Chalcogen Research Articles

Method Development for Simultaneous Determination of Transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and Noble (Pd, Pt, Rh) Metal Volatile Species by Microwave-Induced Plasma Spectrometry Using Ultrasonic Micronebulizer Dual Capillary Sample Introduction System

ABSTRACT The commercial ultrasonic nebulizer NOVA-DUO (Optolab, Warsaw, Poland) has been evaluated for the simultaneous determination of transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and noble (Pd, Pt, Rh) volatile metal species by microwave induced plasma–optical emission spectrometry (MIP-OES). Simultaneous mixing and nebulization of the two solutions (acidified sample and reductant) on the piezoelectric transducer, with the possibility of flow rate adjustment, permits a wide variation of sensitivity. The vapor-phase species were rapidly transported via a stream of Ar carrier to an MIP–OES for simultaneous multi-element determination. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the ultrasonic nebulizer/dual capillary system (USN/DCS) observed at 15 µL min−1 flow rate. An improvement in detection limits was achieved compared with pneumatic nebulization. Detection limits are superior to conventional pneumatic nebulization of elements. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of standard deviation of the blank (LOD, 3σblank criterion, peak height), were 2.49, 1.75, 3.39, 2.13, 4.80, 6.21, 4.26, 2.01, 7.65, 3.92, and 4.65 ng mL−1 for Au, Ag, Cd, Cu, Mn, Ni, Pb, Pd, Pt, Rh, and Zn, respectively. The method offers relatively good precision (RSD ranged from 8 to 12%) for liquid analysis and microsampling capability. The accuracy of the method was verified by the use of digested certified reference materials (NRCC TORT-1, NIES CRM-13, NIST SRM 2710, INCT SBF-4) and by aqueous standard calibration technique. The measured elements content in reference materials was in satisfactory agreement with the certified values.

Critical examination of growth rate for magnesium oxide (MgO) thin films deposited by molecular beam epitaxy with a molecular oxygen flux

The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (≥250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source.

Effect of Glycosylation on Cis/Trans Isomerization of Prolines in IgA1-Hinge Peptide

The hinge region of human immunoglobulin A1 (IgA1), connecting the Fab and Fc regions, is mostly composed of Ser, Thr, and Pro (VPSTPPTPSPSTPPTPSPS); hinge peptide (HP). O-Glycans are naturally attached on only particular five Ser/Thr residues in this region. NMR was employed for analysis of the structural changes in HP upon the glycosylation, especially focusing on the cis/trans isomerization of Pro residues. A series of HP containing (13)C,(15)N-labeled Pro residues were chemically synthesized and enzymatically glycosylated. The signals from cis and trans forms of the labeled Pro were identified by two-dimensional NMR spectroscopy. Cis/trans ratios of the Pro residues at the C-terminal side of the glycosylated Ser/Thr were reduced from 9-10% to 2-3% by the glycosylation. Thermodynamic analyses indicated that the decrease in the cis/trans ratio was enthalpy-driven. Hydrogen-deuterium exchange experiments and NOE-based structure determination revealed that the intraresidue hydrogen bonds between the amide group of GalNAc and carbonyl oxygen of the peptide backbone of GalNAc-Thr are formed in the major trans conformers, which is consistent with the thermodynamic parameters. These hydrogen bonds largely restrict the psi angle of the peptide backbone and, thereby, should make the trans conformation of the C-terminal Pro residue more stable than the cis conformation. Namely, it is predicted that the restricted psi angle causes interresidue steric hindrance for the cis conformation. The appropriate glycosylation of HP probably contributes to the decrease in the unfavorable variety of relative orientations between Fab and Fc in IgA1, through stabilizing the conformation of HP.

Formation of thin nanostructured layers during heterogeneous gas-phase synthesis from small-size volatile metal complexes on the surface of semiconductors and dielectrics

We have developed and verified a new method for the formation of thin nanostructured layers on semiconductor and dielectric substrates by heterogeneous gas-phase synthesis from small-sized volatile metal complexes. Thin nanostructured layers of copper on silicon and silica substrates were successfully formed from small-sized volatile formiate metal complexes using a combined synthesis-transfer process. It is established that copper in the layers deposited by this method predominantly occurs in the metallic (Cu0) state in nanosized grains with a characteristic close-packed structure.

