JP2001347162A - Photocatalytic material with thin titanium dioxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalytic material which performs the clean-up of environmental pollutants and water decomposition while irradiating with light. SOLUTION: A thin film of anatase type titanium dioxide having at least one of (004) and (112) faces as a crystal orientation face in a direction perpendicular to the crystal surface is formed on a substrate. The thickness of the thin film is preferably >=500 nm from the viewpoint of further enhancement of the catalytic activity. A metal or metal oxide is preferably carried on the surface of the thin film from the viewpoint of further enhancement of the catalytic activity by the acceleration of charge separation and ruthenium oxide is particularly desirably used as the metal oxide so as to enhance the photocatalytic activity in water decomposition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalyst material having a titanium oxide thin film, and more particularly to a photocatalyst material for purifying environmental pollutants or decomposing water by irradiating light.

[0002]

2. Description of the Related Art Conventionally, a photocatalyst is used to decompose odor components in an atmosphere to deodorize the water or decompose water to produce hydrogen. Examples of such a photocatalyst include metal compound semiconductors such as titanium oxide, zinc oxide, tungsten oxide, iron oxide, strontium titanate, cadmium sulfide, and cadmium selenide, among which titanium oxide is most widely used. There have been many studies using titanium oxide as a photocatalyst. For example, Japanese Patent Application Laid-Open No. H10-152396 proposes a technique in which a crystal orientation film made of titanium oxide oriented in a specific direction is formed on a substrate surface to obtain various properties such as antibacterial properties.

[0003]

By the way, in the purification of environmental pollutants and the production of hydrogen by water splitting, particularly in the field of water splitting, there is a practical need for improvement of the catalytic activity of titanium oxide. At present, titanium oxide having sufficiently high catalytic activity has not yet been obtained. The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a photocatalyst material having high photocatalytic activity.

[0004]

According to the present invention, a thin film of anatase type titanium oxide having at least one crystal orientation plane of (004) and (112) is formed on a substrate in a direction perpendicular to the crystal surface. A photocatalyst material characterized by the following is provided.

At this time, from the viewpoint of further improving the photocatalytic activity, the thickness of the thin film is preferably 500 nm or more.

[0006] From the viewpoint of further improving the photocatalytic activity by accelerating the charge separation, it is preferable to carry a metal or a metal oxide on the surface of the thin film. Ruthenium oxide is particularly desirable among oxides.

Further, since a thin film of anatase type titanium oxide can be easily formed, it is preferable to use a substrate containing silicon as a main component as the substrate. From the viewpoint of preventing the titanium oxide thin film from peeling off, it is preferable to form a titanium thin film on a substrate containing silicon as a main component and then form the titanium oxide thin film thereon. In order to further improve the photocatalytic activity, it is preferable to further form a platinum thin film between the titanium oxide thin film and the titanium thin film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies to obtain titanium oxide having sufficiently high catalytic activity for practical use. As a result, in titanium oxide, a specific crystal orientation is closely related to catalytic activity. This has led to the present invention.

That is, a major feature of the photocatalyst material of the present invention is that a thin film of anatase-type titanium oxide having at least one crystal orientation plane of (004) and (112) in the direction perpendicular to the crystal surface is formed on a substrate. It is in. In the present invention, the titanium oxide thin film means a thin film made of single crystal or polycrystal. Further, the single crystal thin film,
The whole film includes one composed of a single crystal, and one composed of many crystals having the same three-dimensional crystal orientation.

The titanium oxide formed on the substrate in the photocatalyst material of the present invention must first be of an anatase type. As the crystal structure of titanium oxide, anatase type, rutile type, and blockite type are known, but anatase type titanium oxide is used in the present invention because it shows the highest catalytic activity. Such decomposition by the photocatalytic material is performed by the following operation. That is, when light with a wavelength having energy equal to or greater than the band gap is applied to the photocatalyst, excitation occurs on the surface of the photocatalyst material, and electrons in the valence band jump over the band gap and move to the conduction band. As a result, holes lacking electrons are generated in the valence band and contribute to the oxidation reaction, while electrons move to the conduction band and contribute to the reduction reaction.

The titanium oxide formed on the substrate must have at least one of (004) and (112) crystal orientation planes in a direction perpendicular to the crystal surface. (00
By having at least one of the crystal orientation planes of 4) and (112), the photocatalytic activity is remarkably improved, and purification of environmental pollutants and water decomposition can be performed without any practical problems.

