Kawamura Institute of Chemical Research (Sakura-shi, Chiba, JP) and DIC Corporation (Tokyo, JP) chemists have developed a simple industrial-scale production process for doped titanium oxide with visible light-responsiveness. The titanium oxide is doped with carbon atoms and nitrogen atoms according to U.S. Patent Application 20100062928 and may be used to produce a wide range of other materials.
The doped titanium dioxide is made by burning with heat a layered structure composite laminated alternately with polymer and the titania, which is obtained using a basic polymer with amino group(s) and water-soluble titanium compound, carbon atoms and nitrogen atoms in the polymer are, doped to the crystalline surface of titanium oxide. In making the polymer complex with metal ions beforehand, the metal ions can be also doped to the titanium oxide.
The doped titanium oxide is useful as a semiconductor for solar cells and as a catalyst for fuel cells as well as a visible light-responsive photocatalyst, according to inventors Ren-Hua, Jin Pei-Xin Zhu and Norimasa Fukazawa. It can be used as solar cell parts, as a hydrogen generating catalyst. It can also be used in various regions such as a bacteria preventive agent, a bactericide, an anti-virus, and in cosmetics. Moreover, as a doped titanium oxide shows absorption in near infrared region, it can be also applied for the use of electronic materials, electrical conducting materials, and thermoelectric materials. Doped titanium oxide can also be used as materials for a new nano-reaction field which has possibilities for synthesizing novel functional materials
Research and development of electrode layers in which platinum nano-particles are buried in titanium oxide is considered an important material for polymer electrolyte fuel cells. Hydrogen production is required for practical implementation of fuel cells, and among catalysts for hydrogen production, a composite of titanium oxide and platinum is an effective candidate.
In titanium oxide, the photocatalytic function decomposes spontaneously stain and harmful materials and renders them harmless. The fields of application include housing, automobiles, medical treatment, soil treatment, etc., and the photocatalytic function is ranked as an indispensable technique for constructing a recycling-oriented society. However, in order to engage the photocatalytic function of titanium oxide, it is necessary to use ultraviolet ray as a light source. Taking into account that natural light (sunrays) contains only 3% ultraviolet light and most of the light is visible light, use of sunlight with photocatalyst which absorbs ultraviolet only becomes almost meaningless. In order to use titanium oxide as an effective photocatalyst, it is most important to convert bounds for absorption of titanium oxide itself to visible light, which the researchers succeeded in doing.
FIG. 3.1 is a photograph of high resolution transmission electron microscope (TEM) of a doped titanium oxide.
The production method of a doped titanium oxide includes: using a layered composite of polymer or polymer-metal complex and titania nano-crystal holding interlayer distance on the order of nanometers, preferably from 1 to 3 nm, as precursor, and by burning it with heat, and the precursor is transformed to a titanium oxide doped with impurities. Such production method makes it possible to control the crystal size to about 10 nm.
The process can be used to produce nano-scale materials such as: a layered composite of polyethyleneimine and titania, layered composites of polyethyleneimine and titania containing different amounts of iron ions, and layered composites of polyethyleneimine and titania containing zinc, manganese, copper, cobalt, nickel, as well as layered composites of chromium and titania.
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