Se Molar Ratio Research Articles

Investigation of Hydrothermally Synthesized Ruthenium Selenides as Methanol-Tolerant Oxygen Reduction Catalysts

Ruthenium selenides (RuSe x ) with Ru and Se molar ratios (Ru/Se), 1:1 and 1:2, have been prepared by the hydrothermal method using ruthenium (III) chloride and selenium powder as precursors. Structural and electrochemical characterizations of materials were performed by X-ray diffraction, scanning and transmission electron microscopes, energy-dispersive X-ray analysis, and cyclic and linear sweep voltammetries. The study confirmed that the hydrothermal method produces the nanocrystalline pyrite-type cubic RuSe2 with both Ru/Se ratios. The catalyst material was porous with the average particles size <10 nm. Both the catalysts were highly active for the oxygen reduction reaction (ORR), on the contrary, they were inactive toward the methanol electrooxidation in 0.1 M HClO4. However, RuSe x obtained with x = 1 is found to be more ORR active than one obtained with x = 2. Results of the ORR study performed by a rotating disk electrode in 0.1 M HClO4 favor a four-electron pathway from O2 to H2O.

Cu2ZnSnSe4 thin films prepared by selenization of one-step electrochemically deposited Cu–Zn–Sn–Se precursors

In this research a non-vacuum strategy was reported in facile preparation of kesterite-type Cu2ZnSnSe4 (CZTSe) thin films via selenization of one-step electrochemically prepared Cu–Zn–Sn–Se precursors. The Cu–Zn–Sn–Se precursor films were prepared by electrochemical deposition from electrolytes containing CuSO4, ZnSO4, SnCl4 and H2SeO3, and the substrate is a Mo coated soda-lime glass. The CZTSe thin films were obtained by annealing the electrochemically deposited films in the selenium vapors at the temperature of 550°C. The crystal phases, micro-structures, chemical compositions and optical properties of CZTSe films have been studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometer (ICP-OES), Raman scattering spectrum, and UV–vis absorption spectroscopic means. The results revealed that the electrolytes with Cu:Zn:Sn:Se molar ratio of 3:70:20:3 yields nearly pure phase of kesterite, and a band gap of 0.94eV was determined by spectroscopic measurements.

One-step microwave-assisted synthesis of water soluble CdSe quantum dots for white light-emitting diodes with excellent color rendering

Thiol-capped and red-emitting CdSe quantum dots (QDs) have been successfully synthesized in the air without hot-injection by one-step microwave method with friendly environment. The size and optical properties can be tuned by changing the reaction time, growth temperature, microwave power, and the Cd2+/Se molar ratio. The as-prepared CdSe QDs were mixed with the yellow-emitting YAG:Ce phosphor and coated onto a blue LED chip, a white LED with an excellent color rendering property was obtained. It exhibited a luminous efficiency of 67lm/W and a Ra as high as 85, which is acceptable for general lighting. It indicates that the combination of the phosphor and QD in LEDs should be a good solution to obtain white light sources with high color rendering.

The interactive effects of selenomethionine and methylmercury on their absorption, disposition, and elimination in juvenile white sturgeon

