There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

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

Preparation of Transparent Superhydrophobic Boehmite and Silica Films by Sublimation of Aluminum Acetylacetonate

The quantum yield of hydroxyl radical (⋅OH) production during TiO2 photocatalysis was estimated to be 7×10−5 in aqueous solution by means of a method using terephthalic acid as a fluorescence probe. This value is much lower than the quantum yield of ordinary photocatalytic reactions (∼10−2). Conversely, the quantum yield of hole generation estimated by iodide ion oxidation was equivalent (5.7×10−2) to that of ordinary photocatalytic reactions. This implies that oxidative reactions on TiO2 photocatalyst occur mainly via photogenerated holes, not via ⋅OH.

Quantum yields of active oxidative species formed on TiO2 photocatalyst

The role of active oxygen species in the photocatalytic bactericidal effect was investigated using a thin transparent titanium dioxide (TiO2) film. The viable number of Escherichia coli (E. coli) significantly decreased on the illuminated TiO2 film, and the bactericidal effect was observed even when E. coli was separated from the TiO2 surface with a 50 μm porous membrane. Mannitol, a hydroxyl radical scavenger, inhibited the effect only in the absence of the membrane. In contrast, catalase inhibited the effect in all cases. On the basis of these results, the long-range bactericidal effect of hydrogen peroxide was proposed, together with a cooperative effect due to other oxygen species. © 1997 Elsevier Science S.A.

Photocatalytic bactericidal effect of TiO2 thin films : dynamic view of the active oxygen species responsible for the effect

Photochromic materials, which change their colours reversibly in response to light, can be applied to smart windows, displays and memories1,2,3. Conventional photochromic materials respond in a monochromatic way, so that multicolour photochromism has required several different materials or filters combined appropriately. If multicolour photochromism could be achieved with a simple material, photochromic devices would be find a greater number of applications, including a rewritable colour copy paper or electronic paper4 and a high-density multi-wavelength optical memory. Here we report multicolour photochromism of TiO2 films loaded with silver nanoparticles by photocatalytic means. Its colour, initially brownish-grey, changes under monochromatic visible light to almost the same colour as that of the light; the apparently uniform Ag–TiO2 film can be almost any colour. Behaviour similar to persistent hole-burning effects5,6 is also observed. The colour reverts to brownish-grey under ultraviolet light, and these processes are repeatable.

Akira Fujishima

Papers

Preparation of Transparent Superhydrophobic Boehmite and Silica Films by Sublimation of Aluminum Acetylacetonate

Quantum yields of active oxidative species formed on TiO2 photocatalyst

Photocatalytic bactericidal effect of TiO2 thin films : dynamic view of the active oxygen species responsible for the effect

Multicolour photochromism of TiO2 films loaded with silver nanoparticles.

Photocatalytic activity and photoinduced hydrophilicity of titanium dioxide coated glass