Tsugio Sato

Synthesis of hydrotalcite-like compounds and their physico-chemical properties

Mixed metal hydroxides with hydrotalcite-structure, [M2+1−xMx3+(OH)2]An−x/n·mH2O (M2+ = Mg2+, Ni2+, Co2+, M3+ = Al3+ Fe3+, An− = CO2−3) were synthesized by coprecipitation. For a number of these materials, the physico-chemical properties such as the solid solubility limit of M3+, thermal decomposition, reconstitution reaction mechanism and solubility in water at 25°C, have been studied in detail.

Preparation of nitrogen-doped titania with high visible light induced photocatalytic activity by mechanochemical reaction of titania and hexamethylenetetramine

Nitrogen-doped yellowish rutile titania was prepared by a mechanochemical method. The samples were prepared by high-energy ball milling of a P-25 titania powder with various amounts of hexamethylenetetramine (HMT) under different milling conditions at around room temperature. The effects of the reaction conditions on the phase composition, particle size, specific surface area, amount of nitrogen-doping, microstructure and photocatalysis of nitrogen monoxide destruction were investigated in detail. The high mechanical energy accelerated the transformation of the phase from anatase to rutile, while the presence of HMT decreased the phase transformation. Residual HMT and by-products could be removed by post-milling calcination in air at 400 °C. The nitrogen-doped yellowish titania possessed two absorption edges at around 400 and 550 nm and showed excellent photocatalytic ability for nitrogen monoxide oxidation under visible light irradiation. Irradiation with visible light of wavelength >510 nm allowed nearly 37% nitrogen monoxide to be continuously removed by the nitrogen-doped titania prepared by planetary ball milling of a P-25 titania–10 wt% HMT mixture at 700 rpm for 120 min followed by calcination in air at 400 °C.

Mechanochemical synthesis of SrTiO3−xFx with high visible light photocatalytic activities for nitrogen monoxide destruction

Fluorine doped SrTiO3 powders were prepared by a mechanochemical reaction method. The powders consisted of spherical particles of 20 nm and 0.1–0.2 µm in diameter. The photocatalytic activities of SrTiO3 for the oxidative decomposition of NO under visible light (λ > 400 nm) and near ultraviolet light (λ > 290 nm) irradiation were greatly improved by the fluorine doping. Fluorine doping in the SrTiO3 lattice enhanced its photocatalytic activity under irradiation with visible light (λ > 400 nm) ca. three times. It was also found that the photocatalytic activities of SrTiO3−xFx under both visible light and near ultraviolet light irradiation were higher than those of commercial titania powder (Degussa P-25).

Synthesis and UV-shielding properties of metal oxide doped ceria via soft solution chemical processes

Abstract Ultrafine particles of M 2+ doped ceria (M 2+ =Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ ) for use as a UV filter have been prepared via soft solution chemical routes at 40°C. X-ray diffraction revealed that the prepared doped particles had cubic fluorite structures, although the peak positions changed depending on the kind and amount of the doped metal ion. Doping with 20 mol% Ca 2+ and 20 mol% Zn 2+ resulted in a considerable decrease in the particle size (2–4 nm) and catalytic activity of ceria for oxidation of castor oil. CaO doped cerium dioxide showed excellent UV absorption and transparency in the visible ray region compared with undoped cerium dioxide.

Crystallization of Titania in Liquid Media and Photochemical properties of Crystallized Titania

Titania gels in liquid media crystallized from amorphous to anatase at temperatures as low as 120 ±C, while the onset of crystallization in air was 370 ±C. The crystallization rate in water was much faster than in methanol and n-hexane, and the crystallite size of anatase prepared in water was larger than of those prepared in organic solvents. The crystallized powders were capable of efficient hydrogen evolution following band gap irradiation in the presence of a sacrificial hole acceptor such as methanol. The photocatalytic activity of powder crystallized in methanol was superior to those prepared in water and air.

