JPH11255514A - Production of visible light absorptive titanium oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing titanium oxide having photocatalytic activities even within a region of visual light by the simpler method compared to an ion implantation, and a photocatalyst produced by the method and having the photocatalytic activities within the region of the visual light. SOLUTION: This method for producing visual light absorptive titanium oxide comprises adding a fluorine scavenger to an aqueous solution containing a fluoro complex titanium compound and a metal compound to precipitate the titanium oxide having a doped metal ion derived from the metal compound. The visible light absorptive photocatalyst comprises the titanium oxide produced by the production method and having the doped metal ion. The titanium oxide having the doped metal ion can be a powder or a thin membrane on a substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal oxide-doped titanium oxide useful as a visible light absorbing photocatalyst and a visible light absorbing photocatalyst.

[0002]

2. Description of the Related Art Titanium oxide is known to have a photocatalytic function, and by forming a titanium oxide layer on the surface,
Since it can impart antibacterial properties, antifouling properties, antifogging properties, and the like, applications in a wide range of fields are being promoted.

[0003]

However, the wavelength band of light in which titanium oxide can be used is limited to the ultraviolet region.
In order to effectively use light contained in sunlight, it is desirable that not only light in the ultraviolet region but also light in the visible light region can be used effectively. From this point of view, Yasuno et al. Successfully implanted chromium ions into titanium oxide by ion implantation and succeeded in decomposing NOx with 450 nm light in the visible light region (1996, Proc. In DOE Workshop on). Solar H
ydrogen Production (1996)). Generally, when a semiconductor is doped with a specific metal, an impurity level is generated in the semiconductor, and a new absorption band is generated in the absorption band of the semiconductor. However, it has been said that the photocatalytic reaction does not proceed because electrons and holes generated by photoexcitation of the hand gap are recombined and deactivated on chromium ions. However, Yasuno and colleagues have made it possible to control the solid state properties of titanium oxide by injecting chromium ions into titanium oxide by irradiating a metal ion beam accelerated to high energy.

[0004] Titanium oxide implanted with chromium ions and prepared by the above-mentioned method has a photocatalytic activity even in the visible light region. Although the ion implantation method is a method generalized in the semiconductor industry, it is difficult to apply the ion implantation method as it is to the production of a general-purpose photocatalyst, because the apparatus is large and the operation cost is high.

Accordingly, an object of the present invention is to provide a method for producing titanium oxide having photocatalytic activity even in the visible light region by a method much easier than the ion implantation method. It is a further object of the present invention to provide a photocatalyst having photocatalytic activity in a new visible light region produced by the above method.

[0006]

According to the present invention, there is provided a method of adding a fluorine scavenger to an aqueous solution containing a fluoro complex titanium compound and a metal compound to precipitate titanium oxide doped with metal ions derived from the metal compound. The present invention relates to a method for producing visible light-absorbing titanium oxide, characterized by the following. The present invention also relates to a visible light absorbing photocatalyst comprising titanium oxide doped with metal ions produced by the above production method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The process for producing a visible light absorbing titanium oxide according to the present invention comprises the steps of: adding a fluorine scavenger to an aqueous solution containing a fluorocomplex titanium compound and a metal compound; The deposited titanium oxide is deposited.

[0008] The visible light absorbing titanium oxide of the present invention is obtained by doping metal ions into titanium oxide. Doping titanium oxide with a metal ion imparts visible light absorption to the titanium oxide, so that photocatalytic activity can be exhibited not only by ultraviolet light but also by visible light. As metal ions suitable for doping for the purpose of imparting visible light absorption,
For example, at least one ion selected from the group consisting of chromium ions, iron ions, and vanadium ions can be given. However, the present invention is not limited to these, and any metal ion that can impart visible light absorption may be used. Such metal ions include aluminum, bismuth, erbium, gallium, gadolinium, boromium, indium, lanthanum, lutetium, manganese, niobium, neodymium, praseodymium, platinum, rhodium, scandium, samarium, tin, tantalum, terbium, thulium, Examples of the ion include tungsten, yttrium, ytterbium, and zymconium. The doping amount of the metal ion can be appropriately determined in consideration of the type of the metal ion and the visible light absorption and photocatalytic activity required for titanium oxide. In the production method of the present invention, an aqueous solution containing a fluorocomplex titanium compound and a metal compound is prepared. The aqueous solution containing the fluoro complex titanium compound can be prepared by dissolving titanium oxide in hydrofluoric acid. Alternatively, a titanium hydroxide or oxyhydroxide is dissolved in an aqueous solution of an alkali metal hydrogen difluoride such as ammonium hydrogen difluoride or sodium hydrogen difluoride to synthesize a fluoro complex titanium compound. Can also. The aqueous solution containing the fluoro complex titanium compound and the metal compound can be prepared by mixing the aqueous solution containing the fluoro complex titanium compound and the aqueous solution containing the metal compound.

