JP4883913B2 - Photocatalyst and method for producing the same - Google Patents

Description

  The present invention relates to a photocatalyst and a method for producing the photocatalyst, and more particularly, cleans harmful substances in the air by using light mainly composed of visible light such as a weak fluorescent lamp in the room, decomposes and removes dirt, and provides antibacterial and antifungal properties. The present invention relates to a photocatalyst that exhibits an action and can be applied to various uses, and a method for producing the same.

  When a material having photoconductivity such as titanium oxide is irradiated with light having energy higher than the band gap, electrons and holes are generated. As a result, oxygen species having strong oxidizing power such as superoxide and OH radicals are generated on the surface of the photocatalyst, and harmful components and the like that come into contact can be oxidatively decomposed. Thus, photocatalysts are applied to the interior and exterior of buildings, and sunlight and fluorescent light are used to purify the atmosphere and indoor environments, and to apply to deodorization, antifouling, sterilization, and the like. In general, titanium oxide having high photocatalytic activity and being chemically stable is used as the material having photo-conductivity. However, in order to excite the anatase-type titanium oxide, it is necessary to irradiate ultraviolet rays of 380 nm or less, and for example, a sufficient effect cannot be expected indoors.

Titanium oxide can use only ultraviolet rays, but it is a known technique to use cadmium sulfide or tungsten oxide as a light-semiconductive substance that can use visible light. However, it is known that these optical semiconductors having a small band gap have low quantum efficiency and problems with stability such as photodissolution. Therefore, in order to improve the performance of the photocatalyst, platinum group metals such as Pt, Pd, Rh, Ru, and Ir and various transition metals such as Fe, Co, Ni, Cu, Zn, Ag, Cr, V, and W are added to titanium oxide. Addition is being considered. In particular, it is well known that the addition of platinum group metals has the effect of enhancing the activity of the photocatalyst. For example, a visible light responsive photocatalyst characterized in that a platinum halide compound is supported on the surface of photocatalyst particles having an anisotropic shape such as titanium oxide (see Patent Document 1). Platinum group metals are expensive, and even if only a small amount is supported, the production cost of the photocatalyst is increased, which is not preferable.
Therefore, a visible light responsive photocatalyst in which titanium oxide is doped with nitrogen or sulfur has been proposed and attracted attention. For example, by replacing part of the oxygen sites of the titanium oxide crystal with nitrogen atoms, doping nitrogen atoms between the lattices of the titanium oxide crystal, or doping nitrogen atoms into the crystal grain boundaries of the titanium oxide crystal, etc. A photocatalytic substance having a Ti—O—N structure in which nitrogen is contained in a titanium oxide crystal and exhibiting a photocatalytic action in the visible light region is disclosed (see Patent Document 2). However, in order to produce these photocatalytic substances, (1) titanium oxide is used as a target material, and this is vapor-deposited or ion-plated in an atmosphere containing nitrogen gas. Examples include heat treatment at the following temperatures and (2) heat treatment of titanium oxide in an atmosphere containing ammonia gas, an atmosphere containing nitrogen gas, or a mixed atmosphere of nitrogen gas and hydrogen gas. A manufacturing apparatus and a manufacturing method are required, and there is a problem in applicability.

In addition, as a method for forming a photocatalytic hydrophilic member, an organic titanate is applied to the surface of a base material, hydrolyzed and dehydrated by condensation polymerization, residual organic groups are removed, and an aqueous solution containing tungstic acid is applied, followed by baking at 400 ° C. Thus, a method for producing crystalline titanium oxide and a TiO ₂ / WO ₃ composite oxide has been proposed (see Patent Document 3).
Currently, titanium oxide, which is widely used as a photocatalyst, has excellent optical semiconductivity, in which electrons and holes generated by light irradiation hardly cause recombination, but in order to exhibit photocatalysis, it is 380 nm or less. Therefore, sufficient effects could not be obtained with the weak light in the room. On the other hand, tungsten oxide has long been known as a photocatalyst that has a band gap of 2.5 eV and can use visible light up to 480 nm. However, tungsten oxide has a characteristic in which recombination of electrons and holes easily occurs (low quantum efficiency), and has excellent visible light performance, but is inferior to titanium oxide under ultraviolet irradiation conditions. Further, there is a problem that it has photo solubility (self-solubility) and it is difficult to obtain a photocatalytic effect over a long period of time, and it has not been used at a practical level.

