Determination of Trace Iron(II) in the Presence of Iron(III)

The determination of trace iron(II) is usually interfered by the presence of iron(III) when ortho-phenanthroline colorimetric method is used. In this report a chromogenic reagent which contains ortho-phenanthroline-EDTA mixture has been developed to decrease the interference of ferric ion after adjusting the acidity of sample at 0.1 N by adding the sulfuric acid. The procedure is also simplified by introducing sulfamate buffer solution (pH= 1.5) without adjusting the acidity of sample with sulfuric acid. If iron(III) is not present in the sample, this method is also applicable. The comparative results are exhibited for the present method and the conventional o-phenanthroline method.     

An Internal-Standard Method for Determination of Trace Impurities in Semiconductor Grade Silicon by Neutron Activation Analysis

An internal-standard method^1–4) has been applied for the determination of La, Sb, Au, Cr and Ag in silicon single-crystal by neutron activation analysis using cobalt as an internal-standard element. No chemical separation is required in this case and the precision obtained with the present method is satisfactory.     

Growth of Fe-doped ZnO nanorods using aerosol-assisted chemical vapour deposition via in situ doping

In situ Fe doping of ZnO nanorods (NRs) was performed using aerosol assisted chemical vapour deposition (AA-CVD) technique. As the aerosol generator is located outside the reactor, AA-CVD provides the flexibility to control doping parameters, such as doping timing, doping duration and a wider choice of dopant precursors. The Fe dopant aerosol was flowed into the reactor during the growth of ZnO NRs to achieve in situ doping. The X-ray diffraction analysis indicates that the Fe dopants were introduced into the ZnO lattice and present mainly in the form of Fe²⁺. This result is supported by the X-ray photoelectron spectroscopy analysis as the doublet separation is 13.6 eV, although there is a shift of Fe_1/2 and Fe_3/2 peaks to a lower binding energy levels. A strong green emission of PL of Fe-doped ZnO NRs shows that the NRs have poor crystal quality attributed to the Fe-induced defects (recombination centres). The poor photocatalytic performance in degrading Rhodamine B solution of Fe-doped ZnO NRs further proves that the Fe-induced defects were recombination centres rather than traps. Lastly, the growth mechanism of in situ Fe doping of ZnO NRs was discussed.     

Studies of the structure of Ce3+ centers in SrS phosphors

It is found that the shape of luminescence spectra of SrS−Ce phosphors is independent of both the species and concentration of a cofactor F, Cl, Br, or 1 introduced in the form of ammonium halide at least up to 6.5 at.%. The only exception is F, which, when added as a coactivator with a concentration of 2.4 at.% and above, gives rise to new longwave luminescence bands, part from the luminescence of the Ce³⁺ ion. Analysis has shown that this additional luminescence spectrum is similar to the Ce³⁺ spectrum but is shifted towards the longwave region by about 0.14 eV. The luminescence decay time constant (τ=57 nsec) is very close to Br, I, and small concentrations of F, a model is valid according to which the halogen that substitutes for sulfur and the Ce³⁺ that substitutes for Sr are the closest neighbors not to each other, but to a probable compensator of the charge of Sr vacancies. At high concentrations of fluorine some of the F ions are located at interstitial lattice sites in the immediate neighborhood of Ce³⁺, providing compensation for the charge of Ce³⁺ ions and having a marked effect on them. Tartu University, 18, Ulikooli St., Tartu EE2400, Estonian Republic. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 173–178, March–April, 1997.     

Tip-growth mode and base-growth mode of Au-catalyzed zinc oxide nanowires using chemical vapor deposition technique

Tip-growth and base-growth modes of Au-catalyzed zinc oxide nanowires (ZnO NWs) were synthesized on Au-film pre-deposited silicon substrates using Chemical Vapor Deposition (CVD) technique. The diameter of tip-growth Au-catalyzed ZnO NWs was proportional to the Au film thickness, whereas the areal density of these NWs was inversely proportional to the Au film thickness. It would be more appropriate to explain the growth of Au-catalyzed ZnO NWs by a combination of Vapor–Liquid–Solid and Vapor–Solid (VLS–VS) mechanisms instead of the conventional VLS mechanism, regardless of tip-growth or base-growth mode of Au-catalyzed ZnO NWs. The competition between the VLS and VS mechanism in the effectiveness of capturing the adsorbed Zn and O atoms would determine the final morphology of ZnO NWs. In addition, Au catalyst promoted the growth rate of NWs as compared to the self-catalyzed ZnO NWs.     

