Takashi Shirakashi

Oxygen reduction on Au nanoparticle deposited boron-doped diamond films

Nanoparticle Au was deposited on as grown boron-doped diamond (BDD). The coverage and the morphology of the deposited Au particles were investigated by means of the linear sweep voltammeter and scanning electron microscopy (SEM). From SEM, the gold electrodeposited randomly as small spherical particles with an average diameter of 60nm. The applications of the as grown BDD film deposited by Au for electrocatalytic reduction of the oxygen in acidic solution were investigated. The catalytic efficiency of the Au deposited as grown BDD with the coverage of 0.06 is near 20 times larger than that of polycrystalline gold. The mechanism of the highly electrocatalytic active was investigated by ac impedance and hydrodynamic voltammetric methods.

Photocatalytic ZnO films prepared by anodizing

Photoactive zinc oxide films were prepared by anodizing a zinc plate. Thus, prepared films could decompose acetaldehyde gas with the aid of black lights. The photocatalytic activity was correlated to the XRD peak intensity ratio (1010):(0002).

Preferred orientation and morphology of electrodeposited iron from iron(II) chloride solution

Abstract The effects of each electrolytic condition on current efficiency, Vickers hardness, crystal structure and crystal morphology were studied with respect to the electrodeposited iron films obtained from iron(II) chloride solution. The temperature of the solution was varied from 20 to 60°C, the pH value of the solution varied from 0 to 2, and the applied current density varied from 5 to 100 mAcm −2 . Higher current efficiency was obtained at a higher solution temperature, higher pH value of the solution and lower applied current density. The films thus obtained showed a lower Vickers hardness and a preferred orientation of the (110) plane. Lower current efficiency was obtained at a lower solution temperature, lower pH-value of the solution showed a higher Vickers hardness, and a preferred orientation of the (211) plane. It is thought that these tendencies are related to the contribution of the hydrogen evolution reaction as a side reaction.

Isolation and Growth Characteristics of Nitrilotriacetate-Degrading Bacteria

Abstract Two bacterial strains that degrade nitrilotriacetate (NTA) were isolated from NTA-acclimatized activated sludge. These bacteria grew well in NTA medium with optimal pH around 7. The growth rate constants of the bacteria, strains N-2 and N-5, were 0.046 h−1 and 0.11 h−1 at the concentration of 0.1% NTA (pH 7.0, 25°C), respectively. The growth of each bacterium was inhibited at high concentrations NTA. The growth rate decreased roughly linearly with increasing concentration of NTA. The strains N-2 and N-5 showed maximal cell growth at the concentrations of 0.2% and 0.25% NTA, respectively. The strain N-2 would not grow at the concentration of 0.5% NTA. On the other hand, the strain N-5 showed a little growth under the same conditions. Also, the bacterial growth was almost completely inhibited when divalent metal ions such as Mg++, Ca++, and Fe++ were omitted from the culture medium, or slightly excess EDTA (1 mM) was added to the medium. These results suggest that the bacterial growth inhibition at high concentration of NTA is caused by the sequestration of metal ions in the medium.

Fabrication and Characterization of Diamond Quartz Crystal Microbalance Electrode

Boron-doped diamond film on a quartz crystal electrode was prepared by a reflow technique. The mass sensitivity of this diamond-quartz crystal microbalance (QCM) sensor was determined by performing Fe 2+ electrodeposition. This novel electrochemical QCM sensor was quite stable under several electrochemical experimental conditions. Its wide potential window and significantly low background current are just the same as the performance of a diamond electrode. We also showed that the fabricated diamond-QCM electrode worked satisfactorily as a useful tool for electrochemical microgravimetry by examining hydrogen evolution, oxygen evolution, and oxidation of the diamond surface in acidic solutions. It was found that evolved H 2 inserted into the bulk of as-grown diamond with a storage volume of 0.06 mol/dm 3 in 0.5 M HCl solution, after sweeping the potential from 0 to -3 V at a scan rate of 10 mV/s, in contrast to O-terminated diamond-QCM, which inhibited hydrogen intercalation.