  Recently, a visible light responsive photocatalyst having a response to visible light by doping titanium oxide with nitrogen, carbon, sulfur or the like has been attracting attention. For example, it has been confirmed that a photocatalyst in which titanium oxide is doped with nitrogen surely exhibits a photocatalytic effect by irradiation with visible light, but its performance improvement effect is not sufficient. In addition, there was a case where a part of the ultraviolet performance originally possessed by titanium oxide was impaired by improving the visible light performance.

JP 2004-73910 A WO01 / 10552 gazette JP-A-10-95635

  The present invention provides a photocatalyst excellent in catalytic performance and a method for producing the photocatalyst, and in particular, a visible light responsive photocatalyst that exhibits a photocatalytic effect by irradiation with visible light contained in a room or sunlight, and a method for producing the photocatalyst. It is intended.

According to the study by the present inventors, it has been found that the above problem can be solved by blending titanium oxide, tungsten oxide and iron oxide in a specific ratio. That is, the present invention comprises (1) impregnating an anatase-type titanium dioxide particle having a specific surface area of 30 to 200 m ² / g with a solution obtained by dissolving a tungsten compound and an iron compound, followed by drying, and then 500 to 800 A photocatalyst obtained by calcining at a temperature of 10 to 100 parts by mass of tungsten oxide and 0.3 to 3 parts by mass of iron oxide with respect to 100 parts by mass of titanium oxide. (2) The photocatalyst according to (1) above, wherein the ratio of tungsten oxide to iron oxide is in the range of Fe / W (molar ratio) = 0.03 / 1 to 0.3 / 1, and ( 3 ) tungsten The method for producing a photocatalyst according to the above ( 1 ) or ( 2 ), wherein the compound solution is an aqueous solution of ammonium metatungstate.

  Since the photocatalyst of the present invention works efficiently with light having a wavelength of 420 nm or more, various harmful organic substances such as formaldehyde and acetaldehyde can be efficiently decomposed even by weak indoor light. In the photocatalyst of the present invention, the visible light responsiveness is drastically improved without deteriorating the ultraviolet light performance of titanium oxide. For this reason, the photocatalyst of the present invention exhibits excellent catalytic performance for both visible light and ultraviolet light.

  Furthermore, the photocatalyst of the present invention can be produced simply by impregnating titanium oxide particles with a solution of a tungsten compound and an iron compound, followed by drying and firing. For this reason, it can manufacture easily in air | atmosphere by a normal installation, without having to control special production equipment and gas atmosphere.

In the photocatalyst of the present invention, titanium oxide, tungsten oxide and iron oxide are converted into TiO ₂ , WO ₃ and Fe ₂ O ₃ , respectively, 100 parts by mass, 10 to 100 parts by mass and 0.3 to 3 parts by mass , Preferably, it contains in the ratio of 100 mass parts: 20-50 mass parts: 0.5-1 mass part. Usually, tungsten oxide and iron oxide are present in a form supported on titanium oxide particles. When the proportion of tungsten oxide is less than 10 parts by mass with respect to 100 parts by mass of titanium oxide, sufficient photocatalytic performance with respect to visible light of 420 nm or more cannot be obtained. On the other hand, when the proportion exceeds 100 parts by mass, dispersion into titanium oxide particles The support becomes impossible, the effect of the increase is reduced, and the ultraviolet light performance is lowered. Further, when the ratio of iron oxide is less than 0.3 parts by mass with respect to 100 parts by mass of titanium oxide, sufficient performance improvement cannot be obtained with respect to both visible light and ultraviolet light, whereas it exceeds 3 parts by mass. The effect of increasing the amount is not recognized, and the color tone becomes darker, which is not preferable.

  In the photocatalyst of the present invention, the ratio of tungsten oxide to iron oxide is preferably Fe / W (molar ratio) = 0.03 / 1 to 0.3 / 1, more preferably 0.05 / 1. ~ 0.2 / 1. It is known that the performance of ultraviolet light is lowered when only the tungsten oxide is supported on the titanium oxide particles. By adding iron oxide, charge separation and charge transfer between the tungsten oxide and the titanium oxide are promoted. As a result, it is estimated that the quantum yield is improved. By supporting tungsten oxide and iron oxide on the titanium oxide particles within the above range, a photocatalyst having good photocatalytic performance for both visible light and ultraviolet light can be obtained.

