Adsorption of arsenite and arsenate onto muscovite and biotite mica

Arsenite and arsenate sorption was studied on two silt-sized phyllosilicates, namely muscovite and biotite, as a function of solution pH (pH 3-8 for muscovite, and 3-11 for biotite) at an initial As concentration of 13 microM. The amount of arsenic adsorbed increases with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima correspond to 3.22+/-0.06 mmol kg-1 As(V) at pH 4.6-5.6 and 2.86+/-0.05 mmol kg-1 As(III) at pH 4.1-6.2 for biotite, and 3.08+/-0.06 mmolkg-1 As(III) and 3.13+/-0.05 mmol kg-1 As(V) at pH 4.2-5.5 for muscovite. The constant capacitance surface complexation model was used to explain the adsorption behavior. Biotite provides greater reactivity than muscovite toward arsenic adsorption. Isotherm data obeyed the Freundlich or Langmuir equation for the arsenic concentration range 10(-7)-10(-4) M. Released total Fe, Si, K, Al, and Mg in solution were analyzed. Calculation of saturation indices by PHREEQC indicated that the solution was undersaturated with respect to aluminum arsenate (AlAsO42H2O), scorodite (FeAsO42H2O), and claudetite/arsenolite (As4O6).     

Entrapment of a Pseudo‐Tetrahedral CoII Center by Thioether Sulfur Bound {Co2(μ‐L)} Fragments: Synthesis,Field‐Induced Single‐Ion Magnetism and Catechol Oxidase Mimicking Activity

Simultaneous incorporation of both Co^II and Co^III ions within a new thioether S‐bearing phenol‐based ligand system, H₃L (2,6‐bis‐[{2‐(2‐hydroxyethylthio)ethylimino}methyl]‐4‐methylphenol) formed [Co₅] aggregates [Co^IICo^III₄L₂(μ‐OH)₂(μ_1,3‐O₂CCH₃)₂](ClO₄)₄?H₂O ( 1 ) and [Co^IICo^III₄L₂(μ‐OH)₂(μ_1,3‐O₂CC₂H₅)₂](ClO₄)₄?H₂O ( 2 ). The magnetic studies revealed axial zero‐field splitting (ZFS) parameter, D/hc=?23.6 and ?24.3 cm^?1, and E/D=0.03 and 0.00, respectively for 1 and 2 . Dynamic magnetic data confirmed the complexes as SIMs with U_eff/k_B=30 K ( 1 ) and 33 K ( 2 ), and τ₀=9.1×10^?8 s ( 1 ), and 4.3×10^?8 s ( 2 ). The larger atomic radius of S compared to N gave rise to less variation in the distortion of tetrahedral geometry around central Co^II centers, thus affecting the D and U_eff/k_B values. Theoretical studies also support the experimental findings and reveal the origin of the anisotropy parameters. In solutions, both 1 and 2 which produce {Co^III₂(μ‐L)} units, display solvent‐dependent catechol oxidation behavior toward 3,5‐di‐tert‐butylcatechol in air. The presence of an adjacent Co^III ion tends to assist the electron transfer from the substrate to the metal ion center, enhancing the catalytic oxidation rate.     

NaCu(II)4] cluster from alkali template assembly of two asymmetric end-on azido-bridged [Cu(II)2] units

The cluster [NaCu4L2(N3)2](ClO4) [1; H3L is 2-(2'-hydroxyphenyl)-1,3-bis[3'-aza-4'-(2'-hydroxyphenyl)prop-4'-en-1'-yl]-1,3-imidazolidine] has been synthesized and structurally characterized. Complex 1 is formed by the template assembly of two [Cu2L(N3)] neutral fragments through their weak oxophilic interactions with a central Na+ cation as observed in metallacrowns. The cluster exhibits a combination of ferro- and antiferromagnetic interactions. End-on N3- bridging of copper ions within the [Cu(II)2] units facilitates stabilization of S = 1 magnetic subunits that mutually cancel via antiferromagnetic coupling as mediated by the O...Na+...O bridges.     

Binary α-Fe2O3–Co3O4 nanostructures for advanced oxidation process: Role of synergy for enhanced catalysis

Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H₂O₂ concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe₂O₃–Co₃O₄ shows much higher activity than both Co₃O₄ and α-Fe₂O₃ for the degradation of MB at room temperature and beyond. The binary α-Fe₂O₃–Co₃O₄ shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe₂O₃–Co₃O₄ catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe²⁺/Fe³⁺ or Co²⁺/Co³⁺ redox couple of the binary α-Fe₂O₃–Co₃O₄ catalyst.     

Magnetic moments of decuplet baryons in an independent particle potential model

Magnetic moments of decuplet baryons have been calculated in a relativistic independent quark model with a phenomenological potential in equally mixed scalar-vector harmonic form. Such a model has been successful in describing wide ranging hadronic phenomena in mesonic and baryonic sectors. Using the solutions of the constituent quark orbitals with the model parameters taken from its earlier applications, the magnetic moments of decuplet baryons Δ⁺⁺ and Ω⁻ have been obtained which are in good agreement with the available experimental data. However, the agreement is found to be much better when the magnetic moment ratios such as μ_δ++/μ _p and μ_Ω-/μ_Λ are considered. Model predictions for the magnetic moments of other decuplet baryons together with the charge radii have also been calculated which may be verified in future experiments.     