Involvement of Ca2+ in the flocculation of Kluyvera cryocrescens KA-103

Abstract Kluyvera cryocrescens KA-103 showed a dispersed growth in Ca 2+ -free Polypepton medium, but formed flocs on addition of a sufficient concentration of Ca 2+ to the bacterial cell suspension. Therefore, calcium adsorption properties and flocculation conditions were investigated using bacterial cells cultured in the Ca 2+ -free Polypepton medium. The bacterium required 1.5 mM Ca 2+ or more for good flocculation (F>90%), but a cooperative effect of Na + and Ca 2+ on good flocculation was observed at lower concentrations of Ca 2+ . The Langmuir adsorption isotherm was used to describe the adsorption of Ca 2+ by the bacterial cells.

Isolation and characterization of a Ca++-dependent floc-forming bacterium

Abstract When sewage activated sludge was treated with a commercial proteolytic enzyme, Actinase E, 12% of the sludge was deflocculated. However, most of the deflocculated sludge was sedimented by low-speed centifugation, indicating that only a small part of the sludge was deflocculated to the level of free cells. When bacteria were isolated using the supernant cell suspensin obtained by Actinase treatmemt and the subsequent low-speed centrifugation, two Atinase E-susceptible floc-forming bacteria were isolated. In this study, flocculation in a bacterium which showed better growth in Polypepton medium was investigated. The bacterium required a slight amount of calcium ion for the flocculation. The cell flocs were completely deflocculated not only by Actinase E, but also by EDTA. Deflocculation was also observed when the flocs were suspended in distilled water. In addition, the growth rate of the bacterium was not affected by the calcium ion in the culture medium.

Extracellular polymers in relation to settling properties of activated sludge

Abstract The effects of cetyltrimethylammonium bromide (CTAB) and acid on the settling properties of activated sludge samples from various sources were investigated. The addition of CTAB or acid to mixed liquor resulted in an increase of zone settling velocity (ZSV) and a reduction of 30-min settled sludge volume (SV 30 ). The higher the amount of extracellular polymers (ECPs) extracted from activated sludge, the higher the effectiveness. The amount of cetyltrimethylammonium ion (CTA + ) adsorbed by activated sludge was decreased by the extraction of ECPs and the extracted ECPs precipitated on addition of CTAB. These results indicated that the adsorption sites for CTA + are acidic functional groups in the ECPs. The Langmuir adsorption isotherm was employed successfully to describe the adsorption of CTA + by activated sludge. The equilibrium constants ( K ) for complexes formed between CTA + and the adsorption sites of activated sludge ranged from 10 5.1 to 10 6.0 .

Camparison of mucilage polysaccharides extracted from sewage activated sludge

Abstract The sugar composition of mucilage polysaccharides extracted from activated sludge from five different sewage treatment plats were compared. All the polysaccharides contained rhamnose, fucose, arabisone, xylose, mannose, galactose, glucose, amino sugars, and uronic acids in similar proportions, especially in the neutral sugar fraction. The main components were rhamnose (12–18%), mannose (14–21%), galactose (16–19%), and glucose (15–23%). No significant changes was observed in the sugar composition of activated sludge from a sewage treatment plant over a period of more than one year. Recovery of the mucilage polysaccharides fell to 46% of the initial amount when activated sludge was digested aerobically for 10 days, but the sugar composition was not affected.

Nature of the photographic diamond surface phenomenon on boron-doped diamond

We have recently reported the photo-memory effect on boron-doped semiconducting diamond surfaces, which involves the photoelectrochemical pretreatment and subsequent sensitized deposition of copper and which we have referred to as the ‘photographic diamond surface phenomenon’ [S. Yoshihara, K. Shinozaki, T. Shirakashi, K. Hashimoto, D.A. Tryk, A. Fujishima, Electrochim. Acta 44 (1999) 2711]. In the present work, the origin of this phenomenon was investigated by AC impedance and contact angle methods. After polarization at −0.25 V versus SCE in aqueous H2SO4 solution under UV illumination, the surface exhibited the photographic effect. The polarized surface showed higher surface conductivity and increased hydrophilicity. Also, surface analysis suggested that the polarized surface has a higher surface coverage of hydrogen. These results strongly suggest that this phenomenon is related to changes of the surfacial functional groups induced by photoelectrochemical hydrogen evolution.