Such a titanium oxide thin film having a crystal plane oriented in a specific direction can be formed by a chemical vapor deposition (CVD) method.
VD). Specifically, it is formed by spraying a vaporized titanium alkoxide together with an inert gas onto a heated substrate surface under atmospheric pressure. In order to control the crystal structure, crystal orientation, film thickness, crystal grain size, and particle size distribution of the titanium oxide thin film formed on the substrate surface to the desired ones, the vaporization temperature and supply amount of the organometallic complex, the inert gas The flow rate, the substrate temperature, and the like may be adjusted.

The titanium alkoxide used as a material for forming the titanium oxide thin film includes titanium tetramethoxide, titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, titanium diethoxydiisopropoxide, titanium dimethoxydibutoxide. ,
Titanium tetrakis (2-ethylhexyl oxide), titanium tetrastearyl oxide and the like can be suitably used. As the inert gas to be used, a conventionally known gas such as a nitrogen gas, an argon gas, and a helium gas can be used.However, it is preferable to use a nitrogen gas from the viewpoint of economy and the like. It is particularly preferred to use nitrogen gas. The vaporization temperature of the titanium alkoxide as the raw material may be appropriately determined according to the type of the raw material, but is preferably in the range of 70 to 150 ° C.

The thickness of the titanium oxide thin film is 500 nm
It is preferable that it is above. If the thickness is less than 500 nm, sufficient photocatalytic activity may not be obtained. A more preferred film thickness is 1,000 nm or more. A preferred upper limit is 2,000 nm. The crystal grain size for forming a thin film is preferably in the range of 100 nm or less. This is because the efficiency of the photocatalytic reaction is improved by making the crystal grain size approximately equal to the wavelength of the irradiation light.

In order to further enhance the photocatalytic activity by accelerating the charge separation, a metal or an oxide thereof may be supported on the surface of the titanium oxide thin film. Such metals and metal oxides include Pt, Rh, Pd, Os, I
Metals such as r, Ru, Au, Ag, Cu, Cr, Ba, and oxides thereof, among which are chemically stable noble metals (Pt, Rh, Pd, Os, Ir, Ru, Au,
Ag) and these oxides are preferred. In order to improve the photocatalytic activity in water splitting, ruthenium oxide is particularly desirable among the above-mentioned metal oxides. When these metals or metal oxides are carried on the surface of the thin film, the photocatalytic activity is improved because electrons generated in the titanium oxide thin film by light irradiation easily flow into these metal parts and reduce the substances adsorbed there. It is thought to work. The amount to be supported on the thin film surface may be appropriately determined depending on the substance to be reduced and the use of the photocatalyst material.
The range of ３3 wt% is preferred. In order to support the metal or metal oxide on the titanium oxide thin film, a coating method, an immersion method, a sputtering method, a thermal CVD method,
A conventionally known method such as a CVD method may be used.

The substrate used in the present invention is not particularly limited as long as it can withstand heating during the formation of a thin film by the CVD method. Examples thereof include metals, glass, ceramics, ceramics, plastics, wood, and composites thereof. Can be used. Among them, those containing silicon as a main component are preferable because a thin film of anatase type titanium oxide is easily formed. Examples of the base material containing silicon as a main component include silicone and silica oxide. From the viewpoint of preventing the titanium oxide thin film from peeling, it is preferable to form a titanium thin film on a substrate containing silicon as a main component, and then form the titanium oxide thin film thereon. In order to further improve the photocatalytic activity, it is preferable to further form a platinum thin film between the titanium oxide thin film and the titanium thin film. The holes generated by the light irradiation are used for the oxidation reaction on the titanium oxide thin film,
The generated electrons move to a platinum thin film, where they are used for a reduction reaction. This is because the location of the oxidation / reduction reaction is separated as described above, whereby recombination of electrons and holes is suppressed and the efficiency of the photocatalytic reaction is improved. The above-mentioned thin films are formed by coating method, dipping method, sputtering method, heat C
A conventionally known method such as a VD method and a MOCVD method may be used.

The shape of the base material is not particularly limited, and may be a simple shape such as a sphere, a cylinder, a cylinder, or a plate-like material such as a tile, a wall material, or a floor material; It may be of a shape. In addition, curved mirrors and signs, reflectors, painting and lighting in tunnels, outer walls,
Roof, sash, mirror, showcase, show window,
It can be used for signboards, displays, solar cells, glasses, optical lenses, endoscope lenses, paints, interior parts, and the like. The surface of the base material may be porous or dense.

