The surfactant-sensitized analytical reaction of niobium with some thiazolylazo compounds

Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the color reaction of Nb(V) with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (I_a), 5-(benzothiazolylazo)2,5-naphthalenediol (I_b), 5-(2-benzothiazolylazo)8-hydroxyquinoline (I_c) and 4-(2- benzothiazolylazo)2, -biphenyldiol (I_d) reagents. The formation of a ternary complex of stoichiometric ratio 1:2:2 (Nb-R-CPB) is responsible for the observed enhancement in the molar absorptivity and the Sandell sensitivity of the formed complex, when a surfactant is present. The ternary complex exhibits absorption maxima at 649, 692, 661 and 612 nm, (=3.35×10⁴, 3.59×10⁴, 4.46×10⁴ and 2.79×10⁴ l mol⁻¹ cm⁻¹) on using reagent I_a, I_b, I_c, and I_d, respectively. Beer’s law is obeyed between 0.05 and 2.50 μg ml⁻¹, while applying the Ringbom method for more accurate results is in the range from 0.20 to 2.30 μg ml⁻¹. Conditional formation constants in the presence and absence of CPB for niobium complexes have been calculated. On the basis of a detailed spectrophotometric study, the nature of the chromophoric reagent–surfactant interaction and the peculiar features of the sensitization by CPB are discussed.     

Improved adsorption performance of nanostructured composite by ultrasonic wave: Optimization through response surface methodology,isotherm and kinetic studies

In this work, ultrasound-assisted adsorption of an anionic dye, sunset yellow (SY) and cationic dyes, malachite green (MG), methylene blue (MB) and their ternary dye solutions onto Cu@ Mn-ZnS-NPs-AC from water aqueous was optimized by response surface methodology (RSM) using the central composite design (CCD). The adsorbent was characterized using Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and EDX mapping images. The effects of various parameters such as pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were examined. A total 33 experiments were conducted to establish a quadratic model. Cu@ Mn-ZnS-NPs-AC has the maximum adsorption efficiency (>99.5%) when the pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were optimally set as 6.0, 5 min, 0.02 g, 9, 12 and 12 mg L⁻¹, respectively. Sonication time has a statistically significant effect on the selected responses. Langmuir isotherm model was found to be best fitted to adsorption and adsorption capacities were 67.5 mg g⁻¹ for SY, 74.6 mg g⁻¹ for MG and 72.9 mg g⁻¹ for MB. Four kinetic models (pseudo-first order, pseudo-second order, Weber–Morris intraparticle diffusion rate and Elovich) were tested to correlate the experimental data and the sorption was fitted well with the pseudo-second order kinetic model.     

Elongational flow studies on flexible polymer chains in a pseudo-solvent

The dynamics of isolated high molecular weight (M_H) polymer chains dissolved in a nonentangled semidilute solution of a low molecular weight (M_L) polymer were investigated by monitoring the elongational flow birefringence. Because of its nonentangled nature, a low molecular weight matrix polymer solution is regarded as a pure solvent (a binary pseudo-solvent). A ternary solution consisting of a small amount of a high molecular weight probe polymer and the binary pseudo-solvent is effectively a dilute solution of the probe polymer. It was observed that the birefringence from the orientation and/or stretching of the probe polymer chains starts to increase rather abruptly at a certain critical strain rate, , and the spatial birefringence pattern is localized along the elongation axis, characteristics that are reminiscent of the coil-stretch transition of flexible polymer chains in a simple dilute solution. The relaxation time for the chain extension, _el, defined as the reciprocal of the critical strain rate , was determined at various temperatures, matrix polymer concentrations c_L, and test chain molecular weights M_H. It was found that _el varied with molecular weight as _el~M_H^a , with a ranging from 1.3 to 1.8, which is roughly consistent with the molecular weight dependence of the non-free-draining Zimm relaxation time. A scaled relaxation time _elkT/, which can be used to estimate the radius of gyration R_g of the probe polymer, decreased with increasing c_L, indicating contraction of the high molecular weight polymer due to a screening of the excluded volume effect caused by the matrix polymer in the pseudo-solvent.     