Facile synthesis of homogeneous CsxWO3 nanorods with excellent low-emissivity and NIR shielding property by a water controlled-release process

A systematic investigation of the synthesis of homogenous CsxWO3 nanorods by a designed water-controlled release process was carried out. The results revealed that the uniform rod-like CsxWO3 nanoparticles with a Cs/W atomic ratio of ca. 0.33 can be obtained by using 20 vol% CH3COOH–80 vol% CH3CH2OH mixed solution as a reaction solvent at 240 °C for 20 h. The morphology of products were changed depending on the speed of water-releasing process, meanwhile, the Cs/W atomic ratio could be controlled by both the amount of released water and the reaction temperature. CsxWO3 nanorods showed a high transmittance in the visible light region and excellent shielding ability of near infrared (NIR) lights, indicating that CsxWO3 nanorods have a suitable characteristic as solar filter applications.

Preparation and chemical properties of magnesium aluminium oxide solid solutions

Magnesium aluminium oxide solid solutions were prepared by thermal decomposition of hydrotalcite-like compounds, [Mg1−xAlx,(OH)2](CO3)x2·mH2O, at 500–700°C. The Nad-type solid solutions with a cation defect structure of Mg2(1−x)(2+x)Al2x(2+x)XXXx(2+x)O were formed in the range 0.15 ⩽ Al/(Mg+Al) ⩽ 0.33. Magnesium aluminium oxide hydrated and took up carbonate ion from aqueous solution to reconstruct the hydrotalcite-type structure. Phosphate was also taken up, at a rate that decreased with increasing thermal decomposition temperature from 500 to 700°C, although the nature of the product in this instance was not established. The solid solutions decomposed above 1000°C to MgO and MgAl2O4, which showed no capacity to take up anions.

Synthesis of W18O49 Nanorod via Ammonium Tungsten Oxide and Its Interesting Optical Properties

W(18)O(49) nanorods were synthesized by pyrolyzing (NH(4))(x)WO(3+x/2) nanorods precursors, which were prepared by a hydrothermal reaction using sulfate as a structure-directing agent, in a reductive atmosphere of H(2)(5 vol %)/N(2) at 500 °C for 1 h. W(18)O(49) nanorods showed high transmittance in the visible region as well as excellent shielding properties of NIR lights. A simulated experiment revealed that excellent heat insulating performance can be realized by applying a 70% visible light transparent W(18)O(49) coating on a quartz glass. Meanwhile, the W(18)O(49) nanorods also showed strong absorption of NIR light and instantaneous conversion of photoenergy to heat. In a word, W(18)O(49) nanorods hold interesting optical properties and are a promising material in a wide range of applications.

Synthesis of One-Dimensional Potassium Tungsten Bronze with Excellent near-Infrared Absorption Property

Potassium tungsten oxide nanofibers were successfully synthesized via a facile hydrothermal reaction route in the presence of sulfate. After reduction under a reductive atmosphere of H(2)(5 vol %)/N(2), the potassium tungsten oxide transformed to potassium tungsten bronze. Because of the lack of free electrons, the potassium tungsten oxide (K(x)WO(3+x/2)) showed no NIR shielding performance; however, the potassium tungsten bronze (K(x)WO(3)) showed promising optical characteristics such as high transmittance for visible light, as well as high shielding performance for near-infrared lights, indicating its potential application as a solar filter. Meanwhile, the potassium tungsten bronze (K(x)WO(3)) showed strong absorption of near-infrared light and instantaneous conversion of photoenergy to heat.

Synthesis and photochemical properties of semiconductor pillared layered compounds

Abstract CdS and ZnS mixtures, Fe2O3 and TiO2 pillars were constructed in the interlayer of montmorillonite, layered double hydroxide, H4Nb6O17 and H2Ti4O9 by the intercalation reactions. The thicknesses of the semiconductors incorporated were less than 1 nm and the band gap energies of them were slightly larger than those of normal crystalline ones. The photocatalytic activities of the semiconductors incorporated were superior to those of unsupported ones. The incorporation of semiconductors in the interlayers of semiconducting layered compounds such as H2Ti4O9 and H4Nb6O17 was much more efficient in enhancing the hydrogen production activity than when an insulator such as montmorillonite and layered double hydroxide was used, since the recombination of photo-induced electrons and holes was depressed by the electron transfer from the incorporated semiconductors to the semiconducting host layer.