JP5717500B2 - Method for producing titanium oxide nanotubes - Google Patents

Description

  The present invention relates to a method for producing a titanium oxide nanotube used for a dye-sensitized solar cell, a photocatalyst, a sensor and the like.

  Titanium oxide nanotubes are widely used in applications such as dye-sensitized solar cells, photocatalysts, and sensors.

  Among them, the dye-sensitized solar cell uses titanium dioxide or the like with a modified dye as an active electrode (see Patent Document 1), and has attracted attention as a solar cell that can be easily manufactured at low cost.

  As a method for synthesizing titanium oxide nanotubes, for example, it is known that titanium oxide nanoparticles are heated in a high concentration sodium hydroxide aqueous solution, and the reaction product is washed with water (Patent Document 2).

Japanese Patent Publication No. 8-15097 Japanese Patent Laid-Open No. 10-152323 JP 2010-24132 A

  However, the titanium oxide nanotube obtained by the method of Patent Document 2 has a diameter of about 10 nm and tends to aggregate. In addition, sodium is likely to remain in the titanium oxide nanotube, and when used as a constituent material of a photoelectric conversion element such as a dye-sensitized solar cell, there is a possibility that it becomes an electron trap.

  Considering this, an attempt has been made to remove carbon after forming a coating layer made of particulate titanium oxide on the surface of carbon having high conductivity and high aspect ratio (Patent Document 3).

  However, among carbon, carbon nanotubes contain a heavy metal component as a catalyst, and there is a possibility that the heavy metal component continues to remain after the carbon is removed. In addition, since it is not easy to remove such remaining heavy metal component, this heavy metal component may become an electron trap. Further, it is not easy to form a coating layer made of titanium oxide on the surface of carbon, and surface oxidation treatment (hydrophilization) under severe conditions, addition of a dispersant, and the like are necessary.

  Therefore, an object of the present invention is to provide a simple method for producing a titanium oxide nanotube having a high specific surface area, excellent conductivity, high activity anatase-type crystals, and low heavy metal content.

As a result of intensive studies in view of the above object, the present inventors have coated the surface of a tube-like or fiber-like polyaniline with a coating layer composed of continuous titanium oxide nanoparticles, and then removed the polyaniline to achieve the above problem. The present inventors have found that a titanium oxide nanotube having solved the above can be obtained, and further researched to complete the present invention. That is, this invention includes the manufacturing method of the titanium oxide nanotube of the following items 1-18, the titanium oxide nanotube, and the photoelectric conversion element using this titanium oxide nanotube.
Item 1. A method for producing a titanium oxide nanotube in which particulate titanium oxide (A) is continuous,
(I) forming a coating layer of continuous titanium oxide (A) on the surface of tube-like or fiber-like polyaniline to produce a titanium oxide-polyaniline composite; and (II) the titanium oxide- Heating the polyaniline complex to remove the polyaniline.
Item 2. Item 2. The production method according to Item 1, wherein the heating temperature is 400 to 1000 ° C in the step (II).
Item 3. Item 3. The method according to Item 1 or 2, wherein in step (II), the oxygen partial pressure of the atmosphere during heating is 1 kPa or more.
Item 4. Items 1 to 3, wherein the step (I) is a step of forming a coating layer in which the particulate titanium oxide (A) is continuous on the surface of the tube-like or fiber-like polyaniline by a precipitation reaction from a titanium fluoro complex. The manufacturing method in any one of.
Item 5. Item 5. The production method according to Item 4, wherein the titanium fluoro complex is at least one selected from the group consisting of (NH ₄ ) ₂ TiF ₆ , H ₂ TiF ₆ , Na ₂ TiF ₆ , K ₂ TiF ₆ and TiF ₄ .
Item 6. Item 6. The method according to Item 4 or 5, wherein the step (I) is performed in the presence of a fluoride ion scavenger.
Item 7. Item 7. The method according to Item 6, wherein in step (I), the molar concentration of fluoride ions is twice or more that of the titanium fluoro complex.
Item 8. Step (I) is brought into contact with a titanium oxide sol containing particulate titanium oxide (B) having an average particle diameter of 20 nm or less, and particulate titanium oxide (A) is continuous with the surface of the tube-like or fiber-like polyaniline. Item 4. The production method according to any one of Items 1 to 3, which is a step of forming a coating layer.
Item 9. Item 9. The production method according to any one of Items 1 to 8, wherein an average straight line perpendicular to the major axis of the polyaniline is 8 to 450 nm, and an average length of the major axis of the polyaniline is 0.1 to 100 μm.
Item 10. Particulate titanium oxide (A) is connected,
A titanium oxide nanotube having an average diameter orthogonal to the major axis of 10 to 500 nm and an average length of the major axis of 0.1 to 100 μm.
Item 11. Item 11. The titanium oxide nanotube according to Item 10, wherein the heavy metal content is 1000 ppm or less.
Item 12. Item 12. The titanium oxide nanotube according to Item 10 or 11, wherein the total content of sodium, potassium and iron is 100 ppm or less.
Item 13. Item 13. The titanium oxide nanotube according to any one of Items 10 to 12, wherein the specific surface area is 30 m ² / g or more.
Item 14. Item 14. The titanium oxide nanotube according to any one of Items 10 to 13, wherein the particulate titanium oxide (A) contains anatase-type titanium oxide, rutile-type titanium oxide, brookite-type titanium oxide, or amorphous titanium oxide.
Item 15. Item 15. The titanium oxide nanotube according to any one of Items 10 to 14, wherein the particulate titanium oxide (A) contains anatase-type titanium oxide.
Item 16. Item 16. The titanium oxide nanotube according to any one of Items 10 to 15, wherein the average particle size of the particulate titanium oxide (A) is 1 to 100 nm.
Item 17. The titanium oxide nanotube according to any one of Items 10 to 16, wherein the powder resistance under a pressure of 10 MPa is 1 × 10 ⁷ Ω · m or less.
Item 18. Item 18. A photoelectric conversion element comprising the titanium oxide nanotube according to any one of Items 10 to 17 in a negative electrode.

  According to the present invention, it is possible to easily produce a titanium oxide nanotube having a high specific surface area, excellent conductivity, a highly active anatase-type crystal, and a low heavy metal content. This titanium oxide nanotube is particularly preferably used for a photoelectric conversion element, a photocatalyst, a sensor and the like. In addition, according to the present invention, the heavy metal content can be greatly reduced, so the possibility of becoming an electron trap can be eliminated. Furthermore, in the present invention, when forming a coating layer made of titanium oxide on the surface of polyaniline, it is not always necessary to make the polyaniline hydrophilic or add a dispersing agent, and it can be produced by a simple method.

It is a schematic diagram explaining the movement of the electron in the titanium oxide nanotube of this invention which a particulate titanium oxide (A) continues. It is a schematic diagram explaining the movement of electrons when a particulate titanium oxide (A) is not formed into a tubular shape and a titanium oxide paste is applied to a substrate. 2 is an electron microscope (SEM) photograph of tubular polyaniline produced in Example 1. FIG. 2 is an electron microscope (SEM) photograph of the titanium oxide-polyaniline composite produced in Example 1. FIG. 2 is an electron microscope (SEM) photograph of the titanium oxide nanotube of Example 1. FIG. 2 is an electron microscope (SEM) photograph of a cross section of the titanium oxide nanotube of Example 1. FIG.

