Selective Capture of Toxic Selenite Anions by Bismuth‐based Metal–Organic Frameworks

Chemically durable and effective absorbent materials for selenite (SeO₃^2?) remain highly desirable for contamination remediation. Now a bismuth‐based metal–organic framework (Bi‐MOF, CAU‐17) was used as adsorbent to capture SeO₃^2? anions from aqueous solution with ultrahigh adsorption capacity of 255.3 mg g^?1 and fast kinetics. Furthermore, the adsorbent showed excellent selectivity for SeO₃^2? and was able to work steadily in a broad pH range of 4–11. Density functional theory (DFT) calculation, XANES modeling, and EXAFS fitting suggested that SeO₃^2? anions were immobilized by forming Bi?O?Se bonds (T‐3 structural model) though splitting the O?Bi?O bond in the crystal structure, leading to a structural transformation of CAU‐17 in the solid state.     

Liquid-liquid distribution,spectrophotometric, thermal,IR and Raman studies on selenito uranylates

Uranyl selenite, precipitated from an uranyl solution by selenous acid, redissolves in excess acid to yield a binegative apparently octahedral, anionic complex.The compounds UO₂SeO₃(I), (NH₄)₂[(UO₂)₂(SeO₃)₃(H₂O)₆](II), (NH₄)₂[UO₂(SeO₃)₂](III), K₂[(UO₂)₂(SeO₃)₃(H₂O)₂](IV) and K₂[UO₂(SeO₃)₂(H₂O)₂]H₂O(V) have been prepared and analysed. On basis of their thermal, IR, Raman and X-ray diffraction studies and other properties, a polymeric structure involving bridging oxygen atoms has been suggested.     

Thermal Decomposition Studies of Mixed Rare Earth Hydrogen Selenite Crystals

Mixed rare earth hydrogen selenite crystals, neodymium praseodymium hydrogen selenite (Nd_xPr_1−x(HSeO₃)(SeO₃)⋅2H₂O), Neodymium samarium hydrogen selenite (Nd_xSm_1−x(HSeO₃)(SeO₃)⋅2H₂O) and praseodymium samarium hydrogen selenite (Pr_xSm_1−x(HSeO₃)(SeO₃)⋅2H₂O) were prepared by gel diffusion technique. Simultaneous thermogravimetric and differential thermal analysis were carried out on the grown crystals. Decomposition is observed to occurs in six steps, which gives the evidence of successive losses of H₂O and SeO₂. The final product due to decomposition is a mixed rare earth oxides. FT-IR spectrum of the crystal samples heated at different temperatures complemented to the TG-DTA results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quartz Crystal Microbalance for Selenite Sensing Based on Growth of Cadmium Selenite Crystals Immobilized on a Monolayer of Phosphorylated 11-Mercapto-1-Undecanol

 A quartz crystal microbalance (QCM) sensor for selenite ions in aqueous solution was constructed based on crystal formation of cadmium selenite, immobilized with a self-assembly monolayer (SAM) of phosphorylated 11-mercapto-1-undecanol (MUD) on a QCM gold electrode surface. The mass change caused by the selective adsorption of selenite ions on the cadmium selenite crystals at the solid/solution interface was detected by the QCM. The response (−ΔF) of the modified QCM oscillator increased with increasing selenite ion concentrations in sample solutions, ranging from 9.7×10⁻⁵ to 9.0×10⁻⁴ M at pH 7.4. The synthetic process of anchoring cadmium selenite crystals on the phosphorylated MUD organic film was also followed by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The atomic concentrations measured by XPS confirmed the crystal growth of cadmium selenite on the phosphorylated MUD SAM at the QCM gold electrode surface. From the AFM images, changes in surface topographic features were followed: the MUD SAM and phosphorylated MUD on the QCM gold electrode had similar surface roughness; however the difference for the cadmium selenite film on the phosphorylated MUD SAM was clearly seen. The observed QCM frequency change of the modified QCM oscillator per unit time was found to be proportional to the square of the supersaturation of cadmium selenite, indicating the crystal growth of cadmium selenite at the solid/solution interface. The modified QCM oscillator exhibited selectively strong QCM response to SeO₃ ²⁻ ion. In contrast, the responses to tested interfering anions were almost negligible. The order of anion selectivities of the present modified QCM sensor was SeO₃ ²⁻≫CO₃ ²⁻>SeO²⁻ ₄, SO₄ ²⁻, Br⁻, I⁻, NO₃ ⁻. These selectivities were basically attributable to the differences in solubility products and solubilities for the salts of each anion with cadmium (II) ion. Received May 12, 1998. Revision December 29, 1998.     