Selenium (Se) and mercury (Hg) are prevalent pollutants of industrialized watersheds. However, when co-administered, Se has protective effects on organisms from Hg. The mechanism is not fully understood, but it is thought that Se reduces Hg availability, either by forming biologically inert complexes and/or associating with selenoproteins. Despite concerns with aquatic contaminations, relatively little information is available on the interaction in aquatic organisms. In the present study, the interactive effects of Se and Hg on their absorption, disposition, and elimination were examined in juvenile white sturgeon, a benthic fish species at high risk to exposures of both contaminants. Selenium and Hg were provided as l-selenomethionine (SeMet) and methylmercury (MeHg), respectively. Groups of 10 sturgeon were orally intubated with a single dose of either 0 (control), SeMet (500μg Se/kg body weight; BW), MeHg (850μg Hg/kg BW), or their combination (Se/Hg; 500μg Se/kg and 850μg Hg/kg BW). The blood was repeatedly sampled and urine collected from the fish, over a 48h post intubation period. At 48h, the fish were sacrificed for Se and Hg tissue concentration and distribution. The co-administration of SeMet and MeHg significantly (p<0.05) lowered blood concentrations of both Se and Hg and tissue Se concentrations. Similarly, assimilation of Se and Hg was also reduced significantly. The interaction has a more quantitative effect on Se metabolism because the reduction in the overall tissue Se is a consequence of reduced Se absorption at the gut and not from the metabolic effects after absorption. In contrast, given the pulse increase in blood Hg concentration, tissue redistribution, and increased urinary elimination, the interactive effect on tissue Hg concentration is likely to be post-absorption. Even in the absence of exogenous SeMet, Se and Hg co-accumulated in tissue at a Se:Hg molar ratio greater than 1. Thus, similar to mammals, maintaining at least a 1:1 molar ratio of Se and Hg is of great physiological importance in the white sturgeon. Interestingly, SeMet did not divert Hg from the brain. Allocation of Se from the kidneys may have occurred in order to maintain the high Se:Hg molar ratios in the brain of white sturgeon. In the current study, the combined use of kinetic analysis and that of the conventional approach of measuring tissue concentration changes provided a comprehensive understanding of the interactive effect of SeMet and MeHg on their respective metabolic processes in juvenile white sturgeon.

Influence of mercury and selenium chemistries on the progression of cardiomyopathy in pygmy sperm whales, Kogia breviceps

More than half of pygmy sperm whales (Kogia breviceps) that strand exhibit signs of cardiomyopathy (CMP). Many factors may contribute to the development of idiopathic CMP in K. breviceps, including genetics, infectious agents, contaminants, biotoxins, and dietary intake (e.g. selenium, mercury, and pro-oxidants). This study assessed trace elements in K. breviceps at various stages of CMP progression using fresh frozen liver and heart samples collected from individuals that stranded along US Atlantic and Gulf coasts between 1993 and 2007. Standard addition calibration and collision cell inductively coupled plasma mass spectrometry (ICP-MS) were employed for total Se analysis and pyrolysis atomic absorption (AA) was utilized for total Hg analysis to examine if the Se/Hg detoxification pathway inhibits the bioavailability of Se. Double spike speciated isotope dilution gas chromatography ICP-MS was utilized to measure methyl Hg and inorganic Hg. Immunoblot detection and colorimetric assays were used to assess protein oxidation status. Data collected on trace elements, selenoproteins, and oxidative status were evaluated in the context of animal life history and other complementary histological information to gain insight into the biochemical pathways contributing to the development of CMP in K. breviceps. Cardiomyopathy was only observed in adult pygmy sperm whales, predominantly in male animals. Both Hg:Se molar ratios and overall protein oxidation were greater in males than females and increased with progression of CMP.

49.3: Synthesis of High Quality CdSe Quantum Dots with Tunable Size

AbstractA cheaper, greener approach for the synthesis of highly monodisperse and tunable size CdSe semiconductor quantum dots was developed by thermolysis of a mixed solution of CdO and Se in non‐coordinating solvent 1‐octadecene at 240°C. Systematic vary of the precursor molar ratios allowed the particle size (from 2.5 nm to 5.5 nm) to be tuned and the size distribution (full width at half maximum of photoluminescence spectra from 26 nm to 37 nm) to be controlled. The results revealed that initial Cd:Se molar ratios play an important role in controlling both the size and size distribution of the as‐prepared CdSe quantum dots. Moreover, the obtained CdSe quantum dots are all of zinc blende phase. The possible reason was discussed. The reaction has been conducted in relatively low temperature at 210°C in the absence of expensive organic phosphine ligands, such as trioctylphoshine and trioctylphoshine oxide. This approach has great value for both the laboratory research and industrial application in term of “green chemical principles”.