The photocatalyst of the present invention can be produced by various methods, but is preferably produced by supporting tungsten oxide and iron oxide on titanium oxide particles. Specifically, for example, titanium oxide particles may be impregnated with a solution containing a tungsten compound and an iron compound, dried, and fired at 500 to 800 ° C, preferably 600 to 750 ° C. If the firing temperature is less than 500 ° C., crystallization of tungsten oxide or iron oxide is insufficient and sufficient visible light performance cannot be obtained. On the other hand, if the firing temperature exceeds 800 ° C., crystal phase transition or complexation with titanium oxide occurs. This is not preferable because it causes a significant decrease in performance. As the titanium oxide, anatase-type titanium dioxide having a specific surface area of 30 to 200 m ² / g is preferably used. When the specific surface area is less than 30 m ² / g, the particle size of the supported tungsten oxide becomes large, so that bonding with titanium oxide becomes insufficient, and sufficient catalytic performance cannot be obtained, and the specific surface area is 200 m ² / g. Amorphous titanium oxide exceeding the range is not preferable because it easily dissolves in tungsten oxide or iron oxide during firing.

  Titanium-based composite oxides such as titanium-silicon and titanium-zirconium are known to have the same optical semiconductivity as titanium oxide (see Japanese Patent Publication No. 5-55184). The product can be used in place of titanium oxide.

As the tungsten compound, various raw materials can be used as long as they can generate tungsten oxide by firing or hydrolysis. For example, inorganic and organic tungsten salts such as tungstic acid, tungsten chloride, ammonium paratungstate, ammonium metatungstate, and tungsten isopropyl oxide can be used. Tungsten oxide is known to be a divalent to hexavalent oxide depending on the raw materials used, the preparation method, and the like. WO, W ₂ O ₃ , W ₄ O ₁₁ , WO ₂ , W ₂ O ₅ , W ₃ O ₈ , W ₅ O ₁₄ , and WO ₃ , but the photocatalyst of the present invention is preferably in the form of orthorhombic tungsten trioxide (WO ₃ ). Among the tungsten compounds, ammonium metatungstate is preferably used. The reason for this is that ammonium metatungstate produces orthorhombic tungsten trioxide excellent in crystals by firing, and as a result, a photocatalyst excellent in visible light photocatalytic performance is obtained.

As the iron compound, various raw materials can be used as long as they can produce iron oxide by firing or hydrolysis. For example, inorganic and organic iron salts such as iron chloride, iron nitrate, iron sulfate, iron acetate, and iron oxalate can be used. As the crystal form of iron oxide, it is known that there are various crystal forms such as FeO, α-Fe ₂ O ₃ , and γ-Fe ₂ O _{3. In the} photocatalyst of the present invention, α-Fe ₂ O _It is preferable that the titanium oxide particles are supported in the form ₃ .

The photocatalyst of the present invention can be applied to indoor and outdoor building materials, etc. to decompose and remove harmful substances and odorous substances in the atmosphere using sunlight and indoor light, and to purify wastewater, antifouling, antibacterial Excellent functions such as fendering can be obtained. In particular, since it works effectively even for visible light of 420 nm or less, a good photocatalytic effect can be obtained even under indoor lighting where a sufficient effect has not been obtained. Examples of products to which the photocatalyst of the present invention is applied include ceiling materials, wallpaper, flooring materials, lighting equipment, furniture, building materials such as tiles, clothing, curtains, carpets, carpets, baskets and the like. Moreover, since sunlight can be effectively used outside, it can be applied to road surfaces, blocks, bricks, soundproof walls, light shielding walls, building side walls, roofs, window glass, guardrails, road signs, automobile bodies, ship bottoms, and the like.
(Example)
The invention is further illustrated by the following examples, which illustrate advantageous embodiments of the invention.

Titanium oxide (anatase-type titanium dioxide, specific surface area 82 m ² / g) was added to an impregnating solution obtained by dissolving 2.5 g of ferric nitrate in 30 g of commercially available ammonium metatungstate aqueous solution (WO ₃ equivalent concentration 50 mass%) and 100 g of water. 100 g was added and mixed, dried at 100 ° C. for 5 hours, and then calcined at 650 ° C. for 5 hours to obtain a photocatalyst A. In this catalyst A, tungsten oxide and iron oxide were supported at 15 parts by mass and 0.5 parts by mass with respect to 100 parts by mass of titanium oxide, respectively.

