JP4098005B2 - Photocatalyst and photocatalytic material - Google Patents

Description

【００４３】
【表２】

【００４４】
【発明の効果】
この発明の光触媒は、光源の大部分を占める可視光に応答することにより、光エネルギーを有効に利用でき、これまで効果の小さかった室内などの蛍光灯環境下においても十分に光触媒機能を発揮することができ、さらに暗所でも抗菌機能を発揮することができる。従って、この発明の光触媒を有する材料は、内装材や側壁材などの景観材や外壁材など、より具体的には、自動車、ビルの内外装部品、トンネル照明、浴室・トイレ設備部材、キッチン設備部材、建材、入院施設、そして手術室など、幅広い用途に使用することが可能である。[0001]
[Industrial application fields]
The present invention relates to a photocatalyst, in particular, a visible light responsive photocatalyst that is used for a material that expresses one or both of catalytic activity and hydrophilicity by irradiation with visible light and that particularly requires an environmental purification function. The present invention relates to a photocatalytic material.
[0002]
[Prior art]
In recent years, there has been a strong need for environmental cleanup products with antibacterial, deodorant and antifouling functions due to pollution control and increased health, comfort and cleanliness. Use photocatalysts for this type of product. Technology is drawing attention. The photocatalyst, by the absorption of light energy, superoxide anion of reactive oxygen species excited electrons reduce oxygen (· O ₂ ^-) to generate and holes oxidize water reactive oxygen species hydroxyl It is a substance that oxidizes and decomposes organic substances that come into contact with the surface of the photocatalyst by generating radicals (OH.). Further, the photocatalyst using titanium oxide can exhibit super hydrophilicity with a water contact angle of 5 ° or less.
[0003]
By utilizing these characteristics, in outdoor use, in anti-fogging treatments to ensure visibility, oil resistance, inorganic dust and carbon, which are the main components of urban pollution, and in indoor use, Sanitary treatments such as anti-wrinkle and deodorization can be performed.
[0004]
Here, it is not sufficient that the band gap energy of the photocatalyst is larger than the generation energy of the active oxygen species {2.18 × 10 ^-19 J (1.36 eV)} to cause the above-mentioned reaction of generating the active oxygen species. The O ₂ / O ₂ ⁻ {−0.21 × 10 ⁻¹⁹ J (−0.13 eV)} level and the O ₂ / H ₂ O {1.97 × 10 ^-19 J (1.23 eV)} It must be in a position that sandwiches both levels. In addition, since this redox level is an equilibrium level, an overvoltage is required to generate a reaction of reactive oxygen species, the lower end of the conduction band is more negative than the O ₂ / O ₂ ⁻ level, and valence electrons. The upper end of the belt must be located on the positive side of the 0 ₂ / H ₂ 0 level.
[0005]
Anatase-type titanium oxide, which is currently in practical use as a photocatalytic substance, has a band gap energy of 5.13 because the top level of the valence band is located on the positive side sufficiently away from the O ₂ / H ₂ O level. × 10 ^-19 J (3.2eV), which is large and exhibits photocatalytic activity and hydrophilicity only when irradiated with ultraviolet rays. However, the light from sunlight or fluorescent lamps that serve as the light source has a spectral distribution spectrum of ultraviolet rays of 3 to 4% at most, and the intensity of near ultraviolet rays is 1 to ² mW / cm ² in the sunlight of the daytime. The light from the lamp is only about 1 μW / cm ² . For this reason, the utilization of the light energy by a photocatalyst is performed only in the very limited range. Therefore, in order to make effective use of light energy and to make the photocatalyst exhibit a sufficient function even in a fluorescent lamp environment, it is desired to develop a photocatalytic material that can use visible light.