1. Method for producing titanium oxide nanotubes The method for producing titanium oxide nanotubes of the present invention comprises:
(I) A step of forming a titanium oxide-polyaniline composite by forming a coating layer in which particulate titanium oxide (A) is continuous on the surface of tube-like or fiber-like polyaniline,
(II) A step of removing the polyaniline by heating the titanium oxide-polyaniline composite.

  In the present invention, “tubular” refers to a substantially columnar shape having a cavity in the major axis direction at the center portion thereof. In the present invention, the end portion is not necessarily open, that is, it is not necessary to have a through hole, and a hollow shape in which the end portion is closed may be used. In addition, the “fiber shape” refers to a substantially columnar shape having no cavity at the center portion thereof. Further, in the present invention, “continuous” means that the particulate titanium oxide is in close contact with the adjacent titanium oxide and is not simply obtained by mixing.

In the present invention, “titanium oxide” does not refer only to titanium dioxide (TiO ₂ ), but is composed of dititanium trioxide (Ti ₂ O ₃ ); titanium monoxide (TiO); Ti ₄ O ₇ , Ti ₅ O. _It includes those having a composition deficient in oxygen from titanium dioxide represented by ₉ etc. Further, as represented by the terminal OH group, a group other than Ti—O—Ti resulting from the synthesis of titanium oxide may be included.

<Tube-like or fiber-like polyaniline>
The tube-like or fiber-like polyaniline used in the present invention is not particularly limited. Commercially available polyaniline may be used or synthesized.

  In addition, the tube-like or fiber-like polyaniline has a surface area that is as fine as possible and has a surface area as large as possible, and can produce a continuous nanotube with a long titanium oxide. Therefore, the average diameter perpendicular to the long axis is about 8 to 450 nm. The length is preferably about 0.1 to 100 μm, and the average aspect ratio (average length of the long axis / average diameter orthogonal to the long axis) is preferably about 5 to 2000, and the average diameter orthogonal to the long axis is about 20 to 300 nm, More preferably, the average length of the major axis is about 1 to 10 μm, and the average aspect ratio (average length of major axis / average diameter perpendicular to the major axis) is about 7 to 1,000. The average diameter perpendicular to the major axis of the polyaniline is the average inner diameter of the titanium oxide nanotubes when the titanium oxide nanotubes are produced by the production method of the present invention. Moreover, when polyaniline is a tube shape, the average internal diameter is about 3-300 nm, Preferably it is about 5-100 nm. In addition, the average diameter orthogonal to the long axis, the average length of the long axis, the average aspect ratio, and the inner diameter can be measured, for example, by observation with an electron microscope (SEM or TEM) of 5000 times or more.

Method for synthesizing tube-like or fiber-like polyaniline (I) Oxidation polymerization method The method for synthesizing tube-like or fiber-like polyaniline is not particularly limited. For example, after aniline or a derivative thereof is dissolved in a solvent, the aniline or a derivative thereof may be polymerized.

  The derivative of aniline is not particularly limited, and examples thereof include N-methylaniline, O-methylaniline, O-methoxyaniline, O-chloroaniline, phenylquinone diimine, emeraldine, indamine, aniline sulfonic acid and the like.

  In the present invention, among aniline and derivatives thereof, aniline is preferred because of its low raw material cost.

The molar concentration of aniline or a derivative thereof is preferably 6.4 × 10 ^{−2 to} 1.7 × 10 ⁻¹ mol / l. This molar concentration is the molar concentration of aniline or a derivative thereof relative to the solvent to be dissolved. By setting the molar concentration of aniline or a derivative thereof within the above range, nano-sized tube-like or fiber-like (particularly tube-like) polyaniline can be easily formed.

  The solvent used here may be any solvent as long as aniline or a derivative thereof is finally dissolved, and includes a polar solvent such as water.

  In the present invention, a bicyclic monoterpene may be included in the solvent. Thereby, while making aniline easy to dissolve in water, formation of tube-like polyaniline can be promoted.

  When the bicyclic monoterpene is included in the solvent, the bicyclic monoterpene may be added after the aniline or derivative thereof is added to the solvent, or before the aniline or derivative thereof is added to the solvent. Cyclic monoterpenes may be added. Moreover, you may add a bicyclic monoterpene simultaneously with adding aniline or its derivative (s) to a solvent.

  As the bicyclic monoterpene, it is desirable to use a camphor derivative having a reactive substituent. Examples of the reactive substituent include a halogen group, a sulfo group, a carboxyl group, and a hydroxyl group. As the bicyclic monoterpene, camphorsulfonic acid is particularly preferable. Thus, if a camphor derivative having a reactive substituent is used, it becomes easy to form tube-like or fiber-like (particularly tube-like) polyaniline.

  The addition amount of the bicyclic monoterpene is preferably adjusted so that the molar ratio of aniline or a derivative thereof and the bicyclic monoterpene is 1: 0.3 to 0.7. By setting the addition amount of the bicyclic monoterpene within the above range, nano-sized tube-like or fiber-like (particularly tube-like) polyaniline can be easily formed.

  A method for polymerizing aniline or a derivative thereof is not particularly limited, but in the present invention, an oxidative polymerization method using an oxidizing agent is preferable. Examples of the oxidizing agent include ammonium persulfate, sodium persulfate, potassium dichromate, sodium dichromate, ammonium dichromate, benzoquinone, hydrogen peroxide, and the like, and ammonium persulfate is preferable. Ammonium persulfate can be obtained at a relatively low price on the market, so that the production cost can be reduced.

The molar concentration of the oxidizing agent is preferably 3.9 × 10 ^{−2 to} 1.3 × 10 ⁻¹ mol / l. This molar concentration is the molar concentration of the oxidizing agent relative to the solvent. When the molar concentration of ammonium persulfate is within the above range, efficient oxidative polymerization can be performed, and nano-sized tube-like or fiber-like (particularly tube-like) polyaniline is easily formed at low cost.

  When aniline sulfonic acid is used as the derivative of aniline, and when camphor sulfonic acid is used as the bicyclic monoterpene, sulfonic acid is present. Therefore, when this is subjected to heat treatment, SOx gas that is toxic to the human body is produced. May occur. In order to suppress the generation of SOx gas, a tube-like or fiber-like polyaniline is synthesized and then washed with an alkaline solution. As the alkaline solution, for example, an aqueous ammonia solution can be used. Thereby, a sulfo group or a sulfonic acid can be removed from tube-like or fiber-like polyaniline.

  As a method for suppressing the generation of SOx gas, a SOx gas adsorbing device or the like may be installed in a portion where SOx gas is discharged.

(II) Electrolytic polymerization method In the present invention, the tube-like or fiber-like polyaniline may be synthesized by an electrolytic polymerization method. Specifically, aniline or a derivative thereof may be dissolved in an acidic solution, and electrolytic polymerization (preferably repeated oxidative electrolytic polymerization) may be performed.

