JP2001205094A - Photocatalyst substance and photocatalyst body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photocatalyst for which visible light is used as an operating light and which is more efficient. SOLUTION: A photocatalyst substance film 12 comprising Sn-O-N and Zn-O-N is formed on a base 10 by means of sputtering using SnO2 and ZnO as a target in nitrogen atmosphere. In addition, after sputtering, crystallization is performed by heat treatment. A nitride oxide film in which SnO2 and ZnO crystallines obtained like this are a base and N is incorporated exhibits good photocatalytic action using not only ultraviolet light, but also visible light as the operating light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photocatalytic substance and a photocatalyst capable of operating with visible light.

[0002]

2. Description of the Related Art Heretofore, as materials exhibiting photocatalysis, titanium oxide (TiO ₂ ), iron oxide (Fe ₂ O ₃ ),
Tungsten oxide (WO ₃ ), tin oxide (SnO ₂ ), bismuth oxide (Bi ₂ O ₃ ), niobium oxide (Nb ₂ O ₅ ), nickel oxide (NiO), copper oxide (Cu ₂ O), zirconium oxide (ZrO) ₂ ), zinc oxide (ZnO), strontium titanate (SrTiO ₃ ), iron titanate (FeT
Oxide semiconductors such as iO ₃ ) and silicon oxide (SiO ₂ ) are known. These photocatalytic materials are semiconductors, which absorb light to generate electrons and holes and exhibit various chemical reactions (for example, decomposition of harmful substances) and bactericidal action.

However, the light that can be absorbed by these semiconductors and used for photoreaction (operating light of the catalyst) is limited by the value of the band gap Eg of each substance. For example, in the case of tungsten oxide, λ ≦ 460 nm (Eg =
2.7 eV), and λ ≦ 388 nm (Eg =
3.2 eV).

[0004]

As shown in FIG. 7, the spectrum of sunlight or fluorescent light is 450 to 60.
It has a peak in the wavelength region of 0 nm, and the component of 400 nm or less is very small. On the other hand, many of the above oxide semiconductors absorb only light in a region of 400 nm or less. Therefore, when these photocatalysts composed of oxide semiconductors are used under sunlight or indoor fluorescent light, there is a problem that the light utilization efficiency is low and a sufficient photoreaction cannot be generated.

An object of the present invention is to provide a photocatalyst substance and a photocatalyst that can absorb light in a longer wavelength range and improve the light use efficiency under sunlight and fluorescent light.

[0006]

According to the photocatalytic substance of the present invention, a part of an oxygen site of a metal oxide crystal exhibiting a photocatalytic action is replaced with a nitrogen atom, and a nitrogen atom is inserted between lattices of the metal oxide crystal. It is characterized by doping or disposing nitrogen atoms at grain boundaries of a polycrystalline aggregate of metal oxide crystals.

As described above, when nitrogen atoms N are arranged in an oxide semiconductor, the valence band of the semiconductor that controls the characteristics of oxygen O is affected, and a new energy level is formed inside the band gap of the oxide. , The band gap becomes narrow.
As a result, an oxide before nitrogen doping can also absorb low-energy long-wavelength light, generate electrons and holes, and exhibit photocatalysis. Further, the life of generated electrons and holes is prolonged by doping with nitrogen. Further, structurally, the adsorptivity of organic substances and gas to the surface of the material is increased, and the catalytic activity is improved by this synergistic effect. Therefore, it is possible to improve the photocatalytic efficiency when using sunlight or fluorescent light as a light source, that is, effects such as harmful gas decomposition, water purification, organic matter decomposition, and antibacterial effect.

[0008] Further, it is possible to exhibit wettability of the object surface by irradiation with visible light and anti-fogging performance, and to maintain its properties for a long time.

The metal oxide exhibiting the photocatalytic action includes tin oxide, zinc oxide, strontium titanate, tungsten oxide, zirconium oxide, niobium oxide, iron oxide, copper oxide, iron titanate, nickel oxide, bismuth oxide, Preferably, it is at least one of silicon oxides.