[0006]
Here, in order to exhibit the photocatalytic function by irradiation with visible light, it is necessary that the band gap energy of the photocatalyst is about 4.8 × 10 ⁻¹⁹ J (3 eV) or less that can absorb visible light, and various methods for that purpose are required. Has been proposed. For example, JP-A-11-197512 describes that visible light activity is expressed by ion-implanting a transition metal such as vanadium or chromium into anatase-type titanium oxide and then heat-treating it in the air. Yes. However, this method is disadvantageous in that the apparatus is expensive and it is difficult to process a large area.
[0007]
In addition, Masayoshi Miyoshi et al., Coloring Materials, 73 (12), 580 (2000) reported that anatase-type titanium oxide forms oxygen vacancies by hydrogen plasma treatment and expresses visible light activity. However, if oxygen atoms are removed, an unstable crystal structure tends to be formed, and it is difficult to maintain the photocatalytic action for a long time.
[0008]
In addition, R. Asahi et al., Science, 293, 269 (2001) described that the upper end of the valence band is negative by mixing the 2p orbit of nitrogen with the 2p orbit of oxygen constituting the valence band of anatase-type titanium oxide. It has been reported that visible light activity is expressed when shifted to. However, when oxynitride is synthesized by nitriding titanium oxide, it becomes possible to absorb visible light, but the bottom level of the conduction band varies little and the bottom level of the conduction band is O ₂ / O ₂ ^- from to remain close to the level, activation is insufficient, improvement in activity is desired.
[0009]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art, and exhibits a photocatalyst function and / or hydrophilicity even when irradiated with visible light, and a photocatalyst having high visible light activity and a material having the photocatalyst It is intended to be provided together.
[0010]
[Means for Solving the Problems]
The inventors have shifted the oxygen site of the oxide with elemental nitrogen to shift the upper end of the valence band to the negative side, allowing absorption of visible light, and further exhibiting antibacterial action in the dark, the located on the negative side than the level found that can be sufficiently secured overvoltage reduction reaction, to complete the present invention ^- calcium, titanium complex oxide containing strontium, the lower end of the conduction band O ₂ / O ₂ It came.
[0011]
That is, the present invention is a photocatalyst that exhibits one or both of catalytic activity and hydrophilicity by irradiation with visible light, and is from an oxynitride represented by the following general formula (1) or (2): It is a photocatalyst characterized by comprising.
ATiO _{3- (3/2) x} N _x ---- (1)
AO ・ n (ATiO _{3- (3/2) x} N _x ) ---- (2)
Here, A: one or more selected from Mg, Ca and Sr 0 <x ≦ 0.6
n: natural number
The present invention also provides a photocatalyst material having a photocatalyst layer that exhibits either one or both of catalytic activity and hydrophilicity upon irradiation with visible light on a substrate, wherein the photocatalyst layer comprises the above (1) or A photocatalytic material comprising an oxynitride represented by the general formula (2).
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Below, the photocatalyst of this invention is demonstrated in detail.
As described above, anatase-type titanium oxide, which is currently in practical use as a photocatalyst, exhibits photocatalytic activity only when irradiated with ultraviolet rays. This is because the top level of the valence band of the oxide composed of 2p orbits of oxygen is much more positive than the water oxidation level O ₂ / H ₂ O, and the band gap energy is The reason is that it grows.
[0014]
As a method for developing photocatalytic activity by irradiation with visible light, oxynitride obtained by doping an oxide photocatalyst with a nitrogen element has attracted attention. This is because when the oxygen site of the oxide is doped with nitrogen, N2p, which has an energy level higher than that of oxygen O2p, is also used in the conduction band configuration, and as a result, the upper level of the conduction band shifts to the negative side. This is because the band gap is narrowed and visible light can be absorbed.
[0015]
Therefore, also in the photocatalyst of the present invention, by doping the oxygen site of the oxide with nitrogen element, the upper end level of the conduction band is shifted to the negative side, the band gap is narrowed, and the visible light can be absorbed. .
