ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).

Electrochemical Photolysis of Water at a Semiconductor Electrode

Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

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Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

The surface science of titanium dioxide

Two kinds of cobalt−iron cyanides (Rb0.66Co1.25[Fe(CN)6]·4.3H2O and Co1.5[Fe(CN)6]·6H2O) with different electronic structures have been investigated to understand the photoinduced long-range magnetic ordering. Rb0.66Co1.25[Fe(CN)6]·4.3H2O produces a photomagnetic effect, whereas Co1.5[Fe(CN)6]·6H2O does not respond to light. FT-IR and Mossbauer studies revealed that their oxidation states are expressed as Rb0.66CoIII0.84CoII0.41[FeII(CN)6] and CoII1.5[FeIII(CN)6], respectively. The difference in the oxidation states of the metal atoms in these two compounds has been explained by the Co coordination with H2O or CN ligands. In the case of Rb0.66Co1.25[Fe(CN)6]·4.3H2O, more CN ligands are involved in coordination than expected in the case of Co1.5[Fe(CN)6]·6H2O. A charge-transfer (CT) band from FeII to CoIII is observed at around 550 nm for Rb0.66Co1.25[Fe(CN)6]·4.3H2O. The magnetism of Rb0.66Co1.25[Fe(CN)6]·4.3H2O changed from paramagnetic to ferrimagnetic due to the CT from FeII to CoIII when illuminated a...

Photoinduced Long-Range Magnetic Ordering of a Cobalt-Iron Cyanide.

Changes in hydrophilicity of TiO2 film electrode surfaces by UV light irradiation in an aqueous solution were investigated under potential-controlled conditions. Although no change was observed when the electrode potential of TiO2 was set around its flat-band potential Efb, the photoinduced hydrophilic conversion proceeded at potentials positive of Efb. The hydrophilic conversion rate increased with larger positive potentials, but the addition of hole scavengers decreased the rate, suggesting that the diffusion of photogenerated holes to the surface is the important process for the hydrophilic conversion. Based on these results, we propose a model in which the photoinduced hydrophilicity is initiated by two-hole trapping by a surface lattice oxygen, producing an oxygen defect, followed by the dissociative adsorption of a water molecule at the defect site.

Enhancement of the Photoinduced Hydrophilic Conversion Rate of TiO2 Film Electrode Surfaces by Anodic Polarization

Design and preparation of a novel magnet exhibiting two compensation temperatures based on molecular field theory

Glass surfaces coated with polycrystalline titanium dioxide (TiO2) films were found to exhibit a 0° water contact angle when the surfaces were illuminated with UV light in the air. This highly hydrophilic surface was maintained for more than 1 week in the dark in air. However, ultrasonic treatment in pure water decreased the degree of surface hydrophilicity, yielding a contact angle of approximately 11°. X-ray photoelectron spectroscopic measurements indicated that hydroxyl groups and molecular water adsorption, which govern the surface wettability, were partially removed from the surface by the ultrasonic treatment. The effect of ultrasonic treatment was ascribed to the generation of OH radicals that reoxidized the photoreduced surface, accompanied by the removal of surface-adsorbed water. This has been confirmed by adding acrylamide, a typical OH radical scavenger, to pure water to effectively suppress the hydrophilic-to-hydrophobic reconversion on the TiO2 surface.

Effect of Ultrasonic Treatment on Highly Hydrophilic TiO2 Surfaces

The degradation of 17 beta-estradiol (E2) in water by TiO2 photocatalysis was investigated; concurrently the estrogenic activity of the treated water was evaluated during the photocatalytic reactions by an estrogen screening assay. As a result, 10(-6) M of E2 was totally mineralized to CO2 in 1.0 g L-1 TiO2 suspension under UV irradiation for 3 h. 10 epsilon-17 beta-Dihydroxy-1,4-estradien-3-one and testosterone-like species were elucidated as intermediate products by GC/MS analysis. The mechanisms of E2 degradation by TiO2 photocatalysis were discussed not only experimentally but also theoretically by calculating the frontier electron densities of the E2 molecule. On the basis of the results obtained, it was concluded that the phenol moiety of the E2 molecule, one of the essential functional groups to interact with the estrogen receptor, should be the starting point of the photocatalytic oxidation of E2. This means that the estrogenic activity should be almost lost concurrently with the initiation of the photocatalytic degradation. Actually, the estrogenic activities of the intermediate products were negligible. TiO2 photocatalysis could be applied to water treatment to effectively remove natural and synthetic estrogens without producing biologically active intermediary products.

Akira Fujishima

Papers

Photoinduced Long-Range Magnetic Ordering of a Cobalt-Iron Cyanide.

Enhancement of the Photoinduced Hydrophilic Conversion Rate of TiO2 Film Electrode Surfaces by Anodic Polarization

Design and preparation of a novel magnet exhibiting two compensation temperatures based on molecular field theory

Effect of Ultrasonic Treatment on Highly Hydrophilic TiO2 Surfaces

17 beta-estradiol degradation by TiO2 photocatalysis as a means of reducing estrogenic activity.