When the photocatalyst of the present invention is irradiated with light having a wavelength having energy equal to or greater than the band gap of titanium oxide as a photocatalyst, environmental pollutants existing near the photocatalyst material are oxidized or decomposed and removed. If it is disposed in water, water decomposition occurs and hydrogen is generated. Environmental pollutants that are oxidized or decomposed and removed by photocatalytic reactions include, for example, various biological oxygen demanding substances and air pollutants, as well as pesticides such as herbicides, bactericides, and insecticides, bacteria, and radioactive bacteria. -Microorganisms such as fungi, algae, and molds.

As a light source, sunlight, a fluorescent lamp, a black light, a mercury lamp or the like can be used. Since titanium oxide can only absorb ultraviolet light, an inorganic substance such as chromium oxide may be added so that visible light can also be absorbed. In this case, the added inorganic substance may act as an impurity and recombine the electron-hole pairs generated by light irradiation, so that atoms such as chromium and vanadium are implanted into titanium oxide by ion implantation to be in the visible region. You may make it an absorption band.

Another method for expanding the light absorption range is as follows.
There is a method in which a substance (dye) having an absorption band in the visible region is attached to the surface of titanium oxide. For example, a dye such as an organic compound such as eosin or rhodamine B or a metal complex such as a ruthenium complex absorbs light in the visible region and enters an energy state where electrons are high. Then, when these electrons move to the conduction band of titanium oxide, the state becomes the same as that of titanium oxide itself absorbing the light, and a photocatalytic reaction occurs.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but it should be understood that the present invention is by no means restricted thereto.

(Preparation of Samples) Samples A to C were prepared by forming a thin film of titanium oxide on one side of a substrate having the materials and temperatures shown in Table 1 by MOCVD (metal organic chemical vapor deposition).
And Table 1 also shows the crystal structure and the preferred orientation plane of the formed thin film.

[0023]

[Table 1]

(Evaluation of decomposition performance of environmental pollutants) Samples A, B and C prepared above were placed in a 2 l bag filled with air.
, And acetaldehyde, which is an environmental pollutant, was injected with a syringe. And about 80 kW / c
irradiating ultraviolet light m ^2, and was measured every predetermined time for concentrations in the bag acetaldehyde using Kitagawa acetaldehyde detectors. The results are shown in FIG. As is clear from FIG. 1, all of Samples A, B and C decomposed acetaldehyde, but Sample A which was an anatase type titanium oxide was used.
And B had better decomposition performance than Sample C which was rutile type titanium oxide. The reason why relatively good catalytic activity was observed in this case even with rutile-type titanium oxide, which is considered to have low catalytic activity, is presumably because rutile-type titanium oxide and anatase-type and blockite-type crystal structures were mixed.

(Evaluation of Performance of Photocatalytic Activity) The photocatalytic activities of Samples A, B and C were evaluated by voltammetry. FIG. 2 shows a schematic diagram of the apparatus used. Sample 1,
A platinum electrode 3 and a reference electrode 4 are disposed in an electrolytic cell, and each is connected to a potentiostat 2. Then, the sample 1 is irradiated with ultraviolet light, a voltage V ₁ between the sample and the reference electrode, a voltage between the platinum electrode and the reference electrode, while measurement of the voltage V ₂ respectively, the sample - was measured current I between the platinum electrodes. Further, for comparison, the voltage and the current were measured without performing the ultraviolet irradiation. The results are shown in FIG. 3 with the difference between the voltages V ₁ and V ₂ on the horizontal axis and the current I on the vertical axis. According to FIG. 3, it can be seen that when no ultraviolet light is applied, no current flows even if the potential increases, that is, no catalytic activity is obtained.
In addition, it was found that samples A and B flow more current than sample C, that is, have higher catalytic activity.

