Reduction of Se(VI) to Se(-II) by zerovalent iron nanoparticle suspensions

The reaction of selenate (Se(VI)) with zerovalent iron nanoparticles (nano Fe⁰) was studied using both conventional batch equilibrium and X-ray spectroscopic techniques. Nano Fe⁰ has a high uptake capacity for removal of dissolved Se(VI) reaching concentrations as high as 0.10 Se:Fe molar ratio in the solid product mixture. Kinetic studies of the Se(VI) uptake reaction in batch experiments showed an initial reaction rate (0–30 min) of 0.0364 min^?1 which was four times greater than conventional Fe⁰ powder. Analysis of the oxidation state of Se in the solid products by X-ray absorption near edge structure (XANES) spectroscopy showed evidence for the reduction of Se(VI) to insoluble selenide (Se(-II)) species. Structural analysis of the product by extended X-ray absorption fine structure (EXAFS) spectroscopy suggested that Se(-II) was associated with nano Fe⁰ oxidation products as a poorly ordered iron selenide (FeSe) compound. The fitted first shell Se–Fe interatomic distance of 2.402 (±0.004) Å matched closely with previous studies of the products of Se(IV)-treated Fe(II)-clays and zero-valent iron/iron carbide (Fe/Fe₃C). The poorly ordered FeSe product was associated with Fe⁰ corrosion product phases such as crystalline magnetite (Fe₃O₄) and Fe(III) oxyhydroxide. The results of this investigation suggest that nano Fe⁰ is a strong reducing agent capable of efficient reduction of soluble Se oxyanions to insoluble Se(-II).     

Influence of isomorphous substitution and external hydrostatic pressure on the fundamental light-absorption edge in Sn(Pb)2P2S(Se)6 crystals

The influence of isomorphous substitution and high hydrostatic pressure on the behavior of the fundamental absorption edge (AE) inSn(Pb) ₂ P ₂ S(Se) ₆ ferroelectric crystals is studied. It is shown that the AE in these crystals is caused by an electron-phonon interaction, and oscillation frequencies of interacting phonons correspond to oscillations of the[P ₂ S(Se) ₆]⁴⁻ anion sublattice. Baric and concentration changes of the Uhrbach rule parameters are analyzed. Uzhgorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 23–28, September, 1999.     

Magnetic hyperfine field of Se in nickel measured by means of the DPAC method

The magnetic hyperfine field of Se in nickel was measured by means of the time-differential perturbed angular correlation (DPAC) technique, using the 755–250 keV γ-ray cascade fed in the decay of⁷⁷Br. A value ofB _hf(NiSe)=+15.11(35) T was obtained at room temperature. The half-life of the 250 keV state and the anisotropy of the 755–250 keV cascade were found to beT _1/2=9.68(6) ns andA ₂₂=−0.454(9), respectively.     

TDPAC Measurement of the quadrupole interaction of77Se in arsenic

By TDPAC the quadrupole coupling constant for⁷⁷Se (5/2^–, 248 keV, 9.3 ns) in metallic arsenic was measured to be _Q = 700 ± 60 MHz. The tabulation of electric field gradients (EFGs) for some different sp impurity host combinations shows large values for impurities with 6 valence electrons. If we assume that the selenium impurity is substituted in arsenic, then it is possible to interpret the very high _Q by the assumption of a big EFG and a large quadrupole moment (approximately 1 b) of the excited⁷⁷Se nucleus.     

High spin states in77Se populated by the74Ge(α,n γ) reaction

⁷⁷Se has been investigated by the reaction⁷⁴Ge(α,nγ) at 14 MeV. Gamma singles spectra, gamma angular distributions and gamma-gamma coincidences have been taken. A level scheme has been established, spins and parities have been assigned. States of a rotational band on the 1/2^? ground state, a rotational band on the 5/2^? 249.7 keV state and an anormal band have been identified. Nuclear Reaction ⁷⁴Ge(α,n γ)E _α=14 MeV; measuredE _γ ,I _γ ,γ-γ-Coin.,γ-ang. distr.⁷⁷Se deduced levels,J, π. Enriched target, Ge (Li).     