Mercury exposure and mechanism of response in large game using the Almadén mercury mining area (Spain) as a case study

Mercury (Hg) accumulation, transfer, defense mechanism and adverse effects were studied in red deer (Cervus elaphus) and wild boar (Sus scrofa) from the Almadén mining district (Spain), the largest (285,000t of Hg) and the oldest (more than 2000 years) Hg mine/refining operation site in the world. Red deer (n=168) and wild boar (n=58) liver, kidney, bones (metacarpus), testis and muscle were analyzed for total Hg and selenium (Se) within a range of distances to the Almadén mining district. The highest Hg concentrations were found in kidney (0.092 and 0.103μg/g d.w. for red deer and wild boar, respectively) followed by the levels in liver (0.013 and 0.023μg/g d.w. for red deer and wild boar, respectively). A significant correlation (r=−0.609, p=0.007) was found between Hg concentrations and distance to the Almadén Hg mining district. However, both red deer and wild boar closest to the mining area still showed mercury concentrations well below the concentration associated with clinical signs of Hg poisoning. Highest Se concentrations were found in kidney (2.60 and 6.08μg/g in red deer and wild boar, respectively) and testis (2.20μg/g in red deer). For selenium, differences between red deer and wild boar were statistically significant (p<0.05) in all tissues, concentrations being higher in wild boar than in red deer. In the diagnosis of Se deficiency, the vast majority of the examined red deer livers were deficient. A significant correlation was found between Hg and Se in kidney (r=0.386, p>0.001 for red deer and r=0.567, p=0.005 for wild boar). Liver GSSG concentrations were negatively correlated to total mercury and Hg:Se molar ratio in male deer, which could indicate a hormetic response to Hg exposure. Moreover, a positive association was found between the antioxidant element Se and antioxidant vitamins in red deer tissues.

Synthesis, structural and photocatalytic characteristics of nano-Cu2−x Se

Large-scale synthesis of Cu 2−x Se nanocrystals (nano-Cu 2−x Se) with uniform size was performed via a facile hydrothermal method at room temperature and at 120 °C. Nano-Cu 2−x Se with different structures could be synthesized by changing the reaction/growth time, the Cu:Se molar ratios, and the initial concentration of the precursors. The synthesized nano-Cu 2-x Se was characterized using various techniques, including x-ray powder diffraction, scanning electron microscopy and photocatalytic activity. Systematic studies showed that the reaction time played a key role in controlling the morphology and structure leading to significant influence on the photocatalytic activity of nano-Cu 2−x Se. With increasing reaction/growth time, Cu 2−x Se could transform gradually from a cubic to hexagonal structure and from nanoparticles to nanoplate/nanorod shapes. The photocatalytic characteristics were evaluated by the photo-decoloration of Rhodamine B (RhB) in aqueous solution under visible light irradiation. As-prepared nano-Cu 2−x Se showed good photocatalytic activity under visible light irradiation, indicating potential applications in depollution technologies.

Mercury, selenium and neurochemical biomarkers in different brain regions of migrating common loons from Lake Erie, Canada

