JP2006182575A - Method for manufacturing titanium oxide nanowire structure and titanium oxide nanowire structure obtained by the same method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a new nanowire-shaped titanium oxide structure can be easily manufactured without using an organic solvent, a surfactant or a high concentration alkali with a danger. <P>SOLUTION: The method for manufacturing the titanium oxide nanowire structure comprises subjecting a titanate to hydrothermal treatment under acidic condition meanwhile drying. As the titanate, a titanate having a layered structure, especially a sodium titanate, is preferably used. It is preferable to perform the hydrothermal treatment and drying in an autoclave using a dilute hydrochloric acid having a concentration of 0.01-0.5 mol/L. Wherein the hydrothermal treatment is performed meanwhile slowly drying by gradually evaporating the dilute hydrochloric acid through a small leak from the autoclave. The preferable hydrothermal treatment and drying temperature is within a range of 120-200°C, and the preferable treatment time is 120 h or longer. The obtained titanium oxide nanowire structure can be used in a wide range of fields as photoelectrodes of dye-sensitive solar cells, photocatalysts, optical/electronic materials or the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for easily producing a nanowire-shaped titanium oxide structure from titanate powder.

  In recent years, titanium oxide has been widely used as pigments, paints, adsorbents, cosmetic materials, optical / electronic materials, etc. Recently, as a material for porous electrodes, photocatalysts, catalyst carriers, etc. of dye-sensitized solar cells. Is also attracting attention. In order to further improve the material properties and expand the range of application to new application fields, nanotube shapes (nanometer-sized hollow cylindrical shapes) and nanowire shapes (long with nanometer-sized thickness) A structure of titanium oxide whose structure is controlled to a specific shape (such as fiber shape) has been reported.

  In particular, the titanium oxide nanowire structure has a large specific surface area, so that it can easily adsorb a large amount of dye and can be expected to have good electron conductivity in a one-dimensional direction along the wire. Energetic research and development has been conducted for use as an electrode (for example, see Patent Documents 1 and 2 and Non-Patent Documents 1 and 2).

  At present, several production methods are already known for titanium oxide nanowire structures. As an example, an organic solvent solution of a metal compound is brought into contact with a surfactant and water to be mixed and solidified. A method for producing a metal oxide having a nanowire shape and a nanowire-shaped titanium oxide structure obtained by the production method have been reported (for example, see Patent Document 1 and Non-Patent Document 1). In addition, a method for obtaining a titanium oxide nanowire structure by hydrothermally treating powdered titania with a high-concentration potassium hydroxide aqueous solution has been reported (for example, see Non-Patent Document 2).

  On the other hand, regarding the production of the titanium oxide nanotube structure, a method of hydrothermally treating titanium oxide powder using a high concentration sodium hydroxide aqueous solution has been reported (for example, see Patent Documents 3 and 4). In addition, the present inventors have made extensive studies on the reaction mechanism of titanium oxide nanotube structure formation by hydrothermal treatment of titanium oxide powder using a high concentration sodium hydroxide aqueous solution. It was found that the structure was formed as an intermediate and was then wound to obtain a nanotube-shaped titanium oxide structure. Based on this, the present inventors use a titanate powder having a layered structure instead of a titanium oxide powder as a raw material, and performing hydrothermal treatment with water alone without using a high-concentration base, the nanosheet-shaped oxidation It has been clarified that a titanium oxide structure having a nanotube shape can be easily obtained through a titanium structure, and a patent application has already been filed for this (see Patent Document 5).

JP 2003-34531 A JP 2003-251194 A Japanese Patent Laid-Open No. 10-152323 JP 2002-241129 A Japanese Patent Application No. 2004-228654 "Monthly Eco-Industry June 2004", CM Publishing, June 2004, p42 “Chemical Industry October 2004”, Chemical Industry Company, October 2004, p60

  By the way, the method using a surfactant for the production of a titanium oxide nanowire structure requires the use of a harmful organic solvent in the production process, and the organic solvent and the surfactant can be removed from the final product. It is essential. Therefore, there are problems that the process becomes complicated and the environmental load is large and the processing cost is required. In addition, this method has the disadvantage that the yield of long nanowire structures is low.

  In addition, the production process of titanium oxide nanowire structure by hydrothermal treatment using potassium hydroxide is also accompanied by danger in the manufacturing process because of hydrothermal treatment using high concentration potassium hydroxide aqueous solution, etc. Since the aqueous solution must be processed as waste liquid, there is a problem that the environmental load is large and processing costs are required. Furthermore, since the titanium oxide nanowire structure obtained by this method has low crystallinity, the mechanical strength cannot be maintained, and it is difficult to form a film for a photoelectrode alone.

  This invention is made | formed in view of the above-mentioned actual condition in a prior art. That is, the object of the present invention is to safely and easily remove titanates from mild titanates under mild conditions without using organic solvents, surfactants, and high-concentration alkalis that are dangerous to handle. An object of the present invention is to provide a method for producing a novel titanium oxide structure having a nanowire shape.

