Heavy Anions Research Articles

Electronic polarons and bipolarons in iron-based superconductors: The role of anions

Superconductivity is a fascinating example of how "more is different". It is due to electrons binding into bosonic Cooper pairs, which exhibit coherent behavior across a macroscopic sample. Finding the mechanism responsible for this binding is one of the more difficult tasks of condensed matter physics. For conventional superconductors the solution was given by the BCS theory as being due to exchange of phonons. For the cuprate high-Tc superconductors a widely-accepted explanation is still missing despite intense effort. The recently discovered Fe-based high-Tc superconductors pose now a new challenge. We present here a quantum mechanical theory for pnictides describing the influence of the large electronic polarizability of the heavy anions. We demonstrate that its inclusion results in electronic polarons as the low-energy quasi-particles and also unveils a pairing mechanism for these electronic polarons.

Heavy Metals and Anion Levels in Some Samples of Vegetable Grown Within the Vicinity of Challawa Industrial Area, Kano State, Nigeria

Problem section: Effluents from the surrounding industries such as tannery and textile are used by vegetable farmers for the irrigation of their crops. These effluents may contain some toxic metals which bioaccumulate along the food chain. Moreover the uptake of such toxic metals by crops is governed by their availability and concentration in the soil. Therefore such crops may accumulate heavy metals in excessive amount in their various parts. This may ultimately, adversely affect humans and other species that depend on such crops for food, hence the need to evaluate the pollutant levels in vegetables samples in these areas. Approach: Six vegetable samples of various organs were freshly harvested from ten farms within the vicinity of Challawa industrial areas. The concentration of heavy metals which include, Cu, Zn, Co, Mn, Mg, Fe, Cr, Cd As, Ni and Pb, were determined using Perkin-Elmer analyst 300 Atomic Absorption Spectroscopy (AAS). Levels of some anions (nitrate, nitrite, sulphate and phosphate were determined using Hach direct reading 2000 Spectrophotometer. Results: The results obtained from this analysis revealed that Cr and Fe shows the highest concentrations, while As shows the lowest levels in the whole vegetable organs studied. The concentrations of the anions ranged between 40.00-1300.00 µg g−1 nitrite, 65-1500 µg g−1 nitrate, 122.00-765.00µg g−1 and 12.00-60.00 µg g−1. The leaves contained much higher concentrations of heavy metals and anions than roots and stems. Conclusions: The concentrations of the above parameters were higher than the FAO, WHO/EU and FAO/WHO allowed limit. The high values might be attributed to the used of untreated effluents from textile and tanneries industries by farmers for the irrigation of these vegetables. Thus, the high values of these trace metals and anions in the vegetable samples could put the consumers of these vegetables at health risk. Further works should be carried out in the soil samples were the vegetables are grown.

Heavy Metals and Anion Levels in Some Samples of Vegetable Grown Within the Vicinity of Challawa Industrial Area, Kano State, Nigeria

Problem section: Effluents from the surrounding industries such as tannery and textile are used by vegetable farmers for the irrigation of their crops. These effluents may contain some toxic metals which bioaccumulate along the food chain. Moreover the uptake of such toxic metals by crops is governed by their availability and concentration in the soil. Therefore such crops may accumulate heavy metals in excessive amount in their various parts. This may ultimately, adversely affect humans and other species that depend on such crops for food, hence the need to evaluate the pollutant levels in vegetables samples in these areas. Approach: Six vegetable samples of various organs were freshly harvested from ten farms within the vicinity of Challawa industrial areas. The concentration of heavy metals which include, Cu, Zn, Co, Mn, Mg, Fe, Cr, Cd As, Ni and Pb, were determined using Perkin-Elmer analyst 300 Atomic Absorption Spectroscopy (AAS). Levels of some anions (nitrate, nitrite, sulphate and phosphate were determined using Hach direct reading 2000 Spectrophotometer. Results: The results obtained from this analysis revealed that Cr and Fe shows the highest concentrations, while As shows the lowest levels in the whole vegetable organs studied. The concentrations of the anions ranged between 40.00-1300.00 µg g−1 nitrite, 65-1500 µg g−1 nitrate, 122.00-765.00µg g−1 and 12.00-60.00 µg g−1. The leaves contained much higher concentrations of heavy metals and anions than roots and stems. Conclusions: The concentrations of the above parameters were higher than the FAO, WHO/EU and FAO/WHO allowed limit. The high values might be attributed to the used of untreated effluents from textile and tanneries industries by farmers for the irrigation of these vegetables. Thus, the high values of these trace metals and anions in the vegetable samples could put the consumers of these vegetables at health risk. Further works should be carried out in the soil samples were the vegetables are grown.