A natural abundance Se solid-state NMR study of inorganic compounds

Various inorganic selenium-based compounds were analysed by ⁷⁷Se solid-state NMR, and a distinct difference in chemical shift ranges for compounds where selenium is present as selenide (Se²⁻) ionically and covalently bonded systems was observed. The selenides exhibit a shift range of approximately −700 to −100 ppm, as opposed to 700 to 1600 ppm for the compounds where there tends to be more direct covalent bonding to the selenium. The anisotropic hyperfine shift observed in NbSe₂ is shown to be axially symmetric, where the H₁₁ component is found to be normal to the Se3-trigonal plane.     

77Se and125Te nuclear magnetic resonance investigations in II–VI and IV–VI compounds

The NMR signals of⁷⁷Se or¹²⁵Te have been measured in II–VI and IV–VI-compounds ZnSe, CdSe, HgSe, PbSe and ZnTe, CdTe, HgTe, PbTe relative to aqueous solutions of Na₂SeO₃ or K₂TeO₃. The chemical shifts of about ?600 ppm for⁷⁷Se and of about ?2700 ppm for¹²⁵Te have been compared with theoretical calculations. For⁷⁷Se in hexagonal CdSe an anisotropic chemical shift has been observed and for¹²⁵Te in CdTe and PbTe linesplittings have been found. The linewidths of the⁷⁷Se and¹²⁵Te NMR signals increase with the atomic number of the counterions.     

Structure and optical properties of Se accommodated in channels of AlPO4–5 single crystal

Optical properties are studied for Se species accommodated in channels of an AlPO₄–5 single crystal. Polarized Raman spectra show that the Se species is of helical chain structure with D3symmetry. The optical phonon modes of the Se chains are shifted towards higher frequencies from that of the trigonal Se crystal, because of the loss of inter-chain interactions in Se/AlPO₄–5. High anisotropic absorption spectra have been observed for the Se chains. The lowest excitation energies are shifted towards high energy about 0.6 eV from the band edge transitions of the trigonal Se crystal. The blue shift is attributed to the quantum confinement of carriers in a Se chain with diameter 7.3 Å.     

Preparation and thermoelectric power of SnBi4Se7

Polycrystalline samples of Bi₂Se₃ and a stoichiometric ternary compound in the quasi-binary system SnSe–Bi₂Se₃ have been prepared and characterized by X-ray powder diffraction analysis. At room temperature the carrier concentration values are n?=?1.1?×?10¹⁹?cm^?3 for Bi₂Se₃ and n?=?0.53?×?10¹⁹?cm^?3 for SnBi₄Se₇. The thermoelectric power has been measured over the temperature range 90–420?K. The thermoelectric power of Bi₂Se₃ is higher than that for SnBi₄Se₇, which shows that the Sn impurity has an acceptor character. Therefore, doping Bi₂Se₃ with tin atoms does not improve thermoelectric properties of this material, due to decrease the value of the power factor σS ². Transport properties of the studied polycrystalline samples are characterized by a mixed transport mechanism of free carriers. It is necessary to add more than one Sn atom to the Bi₂Se₃ compound in order to suppress the electron concentration by one electron. Such behaviour of the dopant is explained by the formation of various structural defects. Besides the dominant substitutional defect, Sn_Bi, tin atoms also form uncharged defects, corresponding to seven-layer lamellae of the composition Se–Bi–Se–Sn–Se–Bi–Se which corresponds to the structure of the SnBi₂Se₄.     

Atomic reorientation rates in liquid chalcogenide glasses: NMR in Se and As2Se3

Temperature dependence of the NMR spectrum in liquid Se indicates that atomic reorientation in this molten ring-chain structure glass is governed by a distribution of correlation times with a median of τ^∗ = 5 × 10⁻⁵sec at 220°C. In liquid layer structure glasses at equivalent viscosity, atomic reorientation rates are not sufficient to narrow observed NMR spectra. SeSe and AsSe bonds in glassy Se and As₂Se₃ are distinguishable on the basis of their chemically shifted Se⁷⁷ NMR spectra.     

