₂O, NH₄Cl + NaCl + CaCl₂+ H₂O, and NH₄Cl + NaCl + BaCl₂ + H₂O have been studied at 25 °C. The water activities were measured at total molalities from 0.44 mol⋅kg⁻¹ to saturation for different ionic-strength fractions y of NH₄Cl, y=(0.20,0.50,0.80), and different ionic strength ratios z for other solutes, z=(0.20,0.50 and 0.80) for each value of y. The obtained data allows the calculation of osmotic coefficients.     

Recherche de matériauxa`conductivitéionique ame´liore´e de´rivant des hydrurofluorures de calcium CaF2−xHx: conductivite´ ionique des phases Ca1−yNay(F2−xHx)1−y/2

The doping of CaF_2?xH_x hydridefluorides by aliovalent ions is studied, the aim being the preparation of materials of improved ionic conductivity. It is shown that doping by monovalent Na⁺ ions is possible. Three hydrogen-rich phases, formulated Na_yCa_1?y(F_2?xH_x)_1?y/2 have been studied. Their conductivity is mainly ionic, but, compared with the same doping in CaF₂, the conductivity enhancement is low. This result is interpreted from energetic and structural considerations.     

Structural and optical properties of (Y3+, Tb3+)-codoped sodium bismuth titanate nanoparticles

The present study investigates the effect of (yttrium, terbium) ions codoping on structural and optical properties of sodium bismuth titanate (Na_0.5Bi_0.5TiO₃ or NBT) with the possible practical application as a multi-luminescence material in optoelectronic devices such as light-emitting diodes. The polycrystalline samples of Na_0.5(Y/Tb_xBi_1-x)_0.5TiO₃ (x = 0.00, 0.04, 0.06, and 0.08) were synthesized using solid-state reaction (mixed oxide) technique. Stoichiometric amounts of metal compounds (Na₂CO₃, Y₂O₃, Tb₄O₇, Bi₂O₃, and TiO₂) were mixed via ball milling at 250 rpm for 2 h, and the ground powders were calcined at 700 °C for 2 h. The powders were pressed under uniaxial pressure of 6.87 MPa to obtain green pellets, which were later sintered at 1,000 °C for 2 h to obtain the Na_0.5(Y/Tb_xBi_1-x)_0.5TiO₃ samples. X-ray diffraction analysis suggests that the perovskite phase is established for all (Y³⁺, Tb³⁺)-codoped NBT compositions (x = 0.00–0.08). The presence of NBT functional groups was confirmed by Fourier transform infrared spectroscopy. Raman spectra indicate that (Y³⁺, Tb³⁺) ions induce minor changes to the crystal lattice structure, with no disturbance to the long-range order. X-ray photoelectron spectroscopy results reveal the presence of all the constituent elements in the NBT samples. Scanning electron microscopy confirms the polycrystalline nature of the samples with uniform distribution of multifacetted or nearly spherical grain structures. Transmission electron microscopy and selected area electron diffraction (SAED) images show the presence of nanocrystals in the samples. Ultraviolet diffuse reflectance spectroscopy (UV-DRS) and photoluminescence results illustrate that Na_0.5(Y/Tb_xBi_1-x)_0.5TiO₃ possess wider optical energy band gap (E_g = 3.23–3.27 eV) with promising luminescence applications in the optoelectronic industry.     

Mechanism of the Formation of Molybdenum Metallocarbene Complexes in the Gas Phase

The reactions of Mo⁺ ions and Mo _x O _y ⁺ oxygen-containing molybdenum cluster ions (x = 1-3; y = 1-9) with methane, ethylene oxide, and cyclopropane were studied using ion cyclotron resonance. The formation of a number of organometallic ions, including the metallocarbene MoCH₂ ⁺ , as well as molybdenum oxometallocarbenes Mo _x O _y CH₂ ⁺ (x = 1-3; y = 2, 4, 5, or 8) and Mo _x O _y (CH₄)⁺ ions (x = 1-3; y = 2, 5, or 8), was detected. The upper and lower limits of bond energies in oxometallocarbene complexes were evaluated: 111 > D ⁰ (Mo _x O _y ⁺-CH₂) > 82 kcal/mol (x = 1-3; y = 2, 5, 8).     