The concentration of the fluoro complex titanium compound can be appropriately selected, but in order to improve the transparency and homogeneity of the precipitate, the fluoro complex titanium compound is usually used in an amount of 10 ^{-9 to} 9 as a metal. × 10 ⁻² mol / L, preferably 10 ^{−6 to} 6 × 1
It is preferable to prepare and use an aqueous solution having a concentration of 0 ^-2 mol / L.

As a metal compound for doping titanium oxide with metal ions, for example, Cr (NO ₃ ) _{3
· XH 2 O, VOSiO 4 ·} 2H 2 O, VOCl 3, Cr 2
(SO ₄ ) ₃ · 18H ₂ O, CrCl ₃ · xH ₂ O, FeC
_{l 2 · 4H 2 O, FeCl} 2, FeCl 3 · 6H 2 O, Fe
_{Cl 3, Fe (NO 3)} 2 · 9H 2 O, FeSO 4 · 7H
₂ O, FeSO ₄ , (NH ₄ ) Fe (SO ₄ ) ₃ .xH ₂ O,
Co (NO ₃ ) ₂ .6H ₂ O is exemplified. The concentration of the metal compound is, for example, 10 ⁻⁴ to 10 m per liter of the treatment liquid in consideration of the solubility and the doping amount to titanium oxide.
ol. Further, the metal compound can be supplemented and added during the reaction.

[0011] The fluoride ion scavenger used in the present invention may be any as long as it can trap fluorine ions from an aqueous solution containing a fluoro complex titanium compound and precipitate titanium oxide. Generally, fluoride ion scavengers include:
There are a homogeneous system which is used by being dissolved in a liquid phase, and a heterogeneous system which is a solid. Depending on the purpose, either one of these two may be used or both may be used.

The homogeneous fluoride ion scavenger moves the equilibrium of fluorine ions to precipitate titanium oxide by reacting with hydrogen fluoride to form a stable fluoro complex titanium compound and / or fluoride. Things. Besides boric acid such as orthoboric acid and metaboric acid, examples thereof include aluminum chloride, sodium hydroxide, and aqueous ammonia. Such a capture agent is usually used in the form of an aqueous solution, but may be added in the form of a powder and dissolved in the system. Such addition of the scavenger may be performed once or several times intermittently, or may be performed continuously at a controlled feed rate, for example, at a constant rate.

As the heterogeneous fluoride ion scavenger,
Aluminum, titanium, iron, nickel, magnesium,
Examples thereof include metals such as copper and zinc, ceramics such as glass, and compounds such as silicon, calcium oxide, boron oxide, aluminum oxide, silicon dioxide, and magnesium oxide. When such solid matter is added or inserted into the solution, F near solids ^- are consumed, because its concentration decreases, the chemical equilibrium of the portion is shifted, titanium oxide is precipitated. When such a solid is used, depending on the method of adding or inserting and the reaction conditions, it is also possible to precipitate titanium oxide on the entire surface of the substrate immersed in the aqueous solution,
It is also possible to limit the precipitation to selected localities, i.e. in the vicinity where the solids are present. Alternatively, by using a combination of a homogeneous and a heterogeneous fluoride ion scavenger, the thickness of the deposit thin film on the substrate surface can be partially increased. The homogeneous fluoride ion scavenger is usually used in an amount of 10 ⁻⁴ to 10 equivalents to the equivalent of the fluoride ions in the solution.
It is 1,000%, and preferably used in the range of 10 ^{-2 to} 500%.

