Comparison of the fluoride,arsenate and nitrate anions water depollution potential of a calcined quintinite,a layered double hydroxide compound

The potential for removing anionic pollutants such as F⁻, HAsO₄²⁻, and NO₃⁻ from water by mixed oxides issued from the moderate thermal treatment of quintinite (Mg₄Al₂ LDH) has been studied. This compound shows good trapping properties for F⁻ and HAsO₄²⁻, and a low potential for NO₃⁻, due to the competition with OH⁻. The competition between these three anions and CO₃²⁻ has been envisaged and shows that CO₃²⁻ is able to easily replace F⁻ and NO₃⁻, making the mixed oxides issued from MgAl LDH an inappropriate trap for F⁻ and NO₃⁻. However, only small amounts of arsenic are released after the CO₃²⁻ introduction in water. Moreover, arsenates are able to replace carbonates even at lower concentrations. This means that HAsO₄²⁻ anions present a stronger affinity than CO₃²⁻ for the LDH structure. This makes mixed oxides issued from MgAl LDH very promising materials for the removal of arsenic in polluted waters.     

Sorption of U(VI) from aqueous solutions on layered double hydroxides of Mg,Al, and Nd

Sorption of U(VI) from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd, and also on layered double oxides (LDOs) of Mg and Al was studied. Experiments on sorption of UO₂²⁺ carbonate complexes from aqueous solution on LDO-Mg-Al showed that [UO₂(CO₃)₃]⁴⁻ ions are weakly captured by LDH-Mg-Al formed by contact of LDO-Mg-Al with water. With an increase in the uranium concentration in solution, K _d of U(VI) decreases. For 3.3 × 10⁻³ M [UO₂(CO₃)₃]⁴⁻ solutions, after 24-h contact of the solid and liquid phases, the distribution coefficients do not exceed 1.0 ml g⁻¹ at V/m = 50 ml g⁻¹. From aqueous nitrate solutions, U(VI) is sorbed on LDH-Mg-Al-NO₃ poorly: K _d of U(VI) does not exceed 1.0 ml g⁻¹ at 24-h contact of the solid and liquid phases and V/m = 50 ml g⁻¹. At the same time, U(VI) is efficiently sorbed from aqueous 10⁻³ M UO₂(NO₃)₂ solutions on LDH-Mg-Al and LDH-Mg-Nd with CO₃²⁻ and OH⁻ ions in the interlayer space. After 15-min contact of the solid and liquid phases, K _d of U(VI) exceeds 5 × 10³ ml g⁻¹. With an increase in the UO₂²⁺ concentration to 10⁻¹ M, K _d of U(VI) decreases considerably, becoming lower than 25 ml g⁻¹, but increases to ∼150 ml g⁻¹ with an increase in the contact time of the solid and liquid phases to 24 h. The effect of the Na⁺, Ca²⁺, Cl⁻, and SO₄²⁻ ions and of pH of the initial solution on the U(VI) sorption from aqueous UO₂(NO₃)₂ solutions on LDH-Mg-Al-CO₃ was examined.     

Heterogeneous chemiluminescent assay (generalizing paper)

The results of applying heterogeneous chemiluminescent analysis for determination of micro-components are generalized, and the possibility of using this method for determination of toxic anions in waters is demonstrated. Anions undergo conversion beforehand, which causes formation of new analytical forms, i.e., derivates being active in chemiluminescent reactions with luminol. If volatile products are generated as analytical forms, they undergo gas extraction from the matrix with detection using a chemiluminescent indicator in the carrier gas stream at the interface gas-liquid (aqueous solution of luminol). Thus, the techniques for determination of Cl⁻, Br⁻, I⁻, ClO₃⁻, BrO₃⁻, IO₃⁻, NO₃⁻, NO₂⁻, S², CrO₄²⁻, AsO₂⁻, Cl₂ and chloramines are developed. The detection limit (DL) is 0.5–5.0 μg/l, and the analysis time is 2–9 min. In another case, products of conversion are sorbed from the solution on a solid sorbent, and detection is carried out by a luminol solution on the solid surface. A series of heteropoly acids (phosphorus, arsenic, silicon, and germanium) and their ion associates with cation surfactants, along with other large anions, are determined in the form of sorbable ion associates. The DL is 0.02–0.7 μg/l, and the analysis time is 30 min. The advantages of application of heterogeneous chemiluminescent analysis over analysis in homogeneous media are indicated, and the prospects for development of the theoretical bases and field of application are demonstrated.     