Further, the above-mentioned photocatalytic substance of an oxide semiconductor (nitride oxide) having nitrogen atoms is used as an internal substance, and titanium oxide (TiO ₂ ) or titanium oxide contains nitrogen as an external substance on the surface of the internal substance. It is preferable that a Ti-ON layer formed is formed. By arranging TiO ₂ or Ti—O—N, which is more stable than the nitride oxide, on the outermost surface, the stability can be improved as compared with the case of the nitride oxide alone. In addition, the internal nitric oxide absorbs visible light to generate electrons and holes, which migrate to TiO ₂ and Ti-ON on the surface and have excellent hydrophilicity and antifouling properties on these surfaces. , Organic matter decomposability can be realized.

In Ti-ON, a part of oxygen sites of a metal oxide such as titanium oxide is replaced by a nitrogen atom (N).
A titanium compound in which nitrogen atoms are doped between lattices or nitrogen atoms are arranged at grain boundaries of a polycrystalline aggregate. The TiO-N expresses a photocatalytic action in a visible light region compared to TiO _2. Therefore, also in this layer, a photocatalytic action can be obtained using visible light as operating light.

[0012]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a view showing a configuration of an embodiment, in which a photocatalyst material film 12 is formed on a substrate 10 of SiO ₂ or the like. SnO ₂ ), zinc oxide (ZnO), strontium titanate (SrTiO ₃ ), tungsten oxide (W
O ₃ ), zirconium oxide (ZrO ₂ ), niobium oxide (N
b ₂ O ₅ ), iron oxide (Fe ₂ O ₃ ), copper oxide (Cu ₂ O),
Iron titanate (FeTiO ₃ ), nickel oxide (Ni
O), bismuth oxide (Bi ₂ O ₃ ), silicon oxide (SiO
₂ ) at least one type of crystal has a nitrogen atom (N)
Is arranged.

Here, N has a chemical bond with its metal atom in the above oxide crystal. For example, SnO ₂
If it is, a chemical bond of Sn-N is included. by this,
By narrowing the band gap, it becomes possible to absorb visible light on the long wavelength side.

Such a photocatalytic substance film 12 can be obtained by, for example, sputtering the above-described oxide as a target in a nitrogen gas atmosphere.

Second Embodiment FIG. 2 shows the configuration of a second embodiment. In FIG. 2A, a photocatalytic substance film 12 is formed on a SiO ₂ substrate 10, and a titanium compound film 14 is formed thereon. The photocatalyst material film 12 is a film similar to the first embodiment described above. On the other hand, the titanium compound film 14 is obtained by doping a TiO ₂ film or a TiO ₂ crystal with a nitrogen atom. A part of the oxygen (O) site of the TiO ₂ crystal is replaced with a nitrogen atom (N), and N is inserted between lattices. This is a titanium compound obtained by doping or disposing N at the grain boundary of a polycrystalline aggregate.

Although FIG. 2 shows a two-layer structure, the boundary between the two is not always clear during the heat treatment or the like, and the structure is such that N gradually decreases toward the surface. This case is more preferable from the viewpoint of prolonging the lifetime of the generated electrons and holes.

With this configuration, visible light is absorbed by the photocatalytic substance film 12 close to the substrate 10, and electrons and holes are generated. These are supplied to a titanium compound film (TiO ₂ film or Ti—O—N film) 14 on the film surface. Therefore, on the surface, the titanium compound film 14 exhibits a photocatalytic action.

Thus, Sn-ON and Zn-O-
Stable and a TiO ₂ than like N, by the TiO-N is disposed on the outermost surface, it is possible to improve the stability as compared with the case of Sn-O-N or Zn-O-N and the like alone . Note that T
i-O-N expresses a photocatalytic action in a visible light region compared to TiO _2. Therefore, also in this layer, a photocatalytic action can be obtained using visible light as operating light.

The photocatalyst composed of a photocatalytic substance of a nitric oxide and a titanium compound having a gradient composition as described above is shown in FIG.
As shown in (b), it is also preferable to form particles having a photocatalytic substance portion 22 inside and a titanium compound portion 24 outside. It is preferable that such a particulate photocatalyst is mixed in a binder for a paint and used like a paint.

[0021]

EXAMPLES Example 1 In this example, a photocatalytic substance having a Sn-ON structure in which SnO ₂ crystal is doped with N will be described.

In this embodiment, the photocatalytic substance was prepared by RF magnetron sputtering. The target is 3
An inch diameter SnO ₂ sintered target was used. The target is sputtered in a 40% N ₂ -Ar atmosphere under a pressure of 0.5 Pa, and is crystallized by heat treatment at 550 ° C. for 90 minutes in an N ₂ atmosphere.
An ON film was formed. The input power was 600 W × 2.

