Mechanism of simultaneous removal of Ca2+, Ni2+, Pb2+ and Al3+ ions from aqueous solutions using Purolite® S930 ion exchange resin

The sorption mechanism of Ca²⁺, Ni²⁺, Pb²⁺, and Al³⁺on ion exchange resin S930 has been studied as a function of pH in both mono-component and quaternary systems at ion ratio 1:1:1:1. The equilibrium of ion exchange process in mono-component systems has been followed as an adsorption process and it was tested for Langmuir and Freundlich isotherm equations. The selectivity coefficient of the resin for these cations varied in different manners depending on the pH range. The structural characteristics of pores in the initial resin and the resin after contact with synthetic solutions at pH 3.03 and 3.95 have been investigated by using SEM and EDAX techniques.     

Synthesis of di- and trivalent β″-aluminas by ion exchange

Many of the mono-, di-, and trivalent cations in the periodic chart diffuse rapidly in the β″-alumina structure. β″-Aluminas containing multivalent cations can be synthesized by ion exchange reactions starting with the sodium form of the compound. These facile reactions make it possible to prepare a wide variety of β″-alumina compositions, many of which are metastable and inaccessible by normal synthetic means. This paper describes the methods used to synthesize multivalent β″-aluminas and the preparation of a number of specific transition metal and lanthanide forms of these compounds.     

391 — Electron exchange and photoreduction of NAD+ and NADP+

With aid of polarographic results from redox reactions of NAD⁺ and NADP⁺ their photo-reduction pathway in the presence of isopropanol has been analyzed. In both cases dimerization occurs via a free radical. The structures of the products were evaluated by means of comparable spectra and polarographic waves during the reoxidation process. The dimerization rate constants has been calculated from flash spectroscopy data somewhat higher than the known values from electrochemical measurements. Probable reasons are discussed and the photopolarographic aspects of this system are outlined.     

Determination of the Rate Constants of the Reactions Cr + O2 + M → CrO2 + M and Cr + O2 → CrO + O

Kinetics and Catalysis - The rate constants of the interactions of chromium atoms with molecular oxygen through recombination Cr + O2 + M → CrO2 + M (I) and exchange Cr + O2 → CrO + O...     

Determination of the equilibrium Cr+F− distance in Cr+:NaF and Cr+:KMgF3

The variation of the isotropic superhyperfine constant of the octahedral CrF⁵⁻₆ cluster with the Cr⁺F⁻ distance has been obtained from the results of Hartree-Fock-Roothaan calculations on the t³_2ge²_g-⁶A_1g ground state. The effects of the quality of the 3d basis set, type of core-valence partition, core-projection operators, and cluster-lattice interaction on the A_s(R) curve has been analyzed. From this calculation and the observed values of A_s, it is found that R_e(Cr⁺:NaF)=2.47 ± 0.03 Å and R_e(Cr⁺:KMgF₃) = 2.35 ± 0.03 Å. These are the first Cr⁺F⁻ distances reported to date.     

Specifics of chemical etching of PbTe and Pb1 − x Sn x Te single crystals with I2-DMF solutions

The physicochemical interactions of Pb_{1 ? x} Sn _x Te solid solution and PbTe single crystals with I₂-DMF solutions were studied under reproducible hydrodynamic conditions for the first time. Their dissolution rates were investigated as dependent on the etchant components ratio and the temperature and stirring of etching blends, and the effect of the composition of solid solutions on the parameters of chemical etching was studied. Etchant compositions and the chemicodynamical polishing regimes for the studied single crystals were optimized.     

Charge exchange of O2+ with Cs: spectroscopy and predissociation pathways for the Πg Rydberg states of O2

Electron capture by keV O₂⁺ (X₂Π_g) ions from Cs atoms yields predominantly the ¹Π_g and ³Π_g Rydberg states of O₂ which subsequently predissociate. Through the use oftranslational spectroscopy on the neutral product atoms, we have located a number of vibrational levels of these states and determined the dissociation channels. Furthermore we have observed competition between diabatic and adiabatic behaviour in the dissociating channels.     

Conductometric study of complexation reaction of 4′-nitrobenzo-15-crown-5 with Mn+2, Co+2, Y+3, and ZrO+2 cations in acetonitrile,methanol and their binary solvent solutions

The complexation reactions of Mn²⁺, Co²⁺, Y³⁺, and ZrO²⁺ cations with the macrocyclic ligand, 4′-nitrobenz-15-crown-5 (4′-NB15C5), in acetonitrile (AN), methanol and AN-MeOH binary mixtures have been studied at various temperatures using the conductometric method. The conductance data stand for the Me : L stoichiometric ratio 1 : 1. Values of the formation constants of the complexes were accumulated by plotting molar conductivity curves using the computer program, GENPLOT. The order of stability of the metal-ion complexes in pure AN at 15°C was found to be: (4′-NB15C5 · ZrO)²⁺ > (4′-NB15C5 · Mn)²⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · Y)³⁺. In the case of AN-MeOH binary solvent solutions with 50 and 75 mole percent of AN at the same temperature, the sequence of stability of the complexes was the following: (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · ZrO)²⁺ ≈ (4′-NB15C5 · Co)²⁺ 〉 (4′-NB15C5 · Y)³⁺, and (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · Y)³⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · ZrO)²⁺, respectively. The complexes formed are entropy stabilized in all cases.     

