Tetsu Tatsuma

Photoelectrochemical Anticorrosion and Self-Cleaning Effects of a TiO2 Coating for Type 304 Stainless Steel

We investigated the photoelectrochemical behavior of type 304 stainless steel (SUS 304) with TiO 2 thin film coatings, applied by a spray pyrolysis technique, for the purpose of cathodic photoprotection of the steel from corrosion. The photopotential of TiO 2 -coated SUS 304 was -350 mV vs. Ag/AgCl in an aerated aqueous solution containing 3 wt NaCl (pH 7) under illumination with 10 mW cm -2 ultraviolet (UV) light, which was more negative than the corrosion potential of the bare steel (-100 mV). The photopotential did not change in aqueous solutions containing from 0.01 to 5 wt % NaCl. No corrosion of TiO 2 -coated steel was observed at pH values greater than 3 in 3 wt % NaCl aqueous solution under UV illumination. TiO 2 films with coverages greater than 30% achieved photoprotection ability at pH 6. When the UV light intensity was 3 mW cm -2 , that is, comparable with a typical daylight UV intensity in Tokyo the photopotential of TiO 2 -coated SUS 304 was -220 mV in an aerated 3 wt % NaCl aqueous solution. In addition, the bleaching of methylene blue dye was confirmed on TiO 2 -coated SUS 304 under 1 mW cm -2 UV illumination. We conclude that TiO 2 thin film-coated SUS 304 exhibits both a cathodic photoprotection effect against corrosion and the previously reported photocatalytic self-cleaning effect.

Photovoltaic Properties of Glutathione-Protected Gold Clusters Adsorbed on TiO2 Electrodes

www.MaterialsViews.com C O M M U Photovoltaic Properties of Glutathione-Protected Gold Clusters Adsorbed on TiO 2 Electrodes N IC A By Nobuyuki Sakai and Tetsu Tatsuma * IO N Gold nanoparticles, the sizes of which range from approximately 2 to 100 nm in diameter, have been widely studied from the fundamental and practical points of view, because of their unique optical, electronic, magnetic, and catalytic properties, which are different from that of bulk gold. [ 1 ] Since these properties vary with particle size, it is important to synthesize sizecontrolled gold nanoparticles. Although the mean particle size can be controlled by selecting parameters such as the molar ratio of a gold precursor to stabilizers, reaction temperature, and reducing agents, the size still has some distribution. On the other hand, gold clusters, which are smaller than 2 nm in diameter, have discrete electronic levels due to quantum size effects [ 2 , 3 ] and do not exhibit localized surface plasmon resonance (LSPR) unlike the nanoparticles larger than 2 nm. Such an electronic structure is responsible for unique optical absorption in the visible and near-infrared regions, [ 2 , 4 , 5 ] fl uorescence, [ 6 , 7 ]

OXIDASE/PEROXIDASE BILAYER-MODIFIED ELECTRODES AS SENSORS FOR LACTATE, PYRUVATE, CHOLESTEROL AND URIC ACID

Abstract Enzyme heterobilayer-modified electrodes were fabricated by successively covalently binding to the surface of a tin(IV) oxide plate horseradish peroxidase (HRP), then an oxidase (lactate, pyruvate or cholesterol oxidase or uricase), which liberates hydrogen peroxide by reaction with the respective substrate. The cooperative action of oxidase-HRP leads to an efficient amperometric sensor system with the minimum amount of enzyme immobilized on an electrode.

Electron transport in silver-semiconductor nanocomposite films exhibiting multicolor photochromism

In the multicolor photochromism of TiO2 nanoporous films loaded with photocatalytically deposited Ag nanoparticles, visible light-induced electron transfer from Ag to oxygen molecules plays an essential role. Here we examined the effect of TiO2 on the electron transfer. We found that not only photocatalytically deposited Ag, but also electrodeposited Ag and commercially available Ag nanoparticles in a nanoporous TiO2 film exhibit the multicolor photochromism. The electrodeposited Ag exhibits the multicolor photochromism also in a nanoporous ZnO film, but not in nanoporous indium-tin oxide (ITO) and SiO2 matrices. Photoelectrochemical measurements for the Ag-TiO2 nanocomposite elucidated that some of the photo-excited electrons on Ag are transferred to oxygen molecules via TiO2 and non-excited Ag. Thus, an n-type semiconductor plays an important role in the charge separation between the excited electrons and Ag+. Non-excited Ag on TiO2 also plays an important role in the charge separation and/or catalysis of oxygen reduction. Replacement of the non-excited Ag with Pt accelerated the electron transport from the photo-excited Ag to oxygen molecules and the photochromic behavior.