Gravimetric estimation of bismuth as bismuthyl dichromate

Summary Conditions are described for the quantitative precipitation of bismuthyl dichromate, (BiO)₂Cr₂O₇, and the suitability of this reaction for the gravimetric estimation of bismuth is shown. The use of arsenious oxide as a primary standard for the iodometric titration of excess chromate is emphasised.Sincere thanks of the authors are due to Prof. S. S. Joshi for research facilities and to Dr. G. S. Deshmukh for keen interest in the work.     

Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

The first examples of bismuth fluoride selenites with d⁰-TM/Te^VI polyhedrons, namely, Bi₄TiO₂F₄(SeO₃)₄ ( 1 ), Bi₄NbO₃F₃(SeO₃)₄ ( 2 ), Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ), Bi₂F₂(MoO₄)(SeO₃) ( 4 ) and Bi₂ZrO₂F₂(SeO₃)₂ ( 5 ) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1 – 3 , containing Ti^IV, Nb^V and Te^VI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d⁰-TM/Te^VI octahedrons and selenite/tellurite groups. Interestingly, compound Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ) is the first structure containing Se^IV and mixed-valent Te^IV/Te^VI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO₄ tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO₂F₂(SeO₃)₂]⁶⁻ polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1 – 3 , especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO₃ groups (and TeO₃ in compound 3 ) displayed the largest anisotropy, compared with the bismuth cations and the d⁰-TM/Te polyhedra, which is beneficial to the birefringence.     

Reductive immobilization of <Superscript>79</Superscript>Se by iron canister under simulated repository environment

To understand the fate of ⁷⁹Se in a repository-like environment, the interactions between iron canister surface with dissolved selenite (SeO₃ ²⁻) and selenate (SeO₄ ²⁻) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO₃ layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated. The dominating phase was found to be FeSe_2.     

Diallyldithiocarbamidohydrazine (Dalzin) as an analytical reagent

Summary It has been observed that mercury can be quantitatively precipitated by Diallyldithiocarbamidohydrazine (Dalzin) at a p_H of 3–3.5. It has been separated from nickel, zinc, lead, copper, cadmium and bismuth. The latter three have been kept in solution with the help of EDTA.Part. II: Dutt, N. K., and K. P. Sen Sarma: Anal. chim. Acta (Amsterdam) 15, 102 (1956); cf. Z. analyt. Chem. 155, 353 (1957).     

Acid-Base and Photochemical Reactions of Selenious Acid

Abstract

Spectrophotometric data used in connection with H_A acidity function yield pK₁=?3.3(K₁= [H₂SeO₃][H⁺]/[H₃SeO₃ ⁺]);potentiometric and spectral measurements give for pK₂ and pK₃ data in agreement with the literature. At pH > 10 selenite undergoes a fast photochemical reaction, preceded by a rapidly established acid-base equilibrium. Products of this reaction undergo a slow reaction which is second order in selenite.     