On the other hand, a SnO ₂ film was also formed for comparison. In this case, the target was sputtered in a 20% O ₂ -Ar atmosphere and crystallized by heat treatment at 550 ° C. in an O ₂ atmosphere for 90 minutes.

The crystallinity of the Sn-ON film is determined by X-ray diffraction.
Apparently, tetragonal SnO_Two(110), (10
1), (211) diffraction lines were observed. But these
Is SnO _TwoShift to a slightly lower angle compared to the film
I'm From this, by doping with nitrogen N,
Lattice spacing is SnO_TwoIt is thought to be more widespread.

Also, XPS (X-ray Photoem)
When the chemical bonding state of the nitrogen atom was determined from the measurement result of the nitrogen N1s shell by the issue Spectroscopy, the nitrogen atom in the Sn-ON of the present invention showed a peak derived from the Sn-N bond.

FIG. 3 shows the light absorption spectrum of this film.
The Sn-ON film is made of SnO_TwoLonger absorption edge compared to membrane
It has shifted to the long side. This is because of the N doping,
nO _TwoA new level is formed in the band gap of
This is due to the narrow effective band gap.

The photocatalytic function of this film was evaluated from the decomposition performance of methylene blue. In this evaluation, the decomposition performance of methylene blue applied to the surface of the Sn-ON film was measured at a wavelength of 600 nm.
It was measured as the change in the absorbance (ΔABS) of the membrane at m. Using a 500 W Xe lamp as the irradiation light source, wavelength λ ≧ 2
The wavelength λ ≧ 3 is obtained by irradiating light containing ultraviolet light of 00 nm and by limiting the irradiation wavelength range by an optical filter.
The test was performed for the case where visible light of 80 nm was irradiated.

FIG. 4 shows the result. Thus, Sn
In the -ON film, irradiation ranging from ultraviolet light to visible light (λ ≧ 2
00 nm), a large catalytic activity can be obtained. This is because the catalytic activity in visible light of λ ≧ 380 nm is improved. This is the effect of N doping. It can be said that this result reflects the light absorption spectrum characteristics in FIG.

Embodiment 2 In this embodiment, a photocatalytic substance having a Zn—ON structure in which ZnO crystal is doped with N will be described.

Also in this example, a photocatalytic substance was prepared by RF magnetron sputtering, as in Example 1 described above. As the target, a ZnO sintered target having a diameter of 3 inches was used, and other conditions were the same as in Example 1. That is, the target is sputtered under a pressure of 0.5 Pa in a 40% N ₂ -Ar atmosphere to perform sputtering.
Crystallization was performed by heat treatment at 50 ° C. in an N ₂ atmosphere for 90 minutes to form a Zn—O—N film. Note that the input power was 300 W × 2.

On the other hand, a ZnO film was also formed for comparison. In this case, the target was sputtered in an Ar atmosphere and crystallized by heat treatment at 550 ° C. in an O ₂ atmosphere for 90 minutes.

When the crystallinity of the Zn-ON film was examined by X-ray diffraction, a (002) diffraction line of hexagonal ZnO was observed. However, this diffraction line is slightly shifted to the lower angle side as compared with the ZnO film. From this, it is considered that the lattice spacing is wider than that of ZnO by doping with nitrogen N.

Also, XPS (X-ray Photoem)
When the chemical bonding state of the nitrogen atom was determined from the measurement result of the nitrogen N1s shell by the issue Spectroscopy, the nitrogen atom in the Zn-ON of the present invention showed a peak derived from the Zn-N bond.

FIG. 5 shows the light absorption spectrum of this film.
The absorption edge of the Zn—O—N film is shifted to the longer wavelength side as compared with the ZnO film. This is because Zn doping causes Zn
This is because a new level is formed in the band gap of O and the effective band gap is narrowed.

The photocatalytic function of this film was evaluated from the decomposition performance of methylene blue. In this evaluation, the decomposition performance of methylene blue applied to the surface of the Zn-ON film was measured at a wavelength of 600 n.
It was measured as the change in the absorbance (ΔABS) of the membrane at m. Using a 500 W Xe lamp as the irradiation light source, wavelength λ ≧ 2
The wavelength λ ≧ 3 is obtained by irradiating with light containing ultraviolet light of 00 nm and by limiting the irradiation wavelength range with an optical filter.
The test was performed for the case where visible light of 80 nm was irradiated.