CEF nature of the magnetic excitations in ordered HoNi B C

The magnetic excitations in the antiferromagnetic phase of HoNi₂B₂C are studied by inelastic neutron scattering on single crystals for the first time. Spectra measured at constant T = 2 K along symmetry directions of the reciprocal space are well explained in terms of crystal electric field (CEF) magnetic excitons within the J = 8 ground state multiplet of Ho³⁺. Very modest bandwidth with planar energy dispersion describes the magnetic exciton dynamics. A perturbative model approach consisting of the CEF states in the effective exchange mean-field provides a simple but applicable characterization of the experimental observations. The microscopic determination of the relevant exchange parameters is discussed in connection with previous works on the subject. Received 25 February 2002 / Received in final form 13 May 2002 Published online 14 October 2002 RID="a" ID="a"e-mail: nordal.cavadini@psi.ch     

超硬材料合成触媒中铜的分析方法研究

研究了Cu CAS CTMAB三元络合物体系,结果表明,其络合物组成为1∶4∶4,λmax=596nm,Δλ=166nm,ε=1.2×105,铜(Ⅱ)的浓度在0.002～1.00μg·ml-1范围内遵守比耳定律,用于超硬材料合成触媒中铜的分析,建立了回归方程,并通过显著性检验,获得了满意的结果。     

Preparation of non-stoichiometric (Zn,Fe)S chalcogenides and evaluation of their thermal, optical and electrical properties

Non-stoichiometric ternary chalcogenides, Zn_1−xFe_xS, were prepared by co-precipitation of ZnS and FeS by Na₂S from aqueous solutions containing FeSO₄ and ZnSO₄ and sintering of pellets of the co-precipitate repeatedly between 800 and 1000 °C. The chemical composition of the resulting solids as analyzed by XRF, EDAX, and EPMA, reflected the composition of the solutions from which precipitation was carried out, with Fe contents up to x=0.4.X-ray diffraction indicated the presence of solid solutions, Zn_1−xFe_xS (sphalerite). Electrical resistivity studies indicated that the compounds were semiconducting. From the temperature dependence of the resistivity, thermal bandgaps were found to be decreasing with increasing Fe content, in agreement with values on optical bandgaps as estimated from diffuse optical reflectance measurements as a function of wavelength. TEP (Thermo Electric Power) measurements indicated p-type conductivity for most samples.     

Correlation and prediction of ternary excess enthalpy data

Methods for predicting ternary excess enthalpies from excess enthalpy data for the three binary mixtures involved are examined and tested for forty-two sets of ternary data. In order to study the relation between the performance of the methods and the characteristics of the components in the mixture, the sets of data were classified into four groups according to the chemical nature of their components. The asymmetric equations proposed by Scatchard, Toop, and Hillert are shown to provide accurate predictions. The ratio of the standard deviations between experimental and predicted excess enthalpies and the maximum absolute value of this magnitude is 0.05 or less for most of the systems. These equations are asymmetric with respect to the numbering of components. A rule is given for selecting which component is to be designated as component 1 for systems showing endothermic mixing, exothermic mixing, or a combination of endothermic and exothermic mixing. Correlation methods are also examined and a partial differential approximant is proposed to represent the ternary contribution to the excess enthalpy.     

13C NMR studies on radical anions. Special solvent effects

The determination of radical ions is crucial in mechanistic studies of reactions in which single electron transfer is suspected. A ¹³C NMR method based on the interaction of radical anions with tetrahydrofuran (THF) molecules is presented; measurements of the broadening of the THF α-carbon signal allow determination of the substrate concentration in the range 0.2–1.2 M . The spectacular effect observed on addition of small amounts of benzene greatly improved the method. In addition, studies of the spin-lattice, T₁, and of the transverse nuclear, T₂, relaxation times and of the effects of added co-solvents allow the proposal of the bonding situation and of the degree of coordination in the radical anion-cation-THF molecules' complex.     

Darstellung und Kristallstrukturen der Verbindungen CaPtGa,CaPtIn und CaPd0,4Ga1,6

Preparation and Crystal Structures of the Compounds CaPtGa, CaPtIn and CaPd_0.4Ga_1.6 The new compounds CaPtGa, CaPtIn and CaPd_0.4Ga_1.6 were prepared by heating appropriate mixtures of the elements under an Ar-atmosphere. The results of the structural analysis of single crystals by means of X-ray diffraction are given in the section ?Inhaltsübersicht”?. CaPtGa and CaPtIn are isotypic and form the TiNiSi type structure (Pnma), where the Pt-atoms have a distorted tetrahedral environment consisting of Ga- resp. In-atoms. CaPd_0.4Ga_1.6 crystallizes in the CeCu₂-type structure (Imma), the Cu positions being statistically occupied by Pd- and Ga-atoms.