Electrochemically induced transformations of ruthenium(III) trichloride microcrystals in salt solutions

Ruthenium (III) trichlorid solid crystals have been mechanically attached to gold surfaces and studied by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous solutions of different concentrations containing M⁺Cl⁻, where M⁺=H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺. The RuCl₃ and the complexes formed during the electrochemical transformations show two or more reduction and reoxidation pairs of waves, depending on the experimental conditions (concentration, scan rate, and potential range). The voltammetric peaks are shifted into the direction of higher potentials with increasing electrolyte concentrations except at very high concentrations when the peaks belong to the first reduction/reoxidation processes move oppositely. The mass change was reversible, during reduction mass increase, while during oxidation mass decrease occurred at medium electrolyte concentrations in two, more or less distinct steps. At high or low concentrations the mass excursions are more complex involving different mass increase/decrease regions as a function of potential which vary with the potential range of the measurements. The peak potentials and the electrochemical activity strongly depend on the nature of the cations and pH. It is related to the formation of complexes in different compositions. The mass change decreases with increasing electrolyte concentrations attesting the important role of the water activity and the transport of solvent molecules. It was concluded that in dilute solutions during the first reduction step M⁺ ions enter the surface layer. The strongly hydrated Li⁺ ions transfer water molecules into the microcrystals, while simultaneously with the incorporation of K⁺, Rb⁺, and Cs⁺ ions H₂O molecules leave the surface layer. The opposite transport of ions and solvent molecules occur during oxidation. In the course of further reduction the incorporation of all ions studied except that of Cs⁺ ions is accompanied with water sorption. The number of sorbed water molecules is proportional to the hydration number of these ions. A reaction scheme is proposed in which M⁺ _m-3[Ru^IIICl _m (H₂O) _n ]^3-m · xH₂O (m≥3) and [Ru^IIICl _m (H₂O) _n ]^3-m (Cl⁻)_3-m · xH₂O (m≤3) type complexes are reduced to the respective – or depending on the electrolyte concentration higher or lower – Ru(II)chloro complexes resulting in mixed valence compounds (phases). Taking into account the layered structure of RuCl₃ the electrochemical reduction can be explained as an intercalation reaction in that mixed valence intercalation phases with a general formula M _x ⁺(H₂O) _y [RuCl₃] ^x− are formed from RuCl₃·x H₂O. The reduction/reoxidation waves are related to the redox transformations of Ru(III) to Ru(II) sites, while the composition of the polynuclear complexes and the structure of microcrystals change. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13.−16., 2005.     

Synthesis and Sorption Behaviour of Some Radioactive Nuclides on Sodium Titanate as Cation Exchanger

Crystalline (Na₄TiO₄·0.32H₂O) and amorphous (Na₂TiO₃·1.45H₂O) forms of sodium titanate were prepared by fusion reaction of TiO₂ and Na₂CO₃ at 1100°C in molar ratios of 2:1 and 1:2, respectively. The prepared products were characterized using IR, DTA-TG, X-ray and elemental analyses. Kinetic studies of the order of reaction (n) and activation energy (E _a) for crystallization transformation step (for crystalline sodium titanate only) have been determined from DTA thermogram and their values were found to be 0.87 (univalent order) and 3.97 kJ mol^–1, respectively. Ion exchange capacities and some distribution studies were carried out at different conditions in the presence of some complexing agents (EDTA, boric and citric acids) and the results showed that the capacities of the crystalline form are always less than the amorphous one.     

Microporous Framework (Nb,Fe)-Silicate with Much Potential to Remove Rare-Earth Elements from Waters

Nanoparticles of a new small-pore metal silicate formulated as Na_2.9(Nb_1.55Fe_0.45)Si₂O₁₀ ⋅ xH₂O and exhibiting the structure of previously reported Rb₂(Nb₂O₄)(Si₂O₆) ⋅ H₂O have been synthesized under mild hydrothermal conditions. Replacement of the bulky Rb⁺ by smaller Na⁺ ions was accomplished by stabilizing the framework structure via partial occupancy of the Nb⁵⁺ sites by Fe³⁺ ions. Exploratory ion-exchange assays evidence the considerable potential of this new silicate to remove rare-earth elements from aqueous solutions.