Structural and optical properties of Cu2ZnSn(S,Se)4 films obtained by magnetron sputtering of a Cu2ZnSn alloy target

Results of the study of structural and optical properties of Cu₂ZnSn(S,Se)₄ thin films obtained by sulfitation (selenization) of Cu₂ZnSn films which were sputtered by target direct current magnetron sputtering using a stoichiometric Cu₂ZnSn (99.99%) target are presented. It has been found that Cu₂ZnSn(S,Se)₄ thin films are polycrystalline with a grain size of ~60 nm. The optical bandgap of Cu₂ZnSnS₄ (E ^op _g = 1.65 eV) and Cu₂ZnSnSe₄ (R ^op _g = 1.2 eV) thin films have been determined.

     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

LiGaX2(X=S,Se, Te)的电子结构,光学和弹性性质的第一性原理计算

采用基于第一性原理的密度泛函理论赝势平面波方法,对LiGaX₂(X=S, Se, Te)的能带结构、态密度、光学以及弹性性质进行了理论计算. 能带结构计算表明LiGaS₂ 的禁带宽度为4.146 eV, LiGaSe₂ 的禁带宽度为3.301 eV, LiGaTe₂ 的禁带宽度为2.306 eV; 其价带主要由Ga-4p 层电子和X- np 层电子的能态密度决定; 同时也对LiGaX< 关键词： 电子结构 光学性质 弹性性质 LGX     

Doped Graphene Quantum Dots Modified Zn0.9Cd0.1Se for Improved Photoelectric Properties

S-graphene quantum dots (GQDs), N-GQDs, P-GQDs, and Cl-GQDs are prepared by a solution chemistry method and further incorporated with Zn_xCd_1−xSe by one-step hydrothermal method. In the previous study, Zn_xCd_1−xSe reached the optimal photoelectric performances at the Zn/Cd ratio of 0.9:0.1, so the Zn_0.9Cd_0.1Se were combined with doped GQDs (D-GQDs) to form Zn_0.9Cd_0.1Se/doped-GQDs. The influence of GQDs doped with different elements on the photoelectric properties of Zn_0.9Cd_0.1Se composites is discussed. Compared with pristine Zn_0.9Cd_0.1Se, Zn_0.9Cd_0.1Se/Cl-GQDs, and Zn_0.9Cd_0.1Se/P-GQDs can improve the photocurrent response and current intensity, therein, Zn_0.9Cd_0.1Se/Cl-GQDs reaches the lowest interfacial charge transfer resistance and the highest photocurrent response of 5.48 × 10⁻⁶ A cm⁻². Mott–Schottky analysis shows that the fitting slope of Zn_0.9Cd_0.1Se/Cl-GQDs composites is significantly lower than that of Zn_0.9Cd_0.1Se/GQDs with other doped elements. The results indicate that Zn_0.9Cd_0.1Se/Cl-GQDs composites has the largest carrier density, which is beneficial to charge conduction.     

Influence of the Ga addition on optical properties of Pr in Ge–Sb–Se glasses

Absorption and emission spectra for the ³H₄↔(³F₂, ³H₆) transition of Pr³⁺ ions embedded in Ge–Sb–Se glasses turned out to change systematically upon the introduction of a small amout of Ga. Clear blueshift of the absorption peak wavelengths together with the decrease of absorption cross-section was evident in these glasses containing Ga. We believe that the Ga addition into the conventional covalent selenide glasses makes chemical bonds between rare earth atoms and Se atoms more ionic due to preferential location of the GaSe₄ tetrahedra at the second coordination shell of a rare earth atom. Taking into consideration the hypersensitive nature of the Pr³⁺: ³H₄↔³F₂ transition, the observed blueshift may manifest the enhanced ionicity of the chemical bonds between Pr and Se in the current Ga-containing glasses.     