Weak decay constants of light and heavy pseudoscalar mesons

We investigate the weak leptonic decays of light and heavy pseudoscalar mesons in a relativistic quark model of independent quarks. We perform a static calculation of the decay constantf _M purely on grounds of simplicity. In order to minimize the possible uncertainty in the static calculation, we estimate the ratios of the decay constants which are found to be in good agreement, in the heavy flavor sector, with the predictions of other models available in the literature and existing experimental data. However, there is a noticeable discrepancy in the current prediction for pion decay constant which demonstrates the inherent limitations of the static approximation in the study of non-strange light mesons.     

Synthesis,characterization, and antimicrobial studies of some palladium complexes with an octamethyl tetraazacyclotetradecadiene ligand and isomers of its reduced form

Biologically important tetraaza-macrocyclic ligand 3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene dihydroperchlorate, Me₈[14]diene·2HClO₄ (L₁·2HClO₄) was synthesized by the condensation of 1,2-diaminopropane with acetone in presence of quantitative amount of HClO₄ and three isomeric ligands designated as L_A, L_B and L_C were separated by the reduction of L₁·2HClO₄ with NaBH₄ and fractional crystallization from xylene. The nitrato, nitro, bromido, and iodido complexes of palladium with diene ligand L₁ were prepared by the interaction of L₁·2HClO₄ with K₂[Pd(NO₃)₄], K₂[Pd(NO₂)₄], K₂[PdBr₄], and K₂[PdI₄] (prepared by the reactions with PdCl₂ with KNO₃, KNO₂, KBr, and KI, respectively), respectively. The bromide and iodido complexes of L_A were prepared by the axial substitution reactions with [PdL_ACl₂]Cl₂. By contrast, similar complexes of other isomeric ligands L_B and L_C were prepared by axial addition reactions of [PdL^?][PdCl₄] (L′?=?L_B or L_C) with KBr and KI, respectively. The complexes were characterized on the basis of elemental analysis: IR, ¹H-NMR, UV–Vis spectroscopic analysis, and magnetic and molar conductivity data. The antifungal and antibacterial activities of these compounds have been studied against some phyto-pathogenic fungi and bacteria.     

Irreducible Brillouin conditions and contracted Schrödinger equations for n-electron systems. IV. Perturbative analysis

The k-particle irreducible Brillouin conditions IBCk and the k-particle irreducible contracted Schr?dinger equations ICSEk for a closed-shell state are analyzed in terms of a M?ller-Plesset-type perturbation expansion. The zeroth order is Hartree-Fock. From the IBC2(1), i.e., from the two-particle IBC to first order in the perturbation parameter mu, one gets the leading correction lambda2(1) to the two-particle cumulant lambda2 correctly. However, in order to construct the second-order energy E(2), one also needs the second-order diagonal correction gammaD(2) to the one-particle density matrix gamma. This can be obtained: (i) from the idempotency of the n-particle density matrix, i.e., essentially from the requirement of n-representability; (ii) from the ICSE1(2); or (iii) by means of perturbation theory via a unitary transformation in Fock space. Method (ii) is very unsatisfactory, because one must first solve the ICSE3(2) to get lambda3(2), which is needed in the ICSE2(2) to get lambda2(2), which, in turn, is needed in the ICSE1(2) to get gamma(2). Generally the (k+1)-particle approximation is needed to obtain Ek correctly. One gains something, if one replaces the standard hierarchy, in which one solves the ICSEk, ignoring lambda(k+1) and lambda(k+2), by a renormalized hierarchy, in which only lambda(k+2) is ignored, and lambda(k+1) is expressed in terms of the lambdap of lower particle rank via the partial trace relation for lambda(k+2). Then the k-particle approximation is needed to obtain E(k) correctly. This is still poorer than coupled-cluster theory, where the k-particle approximation yields E(k+1). We also study the possibility to use some simple necessary n-representability conditions, based on the non-negativity of gamma(2) and two related matrices, in order to get estimates for gammaD(2) in terms of lambda2(1). In general these estimates are rather weak, but they can become close to the best possible bounds in special situations characterized by a very sparse structure of lambda2 in terms of a localized representation. The perturbative analysis does not encourage the use of a k-particle hierarchy based on the ICSEk (or on their reducible counterparts, the CSEk), it rather favors the approach in terms of the unitary transformation, where the k-particle approximation yields the energy correct up to E(2k-1). The problems that arise are related to the unavoidable appearance of exclusion-principle violating cumulants. The good experience with perturbation theory in terms of a unitary transformation suggests that one should abandon a linearly convergent iteration scheme based on the ICSEk hierarchy, in favor of a quadratically convergent one based on successive unitary transformations.