JP2007098206A - Photocatalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalyst capable of decomposing environmental pollutants including nitrogen oxides in high efficiency in the light of a wide wavelength region. <P>SOLUTION: The photocatalyst is composed of silica hyperfine particles which are treated with hydrogen fluoride and have <100 μm average particle size. The photocatalyst can be deposited on granular inorganic or organic matter. The photocatalyst being a hyperfine particle can be dispersed in various resins and used as a coating agent. The wavelength region of the light when the photocatalyst can decompose environmental pollutants effectively is 200-800 nm. The organic environmental pollutants other than nitrogen oxides can also be decomposed. The purity of the silica to be treated with hydrogen fluoride is desirably ≥99%, most desirably, ≥99.99%. The silica to be used is desirably artificial silica. Gaseous or liquid hydrogen fluoride can be used when silica hyperfine particles are treated. An aqueous solution of hydrofluoric acid is desirably used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photocatalyst, and more particularly to an ultrafine photocatalyst that is sensitive to irradiation light over a wide wavelength region and that can remove environmental pollutants with unprecedented high efficiency.

Conventionally, titanium oxide has been widely used as a photocatalyst for removing environmental pollutants. However, titanium oxide exhibits a photocatalytic activity only in the region where the wavelength of light is around 400 nm, and in other wavelength regions, it is a photocatalyst. Since the performance could not be demonstrated, the range of use was limited.
Recently, a novel photocatalyst made of hydrohalic acid-treated fused quartz that can exhibit photocatalytic activity from the ultraviolet light to the visible light wavelength (200 nm to 800 nm) has been proposed (for example, Patent Document 1).

  However, the photocatalytic ability at the visible light wavelength is not yet sufficient, and particularly the decomposition rate for harmful substances other than nitric oxide, such as toluene, acetaldehyde, ethanedithiol, etc. is not high, and it is still sufficiently satisfactory for practical use. I can't say that.

JP 2004-290747 A

  An object of the present invention is to provide a photocatalyst that is highly efficient in a wide wavelength region and can decompose not only nitric oxide but also other environmental pollutants.

As a result of intensive studies to develop a photocatalyst capable of decomposing all environmental pollutants with high efficiency, the present inventors have reached the present invention.
That is, the present invention
A photocatalyst comprising ultrafine particles having an average particle diameter of less than 1 μm, containing silica treated with hydrogen fluoride;
A photocatalyst comprising the ultrafine photocatalyst supported on a particulate inorganic or organic material;
A coating agent, wherein the photocatalyst is dispersed in a resin.

The photocatalyst of the present invention has the following effects.
(1) Environmental pollutants can be decomposed with high efficiency even in a wide wavelength range of 200 nm to 800 nm.
(2) Nitrogen oxide as well as other environmental pollutants such as toluene, acetaldehyde, ethanedithiol and the like can be practically decomposed.
(3) Fine particles that can be easily dispersed in various resins and can be suitably used for coating agents and the like.

The silica treated with hydrogen fluoride in the present invention is an inorganic compound represented by SiO ₂ and reacts with hydrogen fluoride to form a portion active as a photocatalyst. Even if one molecule of SiO ₂ is present, it can react with hydrogen fluoride to form an active moiety. The higher the purity of the silica, the more active moieties can be formed. Therefore, the higher the purity of the silica, the better, preferably 90% or more, more preferably 99% or more, and particularly preferably 99.9% or more. Most preferably, it is 99.99% or more.

Silica is the most abundant inorganic compound in nature, and there are many specific examples, for example, quartz sand, sandstone, quartzite, quartzite, quartz, aventurine, chalcedony, jasper;
Natural silica;
Examples thereof include artificial silica such as glass, glass wool, silica gel, silica sol, optical fiber, and fused silica.
Of these, artificial silica is preferable. More preferred are fused silica and silica sol.

For example, fused quartz is a transparent material obtained by melting and solidifying a raw material silicon oxide source such as quartz or silica sand under a strictly controlled condition so that the impurity concentration is 50 ppm or less. Molten glass. Such fused quartz is commercially available from General Electric Company (GE) under the product names Quartz GE124, 144, 214, 219, 224, 254, and the like.
Many artificial quartz crystals are also commercially available, and commercially available products can be applied.

  The ultrafine silica in the present invention is a pulverized product or a refined product thereof, and a synthetic product from a halogenated silane such as chlorosilane is also applicable. For the pulverization, a known pulverization method such as a mortar method, a ball mill method, or a jet mill method can be applied. For the synthesis, a silica sol synthesized from a halogenated silane such as chlorosilane and then dried or a fumed product can be used.