Self-sterilizing and self-cleaning of silicone catheters coated with TiO2 photocatalyst thin films: A preclinical work

TiO(2) photocatalysts were successfully coated on silicone catheters or medical tubes by pretreatment of the silicone surface with a sulfuric acid solution (5 M) for 3 h. The TiO(2) film adhered to the silicone substrate strongly against tensile and bending stresses. On the TiO(2)-coated silicone-catheters under UV illumination, both the bleaching of methylene blue dye and the photocatalytic bactericidal effect on Escherichia coli (E. coli) cells were confirmed. Thus, this type of catheter can be sterilized and cleaned simply by irradiation with low-intensity UV light and can, therefore, be useful in the protection from catheter-related bacterial infections.

Size effects of gold nanaoparticles on plasmon-induced photocurrents of gold–TiO2 nanocomposites

An ITO electrode was coated with a nanoporous TiO2 film, and the film was loaded with Au nanoparticles with different diameters (15, 40 and 100 nm). The electrode exhibited plasmon-induced photocurrents in the presence of Fe(2+/3+) couple under visible light (lambda > 420 nm). The quantum efficiency increased with increasing particle size, whereas the maximum photocurrent density decreased.

Plasmon-induced photoelectrochemistry at metal nanoparticles supported on nanoporous TiO2

Nanoporous TiO(2) films loaded with gold and silver nanoparticles exhibit negative potential changes and anodic currents in response to visible light irradiation, so that the films would potentially be applicable to inexpensive photovoltaic cells, photocatalysts and simple plasmon sensors.

Solid state photovoltaic cells based on localized surface plasmon-induced charge separation

Charge separation induced by localized surface plasmon resonance (LSPR) of gold and silver nanoparticles (AuNPs and AgNPs) are applied to various devices and photoelectrochemical functionalities. Here, we develop all solid state In/TiO2/MNPs/ITO photovoltaic cells (MNP = AuNP or AgNP) by using two-dimensional MNP ensembles. Their quantum efficiencies are higher than those of previously reported solid state cells with hole-transport materials (HTMs) (ITO/TiO2/AuNPs/HTM/Au). The photoresponses from cells without HTMs suggest that the photovoltage generates at the TiO2-MNP interface.

Multichannel quartz crystal microbalance.

Arrays of quartz crystal resonators are fabricated on a single quartz wafer as a multichannel quartz crystal microbalance (MQCM). Three types of four-channel array of 10-MHz resonators are prepared and tested. Mechanical oscillation of each channel is entrapped within the channel almost completely, so that the interference between the channels via the quartz crystal plate is almost negligible. A mass change on each channel is quantitatively evaluated on the basis of Sauerbreys law. Thus, each channel of a MQCM device can be used as an independent QCM. Influence from a longitudinal wave generated from another channel is also negligible compared to the influence from the wave from the monitored channel itself. The simultaneous oscillation of channels is also possible. The potential applicability of MQCM to the two-dimensional mapping of mass changes is demonstrated.

Inhibition effect of covalently cross-linked gel electrolytes on lithium dendrite formation

Methyl methacrylate (MMA) was polymerized in a propylene carbonate–ethylene carbonate mixed solvent (50:50 wt%) containing LiClO4 (1 M) in the presence of a cross-linking agent, triethylene glycol dimethacrylate (TGD) or ethylene glycol dimethacrylate (EGD). The TGD–MMA (or EGD–MMA) molar ratio was 0–8%. A cell was assembled with the resulting gel and lithium electrodes, and was subjected to the electrolysis at 3 mA cm−2 for 1 h. The cross-linked gel electrolytes inhibited lithium dendrite formation. This inhibition effect is explained in terms of the mechanical properties of the gel. More rigid gels suppressed the dendrite formation more effectively, although a brittle gel may result in the formation of sparse, but relatively large dendrites. The EGD-containing gel whose EGD–MMA mol ratio was 4% successfully suppressed the dendrite formation.