Selenium Particles Research Articles

Use of a mechanically dispersed mixture SiO2 + Se as a colorant for obtaining tinted GLASS

A selenium-based colorant obtained by transferring it into micro- and nanostates by mechanical dispersion using the main component of the glass—quartz sand—as the stabilizing matrix is studied. It is determined that with mechanical dispersion of SiO2+ Se mixtures not only does comminution occur but a transition of selenium into other polymorphic modifications could also occur, while the observation of an increase of the color intensity of the glasses synthesized on their basis is most likely due to the stabilization of selenium particles in low-dimension voids of the quartz glass. It has been found that a black heterogeneous mixture SiO2 + Se is characterized by high volatility and simultaneously the highest tinting power.

Reduction of selenite to red elemental selenium by moderately halotolerant Bacillus megaterium strains isolated from Bhitarkanika mangrove soil and characterization of reduced product

Two Gram (+) bacterial strains, BSB6 and BSB12, showing resistance and potential for Se(IV) reduction among 26 moderately halotolerant isolates from the Bhitarkanika mangrove soil were characterized by biochemical and 16S rDNA sequence analyses. Both of them were strictly aerobic and able to grow in a wide range of pH (4–11), temperature (4–40 °C) and salt concentration (4–12%) having an optimum growth at 37 °C, pH ∼7.5 and 7% salt (NaCl). The biochemical characteristics and 16S rDNA sequence analysis of BSB6 and BSB12 showed the closest phylogenetic similarity with the species Bacillus megaterium. Both the strains effectively reduced Se(IV) and complete reduction of selenite (up to 0.25 mM) was achieved within 40 h. SEM with energy dispersive X-ray and TEM analyses revealed the formation of nano size spherical selenium particles in and around the bacterial cells which were also supported by the confocal micrograph study. The UV–Vis diffuse reflectance spectra and XRD of selenium precipitates revealed that the selenium particles are in the nanometric range and crystalline in nature. These bacterial strains may be exploited further for bioremediation process of Se(IV) at relatively high salt concentrations and green synthesis of selenium nanoparticles.

Preparation of nano selenium particles by water solution phase method from industrial dust

Preparation of nano selenium particles by water solution phase method from industrial dust

The So-Called Positive Photo-Electric Emission (Inverse Effect) and the Reality of the Sub-Electron

A few observers have reported the discharge of positive electricity produced by ultra-violet light. Dember found that a metal plate exposed to ultra-violet light in vacuum had the power to communicate a positive charge to a receiving cylinder when the proper accelerating field was applied. His experiments have recently been repeated by DuBridge, who reports that Dember’s results can be entirely accounted for on the basis of the photo-electric effect produced on the collecting cylinder by scattered ultra-violet light against which no precautions had been taken. His conclusions are there is no measurable photo-electric production of either gaseous or metallic positive ions by the range of wave lengths emitted by the quartz mercury lamp. R. Bar and F. Luchsinger working with small particles of paraffin and selenium in a Millikan electron apparatus found that some of the particles showed the inverse effect, that is, they became charged negatively when illuminated by ultra-violet light. This has been construed by some workers as indicating the discharge of positive electricity. However, as these men were only using the ultra-violet light to charge up their particles in order to measure the charge communicated, and were not interested in the source of the photo-electric effect it is natural to assume that no special precautions were taken against the light striking the metallic plates of the condenser. The photo-electrons liberated from these metal surfaces being caught by the paraffin and selenium particles would make it seem as if the particles had lost a positive charge. S. Taubes, working in the same laboratory as Luchsinger and Bar and presumably with the same apparatus, reported this inverse effect when dealing with particles that had a large positive charge and showed that it is due to the photo-electrons given off by the condenser plates, for when these were coated with paraffin the inverse effect entirely disappeared. M. Hake, working at Vienna and using a diminutive Millikan electron apparatus designed by Professor Ehrenhaft, has recently reported results on nineteen different materials. He found that metals show both the inverse and the normal effect, depending on the gas in which the metal particles are suspended, and that some insulators, for example glycerine, always show the inverse effect in all gases. Wasser, working in the same laboratory as Hake gives results on mercury drops in N and CO2. He claims that drops of larger radius than 1.9 x 10-5 cm. always show the normal effect, that those between 1.1 and 1.9 x 10-5 cm. show both normal and the inverse effect, while those of smaller radius than 1.1 x 10-5 cm. always show the inverse effect. The following investigation was undertaken to test the correctness of the foregoing conclusions and to determine whether the changes in charge experienced by minute mercury droplets are of a magnitude corresponding to the electronic charge or to a charge smaller than this, as the Vienna physicists have maintained.