[0016]
Examples of oxynitride photocatalysts include anatase-type TiO _2-x N _x and titanium, niobium and tantalum perovskite or layered perovskite materials such as LaTaON ₂ , CaTaON ₂ , SrTaON ₂ , BaTaON ₂ , LaTiO ₂ N , Ca _1-X La _x Ti0 _3-x Nx _x , CaNbON ₂ , SrNbON ₂ , BaNbON ₂ and LiLaTaNO ₆ are known, but practically from the viewpoint of cost, safety and stability, The photocatalytic material is advantageously titanium-based and is preferred. Here, the titanium base indicates that the ratio of the titanium element contained in the transition metal element forming the conduction band is 50 atom% or more.
[0017]
Furthermore, in the photocatalyst of the present invention, the lower end potential of the conduction band is positioned more negative than the O ₂ / O ₂ ⁻ (−0.21 × 10 ⁻¹⁹ J) level in order to activate the photocatalytic reaction exhibited by visible light. Therefore, it is important to secure an overvoltage of the reduction reaction by using the titanium composite oxide as a base, and efficiently promote charge separation and generation of active oxygen. For example, in the case of perovskite strontium titanate, the lower end potential of the conduction band is about −0.32 × 10 ⁻¹⁹ J (−0.2 eV), and an overvoltage can be secured.
[0018]
Here, the element complexed with titanium oxide is an alkaline earth metal that is inexpensive and safe, and that exhibits an antibacterial property without being involved in the structure of the conduction band, specifically, Mg. It is important to use at least one selected from Ca, Sr. The crystal structure of complex oxides of these elements and titanium is mainly in the case of Mg: ilmenite structure (MgTiO ₃ ), spinel structure (Mg ₂ TiO ₄ ), pseudo-brookite structure (MgTi ₂ O ₅ ), or reverse spinel Structure (Mg ₂ TiO ₄ ), while Ca and Sr are mainly perovskite structures (general formula: ATiO ₃ ) or layered perovskite structures {general formula: AO · n (ATiO ₃ )}, and Mg, Ca and Sr When two or more are selected, the above structure or the perovskite structure is obtained, but the crystal structure is not limited thereto. Preferably, Mg has an ilmenite structure, and Ca and Sr have a perovskite structure or a layered perovskite structure (n: 1 to 3).
[0019]
The photocatalyst satisfying the above-described requirements can be expressed by the following general formula (1) or (2).
ATiO _{3- (3/2) x} N _x ---- (1)
AO ・ n (ATiO _{3- (3/2) x} N _x ) ---- (2)
Here, A: one or more selected from Mg, Ca and Sr 0 <x ≦ 0.6
n: Natural number The oxynitride according to the above general formula is compensated for charge by oxygen deficiency when titanium is reduced to take a low oxidation state.
[0020]
The nitrogen substitution amount described above varies depending on the synthesis conditions, but x in the above formula is in a range satisfying 0 <x ≦ 0.6. That is, when the amount of nitrogen substitution is small, the shift to the negative side of the upper end of the valence band is insufficient, and a band gap that can absorb visible light cannot be formed. On the other hand, when the amount of nitrogen substitution is too large, oxygen vacancies are generated for charge compensation and the crystal structure becomes unstable. Therefore, a range satisfying 0 <x ≦ 0.6 is set. Preferably, x is in the range of 0.05 to 0.5.
At this time, at least 1/2 of the nitrogen substitution amount is lost in the oxygen site for charge compensation.
[0021]
In addition, it is preferable to form the photocatalyst of this invention as a thin film on a base material, and to use for various uses. Base materials include inorganic materials such as ceramics, tile, concrete, glass and brick, aluminum, stainless steel, various plated steel sheets, chemical treated steel sheets and painted steel sheets, resin such as acrylic and polycarbonate, and wood. Organic materials can be used.
[0022]
Next, a method for synthesizing the above oxynitride will be specifically described.