  Examples of aniline derivatives include those described above.

  The molar concentration of aniline or a derivative thereof is preferably 0.01 to 3 mol / l. This molar concentration is the molar concentration of aniline or a derivative thereof relative to the solvent to be dissolved. By setting the molar concentration of aniline or a derivative thereof within the above range, nano-sized tube-like or fiber-like (particularly tube-like) polyaniline can be easily formed.

The acid contained in the acidic solution for dissolving the aniline or its derivative is not particularly limited, for example, fluoroboric acid (HBF _4), hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, organic sulfonic acids (e.g., dodecylbenzene Sulfonic acid) and the like, and hydrochloric acid, sulfuric acid, and borohydrofluoric acid (HBF ₄ ) are preferable.

  The molar concentration of the acid is preferably 0.01 to 1 mol / l. This molar concentration is the molar concentration of the acid with respect to the solvent described later. By setting the molar concentration of the acid within the above range, aniline is easily dissolved in the solvent during the reaction.

  Any solvent can be used as long as it can dissolve aniline or a derivative thereof. Examples thereof include water, a mixed solvent of water and an organic solvent, and the like. In this case, the organic solvent is not particularly limited, and various alcohols, tetrahydrofuran (THF) and the like can be used. In particular, water is preferable.

  Repeated oxidative electropolymerization can be performed by, for example, cyclic voltammetry (CV), a direct current voltage application method, or the like. As such a system and apparatus for electrochemical polymerization, known ones can be used.

<Particulate titanium oxide (A)>
The crystal structure of the particulate titanium oxide (A) is not particularly limited, but when the titanium oxide nanotube of the present invention is used for a photoelectric conversion element, a photocatalyst, etc., an anatase type titanium oxide having a high activity is used. It is preferable to include. The particulate titanium oxide (A) is not limited to only anatase-type titanium oxide, and may include rutile-type titanium oxide, brookite-type titanium oxide, and the like. In addition to crystalline titanium oxide, amorphous titanium oxide may be included. However, 70% by weight or more of the particulate titanium oxide (A) is preferably anatase type titanium oxide.

  The crystal structure of the particulate titanium oxide (A) can be measured by, for example, X-ray diffraction method, Raman spectroscopic analysis or the like.

  The average particle diameter of the particulate titanium oxide (A) is preferably from 1 to 100 nm, more preferably from 1 to 50 nm, from the viewpoint that the specific surface area can be increased to adsorb more dye and absorb light. However, when the titanium oxide nanotube of the present invention is used for a photoelectric conversion element, from the viewpoint of light confinement effect inside the battery, titanium oxide particles having a large light scattering, that is, an average particle diameter larger than 100 nm are used in combination. May be. In addition, an average particle diameter can be measured by electron microscope (SEM) observation etc., for example.

<Process (I): Titanium oxide coating process>
In the present invention, the method for forming a coating layer in which particulate titanium oxide (A) is continuous on the surface of tube-like or fiber-like polyaniline is not particularly limited. For example, an easy method includes a wet method in which a titanium oxide sol containing particulate titanium oxide (B), a titanium tetrachloride solution, a titanium sulfate solution, a titanyl sulfate solution, or the like is brought into contact with a tube-like or fiber-like polyaniline.

  However, compared to these methods, a method of forming a coating layer in which particulate titanium oxide (A) is continuous on the surface of a tube-like or fiber-like polyaniline by precipitation reaction from a titanium fluoro complex is preferable. The reason is as follows.

  (1) The average particle diameter of the particulate titanium oxide (A) in the coating layer can be about several nm, and the specific surface area of the finally obtained titanium oxide nanotube of the present invention can be increased.

  (2) It is a simple technique that may be allowed to stand by bringing a tube-like or fiber-like polyaniline at normal temperature and pressure into contact with a reaction solution containing a titanium fluoro complex and allowing it to stand.

  (3) The particulate titanium oxide (A) in the coating layer formed on the surface of the tube-like or fiber-like polyaniline has a large number of anatase-type crystals even when the reaction is performed at room temperature and pressure. That is, the particulate titanium oxide in the finally obtained titanium oxide nanotube also has many anatase type crystals.

  (4) Crystallinity can be improved by firing the obtained titanium oxide-polyaniline composite. Moreover, since rutile type titanium oxide does not generate | occur | produce until the baking temperature is about 800 degreeC, it is especially preferable when many anatase type titanium oxides with high photoactivity are included.

  (5) Particulate titanium oxide (A) can be deposited only on the surface of the polyaniline due to the nitrogen atoms of the tube-like or fiber-like polyaniline in particular. It is also possible to prevent product formation.

  In addition, when tube-like or fiber-like polyaniline is immersed in a solution of titanium alkoxide or titanium alkoxide in ethanol instead of a titanium oxide sol containing crystalline titanium oxide, it precipitates on the surface of the tube-like or fiber-like polyaniline. The only titanium oxide to be used is amorphous titanium oxide, and the coating is incomplete. Further, amorphous titanium oxide can be crystallized by heat treatment, but the specific surface area of the titanium oxide-polyaniline composite is reduced. In this case, titanium oxide is easily converted into a rutile type, and is converted into a rutile type at, for example, about 600 ° C.

  In addition, when tube-like or fiber-like polyaniline is simply immersed in a dispersion in which particulate titanium oxide is dispersed, the surface of the tube-like or fiber-like polyaniline is not coated with titanium oxide, and polyaniline and A simple mixture with titanium oxide is formed. For this reason, a titanium oxide nanotube cannot be obtained even if baked.

Precipitation Method from Titanium Fluoro Complex Precipitation method from titanium fluoro complex is a method in which tube-like or fiber-like polyaniline is brought into contact with a reaction solution containing titanium fluoro-complex, and particles are formed on the surface of tube-like or fiber-like polyaniline. This is a method of forming a coating layer composed of continuous titanium oxide (A). Specifically, although not limited thereto, a tube-like or fiber-like polyaniline dispersion may be immersed in a reaction solution containing a titanium fluoro complex. Moreover, you may add the titanium fluoro complex or the aqueous solution of a titanium fluoro complex to the dispersion liquid of tube-like or fiber-like polyaniline.

  The dispersion medium for dispersing the tube-like or fiber-like polyaniline is not particularly limited, and examples thereof include water or a mixed solvent of water and alcohol.

  A dispersion operation may be added to the dispersion containing the tube-like or fiber-like polyaniline so that the surface of the tube-like or fiber-like polyaniline is uniformly coated later with the particulate titanium oxide (A).

  Further, a surfactant may be added to improve dispersibility. As the surfactant, any of a cation system, an anion system and a nonionic system can be used, and a known or commercially available one may be used.

The titanium fluoro complex is not particularly limited. For example, ammonium hexafluorotitanate ((NH ₄ ) ₂ TiF ₆ ), hexafluorotitanate (H ₂ TiF ₆ ), sodium hexafluorotitanate (Na ₂ TiF ₆ ), potassium hexafluorotitanate (K ₂ TiF ₆ ), titanium fluoride (IV) (TiF ₄ ) and the like, and (NH ₄ ) ₂ TiF ₆ or H ₂ TiF ₆ is preferable.