  In the course of studying a method for easily obtaining a nanotube-shaped titanium oxide structure via a nanosheet-shaped titanium oxide structure by hydrothermal treatment of the titanate described above, the present inventors solve the above-mentioned problems. A simple treatment of titanate under specific conditions reveals that a nanowire-shaped titanium oxide structure different from the hollow nanotube shape can be obtained, and the present invention is completed based on this. It came to.

  That is, this invention is a manufacturing method of the titanium oxide nanowire structure characterized by performing a hydrothermal treatment and a drying process on acidic conditions on a titanate. As the raw material titanate, a titanate having a layered structure is preferably used, and sodium titanate is particularly preferably used.

  In the present invention, the hydrothermal treatment is preferably performed by placing titanate in an acidic aqueous solution and heating in an autoclave (pressure vessel). As the acid, any acid can be used as long as it shows acidity. In particular, hydrochloric acid that evaporates with water is preferably used. The hydrochloric acid concentration is preferably dilute hydrochloric acid in the range of 0.01 to 0.5 mol / L.

  In addition, it is preferable to adopt a method of gradually evaporating and removing water during the hydrothermal treatment of the titanate during the drying treatment. When heating in an autoclave, the moisture is gradually removed by a slight leak. It can be carried out.

The hydrothermal / drying treatment temperature (heating temperature) is preferably in the range of 120 to 200 ° C., and the hydrothermal / drying treatment time (heating time) is preferably 120 hours or more.
The product obtained by the hydrothermal drying process is washed with water and dried again to obtain a titanium oxide powder containing a titanium oxide nanowire structure.

According to the present invention, as described above, the titanate powder used as a raw material is subjected to a very simple operation in which water is gradually evaporated and dried while performing hydrothermal treatment for a certain time in water under acidic conditions. A nanowire-shaped titanium oxide structure can be easily produced without using a high-concentration alkaline aqueous solution that is dangerous.
In the method of the present invention, after the hydrothermal / drying treatment, the product may be simply washed with water and dried again, and does not use organic solvents / surfactants or high-concentration alkalis that cause environmental pollution. Therefore, there is an advantage that the process of separating them and the treatment of the waste liquid are not required.

  The present invention provides a nanowire-shaped titanium oxide structure that is safe and simple without using organic solvents, surfactants, high-concentration alkalis, and the like that are used in conventional nanowire-shaped titanium oxide structures. In this method, titanate powder having a layered structure similar to the nanosheet shape is heated in water for a certain period of time under acidic conditions. A nanowire-shaped titanium oxide structure can be easily obtained only by (hydrothermal / drying treatment).

As the starting material, titanate is used, but titanate powder having a layered structure similar to the nanosheet shape is usually used. For example, the titanate having a typical layered structure is sodium titanate (Na ₂ Ti ₃ O ₇ ), which may be a commercial product, but synthesized by the method shown below. It may be.

  Regarding the formation process of the nanowire-shaped titanium oxide structure according to the present invention, in the case of sodium titanate, it is a layered structure in which sodium ions are interposed between titanate layers, and this is constant at a temperature of 120 ° C. or more in water. When hydrothermal treatment is performed for more than this time, water molecules gradually enter between the titanate layers and the titanate layers are gradually peeled off to form nanosheet-shaped titanium oxide, and some or all of these nanosheets are under acidic conditions It is presumed that the nanowire-shaped titanium oxide structure is finally formed by fission in the lower drying process. Further, it is presumed that a part of the above-mentioned peeled titanic acid layer is split into fibers without passing through a nanosheet, and a nanowire-shaped titanium oxide structure is directly formed.

Hereinafter, an example is given and demonstrated about the method of this invention.
First, the raw material sodium titanate powder is a mixture of sodium carbonate powder and anatase-type titanium dioxide powder (for example, ST-01 of Ishihara Sangyo Co., Ltd.) in a molar ratio of 1: 3 and ground using a mortar or the like. However, it is obtained by baking in air at about 1000 ° C. for 2 hours.

  Next, the obtained sodium titanate powder is mixed with dilute hydrochloric acid having a concentration of 0.01 to 0.5 mol / L, placed in an autoclave and heated. In this case, a ratio of about 10 ml of diluted hydrochloric acid with respect to 0.1 g of sodium titanate powder is desirable.

  At that time, a minute leak (leakage) is caused so that dilute hydrochloric acid slowly evaporates from the autoclave. In order for the hydrothermal reaction to proceed sufficiently, it is important to allow sufficient time so that this evaporation occurs rapidly and does not dry quickly. preferable. The optimum conditions for the drying speed depend on the hydrothermal / drying temperature / time and the shape and type of the raw titanate.

  Preferred conditions for the hydrothermal / drying treatment are a treatment temperature of 120 to 200 ° C. and a treatment time of 120 hours or more, more preferably a treatment temperature of 140 to 180 ° C. and a treatment time of 120 to 480 hours. The optimum processing conditions depend on the raw titanate.