(Evaluation of performance of water splitting) Ruthenium chloride (R
Samples A, B, and C were immersed in a solution having a uCl ₄ ) concentration of 0.5 mM and then baked, whereby ruthenium oxide was supported on the surfaces of Samples A, B, and C. These were designated as samples A ', B', and C '. 10 ml of pure water was placed in a quartz glass tube, and samples A, B, and C and these samples A ′, B ′, and C ′ were each 2 × 2 cm ^2.
And placed in pure water, and then irradiated with ultraviolet light to measure the amount of dissolved oxygen in the pure water. The results are shown in FIGS. According to FIG. 4, samples A and B, which are anatase-type titanium oxides, had a higher maximum dissolved oxygen concentration immediately after irradiation with ultraviolet light than sample C, which was a rutile-type titanium oxide. That is, Samples A and B were superior to Sample C in water decomposition. This is the same for the sample having ruthenium oxide supported on the surface. According to FIG. 5, the samples A ′ and B ′ were superior to the sample C ′ in water decomposition. In addition, comparing the results of FIG. 4 and FIG. 5, it was found that the sample supporting ruthenium oxide had better water splitting performance than the sample not supporting ruthenium oxide. After UV irradiation, the dissolved oxygen concentration showed the highest value and then gradually decreased with time. The reason is that holes and electrons generated in the sample by UV irradiation accelerated water decomposition immediately after irradiation. Although the oxygen concentration increases, it is assumed that the dissolved oxygen concentration decreases over time because dissolved oxygen in the pure water takes in the electrons on the sample surface to become oxygen ions and adsorbs on the sample surface.

[0027]

According to the first aspect of the present invention, a thin film of anatase type titanium oxide having at least one crystal orientation plane of (004) and (112) in the direction perpendicular to the crystal surface is formed on the substrate. A higher photocatalytic activity was obtained than in Example 1.
According to the invention of claim 2, the thickness of the titanium oxide thin film is set to 500 n
m or more, the photocatalytic activity could be further improved. According to the third aspect of the present invention, since the metal or metal oxide is supported on the surface of the titanium oxide thin film, the charge separation is promoted, and the photocatalytic activity can be further improved.
According to the invention of claim 4, since the ruthenium oxide among the metal oxides is supported on the surface of the titanium oxide thin film, the photocatalytic activity in water splitting can be improved. According to the fifth aspect of the present invention, since a base material containing silicon as a main component is used, anatase type titanium oxide is easily formed. According to the sixth aspect of the present invention, since a titanium thin film is formed on a substrate containing silicon as a main component and a titanium oxide thin film is formed thereon, the peeling of the titanium oxide thin film can be effectively prevented. According to the invention of claim 7, a platinum thin film is formed on a substrate containing silicon as a main component, a titanium thin film is formed thereon, and a titanium oxide thin film is formed thereon, so that the photocatalytic activity is significantly improved. I was able to.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of acetaldehyde decomposition performance.

FIG. 2 is a schematic configuration diagram of a measurement device using a voltammetry method.

FIG. 3 is a diagram showing a result measured by the measuring device of FIG. 2;

FIG. 4 is a diagram showing performance evaluation of water splitting.

FIG. 5 is a diagram showing performance evaluation of water splitting.

[Explanation of symbols]

 1 sample 2 potentiostat 3 platinum electrode 4 reference electrode

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C01G 23/047 C01G 23/047 C04B 41/50 C04B 41/50 C30B 29/10 C30B 29/10 // C23C 16/40 C23C 16/40 (72) Inventor Hideo Nojima 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 4F100 AA17B AA20A AA21B AB01B AB12C AB24D AH06A AK52A AT00A BA02 BA03 BA04 BA07 BA10A BA10B EH JL08 JM02B JM02C JM02D YY00B 4G047 CA02 CB04 CB08 CC03 CD02 CD07 4G069 AA03 BA04A BA04B BA18 BA48A BB02A BB02B BB04A BB04B BC50A BC50B BC70A BC70B BC75A BC75B CA10 EC17 EB03 A07 EC03 EA3X03 EB04 BA42 BA46 BB01 BB03 CA04 CA12 LA11

Claims (7)

[Claims] 1. A photocatalyst material comprising a thin film of anatase type titanium oxide having at least one crystal orientation plane of (004) and (112) formed on a substrate in a direction perpendicular to the crystal surface. 2. The photocatalyst material according to claim 1, wherein said thin film has a thickness of 500 nm or more. 3. The photocatalyst material according to claim 1, wherein a metal or a metal oxide is supported on the surface of the thin film. 4. The photocatalyst material according to claim 3, wherein said metal oxide is ruthenium oxide. 5. The photocatalyst material according to claim 1, wherein said base material contains silicon as a main component. 6. The photocatalyst material according to claim 5, wherein a titanium thin film is formed on a substrate containing silicon as a main component, and the titanium oxide thin film is formed thereon. 7. The photocatalyst material according to claim 6, wherein a platinum thin film is further formed on the titanium thin film, and the titanium oxide thin film is formed thereon.