That is, oxynitride is an oxide of titanium and one or more selected from magnesium, calcium and strontium, or a precursor thereof, such as ammonia gas, ammonia-containing gas, nitrogen gas, or N ₂ / H ₂ gas. In the atmosphere, the synthesis can be performed by heat treatment at 400 to 1200 ° C. for 1 to 120 minutes, preferably 500 to 700 ° C. for 5 to 60 minutes, but it is not particularly limited to this treatment. The ammonia-containing gas is a mixture of ammonia gas and a non-oxidizing gas such as argon or nitrogen, and the mixing ratio of the non-oxidizing gas is 10 to 90% by volume, preferably 20 to 70% by volume.
[0023]
When synthesizing a powder, titanium dioxide and one or more compounds selected from oxides, hydroxides and carbonates of magnesium, calcium and strontium are mixed, and the mixture or the mixture is heated. The precursor material thus combined is subjected to nitriding treatment under the above conditions.
[0024]
In addition, when forming a photocatalyst as a thin film on a base material, after coating the thin film which consists of the said oxide or the precursor of an oxide on a base material, a nitriding process is given to said film on the said conditions. Although a thin film made of an oxide or an oxide precursor can be coated by a sol-gel method, it is not particularly limited to the sol-gel method. The coating liquid used for sol-gel film formation can be manufactured by the method shown below, for example. That is, 1 to 2 mol of a chelating agent such as acetylacetone, diethylene glycol or ethyl acetoacetate is mixed with 1 mol of titanium alkoxide in alcohol, followed by carboxylic acid such as oxalic acid or acetic acid, boric acid, hydrochloric acid, nitric acid, sulfuric acid as an acid catalyst. Alternatively, 0.01 to 0.1 mol of an inorganic acid such as phosphoric acid is added, and then 1 to 2 mol of water is gradually added to prepare a partially hydrolyzed solution. Next, an alcohol solution in which the chelating agent is mixed with magnesium, calcium and strontium alkoxides, an inorganic salt such as nitrate or chloride, or an alcohol solution of an organic acid salt such as acetate or oxalate is added to the partially hydrolyzed solution. And ripen to make a sol solution.
[0025]
Other methods include aqueous crystalline titanium oxide sols such as anatase and brookite, amorphous titanium oxide aqueous solutions such as peroxotitanic acid and orthotitanic acid, or a mixed aqueous solution thereof with an aqueous solution of the above inorganic salt or organic salt in a predetermined ratio. To make a coating solution. At this time, when the coating solution is gelled by mixing the aqueous solution of the inorganic salt or organic salt, an organic acid such as lactic acid, malic acid and citric acid is added to the aqueous titanium oxide solution in advance to form a titanium complex. If this is done, gelation can be prevented. Or you may mix | blend said inorganic salt or organic salt in a starting material previously at the time of the synthesis | combination of the said titanium oxide aqueous solution.
[0026]
The method of forming a film on the substrate is to adjust the coating solution to 0.1 to 10% by mass, preferably 0.5 to 5% by mass in terms of oxide, and apply the coating solution to the substrate by spraying, dipping or brushing. To form a dry film.
[0027]
Here, in the above-described film, it is particularly effective to contain silica or silicon oxynitride for maintaining the hydrophilicity for a long time. Silica or silicon oxynitride is contained in the range of 10 to 80% by mass, more preferably 20 to 50% by mass, based on the solid content of the photocatalyst. This is because the hydrophilicity can be maintained over a long period of time and the effect of the photocatalytic activity can be sufficiently exerted by containing in the range of 10% by mass to 80% by mass.
[0028]
【Example】
Next, examples of the present invention will be described in detail, but the present invention is not limited to these examples.
