Mitsunobu Iwasaki

Photocatalytic activity of rutile-anatase coupled TiO2 particles prepared by a dissolution-reprecipitation method.

Rutile TiO(2) particles were partly dissolved into aqueous solutions of H(2)SO(4), and the Ti(4+) ions were reprecipitated by adding NH(3) aq. Rutile-anatase coupled TiO(2) particles were prepared by heating the solid recovered after centrifugation of the suspension. The content of anatase (c(A), wt%) could be controlled arbitrarily by changing the dissolved amount of rutile. The photocatalytic activity for the gas-phase oxidation of acetaldehyde was evaluated. The first-order rate constant, k, strongly depended on both c(A) and heating temperature (T(c)), increasing with an increase in T(c) at T(c)</=800 degrees C. The sample with c(A)=0.5 wt% prepared at T(c)=800 degrees C exhibited a much higher level of activity (k=0.94 h(-1)m(-2)) than those of pure rutile (k=0.08 h(-1)m(-2)) and anatase (k=0.34 h(-1)m(-2)). This remarkable enhancing effect was explained mainly in terms of photoinduced interfacial electron transfer from anatase to rutile.

Rapid electroplating of photocatalytically highly active TiO2-Zn nanocomposite films on steel

Nanocomposite films consisting of TiO2 and Zn with thickness of 10–15 μm (TiO2-Zn) have been electrodeposited on steel plates by rapid plating from a ZnSO4-based bath (Id > 10 A dm−2). Upon addition of NH4NO3 to the bath (<0.3 g L−1), the uptake of TiO2 in the film significantly increased. Glow discharge optical emission spectrometry clarified that TiO2 particles were incorporated throughout the film and the loaded amount increased near the surface. The first-order rate constant (k/h−1) for gas-phase CH3CHO oxidation was employed as an indicator of the photocatalytic activity. The k value for the TiO2-Zn film prepared at Id = 12 A dm−2 (0.20 h−1) was comparable to that for the sample from a ZnCl2-based bath at Id = 4 A dm−2 (0.27 h−1). X-ray diffraction measurements indicated that a TiO2-ZnO nanocomposite layer was generated on the surface by the heat treatment in air at 673 K for 6 h. Consequently, the photocatalytic activity was further improved (k = 0.29 h−1); this effect was explained in terms of the synergy of TiO2 and ZnO in photocatalysis.

Photocatalytically Highly Active Nanocomposite Films Consisting of TiO2 Particles and ZnO Whiskers Formed on Steel Plates

Nanocomposite films consisting of TiO 2 particles and Zn (thickness, 10 to 15 μm) were formed on steel plates (TiO 2 -Zn/steel) by using an occlusion electrodeposition method. Scanning electron micrographs demonstrated that TiO 2 particles were incorporated throughout the film. The TiO 2 uptake increased significantly with addition of NO 3 - ions to the electrodeposition bath. A positive correlation was observed between the TiO 2 uptake and the photocatalytic activity for gas-phase oxidation of CH 3 CHO. Postannealing of the TiO 2 -Zn/steel sample in air at 673 K produced ZnO whiskers with a preferred orientation of (1011) plane, while the same treatment of the Zn/steel sample yielded granular ZnO polycrystals. The TiO 2 particles-ZnO whiskers composite film exhibited a very high photocatalytic activity, which was greater than of the TiO 2 -Zn/steel sample by a factor of 1.5.

Synthesis of nanometer-sized hematite single crystals through NAC-FAS method

Nanometer-sized spherical hematite single crystals were prepared by heating the precipitate which was synthesized from Fe(OH)(CH3COO)2 and NaOH in alkaline ethanol-water solutions without the deliberate addition of surfactants or adsorbing ligands. Hematite nanocrystals (5–10 nm in diameter) and ferrihydrite (<5 nm) were obtained from the mixture of H2O/EtOH (Rs) = 100 ml/100 ml as a initial medium, whereas goethite, hematite (20–40 nm), and ferrihydrite were precipitated at Rs = 200/0. Adsorbing ligands such as acetoxy groups and ethanol on particles retarded the hematite growth and goethite formation. TEM observation of the particles prepared at Rs = 100/100 with heat treatment at 400°C for 2 hours showed them consisting of single spherical hematite crystals 22 nm in mean diameter with narrow size distribution. Various individual effects were investigated for their contributions to crystal structure and size of precipitates; they included NaOH to Fe(OH)(CH3COO)2 ratio, solvent, dropping rate of alkaline solution, and aging time.

Fabrication of platy apatite nanocrystals loaded with TiO2 nanoparticles by two-step emulsion method and their photocatalytic activity

Nanometer-sized TiO(2) island structure on the platy hydroxyapatite nanocrystals (HAp) has been accomplished by two-step emulsion process. At the first step, platy HAp nanocrystals, of which size was in the range of 70-200 nm after heat-treatment at 1078 K for 1 h, were prepared using the W/O emulsion system. Before the second step, HAp nanocrystals were immersed in NaH(2)PO(4) solution for the formation of hydroxyl group on their surface. In the following, titanium tetraisopropoxide reacted with the hydroxyl group of HAp surface to form TiO(2) nanoparticles on the surface of HAp nanocrystals, which were dispersed in the micrometer-sized methanol droplets of polyethylene cetylether-cyclohexane mixture (methanol/oil emulsion). The resulting hydroxyapatite nanocrystals loaded with TiO(2) nanoparticles showed the high photocatalytic activity comparing to the commercial TiO(2) catalyst.