Growth Mechanism of Amorphous Selenium Nanoparticles Synthesized byShewanellasp. HN-41

Shewanella sp. HN-41 was exploited for selenium nanoparticles synthesis from aqueous selenite compounds under anaerobic conditions. Various reaction conditions, including reaction time, initial biomass, and initial selenite concentration, were systematically investigated to determine their effects on particle size distribution and formation rate. The biomass concentration of Shewanella sp. HN-41 had no significant effect on average particle size but strongly influenced reduction rate and size distribution. Initial selenite concentration (0.01-1.0 mM) also had no significant effect on the average particle size, but affected the early growth stage mechanism of selenium particle production, which was modeled using a Michaelis Menten model. The HR-TEM and SAED patterns indicated that the synthesized selenium nanoparticles were amorphous.

Fabrication of Selenium Rods by Solution Method

Microrods of selenium metal from commercial selenium powder have been fabricated via solution method in high boiling solvents. The directional growth of selenium particles is believed to be due to reduction of selenium to its lower oxidation state and regaining to its zero-valent state. It is also opined that the rod-shaped morphology resulted due to formation of intermediate submicron size particles that grow further due to nucleation process. The SEM showed the rods are of ∼ 100 nm in diameter and a few microns in length. The broadened XRD pattern suggests particle size reduction with respect to bulk powder.

Biological Alkylation and Colloid Formation of Selenium in Methanogenic UASB Reactors

Bioalkylation and colloid formation of selenium during selenate removal in upflow anaerobic sludge bed (UASB) bioreactors was investigated. The mesophilic (30 degrees C) UASB reactor (pH = 7.0) was operated for 175 d with lactate as electron donor at an organic loading rate of 2 g COD L(-1) d(-1) and a selenium loading rate of 3.16 mg Se L(-1) d(-1). Combining sequential filtration with ion chromatographic analysis for selenium oxyanions and solid phase micro extraction gas chromatography mass spectrometry (SPME-GC-MS) for alkylated selenium compounds allowed to entirely close the selenium mass balance in the liquid phase for most of the UASB operational runtime. Although selenate was removed to more than 98.6% from the liquid phase, a less efficient removal of dissolved selenium was observed due to the presence of dissolved alkylated selenium species (dimethylselenide and dimethyldiselenide) and colloidal selenium particles in the effluent. The alkylated and the colloidal fractions contributed up to 15 and 31%, respectively, to the dissolved selenium concentration. The size fractions of the colloidal dispersion were: 4 to 0.45 mum: up to 21%, 0.45 to 0.2 mum: up to 11%, and particles smaller than 0.2 mum: up to 8%. Particles of 4 to 0.45 mum were formed in the external settler, but did not settle. SEM-EDX analysis showed that microorganisms form these selenium containing colloidal particles extracellularly on their surface. Lowering the temperature by 10 degrees C for 6 h resulted in drastically reduced selenate removal efficiencies (after a delay of 1.5 d), accompanied by the temporary formation of an unknown, soluble, organic selenium species. This study shows that a careful process control is a prerequisite for selenium treatment in UASB bioreactors, as disturbances in the operational conditions induce elevated selenium effluent concentrations by alkylation and colloid formation.