Evaluation of the quality of drinking water in regions of Greece

The present work is a comprehensive evaluation of drinking water quality from various regions of Greece. The physicochemical parameters investigated were conductivity, total dissolved solids and pH, as well as related to the treatment of drinking water such as chloride, potassium, calcium, magnesium and sodium, heavy metals (including cadmium, copper, lead, chromium and nickel), anions and cations such as fluoride, bromide, nitrates, nitrites, ammonium, sulphates and phosphates, as well as dissolved organic carbon. The parametric values set in accordance with the Directive 98/83/EC were exceeded in the cases of lead (in 2.7% of the samples analysed), chloride (2.4%) and nickel (2.1%). Ammonium, sodium, fluoride, sulphates, nitrates and conductivity were lower than the upper limits by 2% of the total number of samples analysed. The majority of problems were identified in the Cyclades islands, particularly those characterized by scarcity of water resources. The main problems related to drinking water quality are associated with the conditions of the water supply networks, the pollution of ‘parent’ water and in particular the contamination of groundwater with pollutants of both anthropogenic and natural origin, as well as the intrusion of seawater in aquifers.

Near-Infrared Optical Characteristics of Chalcogenide-Bound Nd3+ Molecules and Clusters

The optical properties of the nanoscale neodymium ceramic cluster (THF)8Nd8O2Se2(SePh)16 (Nd8) and molecular (DME)2Nd(SC6F5)3 (Nd1) were studied by optical absorption, photoluminescence, and time-resolved spectroscopy. Both complexes exhibited emission characteristic of solid-state materials with bands centered at 927, 1078, 1360, and 1843 nm for Nd8 and 897, 1071, 1347, and 1824 nm for Nd1. The observed red-shift in the absorption and emission bands of Nd8 is attributed to the increased covalency and nephelauxetic effect. Using the calculated radiative decay time, the quantum efficiency of the 4 F3/2 f 4 I11/2 transition is calculated to be 16% in Nd8 and 9% in Nd1 with corresponding stimulated emission cross sections of 3.04 10 -20 cm 2 in Nd8 and 1.61 10 -20 cm 2 in Nd1 that are comparable to those of solid-state inorganic systems. This efficiency is the highest reported value for “molecular” neodymium compounds. This finding, along with the novel 1.8 Im emission, is attributed to the absence of direct Nd 3+ coordination with fluorescence quenching vibrational groups such as hydrocarbon or hydroxide groups. The direct coordination of S, Se, and F accounts for the improved fluorescence spectral properties, because these heavy anions facilitate a low phonon energy host environment for neodymium. Monte Carlo simulation permitted analysis of energy transfer processes to show the primary source of fluorescence quenching. Cross relaxation is responsible for the quenching of the 4 F3/2 f 4 I15/2 emission whereas excitation migration quenches the 4 F3/2 f 4 I9/2 emission. These processes are mediated by a dipole-dipole interaction for Nd8 and a quadrupole-quadrupole interaction for Nd1.