  The solvent used in the reaction solution containing the titanium fluoro complex is not particularly limited as long as it can dissolve the titanium fluoro complex, and examples thereof include water, a mixed solvent of water and alcohol, and the like. In addition, what is necessary is just to use a well-known or commercially available alcohol.

  The molar concentration of the titanium fluoro complex is not particularly limited, but is preferably 0.01 to 0.3 mol / l, and more preferably 0.03 to 0.25 mol / l.

In the present invention, the contact between the tube-like or fiber-like polyaniline and the reaction solution containing the titanium fluoro complex is preferably performed in the presence of a fluoride ion scavenger. Thereby, particulate titanium oxide (A) becomes easier to precipitate on the surface of tube-like or fiber-like polyaniline. The fluoride ion scavenger is not particularly limited, and boric acid (H ₃ BO ₃ ), aluminum chloride, aluminum, and the like can be used.

  The molar concentration of the fluoride ion scavenger is not particularly limited, but is preferably 0.02 to 1.0 mol / l, and more preferably 0.03 to 0.8 mol / l.

  The molar concentration of the fluoride ion scavenger is preferably changed according to the molar concentration of the titanium fluoro complex. The molar concentration of the fluoride ion scavenger is preferably 2 times or more, particularly 2 to 5 times the molar concentration of the titanium fluoro complex.

  If it carries out as mentioned above, the coating layer which a particulate titanium oxide (A) continues on the surface of tube-like or fiber-like polyaniline can be formed, and a titanium oxide-polyaniline composite_body | complex can be manufactured.

  The titanium oxide-polyaniline complex obtained here may be washed with pure water, an acid or alkali aqueous solution, or an organic solvent such as alcohol. Thereby, an unreacted raw material, a reaction initiator, etc. can be removed.

  Said process (I) can be advanced also under normal temperature and a normal pressure, without heating or pressurizing especially. Preferred conditions are 20 to 50 ° C. and 0.05 to 0.2 MPa.

  Moreover, said process (I) is a wet reaction. In order to remove the solvent remaining in the titanium oxide-polyaniline complex, it is preferably dried. The drying method may be hot air drying or vacuum drying. For example, when the solvent is water, the preferable drying temperature is 100 ° C. or higher, more preferably 150 ° C. or higher.

A wet method using a titanium oxide sol containing particulate titanium oxide (B) A wet method using a titanium oxide sol containing particulate titanium oxide (B) is a tube-like or fiber-like polyaniline and a particulate titanium oxide (B). This is a method of forming a coating layer in which particulate titanium oxide (A) is continuous on the surface of a tube-like or fiber-like polyaniline by contacting with a titanium oxide sol containing. Specifically, although not limited to this, tube-like or fiber-like polyaniline may be immersed in a titanium oxide sol containing particulate titanium oxide (B).

  The titanium oxide sol may be synthesized from an aqueous solution of titanium chloride, titanium sulfate, titanyl sulfate or the like, or may be synthesized by mixing titanium alkoxide in an acidic solution. There is no restriction | limiting in particular as a titanium alkoxide, A well-known or commercially available thing can be used. For example, titanium ethoxide, titanium isopropoxide, titanium n-butoxide, titanium t-butoxide and the like can be mentioned, and titanium isopropoxide is preferable. When the titanium oxide sol is produced in this manner, the average particle diameter of the existing particulate titanium oxide (B) can be 0.5 to 20 nm, preferably 1 to 10 nm.

  A titanium oxide sol using titanium alkoxide as a raw material can be produced by dropping titanium alkoxide in a dispersion medium. The dispersion medium is not particularly limited, and an aqueous solution of nitric acid, aqueous solution of acetic acid, aqueous solution of oxalic acid, aqueous solution of hydrochloric acid, or a mixed solution thereof may be used. If titanium alkoxide is added and heated, the crystallinity of titanium oxide is increased. Can be improved.

  In addition, the preferable conditions of said wet method are 10-90 degreeC and 0.05-0.2 MPa.

Titanium oxide-polyaniline composite The titanium oxide-polyaniline composite thus obtained has a structure in which the surface of a tube-like or fiber-like polyaniline is coated with a coating layer in which particulate titanium oxide (A) is continuous. Is the body.

  The thickness of the coating layer is preferably 2 to 250 nm, more preferably 5 to 200 nm, from the viewpoint of coating titanium oxide without defects and obtaining a tube-shaped titanium oxide nanotube. The thickness of the coating layer is as it is when the titanium oxide nanotube of the present invention is produced. In addition, the thickness of a coating layer can be measured by electron microscope (SEM or TEM) observation etc., for example.

  The titanium oxide-polyaniline composite thus obtained has a titanium or titanium oxide nanotubes free from defects, so that the coverage of the particulate titanium oxide on the surface of the tube-like or fiber-like polyaniline is 70 to 100%, particularly Is preferably 85 to 100%. The surface element ratio of carbon / titanium is preferably 0/100 to 70/30 (atomic ratio), more preferably 0/100 to 50/50 (atomic ratio). In addition, the surface coverage (ratio of the portion covered with the coating layer on which the particulate titanium oxide (A) is continuous on the surface of polyaniline) can be determined by, for example, observation with an electron microscope (SEM or TEM) or the like. The surface element ratio of carbon / titanium can be measured by, for example, X-ray photoelectron spectroscopy.

<Process (II): Polyaniline removal process>
In step (II), the titanium oxide-polyaniline complex obtained in step (I) is heated to remove polyaniline. Thereby, there is an advantage that the conductivity of the titanium oxide nanotube is improved while the ratio of the anatase type crystal of titanium oxide is increased.

  In the step (II), it is only necessary to remove the polyaniline, and the method is not particularly limited, but it is easy to eliminate the oxidation. For example, in the case of heating in air to oxidize and disappear, the heating temperature is preferably 400 ° C. or higher, more preferably 500 ° C. or higher. The upper limit of the heating temperature is not particularly limited, but is about 1000 ° C.

  The atmosphere in the step (II) is preferably 1 kPa or more, particularly preferably 50 kPa or more, although a preferable oxygen partial pressure varies depending on the heat treatment temperature.

  Specifically, when the heating temperature is 400 ° C., the oxygen partial pressure is preferably 15 kPa or more, and when the heating temperature is 600 ° C., the oxygen partial pressure is preferably 10 kPa or more, and the heating temperature is 800 ° C. In this case, the oxygen partial pressure is preferably 2 kPa or more, and when the heating temperature is 1000 ° C., the oxygen partial pressure is preferably 0.2 kPa or more.

Titanium oxide nanotube The titanium oxide nanotube of the present invention thus obtained is a tubular structure in which particulate titanium oxide (A) is continuous. Thereby, the fine unevenness | corrugation exists in the surface of the titanium oxide nanotube of this invention. If a titanium oxide nanotube having fine irregularities on the surface is used as a photoelectric conversion element such as a dye-sensitized solar cell, a large amount of the dye is supported and incident light can be efficiently absorbed. Then, electrons are generated efficiently, and the adjacent titanium oxides are in intimate contact with each other as shown in FIG. 1. Therefore, the electrons can be efficiently transferred to the transparent electrode through the adjacent titanium oxide.