18O-isotope exchange behavior and oxidation activity of La1-xSrxMnO3+δ

Different preparation routes derived both from the usual high-temperature solid state synthesis and the sol-gel process were applied for the synthesis of crystalline La_1-xSr_xMnO₃₊ phases with 0x 0.2. They were investigated by means of temperature programmed isotope exchange (TPIE) under various conditions. The ¹⁸O isotope exchange experiments yielded information on the dependence of the oxygen mobility on temperature and the Mn⁴⁺/Mn³⁺ratio. Both are related to the defect structure of the solid. TPIE was applied for studying the interaction between ¹⁸O₂ and CH₄ under static conditions and was compared with results obtained from catalytic investigations, i.e. the behavior of La_1-xSr_xMnO₃₊ (0x0.2) in both CO and CH₄ oxidation with normal oxygen ¹⁶O₂ under steady flow conditions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Structural and spectral consequences of ion pairing II. a theoretical study of CIO−3Li+ and ClO−3Na+

The structure of ClO⁻₃M⁺ ion pairs (M = Li, Na) has been examined with the aid of ab initio molecular orbital calculations. The calculations support recent experimental findings that ClO⁻₃ M ion paris have C_3v rather than C_s configurations. Results from these studies also show that the metal cation prefers to coordinate at the base of the chlorate anion pyramidal structure along the C₃ axis. Calculated vibrational frequencies, intensities, isotopic frequency shifts, and isotopic substituted frequency and intensity patterns render support to this conclusion. New vibrational assignments of observed and some unassignable bands from previous matrix-isolation and molten gas phase spectroscopic studies of ClO⁻₃M⁺ ion pairs are provided.     

Dielectric and conductivity studies of 90 MeV O7+ ion irradiated poly(ethylene oxide)/montmorillonite based ion conductor

In the present work effect of 90 MeV O⁷⁺ ions with five different fluences on poly(ethylene oxide) (PEO)/Na⁺-montmorillonite (MMT) nanocomposites has been investigated. PEO/MMT nanocomposites were synthesized by solution intercalation technique. With the increase in irradiation fluence, gallery spacing of MMT increases in the composite and an exfoliated nanostructure is obtained at the fluence of 5?×?10¹² ions/cm² as revealed by X-ray diffraction results. Highest room temperature ionic conductivity of 4.2?×?10^?6?S?cm^?1 was found for the fluence 5?×?10¹² ions/cm², while the conductivity for unirradiated polymer electrolyte was found to be 7.5?×?10^-8?S?cm^?1. The increase in intercalation of PEO chains inside the galleries of MMT results in the increase in interaction between Na⁺ cation and oxygen heteroatom leading to the increase in ionic conductivity of the composites. Surface morphology and interactions among the various constituents in the nanocomposites at different fluence have been examined by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The appearance of peak for each fluence in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite electrolyte films. With the increase in ion fluence the peak shifts towards higher frequency side, suggesting decrease in the relaxation time.     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.     

Enthalpies of dissolution of NaVO3 · 2H2O in aqueous chloric acid and the standard formation enthalpy of the VO 2 + ion

The enthalpies of dissolution of sodium metavanadate dihydrate in aqueous solutions of chloric acid and sodium perchlorate were measured by calorimetry at 298.15 K at ionic strengths of I = 0.3, 0.4, 0.5, 0.6, and 1.0 M. The standard formation enthalpy of the VO ₂ ⁺ ion in aqueous solution was calculated from the resulting experimental data.     

A CAS SCF CI study of the 1Σ+g and 3IIu states of the C2 molecule and the 4Σ−g and 2IIu states of the C+2 ion

Ab initio calculations of the X ¹Σ⁺_g and a ³II_u states of C₂ and the X⁴Σ⁻_g and a²II_u states of the C⁻₂ molecular ion are performed to determine the corresponding potential curves around the potential minima and at the dissociation limits. A large Gaussian basis set augmented by three d-type polarization functions on each carbon center is used to approximate the molecular orbits. The calculations are done at the complete-active-space SCF and multi-reference configuration interactions level. Spectroscopic constants and rotation—vibration energies are derived from the ab initio calculated potentials. Good agreement between theory and experiment is obtained for the X¹Σ⁺_g and a ³II_u states of C₂. In the earlier tentative assignment of the observed electronic transition around 2490 Å to the ²Σ⁻_g ← ²II_u system in C⁺₂, the lower state is confirmed by the present calculations to be C⁺ ₂ (²II_u).     

FeCl3 · 6H2O-Catalyzed Acceleration of the Acylation of Sodium Azide with N-Acylbenzotriazoles

Catalyzed by ferric chloride hexahydrate (FeCl₃ · 6H₂O), the acylation of sodium azide with N-acylbenzotriazoles was greatly accelerated in a mixed solvent of acetone and water. Thus, good to excellent yields of a variety of acyl azides were obtained at room temperature in a short time. Furthermore, because of the complete conversion of N-acylbenzotriazoles and the easy removal of the by-product, purification by column chromatography was no longer required, which made the protocol suitable for large-scale preparation.