A thermodynamic approach to the hydration of sulphate-resisting Portland cement

A thermodynamic approach is used to model changes in the hydrate assemblage and the composition of the pore solution during the hydration of calcite-free and calcite-containing sulphate-resisting Portland cement CEM I 52.5 N HTS. Modelling is based on thermodynamic data for the hydration products and calculated hydration rates for the individual clinker phases, which are used as time-dependent input parameters. Model predictions compare well with the composition of the hydrate assemblage as observed by TGA and semi-quantitative XRD and with the experimentally determined compositions of the pore solutions. The calculations show that in the presence of small amounts of calcite typically associated with Portland cement, C–S–H, portlandite, ettringite and calcium monocarbonate are the main hydration products. In the absence of calcite in the cement, however, siliceous hydrogarnet instead of calcium monocarbonate is observed to precipitate. The use of a higher water-to-cement ratio for the preparation of a calcite-containing cement paste has a minor effect on the composition of the hydrate assemblage, while it significantly changes the composition of the pore solution. In particular, lower pH value and higher Ca concentrations appear that could potentially influence the solubility and uptake of heavy metals and anions by cementitious materials.

Laser photodetachment electron spectroscopy studies of heavy atomic anions

Laser photodetachment electron spectroscopy (LPES) experiments have been performed at the Negative Ion Research Facility at the University of Nevada, Reno, using a crossed ion-laser beams apparatus to investigate the structure and dynamics of heavy atomic anions. A small ion accelerator is used to produce monoenergetic beams of negatively-charged atomic ions. Ejected electrons (photoelectrons), produced by the collision of the ions with linearly-polarized photons, are collected and their kinetic energy is measured with a hemispherical-sector electrostatic analyzer. The resultant photoelectron spectrum is used to determine the electron affinity (EA) of several of the lanthanides, while limits on the electron affinities for others are inferred. In addition, the angular asymmetry parameters and angular distribution patterns of photoelectrons created by laser photodetachment of several heavy atomic anions, as well as the spectral dependence of those angular distributions, have been determined. Electron affinities and photoelectron angular distribution asymmetry parameters can offer crucial information regarding the electronic structures of these heavy atomic anions, and represent key information for models of these complex systems.

Mass-balance estimation of heavy metals and selected anions at a landfill receiving MSWI bottom ash and mixed construction wastes

An estimation of the heavy metal and anion mass-balance was made for municipal solid waste incinerator bottom ash deposited at a construction and industrial waste landfill. The mass-balance was found by comparing the content of metals and anions in the landfill leachate to the metal and anion content in the deposited bottom ash. The discharge of heavy metals ranged from 0.001% for Pb to 0.55% for Cr, which is approximately at the same level as in regular municipal solid waste (MSW) landfills. Landfilled organic material and silicates from construction waste might have contributed to the retention of metals. Chloride, and to a lesser extent sulphate, appeared to be readily released from the landfill. It was estimated that a mass corresponding to 80% of the Cl − and 18% of the SO 4 2− in the bottom ash was discharged annually. Low retention, especially of chloride, may lead to a rapid decline in the discharge of this ion in the future when the landfilling of bottom ash is discontinued.

The uranium absorption of Brassica juncea : The effect on the heavy metal absorption capacity under the coexistence of another heavy metal and anion

The uranium absorption of Brassica juncea : The effect on the heavy metal absorption capacity under the coexistence of another heavy metal and anion

Tetracopper(I) phosphonitocavitand: synthesis, halide anion inclusion and optical nonlinearity

Treatment of tetraphosphonitoresorcinarene [(CH 3) 2CHCH 2CHC 6H 2O 2PPh] 4 ( 1) with an excess [CuCl] powder in the presence of pyridine (py) yielded a tetracopper(I) phosphonitocavitand [pyH][ 1·Cu 4( μ-Cl) 4( μ 4-Cl)] ( 2). The Included μ 4-Cl in 2 was easily substituted by heavy halide anion to give [pyH][ 1·Cu 4( μ-Cl) 4( μ 4-X)] (X=Br, 3; I, 4). The complexes 2, 3, and 4 have been characterized by X-ray structure determinations. The similar structure contains four coplanar cupper atoms bridged by four μ-Cl and one central trapped μ 4-X atoms in the inside of the closing bowl-shaped cavitand. The third-order nonlinear optical properties of 2 as a typical metal-cavitand complex were investigated in this paper.

