Atsuo Yasumori

Large-Scale Fabrication of Ordered Nanoporous Alumina Films with Arbitrary Pore Intervals by Critical-Potential Anodization

Various ordered nanoporous alumina films with arbitrary pore intervals from 130 to 980 nm were fabricated on aluminum by a critical-potential anodization approach with sulfuric, phosphoric, oxalic, glycolic, tartaric, malic, and citric acid electrolytes under 70-450 V. The pore intervals of the porous alumina films were linearly proportional to applied potentials, with corresponding dominated territories to the electrolytes. In addition to pore interval, the self-ordering extent of pore arrangement was also improved with increasing anodizing potentials, leading to highly ordered porous alumina films at critical-high potentials. A cell separation phenomenon occurred for the films formed in sulfuric and glycolic acid solutions at the critical potentials, thus leading to the formation of highly ordered alumina nanotubule arrays. The critical-potential anodization in the other electrolytes produced self-organized porous alumina films with two-layered pore walls and pore bases. The basic principle for achieving porous alumina films with desired pore intervals is controlling the balance of the growth of barrier layer and the pore generation by adjusting the acidity, the concentration, and temperature of electrolytes. The porous alumina films formed in various electrolytes were transparent, and the transmittances of the films were inversely proportional to the applied potentials or the pore intervals.

Size- and Shape-Controlled Conversion of Tungstate-Based Inorganic–Organic Hybrid Belts to WO3 Nanoplates with High Specific Surface Areas

Two-dimensional monoclinic WO(3) nanoplates with high specific surface areas are synthesized through a novel conversion process using tungstate-based inorganic-organic hybrid micro/nanobelts as precursors. The process developed involves a topochemical transformation of tungstate-based inorganic-organic hybrid belts into WO(3) nanoplates via an intermediate product of H(2)WO(4) nanoplates, utilizing the similarity of the W-O octahedral layers in both H(2)WO(4) and WO(3). The as-obtained WO(3) nanoplates show a single-crystalline nanostructure with the smallest side along the [001] direction. The WO(3) nanoplates are 200-500 nm x 200-500 nm x 10-30 nm in size, and their specific surface areas are up to 180 m(2) g(-1). Photocatalytic measurements of visible-light-driven oxidation of water for O(2) generation in the presence of Ag(+) ions indicate that the activity of the as-obtained WO(3) nanoplates is one order of magnitude higher than that of commercially available WO(3) powders.

Eu-Doped CaAl2Si2O8 Nanocrystalline Phosphors Crystallized from the CaO – Al2O3 – SiO2 Glass System

A new process to synthesis Eu-doped CaAl 2 Si 2 O 8 (CaAl 2 Si 2 O 8 :Eu) nanocrystals coated with SiO 2 is proposed. In this process, CaAl 2 Si 2 O 8 :Eu nanocrystals were precipitated in a SiO 2 -rich matrix through phase separation and crystallization. Eu-doped CaO-Al 2 O 3 -SiO 2 system glasses, with a composition of (x - 1)SiO 2 -(100 - x)CaAl 2 O 4 -1Si mol % in the immiscibility region, were prepared by a conventional melt-quenching process. They were heat-treated for phase separation and crystallization to precipitate the CaAl 2 Si 2 O 8 :Eu crystals into the phase separated glass. We succeeded in obtaining CaAl 2 Si 2 O 8 :Eu crystals in a SiO 2 -rich matrix, composed of glass and α-cristobalite phase. These glasses and glass ceramics show blue luminous properties due to the 4f 7 -4f 6 5d 1 transition of the Eu 2+ ions. The blue-emission intensity of the glass ceramics containing CaAl 2 Si 2 O 8 :Eu significantly depended on the heat-treatment time for phase separation and crystallization.

Preparation of water-dispersible TiO2 nanoparticles from titanium tetrachloride using urea hydrogen peroxide as an oxygen donor

TiO2 nanoparticles were prepared from titanium tetrachloride (TiCl4) in CH2Cl2 at 80 °C for 30 h, 42 h and 70 h using urea hydrogen peroxide (UHP) as an oxygen donor with a TiCl4u2006:u2006UHP molar ratio of 1u2006:u20062. The XRD patterns and Raman spectroscopy results showed that the products consisted of anatase TiO2. IR and solid-state 13C NMR with cross polarization and magic angle spinning techniques revealed the presence of urea. TEM observation revealed that the products prepared by the reactions for 30 and 42 h consisted of water-dispersible spheroid nanoparticles with a long axis of ~5 nm, while an aggregation of nanoparticles was evident upon reaction for 70 h. Thermogravimetry, inductively-coupled plasma emission spectrometry and CHN analysis showed that the amount of urea increases in the following order: TiO2_42h, TiO2_70h, TiO2_30h. The photocatalytic activity of the products dispersible in water (TiO2_30h and TiO2_42h) was estimated based on the degradation behaviour of methylene blue, and TiO2_42h showed higher photocatalytic activity than TiO2_30h. It is proposed that TiCl4 was directly oxidized by UHP to form anatase TiO2 in the early stage of the process.