Elemental selenium particles at nano-size (Nano-Se) are more toxic to Medaka ( Oryzias latipes) as a consequence of hyper-accumulation of selenium: A comparison with sodium selenite

Recent studies have shown that elemental selenium particles at nano-size (Nano-Se) exhibited comparable bioavailability and less toxicity in mice and rats when compared to sodium selenite, selenomethinine and methylselenocysteine. However, little is known about the toxicity profile of Nano-Se in aquatic animals. In the present study, toxicities of Nano-Se and selenite in selenium-sufficient Medaka fish were compared. Selenium bioaccumulation and subsequent clearance in fish livers, gills, muscles and whole bodies were examined after 10 days of exposure to Nano-Se and selenite (100 μg Se/L) and again after 7 days of depuration. Both forms of selenium exposure effectively increased selenium concentrations in the investigated tissues. Surprisingly, Nano-Se was found to be more hyper-accumulated in the liver compared to selenite with differences as high as sixfold. Selenium clearance of both Nano-Se and selenite occurred at similar ratios in whole bodies and muscles but was not rapidly cleared from livers and gills. Nano-Se exhibited strong toxicity for Medaka with an approximately fivefold difference in terms of LC 50 compared to selenite. Nano-Se also caused larger effects on oxidative stress, most likely due to more hyper-accumulation of selenium in liver. The present study suggests that toxicity of nanoparticles can largely vary between different species and concludes that the evaluation of nanotoxicology should be carried out on a case-by-case basis.

Surfactant assisted synthesis and spectroscopic characterization of selenium nanoparticlesin ambient conditions

In this work, an attempt has been made to synthesize well-distributed stable selenium (Se)particles of nanosize dimensions via an aqueous micellar solution by the assistance ofsurfactants of two different polarities (anionic, sodium bis(2-ethylhexyl)sulfosuccinate(AOT) and cationic, hexadecyltrimethylammonium bromide (CTAB)). The morphology ofthe particles was examined with transmission electron microscopy (TEM). X-ray analysisreveals that the particles have a monoclinic structure. The band gap of the particles wasdetermined from UV–visible optical spectroscopic results. The size variation was estimatedby employing a quantum confinement effect equation. The evolution of the seleniumnanoparticles in AOT and CTAB micellar media was corroborated with the time-dependentabsorption spectra. The influence of hydrazine hydrate concentrations on the formationkinetics of Se nanoparticles was also investigated. The capping ability of the surfactants hasbeen quantitatively evaluated from Fourier transform infrared (FTIR) studies.

Synthesis of selenium nanoparticles in the presence of silk fibroin

This paper describes a solution-phase approach to the synthesis of selenium nanoparticles by reducing selenious acid solution with ascorbic acid in the presence of silk fibroin. The monodispersed spherical selenium colloid particles obtained were very stable in silk fibroin solution and characterized by Atomic force microscopy and X-ray techniques. The influences of temperature and ultrasonication on the morphology of selenium nanoparticles were also discussed. The experiments showed that the selenium nanoparticles with various morphologies could be obtained under different temperatures and the appropriate ultrasonication time was 60 min. This result indicated that the silk fibroin molecules intimately associated with the surface of the selenium particles and controlled the growth particles.

Se(VI) Reduction and the Precipitation of Se(0) by the Facultative Bacterium Enterobacter cloacae SLD1a-1 Are Regulated by FNR

The fate of selenium in the environment is controlled, in part, by microbial selenium oxyanion reduction and Se(0) precipitation. In this study, we identified a genetic regulator that controls selenate reductase activity in the Se-reducing bacterium Enterobacter cloacae SLD1a-1. Heterologous expression of the global anaerobic regulatory gene fnr (fumarate nitrate reduction regulator) from E. cloacae in the non-Se-reducing strain Escherichia coli S17-1 activated the ability to reduce Se(VI) and precipitate insoluble Se(0) particles. Se(VI) reduction by E. coli S17-1 containing the fnr gene occurred at rates similar to those for E. cloacae, with first-order reaction constants of k = 2.07 x 10(-2) h(-1) and k = 3.36 x 10(-2) h(-1), respectively, and produced elemental selenium particles with identical morphologies and short-range atomic orders. Mutation of the fnr gene in E. cloacae SLD1a-1 resulted in derivative strains that were deficient in selenate reductase activity and unable to precipitate elemental selenium. Complementation by the wild-type fnr sequence restored the ability of mutant strains to reduce Se(VI). Our findings suggest that Se(VI) reduction and the precipitation of Se(0) by facultative anaerobes are regulated by oxygen-sensing transcription factors and occur under suboxic conditions.