The First UV Nonlinear Optical Selenite Material: Fluorination Control in CaYF(SeO3)2 and Y3F(SeO3)4

It is a great challenge to develop UV nonlinear optical (NLO) material due to the demanding conditions of strong second harmonic generation (SHG) intensity and wide band gap. The first ultraviolet NLO selenite material, Y₃F(SeO₃)₄, has been obtained by control of the fluorine content in a centrosymmetric CaYF(SeO₃)₂. The two new compounds represent similar 3D structures composed of 3D yttrium open frameworks strengthened by selenite groups. CaYF(SeO₃)₂ has a large birefringence (0.138@532 nm and 0.127@1064 nm) and a wide optical band gap (5.06 eV). The non-centrosymmetric Y₃F(SeO₃)₄ can exhibit strong SHG intensity (5.5×KDP@1064 nm), wide band gap (5.03 eV), short UV cut-off edge (204 nm) and high thermal stability (690 °C). So, Y₃F(SeO₃)₄ is a new UV NLO material with excellent comprehensive properties. Our work shows that it is an effective method to develop new UV NLO selenite material by fluorination control of the centrosymmetric compounds.     

Oxidation of selenite by alkaline ferricyanide using osmium tetroxide as a catalyst

Summary Oxidation of selenite to selenate by alkaline ferricyanide catalysed by osmium tetroxide was followed by direct and indirect procedures. Either the ferrocyanide was titrated with selenite solution at 8–10% overall alkalinity or vice versa using amperometric or potentiometric end point. In the indirect procedure the excess ferricyanide was determined by amperometric titration with arsenious oxide at 10–15% alkalinity, and the ferrocyanide with ceric sulphate using o-phenanthroline or amperometric indicator. A cerimetric determination of ferricyanide based on this reaction is described.Sincere thanks of the authors are due to Dr. S. S. Joshi, D. Sc. (London), for kind interest in the work.     

Fabrication of a magmolecule using nanoparticle and evaluation of its adsorption capacity for selenium ions from nuclear wastewater

The purpose of present study is to fabrication of a magmolecule (amino-functionalized magnetite nanoparticles) and evaluation of its adsorption capacity for selenite (SeO₃ ^2?) ions from nuclear wastewater. To accomplish this, synthesized magnetite nanoparticles is coated with a layer of SiO₂ in order to be chemically stable and then functionalized with 3-aminopropyl triethoxysilane (APTES) to be more effective. Adsorption of SeO₃ ^2? ions was investigated in batch technique. The effect of parameters such as solution pH, presence of competing anions using sulfuric acid and nitric acid (NO₃ ^?, HSO₄ ^? and SO₄ ^2?) and temperature were studied. Maximum adsorption occurred at pH 2.4 for magnetite (naked nanoparticle) and 1.7 for functionalized nanoparticles, while the dose of adsorbent was 1 g/L and selenite ion concentration was 50 mg/L. sulfuric acid was selected as the better acidic agent for controlling pH of solution. Thermodynamic parameters were also calculated and it has been found that the adsorption was endothermic. The obtained result showed that the naked particles had more adsorption capacity but it has been suggested usage of functionalized particles in the magmolecule process duo to stability and reusable capability.     

Chemical vapor transport and solid-state exchange synthesis of new copper selenite bromides

A new dimorphic copper selenite bromide, Cu₅(SeO₃)₄Br₂ was obtained via chemical transport reactions. α-Cu₅(SeO₃)₄Br₂, monoclinic (1m) and β-Cu₅(SeO₃)₄Br₂, triclinic (1a) polymorphs were produced simultaneously upon reaction of amorphous, partially dehydrated copper selenite and copper bromide. 1m is similar to Cu₅(SeO₃)₄Cl₂, whereas 1a is distantly related to Ni₅(SeO₃)₄Br₂ and Co₅(SeO₃)₄Br₂. Attempts to reproduce synthesis of 1a via exchange reaction between Na₂SeO₃ and CuBr₂ resulted in a new Na₂[Cu₇O₂](SeO₃)₄Br₄ (2). Current study demonstrates for the first time, that both chemical vapor and exchange reactions can be employed in preparation of new selenite halides.     

Formation of SeO-2 radical anions at 92 K during the photobleaching of e-t in gamma-irradiated NaOH (10 M) aqueous glasses (77 K) containing selenite ions

Although the selenite ion, SeO^2-₃ is an inefficient scavenger of excess electrons (e^-_m, e^-_dry) generated in irradiated alkali metal hydroxide aqueous glasses at low temperatures, post-irradiation photostimulation of trapped electrons (e^-_t) in irradiated NaOH (10 M) glasses containing this chemical additive leads, unexpectedly, to the formation of SeO^-₂ radical anions.     