Use of Purbe diagrams in prediction of optimum conditions of separation and determination of halogens in natural objects using ionometry

Directional oxidation in the solution of X ⁻ ion being determined down to elementary halogen X ₂ and separation of it using gas extraction is promising for the separation of halogenide ions (Cl⁻, Br⁻, I⁻). The coinciding Purbe diagrams for redox systems of halogens X ⁻/X ₂ and most widely used oxidizers, namely, MnO₄⁻/MnO₂, MnO₄⁻/Mn²⁺, PbO₂/Pb²⁺, Cr₂O₇⁻/Cr³⁺, HNO₂/NO, were fragmentarily plotted. The predicted working pH intervals of the medium for directional quantitative oxidation of the given halogenide ion by a particular oxidizer were ascertained graphically using the diagrams. The possible schemes for the independent ionometric determination of Cl⁻, Br⁻ and I⁻ ions were proposed.     

Influence of synthesis conditions on particle morphology of nanosized Cu/ZnO powder by polyol method

Cu/ZnO in nanosizes have been synthesized using ethylene glycol at various conditions. The effects of reaction temperature, extent of reduction, various precursors such as CuX₂·nH₂O, ZnX₂·nH₂O (X = Cl⁻, NO₃⁻, CH₃CO₂⁻), the addition of water and the removal of volatile compounds including water were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Cu/ZnO powders with an average diameter of as low as 50 nm was obtained with a very low polydispersity in the absence of a protective polymer. Ethylene glycol oxidation products were also identified by Fourier transform infrared (FTIR) spectroscopy. The morphology of Cu/ZnO powders and the yield of powders are found to be strongly dependent on the synthesis conditions.     

Effects of pH and concentration on ability of Cl<Superscript>−</Superscript> and NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> to intercalate into a hydrotalcite-like compound during its synthesis

In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl⁻, which has a higher charge density than NO₃⁻, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl⁻ into the HT interlayer; and (ii) for HTs with lower Mg: Al molar ratios, OH⁻, which has a higher charge density than Cl⁻ and NO₃⁻, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl⁻ and NO₃⁻. Furthermore, we showed that high concentrations of Cl⁻ and NO₃⁻ in solution regulated their intercalation into the HT interlayer. The high activity of Cl⁻ and NO₃⁻ in solution would facilitate the anions’ reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs.     

Oxidation of carbohydrazide with nitric acid

The kinetics of carbohydrazide oxidation with nitric acid in aqueous solutions was studied. In the range [HNO₃] = 3–7 M, the reaction rate is described by the equation −d[(NH₂NH)₂CO]/dt = k[(NH₂NH)₂CO][HNO₃] ⁿ , where n = 3.6 and 2.9 at 70 and 90°C, respectively. The constant k = (6.65 ± 0.23) × 10⁻⁴ l^2.9 mol^−2.9 h⁻¹ at 90°C, and the activation energy of the reaction in 7 M HNO₃ is 124 kJ mol⁻¹. The Fe(III) and especially Tc(VII) ions considerably accelerate the reaction, whereas the uranyl ions accelerate it insignificantly. The reaction mechanism in which the reactive species oxidizing carbohydrazide is nitronium ion NO₂⁺ was suggested.     

Siloxane removal from biogas by biofiltration: biodegradation studies

Recently a lot of attention has been focused on volatile methyl siloxanes (VMSs) in biogas because of the costly problems deriving from the formation of silicate-based deposits in biogas-fuelled power plant equipments. Currently, VMSs are removed from biogas with high operational costs by adsorption on activated carbons. Biofiltration could be a cost-effective and environmentally friendly alternative to current technologies, leading to a decrease in the cost of biogas treatment, therefore enhancing its use for power generation. This document presents the results of biodegradation studies on VMSs aimed to investigate the possibility of using biofiltration to treat biogas. Growth of bacteria isolated from activated sludge with octamethylcyclotetrasiloxane (D4) in the vapour phase as the only carbon source was observed. 16S-rDNA-sequencing showed that the mixed population mainly contained γ-proteobacteria; within these, Pseudomonas was the dominating genus. A biotrickling filter was set up to treat different air flows with a siloxane concentration varying between 45 and 77 mg m⁻³. Measurements on the gas output revealed removal efficiency up to 20% compared to a control in sterile conditions.     

