Application of novel SIMS technique for imaging the active sites of oxygen reduction at the SOFC cathode/electrolyte interfaces

The oxygen reduction active sites were visualized around the O₂/SOFC cathode/electrolyte triple phase boundaries (TPB) by the¹⁶O/¹⁸O exchange techniques and secondary ion mass spectrometry (SIMS) analysis. The higher¹⁸O concentration is observed on the cathode top surfaces (La_0.9Sr_0.1MnO₃-mesh, Au-mesh, and Ag-porous), which suggested the promotion of oxygen adsorption and oxygen surface exchange at the cathode. The oxygen diffusion through the bulk of cathode occurred at the La_0.9Sr_0.1MnO₃-mesh and the Ag-porous cathodes, not at the Au-mesh cathode. On the YSZ surfaces after removing the cathode, the active sites for oxygen incorporation were analyzed by SIMS. The active sites for oxygen incorporation were at the La_0.9Sr_0.1MnO₃/YSZ interface as well as the TPB. On the other hand, the active sites for oxygen incorporation are limited to the TPB in the case of the Au-mesh removed YSZ surface. From the SIMS analysis, the expansion of the active sites for oxygen incorporation is less than a few μm from the TPB lines. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions

Oxide heterojunctions made of p-type La_0.8Sr_0.2MnO₃ (LSMO) and niobium-doped n-type SrTiO₃ (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency γ are estimated to be 8.3×10¹² cm⁻² and 11% at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and γ are 3.0×10¹³ cm⁻² and 27%, respectively.     

Gas-stirred solvent extraction with propylene carbonate for separation and direct polarographic determination of thallium (III)

Gas-stirred propylene carbonate (PC) extraction can be performed by bubbling nitrogen without loss of volume. This extraction technique has proved to be highly useful for the separation and subsequent direct polarographic estimation of Tl(III) in the recovered PC phase. Tl(III) can be determined by differential-pulse polarography over the concentration range of 0.4 10 g ml^–1 without any interferences due to most metal ions such as Pb(II), Bi(III), Cu(II), Sb(III) and As(III). This proposed technique would be possible to use as a simple extraction step prior to the final estimation by instrumental method of analysis such as atomic absorption spectrometry or spectrophtometry.     

Spectrophotometric determination of nitrate and nitrite in water and some fruit samples using column preconcentration

A sensitive analytical method for the simultaneous assay of nitrate and nitrite in water and some fruit samples is presented. The method is based on nitrite determination using the diazotization-coupling reaction by column preconcentration and on the reduction of nitrate to nitrite using the Cd-Cu reductor column. Nitrite is diazotized with sulfanilamide (SAM) in the pH range 2.0-5.0, sulfamethizole (SM) in pH 1.8-5.6 and sulfadimidine (SD) in pH 1.8-4.0 in a hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were coupled with sodium 1-naphthol-4-sulfonate (NS) in the pH range 9.0-12.0 for the SAM-NS system, pH 8.6-12.0 for the SM-NS system and pH 9.4-12.0 for the SD-NS system to be retained on naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent packed in a column. The solid mass is dissolved out from the column with 5 ml of dimethylformamide (DMF) and the absorbance is measured by a spectrophotometer at 543 nm for SAM-NS, 537 nm for SM-NS and 530 nm for SD-NS. The calibration graph was linear over 30-600 ng NO(2)-N and 22-450 ng NO(3)-N in 15 ml of final aqueous solution (i.e. 2-40 ng NO(2)-N ml(-1) and 1.5-30 ng NO(3)-N ml(-1) in aqueous sample) for three systems. The detection limits were 1.4 ng NO(2)-N ml(-1) and 1.1 ng NO(3)-N ml(-1) for SAM-NS, 1.2 ng NO(2)-N ml(-1) and 0.89 ng NO(3)-N ml(-1) for SM-NS, 1.0 ng NO(2)-N ml(-1) and 0.75 ng NO(3)-N ml(-1) for SD-NS, respectively. The concentration factor is eight for SAM-NS and SM-NS, and 12 for SD-NS. Interferences from various foreign ions have been examined and the method was successfully applied to the determination of low levels of nitrate and nitrite in water and some fruit samples.     