Common loons (Gavia immer) can be exposed to relatively high levels of dietary methylmercury (MeHg) through fish consumption, and several studies have documented MeHg-associated health effects in this species. To further study the neurological risks of MeHg accumulation, migrating loons dying of Type E botulism were collected opportunistically from the Lake Erie shore at Long Point (Ontario, Canada) and relationships between total mercury (THg), selenium (Se), and selected neurochemical receptors and brain enzymes were investigated. THg concentrations were 1-78 μg/g in liver; and 0.3-4 μg/g in the brain (all concentrations reported on a dry weight basis). A significant (p < 0.05) positive correlation was found between THg in liver and THg in 3 subregions of the brain (cerebral cortex: r = 0.433; cerebellum: r = 0.293; brain stem: r = 0.405). THg varied significantly among different brain regions, with the cortex having the highest concentrations. Se levels in the cortex and cerebellum were 1-29 and 1-10 μg/g, respectively, with no significant differences between regions. Se was not measured in brain stem due to insufficient tissue mass. There were molar excesses of Se over mercury (Hg) in both cortex and cerebellum at all Hg concentrations, and a significant positive relationship between THg and the Hg:Se molar ratio (cortex: r = 0.63; cerebellum: r = 0.47). No significant associations were observed between brain THg and the N-methyl-D-aspartic acid (NMDA) receptor concentration, nor between THg and muscarinic cholinergic (mACh) receptor concentration; however, brain THg levels were lower than in previous studies that reported significant Hg-associated changes in neuroreceptor densities. Together with previous studies, the current findings add to our understanding of Hg distribution in the brain of common loons, and the associations between Hg and sub-lethal neurochemical changes in fish-eating wildlife.

Biostrome communities and mercury and selenium bioaccumulation in the Great Salt Lake (Utah, USA)

The Great Salt Lake has a salinity near 150 g/L and is habitat for over 200 species of migratory birds. The diet of many of these birds is dependent on the food web of carbonaceous biostromes (stromatolites) that cover 260 km 2 of the lake's littoral zone. We investigated the biostrome community to understand their production processes and to assess whether they are a potential vector for bioconcentration of high mercury and selenium levels in the lake. The periphyton community of the biostromes was > 99% colonial cyanobacteria. Periphyton chlorophyll levels averaged 900 mg m −2 or nine times that of the lake's phytoplankton. Lake-wide estimates of chlorophyll suggest that their production is about 30% of that of the phytoplankton. Brine fly ( Ephydra gracilis) larval densities on the biostromes increased from 7000 m −2 in June to 20000 m −2 in December. Pupation and adult emergence halted in October and larvae of various instars overwintered at temperatures < 5 °C. Mean total dissolved and dissolved methyl mercury concentrations in water were 5.0 and 1.2 ηg L −1. Total mercury concentrations in the periphyton, fly larvae, pupae, and adults were, respectively, 152, 189, 379 and 659 ηg g −1 dry weight, suggesting that bioconcentration is only moderate in the short food web and through fly developmental stages. However, common goldeneye ducks ( Bucephala clangula) that feed primarily on brine fly larvae at the Great Salt Lake had concentrations near 8000 ηg Hg g −1 dry weight in muscle tissue. Data from a previous study indicated that selenium concentrations in periphyton, brine fly larvae and goldeneye liver tissue were high (1700, 1200 and 24,000 ηg g −1, respectively) and Hg:Se molar ratios were < 1.0 in all tissues, suggesting that the high mercury concentration in the ducks may be partially detoxified by combining with selenium. The study demonstrated that the high mercury levels in the Great Salt Lake are routed through the biostrome community resulting in invertebrate prey that may provide health risks for birds and humans that consume them.

Evidences of non-reactive mercury–selenium compounds generated from cultures of Pseudomonas fluorescens

This work was designed to determine chemically inert mercury–selenium (Hg–Se) compounds formed in a culture of Pseudomonas fluorescens exposed to Hg 2+ and Se IV (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg 0 and non-reactive Hg were determined in two series of cultures containing 0.0–6.00 μg L −1 Se IV (0.0–76.0 μmol L −1) in combination with low 5.00 μg L −1 (0.025 μmol L −1) or high 100 μg L −1 (0.500 μmol L −1) Hg 2+. It was found that Hg 0 formed in the culture decreased with the increase of initial Se IV, while the non-reactive Hg increased with the Se IV. In cultures with low initial [Hg 2+], a median Se IV (2.0 μg L −1 or 25.3 μmol L −1) resulted in about 70% of the added Hg 2+ sequestered as non-reactive Hg, and in culture with high initial Hg 2+, about 40% was sequestered. P. fluorescens was proved to be indispensible for the formation of the non-reactive Hg–Se compounds. The Hg:Se molar ratio in the non-reactive Hg–Se compounds was close to 1, suggesting the existence of mercuric selenide in cells. Mechanisms for the formation of the non-reactive Hg–Se compounds are proposed.