Pr4(SeO3)2(SeO4)F6 und NaSm(SeO3)(SeO4): Selenit‐Selenate der Selten‐Erd‐Elemente

Pr₄(SeO₃)₂(SeO₄)F₆ and NaSm(SeO₃)(SeO₄): Selenite‐Selenates of Rare Earth Elements Light green single crystals of Pr₄(SeO₃)₂(SeO₄)F₆ have been obtained from the decomposition of Pr₂(SeO₄)₃ in the presence of LiF in a gold ampoule. The monoclinic compound (C2/c, Z = 4, a = 2230.5(3), b = 710.54(9), c = 835.6(1) pm, β = 98.05(2)°, R_all = 0.0341) contains two crystallographically different Pr³⁺ ions. Pr(1)³⁺ is attached by six fluoride ions and two chelating SeO₃^2– groups (CN = 10), Pr(2)³⁺ is surrounded by four fluoride ions, three monodentate SeO₃^2– and two SeO₄^2– groups. One of the latter acts as a chelating ligand, so the CN of Pr(2)³⁺ is 10. The selenite ions are themselves coordinated by five and the selenate ions by four Pr³⁺ ions. The coordination number of the F^– ions is three and four, respectively. The linkage of the coordination polyhedra leads to cavities in the crystal structure which incorporate the lone pairs of the selenite ions. The reaction of Sm₂(SeO₄)₃ and NaCl in gold ampoules yielded light yellow single crystals of NaSm(SeO₃)(SeO₄). The monoclinic compound (P2₁/c, Z = 4, a = 1066.9(2), b = 691.66(8), c = 825.88(9) pm, β = 91.00(2)°, R_all = 0.0530) contains tenfold oxygen coordinated Sm³⁺ ions. The oxygen atoms belong to five SeO₃^2– and two SeO₄^2– ions. Two of the SeO₃^2– groups as well as one of the SeO₄^2– groups act as a chelating ligand. The sodium ions are surrounded by five SeO₄^2– ions and one SeO₃^2– group. One of the selenate ions is attached chelating leading to a coordination number of seven. Each selenite group is coordinated by six (5 × Sm³⁺ and 1 × Na⁺), each selenate ion by seven cations (5 × Na⁺ and 2 × Sm³⁺).     

Chemical consequences of thermal neutron capture in alkali selenates—V transfer annealing in K2SeO4

The annealing of ⁷⁵Se labelled SeO₃²⁻ ion introduced into a K₂SeO₄ matrix (3 ppm) has been investigated. The analysis of the annealing curves shows the kinetics to be close to first order. Three different steps are observed for the annealing, which may correspond to different positions of the dopant ion in the matrix. The selenite ion anneals through the capture of a neighbouring oxygen ligand. Comparing with the thermal annealing of irradiated K₂SeO₄ leads to the conclusion that the SeO₃²⁻ ion is not present as a coil species.     

Oxidations with potassium permanganate in the presence of fluoride

Summary Quadrivalent selenium can be determined with fair accuracy by mixing with an excess of KMnO₄ in the presence of 25–75 ml of 2% NaF solution and 4–7 ml of 9 N sulfuric acid. After leaving the reaction mixture for 10–30 minutes the excess KMnO₄ is estimated by one of the following procedures: A) Titration of the excess KMnO₄ with monovalent mercury, B) Adding an excess of Hg₂ ²⁺ solution to react with the excess KMnO₄ followed by titrating the excess mercurous with KMnO₄ solution.Part I: Issa, I. M., and M. Hamdy, Z. analyt. Chem. 172, 94 (1980).     

