GC determination of volatile organoiodine and organobromine compounds in Arctic seawater and air samples

Summary During September 1992 seawater and air samples were collected on Spitzbergen, Norway, and the concentrations of volatile organoiodine and organobromine compounds of biogenic origin were determined by a GC system supplied with a capillary column and an electron capture detector. A purge and trap technique was used to isolate the organohalogen compounds from the seawater samples, whereas the air samples were collected by an adsorption tube filled with Carbosieve S-III. The iodinated compounds CH₃I, CH₂I₂, CH₂C1I, CH₃CH₂CH₂I and CH₃CHICH₃ were determined in Arctic seawater and air samples with mean concentrations in the range of (0.3–6.2) ng/l and (0.7–2) pptv, respectively. This is the first time that 1- and 2-propyl iodide could be analysed both in atmospheric samples and in seawater samples of the Arctic. CH₂Br₂, CHBr₃, CH₂BrCl, CHBrCl₂ and CHBr₂Cl were determined as biogenic brominated methanes in mean concentrations of (0.1–164) ng/l and (0.1–0.5) pptv in seawater and air samples, respectively. The highest concentrations in seawater samples were found for CH₂I₂ and CHBr₃, respectively, whereas in air samples the most abundant iodinated compound was CH₃I and the most abundant brominated compounds with equal mean concentrations were CH₂Br₂ and CHBr₃. Significant differences were found in the seawater concentration from the middle of the fjord and the shore site, compared with samples from a field of algae. In all cases the concentration was higher for the samples from the field of algae with an especially high excess by a factor of 4–9 for CH₂I₂ and CHBr₃. This result shows that algae are an important biological species in the polar region for the production of these halogenated substances. Whereas the brominated compounds in seawater samples correlate well with each other, CH₃I or any other iodinated compound does not correlate with the bromomethanes. This indicates a different biogenic mechanism for their formation. Under certain preconditions the annual flux from the Arctic Ocean to the atmosphere could be calculated for CH₃I to be 4×10⁹ g, for CHBr₃ to be 5.4×10¹⁰ g, which is an essential contribution to the total global budget of these important atmospheric trace gases.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

CO Hydrogenation over Re-Co Bimetallic Catalysts Supported over SiO2, Al2O3 and NaY Zeolite

The promotion of rhenium on the reduction of Co²⁺ ions in cobalt based samples prepared by various methods, such as, sol/gel technique, incipient wetness impregnationof Al₂O₃ and NaY, has been investigated in the CO hydrogenation. Among the samples the reducibility of the sol/gel, Re-Co/Al₂O₃ and Re-Co/NaY(IM) were the highest compared to Re-Co/NaY (IE) [8]. In addition to facilitating reduction of Co²⁺ ions, the rhenium increased the rate of reaction and the formation ofC₅₊ hydrocarbons at 10 bar pressures. The samples pretreated in various manner, revealed an about five fold increase in activity and an increase in the chain length in the NaYsupported sample while the activity and selectivity changed in various way in the sol/gel prepared samples. Simultaneously, rhenium increased the amount of olefins of low carbon numbers.In the mechanism the rhenium provides an action preventing fast deactivation of cobalt.     

Effects of the Brookite Phase on the Properties of Different Nanostructured TiO2 Phases Photocatalytically Active Towards the Degradation of N-Phenylurea

Different sol-gel synthesis methods were used to obtain four nanostructured mesoporous TiO₂ samples for an efficient photocatalytic degradation of the emerging contaminant N-phenylurea under either simulated solar light (1 Sun) or UV light. Particularly, two TiO₂ samples were obtained by means of as many template-assisted syntheses, whereas other two TiO₂ samples were obtained by a greener template-free procedure, implying acidic conditions and, then, calcination at either 200 °C or 600 °C. In one case, anatase was obtained, whereas in the other three cases mixed crystalline phases were obtained. The four TiO₂ samples were characterized by X-ray powder diffraction (followed by Rietveld analysis); Transmission Electron Microscopy; N₂ adsorption/desorption at −196 °C; Diffuse Reflectance UV/Vis spectroscopy and ζ-potential measurements. A commercial TiO₂ powder (i. e., Degussa P25) was used for comparison. Differences among the synthesized samples were observed not only in their quantitative phase composition, but also in their nanoparticles morphology (shape and size), specific surface area, pore size distribution and pH_IEP (pH at isoelectric point), whereas the samples band-gap did not vary sizably. The samples showed different photocatalytic behavior in terms of N-phenylurea degradation, which are ascribed to their different physico-chemical properties and, especially, to their phase composition, stemming from the different synthesis conditions.     