On the origin of decomposition of triphenyl phosphite ozonide accelerated by ammonia or pyridine water solution

The decomposition of triphenyl phosphite ozonide (TPPO) has been well recognized as a potential source of singlet oxygen (O 2, 1Δ g) for the chemical oxygen–iodine laser. Experimental observations suggested that ammonia or pyridine water solution can accelerate the decomposition of TPPO, and hydroxyl ion is responsible for accelerating singlet oxygen liberation during this decomposition. In this paper, we studied the mechanism of OH −-accelerated reaction using density functional theory (DFT) at B3LYP/6-31+G* levels of theory. The calculations reveal a favorable free energy pathway for hydroxide-accelerated decomposition of TPPO, i.e. nucleophilic addition at phosphorus, followed by elimination of phenoxy group and subsequent liberation of singlet oxygen. The solvent effects were studied using a polarizable continuum model. The frontier molecular orbitals of the ozonides, atom–atom Wiberg bond index and corresponding atomic charges were also investigated to shed further light on the reaction pathway.

Effect of on-demand inhalation of dry oxygen on nasal mucociliary clearance

To determine whether nasal mucociliary clearance is affected by dry oxygen delivered on demand. Saccharin nasal transit time was measured as an index of nasal mucociliary clearance. One group of patients was given dry oxygen via a nasal cannula and a demand delivery system, and another group was given dry oxygen by continuous inhalation. In each group, continuous inhalation of humidified oxygen served as the control. Saccharin transit time was measured before and after 8 hours of oxygen inhalation. The subjects were 25 patients with chronic respiratory failure who were receiving home oxygen therapy via nasal cannula. All the subjects were clinically stable (age 72.1, mean +/- SE), %VC 46.6 +/- 3.0. FEV/FVC% 9.0 +/- 1.5, PaO2 55.7 +/- 2.0 Torr. PaCO2 53.9 +/- 1.9 Torr). Saccharin transit time after inhalation of dry oxygen on demand did not differ from that after continuous inhalation of humidified oxygen (15.6 +/- 1.5 vs 14.9 +/- 1.4 min). Saccharin transit time after continuous inhalation of dry oxygen was significantly lower than that after continuous inhalation of humidified oxygen (26.6 +/- 5.4 vs 16.7 +/- 2.6 min. p > 0.05). We conclude that using the demand oxygen delivery system with a nasal cannula for 8 hours had no adverse effects on nasal mucociliary clearance.

Controlled incorporation of mid-to-high Z transition metals in CVD diamond

We report on a general method to fabricate transition metal related defects in diamond. Controlled incorporation of Mo and W in synthetic CVD diamond was achieved by adding volatile metal precursors to the diamond chemical vapor deposition (CVD) growth process. Effects of deposition temperature, grain structure and precursor exposure on the incorporation efficiency were systematically studied, and doping levels of up to 0.25 at.% have been achieved. The metal atoms are uniformly distributed throughout the diamond grains without any indication of inclusion formation. These results are discussed in context of the kinetically controlled growth process of CVD diamond.

The relation between Acid Volatile Sulfides (AVS) and metal accumulation in aquatic invertebrates: Implications of feeding behavior and ecology

The present study evaluates the relationship between Acid Volatile Sulfides (AVS) and metal accumulation in invertebrates with different feeding behavior and ecological preferences. Natural sediments, pore water and surface water, together with benthic and epibenthic invertebrates were sampled at 28 Flemish lowland rivers. Different metals as well as metal binding sediment characteristics including AVS were measured and multiple regression was used to study their relationship with accumulated metals in the invertebrates taxa. Bioaccumulation in the benthic taxa was primarily influenced by total metal concentrations in the sediment. Regarding the epibenthic taxa metal accumulation was mostly explained by the more bioavailable metal fractions in both the sediment and the water. AVS concentrations were generally better correlated with metal accumulation in the epibenthic invertebrates, rather than with the benthic taxa. Our results indicated that the relation between AVS and metal accumulation in aquatic invertebrates is highly dependent on feeding behavior and ecology.