Invention Example 1
After spray-coating MgTiO ₃ coating solution on a heat-resistant glass substrate coated with silica, pre-baked at 600 ° C for 60 minutes, and then subjected to nitriding treatment at 600 ° C for 10 minutes in a 100 ml / min ammonia stream. Thus, a test body was produced. The obtained photocatalyst film was an ilmenite type, and the adhesion amount was 0.63 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0029]
Invention Example 2
In Invention Example 1, except for using CaTiO ₃ coating liquid instead of the MgTiO ₃ coating solution, in the same manner as in Inventive Example 1 to obtain a coated with a photocatalyst to a substrate specimen. The obtained photocatalyst film was a perovskite type, and the adhesion amount was 0.60 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0030]
Invention Example 3
A test body in which a substrate was coated with a photocatalyst was obtained in the same manner as in Invention Example 1 except that a Ca ₃ Ti ₂ O ₇ coating solution was used instead of the MgTiO ₃ coating solution in Invention Example 1. The Ca ₃ Ti ₂ O ₇ coating solution was prepared by adding 0.3 mol of citric acid to an aqueous peroxotitanic acid solution prepared by mixing 0.1 g of titanium with 300 g of hydrogen peroxide solution and 100 g of aqueous ammonia, and further adding 0.15 calcium acetate. Synthesized by adding mol. The obtained photocatalyst film was a layered perovskite type, and the adhesion amount was 0.65 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0031]
Invention Example 4
Rutile-type titanium oxide powder: 0.1 mol and calcium carbonate: 0.01 mol were mixed, calcined at 1000 ° C for 60 minutes, and the resulting powder was pulverized, then at 60 ° C at 600 ° C in an ammonia stream of 100 ml / min. A nitriding treatment was performed for a minute to obtain a photocatalyst powder. The obtained photocatalyst powder was a perovskite type. About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 2.
[0032]
Invention Example 5
Photocatalyst powder was obtained in the same manner as in Invention Example 4 except that strontium carbonate was used instead of calcium carbonate in Invention Example 4. The obtained photocatalyst powder was a perovskite type. About the characteristic of this photocatalyst powder, it measured and evaluated by the method mentioned later. The results are shown in Table 2.
[0033]
Invention Example 6
In Example 1, a test specimen in which the substrate was coated with photocatalyst powder was obtained in the same manner as in Example 1, except that a coated steel sheet coated with enamel was used instead of heat-resistant glass. In addition, the obtained photocatalyst was an ilmenite type, and the adhesion amount was 0.70 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0034]
Invention Example 7
In Invention Example 1, a test body having a substrate coated with photocatalyst powder was obtained in the same manner as in Invention Example 1, except that a coated steel plate was used instead of heat-resistant glass as the substrate. In addition, the obtained photocatalyst was an ilmenite type, and the adhesion amount was 0.70 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0035]
Invention Example 8
In Invention Example 2, a test specimen in which the substrate was coated with photocatalyst powder was obtained in the same manner as in Invention Example 2, except that a coated steel sheet coated with enamel was used instead of heat-resistant glass as the substrate. The obtained photocatalyst was a perovskite type, and the adhesion amount was 0.65 g / m ² . About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0036]
Comparative Example 1
After spraying an aqueous TiO ₂ coating solution onto a heat-resistant glass substrate coated with silica, pre-baked at 500 ° C for 30 minutes, and then subjected to nitriding treatment at 600 ° C for 10 minutes in a 100 ml / min ammonia stream. To prepare a test body. In addition, the obtained photocatalyst film | membrane was an anatase type, and the adhesion amount was 0.68 g / m < ² >. About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 1.
[0037]
Comparative Example 2
The anatase-type titanium oxide powder was subjected to nitriding treatment at 600 ° C. for 60 minutes in an ammonia stream of 100 ml / min to obtain a photocatalyst powder. The obtained photocatalyst powder was anatase type. About the characteristic of this photocatalyst, it measured and evaluated by the method mentioned later. The results are shown in Table 2.
[0038]
Here, the antibacterial test, the measurement of the contact angle of water, and the gas decomposition test shown below were carried out through each of the photocatalysts, and the characteristics thereof were evaluated.