Zur Bestimmung des Selens mit Eisen (II)-sulfat

Zusammenfassung Für die im Prinzip bekannte gravimetrische Bestimmungsmethode von SeO₃ ^2– und SeO₄ ^2– in salzsaurer Lösung mit FeSO₄ wird eine zuverlässige Vorschrift ausgearbeitet. Außerdem wird eine neue maßanalytische Bestimmungsmethode für SeO₃ ^2– und SeO₄ ^2– beschrieben. Die Nebeneinanderbestimmung von SeO₃ ^2– und SeO₄ ^2– nach diesem Verfahren gelingt mit Hilfe einer geeigneten Apparatur in einem Arbeitsgang.Für die Bestimmung von SeO₃ ^2– in tellurhaltigen Lösungen wird eine Trennungsmöglichkeit angeführt.Dem Institutsvorstand, Herrn Prof. Dr. Robert Strebinger,, danke ich für das fördernde Interesse an dieser Arbeit.     

Polymorphism in mercury(I) selenite(IV): preparation, crystal structures of α-, β-and γ-Hg2SeO3, and thermal behavior of the α- and β-modification

Mercury(I) selenite(IV) is polymorphic and crystallizes at least in three modifications, named α-, β-and γ-Hg₂SeO₃. Polycrystalline β-Hg₂SeO₃ was prepared by precipitation of a concentrated mercurous nitrate solution with selenous acid. Hydrothermal treatment of the colorless β-Hg₂SeO₃ powder in demineralized water at 250°C (10 days) yields light-yellow single crystals of α-Hg₂SeO₃ which show the highest density of the three modifications. Colorless needle-shaped single crystals of β-Hg₂SeO₃ and very few single crystals of γ-Hg₂SeO₃ co-crystallize from strongly diluted Hg₂(NO₃)₂ and H₂SeO₃ solutions and were grown by a diffusion technique. All crystal structures were solved and refined from single crystal diffractometer data sets and are based on Hg₂²⁺ dumbbells and trigonal pyramidal SeO₃²⁻ anions as the main building units. A common structural feature of all modifications is the formation of open channels extending parallel to the shortest crystallographic axis. The non-bonding orbitals of the Se^IV atoms are stereochemically active and protrude into the channels. Upon heating in an open system under N₂ atmosphere, both α- and β-Hg₂SeO₃ decompose in a well-separated three-step mechanism. The first step (T > 250°C) involves disproportionation into elementary mercury and α-HgSeO₃ which at ca. 400°C subsequently transforms into β-HgSeO₃. The second step between T = 400 and 500°C is accompanied by a loss of Hg and SeO₂ and the formation of the basic salt Hg₃SeO₆. In the third step, at temperatures between T = 500° and 600°C, this material decomposes completely. Upon heating in a closed system (sealed silica capillaries), β-Hg₂SeO₃ transforms between 320-340°C into the more dense α-Hg₂SeO₃ which on further heating likewise converts into elementary mercury and β-HgSeO₃.     

Synthesis, crystal structure and magnetic property of a new nickel selenite chloride: Ni5(SeO3)4Cl2

The new nickel selenite chloride, Ni₅(SeO₃)₄Cl₂, was obtained by high-temperature solid state reaction of NiCl₂, Ni₂O₃ and SeO₂ in a 1:2:4 molar ratio at 700 °C in an evacuated quartz tube. Its structure was established by single-crystal X-ray diffraction. Ni₅(SeO₃)₄Cl₂ crystallizes in the triclinic system, space group P-1 (No. 2) with cell parameters of a=8.076(2), b=9.288(2), c=9.376(2) Å, α=101.97(3), β=105.60(3), γ=91.83(3)° and Z=2. All nickel(II) ions in Ni₅(SeO₃)₄Cl₂ are octahedrally coordinated by selenite oxygens or/and chloride anions (([Ni(1)O₅Cl], [Ni(2)O₄Cl₂], [Ni(3)O₅Cl], [Ni(4)O₆] and [Ni(5)O₄Cl]). The structure of the title compound features a condensed three-dimensional (3D) network built by Ni(II) ions interconnected by SeO₃²⁻ anions as well as Cl⁻ anions. Magnetic property measurements show strong antiferromagnetic interaction between nickel(II) ions.