Spatial and temporal trends of selected trace elements in liver tissue from polar bears (Ursus maritimus) from Alaska, Canada and Greenland

Spatial trends and comparative changes in time of selected trace elements were studied in liver tissue from polar bears from ten different subpopulation locations in Alaska, Canadian Arctic and East Greenland. For nine of the trace elements (As, Cd, Cu, Hg, Mn, Pb, Rb, Se and Zn) spatial trends were investigated in 136 specimens sampled during 2005-2008 from bears from these ten subpopulations. Concentrations of Hg, Se and As were highest in the (northern and southern) Beaufort Sea area and lowest in (western and southern) Hudson Bay area and Chukchi/Bering Sea. In contrast, concentrations of Cd showed an increasing trend from east to west. Minor or no spatial trends were observed for Cu, Mn, Rb and Zn. Spatial trends were in agreement with previous studies, possibly explained by natural phenomena. To assess temporal changes of Cd, Hg, Se and Zn concentrations during the last decades, we compared our results to previously published data. These time comparisons suggested recent Hg increase in East Greenland polar bears. This may be related to Hg emissions and/or climate-induced changes in Hg cycles or changes in the polar bear food web related to global warming. Also, Hg:Se molar ratio has increased in East Greenland polar bears, which suggests there may be an increased risk for Hg(2+)-mediated toxicity. Since the underlying reasons for spatial trends or changes in time of trace elements in the Arctic are still largely unknown, future studies should focus on the role of changing climate and trace metal emissions on geographical and temporal trends of trace elements.

Mercury in canned tuna: The importance of selenium

To the Editor: The recent article by Gerstenberger et al. [1], reported the mercury (Hg) concentrations, but did not report the selenium (Se) contents of the tuna. Since methylmercury is, by biochemical definition, a highly specific irreversible inhibitor of Se-dependent enzymes [2], it is necessary to measure both Hg and Se to accurately assess risks associated with Hg exposures. The brain and neuroendocrine tissues depend upon Se-dependent enzymes to prevent and reverse oxidative damage that would otherwise accompany their high rates of oxygen consumption. Because the affinity of Hg for Se is approximately a million times higher than its affinity for sulfur [3], the Seenzymes are uniquely vulnerable to inhibition by high methylHg exposures. However, rather than impairing Se enzymes, eating ocean fish such as tuna that are known to provide far more Se than Hg actually enhances nutritional Se status, explaining why ocean fish consumption has repeatedly been shown to prevent, rather than contribute to Hg toxicity [2]. In contrast, consumption of meats of predatory whales and sharks that are known to contain far more Hg than Se has been shown to be hazardous. Current U.S. Environmental Protection Agency (U.S. EPA) risk criteria are based on a study of human Hg exposures that arose predominantly from eating pilot whale meats. Since pilot whale meats are virtually unique in having exceedingly high Hg to Se molar ratios (5:1), as well as Hg contents in excess of 3 ppm [4], this is clearly a food to avoid. In contrast, ocean fish are Se-rich and have Hg to Se molar ratios that are typically on the order of 1:5, which may explain why ocean fish consumption has been shown to counteract Hg toxicity from whale meat consumption [5]. Although blood Hg and blood Hg to Se molar ratios in children exposed in utero are highly correlated [6], relationships between Hg exposures and risk are most accurately predicted from the perspective of Hg to Se molar ratios. Therefore, the selenium-health benefit value (Se-HBV) is preferable since it incorporates both the relative and the absolute amounts of Se intake and Hg exposure in a single criterion. Health benefits are directly associated with positive Se-HBVs, whereas adverse health effects are directly proportional to negative Se-HBVs [2]. Since methylmercury is an enzyme inhibitor, its chemical reactions are clearly second order. Therefore, attempting to