  After the hydrothermal drying treatment, the product is washed with distilled water and dried again to obtain a titanium oxide white powder containing a nanowire-shaped titanium oxide structure. The drying after the washing is preferably performed at a temperature of about 60 ° C. in air for about 4 hours.

  The titanium oxide nanowire structure obtained by the present invention usually has a wire thickness of about 10 to 500 nm and a length of about 0.5 to 50 μm, and exhibits a brookite structure crystallinity.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by this Example. In addition, the shape of the obtained product was confirmed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Furthermore, the crystal form of the product was confirmed by measuring the XRD pattern.

  As the starting material, sodium titanate synthesized from the anatase-type titanium dioxide powder ST-01 (Ishihara Sangyo Co., Ltd.) by the above method was used. While adding 0.15 g of this sodium titanate powder to 15 ml of dilute hydrochloric acid with a concentration of 0.05 M, and heating it at a temperature of 170 ° C. for 168 hours in an autoclave with a volume of 30 ml, the dilute hydrochloric acid is gradually removed by minute leaks. Continue to evaporate and finally dry completely. Then, after washing with distilled water, the product was dried in air at 60 ° C. for about 4 hours to obtain a white powder product.

In FIG. 1, the scanning electron microscope (SEM) photograph of the obtained white powder-like product is shown. As can be seen in FIG. 1, it can be confirmed that a long fiber shape (nanowire shape) structure having a thickness of several tens to several hundreds of nanometers and a length of micrometers is generated. Furthermore, the part (brush shape) by which a part of sheet-like thing is torn and can be confirmed can be confirmed. The observation of this brush-shaped structure is that the titanate layer gradually peels off to form nanosheet-shaped titanium oxide, and some or all of these nanosheets break into fibers during the drying process under acidic conditions. This suggests that a nanowire-shaped titanium oxide structure is finally formed.
For comparison, FIG. 2 shows an SEM photograph of the raw material sodium titanate powder, but here no nanowire-like structure is seen.

  FIG. 3 shows a low-power transmission electron microscope (TEM) photograph of the obtained white powdered titanium oxide. FIG. 3 clearly shows that a nanowire shape having a length of micrometer size is generated. Furthermore, it can be seen from the high-magnification TEM photograph in which the nanowire-shaped tip portion shown in FIG. 4 is enlarged that the nanowire shape is formed by a cylindrical structure having a thickness of several tens of nanometers.

  Moreover, about the crystallinity of the produced | generated titanium oxide nanowire structure, it was confirmed that it is a titanium oxide of a brookite structure from the measurement result of the space | interval and XRD pattern in a lattice image obtained by expansion of a TEM photograph.

In the present invention, a novel titanium oxide nanowire structure can be produced very easily by hydrothermal treatment and drying under acidic conditions without using environmental pollutants, and the obtained titanium oxide nanowire structure can be dye-sensitized. In addition to photoelectrode materials for solar cells, it can be used in a wide range of fields as photocatalysts and photo / electronic materials.
In addition, if the titanium oxide nanowire structure is produced by the method of the present invention, it is not necessary to use an organic solvent / surfactant or a high-concentration alkaline aqueous solution, so that the processing cost can be reduced and the environmental load is also reduced.
Furthermore, based on the simple manufacturing method provided by the present invention, it is expected to develop a new method for controlling the shape of titanium oxide and to manufacture a titanium oxide structure having a completely new shape.

It is a scanning electron microscope (SEM) photograph of an example of the titanium oxide nanowire structure in the present invention. It is a scanning electron microscope (SEM) photograph of the sodium titanate powder used as a raw material in the present invention. It is a transmission electron microscope (TEM) photograph of an example of the titanium oxide nanowire structure in this invention. It is a transmission electron microscope (TEM) photograph of another example of the titanium oxide nanowire structure in the present invention.

Claims (11)

  A method for producing a titanium oxide nanowire structure comprising subjecting titanate to hydrothermal treatment and drying treatment under acidic conditions.   The method for producing a titanium oxide nanowire structure according to claim 1, wherein a titanate having a layered structure is used as the titanate.   The method for producing a titanium oxide nanowire structure according to claim 1 or 2, wherein sodium titanate is used as the titanate.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 3, wherein the hydrothermal treatment is performed using an aqueous hydrochloric acid solution.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 4, wherein the hydrochloric acid concentration in the hydrothermal treatment is 0.01 to 0.5 mol / L.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 5, wherein the drying process gradually evaporates and removes moisture by a slight amount of leak while performing hydrothermal treatment.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 6, wherein the hydrothermal treatment and the drying treatment are performed in an autoclave.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 7, wherein the temperature of the hydrothermal treatment and the drying treatment is 120 to 200 ° C.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 8, wherein a time of the hydrothermal treatment and the drying treatment is 120 hours or more.   The method for producing a titanium oxide nanowire structure according to any one of claims 1 to 9, wherein after completion of the hydrothermal treatment and the drying treatment, it is washed with water and dried again.   The titanium oxide nanowire structure obtained by the manufacturing method of any one of Claims 1-10.