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

Reversible surface wettability conversion on titanium dioxide (TiO2) single crystals has been achieved, and its mechanism has been examined by means of contact angle measurement and X-ray photoelectron spectroscopy (XPS). A UV light illuminated TiO2 single-crystal surface exhibited a 0° contact angle for both water and oil, indicative of a highly amphiphilic surface against its native hydrophobic surface. This was ascribed to photoreduction of surface Ti4+ to Ti3+ at definite sites, leading to preferential adsorption of dissociative water on top. A long-term storage of the highly amphiphilic surface resulted in reconversion of the surface wettability. It was found that the amphiphilic-to-hydrophobic reconversion is due to the replacement of the adsorbed hydroxyl groups by oxygen, which returns the surface geometric and electronic structures similar to the native TiO2 surface. The result of angle-resolved XPS measurement revealed that the surface reactions occurred at the uppermost layers of the single cry...

Studies of Surface Wettability Conversion on TiO2 Single-Crystal Surfaces

HIGH-DENSITY information storage is becoming an increasingly important technological objective. The 'heat-mode' storage techniques (in which only the thermal energy of laser light is used in the recording process and hence information usually stored as a physical change of the storage media) that are used in current optical memories are limited by the diffraction properties of light1, and the alternative 'photon-mode' (in which information is stored as a photon-induced chemical change of the storage media) has attracted attention recently for high-density storage. The most promising candidates for realizing this mode seem to be photochro-ism and photochemical hole burning; but these have some intrinsic drawbacks1,2. Here we present a novel 'photon-mode' technique that uses the photoelectrochemical properties of a Langmuir-Blodgett film of an azobenzene derivative. The system can be interconverted photochemically or electrochemically between three chemical states, and this three-state system is shown to provide a potential storage process that allows for ultra-high storage density, multi-function memory and non-destructive information readout.

Photoelectrochemical information storage using an azobenzene derivative

Kinetics on the photoinduced hydrophilic conversion processes of the TiO2 surface was investigated. First, we show that there exist linear relationships between the reciprocal of the contact angle and the UV irradiation time and use the slope of this straight line as the hydrophilic conversion rate, which is independent of the initial value of the contact angle. Second, we examine the relationships between the reciprocal of the contact angle and the reconstruction of the surface hydroxyl groups and show that the reciprocal of the contact angle corresponds to the density of the surface hydroxyl groups reconstructed by UV irradiation. Finally, the dependence of the hydrophilic conversion on various parameters such as the incident UV intensity, the wavelength of irradiated light, and the concentration of the hole scavenger are quantitatively investigated with the proposed hydrophilic conversion rate. These results show that the photoinduced hydrophilic conversion proceeds competitively with the photocatalyti...

Quantitative Evaluation of the Photoinduced Hydrophilic Conversion Properties of TiO2 Thin Film Surfaces by the Reciprocal of Contact Angle

Electrochemical Evidence for the Mechanism of the Primary Stage of Photosynthesis

The photocatalytic decomposition efficiency of gaseous 2-propanol was studied using a titanium dioxide thin film under very weak UV light; the incident UV light intensity was 36 nW−45 μW·cm-2. Under such low-intensity UV illumination, the value of the quantum yield (QY) increased gradually with decreasing number of absorbed photons and finally saturated (28%) for a number of absorbed photons less than 4 × 1011 quanta·cm-2·s-1 for an initial 2-propanol concentration of 1000 ppmv. Thus, purely light-limited conditions were reached. For lower initial concentrations, the QY values decreased, but the same maximum QY value as that for 1000 ppmv was also approached with decreasing light intensity. We discuss these results in terms of the normalized absorbed photon number (Inorm/s-1), a parameter that we have defined as the ratio of the number of absorbed photons ([photon]ab) to the number of adsorbed 2-propanol molecules ([M]ad). When all of the experimental QY values were plotted as a function of Inorm, all of ...

Akira Fujishima

Papers

Studies of Surface Wettability Conversion on TiO2 Single-Crystal Surfaces

Photoelectrochemical information storage using an azobenzene derivative

Quantitative Evaluation of the Photoinduced Hydrophilic Conversion Properties of TiO2 Thin Film Surfaces by the Reciprocal of Contact Angle

Electrochemical Evidence for the Mechanism of the Primary Stage of Photosynthesis

Kinetics of photocatalytic reactions under extremely low-intensity uv illumination on titanium dioxide thin films