  When the titanium oxide (A) is not formed into a tubular shape and a titanium oxide paste is applied to the substrate, the resistance of the grain boundaries is large and the electron flow is poor as shown in FIG. In addition, the diffusion of the electrolyte in the mesoporous structure deteriorates.

Although the resistivity of the titanium oxide nanotube of the present invention varies depending on the application, the powder resistance under 10 MPa is preferably 10 ⁷ Ω · m or less, and more preferably 6 × 10 ⁶ Ω · m or less. The powder resistance is preferably as small as possible, and the lower limit is not particularly limited, but is about 1 Ω · m. The method for measuring the powder resistance of the titanium oxide nanotubes is not particularly limited. For example, the current value is measured by processing a plate with a thickness of 0.3 mm at a pressure of 10 MPa and applying a voltage of 1 V between the pellets. It can be measured by measuring.

  The titanium oxide nanotube of the present invention has a sufficient surface area and efficiently transmits electrons, so that the average diameter orthogonal to the long axis is 10 to 500 nm (particularly 30 to 400 nm), and the average length of the long axis is 0.1 to 100 μm (especially 1 to 10 μm when contained in a coating solution or supported on a substrate) and an average aspect ratio of 5 to 2000 (especially 7 to 1000) are preferable. In the present invention, the diameter of the titanium oxide nanotube refers to the outer diameter.

The titanium oxide nanotube of the present invention has a specific surface area of 30 m ² / g from the viewpoint of increasing the surface area, carrying a large amount of dye, and efficiently absorbing incident light when used for a photoelectric conversion device. The above is preferable, and 50 m ² / g or more is more preferable. The larger specific surface area is preferred, and the upper limit is not particularly limited, but is about 1000 m ² / g. The specific surface area can be measured by the BET method or the like.

  In the titanium oxide-polyaniline composite of the present invention, the heavy metal content is preferably 1000 ppm or less, and more preferably 100 ppm or less. By setting it within this range, when used as a constituent material of a photoelectric conversion element such as a dye-sensitized solar cell, it can be suppressed that it becomes an electron trap. In the present invention, the heavy metal in the heavy metal content mentioned above refers to carbon nanotubes other than sodium, potassium and the like mixed when heated in a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution to obtain a titanium oxide nanotube. This is intended to be iron or the like mixed when a titanium oxide layer is stacked using carbon as a template and carbon nanotubes are removed. Moreover, heavy metal content can be measured by ICP method etc., for example.

2. Applications The titanium oxide nanotubes of the present invention can be used for, for example, photoelectric conversion elements such as dye-sensitized solar cells, photocatalysts, sensors and the like. When the titanium oxide nanotube of the present invention is used in a photoelectric conversion element such as a dye-sensitized solar cell, it can be used as a conductive auxiliary material by mixing with the titanium oxide layer of the negative electrode. In this case, it can be expected to improve conductivity, improve light diffusion, improve electrolyte diffusion by changing the pore size, and the like.

  When the titanium oxide nanotube of the present invention is used in a photoelectric conversion element, specifically, the following configuration can be employed.

  The photoelectric conversion element of the present invention includes at least a conductive substrate (negative electrode substrate), a semiconductor layer, a charge transport layer, and a counter electrode (positive electrode).

  The conductive substrate usually has an electrode layer on the substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Colorless or colored resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. In addition, the board | substrate in this invention has a smooth surface at normal temperature, The surface may be a plane or a curved surface, and may deform | transform by stress.

In addition, the material of the conductive film that acts as an electrode is not particularly limited, and examples thereof include metals such as gold, silver, chromium, copper, tungsten, and titanium, metal thin films, and conductive films made of metal oxides. As the metal oxide, for example, Indium Tin Oxide (ITO (In ₂ O ₃ : Sn)), or Fluorine doped Tin Oxide (FTO (SnO ₂ )) obtained by doping a metal oxide such as tin or zinc with a small amount of another metal element. : F)), Aluminum doped Zinc Oxide (AZO (ZnO: Al)), Antimony doped Tin Oxide (ATO (SnO ₂ : Sb)), and the like are preferably used.

  The film thickness of the conductive film is usually 100 to 10,000 nm, preferably 500 to 3000 nm. The surface resistance (resistivity) is appropriately selected, but is usually 0.5 to 500 Ω / sq, preferably 1 to 50 Ω / sq.

  The method for forming the conductive film is not particularly limited, and a known method can be appropriately employed depending on the type of metal or metal oxide used. Usually, a vacuum deposition method, an ion plating method, a CVD method, a sputtering method, or the like is used. In any case, it is preferable that the substrate temperature is in the range of 20 to 700 ° C.

  The counter electrode (counter electrode) in the photoelectric conversion element of the present invention may have a single layer structure made of a conductive material, or may be composed of a conductive layer and a substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Alternatively, the counter electrode may be formed by applying, plating, or vapor-depositing (PVD, CVD) a conductive material directly on the charge transport layer.

  As the conductive material, metals such as platinum, gold, nickel, titanium, aluminum, copper, silver, and tungsten, and materials having a small specific resistance such as carbon materials and conductive organic substances are used.

  A metal lead may be used for the purpose of reducing the resistance of the counter electrode. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, silver or tungsten, and particularly preferably made of aluminum or silver.

  As the semiconductor layer, one made of the above-described titanium oxide nanotube of the present invention is used.

  The method for forming the semiconductor layer on the conductive substrate is not particularly limited, and examples thereof include a method of preparing a paste containing the titanium oxide nanotube of the present invention, applying the paste on the conductive substrate, and baking it. At this time, water, an organic solvent, or the like can be used as a solvent for the paste.

  The organic solvent is not particularly limited as long as it can disperse the titanium oxide nanotubes of the present invention. For example, alcohols such as ethanol, methanol and terpineol, and glycols such as ethylene glycol, polyethylene glycol, propylene glycol and polypropylene glycol can be used. These solvents are usually used by mixing in consideration of dispersibility, volatility and viscosity. The proportion of the solvent in the paste is 50 to 90% by weight, particularly 70 to 85% in terms of providing fluidity during coating, maintaining the thickness after coating, and forming porous titanium oxide. % By weight is preferred.

  As a component of the dispersion liquid, a thickener or the like may be included in addition to the above solvent.

  Examples of the thickener include alkyl celluloses such as methyl cellulose and ethyl cellulose. Among these, alkyl cellulose, particularly ethyl cellulose can be preferably used.

  The proportion of the thickener in the paste is preferably 2 to 20% by weight, particularly 3 to 15% by weight from the viewpoint of balancing the fluidity during coating and the thickness after coating.