Recent advances in chalcogenide glasses

Compared to oxide-based glasses, vitreous materials involving chalcogens form a rather new family of glasses which have received attention, mainly because of their transmission in the mid-infrared. Indeed as low phonon compounds, these heavy-anion glasses allow the fabrication of molded optics for infrared cameras as well as infrared fibers operating in a large spectral range. These waveguides, when correctly tapered, allows the development of a new generation of sensitive evanescent-wave optical sensors which have been used for biomedical applications. Here we will focus on the spectral analysis of biomolecules present in human lung cells by measuring their infrared signatures. Because they contain heavy polarizable anions as well as lone-pair electrons, these glasses exhibit very large non-linear properties compared to silica and are candidates for fast optical switching and signal regeneration in telecom. Due to the technological interest in chalcogenide glasses, more information is needed on their structural organization and 77Se NMR spectroscopy appears to be a useful tool for checking the local environment of the Se atoms.

1D and 2D network of ReO 4− bonded azoimidazoles

1-Alkyl-2-(arylazo)imidazoles are π-acidic, bidentate chelating molecules. In acid medium imidazole- N centers are protonated and can extract heavy anions. One such example is the binding with ReO 4 − in acidic medium. 1-Alkyl-2-(arylazo)imidazolium-perrehenate shows hydrogen bonded 1D network. Inclusion of H 2O into the molecular frame of 1D increases the dimensionality to 2D network.

Modelling heavy metal and anion effects on physical and mechanical properties of Portland cement by means of factorial experiments

The aim of the present work was to investigate the influence of a number of heavy metals (Cd, Cr(III), Cu, Pb and Zn), as well as anions (CI‐, SO2‐ 4 ) on the physical and mechanical properties of cementitious pastes, including setting time, bulk density and unconfined compressive strength. The above mentioned species and their concentrations were selected in order to simulate addition of 20% municipal solid waste incinerator ash to Portland cement. Spiking experiments were performed according to a 27–3 IV fractional factorial design by addition of pure compounds containing the contaminants of interest to Portland cement. The results from the experimental campaign, which were interpreted using statistical analysis techniques, showed that the investigated contaminants variously affected the hydration process of cement. The ranking for final setting time values was Zn(NO3)2 > K2SO4 > NaCl > mean response > Cr(NO3)3 > NaCl+Cr(NO3)3, Cd(NO3)2+Pb(NO3)2 or CuCl2+Zn(NO3)2 interaction, whereas the ranking for UCS values during hardening was Zn(NO3)2 > CuCl2 > NaCl+K2So4, CuCl2+Pb(NO3)2 or Cd(NO3)2+Zn(NO3)2 interaction > mean response. Conversely, none of the selected contaminants was found to significantly influence ultimate strength.

Soil and soil solution chemistry of a New Zealand pasture soil amended with heavy metal-containing sewage sludge

The disposal of wastewater treatment sewage sludge onto agricultural land in New Zealand has led to the development of guidelines for the upper limit concentrations for total heavy metals in the underlying soil. However, those soil biological and biochemical processes now known to be most sensitive to environmental change are being used internationally to set new soil limits. The soil solution chemistry of a pasture soil amended with heavy metals has been used to assess the bioavailability of several important heavy metals. Field trial plots were treated with both spiked (Cu, Ni, or Zn) and unspiked sewage sludge to raise total soil metal concentrations, both above and below the current New Zealand guideline values. Soils were sampled pre-amendment in 1997 and post-amendment in 1998, 1999, and 2000. Soil solutions were extracted by centrifugation and analysed for pH, for concentrations of heavy metals, major cations and anions, and dissolved organic carbon. Heavy metal speciation was calculated with the GEOCHEM-PC model.Soil solution concentrations of Cu, Ni, and Zn increased with increasing levels of metal in the spiked sludge, reflecting increases in total soil metal concentrations. Cu concentrations changed little with time, but those of Ni and Zn tended to decrease. Cu was much more adsorbed by the soil than was Ni or Zn. The free metal ions, Cu2+, Ni2+, and Zn2+ (representing the most 'bioavailable' fraction), were the dominant metal species in the soil solutions. Variations in free metal ion percentages with metal-spiking level depended on the balance between organic and sulfate complexation for Cu, but on sulfate complexation alone for Ni and Zn. Cu and Ni free metal-ion activities in soil solution were relatively low even at the highest metal loadings in the soil, but may be high enough to cause toxicity problems. Zn activities were very much higher, and at the regulatory limit for zinc likely to affect sensitive biological and biochemical properties of the soil.