  In Example 1, Photocatalyst B was obtained in the same manner as Example 1 except that the calcination temperature was changed to 750 ° C.

  In Example 1, photocatalysts C and D having different contents of each component were prepared in the same manner as in Example 1 except that the amounts of ammonium metatungstate and ferric nitrate were changed.

  In Example 1, photocatalysts D having different content ratios of the respective components were prepared in the same manner as in Example 1 except that the amounts of ammonium metatungstate and ferric nitrate were changed.

Reference example 1

  In Example 1, photocatalyst a was obtained in the same manner as in Example 1 except that ferric nitrate was not added.

Reference example 2

  Commercially available tungsten oxide (manufactured by Wako Pure Chemical Industries) was used as catalyst b.

Reference example 3

  Commercially available titanium oxide used in Example 1 was used as photocatalyst c.

  Table 1 shows the composition ratio, firing temperature, and Fe / W (molar ratio) of the catalysts A to D and a to c.

Test example 1

For the photocatalysts A to D and the catalysts a to c obtained in Examples 1 to 4 and Reference Examples 1 to 3, the acetaldehyde decomposition performance was measured by the closed system test method described below. The test piece was prepared by dispersing photocatalyst powder in ethanol and applying it to one side of a 150 × 70 mm glass plate so as to have a coating amount of 20 g / m ² and drying at 60 ° C. The test piece was placed in a 5 L reactor, acetaldehyde was injected so that the initial gas concentration was 10 ppm, and light was irradiated. The photocatalytic performance was compared by changing the light irradiation conditions as follows and measuring the acetaldehyde concentration by irradiation with visible light and ultraviolet light over time by gas chromatography.
<Visible light performance>
Irradiation was performed from the outside of the reactor using two 4 W fluorescent lamps (Toshiba FL4D daylight color) as a light source. The lamp irradiation surface of the reactor was subjected to a performance test under the condition that an ultraviolet cut film (trade name “UV Guard” manufactured by Fuji Film Co., Ltd.) was attached to the quartz glass surface and ultraviolet rays of 420 nm or less were completely cut. The acetaldehyde concentration in the reactor after 180 minutes in each sample was measured, and the results are shown in Table 1 as visible light photocatalytic performance. The lower the gas concentration after the lapse of time, the better the photocatalytic performance by visible light. Moreover, about Example 3, Reference example 2, and Reference example 3, the attenuation | damping result of the acetaldehyde density | concentration in a test was shown in FIG.
<Ultraviolet light performance>
An ultraviolet light performance test was carried out in the same manner as described above except that a 4 W black light (Toshiba FLBLB) was used as the light source and no ultraviolet cut film was applied. The acetaldehyde concentration in the reactor after 30 spectral irradiations of each sample was measured. The results are shown in Table 1 as ultraviolet photocatalytic performance. Moreover, about Example 3, Reference example 2, and Reference example 3, the attenuation | damping result of the acetaldehyde density | concentration in a test was shown in FIG.

上記結果から、本発明の光触媒は、可視光および紫外光のいずれに対しても優れた触媒活性を発揮することがわかる。

From the above results, it can be seen that the photocatalyst of the present invention exhibits excellent catalytic activity for both visible light and ultraviolet light.

It is a graph which shows attenuation | damping with time of the acetaldehyde density | concentration in the visible light performance test of Example 3, Reference Example 2, and Reference Example 3. It is a graph which shows attenuation | damping with time of the acetaldehyde density | concentration in the ultraviolet-light performance test of Example 3, Reference Example 2, and Reference Example 3.

Claims (3)

A photocatalyst obtained by impregnating a solution obtained by dissolving a tungsten compound and an iron compound into anatase-type titanium dioxide particles having a specific surface area of 30 to 200 m ² / g, followed by drying and firing at 500 to 800 ° C. The content ratio is 10 to 100 parts by mass of tungsten oxide and 0.3 to 3 parts by mass of iron oxide with respect to 100 parts by mass of titanium oxide . The photocatalyst according to claim 1, wherein the ratio of tungsten oxide to iron oxide is in the range of Fe / W (molar ratio) = 0.03 / 1 to 0.3 / 1. The method for producing a photocatalyst according to claim 1 or 2 , wherein the solution of the tungsten compound is an aqueous solution of ammonium metatungstate.

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