One-pot Microwave Assisted Synthesis of Homogeneously Alloyed CdSe xTe 1- x Nanocrystals with Tunable Photoluminescence

Aqueous soluble homogeneously alloyed CdSe x Te 1- x (0 ≤ x ≤ 1) semiconductor nanocrystals (NCs) were synthesized by co-reduction of sodium selenite (Na 2SeO 3) and sodium tellurite (Na 2TeO 3) at 120 °C under microwave irradiation. The optical modulation of the photoluminescence (PL) between 600 and 710 nm could be facilely demonstrated through changing molar ratios of Se to Te. The PL quantum yields (QYs) of CdSe x Te 1- x NCs were lower than that of CdTe NCs. On the other hand, it could be higher than that of CdSe NCs.

“One-pot” synthesis and shape control of ZnSe semiconductor nanocrystals in liquid paraffin

In this paper, we demonstrated a “one-pot” strategy for synthesizing ZnSe nanocrystals (NCs) in liquid paraffin. All materials, including Zn source, Se source, and ligand, were mixed in liquid paraffin beforehand, which avoided the injection of Se source at high temperature. The resultant ZnSe NCs possessed high photoluminescence quantum yields and narrow size distribution. Moreover, the size, shape, and crystal phase of NCs were controllable by altering the experimental variables, such as precursor concentration, Zn:Se molar ratio, and heating rate. Because the raw materials used here were low-cost and environmentally friendly, this “one-pot” synthetic protocol would facilitate the commercial scale synthesis of high-quality ZnSe NCs.

Accumulation of mercury and selenium in the brain of river otters ( Lontra canadensis) and wild mink ( Mustela vison) from Nova Scotia, Canada

Total Hg, methyl-Hg (MeHg) and Se levels were measured in the brain of river otters ( Lontra canadensis) and wild mink ( Mustela vison) carcasses collected from Nova Scotia, Canada. Total Hg concentrations in the otters' brain were highly variable, ranging from 0.3 to 18.0 μg/g dw and were significantly higher in animals caught from inland areas of the province versus coastal animals. Similarly, inland otters contained significantly more MeHg in the brain than did coastal otters. MeHg was highly correlated with total Hg in both inland and coastal otters and represented on average approximately 82% of the total Hg. Selenium concentrations in the otter brain ranged from 1.0 to 7.8 μg/g dw but unlike Hg, there was no significant difference in Se levels between inland and coastal otters. There was a significant positive relationship between Se and total Hg concentrations in the otters with the molar ratio of Se:Hg approximately 1:1 for animals having an Hg concentration > 18 nmol/g dw. The non-random sampling protocol for the mink precluded extensive statistical analysis of the data. However, unlike otters, virtually all (i.e. 98%) of the total Hg in mink brain was present as MeHg in both inland and coastal mink. Also unlike the otter results, Se concentrations showed no relationship with either total or MeHg in both inland and coastal mink. The data suggest that mink and otters may have different mechanisms for managing high levels of Hg in the brain.

A novel “green” synthesis of starch-capped CdSe nanostructures

This paper reports a “green” facile, room temperature, one-pot synthesis of starch-capped CdSe nanostructures with an obvious quantum confinement effect via a novel non-organometallic method. It is found that by simply tuning the Cd:Se molar ratio, dots and elongated particles of high aspect ratio could be prepared selectively in the presence of the same ligand concentration without any post-treatment. Spherical particles were produced at 1:1 ratio, while elongated particles were produced at 0.5:1 Cd:Se ratio. The X-ray diffraction (XRD) analysis showed that the particles were predominantly of wurtzite structure, with sharp diffraction patterns regardless of their size and shapes. We inferred that the elongated particles are formed by self-reorganisation occurring via adhesion between the spherical nanoparticles as a result of dipole–dipole interactions.