FIG. 6 shows the result. Thus, Zn
In the -ON film, irradiation ranging from ultraviolet light to visible light (λ ≧ 2
00 nm), a large catalytic activity can be obtained. This is because the catalytic activity in visible light of λ ≧ 380 nm is improved. This is the effect of N doping. It can be said that this result reflects the light absorption spectrum characteristics in FIG.

"Others" In addition to the two embodiments of tin oxide (SnO ₂ ) and zinc oxide (ZnO), strontium titanate (SrTiO ₃ ) and tungsten oxide (W
O ₃ ), zirconium oxide (ZrO ₂ ), niobium oxide (N
b ₂ O ₅ ), iron oxide (Fe ₂ O ₃ ), copper oxide (Cu ₂ O),
Iron titanate (FeTiO ₃ ), nickel oxide (Ni
O), bismuth oxide (Bi ₂ O ₃ ), silicon oxide (SiO
₂ ) at least one type of crystal has a nitrogen atom (N)
Can be used.

In the above description, an example in which a thin film is formed by sputtering using an oxide target has been described. However, these photocatalytic properties are inherent to the material, such as sputtering using a metal target,
Similar characteristics can be obtained in the form of a thin film formed by vapor deposition, a thin film formed by a sol-gel method, or a fine powder.

[0039]

As described above, by arranging nitrogen atoms in a metal oxide semiconductor exhibiting a photocatalytic action, even low-energy long-wavelength light is absorbed, and electrons and holes are generated to generate photocatalysts. An effect can be exhibited. Therefore, the photocatalytic efficiency when sunlight, fluorescent light is used as the light source,
That is, effects such as harmful gas decomposition, water purification, organic matter decomposition, and antibacterial effect can be improved.

In addition, by disposing TiO ₂ or Ti—O—N, which is more stable than nitric oxide, on the surface of the above-mentioned photocatalytic substance of nitric oxide, compared with the case of nitric oxide alone. Stability can be improved. In addition, the internal nitric oxide absorbs visible light to generate electrons and holes, which migrate to TiO ₂ and Ti-ON on the surface and have excellent hydrophilicity and antifouling properties on these surfaces. , Organic matter decomposability can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment.

FIG. 2 is a diagram illustrating a configuration of a second embodiment.

FIG. 3 is a view showing a light absorption spectrum of Example 1.

FIG. 4 is a diagram showing a photocatalytic function of Example 1.

FIG. 5 is a diagram showing a light absorption spectrum of Example 2.

FIG. 6 is a diagram showing a photocatalytic function of Example 2.

FIG. 7 is a diagram showing emission spectra of sunlight and fluorescent light.

[Explanation of symbols]

10 substrate, 12 photocatalytic substance film, 14 titanium compound film.

Continuing from the front page (72) Inventor Takeshi Owaki 41, Chukumi Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 at Toyota Central Research Laboratory Co., Ltd. Address 1 Toyota Central R & D Co., Ltd. F-term (reference) 4G069 AA02 AA08 BA48A BA48C BC12A BC12B BC12C BC22A BC22B BC22C BC25A BC25B BC25C BC31A BC31B BC31C BC35A BC35B BC35C BC50A BC50B BC50C BCBC BCBC BCB BCBC BC68A BC68B BC68C BD05A BD05B BD05C CA01 CA11 FB02

Claims (3)

[Claims] 1. A method for substituting a part of an oxygen site of a crystal of a metal oxide exhibiting a photocatalytic action with a nitrogen atom, doping a nitrogen atom between lattices of a crystal of the metal oxide, or a polycrystalline assembly of a crystal of the metal oxide. Photocatalytic substance with nitrogen atoms arranged at the grain boundaries of the body. 2. The photocatalytic substance according to claim 1, wherein the metal oxide exhibiting the photocatalytic action is tin oxide, zinc oxide, strontium titanate, tungsten oxide, zirconium oxide, niobium oxide, iron oxide, copper oxide, A photocatalytic substance that is at least one of iron titanate, nickel oxide, bismuth oxide, and silicon oxide. 3. A photocatalytic substance according to claim 1 or 2 as an internal substance, and titanium oxide or titanium oxide containing nitrogen in titanium oxide as an external substance on the surface of the internal substance.
A photocatalyst formed with a -N layer.