Is there really a diagnostically useful relationship between the carbon–oxygen stretching frequencies in metal carboxylate complexes and their coordination mode?

An investigation into the relationship between the asymmetric and symmetric stretching modes of ancillary carboxylate ligands and their mode of binding in a family of manganese(III) complexes of tetradentate N(2)O(2) Schiff base ligands, which includes comparison of an (18)O isotopically labelled derivative, has been undertaken. The results suggest that caution should be employed in using this technique to assign the binding mode of the carboxylate ligands in these complexes despite its very extensive use in the literature.

10.1007/s11476-008-2002-x

The distribution of radioactive Cs and heavy metals (V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Hg, and Pb) in the lichen-substrate system and in lichen tissues were examined using the example of Cladonia genera. The upper podetia-lower podetia-dead podetia-base-substrate system was sampled at 32 sites in Novosibirsk oblast and Altai administrative territory, 16 of which were selected for detailed studying of the trace element distribution in the upper and lower podetia using cold press and the modified Dexter technique. One in vivo and two in vitro experiments simulated the influence of metal-rich atmospheric fallouts on the lichen carpet. The lichen carpet was irrigated by solution of metal nitrates (Co, Cu, Zn, Cd, Hg, and Pb) in the former case and loaded in these solution during the latter experiment. The experiment performed in the laboratory conditions (in vitro) was aimed at studying the dynamics of metal accumulation in lichen constituents and their subsequent extraction with distilled water to monitor metal sorption on the podetium cell walls. The metal contents and the activity of radioactive Cs in the lichen samples, including lichen cell sap, as well as in the base and substrate, were determined by atomic-absorption and gamma spectroscopic methods. In terms of accumulation, the elements are subdivided into two groups. The lowest contents of Group-1 elements (137 Cs, Zn, Cd, Hg, and Pb) were found in the substrate, and the highest contents, detected at the base and dead podetium, are presumably of technogenic origin. The Group-2 elements (Cr, Mn, Co, Ni, and Cu) enrich the substrate. It was established that the elements are mainly accumulated in lichens in cell walls and the membrane. The lichen sap and water-soluble compounds of protoplasma contain less than 0.1% of the total element content in the tissue. Most Zn, Cd, Co, and Pb ions (about 80% of the total absorbed amount) migrated from experimental solution into lichen cells during the first 12 h.

Investigation of heavy metal partitioning influenced by flue gas moisture and chlorine content during waste incineration

The impact of moisture on the partitioning of the heavy metals including Pb, Zn, Cu and Cd in municipal solid waste (MSW) was studied in a laboratory tubular furnace. A thermodynamic investigation using CHEMKIN software was performed to compare the experimental results. Simulated waste, representative of typical MSW with and without chlorine compounds, was burned at the background temperature of 700 and 950°C, respectively. In the absence of chlorine, the moisture content has no evident effect on the volatility of Pb, Zn and Cu at either 700 or 950°C, however, as flue gas moisture increasing the Cd distribution in the bottom ash increased at 700°C and reduced at 950°C, respectively. In the presence of chlorine, the flue gas moisture reduced the volatility of Pb, Zn and Cu due to the transformation of the more volatile metal chlorides into less volatile metal oxides, and the reduction became significant as chlorine content increase. For Cd, the chlorine promotes its volatility through the formation of more volatile CdCl 2. As a result, the increased moisture content increases the Pb, Zn, Cu and Cd concentrations in the bottom ash, which limits the utilization of the bottom ash as a construction material. Therefore, in order to accumulate heavy metals into the fly ash, MSW should be dried before incineration.