A Rapid Hot-Injection Method for the Improved Hydrothermal Synthesis of CdSe Nanoparticles

Cadmium selenide (CdSe) quantum dots were prepared in high-temperature water via a rapid hot-injection method intended to mimic conventional synthesis in organic solvents. The nanocrystals were smaller than those previously produced hydrothermally under nonisothermal conditions when using the same process parameters. It is possible that the nucleation and growth events were greatly influenced by the present injection method. In general, the physical and optical properties of the nanocrystals were influenced by the experimental conditions. Variations in reaction temperature (200−240 °C), reaction time (1−10 min), pH (7−11), Cd:Se molar ratio (4:1−40:1) and Cd:stabilizer molar ratio (0.24−1.18) affected the mean particle size, distribution of sizes, and quantum yield. As-prepared nanoparticles exhibited quantum yields in excess of 5%.

Selenium Health Benefit Values as Seafood Safety Criteria

Selenium (Se) is absolutely required for activity of 25-30 genetically unique enzymes (selenoenzymes). All forms of life that have nervous systems possess selenoenzymes to protect their brains from oxidative damage. Homeostatic mechanisms normally maintain optimal selenoenzyme activities in brain tissues, but high methylmercury (MeHg) exposures sequester Se and irreversibly inhibit selenoenzyme activities. However, nutritionally relevant amounts of Se can replace the Se sequestered by MeHg and maintain normal selenoenzyme activities, thus preventing oxidative brain damage and other adverse consequences of MeHg toxicity. Findings of studies that seem contradictory from MeHg exposure perspectives are entirely consistent from MeHg:Se molar ratio perspectives. Studies that have reported dose-dependent consequences of maternal MeHg exposures on child development uniformly involved seafoods that contained much more Hg than Se. Meanwhile more typical varieties of ocean fish contain much more Se than Hg. This may explain why maternal MeHg exposure from eating ocean fish is associated with major IQ benefits in children instead of harm. Therefore, instead of being avoided, ocean fish consumption should be encouraged during pregnancy. However, the safety of freshwater fish consumption is less certain. In freshwater fish, MeHg bioaccumulation and toxicity are both inversely related to Se bioavailability. Their Se can be far lower than their MeHg contents, potentially making them more dangerous than pilot whale meats. Therefore, to provide accurate and appropriate regulatory advice regarding maternal consumption of seafoods and freshwater fish, Hg:Se molar ratios need to be incorporated in food safety criteria.

Controlled Solvothermal Synthesis of Nanosheets, Nanobelts, and Ultralong Nanobelt Arrays with Honeycomb-Like Micropatterns of ZnSe on Zinc Substrate

Nanosheets, nanobelts, and ultralong nanobelt arrays with honeycomb-like micropatterns of ZnSe were synthesized via a solvothermal reaction of Zn with Se and KBH(4) in ethylenediamine at 200 degrees C for 24 h and subsequent annealing. The control over these nanostructures with different morphologies was achieved by adjusting the KBH(4)/Se molar ratio. The role of KBH(4) in the formation of ZnSe(en)(0.5) nanobelts with different length-to-width ratios was investigated, and a possible mechanism was also proposed to account for the growth and conversion of these precursor nanostructures into ZnSe nanostructures. Current-voltage behaviors of the ultralong nanobelt arrays with honeycomb-like micropatterns were investigated. In addition, variable-aspect ratio ZnS nanosheets and nanowires were also synthesized by adjusting the KBH(4)/thiourea molar ratio in the Zn-thiourea-KBH(4)-ethylenediamine solvothermal system. The results suggest that this method may be employed for the controllable synthesis of other II-VI semiconductor nanostructures such as ZnTe, NiS, MnS, and so forth and provides opportunities for both fundamental research and technological applications.