Crystallization and Shape Evolution of Single Crystalline Selenium Nanorods at Liquid−Liquid Interface: From Monodisperse Amorphous Se Nanospheres toward Se Nanorods

The reduction of selenious acid solution with hydrazine hydrate in the presence of poly(vinylpyrrolidone) (PVP) can produce a stable dispersion of uniform and amorphous selenium particles capped with PVP with a size of 100 nm. Further addition of a solvent with low polarity such as n-butyl alcohol into this aqueous solution and mild stirring result in the transportation of amorphous selenium particles onto a liquid-liquid interface between water and n-butyl alcohol. Subsequent crystallization and shape evolution on this interface occurred and finally resulted in the formation of single crystalline selenium nanorods. The results demonstrated that the enrichment of nanoparticles with amphiphilic property at a liquid-liquid interface between a polar solvent and another solvent of low polarity can result in crystallization and phase transformation for the formation of nanostructures.

TEM Study of PM2.5 Emitted from Coal and Tire Combustion in a Thermal Power Station

The research presented here was conducted within the scope of an experiment investigating technical feasibility and environmental impacts of tire combustion in a coal-fired power station. Previous work has shown that combustion of a coal+tire blend rather than pure coal increased bulk emissions of various elements (e.g., Zn, As, Sb, Pb). The aim of this study is to characterize the chemical and structural properties of emitted single particles with dimensions <2.5 microm (PM2.5). This transmission electron microscope (TEM)-based study revealed that, in addition to phases typical of coal fly ash (e.g., aluminum-silicate glass, mullite), the emitted PM2.5 contains amorphous selenium particles and three types of crystalline metal sulfates never reported before from stack emissions. Anglesite, PbSO4, is ubiquitous in the PM2.5 derived from both fuels and contains nearly all Pb present in the PM. Gunningite, ZnSO4-H2O, is the main host for Zn and only occurs in the PM derived from the coal+tire blend, whereas yavapaiite, KFe3+(SO4)2, is present only when pure coal was combusted. We conclude that these metal sulfates precipitated from the flue gas, may be globally abundant aerosols, and have, through hydration or dissolution, a major environmental and health impact.

Pyridine-2,6-Bis(Thiocarboxylic Acid) Produced by Pseudomonas stutzeri KC Reduces and Precipitates Selenium and Tellurium Oxyanions

The siderophore of Pseudomonas stutzeri KC, pyridine-2,6-bis(thiocarboxylic acid) (pdtc), is shown to detoxify selenium and tellurium oxyanions in bacterial cultures. A mechanism for pdtc's detoxification of tellurite and selenite is proposed. The mechanism is based upon determination using mass spectrometry and energy-dispersive X-ray spectrometry of the chemical structures of compounds formed during initial reactions of tellurite and selenite with pdtc. Selenite and tellurite are reduced by pdtc or its hydrolysis product H(2)S, forming zero-valent pdtc selenides and pdtc tellurides that precipitate from solution. These insoluble compounds then hydrolyze, releasing nanometer-sized particles of elemental selenium or tellurium. Electron microscopy studies showed both extracellular precipitation and internal deposition of these metalloids by bacterial cells. The precipitates formed with synthetic pdtc were similar to those formed in pdtc-producing cultures of P. stutzeri KC. Culture filtrates of P. stutzeri KC containing pdtc were also active in removing selenite and precipitating elemental selenium and tellurium. The pdtc-producing wild-type strain KC conferred higher tolerance against selenite and tellurite toxicity than a pdtc-negative mutant strain, CTN1. These observations support the hypothesis that pdtc not only functions as a siderophore but also is involved in an initial line of defense against toxicity from various metals and metalloids.

