Seishiro Ito

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.

Acceleration of Oxidations and Retardation of Reductions in Photocatalysis of a TiO2 / SnO2 Bilayer‐Type Catalyst

An anatase TiO 2 film (75 ± 5 nm thick) was formed on SnO 2 film (580 ± 80 nm thick) coated soda-lime glass by a sol-gel method (TiO 2 /SnO 2 /glass). Depth profiles of the compositions determined hy X-ray photoelectron spectroscopy confirmed that the amounts of Na + and F - ions are negligibly small throughout the TiO 2 film. The activities for four kinds of photocatalytic reactions (v) were examined under no external applied potential in comparison with those of a TiO 2 /quartz standard sample (ν 0 ), The TiO 2 /SnO 2 /glass bilayer-type photocatalyst showed remarkably higher activities for oxidations (ν/ν 0 = 3.0 ± 0.2), whereas the activities for reductions are lower (ν/ν 0 = 0.62 ± 0.03). These results could be explained by efficient charge separation via the interfacial electron transfer from TiO 2 to SnO 2 .

Patterning Effect of a Sol-Gel TiO2 Overlayer on the Photocatalytic Activity of a TiO2/SnO2 Bilayer-Type Photocatalyst

TiO2 films with a thickness of 75 ± 5 nm (anatase) were formed on SnO2-film (580 ± 80 nm) coated soda-lime glass substrates (SnO2/SL-glass) by a sol-gel method. Although the photocatalytic activity for CH3CHO oxidation (λex > 300 nm) significantly exceeded that of a standard TiO2/quartz sample, it decayed with illumination time (t) at t > 0.75 h. Stripes of anatase TiO2 films of 40 nm in thickness and 1 mm in width were prepared on the SnO2/SL-glass substrate in a 1-mm pitch by photolysis of an organically modified sol-gel film. The TiO2 patterning further increased the photocatalytic activity by a factor of 4.1 as compared to the non-patterned sample, and it was also maintained at 0 < t < 2 h. The flat band potentials of the TiO2 and SnO2 films are determined to be −0.34 and +0.07 V (vs. SHE), respectively, at pH = 7 by the Mott-Schottky plots. On the basis of the results, the outstanding patterning effects could be rationalized in terms of the vectorial charge separation at the interface between TiO2 and SnO2.

Heterosupramolecular photocatalysis: oxidation of organic compounds in nanospaces between surfactant bilayers formed on TiO2Electronic supplementary information available: further characterization data and experimental details. See http://www.rsc.org/suppdata/cc/b2/b204593a/

A heterosupramolecular photocatalyst consisting of TiO2 and a cationic surfactant bilayer formed on the surface has achieved a very high level of activity in the oxidation of 2-naphthol through the cooperation of the inorganic and organic components.

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.

The effect of nanometre-sized Au particle loading on TiO2 photocatalysed reduction of bis(2-dipyridyl)disulfide to 2-mercaptopyridine by H2O

TiO2 photocatalysed reduction of bis(2-dipyridyl)disulfide (RSSR) to 2-mercaptopyridine by H2O is enhanced significantly by incorporation of nanometre-sized Au particles. The rate is strongly dependent on the amount of Au loaded (x wt.%), passing through a maximum at x∽0.3, while it is almost independent of the Au particle size in the 4.3–11 nm range. Comparison of the effects of Au and Ag loading reveals that the rate constant of the Au(0.25 wt.%)/TiO2 system is greater than that of the Ag(0.24 wt.%)/TiO2 system by a factor of 2.6 and the activation energy of the former is about two-thirds that of the latter. The enhancing effect of the Au loading is discussed in terms of kinetic and molecular orbital considerations.

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.

One-pot alkaline vapor oxidation synthesis and electrocatalytic activity towards glucose oxidation of CuO nanobelt arrays

CuO nanobelt arrays supported on copper substrates are synthesized by a simple and one-pot low-temperature vapor oxidation method. The CuO nanobelt arrays show high electrocatalytic activity towards glucose oxidation.

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.

Synthesis of TiO2 nanocoral structures in ever-changing aqueous reaction systems.

A far-from-equilibrium strategy is developed to synthesize coral-like nanostructures of TiO(2) on a variety of surfaces. TiO(2) nanocoral structures consist of anatase base film and rutile nanowire layers, and they are continuously formed on substrates immersed in aqueous TiOSO(4)-H(2)O(2). The sequential deposition of TiO(2) starts with hydrolysis and condensation reactions of titanium peroxocomplexes in the aqueous phase, resulting in deposition of amorphous film. The film serves as adhesive interface on which succeeding growth of rutile nanowires to occur. This initial deposition reaction is accompanied by shift in pH of the reaction media, which is favorable condition for the growth of rutile nanocrystals. During the growth of rutile nanocoral layers, the amorphous base films are transformed to anatase phase. These sequential deposition reactions occur at temperatures as low as 80 °C, and the mild synthetic condition allows the use of a wide range of substrates such as ITO (indium tin oxide), glass, and even organic polymer films. The thickness of nanocoral layer is controllable by repeating the growth reaction of rutile nanocorals. TiO(2) nanocorals show photocatalytic activity as demonstrated by site-specific reduction of Ag(I) ions, which proceeds preferentially on the rutile nanowire layer. The rutile nanowire layer also shows photocatalytic decomposition of acetaldehyde, which is promoted upon increase of the thickness of the nanowire layer. The use of temporally transforming reaction media allows the formation of biphasic TiO(2) nanocoral structures, and the concept of nonequilibrium synthetic approach would be widely applicable to developing structurally graded inorganic nanointerfaces.