Towards the Discrimination of Carboxylates by Hydrogen‐Bond Donor Anion Receptors

The binding constants (log K_ass) of small synthetic receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate, acetate, benzoate and lactate, in 0.5 % H₂O/[D₆]DMSO by using the relative NMR‐based measurement method. As a result, four separate binding affinity scales (ladders) including thirty‐eight receptors were obtained with the scales anchored to indolocarbazole. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen‐bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactate<benzoate<acetate≤trimethylacetate, which holds with all investigated receptors. Nevertheless, there are a number of occasions when the binding order changes with changing of the carboxylate anion, sometimes quite substantially. Principal component analysis (PCA) reveals that this is primarily connected to preferential binding of trimethylacetate, supposedly caused by an additional hydrophobic/solvophobic interaction. These findings enable making better predictions, which receptor framework or cavity is best suited for carboxylate anions in receptor design.     

Degradation of organic dye using ZnO nanorods based continuous flow water purifier

Zinc oxide (ZnO) is a common semiconductor material uses in waste water treatment. However, utilizing of ZnO particles could be easily drained away by water and charged into the water system during the photocatalytic treatment. This could result of forming secondary pollution in the water system. Hence, it is necessity to grow ZnO nanorods on polyethylene terephthalate (PET) fiber to minimize the above mentioned problem. In this work, ZnO nanorods were grown on the flexible PET fiber in large quantity using a sol–gel method at low temperature (90 °C). A layer of 1-dodacanethiol polymer was per-coated on the PET fiber to improve the deposition of ZnO seed layer prior to the growth of ZnO nanorods. The PET fiber was covered with high areal density of ZnO nanorods (10.2 ± 0.8 NRs/μm²). Subsequently, this PET fiber was inserted into a glass tube for the setup of continuous flow water purifier. The photocatalytic study for degradation of Rhodamine B solution using this setup indicated that the reaction followed 1st order kinetic with rate constant of 1.28 h^?1. The ZnO nanorods were still intact with the fiber after the photocatalytic study. Thus, it is possible to upscale this setup as water purifier to purify the water system.     

OSL and TSL interrelations in SrSO4:Eu

Thermoluminescence (TL), dose-dependence of TL, optically stimulated luminescence (OSL), and EPR of Eu-doped strontium sulphate are studied. Eu enters the host lattice in 2+ charge state and does not change the charge state during energy storage and release. OSL disappears during pulse-step annealing of excited luminophor at the temperatures corresponding to dosimetric TL peak. Dosimetric TL peak can be destroyed by a continuous optical stimulation of excited sample. Ionizing radiation creates radiation defects in the host lattice, with the ionized sulphate anions being stable hole centres well above room temperature. Optical stimulation in the blue band (460–470 nm) causes the captured holes to be transported to the luminescence centres, similarly acts the heating of luminophor. The model of energy storage and release is discussed.     

Storage mechanism and OSL-readout possibility of Li2B4O7:Mn (TLD-800)

Thermoluminescence, dose dependences, and EPR of Mn-doped lithium tetraborate are studied. Mn is shown not to change a charge state during energy storage and release. Mn²⁺ amount decreases only at very high doses. The amount of Mn²⁺ depends on the sintering temperature and increases with temperature increase due to reduction of Mn from a higher oxidation state. X-irradiation creates optical absorption bands in Li₂B₄O₇:Mn. Optical stimulation in the UV band is effective for OSL-readout and destroys dosimetric TL peaks. The model of energy storage and release is discussed.     

High energy and power density of self-grown CuS@Cu2O core-shell supercapattery positrode

Journal of Solid State Electrochemistry - A self-grown copper sulfide@copper oxide (CuS@Cu2O) positrode synthsis by a hydrothermal method followed by 2&nbsp;h of air annealing method (at...