Ce2[SeO3]3 and Pr2[SeO3]3: Non‐Isostructural Oxoselenates(IV) of the Light Lanthanoids

AbstractThe crystal structures of Ce2[SeO3]3 and Pr2[SeO3]3 have been refined from X‐ray single‐crystal diffraction data. The compounds were obtained using stoichiometric mixtures of CeO2, SeO2, Ce, and CeCl3 (molar ratio 3:3:1:1) or Pr6O11, SeO2, Pr, and PrCl3 (molar ratio 3:27:1:2) heated in evacuated sealed silica tubes at 830 °C for one week. Ce2[SeO3]3 crystallizes orthorhombically (space group: Pnma), with four formula units per unit cell of the dimensions a = 839.23(5) pm, b = 1421.12(9) pm, and c = 704.58(4) pm. Its structure contains only a single crystallographically unique Ce3+ cation in tenfold coordination with oxygen atoms arranged as single‐face bicapped square antiprism and two different trigonal pyramidal [SeO3]2− groups. The connectivity among the [CeO10] polyhedra results in infinite sheets of face‐ and edge‐sharing units propagating normal to [001]. Pr2[SeO3]3 is monoclinic (space group: P21/n) with twelve formula units per unit cell of the dimensions a = 1683.76(9) pm, b = 705.38(4) pm, c = 2167.19(12) pm, and β = 102.063(7)°. Its structure exhibits six crystallographically distinct Pr3+ cations in nine‐ and tenfold coordination with oxygen atoms forming distorted capped square antiprisms or prisms (CN = 9), bicapped square antiprisms and tetracapped trigonal prisms (CN = 10), respectively. The [PrO9] and [PrO10] polyhedra form double layers parallel to (111) by edge‐ or face‐sharing, which are linked by nine different [SeO3]2− groups to build up a three‐dimensional framework. In both compounds, the discrete [SeO3]2− anions (d(Se4+–O2−) = 166–174 pm) show the typical Ψ1‐tetrahedral shape owing to the non‐bonding “lone‐pair” electrons at the central selenium(IV) particles. Moreover, their stereochemical “lone‐pair” activity seems to flock together in large empty channels running along [010] in the orthorhombic Ce2[SeO3]3 and along [101] in the monoclinic Pr2[SeO3]3 structure, respectively.

Synthesis, Characterization, and Optical Properties of AuSe Nanoalloys

A solution phase approach to synthesize a new metal-semiconductor nanocomposite, AuSe nanoalloy has been reported. The synthesis has been achieved through UV-photoactivation of preformed Au and Se nanoparticles in micelle. Non-ionic surfactant Triton X-100 was exploited as a micellar medium for effective fusion of gold and selenium particles under UV. Both physical and chemical studies have been performed to characterize the composition and morphology of the particles. UV-visible, TEM, SEM, XPS and AFM analyses were done for characterization purpose. The optical properties of nanocomposites have been substantiated through their interaction with a fluorescent probe, eosin in aqueous solution. The spectroscopic investigation of dye-metal-semiconductor assembly has been examined critically. It has been found that the dye experiences J and H types of aggregation on the surfaces of gold and selenium nanoparticles respectively. Again, the composition dependent change of the emission profile of the probe on different nanocomposite surfaces has been rationalized in accordance with the molecular dimerization of the dye.

Reactions of Biological Oxidants with Selenourea: Formation of Redox Active Nanoselenium

Reactions of biological oxidizing agents, such as hydroxyl radicals ((*)OH), singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), and peroxynitrite (ONOO(-)) with selenourea were studied. The kinetics of the reactions was followed using time-resolved techniques, and the bimolecular rate constants were determined. In all these reactions, under aerated conditions, elemental red selenium was produced as one of the reaction products. The average size of the selenium particles could be controlled and stabilized in the range of 20-100 nm with the addition of bovine serum albumin (BSA) or sodium dodecyl sulfate (SDS). The particles were characterized by dynamic light scattering studies (DLS), which revealed that the size and distribution of the particles depended mainly on the amount of selenourea undergoing oxidation. Other factors such as the nature of the oxidant and the concentration of the stabilizer also are important in stabilizing the particles. Nanoselenium-reduced ABTS(*-) to colorless ABTS(2-) (ABTS = 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) and oxidized dichlorodihydrofluoresecein diacetate (DCFA) to fluorescent dichlorofluorescein (DCF) indicating its ability to participate in redox and free radical reactions. The reactivity of selenium nanoparticles with these systems varied linearly with the surface area of the particles. The studies demonstrate that selenourea undergoes oxidation with both one-electron and two-electron oxidants to produce elemental selenium, which, on stabilization to nanometer size, exhibits size-dependent redox activity.