  The ratio of the solid content in the paste is preferably 10 to 50% by weight, particularly preferably 15 to 30% by weight from the viewpoint of the balance between the fluidity at the time of coating and the thickness after coating, as described above. Furthermore, it is preferable that 0.1 to 90% by weight (further 0.2 to 80% by weight (particularly 0.5 to 60% by weight)) of the titanium oxide nanotube of the present invention is contained with respect to the solid content.

  In the photoelectric conversion element of the present invention, a semiconductor layer having a dye supported (adsorbed, contained, etc.) on the semiconductor layer is used for the purpose of improving the light absorption efficiency of the semiconductor layer.

  The dye is not particularly limited as long as it has absorption characteristics in the visible region and near infrared region, and improves (sensitizes) the light absorption efficiency of the semiconductor layer. However, metal complex dyes, organic dyes, natural dyes, semiconductors, etc. Is preferred. In addition, in order to impart adsorptivity to the semiconductor layer, a functional group such as a carboxyl group, a hydroxyl group, a sulfonyl group, a phosphonyl group, a carboxylalkyl group, a hydroxyalkyl group, a sulfonylalkyl group, or a phosphonylalkyl group is included in the dye molecule. Those having a group are preferably used.

  As the metal complex dye, for example, a ruthenium, osmium, iron, cobalt, zinc, or mercury complex (for example, mellicle chromium), metal phthalocyanine, chlorophyll, or the like can be used. Examples of organic dyes include, but are not limited to, cyanine dyes, hemicyanine dyes, merocyanine dyes, xanthene dyes, triphenylmethane dyes, metal-free phthalocyanine dyes, and the like. . As a semiconductor that can be used as a dye, an amorphous semiconductor having a large i-type light absorption coefficient, a direct transition semiconductor, or a fine particle semiconductor that exhibits a quantum size effect and efficiently absorbs visible light is preferable. Usually, one of various semiconductors, metal complex dyes and organic dyes, or two or more kinds of dyes can be mixed in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency. Moreover, the pigment | dye to mix and its ratio can be selected so that it may match with the wavelength range and intensity distribution of the target light source.

  As a method for adsorbing the dye on the semiconductor layer, for example, a solution in which the dye is dissolved in a solvent is applied on the semiconductor layer by spray coating, spin coating, or the like, and then dried. In this case, the substrate may be heated to an appropriate temperature. Alternatively, a method in which the semiconductor layer is immersed in a solution and adsorbed can be used. The immersion time is not particularly limited as long as the dye is sufficiently adsorbed, but is preferably 10 minutes to 30 hours, more preferably 1 to 20 hours. Moreover, you may heat a solvent and a board | substrate when immersing as needed. The concentration of the dye in the case of forming a solution is about 1 to 1000 mmol / L, preferably about 10 to 500 mmol / L.

  The solvent to be used is not particularly limited, but water and an organic solvent are preferably used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butanol; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, and the like. Nitriles; aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene; aliphatic hydrocarbons such as pentane, hexane, heptane; alicyclic hydrocarbons such as cyclohexane; acetone, methyl ethyl ketone Ketones such as diethyl ketone and 2-butanone; ethers such as diethyl ether and tetrahydrofuran; ethylene carbonate, propylene carbonate, nitromethane, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, dimethoxy Ethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxyethane, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyl phosphate Dimethyl, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), Examples thereof include triphenyl polyethylene glycol phosphate and polyethylene glycol.

  In order to reduce the interaction such as aggregation between the dyes, a colorless compound having properties as a surfactant may be added to the dye adsorption liquid and co-adsorbed to the semiconductor layer. Examples of such colorless compounds include steroid compounds such as cholic acid having a carboxyl group or sulfo group, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, sulfonates, and the like.

  It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Washing is preferably performed using acetonitrile, an alcohol solvent or the like in a wet washing tank.

  After adsorbing the dye, a semiconductor using an amine, a quaternary ammonium salt, a ureido compound having at least one ureido group, a silyl compound having at least one silyl group, an alkali metal salt, an alkaline earth metal salt, etc. The surface of the layer may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferred quaternary ammonium salts include tetrabutylammonium iodide, tetrahexylammonium iodide and the like. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.

  The charge transport layer contains a charge transport material having a function of replenishing electrons to the oxidant of the dye. The charge transport material used in the present invention is a charge transport material in which ions are involved. A solution in which a redox counter ion is dissolved, a gel electrolyte composition in which a polymer matrix gel is impregnated with a solution of a redox pair, a solid electrolyte composition, etc. Is mentioned.

The electrolyte solution as a charge transport material involving ions is preferably composed of an electrolyte, a solvent, and an additive. Examples of the electrolyte used in the electrolytic solution, iodine and iodide (LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, quaternary ammonium such as imidazolium iodide A combination of bromine and bromide (metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr, CaBr ₂ , quaternary ammonium compound bromide such as tetraalkylammonium bromide, pyridinium bromide, etc.) Examples thereof include metal complexes such as Russianate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, and hydroquinone-quinone. Among them, an electrolyte obtained by combining I ₂ and LiI or a quaternary ammonium compound iodine salt such as pyridinium iodide or imidazolium iodide is preferable. The electrolyte may be used as a mixture.

  Any solvent can be used as long as it is generally used in electrochemical cells and batteries. Specifically, acetic anhydride, methanol, ethanol, tetrahydrofuran, propylene carbonate, nitromethane, acetonitrile, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, ethylene carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxy Ethane, propiononitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethyl sulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyldimethyl phosphate, tributyl phosphate, phosphorus Tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, phosphoric acid Tridecyl, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), triphenyl polyethylene glycol phosphate, polyethylene glycol, and the like can be used. In particular, propylene carbonate, ethylene carbonate, dimethyl sulfoxide, dimethoxyethane, acetonitrile, γ-butyrolactone, sulfolane, dioxolane, dimethylformamide, dimethoxyethane, tetrahydrofuran, adiponitrile, methoxyacetonitrile, methoxypropionitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide Dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate and the like are preferable. Also, room temperature molten salts can be used. Here, the room temperature molten salt is a salt composed of an ion pair that is melted at room temperature (that is, in a liquid state) and usually has a melting point of 20 ° C. or lower and is a liquid at a temperature exceeding 20 ° C. Is a salt. The solvent may be used alone or in combination of two or more.

  Further, it is preferable to add a basic compound such as 4-t-butylpyridine, 2-picoline, or 2,6-lutidine to the above-described molten salt electrolyte composition or electrolytic solution. A preferable concentration range when adding the basic compound to the electrolytic solution is 0.05 to 2 mol / L. When added to the molten salt electrolyte composition, the basic compound preferably has an ionic group. The blending ratio of the basic compound with respect to the entire molten salt electrolyte composition is preferably 1 to 40% by weight, more preferably 5 to 30% by weight.

  The material that can be used as the polymer matrix is not particularly limited as long as the polymer matrix alone, or the solid state or gel state is formed by the addition of a plasticizer, the addition of a supporting electrolyte, or the addition of a plasticizer and a supporting electrolyte. Generally used so-called polymer compounds can be used.