Preparation of Ce3+-Doped Inorganic-Organic Hybrid Materials Using Functionalized Silanes

Ce3+-doped, inorganic-organic hybrid monoliths were prepared from Si(OCH3)4, CH3 Si(OCH3)3, CeCl3 and various functionalized silanes (FSs) such as amino- (APTM), glycidyloxy- (GPTM), trifluoro- (TFTM) and chloro-(CPTM) silanes at 60°C by the sol-gel process. The functional groups of silane coupling agents coordinated with Ce3+ ions in the inorganic-organic materials. Ce3+-doped materials were transparent under the preparation conditions of FS/Ce3+ ratio of 100 and 1.0 × 10−4 mol/cm3 of Ce3+ concentration. Optical properties such as absorption spectra, emission spectra and fluorescence quantum yield for the Ce3+-doped hybrid materials were strongly affected by the Ce3+ ion environment. Emission spectra were observed for the Ce3+-doped materials below 400 nm. The emission intensities of the materials prepared from TFTM, CPTM and without FS were approximately 100 times as much as those of materials prepared from APTM and GPTM. The fluorescence quantum yield was highest (11%) for the material prepared from TFTM hybrid materials.

Synthesis of nanometer-sized WO 3 particles by facile wet process and their photocatalytic properties

Nanometer-sized WO3 particles were prepared from alkaline alcohol-water mixture with WCI6 and NH3 under reflux. The resultant particles at various NH3/W mole ratios were well crystallized ranging 5-20nm in diameter and the surface area was in the range of 13.70-32.50 m2g-1. Samples synthesized at NH3/W = 3.2 and 12.9 ratio (mol/mol) had an absorption edge in the visible light range and showed the photocatalytic activity under the irradiation of visible light, and the surface area and the crystallinity of those powders had a strong effect on the photocatalytic degradation. When ln(C0/C)(C0: initial concentration of acetaldehyde, C: final concentration of acetaldehyde after irradiation) was plotted against photoirradiation time, the degradation velocity constant (k) against acetaldehyde estimated from the slope of lines was 12.4 h-1g-1 at NH3/W = 3.2 and 13.9 h-1g-1 at NH3/W = 12.9 ratio (mol/mol), respectively.

Synthetic Conditions and Color Characteristics of Tantalum Oxynitride Prepared via Liquid- Process

Tantalum oxynitrides, such as TaON, exhibit promising color properties and can be employed as nontoxic yellow pigments containing no heavy metals. We have developed a process for preparing nitrides or oxynitrides involving the vacuum-calcination of a precursor material obtained via reaction between a metal halide and liquid . Herein, we describe the synthetic conditions of the liquid- process that affect the color, and thus the color characteristics, of the resulting pigments. Reaction and postreaction treatment conditions were adjusted to obtain the desired yellow color. The liquid- process was performed using 1.0 eq of (relative to ) as the oxygen source and 30.0 eq of KCl (relative to ) as flux. Calcination of the precursor at 1073 K under vacuum was followed by recalcination from room temperature to 973 K at rate of 10 K under air. A powder with a color index of , , and was obtained.

Blue emission of YMO4:Eu2+ (M=V,P) nanocrystals prepared through facile wet process

Nanometer-sized YPO4:Eu and YVO4:Eu particles were prepared from alkaline alcohol-water mixture with Y(NO3)3 6H2O, EuCl3 and H3PO4 (or NH4VO4) under reflux. The resultant particles were well crystallized ranging 10-50 nm in diameter by changing reaction conditions. Europium ions in YPO4:Eu and YVO4:Eu was successfully reduced to Eu2+ ions by sodium borohydride under reflux. The peak position of blue emission due to Eu2+ ions (4f-5d transition) in nanocrystals was different among the materials (Y2O3, YVO4 and YPO4).

Preparation of La2O3-TiO2-SiO2 Inorganic-Organic Hybrid Materials and Their Optical Properties

Inorganic-organic hybrid materials in La2O3-TiO2-SiO2 system were prepared from La(NO3)3, titanium tetraisopropoxide, and silicon alkoxides. Ternary transparent materials prepared from glycidyloxypropyltrimethoxysilane (GPTS) were obtained in a wide composition region (La2O3 ≤ 50 mol%, TiO2 ≤ 40 mol%). Hybrid materials prepared using methyltrimethoxysilane (MTMS) at MTMS/TMOS = 1 were transparent in the composition of La2O3 ≤ 30 mol% and TiO2 ≤ 25 mol%. La(NO3)3 crystallines or TiO2 small particles were precipitated in translucent materials. La2O3 content strongly affected the bulk density compared with TiO2 content. Absorption edge of the hybrid materials was shifted to longer wavelength as TiO2 and La2O3 contents increased. Partial coefficient of refractive index for the three metal oxides increased in the order SiO2 < TiO2 < La2O3 for both hybrid materials.