New chalcogenide glass chemical sensors for S2- and dissolved H2S monitoring

A non-optimised treatment of wastewaters containing organic and biological substances is very often accompanied by an accidental emanation of hydrogen sulphide H2S and therefore leads (i) to an undesirable odour in the vicinity of water treatment plants, and (ii) to a potential hazard for the neighbouring population. Fast, sensitive and reliable monitoring devices hence of significant importance. Chalogenide and chalcohalide glass are new promising membrane material for detection of heavy metal ions and toxic anions and particularly well adapted for continuous in situ monitoring and industrial process control. In the present paper, we will discuss analytical characteristics of new chalcogenide glass chemical sensors for detection of S2- and dissolved H2S, which slow reliable process control to be carried out at natural pH of wastewaters.

Near-threshold photodetachment of heavy alkali-metal anions

We calculate near-threshold photodetachment cross sections for Rb{sup -}, Cs{sup -}, and Fr{sup -} using the Pauli equation method with a model potential describing the effective electron-atom interaction. Parameters of the model potential are fitted to reproduce ab initio scattering phase shifts obtained from Dirac R-matrix calculations. Special care is taken to formulate the boundary conditions near the atomic nucleus for solving the Pauli equation, based on the analytic solution of the Dirac equation for a Coulomb potential. We find a {sup 3}P{sub 1}{sup o} resonance contribution to the photodetachment cross section of Rb{sup -}, Cs{sup -}, and Fr{sup -} ions. Our calculated total photodetachment cross sections for Cs agree with experiments after tuning the resonance position by 2.4 meV. For Rb{sup -} and Fr{sup -} the resonance contribution is much smaller than for Cs. We therefore also provide angle-differential cross sections and asymmetry parameters which are much more sensitive to the resonant contribution than total cross sections.

Fractional factorial design to investigate the influence of heavy metals and anions on acid neutralization behavior of cement-based products.

A major concern of cement-based solidification/stabilization of hazardous wastes is the interaction of waste contaminants on cement properties. Literature contains many examples of studies on the interference of individual contaminants on cement properties. Conversely, little information is available on how the interactions between contaminants affectthe properties of cement/waste systems. This paper provides a discussion on the interference mechanisms exerted by seven contaminants, five heavy metals and two anions, on cement hydration. The seven contaminants were selected on the basis of the typical composition of municipal solid waste incineration (MSWI) fly ash. Spiking experiments using pure compounds were performed according to a 2IV(7-3) fractional factorial design to simulate addition of MSWI fly ash to ordinary Portland cement. The acid neutralization behavior of the laboratory cement-contaminant mixtures was studied to detect the presence of solid phases responsible for the buffering capacity of the solid matrix. The results from the experimental work showed that Zn, Cl-, and SO4(2-) were the major factors influencing, occasionally in combination with other contaminants, strength and acid neutralization capacity of the cementitious products. The release of Cd, Cr, Cu, and Pb in the eluates as a function of pH also suggested possible chemical immobilization mechanisms of such metals within the hardened matrix.