Hydrogen gas-sensing properties of Pt/WO3 thin film in various measurement conditions

A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO3). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO3 thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO3 thin films prepared at 400xa0°C showed the largest change in optical transmittance and electrical conductivity when exposed to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance of W5+ in the thin films depend on the equilibrium reaction between injection and rejection of H+ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations.

Investigation of Electrical Hydrogen Detection Properties of Pt/WO3 Thin Films Prepared by Sol-Gel Method

Platinum (Pt)nanoparticle-dispersed tungsten trioxide (WO3) thin film is a gasochromic material that changes color from transparent to blue in an H2 gas atmosphere. The electrical conductivity of Pt-nanoparticle-dispersed WO3 is dependent on inserted protons and electrons, though the material is insulator in air, because these electrons and protons work as electrical carriers in WO3. In this study, Pt-nanoparticle-dispersed WO3 thin films were prepared using the sol-gel process, and the optical and electrical properties were evaluated in an atmosphere with or without H2 gas. Pt/WO3 thin films prepared at 400°C showed the largest change in electrical conductivity when exposed to 1% H2 gas compared with thin films prepared at other temperatures. The electrical conductivity of the film was dependent on an H2 gas concentration in the range from 100 ppm to 1%. Pt/WO3 thin films prepared by the sol-gel process are expected to be used for H2 gas sensor devices due to the linear relationship between the electrical conductivity and H2 gas concentration.

Preparation of gold nanoparticle-loaded silica gels and their localized surface plasmon resonance sensing properties

AbstractnLocalized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) has been used for biosensing and chemical sensing applications because the LSPR peak wavelength depends on the dispersion state and local refractive index of the surrounding medium. In this study, AuNP-loaded silica gels were prepared as sensing chips with high transparency and solution holding capability. The silica gels were prepared at various sintering temperatures from 500 to 900xa0°C, and the AuNPs precipitated in the gels by using a subsequent thermal reduction process. At sintering temperatures of 700, 800, and 900xa0°C, transparent and crack-free AuNP-loaded silica gels were obtained. Transmission electron microscopy observation revealed the AuNP size to be approximately 20xa0nm, and they were highly dispersed in all the silica gel samples. However, the sintering temperature of the silica gels strongly affected the LSPR property of the AuNPs and the porous property of the silica gel. The samples sintered at higher temperature exhibited a lower LSPR sensing ability against the refractive index of immersing solvents. The low sensing ability was considered as a result of a decrease in the contact area between the AuNPs and immersing solvent caused by an increase in the silica gel density with sintering temperature.

Magnetic properties of phase separated Fe3O4-TiO2-SiO2 glasses prepared from a two-liquids immiscible melt

The glassy composite materials were prepared by quenching the phase separated melts in two-liquids immiscibility region of Fe3O4-TiO2-SiO2 ternary system. The fine phase-separation textures which consisted of Fe-Ti rich phase and Si rich one were formed in the samples, and the precipitation of Fe3O4-TiO2 solid solution was observed in the samples of the specific compositions. The samples containing Fe3O4-TiO2 solid solution showed ferrimagnetic properties on their magnetization curves. In low Fe3O4-TiO2 content, coercivity increased with increase of Fe3O4-TiO2 content since the precipitated particles in the samples grew and had single magnetic domain. In high Fe3O4-TiO2 content, the coercivity decreased with increase of Fe3O4-TiO2 content because the magnetostatical interparticle interaction among the precipitated particles appeared. These results indicate that the magnetic properties of the composite materials owing to the crystalline phase and its size can be controlled by utilizing the phase separation in this system.

Magnetic properties of glass ceramic in Fe3O4-MnO2-SiO2 system

The magnetic glass-ceramics was prepared by a melt-quenching method with the phase-separated melts in two-liquids stable immiscibility region of Fe3O4-MnO2-SiO2 system. The obtained glass-ceramics had spinel single phase of Fe3O4-MnO2 solid solution, and showed ferromagnetic properties. The saturated magnetization became a maximum by adding a small amount of MnO2 with low coercive force. These properties of both high magnetization and low coercive force by Mn doping are very effective to realize the magnetic materials for the hyperthermia treatment.

Photo Etching of Polyimide Thin Film by TiO 2 Micro Wire Prepared Using Phase Separation-Selective Leaching Method

TiO 2 photocatalysts have a strong oxidation ability for organic compounds under UV irradiation. The surfaces of polyimide and polymethyl methacrylate (PMMA) were photocatalytically machined using a porous TiO 2 wire prepared by phase separation and selective leaching with elongation. After UV irradiation, these surfaces were decomposed along the length of the TiO 2 wire. Such surface decomposition depended on the irradiation angle of UV light and irradiation time. The machining rate of PMMA was higher than that of the polyimide.