  Examples of the polymer compound exhibiting characteristics as the polymer matrix include hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and methyl acrylate. And polymer compounds obtained by polymerizing or copolymerizing monomers such as ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. These polymer compounds may be used alone or in combination. Among these, a polyvinylidene fluoride polymer compound is particularly preferable.

  The charge transport layer can be formed by one of two methods. The first method is a method in which a semiconductor layer and a counter electrode are bonded together, and a liquid charge transport layer is sandwiched between the gaps. The second method is a method in which a charge transport layer is provided directly on the semiconductor layer, and a counter electrode is provided thereafter.

  In the case of the former method, when sandwiching the charge transport layer, a normal pressure process using capillary action by dipping or the like, or a vacuum process in which the gas phase in the gap is replaced with a liquid phase at a pressure lower than normal pressure can be used. .

  When a wet charge transport layer is used in the latter method, a counter electrode is usually applied in an undried state and measures for preventing liquid leakage at the edge portion are taken. Moreover, when using a gel electrolyte composition, you may solidify by methods, such as superposition | polymerization, after apply | coating this with a wet method. Solidification may be performed before or after applying the counter electrode.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Example 1
5 g of aniline was added to 500 g of water, 6.23 g of (±) -camphor sulfonic acid was added with ice cooling, and the mixture was stirred for 15 minutes. 12.4 g of ammonium persulfate was added, and the mixture was stirred for 1 minute and allowed to stand for 25 hours (aniline: 0.107 mol / l, (±) -camphor sulfonic acid: 0.054 mol / l, ammonium persulfate: 0.109 mol / l l). The obtained dark green reaction solution was filtered under reduced pressure, washed with 1 L of water three times, and vacuum dried at 200 ° C. to obtain 4.7 g of a dark green solid. When this solid was observed with a scanning electron microscope (SEM), tubular polyaniline having an average outer diameter of about 200 nm, an average length of about 2 μm, an average aspect ratio of about 10, and an average inner diameter of about 10 nm could be confirmed. FIG. 3 is an electron microscope (SEM) photograph of the tubular polyaniline.

0.06 g of this polyaniline was put into 6 g of water, and ultrasonic dispersion was performed. When 3 g of 1M (NH ₄ ) ₂ TiF ₆ aqueous solution was added to this dispersion and ₆ g of 1M H ₃ BO ₃ aqueous solution was added and reacted at room temperature for 24 h, a dark green precipitate was obtained (polyaniline: 0.043 mol). / L, (NH ₄ ) ₂ TiF ₆ : 0.2 mol / l). The precipitate was washed with pure water, filtered under reduced pressure, and vacuum dried at 200 ° C. to obtain 0.18 g of a dark green solid. This solid was observed by SEM, and it was confirmed that a titanium oxide-polyaniline structure in which the surface of the tube-shaped polyaniline was coated with particulate titanium oxide was obtained. FIG. 4 is an electron microscope (SEM) photograph of the titanium oxide-polyaniline complex obtained here.

  When this titanium oxide-polyaniline structure was heat-treated in the air (oxygen partial pressure was 19.6 kPa) at 550 ° C. using an electric furnace, particulate titanium oxide having an average particle diameter of about 10 nm was connected, and the average outer diameter was about It was confirmed that titanium oxide nanotubes having a thickness of 250 nm, an average length of about 2 μm, an average aspect ratio of about 8, and an average inner diameter of about 150 nm were obtained. 5 is an electron microscope (SEM) photograph of the titanium oxide nanotubes obtained here, and FIG. 6 is an electron microscope (SEM) photograph of a cross section of the titanium oxide nanotubes obtained here.

When the specific surface area of this material was measured by the BET method, it had a high specific surface area of 120 m ² / g. Further, when an X-ray crystal structure analysis was performed, it was found that anatase-type titanium oxide was the main component (about 100% by weight).

  When the heavy metal content of this material was measured by the ICP method, the heavy metal concentration was below the detection limit (5 ppm or less).

Moreover, when this material was processed into a flat plate having a thickness of 0.3 mm at a pressure of 10 MPa and a voltage of 1 V was applied between the pellets, it was confirmed that the powder resistance was 4 × 10 ⁵ Ω · m.

Example 2
The experiment was conducted in the same manner as in Example 1 except that the heat treatment conditions for removing polyaniline were 650 ° C. in the air (oxygen partial pressure was 19.6 kPa). Then, particulate titanium oxide having an average particle diameter of about 13 nm is connected, and titanium oxide nanotubes having an average outer diameter of about 250 nm, an average length of about 2 μm, an average aspect ratio of about 8 and an average inner diameter of about 160 nm are obtained. confirmed.

When the specific surface area of this material was measured by the BET method, it had a high specific surface area of 80 m ² / g. Further, when an X-ray crystal structure analysis was performed, it was found that anatase-type titanium oxide was the main component (about 100% by weight).

  When the heavy metal content of this material was measured by the ICP method, the heavy metal concentration was below the detection limit (5 ppm or less).

Moreover, when this material was processed into a flat plate having a thickness of 0.3 mm at a pressure of 10 MPa and a voltage of 1 V was applied between the pellets, it was confirmed that the powder resistance was 2 × 10 ⁵ Ω · m.

Example 3
5 g of aniline was added to 500 g of water, and 5.5 g of S-(+)-camphor sulfonic acid was added with ice cooling, followed by stirring for 15 minutes. 12.4 g of ammonium persulfate was added, and the mixture was stirred for 1 minute and then allowed to stand for 15 hours (aniline: 0.107 mol / l, S-(+)-camphor sulfonic acid: 0.047 mol / l, ammonium persulfate: 0.0. 109 mol / l). The obtained dark green reaction solution was filtered under reduced pressure, washed with 1 L of water three times, and vacuum dried at 200 ° C. to obtain 4.8 g of a dark green solid. When this solid was observed with a scanning electron microscope (SEM), tubular polyaniline having an average outer diameter of about 250 nm, an average length of about 2 μm, an average aspect ratio of about 8 and an average inner diameter of about 10 nm could be confirmed.

  When 12.0 g (0.2 mol) of acetic acid was added to 56.8 g (0.2 mol) of titanium isopropoxide and stirred, a viscous uniform and transparent solution was obtained. When 290 g of water and 4 ml of concentrated nitric acid were added to this solution and heated to 80 ° C., a cloudy sol containing titanium oxide having an average particle diameter of about 4 nm was obtained (titanium oxide: 0.56 mol / l).

  In 100 ml of this sol, 0.1 g of the above polyaniline was immersed, and further stirred, filtered under reduced pressure, and dried at 200 ° C. under vacuum.

  The obtained solid was observed with a TEM, and the surface of the tube-shaped polyaniline was covered with a coating layer composed of continuous particulate titanium oxide having an average particle diameter of about 4 nm, an average outer diameter of about 280 nm, and an average length of about It was confirmed that the thickness was 2 μm, the average aspect ratio was about 7, and the average inner diameter was about 10 nm.

Moreover, when the specific surface area was measured by the BET method, it had a high specific surface area of 100 m ² / g. Further, when an X-ray crystal structure analysis was performed, it was found that it had a weak anatase type crystal structure.