Structural and optical properties of barium titanate modified bismuth borate glasses

Glass samples with composition (70B₂O₃–29Bi₂O₃–1Dy₂O₃) modified with Barium titanate (BT), where BT is added in different successive weight percents, have been synthesized by conventional melt quenching technique. X-ray diffraction studies were performed in order to confirm the amorphous nature of the samples. The density of the samples has been found to decrease with an increase in the BT content, whereas an opposite trend has been observed in the molar volume. The analysis of FTIR and Raman spectra of the samples depicts that the glass network is built up of mainly BiO₆, BiO₃, BO₃ and BO₄ units. Its detailed analysis also revealed that the glass structure depends upon the amount of BT in the glass matrix and hence it acts as a modifier in the glass network. Introduction of BT into the glass matrix leads to the conversion of BO₃ trigonal units into BO₄ tetrahedral units, which results in a decrease in the degree of disorder in the glass network and makes the glass system more stable. The values of Urbach energy obtained for the prepared samples also confirmed the decrease in disorder in the glass network. The optical absorption measurements carried out for well-polished samples show a decrease in optical band gap energy with an increase in BT content whereas the molar refractivity shows the reverse trend. The Hydrogenic excitonic model applied to the studied glasses suggested that the present glass system favors direct transitions. The metallization criterion of the presently studied samples suggests that the prepared glasses may be potential candidates for nonlinear optical applications.     

Effects of crystallinity, {001}/{101} ratio,and Au decoration on the photocatalytic activity of anatase TiO2 crystals

Anatase TiO₂ nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF₂ precursors. The as-prepared TiO₂ samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N₂ adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800 °C. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO₂ samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF₂ at 700 and 800 °C.     

Thermoanalytical investigation of calcium chromate

Thermoanalytical methods have been used to study calcium chromate (CaCrO₄) samples. Thermal decomposition temperatures determined by TG in vacuum and by DTA in air could not be successfully used for screening purposes. Other thermogravimetry studies in air indicate that TG can be an effective quality control tool in screening out samples which have an assay value below 97.0% CaCrO₄. More complete analyses using TG in an argon atmosphere gave good results for CaCO₃ and H₂O content as well as for total CaCrO₄. Reliable measurement of Ca(OH)₂ was not achieved. Effluent gas analysis—mass spectrometry was used to identify gaseous products as a function of temperature, in order to verify interpretation of TG curves.Thermogravimetry, differential scanning calorimetry, nuclear magnetic resonance, and mass spectrometry have been used in an effort to explain the unusual weight loss observed between 400 and 600°C for many CaCrCO₄ samples. Ca(OH)₂ decomposition is not the primary cause of this weight loss, as originally suspected, but instead the loss appears to be due to volatization of H₂O trapped in the CaCrO₄ crystal.     

Influence of ceria preparation method on the performance of CuO/CeO2 catalysts

Ceria were prepared by various processes. The prepared samples and commercial ceria were used as supports to prepare the CuO/CeO₂ catalysts via an impregnation method. The samples were characterized by using TEM, XRD, H₂-TPR, and their catalytic activities in low-temperature CO oxidation were also investigated.     