Fabrication of high-electron-mobility ZnO epilayers by chemical vapor deposition using catalytically produced excited water

Hot H 2O jet evolved by the exothermic reaction of H 2 with O 2 on a Pt-dispersed ZrO 2 catalyst was employed for gas-phase hydrolysis of dimethyl zinc to fabricate thin ZnO films. The X-ray diffraction pattern and photoluminescence spectra showed that the ZnO epilayers directly grown on a-sapphire substrate at 873 K had a defect free crystal structure close to a single crystal. The as-grown ZnO epilayers exhibited average transparency higher than 90% in the visible and infrared regions (400–2000 nm). The epilayers had high electron mobilities of 140–170 cm 2 V −1 s −1 and low residual electron concentrations of 1.7–6×10 17 cm −3 that are significantly better than those for ZnO films so far reported by conventional chemical vapor deposition and any other energy-consuming physical method such as pulse laser deposition and molecular beam epitaxy. The present method uses the chemical energy from only H 2 and O 2, which is energy-saving and ecologically friendly, while it is superior in high-quality ZnO fabrication. It is also pointed out that the method raises unlimited possibilities for a wide range of the fabrication of high-quality metal oxide epilayers, because of the availability for various volatile alkyl metals.

Global dispersal of Pb by large-volume silicic eruptions in the Parana-Etendeka large igneous province

Volcanism from large igneous provinces is often inferred to have had a significant global environmental impact, but demonstrating synchronicity between the volcanism and sedimentary records of environmental change is not straightforward. Several studies use sediment Pb isotopes to fingerprint the timing of input of volcanic Pb from a particular large igneous province. Published data on Ocean Drilling Program Site 1149B sediments in the Pacific Ocean, associated with the Valanginian δ 13 C excursion that has been linked to the Parana-Etendeka volcanism in central South America and Namibia, require input of radiogenic Pb. The Pb isotope analyses of Parana-Etendeka lavas show that this radiogenic Pb is uniquely associated with the large-volume silicic eruptions rather than the effusive basaltic lavas. This strengthens the case for a temporal link between the Parana-Etendeka volcanism and the Valanginian δ 13 C excursion. Although basaltic magmatism dominates the province (>95%), there is no evidence for Pb associated with volatile metal degassing from such eruptions in the Site 1149B sediments on the other side of the globe, suggesting that eruption columns produced by the basaltic eruptions did not reach the stratosphere. Instead, the widespread global dispersal of Pb is apparently linked to the ability of large-volume (>1000 km 3 ) silicic eruptions to loft aerosols into the upper stratosphere.

Unusual Bonding in Trisilaallene and Related Heavy Allenes

The synthesis, X-ray and spectroscopic analysis, and unusual bonding and structure among heavy group-14 element congeners of allene (heavy allenes) [R(2)M=M'=MR(2); M = M' = Si (1a), M = Si, M' = Ge (1b), M = Ge, M' = Si (1c), and M = M' = Ge (1d)] are comparatively discussed. Using DFT calculations and PMO theory, the origin of the bent and fluxional skeleton of the heavy allenes is ascribed to the Jahn-Teller distortion associated with the effective pi-sigma* mixing (pi-sigma* distortion). This type of distortion is suggested to be a key concept for qualitative description of the unusual bonding of unsaturated compounds of heavy main-group elements.

Behaviour of heavy metals in the partial oxidation of heavy fuel oil

The behaviour of heavy metals in the partial oxidation of heavy fuel oils under a pressure of up to 100 bar (10 MPa) has been investigated. The tests were carried out in a 5 MW HP POX (High Pressure Partial Oxidation) test plant, that is operated by the IEC (Department of Energy Process Engineering and Chemical Engineering, TU Bergakademie Freiberg) in cooperation with Lurgi GmbH. In several test campaigns preheated oil with a viscosity of up to 300 cSt (= 300 mm 2/s) at the burner inlet has been gasified. The heavy metals nickel Ni, iron Fe and vanadium V occur in heavy residual oils in considerable concentration and may seriously impact the gasification itself and the synthesis gas conditioning and usage. While iron is largely recovered in the gasification residue, the recovery rates of nickel and vanadium depend on the process conditions. Volatile nickel compounds were detected in the raw synthesis gas. It was found that an incomplete carbon conversion enables the capture of nickel Ni and vanadium V in the solid residue phase and can thus mitigate the problem of volatile metal compounds in the raw synthesis gas.