Completely stereocontrolled synthesis of the right fragment of salinomycin,a polyether antibiotic,by means of the chelation-controlled grignard reaction

In the course of our synthetic study of salinomycin ($\text{1}$), an ionophorous polyether antibiotic, the γ-lactone ($\text{2}$) corresponding to the C-21～C-30 fragment (the right fragment) of $\text{1}$ was synthesized from D-mannitol and ethyl L-lactate as chiral starting materials. The complete stereocontrol for the construction of new chiral centers has been achieved by means of the chelation-controlled Grignard reaction and the tetrahydropyran synthesis via the acid catalyzed epoxide ring opening.     

Selective extraction of gallium from aluminum and indium using tripod phenolic ligands

Solvent extraction of trivalent group 13 metal cations such as aluminum, gallium and indium with tripod quadridentate phenolic ligand, tris(2-hydroxy-3,5-dimethylbenzyl)amine (H(3)tdmba), was investigated as fundamental study for their mutual separation. Gallium was extracted almost quantitatively as Ga(tdmba) (logK(ex)=-6.66+/-0.06 on using chloroform as extraction solvent), whereas aluminum and indium were hardly extracted due to steric hindrance on complexation of them with the ligand. The extracted Ga species was estimated as trigonal bipyramidal complex with one H(2)O molecule. Furthermore, extractability of Ga was increased by changing the ligand to more acidic tris(5-chloro-2-hydroxy-3-methylbenzyl)amine (H(3)tcmba) (logK(ex)=-6.18+/-0.18 on using dichloroethane as extraction solvent).     

Studies on the Syntheses of Multilayered [2. 2] Paracyclophanes

It is well-known that a number of double-layered compounds such as [2. 2]paracyclophane show anomalous physical and chemical properties due to the transannular π-electronic interaction between the stacked aromatic rings.²) Moreover, the interaction significantly increases with an increase of the layers as observed in a series of multilayered [2. 2]paracyclophanes³) and thereby it is of great interest to search a possibility of an organic semiconductor or its suitable model in them or their derivatives. However, such a study has been severely limited by great difficulty on the syntheses of the layered cyclophanes. While a number of synthetic methods have been developed for cyclophanes,²) only 1,6-Hofmann elimination method has so far been adopted to the preparation of multilayered [2.2]paracyclophanes.³) In practice, however, the yield is very low and becomes markedly poor with the increasing layers. Now we have studied some practical improvements on the preparation of multilayered [2.2]paracyclophanes.     

Periodic arrays of submicron Si and Ni dots on SiO2 fabricated using linearly polarized Nd:YAG pulsed laser

Periodic arrays of submicron Si and Ni dots were fabricated by only irradiating a linearly polarized Nd:YAG pulsed laser beam to Si and Ni thin films deposited on silicon dioxide (SiO₂) film. The interference between an incident beam and a scattered surface wave leads to the spatial periodicity of beam energy density distribution on the surface of the irradiated samples. A thin film was melted using a laser beam, and the molten film was split and condensed owing to its surface tensile according to the periodic energy density distribution. Then, the fine lines (line and space structure) were formed periodically. After the formation of fine lines, the sample was rotated by 90°, and the laser beam was irradiated. The periodic energy density distribution was generated on the fine lines, and the lines were split and condensed. Eventually, the periodically aligned submicron dots were fabricated on the SiO₂ film. PACS 79.20.Ds; 42.62.-b; 81.40.-z     

Effects of the molecular properties of mixed solvents on the elution of alkyl benzoates in RPLC.

The retention behavior and mechanism of methyl, ethyl, propyl, isopropyl, buthyl and isobuthyl benzoates have been studied at different eluent compositions of aqueous mixtures with water-soluble organic solvents (methanol, ethanol, 1-propanol, 2-propanol, acetonitrile (AN), 1,4-dioxane and tetrahydrofuran (THF)) in RPLC. The retention of the solutes is discussed based on the solvent composition, solvent polarity (ETN value), preferential solvation, hydrogen bonding and solvent clusters of the eluents. The smaller ETN values and the larger preferential solvation of the mixed solvent eluted the solutes faster. The IR spectra of HDO suggested that the solvents, except for methanol and ethanol, break the hydrogen bonding between water molecules, resulting in fast elution of the solutes. Based upon the results, we chose an optimum solvent composition for the separation of benzoates and applied it to the determination of the benzoates in clove.