Screening and optimization of media constituents for decolourization of Mordant Blue-9 dye by Phanerochaete chrysosporium

Decolourization of Mordant Blue-9 (MB-9) by the white-rot fungi Phanerochaete chrysosporium MTCC 787 was investigated by screening and optimization of the media constituents used for growing the fungus. Both % decolourization and specific removal of MB-9 by the fungus were taken as the responses to screen and optimize the media constituents using statistically valid Plackett–Burman and response surface methodology (RSM) design of experiments, respectively. Amongst the media constituents screened, glucose, veratryl alcohol, KH₂PO₄ and CaCl₂ were selected as the most important (P value < 0.05) media constituents for MB-9 dye decolourization; the other media constituents, viz. MgSO₄, tween 20, NH₄Cl₂ and inoculum size were, however, found to be insignificant in the study. Central composite design followed by RSM used in optimizing the important media constituents for enhancing the decolourization of MB-9 dye revealed optimum combinations of glucose, 13.46 g l⁻¹; veratryl alcohol, 9.30 mM; KH₂PO₄, 24.52 g l⁻¹; CaCl₂, 2.18 g l⁻¹; MgSO₄, 9.89 g l⁻¹; NH₄Cl₂, 4.68 g l⁻¹; tween 20, 0.050% and inoculum size, 0.8 OD₆₅₀, which gave a maximum % dye decolourization of 100% and specific dye removal of 0.1571 mg U⁻¹.     

Investigations into the application of a combination of bioventing and biotrickling filter technologies for soil decontamination processes—A transition regime between bioventing and soil vapour extraction

Bioventing has emerged as one of the most cost-effective in situ technologies available to address petroleum light-hydrocarbon spills, one of the most common sources of soil pollution. However, the major drawback associated with this technology is the extended treatment time often required. The present study aimed to illustrate how an intended air-injection bioventing technology can be transformed into a soil vapour extraction effort when the air flow rates are pushed to a stripping mode, thus leading to the treatment of the off-gas resulting from volatilisation. As such, a combination of an air-injection bioventing system and a biotrickling filter was applied for the treatment of contaminated soil, the latter aiming at the treatment of the emissions resulting from the bioventing process. With a moisture content of 10%, soil contaminated with toluene at two different concentrations, namely 2 and 14 mg g soil⁻¹, were treated successfully using an air-injection bioventing system at a constant air flow rate of ca. 0.13 dm³ min⁻¹, which led to the removal of ca. 99% toluene, after a period of ca. 5 days of treatment. A biotrickling filter was simultaneously used to treat the outlet gas emissions, which presented average removal efficiencies of ca. 86%. The proposed combination of biotechnologies proved to be an efficient solution for the decontamination process, when an excessive air flow rate was applied, reducing both the soil contamination and the outlet gas emissions, whilst being able to reduce the treatment time required by bioventing only.     

Localization of U(VI) on nickel hydroxide from aqueous solution in the presence of complexing anions at 25°C

Sorption and coprecipitation of U(VI) from aqueous solution containing various complexing anions (CO₃^25-, SO₄²⁻, H₂EDTA²⁻) with the Ni(OH)₂ solid phase at 25°C was studied. Uranium(VI) is not noticeably sorbed on the Ni(OH)₂ solid phase from aqueous solutions containing CO₃²⁻ and SO₄²⁻. The distribution coefficients K _d are less than 1.0 ml g⁻¹ throughout the examined range of [U(VI)]: [L] ratios (L = CO₃²⁻, SO₄²⁻) at V/m ≥ 100 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In the presence and in the absence of H₂EDTA²⁻, the degree of the U(VI) sorption is essentially the same (K _d ∼90–140 ml g⁻¹ at V/m ≥ 100 ml g⁻¹). Uranium(VI) does not coprecipitate with Ni(OH)₂ from aqueous solutions containing SO₄²⁻ and H₂EDTA²⁻. The distribution coefficients K _d are less than 0.001 ml g⁻¹ at V/m ≥ 200 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In solutions containing CO₃²⁻, the U(VI) capture by the Ni(OH)₂ precipitate depends on the [CO₃²⁻]: [U(VI)] ratio. The higher the [CO₃²⁻]: [U(VI)] ratio, the more strongly U(VI) coprecipitates with Ni(OH)₂.     