Characterization of combustion‐derived individual fine particulates by computer‐controlled scanning electron microscopy

AbstractParticulate matter (PM) emission from the combustion of solid fuels potentially poses a severe threat to the environment. In this article, a novel approach was developed to examine the properties of individual particles in PM. With this method, PM emitted from combustion was first size‐segregated. Subsequently, each size was characterized by computer‐controlled scanning electron microscopy (CCSEM) for both bulk property and single particle analysis. Combustion of bituminous coal, dried sewage sludge (DSS) and their mixture were conducted at 1200°C in a laboratory‐scale drop tube furnace. Three individual sizes smaller than 2.5 μm were investigated. The results indicate that a prior size‐segregation can greatly minimize the particle size contrast and phase contrast on the backscattered images during CCSEM analysis. Consequently, high accuracy can be achieved for quantifying the sub‐micron particles and their inherent volatile metals. Regarding the PM properties as attained, concentrations of volatile metals including Na, K, and Zn have a negative relationship with particle size; they are enriched in the smallest particles around 0.11 μm as studied here. Strong interactions can occur during the cofiring of coal and DSS, leading to the distinct properties of PM emitted from cofiring. The method developed here and results attained from it are helpful for management of the risks relating to PM emission during coal‐fired boilers. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Effect of carbon particles on heavy metal emissions under ash-melting conditions

In Japan, incineration ash is subjected to a melting process to reduce waste volume and to stabilize hazardous heavy metals. In previous articles, we reported that large quantities of volatile metals are emitted under ash-melting conditions at temperatures higher than 1200°C and that such emissions are considerably increased under reducing conditions. However, the emission behavior in the presence of large amounts of char particles was unclear, and we suspected that emissions under these conditions might differ from emissions under the previous conditions. Therefore, we investigated heavy metal emissions and the melting characteristics of ash in the presence of carbon particles. In this experiment, a small crucible with ash and carbon was rapidly heated using a high-frequency induction-heating furnace to simulate the melting ash gasification with carbon. As a result, it was found that additive carbon can promote emissions of heavy metals such as zinc and lead and control the melt of the ash.

Inductively coupled plasma reactive ion etching of bulk ZnO single crystal and molecular beam epitaxy grown ZnO films

Dry etching processes for bulk-single crystal zinc oxide (ZnO) and molecular beam epitaxy (MBE) grown ZnO have been investigated using inductively coupled plasma (ICP) of CH4 and SiCl4 based plasma chemistry. The CH4-based chemistry showed a higher etch rate than the SiCl4 based chemistry, presumably due to the formation of highly volatile metal organic zinc compound. The influence of base pressure, radio frequency table power, and ICP power on etch rate was studied. Auger electron spectroscopy has been employed to examine the surface stoichiometry of etched ZnO using both plasma chemistries. Furthermore, with optimized process parameters, the effect of plasma etching on the optical properties of MBE grown ZnO film is studied. An enhancement of the band edge luminescence along with almost complete suppression of defect level luminescence in hydrogen-containing plasma treated ZnO film has been observed.

Coinitiators based on group 14 elements in photoinitiating systems for radical and cationic polymerization

Coinitiators based on group 14 elements in photoinitiating systems for radical and cationic polymerization

Partitioning characteristics and particle size distributions of heavy metals in the O 2/RFG waste incineration system

This study applies the oxygen/recycled flue gas (O 2/RFG) combustion technology for waste incineration and investigates the effects of different RFG rates on the concentrations of gas pollutants as well as the partitioning characteristics and particle size distributions of five heavy metals (Cr, Cu, Pb, Zn, and Cd). Experimental results show that the combustion efficiency can be improved and the concentration of CO 2 is increased by appropriately controlling the RFG rate in the O 2/RFG incineration system. The partitioning characteristics and size distributions of heavy metals in O 2/RFG combustion system are different from those in general air combustion system. Under O 2/RFG combustion system, the partitioning percentages of heavy metals in sand bed, bottom ash, and collected ash are increased. The particle size distributions of heavy metals display the triple-peak curves. As the RFG rate rises, the concentrations of volatile heavy metals are increased in small-size (<1 μm) fly ash, decreased in medium-size (1–10 μm) fly ash and increased in large-size (>10 μm) fly ash. These phenomena will benefit to increase the overall control efficiency of heavy metals in the incineration system.