Size Effect of Colloidal Selenium Particles on the Inhibition of LPS-Induced Nitric Oxide Production

We have studied the size-dependent inhibition capabilities of colloidal selenium (Se) particles on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 cells. Four particle sizes of the nano-Se, ranging from 45 ˜ 220 nm in diameter, were examined. All of them, unlike their bulk material, show clear capabilities of inhibition and a trend dependent on the particles size. The inhibition becomes more potent as the particle size increases. It indicates that pursuing the reduction of colloidal sizes into nanoscale is not favoured in this biological system.

Similarities between the Abiotic Reduction of Selenite with Glutathione and the Dissimilatory Reaction Mediated by Rhodospirillum rubrum and Escherichia coli

Various mechanisms have been proposed to explain the biological dissimilatory reduction of selenite (SeO3(2-)) to elemental selenium (Se(o)), although none is without controversy. Glutathione, the most abundant thiol in the eukaryotic cells, the cyanobacteria, and the alpha, beta, and gamma groups of the proteobacteria, has long been suspected to be involved in selenium metabolism. Experiments with the phototrophic alpha proteobacterium Rhodospirillum rubrum showed that the rate of selenite reduction was decreased when bacteria synthesized lower than normal levels of glutathione, and in Rhodobacter sphaeroides and Escherichia coli the reaction was reported to induce glutathione reductase. In the latter organism superoxide dismutase was also induced in cells grown in the presence of selenite, indicating that superoxide anions (O2-) were produced. These observations led us to investigate the abiotic (chemical) reduction of selenite by glutathione and to compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. Our findings imply that selenite was first reduced to selenodiglutathione, which reached its maximum concentration within the 1st min of the reaction. Formation of selenodiglutathione was paralleled by a rapid reduction of cytochrome c, a known oxidant for superoxide anions. Cytochrome c reduction was inhibited by superoxide dismutase, indicating that O2- was the source of electrons for the reduction. These results demonstrated that superoxide was produced in the abiotic reduction of selenite with glutathione, thus lending support to the hypothesis that glutathione may be involved in the reaction mediated by R. rubrum and E. coli. The second phase of the reaction, which led to the formation of elemental selenium (Se(o)), developed more slowly. Se(o) precipitation reached a maximum within 2 h after the beginning of the reaction. Secondary reactions leading to the degradation of the superoxide significantly decreased the yield of Se(o) in the abiotic reaction compared with that of the bacterially mediated selenite reduction. Abiotically formed selenium particles showed the same characteristic orange-red color, spherical structure, and size as particles produced by R. rubrum, again providing support for the hypothesis that glutathione is involved in the reduction of selenite to elemental selenium in this organism.

Acute Pulmonary Inflammation Induced by Lung Overloading with Selenium Particles: Leukocyte Response and In Situ Detection of Selenium at High Resolution

The kinetics of the acute inflammatory response of the lung was triggered in CD-1 mice by a single intratracheal instillation of a large amount of Se (10 mg); it was studied by quantitative cytology of bronchoalveolar lavage samples, light microscopy, and scanning electron microscopy coupled with x-ray elemental microanalysis. Bronchoalveolar lavage leukocytes were mostly neutrophils and increased from 12 to 24 h of Se treatment and decreased at 72 h. Only less than half of the granulocytes showed ingested Se particles; in contrast, virtually all BAL macrophages contained Se particles. Scanning electron microscopy coupled with X-ray elemental microanalysis revealed that the intracellular Se particles were heterogeneous in size (diameters from 0.4 and up to 14 μm), and that Se inclusions were sometimes accumulated at a pole of the cell. At 72 h after instillation of the particles, Se-loaded alveolar macrophages were migrated in the interstitial space of the alveoli. Se-positive regions had a focal distribution in the lung; accumulation of inflammatory cells erased the alveolar architecture of these areas of the deep lung. Our data indicates that Se overloading of the lung results in: (1) an acute inflammatory response that is dominated by neutrophils; (2) early removal of Se done mostly by alveolar macrophages, and (3) formation of focal areas of invasion of the lung parenchyma by inflammatory infiltrates.