Papers by Author: Tsugio Sato

Abstract: Titanium carbide has been attractive for years an engineering ceramics due to its high hardness, high melting point, and good chemical stability. Similarly, titanium dioxide has excellent anti-microbial ceramic material by photon energy. In this study, the anatase type titanium dioxide layer prepared by oxidation of the titanium carbide powder by high temperature oxidation in air atmosphere was investigated in order to determine the possibility of its photocatalyst materials by radiant energy. TiC powder samples of different grain size were gained by ball mill. These samples were oxidized at room temperature to high temperature. The samples exhibited a steady mass gain with increasing oxidation temperature. Based on the results of the X-ray diffraction analysis, anatase type TiO₂ was detected on the titanium carbide samples. It is considered, the titanium carbide showed convension anatase type titanium dioxide layer produced by oxidation.

Abstract: Different valences of metal ions such as Fe3+ and Nb5+ were co-doped with nitrogen ion into titanium dioxide by hydrothermal method using metal chlorides and hexamethylenetetramine as the sources of metal ions and nitrogen ion, respectively. The co-doping of low-content metal ion showed no noticeable influence on the crystalline phases and specific surface area (S.S.A.) of the samples. Doping with Fe ion could significantly enhance the absorption in visible light region, but doping with Nb ion showed almost no effect. The photocatalytic activities of the samples were determined for the oxidative destruction of NO gas under various wavelengths. Co-doping with Nb ion improved the deNOx ability, but co-doping with Fe ion depressed it, indicating that co-doping with higher valence metal ion was effective in reducing the vacancy in the lattice which acts as the recombination center of the photo-induced electrons and holes, and achieving higher photocatalytic activity.

Abstract: Nitrogen doped titania was coupled with the commercial titania nanoparticles by mechanical milling in liquid medium. When small amount of nitrogen doped titania was added into the commercial titania, higher intensity and longer lifetime of 1O2 was observed, and the photocatalytic activity was efficiently improved. The TiO2-xNy acts as the acceptor of photoinduced holes. The recombination of the electron-hole was effectively depressed by the heterogeneous electron transfer. This could be an effective way to obtain high active photocatalyst.

Abstract: Vanadium doped, nitrogen doped, and vanadium and nitrogen co-doped SrTiO3 powders with size of 20-30 nm in diameter were prepared by high energy milling method respectively. It was found that compared with those of pure SrTiO3, the photocatalytic activities of these three doped SrTiO3 samples for decomposing NO under visible light (λ>400 nm) and near ultraviolet light (λ>290 nm) irradiation were improved, and the co-doped sample exhibited the highest photocatalytic activity. 43.2% NO could be eliminated under the irradiation of light with wavelength larger than 400nm, about 3 times higher than that by pure SrTiO3. The photocatalytic activity of this sample near ultraviolet range is about 1.7 times higher than that of pure SrTiO3. The high visible light photocatalytic activity of this substance may be due to the high visible light absorption and large specific surface area.

Abstract: White nanoparticles of calcia-doped ceria were prepared from the precipitate by reacting CeCl3-CaCl2 mixed solution with NaOH solution at pH 12 and the oxidation with hydrogen peroxide solution at 40oC, followed by the calcination at 700oC for 1 h. Ceria particles generated far less singlet oxygen and caused far less damage to the DNA plasmids upon UV illumination than either the titania or the zinc oxide reference pigments.

Abstract: Highly crystalline titania nano-particles were synthesized by hydrothermal method using novel stable water-soluble titanium complexes. It was confirmed that single phase anatase, rutile and brookite, which can be rarely synthesized as a single phase, can be obtained by varying the ligand in the complex and pH of the aqueous solution. TEM observations and BET specific surface area measurements had shown that these samples consisted of nanosized particles of 5~200 nm and had high specific surface areas of 25~150 m2/g. According to UV-visible diffuse reflectance spectra, these titania samples absorbed light in the visible region (λ > 400 nm). Photocatalytic activities in NO oxidation reaction exhibited by synthesized titania powders under the irradiation by UV- visible light were higher than the activity of the commercial TiO2 photocatalyst P25 (Degussa). Especially, under illumination by only visible light of above 510 nm wavelength, photocatalytic activity of the obtained specimens exceeded that of P25 more than four times. We also clearly demonstrated that single phase brookite had high photocatalytic activity for NO oxidation.

Abstract: White nanoparticles of calcia-doped ceria were prepared from the precipitate by reacting CeCl3-CaCl2 mixed solution with NaOH solution at pH 12 and the oxidation with hydrogen peroxide solution at 40oC, followed by the calcination at 700oC for 1 h. The sample before calcination contained significant amount of OH- in the lattice and was yellow, but the powders calcined above 700oC were white, indicating that cationic defect formed by replacing O2- with OH- played as the color center. Calcia-doped ceria particles were coated with amorphous silica by means of seeded polymerization technique using hydrolysis of tetraethylorthosilicate (TEOS) or acid hydrolysis of sodium silicate. The silica coating by seeded polymerization with TEOS was much more efficient for the reduction of catalytic activity of ceria for the oxidation of organic materials than that by acid hydrolysis of sodium silicate. It is confirmed that ceria particles caused far less damage to the DNA plasmids upon UV illumination than either the titania or the zinc oxide reference pigments.

Abstract: Novel superstructures of zinc oxide thin film with nano-rods and nano-screws were prepared via soft solution route without any polymer additives. The thin film of ZnO could be produced directly on the substrates. The yield of nano-rod and/or nano-screw was almost 100%. Small amount of nano-disk superstructure was also obtained. The superstructures of the film changed depending on the kind of treatment organic solvent such as methanol, butanol, i-propanol, hexane, etc. Monodispersed or symbiotic/multipod ZnO nanorods with hexagonal cross section or screw microstructure were successfully prepared.

Abstract: Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of its excellent UV light absorption property and low catalytic ability for the oxidation of organic materials superior to undoped ceria. The performance of calcia doped ceria needs more enhancement through further control of its oxidation catalytic activity and improvement of its covering ability. In order to reduce the oxidation catalytic activity further, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique. Generally, nanoparticles of calcia doped ceria do not provide a good coverage for human skin because of the agglomeration of the nanoparticles. The platy particles are required to enhance the covering ability of calcia doped ceria. This can be accomplished by synthesis of calcia-doped ceria/plate-like material (e.g., potassium lithium titanate (K0.8Li0.27Ti1.73O4) and mica) nanocomposite with subsequent silica coating. Calcia-doped ceria/plate-like material was prepared by soft chemical method followed by silica coating via seeded polymerization technique. Silica coated calcia-doped ceria/plate-like material nanocomposite was characterized by X-ray diffraction, SEM, TEM, XPS and FT-IR.

Abstract: Because of the low refractive indices, plate-like cerium phosphates (CePs) are expected to be used as one of active ingredients in personal suncare cosmetics. Plate-like Ce2(PO4)2HPO4･H2O particles were synthesized via solvothermal reactions of Ce(NH4)2(NO3)6 or Ce(SO4)2･4H2O in phosphoric acid with or without nitric acid and sulfuric acid solutions. The variation of morphology of Ce2(PO4)2HPO4･H2O particles significantly depended on the variety of cerium salt, isothermal temperature and time, although all reaction products consisted of plate-like particles. This plate-like compound showed excellent UV light absorption and transparency in the visible light region. Consequently, it is suggested that the plate-like Ce2(PO4)2HPO4･H2O particles might be used as suncare products to give an ideal optical effect of both UV-shielding ability and transparency in the visible light region, as well as a good feeling on the skin.