Mitsuyuki Soma

Photocatalytic decomposition of water vapour on an NiO–SrTiO3 catalyst

The photodecomposition of water vapour proceeds steadily for more than 100 h on NiO–SrTiO3 powder and stops immediately when the water vapour is removed.

Correlation between vibrational spectra and electrical conductivity of polythiophene

Abstract Polythiophene films synthesized by electrochemical polymerization under various conditions were undoped and redoped maximally with iodine. The electrical conductivity of the redoped films was in the range 2 × 10 2 − 5.9 S cm −1 . Vibrational spectra of the undoped films were analysed on the basis of those of model compounds including 2,2′-bithiophene, 2,2′:5′,2″-terthiophene and 2,2′:5′,2″:5″,2′-quaterthiophene. First, the intensity ratio of the infrared CH out-of-plane bending bands at 697 (2-substituted thiophene) and 787 cm −1 (2,5-substituted thiophene) is a clue to the degree of polymerization. Secondly, the intensity ratio of the infrared double-bond symmetric and antisymmetric stretching bands reflects the distribution in length of the conjugated segment. Finally, the intensities of three Raman bands at 1155, 682 and 652 cm −1 give information about the amount of distorted structure around the inter-ring C-C bonds. From the comparison of the spectroscopic and conductivity data, it is concluded that a high degree of polymerization alone is not adequate for a doped film to have high electrical conductivity but abundance of long conjugated coplanar segments is the requisite condition.

Metal-support interaction in alumina-supported Pt catalysts

Abstract The suppression of hydrogen chemisorption (a drastic decrease of the H 2 chemisorption capacity by H 2 pretreatment at 500 °C and its recovery by O 2 pretreatment at 450 °C followed by reduction in H 2 at 300 °C) in the case of Pt Al 2 O 3 was studied by volumetric adsorption of H 2 , the consumption measurements of H 2 and O 2 during the pretreatments, XPS, and ir. The extent of the suppression was increased remarkably when the sulfur content in the catalysts became high (as high as 0.3 in terms of the atomic ratio S Pt ), However, XPS and ir results showed little change both in the total amount of sulfur and in the relative amount of sulfide and sulfate through the course of the pretreatments. Furthermore, there was the close correlation between the decrease (or increase) in the amount of H 2 chemisorption and the amount of H 2 (or O 2 ) consumption during the pretreatments. These results indicate that the suppression cannot be explained with such a simple mechanism as poisoning via reversible redox reaction of sulfur. We propose the following reaction as a plausible redox reaction taking place during the pretreatments: Pt + A1 2 O 3 Pt · Al 2 O 2 [ or PtAl 2 3 · 2 3 ( A 1 2 O 3 ] where Pt · Al 2 O 2 represents the composition of surface species consistent with the quantity of H 2 (and O 2 ) consumed. This mechanism suggests the existence of a metal-support interaction in the Pt Al 2 O 2 system. The role of sulfur is presumably to catalyze (as a promoter) this reaction, although the detailed mechanism will be the subject of further investigation.

Nuclear magnetic resonance and X-ray photoelectron spectroscopic investigation of lithium migration in montmorillonite

When Li-saturated montmorillonite is heated to 200–300 °C, the Li ions migrate from interlayer positions to sites in the layer structure. However, the identity of these sites has not been clearly established. Here we have investigated the migration of Li ions in montmorillonite, after heat treatment at 250 °C, using chemical and instrumental analyses. The latter include X-ray diffractometry (XRD), 7Linuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Heating causes a large reduction in cation exchange capacity (CEC) and an almost complete loss of interlayer expansion with glycerol as shown by XRD. Static and magic angle spinning (MAS) 7Li-NMR spectroscopy shows that the quadrupole coupling constant of Li increases markedly over the corresponding value for unheated Li-montmorillonite (where Li occupies exchange sites in the interlayer space) and for hectorite (where Li is located in the octahedral sheet). This would indicate that, in heated montmorillonite, Li occupies structural sites of low symmetry which, however, cannot be identified with octahedral vacancies in the layer structure as is commonly assumed. XPS shows that the binding energy (BE) for Li in unheated montmorillonite is comparable to that for other exchangeable cations. Heating broadens the Li 1s band and decreases the BE. The BE for Li in heated montmorillonite is significantly higher than that in either spodumene or lepidolite, where Li is known to occupy octahedral sites. The combined data suggest that heating induces Li to migrate from interlayer sites to ditrigonal cavities in the tetrahedral sheet, rather than into vacancies in the octahedral sheet, of montmorillonite.

