Nippon Oil Corporation (Tokyo, JP) and Kanagawa Academy of Science and Technology (Kanagawa, JP) jointly earned U.S. Patent 7,687,431 for a method for manufacturing nanotube-shaped titania. The tube diameter ranges from 5 to 500 nanometers (nm). The nanotube-shaped titania is expected to be used in various applications on the basis of its various characteristics such as propagation properties for electrons, holes, phonons, and complexes thereof, magnetic properties, optical properties, chemical catalytic properties, and the like.
According to inventors Keisuke Nakayama, Takaya Kubo, Yoshinori Nishikitani and Hideki Masuda, nanotube-shaped titania having an aspect ratio of 6 or greater can be produced by anodizing a titanium metal or an alloy containing mainly titanium in an electrolyte solution containing a halogen atom-containing ion, such as a perchloric acid aqueous solution.
Titania has excellent properties such as ultraviolet absorbability, adsorbability and the like, and thus has been widely used as a material for pigments, paints, cosmetics, ultraviolet shielding agents, catalysts, catalyst supports, and various electronics components. Further, recently considerable attention has been paid to the photocatalytic activity and amphipathic properties of titania exhibited when titania absorbs ultraviolet light. It has been confirmed that titania is effective in decomposing hazardous organic substances, eliminating air pollutants, sterilizing, and self-cleaning.
The nanotube-shaped titania with an aspect ratio of 6 or greater can be produced by anodizing a titanium metal or an alloy containing mainly titanium in the following manner.
Anodization carried is a technique wherein a voltage is applied to an anode made of titanium or an alloy thereof and a cathode made of any electrically conductive material in an electrolyte so as to form an oxide of titanium on the anode. During the anodization, titanium or an alloy only needs to be the anode at least once. The anodization includes a case wherein titanium or an alloy can be the anode and the cathode alternately.
Titanium and an alloy used in manufacturing the titania nanotubes may be any commercially pure titanium the quality of which is modified with oxygen, iron, nitrogen, or hydrogen, or any low-alloy titanium with a certain degree of press-moldability. Examples of such titanium and alloys include various commercially pure titanium of JIS classes 1 to 4, titanium alloys with anticorrosion properties improved by adding nickel, ruthenium, tantalum, palladium, or the like, and titanium alloys containing aluminum, vanadium, molybdenum, tin, iron, chromium, niobium, or the like. The titanium alloy used herein denotes an alloy containing 50 percent or more of titanium.