Solvothermal synthesis of highly active Bi2WO6 visible photocatalyst

Uniform Bi₂WO₆ spheres with high visible light activity were prepared via a solvothermal route. A variety of techniques including transmission electron micrographs (TEM), X-ray powder diffraction (XRD), N₂ adsorption, FT-IR spectra, and UV–Vis spectra were employed to characterize the structure of the Bi₂WO₆ materials so obtained. The results show that the sphere-like Bi₂WO₆ samples were successfully prepared. And, under the photocatalytic degradation of Rhodamine B, the samples demonstrated high activity, three times higher than that of a sample from the solid-state method. Moreover, the uniform structure made the sample easy to separate from the reaction solution, providing an intrinsic advantage to the normal Bi₂WO₆ samples.     

Innovative method for carbon dioxide determination in human postmortem cardiac gas samples using headspace-gas chromatography–mass spectrometry and stable labeled isotope as internal standard

A novel approach to measure carbon dioxide (CO₂) in gaseous samples, based on a precise and accurate quantification by ¹³CO₂ internal standard generated in situ is presented. The main goal of this study was to provide an innovative headspace-gas chromatography–mass spectrometry (HS-GC–MS) method applicable in the routine determination of CO₂. The main drawback of the GC methods discussed in the literature for CO₂ measurement is the lack of a specific internal standard necessary to perform quantification. CO₂ measurement is still quantified by external calibration without taking into account analytical problems which can often occur considering gaseous samples. To avoid the manipulation of a stable isotope-labeled gas, we have chosen to generate in situ an internal labeled standard gas (¹³CO₂) on the basis of the stoichiometric formation of CO₂ by the reaction of hydrochloric acid (HCl) with sodium hydrogen carbonate (NaH¹³CO₃). This method allows a precise measurement of CO₂ concentration and was validated on various human postmortem gas samples in order to study its efficiency.     

Determination of organic carbon in water with a silver-catalyzed peroxydisulfate wet chemical oxidation method

The application of Ag(I) catalysis of S₂O₈^2? to the oxidation of organic carbon to CO₂ for determination of dissolved organic carbon in aqueous samples is described. The resulting method combines to a significant degree the speed of high-temperature combustion methods and the sensitivity of wet chemical oxidation. For some samples, a higher oxidation efficiency has been observed than with an uncatalyzed wet chemical oxidation method.     

Determination of trace elements in fly ash samples by FAAS after applying different digestion procedure

The fly ash samples obtained from Kangal Power Plant were prepared for FAAS analysis by a new approach. The trace elements of the fly ash samples were leached with appropriate solvents under suitable conditions. The leaching method is known as an effective technique for substances dissolving very hard and refractory materials. The leaching effects of solvents and their mixtures were investigated on fly ash samples that are used largely in analysis of soil and sediment samples.The fly ashes mainly consist of glassy aluminosilicates. The major components of the samples are SiO₂, Al₂O₃, CaO and Fe₂O₃. Therefore, decomposition of the silicate lattice of the fly ash is required for liberation of trace elements. The dissolution process can be completed by using a mineral acid such as concentrated HCl. This technique has an advantage that the fly ash can be dissolved without any oxidation at room temperature.Maximum element recoveries were obtained by the procedure of 37% HCl leaching after the samples were treated with 2.0 ml of concentrated HF. It was also observed that maximum mass loss occurred in this procedure. The effect of the four leaching reagents, which are HCl, HNO₃, HClO₄ and HNO₃ + HClO_4, were investigated on fly ash samples that were treated with concentrated HF. An optimum leaching method was determined based on the confidence of analytical results and element recovery rates.     

Efficient photocatalytic degradation of methyl orange dye using facilely synthesized α-Fe2O3 nanoparticles

In this paper, α-Fe₂O₃ nanoparticles were fabricated via the combustion process using glucose and sucrose as organic fuels for the first time. The fabricated products were characterized using XRD, FT-IR, HR-TEM, and UV–vis spectrophotometer. The average crystallite size of the α-Fe₂O₃ samples, which were synthesized using glucose and sucrose fuels, is 27.25 and 6.13 nm, respectively. The HR-TEM images confirmed the presence of spherical and irregular shapes with an average diameter of 31.92 and 8.83 nm for the α-Fe₂O₃ samples, which were synthesized using glucose and sucrose fuels, respectively. The optical energy gap of the α-Fe₂O₃ samples, which were synthesized using glucose and sucrose fuels, is 2.00 and 2.48 eV, respectively. Additionally, the synthesized α-Fe₂O₃ samples were employed as a photocatalyst for the degradation of methyl orange dye under UV irradiations in the absence and presence of hydrogen peroxide. The optimum pH, irradiation time, and dose of α-Fe₂O₃ that achieved the highest degradation efficiency in the presence of hydrogen peroxide (82.17 % in the case of using an α-Fe₂O₃ sample which was synthesized using glucose or 95.31 % in the case of using an α-Fe₂O₃ sample which was synthesized using sucrose) are 3, 100 min, and 0.05 g, respectively.     