Rigid, Microporous 3D Molecular Frameworks Derived from 3-Amino-1,2,4-triazole

The 3-amino-1,2,4-triazole (AmTAZ) ligand is a promising molecular species for formation of robust porous coordination polymers. We have recently crystallized two unusual cubic cage structures which possess μ₂−O ²⁻ and μ₃−S ²⁻ bridges, respectively. Although nitrate anions occupy the pore in these two cationic frameworks, we anticipate that similar materials with open pores can be formed by the incorporation of the charge-compensating anion into the framework structure.     

DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> activity of Ag/γ–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites prepared via the solvothermal route

Ag/γ–Al₂O₃ with silver loading of 3 wt.% were prepared by the solvothermal-calcination reaction of AgNO₃ in mixed water-alcohol solutions at 50–250 °C for 0–120 min, followed by calcinations at 550 °C for 2 h using γ-Al₂O₃ (SSA: 120–409 m² g⁻¹), γ-AlOOH (SSA: 270 m² g⁻¹), Al(OH)₃ (SSA 10 m² g⁻¹), Al(OCH(CH₃)₂)₃ and Al(NO₃)₃ as an aluminum source. The resultant product produced by the solvothermal reaction was Ag/γ–AlOOH even though a different aluminum source was used and Ag/γ–AlOOH was converted to Ag/γ–Al₂O₃ by the following calcinations. However, the characteristics of them changed greatly depending on the alumina source. The deNO _x catalytic performance of Ag/γ–Al₂O₃ also greatly changed depending on the aluminum precursor and solvothermal solvent in the order γ-AlOOH = γ-Al₂O₃ >> Al(OCH(CH₃)₂)₃ >> Al(NO₃)₃ > Al(OH)₃ and methanol = ethanol > 1-propanol > butanol >> hexanol, since the amount and size of silver particle impregnated and specific surface area of the product changed markedly. Ag/γ–Al₂O₃ prepared by solvothermal-calcination method consisted of homogeneously dispersed fine particles of silver and showed better performance for NO _x decomposition than that by conventional impregnation-calcination method.     

Tuning anti-microbial activity of poly(4-vinyl 2-hydroxyethyl pyridinium) chloride by anion exchange reactions

A series of new bioactive polymers with pendant choline analogous group was prepared by anion exchange reaction direct at the quaternary nitrogen of the polycation. Poly(4-vinyl 2-hydroxyethyl pyridinium) chloride was prepared in situ by simultaneous polymerization and quaternization of 4-vinyl pyridine with 2-chloroethanol that also acts as catalyst. The counter anion (Cl⁻) of the polycation was exchanged by anion exchange reaction with Br⁻, ⁻OH, ⁻SH, NO₃ ⁻, BF₄ ⁻ or CF₃COO⁻. Evidence of anion exchange was obtained by the characterization of the resultant polymers. The nature of the counter anion has profound effect on their properties including strong anion-dependent anti-microbial activity against bacteria and fungus. Polymer containing ⁻OH was observed to be the most potent anti-microbial agent with the lowest minimum inhibitory concentration against both the classes of microbes studied.     

Pyreno-chalcone dendrimers as an additive in the redox couple of dye-sensitized solar cells

Novel pyreno-chalcone dendrimers 1, 2, and 3 were synthesized and their ability to act as an additive in the redox couple (I⁻/I₃ ⁻) of dye-sensitized nanocrystalline TiO₂ solar cell has been tested. The redox couple doped with pyreno-chalcone dendrimer 3 gave a short circuit photocurrent density (J _sc) of 7.40 mA/cm², open circuit voltage (V _oc) of 820 mV, and a fill factor of 0.51, corresponding to an overall conversion efficiency (η) of 7.89% under 40 mW/cm² irradiation.     