Properties of Portland cement — stabilised MSWI fly ashes

In the present paper, the properties of Portland cement mixtures containing fly ashes (FA) collected at four different Italian municipal solid waste incineration (MSWI) plants were investigated. In particular, physical/mechanical characteristics (setting time, unconfined compressive strength (UCS) and shrinkage/expansion), as well as the acid neutralisation behaviour of the solidified products were considered. The FA composition, revealing enrichment in heavy metals, chlorides and sulphates, significantly altered the hydration behaviour of Portland cement. Consequently, for some of the investigated FA the maximum allowable content for the mixtures to achieve appreciable mechanical strength was 20 wt.%. Even at low FA dosages setting of cement was strongly delayed. In order to improve the properties of FA/cement mixtures, the use of additives was tested. Moreover, the acid neutralisation capacity (ANC) of the solidified products was evaluated in order to assess the ability of the matrix to resist acidification, and also to provide information on hydration progression, as well as on heavy metal release under different pH conditions. Comparison of the results from the present work with previous studies carried out on spiked mixtures lead to the conclusion that the mechanical properties of the stabilised FA could not be predicted based on the effect exerted by heavy metals and anions only, even when the dilution effect exerted on cement was taken into account. It was likely that a major role was also played by alkalis, which were present in the FA at much higher concentrations than in cement.

NaZr2N2SCl: Ein flußmittelstabilisiertes Derivat von Zirconium(IV)-Nitridsulfid (Zr2N2S)

NaZr2N2SCl: A Flux-Stabilized Derivative of Zirconium(IV) Nitride Sulfide (Zr2N2S) The oxidation of zirconium metal with elemental sulfur and sodium azide (NaN3) should give access to zirconium(IV) nitride sulfide, Zr2N2S, which could crystallize isotypically with the trigonal rare-earth(III) oxide sulfides M2O2S (M = Y, La–Lu). Appropriate molar admixtures of these reactants together with NaCl added as flux were heated for seven days at 850 °C in torch-sealed evacuated silica tubes. As main product, however, pale yellow platelets with the composition NaZr2N2SCl (trigonal, R 3 m; a = 363.56(3), c = 2951.2(4) pm; Z = 3) emerged as single crystals. This pseudo-quaternary compound crystallizes isotypically with e. g. LixEr2HyCl2 (x ≤ 1, y ≤ 2) in a (doubly) stuffed ZrBr-type structure and contains at least structural domains of the hypothetical Ce2O2S-analogous Zr2N2S. Zr4+ resides in monocapped trigonal anti-prismatic sevenfold coordination of the anions (d(Zr–N) = 218 (3 ×) and 220 pm (1 ×), d(Zr–S/Cl) = 266 pm, 3 ×). Closest packed double-layers of Zr4+ with all tetrahedral interstices occupied with N3– are sandwiched by layers of isoelectronic S2– and Cl– anions. These anionic six-layer slabs (S/Cl–Zr–N–N–Zr–S/Cl) pile up parallel (001) in a cubic closest packed fashion. Charge balance and structural consistence occurs between these layers by intercalation of Na+ within octahedral voids (d(Na–S/Cl) = 282 pm, 6 ×) of double-layers of the indistinguishable heavy anions (S2– and Cl–).

Role of Transient Cross-Links for Transport Properties in Silver−Polymer Electrolytes

The interaction of the silver cation of AgClO4 with carbonyl oxygen in poly(2-ethyl-2-oxazoline) (POZ) was found to be similar to that of AgBF4 by infrared and Raman spectroscopic results. The two silver salts are similar in molecular size and lattice energy. However, the two silver−polymer electrolytes showed remarkably different gas transport properties. The POZ:AgClO4 membrane showed very low gas permeance compared with the POZ:AgBF4 at the 1:1 [CO]:[Ag] mole ratio. The difference in the transport properties has been attributed mostly to the changes in chain mobility upon both the formation of transient cross-links by silver cations and the dangling of the heavy anions on the main chain. The changes in chain mobility were characterized by the glass transition temperature and the intersegmental d spacing. The extent of the transient cross-links seems to be strongly associated with the coordination number of the silver cation; the silver cation in AgClO4 has a higher coordination number than that in AgBF4. The structure difference for the two systems was also confirmed by the difference in the bond length between the cation and anion calculated from ab initio methods, despite the very similar lattice energies for two salts. Thus, the gas transport properties were successfully used to monitor the role of the transient cross-link as well as of the neighboring counteranion on the structure and physical properties of polymer electrolytes.