Characterization of mesoporous nanocrystalline TiO2 photocatalysts synthesized via a sol-solvothermal process at a low temperature

Nanocrystalline TiO₂ samples with mesoporous structure were prepared via a solvothermal treatment of surfactant-stabilized TiO₂ sols. The samples were obtained from media of different acidities including nitric acid, deionized water, and ammonia (denoted as HT-1, HT-2 and HT-3, respectively). These samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂-sorption (BET surface area), micro-Raman spectroscopy, infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were tested by the self-photosensitized degradation of an azo dye, Mordant Yellow 10 (MY), in aqueous solution under visible light irradiation. The results reveal that all three samples have high surface area and are pure anatase phase. The sample prepared in nitric acid medium possesses the most ideal mesoporous structure and also exhibits a blue shift in the Raman spectrum. All three samples show much higher photocatalytic activity than the commercial P-25. The activity order of the three samples is HT-1>HT-2>HT-3.     

Determination of aluminium in bulk coal samples by neutron activation analysis

The determination of Al₂O₃, in bulk coal samples to an accuracy of about 0.2% Al₂O₃ has been achieved by means of a thermal-neutron activation technique based on the reaction ²⁷Al(n,γ)²⁸Al. In the analysed samples, which had widely different compositions, the Al₂O₃ concentrations ranged from 1 to 11% and the ash contents from 7 to 40%. Al₂O₃ concentrations measured by x-ray fluorescence showed a linear relationship with both the 1.78-MeV γ-ray count following the decay of ²⁸Al and the thermal-neutron count near the samples during irradiation. The linear relationship, which was obtained by regression analysis of the experimental data, determined the Al₂O₃concentrations with a standard deviation of 0.24% Al₂O₃. The particle sizes in the samples ranged from —0.5 to —40 mm, the moisture contents ranged from 1 to 6%, and the sample weights ranged from 8 to 11 kg. However, inclusion of these parameters in the regression analysis did not significantly improve the results for Al₂O₃.     

Determination of Total Fluoride in Oral Products by Using of Potentiometry With Ion Selective Electrode: A Critical Study

ABSTRACT

In this work, a critical study of the determination of fluoride in oral products with an ion selective electrode was performed. The influence of the type of fluorine compound in the sample as well as the practical factors involved in the analysis were investigated. Fluoride could be determined, directly, in samples where it is in the form of NaF or SnF₂. However, in samples where it is as MFP (sodium monofluorophosphate) an acid treatment was needed for removal of fluoride from the PO₄F^2? ion. In both cases, problems were noted related to the continuous use of the electrode, caused by the adsorption of fluoride ions onto the electrode surface. This problem was solved by using of KOH and Al₂(SO₄)₃ solutions. Good results were obtained for the analysis of real commercial samples.     

Determination of nitrogen in UO2 by Kjeldahl spectrophotometry

A method for the dissolution of sintered UO₂ samples and the determination of ammonium ions in the solution by spectrophotometry for the chemical quality control of UO₂ fuel for nitrogen is described. The acid mixture used simplifies the problem of recovery of uranium from the waste generated during the analysis of nitrogen. Nitrogen content in ppm in the sintered UO₂ samples is determined within an RSD of 10%.     