[Antimicrobial test]
The antibacterial activity was evaluated in accordance with the photoirradiation film adhesion method of the Antibacterial Product Technology Council.
That is, after inoculating 0.1 ml of a bacterial solution with a bacterial concentration of 1.5 × 10 ⁶ cells / ml on a 5 × 5 cm size test specimen, the polyethylene film was put on and closely adhered, and this was set in a transparent petri dish at a temperature of 25 The lid was covered under the condition of 90 ° C. and relative humidity of 90% or more, and kept for 4 to 24 hours in a dark place and for 4 hours in an environment irradiated with 1000 lux of visible light with a white fluorescent lamp. Thereafter, surviving bacteria were washed out from the test specimen with physiological saline, cultured in NA medium at 35 ° C. for 24 hours, and the number of viable bacteria was measured.
[0039]
Here, the antibacterial activity was considered to be acceptable if the number of viable bacteria was 10 or less per specimen. The fungus is Staphylococcus aureus IFO 12732, and the white fluorescent lamp is equipped with an ultraviolet cut film (King Seisakusho Co., Ltd .: ObjcC) with an ultraviolet intensity of 0.1 μW / cm ² or less (UV intensity: 365 nm) Measured). The antibacterial test was conducted for Invention Examples 1, 2, 3, 6, 7, 8 and Comparative Example 1.
[0040]
[Contact angle]
The test specimen was irradiated with 1000 lux of visible light for 8 hours using the white fluorescent lamp described above, and then 20 μL of ion-exchanged water was dropped using a microsyringe. The contact angle of water was measured by a three-point method using a meter (Kyowa Interface Science Co., Ltd., CA-X). The contact angle was measured for Invention Examples 1, 2, 3, 6, 7, 8 and Comparative Example 1.
[0041]
[Gas decomposition test]
A petri dish containing 1 g of the photocatalyst powder was placed on the bottom of a glass container having a volume of 5 liters, and after capping, acetaldehyde was injected to adjust to 100 ppm. After the adsorption equilibrium was confirmed, visible light of 1000 lux was irradiated using the white fluorescent lamp.
The acetaldehyde concentration was measured with a gas chromatograph (Shimadzu Corporation: GC-17A). The gas decomposition test was conducted for Invention Examples 4 and 5 and Comparative Example 2.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
【The invention's effect】
The photocatalyst of the present invention responds to visible light that occupies most of the light source, so that light energy can be used effectively, and exhibits a photocatalytic function sufficiently even in a fluorescent lamp environment such as a room where the effect has been small so far. Furthermore, the antibacterial function can be exhibited even in the dark. Therefore, the material having the photocatalyst of the present invention is a landscape material such as an interior material or a side wall material or an outer wall material, more specifically, an automobile, an interior / exterior part of a building, a tunnel lighting, a bathroom / toilet facility member, a kitchen facility. It can be used for a wide range of applications such as components, building materials, hospitalized facilities, and operating rooms.

Claims (2)

A photocatalyst that exhibits one or both of catalytic activity and hydrophilicity upon irradiation with visible light, characterized by comprising an oxynitride represented by the following general formula (1) or (2) photocatalyst.
ATiO _{3- (3/2) x} N _x ---- (1)
AO ・ n (ATiO _{3- (3/2) x} N _x ) ---- (2)
Here, A: one or more selected from Mg, Ca and Sr 0 <x ≦ 0.6
n: natural number A photocatalytic material having a photocatalytic layer on a substrate that exhibits either or both of catalytic activity and hydrophilicity by irradiation with visible light, wherein the photocatalytic layer has the general formula (1) or (2) below: A photocatalytic material comprising an oxynitride represented by the formula:
ATiO _{3- (3/2) x} N _x ---- (1)
AO ・ n (ATiO _{3- (3/2) x} N _x ) ---- (2)
Here, A: one or more selected from Mg, Ca and Sr 0 <x ≦ 0.6
n: natural number