In the production method of the present invention, the aqueous solution containing the fluoro complex titanium compound and the metal compound may contain titanium oxide particles as seed crystals. The seed crystal is in the range of 0.001 to 10 μm, preferably 0.0
Fine particles having a size of about 01 to 1 μm are preferable.
It can be appropriately determined in consideration of the amount of titanium oxide to be deposited and the like. The precipitation rate can be controlled by selecting the particle size and the amount of the seed crystal to be added. If necessary, seed crystals can be replenished during the precipitation.

In the production method of the present invention, the titanium oxide particles doped with metal ions precipitated in the aqueous solution are recovered from the aqueous solution, and the titanium oxide particles doped with the metal ions are recovered.
(Powder) can be obtained. The recovery of the titanium oxide particles from the aqueous solution can be performed by a conventional method. Or,
According to the production method of the present invention, the substrate can be immersed in an aqueous solution, and a metal oxide-doped titanium oxide thin film can be deposited on the substrate. The substrate can be made of, for example, glass or plastic (organic polymer material). The plastic may be a thermoplastic resin or a thermosetting resin. Since the production method of the present invention does not require heating, there is an advantage that it can be applied to a plastic substrate having poor heat resistance. The shape and form of the plastic substrate are arbitrary, and are not limited to plate shapes, and those having complicated shapes can also be used. For example,
It can be a bulk, plate, or porous body.

Further, if necessary, the substrate has an underlayer on the surface on which the photocatalytic thin film is formed, so that the adhesion between the substrate and the thin film is improved and the deterioration of the substrate due to the photocatalytic action of the thin film is prevented. It is preferable from the viewpoint of. As such an underlayer, for example, SiO ₂ , Al ₂ O ₃ , Zr
Examples include an oxide layer such as O ₂ and ITO, and a fluoride layer such as CaF ₂ . The thickness of the underlayer can be about 0.1 to 1 μm from the viewpoint of sufficiently exhibiting the effect of the underlayer. The underlayer can be formed by a dry method such as a vacuum evaporation method or a sputtering method, or a wet method such as an aqueous solution method or a sol-gel method.

The substrate may be immersed in the aqueous solution of the fluoro complex compound before, during or after the addition or insertion of the fluoride scavenger. However, when using a substrate that may be affected by the system, attention must be paid to the composition of the solution, the reaction conditions, and the timing of immersion. The precipitation reaction temperature can be arbitrarily set as long as the system maintains an aqueous solution, but is preferably in the range of 10 to 80 ° C. The reaction time is also arbitrary. For example, when the target precipitate is large, the reaction time can be lengthened accordingly.

The thus obtained powder and thin film of metal ion-doped titanium oxide are preferably subjected to a heat treatment to make the doping level of metal ions uniform.
Heat treatment for uniform doping level, for example, 400
It can be performed at a temperature of about 600 ° C. for about 5 to 120 minutes. The heat treatment conditions can be appropriately determined in consideration of the metal ions to be doped, the required doping level, and the like.
In addition, when the metal ion-doped titanium oxide is a thin film provided on a substrate, the heat treatment conditions for making the doping level uniform are determined in consideration of the material of the substrate.

[0019]

The present invention will be described in more detail with reference to the following examples. Example 1 30 mg of TiO ₂ anatase fine particles were previously suspended in 400 ml of pure water. To this suspension, 2.8 g of ammonium hexafluorotitanate (NH ₄ ) ₂ TiF ₆ was added and stirred to dissolve. Next, 0.35 g of chromium nitrate [Cr (NO ₃ ) ₃ .xH ₂ O] was added and dissolved to obtain a treatment liquid. While maintaining the treatment liquid thus prepared at 35 to 40 ° C., 10 g of boron oxide was added and stirred. Thereafter, a 50 × 70 × 1 mm non-alkali glass substrate was immersed in this treatment liquid. 4.5 while maintaining this state
Left for hours. After the elapse of the treatment time, the substrate was taken out of the water bath, washed with water, and dried. Further, the substrate was placed in an electric furnace, heated to 500 ° C., and held for 1 hour to obtain a substrate on which the chromium ion-doped titanium oxide thin film of the present invention was formed. The transmission spectrum of this substrate is shown as (a) in FIG.
Chromium ion doped titanium oxide thin film is titanium oxide thin film
It can be seen that the absorption edge is shifted to the longer wavelength (visible light) side as compared with (c). The titanium oxide thin film is made of chromium nitrate [Cr
It was prepared under the same conditions except that a processing solution not containing (NO ₃ ) ₃ .xH ₂ O] 0.35 g was used.