Surface characterization of acid-leached olivines by X-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectroscopy was used to study the surface alteration of olivines (fayalite and forsterite) during acid dissolution (0.05 mol 1 −1 H 2 SO 4 at room temperature for one day). The abundances of Fe and Mg, relative to Si, in the near surface of olivines decreased after acid dissolution. The divalent cations in the fayalite were removed more readily than those in the forsterite. After acid dissolution, the Si 2s and O 1s spectra of fayalite were deconvoluted to contributions from unleached and leached phases. The Si 2s and O 1s binding energies were higher for the leached phase relative to the unleached phase, and comparable to those of silicon dioxide (quartz and silica gel), indicating that SiO 2 · n H 2 O formed on the mineral surface. Scanning electron micrographs of the leached olivine grains showed a harshly etched structure for fayalite and a locally etched structure for forsterite, indicating that the dissolution proceeded heterogeneously.

Photosynthetic pigments and perylene in the sediments of southern basin of Lake Baikal

Depth profiles of carotenoids, chlorophylls and related pigments in the sediments of the southern basin of Lake Baikal were analyzed. The photosynthetic pigments were found to be preserved through the sediment cores which spanned several hundreds years. Pigments originating from green algae, diatoms, Cryptophyceae and cyanobacteria were abundant in the sediments and a major part of chlorophylls a and b were preserved as pheophytin. Biogenic perylene was detected throughout the core layers and its presence indicates that the sediment had been anoxic.

Non-stoichiometric dissolution of lanthanum fluoride (LaF3) and its relevance to a process of ion-selective charge separation at the solid ⋯ solution interface

Abstract The solubilities of lanthanum fluoride (LaF3) powder and single crystals were measured in various aqueous electrolyte solutions. In contrast with the classical assumption of the stoichiometric dissolution of LaF3, it was found that the dissolution of the component cation La3+ was undetectable and the fluoride ion dissolved preferentially: cF−> 3cLa3+ where c is the ion concentration. X-ray photoelectron spectroscopy (XPS) of the LaF3 surface treated with electrolyte solutions corroborated this observation. As a result of the preferential fluoride dissolution, charge separation was expected to occur in such a way that the LaF3 surface would have positively charged “fluoride-vacancies”. This was confirmed by changes in membrane potential as a function of the fluoride dissolution the adsorption of an anionic adsorption marker (eosin Y) on the solid surface. It was also found that the preferential dissolution of fluoride ions was accompanied by simultaneous adsorption of almost the same amount of electrolyte anions (e.g. NO 3−) onto the LaF3 surface. This was confirmed by both solution measurements and surface analysis by diffuse reflectance IR Fourier transform (DRIFT) spectrometry. The result of this anion adsorption was explained in terms of ion exchange to ensure electroneutrality in the bulk of the adjacent electrolyte solution, which would otherwise be violated by the preferential fluoride dissolution. The anionic adsorption marker and DRIFT measurements were used to characterize further the above-mentioned ion exchange and selective uptake of fluoride ions into the “fluoride vacancies”. Release of the adsorbed eosin Y or electrolyte anions, such as NO3−, from the LaF3 surface was found to be induced by F− or OH− ions only. On the basis of this observation, the response mechanism of the fluoride ion-selective electrodes was discussed.

Triphenyltin compounds in mussels in Tokyo Bay after restriction of use in Japan

The changes in the concentration of triphenyltin (TPT) in mussels (Mytilus edulis) have been monitored since the restriction of TPT usage in marine antifouling paints started in 1989 in Japan. Mussels were collected at two locations in Tokyo Bay from 1989 to 1991. The TPT concentration in mussels has rapidly decreased at both sites. The average half life of TPT in mussels in Tokyo Bay was calculated to be 133 days. No significant decrease of TPT concentration was observed in the sediment at the center of the bay.

Characterization of arsenic in lake sediments by X-ray photoelectron spectroscopy

Arsenic in the sediments of Lake Usori (Usori-ko or Osoresan-ko) and Lake Mashu (Mashu-ko) has been characterized by X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy and shown to exist as sulfide and arsenite, respectively. In the Lake Mashu sediment, surface concentration of As determined by XPS was significantly higher than the average concentration.

Olefin metathesis over well-defined active fixed molybdenum catalysts. Structure and oxidation state of the active site and reaction mechanism

Fixed Mo catalysts (supported molecular catalysts), synthesised using the facile reaction between Mo (π-C3H5)4 and the surface acidic OH groups of alumina, silica and silica–alumina, were found to be very active for propene and but-1-ene metathesis in the temperature range 268–308 K. The isolated and coordinatively unsaturated Mo4+ species which are chemically bonded to the support surface are the active species. The nature of the ligands and supports coordinated to the Mo4+ ions produce different catalytic activities and selectivities. The support also works as a reservoir/supplier of reactants. Metathesis on fixed Mo catalysts is explained by a one-site chain mechanism involving carbene intermediates.