  When this titanium oxide-polyaniline structure was heat-treated at 600 ° C. in the air (oxygen partial pressure was 19.6 kPa) using an electric furnace, particulate titanium oxide having an average particle diameter of about 12 nm was connected, and the average outer diameter was about It was confirmed that titanium oxide nanotubes having an average length of about 280 nm, an average length of about 2 μm, an average aspect ratio of about 7, and an average inner diameter of about 160 nm were obtained.

When the specific surface area of this material was measured by the BET method, it had a high specific surface area of 110 m ² / g. Moreover, when X-ray crystal structure analysis was performed, it turned out that anatase type titanium oxide is a main component (80 weight%).

  When the heavy metal content of this material was measured by the ICP method, the heavy metal concentration was below the detection limit (5 ppm or less).

Moreover, when this material was processed into a flat plate having a thickness of 0.3 mm at a pressure of 10 MPa and a voltage of 1 V was applied between the pellets, it was confirmed that the powder resistance was 3 × 10 ⁵ Ω · m.

Comparative Example 1
It carried out similarly to Example 3 using the liquid which disperse | distributed 5 g of anatase type titanium oxide nanoparticles with an average particle diameter of 10 nm to 100 ml of water instead of the sol containing titanium oxide. Although the obtained solid was observed by SEM, titanium oxide nanotubes were not obtained, and only the raw material titanium oxide nanoparticles were observed. This is presumably because the titanium oxide nanoparticles could not be coated on the surface of polyaniline as a result of using a dispersion of titanium oxide nanoparticles, resulting in a simple mixture.

Comparative Example 2
An experiment was conducted in the same manner as in Example 3 using a solution in which 5 g of titanium isopropoxide was dissolved in 100 g of isopropanol instead of the sol containing titanium oxide.

When the obtained solid was observed with SEM, tube-shaped titanium oxide was hardly observed, the specific surface area was as low as 10 m ² / g, and X-ray crystal structure analysis was performed. As a result, rutile titanium oxide was the main component. there were.

Comparative Example 3
Carbon nanotubes (manufactured by Osaka Gas, diameter 30 nm, length 10 μm) were treated with concentrated sulfuric acid at 90 ° C. for 6 hours, washed with pure water to pH 5 or higher, and vacuum dried at 150 ° C. 0.4 g of the carbon nanotube having a hydrophilic surface was added to 60 g of a 5 wt% aqueous solution of polyethylene oxide alkylamine, and subjected to ultrasonic dispersion for 5 minutes. Thereafter, 30 g of 1M (NH ₄ ) ₂ TiF ₆ aqueous solution and 60 g of 1M boric acid aqueous solution were added and allowed to stand for 24 hours. As a result, carbon nanotubes coated with titanium oxide (average outer diameter: about 125 nm, average length: about 5 μm) 1.5 g of an average aspect ratio of about 40 and an average inner diameter of about 12 nm).

  This material was vacuum dried at 200 ° C. and then heat-treated in air (oxygen partial pressure was 19.6 kPa) at 650 ° C. using an electric furnace. As a result, particulate titanium oxide having an average particle diameter of about 14 nm was connected. It was confirmed that a titanium oxide nanotube having an average outer diameter of about 110 nm, an average length of about 2.5 μm, an average aspect ratio of about 22.7, and an average inner diameter of about 40 nm was obtained.

  However, when the metal content of this substance was measured by the ICP method, it contained 3000 ppm of iron.

Claims (19)

A method for producing a titanium oxide nanotube in which particulate titanium oxide (A) is continuous,
(I) A step of forming a titanium oxide-polyaniline composite by forming a coating layer in which particulate titanium oxide (A) is continuous by precipitation reaction from a titanium fluoro complex on the surface of a tube-like or fiber-like polyaniline. And (II) heating the titanium oxide-polyaniline complex to remove polyaniline. The manufacturing method of Claim 1 whose heating temperature is 400-1000 degreeC in process (II). The manufacturing method of Claim 1 or 2 whose oxygen partial pressure of the atmosphere at the time of a heating is 1 kPa or more in process (II). Is at least one selected from the group of titanium fluoro complex is composed of _{(NH 4) 2 TiF 6,} H 2 TiF 6, Na 2 TiF 6, K 2 TiF 6 and TiF _4, to any one of claims 1 to 3 The manufacturing method as described. The manufacturing method according to any one of claims 1 to 4, wherein the step (I) is performed in the presence of a fluoride ion scavenger. The production method according to claim 5 , wherein in step (I), the molar concentration of fluoride ions is twice or more that of the titanium fluoro complex. A method for producing a titanium oxide nanotube in which particulate titanium oxide (A) is continuous,
(I) A coating layer in which particulate titanium oxide (A) is connected to the surface of a tube-like or fiber-like polyaniline by contacting with a titanium oxide sol containing particulate titanium oxide (B) having an average particle diameter of 20 nm or less. Forming a titanium oxide-polyaniline composite , and
(II) A step of removing the polyaniline by heating the titanium oxide-polyaniline composite.
Including the method. The manufacturing method of Claim 7 whose heating temperature is 400-1000 degreeC in process (II). The manufacturing method of Claim 7 or 8 whose oxygen partial pressure of the atmosphere at the time of a heating is 1 kPa or more in process (II). The average diameter is 8～450Nm, The process according to any one of claims 1 to 9 average length of the major axis of said polyaniline is a 0.1~100μm perpendicular to the longitudinal axis of the polyaniline. The titanium oxide nanotube is composed of continuous titanium oxide (A),
The production method according to any one of claims 1 to 10, which is a titanium oxide nanotube having an average diameter perpendicular to the major axis of 10 to 500 nm and an average length of the major axis of 0.1 to 100 µm. The manufacturing method of the titanium oxide nanotube in any one of Claims 1-11 whose heavy metal content of the said titanium oxide nanotube is 1000 ppm or less. The manufacturing method of the titanium oxide nanotube in any one of Claims 1-12 whose total content of the sodium, potassium, and iron of the said titanium oxide nanotube is 100 ppm or less. Method for producing a titanium oxide nanotube according to any one of the titanium oxide according to claim specific surface area of nanotubes is 30 m 2 / ^g or more 1-13. The method for producing a titanium oxide nanotube according to any one of claims 1 to 14 , wherein the particulate titanium oxide (A) comprises anatase type titanium oxide, rutile type titanium oxide, brookite type titanium oxide or amorphous titanium oxide. The method for producing a titanium oxide nanotube according to any one of claims 1 to 15 , wherein the particulate titanium oxide (A) contains anatase-type titanium oxide. Method for producing a titanium oxide nanotube according to any average particle diameter of claims 1 to 16, which is a 1~100nm of titanium oxide particles (A). The method for producing a titanium oxide nanotube according to any one of claims 1 to 17 , wherein the powder resistance of the titanium oxide nanotube under a pressure of 10 MPa is 1 x 10 ⁷ Ω · m or less. A method for producing a photoelectric conversion element , comprising mixing a titanium oxide nanotube obtained by the method for producing a titanium oxide nanotube according to any one of claims 1 to 18 in a titanium oxide layer of a negative electrode.

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