Papers by Author: Hiromi Yamashita

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Authors: Hiromi Yamashita, Yoshikatsu Nishida, Osamu Chiyoda, Hiroyuki Nose, Masaki Narisawa, Tesutaro Ohmichi, Iwao Katayama
Abstract: TiO2/SiC was prepared by oxidizing the TiC-SiC precursor obtained by carbothermic reduction process of TiO2-SiO2 binary oxide. An XRD analysis indicated the formation of the mixture of anatase and rutile phases of TiO2 crystalline after the oxidation of TiC-SiC sample. TiO2/SiC photocatalyst exhibited a higher photocatalytic reactivity than TiO2-SiO2 binary oxide prepared by the conventional sol-gel method. These results indicate the advantages of SiC nano powders as catalyst support of the TiO2 photocatalysts, and TiO2/SiC photocatalyst is effective for the degradation of organic compounds diluted in water.
Authors: Iwao Katayama, Yusuke Sendai, Dragana Zivkovic, Dragan Manasijević, Zivan Zivkovic, Hiromi Yamashita
Abstract: EMF of galvanic cell with zirconia –based solid electrolytes was measured to determine the activity of Ga in liquid Ga-Sb-Tl alloys between 946 and 1233 K along the tree pseudobinary lines of Ga-(Sb/Tl), (xSb/xTl = 1/3, 1/1 and 3/1) The cell used was: Ga,Ga2O3|(ZrO2)0.92(Y2O3) 0.08|Ga-Sb-Tl, Ga2O3. The activity of Ga (aGa ) was derived by :-3EF = RT ln aGa , where E is cell potential, F is Faraday’s constant, R is gas constant and T is cell temperature. The activity of Ga shows slight negative deviations from ideality in the section with positive deviation from ideality in the whole composition range. The activity of gallium shows slight negative deviations from Raoult’s law in the section with xSb/xTl = 3/1, moderately positive deviations in xSb/xTl =1/1 section and large positive deviations in xSb/xTl =1/3 section.
Authors: Shinichi Kawasaki, Yusuke Okada, Shuai Yuan, Kohsuke Mori, Hiromi Yamashita
Abstract: The synthesis of the hydrophobic mesoporous silica MS(F) was performed using tetraethyl orthosilicate, triethoxyfluorosilane as the source of the fluoride and dodecylamine as templates. The TiO2 loaded on the hydrophobic MS(F) (TiO2/MS(F)) exhibited the efficient photocatalytic performance for the degradation of alcohols (iso-butanol) diluted in water. The photocatalytic reactivity for the degradation increased with increasing the content of fluoride ions on these photocatalysts. The hydrophobic mesoporous surface is suitable as the photocatalytic reaction field for the degradation of organic compounds diluted water.
Authors: Masanori Tomonari, Kohsuke Mori, Hiromi Yamashita
Abstract: For the synthesis of the nano-sized Ag metal particle, the sodium borohydride for the reducing agent was added into the aqueous solution of the AgNO3 with 3-mercapto-propionic acid as protective agent. Because the surface of nano-sized Ag metal particle was protected by the adsorbed 3-mercapto-propionic acid, the synthesis of the aqueous colloid system with high density became possible. The negative charge of carboxylate anion protect the aggregation of metal particles in the solution of high pH value (pH > 5), but the aggregation was occurred in the solution of low pH value (pH < 2). By changing the quantity of the agent of propionic acid and the pH value of solution, the particle size can be controlled optionally in the range of 50~200 nm.
Authors: B. Neppolian, Hiromi Yamashita, Yusuke Okada, H. Nishijima, Masakazu Anpo
Abstract: TiO2 photocatalysts prepared by a novel multi-gelation method showed good photocatalytic activity for the degradation of 2-propanol diluted in water by the control of parameters such as particle size, surface area, crystallinity, pore-volume, pore-diameter as well as anatase and rutile phase composition by changing the number of pH swings during preparation. In particular, with this method the phase transition from anatase to rutile at higher pH swing times can be controlled and high purity and uniformity of the TiO2 particles which leads to higher photocatalytic activity of the particles can be achieved. From our experimental results, it has been observed that TiO2 catalysts prepared by this unique multi-gelation method, i.e., adopting variations in the pH swing, significantly shows higher photocatalytic activity for the degradation of 2- propanol diluted in water. It can be considered a viable alternative over existing commercial methods for the preparation of photofunctional catalysts.
Authors: Shuai Yuan, Shusuke Oakada, Keiichi Maki, Yasutaka Kuwahara, Masanori Tomonari, Shinichi Kawasaki, Kohsuke Mori, Hiromi Yamashita
Abstract: The fluorine-modified mesoporous silica HMS(F20) was synthesized by using the mixture of TEFS(SiF(OC2H5)3) and TEOS(Si(OC2H5)4) as the silica source. The specific surface and pore size distribution were characterized by N2 adsorption and the hydrophilic-hydrophobic property was measured by water adsorption. The photocatalytic activities of TiO2 nanoparticles loaded on HMF(F20) and HMS were investigated for the degradation of iso-butanol diluted in water. The results show that the fluorine-modified mesoporous silica HMS(F20) has higher hydrophobic property than HMS and the TiO2/HMS(F20) exhibits the higher photocatalytic activity than TiO2/HMS. The hydrophobic mesopores benefit the condensation of hydrophobic organic compounds diluted in water, which results in higher photocatalytic degradation efficiency.
Authors: Masaki Narisawa, Yayoi Satoh, Ryuichi Sumimoto, Takashi Kamegawa, Hiromi Yamashita
Abstract: Melt spinnable silicone resin with a low carbon content was spun to fiber form with an averaged diameter of 16.8 m. When the resin fiber was cured by SiCl4 vapor and pyrolyzed at 1273K in inert atmosphere, Si-O-C fiber with smooth surface was obtained. The measured tensile strength was relatively low. The fiber, however, showed oxidation resistance during high temperature exposure under an air flow. When the fiber was cured by TiCl4 with an increased vapor pressure at 313K, 40% mass gain was observed after the curing. SiO2-TiO2 fiber was obtained by pyrolysis in an air flow, while SiOC-TiO2 fiber was obtained by pyrolysis in an inert atmosphere. Structure of TiO2 and the resulting fiber surface morphology strongly depended on the temperature and the atmosphere during the pyrolysis.
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