Effect of surface treatments on the localized corrosion resistance of the AA2198-T8 aluminum lithium alloy welded by FSW process

In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198-T8 Al-Cu-Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post-anodizing treatments. The post-anodizing treatments were (1) hydrothermal treatment in Ce (NO₃)₃ 6H₂O solution; (2) hydrothermal treatment in Ce (NO₃)₃ 6H₂O solution with H₂O₂; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis-1,2-(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L⁻¹ NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce-containing solutions presented the best corrosion resistance, especially when used without peroxide.     

Non-Stoichiometric CoFe2O4 Nanoparticles Supported on an Amorphous Silica Matrix

Non-Stoichiometric CoFe₂O₄ nanoparticles dispersed in an silica matrix with a silica content of 87 wt% and Co/Fe molar ratio of 1:1, were prepared by the sol-gel method using an ethanolic solution of tetraethoxysilane and either iron(III) and cobalt(II) nitrates or iron(II) and cobalt(II) acetates. The influence of different metal precursors on the xerogels were examined by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and N₂ physisorption measurements at 77 K. Magnetic properties of the samples were investigated by field cooled FC and zero field cooled ZFC measurements.Depending on the metal precursor, different spinel oxides of a few nanometers were observed in the samples treated at 350°C. After heating at 900°C non-stoichiometric CoFe₂O₄ was formed in both samples, whose average particle size was only slightly larger than in samples treated at 350°C.     

Effect of the mechanochemical treatment of a V<Subscript>2</Subscript>O<Subscript>5</Subscript>/MoO<Subscript>3</Subscript> oxide mixture on its properties

The mechanochemical treatment of a V₂O₅/MoO₃ oxide mixture (V/Mo = 70/30 at %) was performed in planetary and vibratory mills under varying treatment times and media. The resulting samples were characterized using XRD analysis, micro-Raman spectroscopy, and XPS; their specific surface areas and catalytic activities in n-butane and benzene oxidation reactions were determined. It was found that the treatment of the oxide mixture in water resulted in chaotic degradation of the parent oxides, a decrease in crystallite sizes, and an increase in the specific surface area at a sufficiently uniform oxide distribution over the sample. The treatment in ethanol was accompanied by an anisotropic deformation of the V₂O₅ crystal by layer sliding in parallel to the vanadyl plane (010) and a chaotic degradation of MoO₃ crystals. This process was accompanied by the partial nonuniform supporting of vanadium oxide crystals onto the surface of molybdenum oxide to increase the V/Mo ratio on the sample surface. In this case, the particle size of oxides decreased and the specific surface areas of samples increased. It was found that the treatment of the oxide mixture in air (dry treatment) resulted in the most significant decrease in the sizes of V₂O₅ and MoO₃ crystals and a growth in the specific surface area. The amorphization of the parent oxides and the formation of MoV₂O₈ were observed as the treatment time was increased; in this case, an excess of amorphous vanadium oxide was supported onto the surface of this compound. It was found that, in all types of mechanochemical treatment, the binding energies of the core electrons of vanadium and molybdenum remained almost unchanged to indicate the constancy of the oxidation states of these elements. Mechanochemical treatment resulted in an increase in the activity of the samples in n-butane and benzene oxidation reactions and in an increase in the selectivity of maleic anhydride formation. In this case, an increase in the specific catalytic activity of the samples correlated with a decrease in the crystallite size of vanadium oxide, whereas selectivity correlated with an increase in the relative concentration of the V₂O₅ plane (010). In these reactions, samples after dry treatment exhibited a maximum activity, which can be related to the formation of MoV₂O₈.     

Thermoelectric properties of Ru2Si2 prepared by spark plasma sintering method

Electrical conductivities, Seebeck coefficients and thermal diffusivities were measured for Ru₂Si₃ samples with different densities prepared by spark plasma sintering method and an Rh-doped sample prepared by the floating zone melting and spark plasma sintering methods. Electrical conductivities, Seebeck coefficients and thermal diffusivities increased with sample density for undoped Ru₂Si₃. The thermoelectrical figure of merit also increased with sample density. Electrical conductivity of the 4% Rh-doped sample was larger than that of our previous samples prepared by floating zone melting method. Values of Seebeck coefficients were similar for samples prepared by either method. This revised version was published online in August 2006 with corrections to the Cover Date.