Example 2 The procedure was performed except that the addition amount of chromium nitrate [Cr (NO ₃ ) ₃ .xH ₂ O] was 1.0 g, and the immersion of the glass substrate in the treatment liquid was maintained at 30-40 ° C. In the same manner as in Example 1, a chromium ion-doped titanium thin film of the present invention was formed on a substrate. The transmission spectrum of this substrate is shown as (b) in FIG. It can be seen that the absorption edge of the chromium ion-doped titanium oxide thin film is shifted to the longer wavelength (visible light) side as compared with the titanium oxide thin film (c).

Example 3 A treatment liquid was prepared using 1.0 g of ferric nitrate [Fe (NO ₃ ) ₃ .xH ₂ O] instead of chromium nitrate [Cr (NO ₃ ) ₃ .xH ₂ O]. An iron ion-doped titanium thin film of the present invention was formed on a substrate in the same manner as in Example 2 except for the above. The transmission spectrum of this substrate is
This is shown as (a) in FIG. The absorption edge of the iron ion-doped titanium oxide thin film is longer at the longer wavelength (visible light) side than the titanium oxide thin film (c).
It can be seen that the shift is 5 to 30 nm.

Example 4 Salad oil was added to the iron ion-doped titanium oxide thin film and the titanium oxide thin film prepared in Example 3, respectively, at 0.1 mg / cm ^2.
At a rate of Next, both are black light (10W)
Placed below, oil resolution was compared from weight loss. As a result, in each case, the oil was completely decomposed in 7 to 10 days. Further, the same decomposition experiment was performed using an incandescent lamp having a small amount of ultraviolet light instead of the black light. As a result, while weight loss was hardly observed in the titanium oxide thin film, oil weight loss was observed in the iron ion-doped titanium oxide thin film at a rate of about 1/5 when black light was used.

[0023]

According to the present invention, titanium oxide having photocatalytic activity even in the visible light region can be produced by a method much simpler than the ion implantation method. Further, the titanium oxide doped with metal ions obtained by the method of the present invention is a photocatalyst having excellent absorption in the visible light region as compared with titanium oxide and having more excellent photocatalytic activity than titanium oxide.

[Brief description of the drawings]

1 shows transmission spectra (a) and (b) of a substrate on which a chromium ion-doped titanium thin film prepared in Examples 1 and 2 is formed, and transmission spectra (c) of a substrate on which a titanium oxide thin film is formed.

FIG. 2 shows a transmission spectrum (a) of a substrate on which an iron ion-doped titanium thin film prepared in Example 3 was formed and a transmission spectrum (b) of a substrate on which a titanium oxide thin film was formed.

Claims (8)

[Claims] 1. A visible light absorbing agent comprising adding a fluorine scavenger to an aqueous solution containing a fluorocomplex titanium compound and a metal compound to precipitate titanium oxide doped with metal ions derived from the metal compound. A method for producing titanium oxide. 2. The method according to claim 1, wherein the metal ions are at least one ion selected from the group consisting of chromium ions, iron ions, and vanadium ions. 3. The production method according to claim 1, wherein the aqueous solution contains a seed crystal composed of titanium oxide. 4. The titanium oxide particles doped with metal ions precipitated in the aqueous solution are recovered from the aqueous solution.
4. The production method according to any one of 3. 5. The production method according to claim 1, wherein the substrate is immersed in an aqueous solution, and a thin film of titanium oxide doped with metal ions is deposited on the substrate. 6. The method according to claim 1, wherein the titanium oxide doped with the precipitated metal ions is subjected to a heat treatment for making the doping level uniform. 7. A visible light-absorbing photocatalyst comprising titanium oxide doped with metal ions produced by the production method according to claim 1. Description: 8. The photocatalyst according to claim 7, wherein the titanium oxide doped with metal ions is a powder or a thin film on a substrate.