AC impedance and dielectric spectroscopic studies of Mg<Superscript>2 + </Superscript> ion conducting PVA–PEG blended polymer electrolytes

Polyvinyl alcohol (PVA)–polyethylene glycol (PEG) based solid polymer blend electrolytes with magnesium nitrate have been prepared by the solution cast technique. Impedance spectroscopic technique has been used, to characterize these polymer electrolytes. Complex impedance analysis was used to calculate bulk resistance of the polymer electrolytes. The a.c.-impedance data reveal that the ionic conductivity of PVA–PEG–Mg(NO₃)₂ system is changed with the concentration of magnesium nitrate, maximum conductivity of 9·63 × 10^− 5 S/cm at room temperature was observed for the system of PVA–PEG–Mg(NO₃)₂ (35–35–30). However, ionic conductivity of the above system increased with the increase of temperature, and the highest conductivity of 1·71 × 10^− 3 S/cm was observed at 100°C. The effect of ionic conductivity of polymer blend electrolytes was measured by varying the temperature ranging from 303 to 373 K. The variation of imaginary and real parts of dielectric constant with frequency was studied.     

Conductometric gas sensing studies of tert-butyl silicon-[bis ethyloxy]-phthalocyanine LB films

Ultrathin Langmuir-Blodgett film properties of tert-butyl silicon-[bis ethyloxy]-phthalocyanine (tbPcSi(OC₂ H₅)₂) have been studied and characterised. Surface pressure–area isotherms reveal an area per molecule of around 0.85 nm², and that a compact ‘solid’ phase occurs in the region 10–30 m N m⁻¹. LB films of different thicknesses were deposited onto gold interdigitated electrodes on glass in order to facilitate I–V measurements and assess the conductometric sensing properties in response to 5 ppm NO₂. The I–V characteristic is Ohmic and yields conductivity in the range comparable to that obtained for other phthalocyanine monomers. The gas sensing behaviour of these films in response to NO₂ was investigated and modelled using a double exponential model. Preliminary UV–visible spectroscopic investigations indicate that the film also responds optically. This work was partially supported by the Physics and Astronomy Department, University of Sheffield.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Thermodynamic and quasi-chemical modeling of point defects in CdTe〈I〉

The carrier concentration and the densities of predominant point defects in CdTe〈I〉 crystals have been calculated as functions of two-step annealing parameters using quasi-chemical and thermodynamic modeling. We have identified the dominant native and impurity defect species, which govern the electrical properties of the material, and proposed a compensation model that takes into account not only native defects, I_Te⁺ substitutional defects, and their complexes with native point defects, such as (V _Cd²⁻I_Te⁺)⁻, and (V _Cd²⁻2I_Te⁺)⁰, but also DX ⁻ centers. The equilibrium constants of formation of the V _Cd²⁻I_Te⁺)⁻, defect complex and center have been evaluated.     

Preparation of SiB4±x and SiB6 plates by chemical vapour deposition of SiCl4 + B2H6 system

SiB_4±x and SiB₆ plates were prepared by chemical vapour deposition (CVD) using SiCl₄, B₂H₆ and H₂ gases under the conditions of deposition temperatures (T _dep) from 1323–1773 K, total gas pressures (P _tot) from 4–40 kPa and B/Si source gas ratio (m _B/Si=2B₂H₆/SiCl₄) from 0.2–2.8. The effects of CVD conditions on the morphology, structure and composition of the deposits were examined. High-purity and high-density SiB_4±x and SiB₆ plates about 1 mm thick were obtained at the deposition rates of 71 and 47 nm s⁻¹, respectively. The lattice parameter, composition and density of CVD SiB_4±x plates were dependent on their non-stoichiometry. The lattice parameter,a, was 0.6325 nm, butc ranged from 1.262–1.271 nm.The B/Si atomic ratio ranged from 3.1–5.0, and the density ranged from 2.39–2.45×10³ kg m⁻³. The CVD SiB₆ plates showed constant values of lattice parameters (a=1.444 nm,b=1.828 nm,c=0.9915 nm), composition (B/Si=6.0) and density (2.42×10³ kg m⁻³), independent of CVD conditions.