Theoretical investigations on the g factors and local structures for Cu2+ in the ZnX (X= O,S and Se) nanocrystals

ABSTRACT

The g factors and local structures for Cu²⁺ in the ZnX (X = O, S and Se) nanocrystals at room temperature are theoretically investigated by the perturbation calculations for a tetragonally distorted tetrahedral 3d⁹ cluster in a consistent way, and the isotropic g factor is predicted for the ZnS:Cu²⁺ nanocrystals at room temperature. The bond angles θ between the four equivalent Cu²⁺?X^2? bonds and the C₄ axis are found to be about 1.26°, 1.24° and 1.07°, respectively, larger in the ZnO, ZnS and ZnSe nanocrystals than that (θ₀ ≈ 54.74°) for an ideal tetrahedron, inducing tetragonally compressed tetrahedra. The declining tendency (ZnO > ZnS > ZnSe) of the tetragonal angular distortion Δθ (= θ ? θ₀) can be ascribed to the decreasing strength of the dynamic Jahn–Teller effect via the vibration interactions of the [CuX₄]^6? groups due to the weakening Cu²⁺?X^2? bonding. The isotropic g factors are attributable to the appropriate Δθ due to the dynamic Jahn–Teller effect and the internal stress. The slightly increasing (ZnO < ZnS < ZnSe) g factors can be illustrated by the declining cubic field parameter Dq, angular distortion Δθ and covalency factor N of the systems.     

Mesobonding (Se,Se) pairs in Si

Using symmetry, qualitative analyses of g-shift data for the (Se,Se)⁺ deep level in Si, and the general features of the electronic structure of Si, we find the mesobonding model of (Se,Se) substitutional pairs in Si to be preferred over the ordinary model -- without relying on any detailed model Hamiltonian.     

Isolated modes and percolation in the lattice dynamics of (Be,Zn)Se

The mixed II–VI semiconductor Zn_{1??? x} Be _x Se possesses non-trivial vibration properties, because its two constituent compounds, ZnSe and BeSe, show very different degrees of covalency and hence high elastic contrast. An anomalous Be–Se vibration line has been observed, mostly at intermediate Be content, in the Raman spectra of thin (Zn,Be)Se films. In order to explain the microscopic origin and detailed composition of these lines, a first-principles calculation of the vibration frequencies in a mixed crystal has been performed, with the frozen-phonon technique and supercell setup within the density functional theory, using the SIESTA method, which uses norm-conserving pseudopotentials and strictly localized numerical basis functions. The calculations confirmed an earlier assumption that the anomalous Be–Se line appears due to the formation of continuous chains of a more rigid Be-rich pseudo-continuous phase formed within the more soft Zn-rich host region on crossing the Be–Se bond percolation threshold (x?～?0.19). Different local deformations in percolated and non-percolated regions affect the interatomic elastic interactions and split the corresponding vibration lines. Besides confirming the percolation model qualitatively, the calculation provides details concerning the vibration patterns in different phonon modes.     

Proton occupancies in the even Se ground states via the (d, 3He) reaction

The spectroscopic factors for the levels of^{73,75,77,79,81}As have been measured in the Se(d, ³He)As reactions at 25.2 MeV. The proton occupation numbers deduced for the even Se isotopes show that the striking change in proton configuration, observed for the Ge isotopes between N ? 40 and N ? 42, does persist for the Se isotopes. This change is not reproduced, either by a model calculation using spectral distribution methods or by proton wave functions recently suggested for the Se isotopes to explain the results of the Se(d, ⁶Li)Ge reactions.     

Flow‐Injection Online Reduction Atomic Fluorescence Spectrometry Determination of Se(IV) and Se(VI) with Electrochemical Hydride Generation

Abstract

A new flow‐injection online reduction electrochemical hydride generation system for the determination of Se(IV) and Se(VI) by atomic fluorescence spectrometry (AFS) was developed. In the system, an electromagnetic induction oven was used as heating resource to reduce Se(VI) to Se(IV) and a homemade tubular electrolytic cell as hydride generator. All analytical procedures were automatically controlled by a computer. The conditions of online reduction, including temperature, HCl concentration, and reduction time, have been studied in detail. The detection limits (3σ) of Se(IV) and Se(VI) in aqueous solution were 0.26 µg L^?1 and 0.23 µg L^?1, respectively. The precision for 11 replicate measurements of 50 µg L^?1 Se(IV) and Se(VI) was 2.2% and 2.5%. This proposed method has been applied to the determination of Se(IV) and Se(VI) in springwater samples.