  The shape of the ultrafine silica in the present invention is not particularly limited, but the pulverized product is not necessarily spherical but may be angular or elliptical. The average particle size of the primary particles is usually less than 1 μm. Preferably it is 800 nm or less, More preferably, it is 500 nm or less, More preferably, it is 300 nm or less, Most preferably, it is 100 nm or less. Here, the average particle diameter refers to the volume average particle diameter. The volume average particle diameter is measured according to a particle diameter distribution measuring method by a laser diffraction / scattering method of a JIS R1629-1997 fine ceramic raw material. The primary particles mean the smallest uniform particles, and are distinguished from secondary particles that can be formed by agglomeration or aggregation of primary particles. In the present invention, the presence of secondary particles in addition to primary particles is not denied.

The hydrogen fluoride used in the present invention is not limited even if it is gaseous or liquid, but is preferably hydrofluoric acid which is an aqueous solution thereof. For example, gas reacts easily by contact with silica. The hydrofluoric acid treatment is performed, for example, by immersing the above silica in a hydrofluoric acid aqueous solution, followed by washing with water and drying. Since hydrogen fluoride can react at a maximum of 1 mol with respect to 1 mol of SiO ₂ , the remaining hydrogen fluoride may be removed by using excessive hydrogen fluoride. However, in the case of particles, even if they are fine particles, they hardly react with the inside even if the surface reacts. Even if only the surface of the fine particles reacts, the surface is activated and a photocatalytic effect can be exerted, so that the amount of hydrogen fluoride relative to silica may be arbitrary. The concentration of the aqueous solution in the case of using hydrofluoric acid is preferably 1 to 50% by mass, more preferably 5 to 20% by mass, which is easy to use. Also in the case where the silica sol is treated with hydrofluoric acid, it is preferable that the concentration other than the solid content of silica is within the above range. For example, the amount of hydrofluoric acid is preferably 3 to 20 times, more preferably 5 to 10 times the volume of fine particles.

  The time required for the hydrofluoric acid treatment varies depending on the temperature and concentration, but in general, a high concentration aqueous solution may be used for a short time, and a low concentration aqueous solution may be used for a long time, preferably 5 to 60 minutes. Selected by range. The reaction temperature is preferably 0 ° C. or higher and 50 ° C. or lower, more preferably 5 ° C. or higher and 30 ° C. or lower.

In the case of hydrofluoric acid treatment, the solid content is separated from the aqueous solution, and the solid content is dried. In this case, you may wash with distilled water 2-5 times. Examples of the separation method include a method of removing the liquid by decantation after standing, removing a liquid by centrifugation, and filtering using a filter. Drying is performed from atmospheric drying to reduced pressure drying to vacuum drying. The drying temperature is preferably 0 to 100 ° C, more preferably 10 to 60 ° C. The drying time is preferably 10 minutes to 10 hours.
In the method of hydrogen fluoride treatment, ultrafine particles having a particle size of less than 1 μm may be treated with hydrogen fluoride, or may be pulverized to a particle size of less than 1 μm after drying with a hydrogen fluoride treatment having a particle size of 1 μm or more. The former is preferred.

Thus, silica is activated by the hydrogen fluoride treatment because when SiO ₂ and HF come into contact with each other, Si on the surface binds to F, thereby attracting the bound electrons to the F side and weakening the back pound bond. As a result, it is attacked by the separated H ⁺ F ⁻ molecules, the back pound is cut, and the outermost surface Si is fluorinated, while at the same time one of the bonds in the layer immediately below is hydrogenated. Such a state propagates one after another, and finally, the outermost surface Si is separated in the form of SiF ₄ , and SiH ₃ radicals remain on the surface.
However, the SiH ₃ radical has a very weak Si—Si bond with Si in the next layer, and since the bond electrons are weakly attracted to the H side, it is easily cleaved and easily replaced by H of the HF molecule. It is considered that H is exposed to the Si (111) surface by being in the form of SiH, and is activated.
In this way, a silica photocatalyst treated with hydrogen fluoride is obtained.

  The ultrafine photocatalyst of the present invention can be easily dispersed in various resins and can be used as a coating agent or the like. The resin is preferably a thermoplastic resin or thermosetting resin having a weight average molecular weight of 10,000 or more, more preferably 100,000 or more. For example, acrylic resin, polycarbonate, polystyrene, polyurethane, polyester, fluororesin, silicone resin, polyimide , Polyvinyl chloride, epoxy resins, and the like, and mixtures thereof, composite resins, and the like are used as usual paints and coating agents. The weight average molecular weight can be measured by GPC method (gel permeation chromatography method). The content of the ultrafine photocatalyst of the present invention in the resin is preferably 1 to 200 g, more preferably 5 to 100 g, relative to 100 parts by weight of the resin. As a method of dispersing the ultrafine photocatalyst in the resin, a conventionally known dispersion method can be applied.

  The ultrafine photocatalyst of the present invention may be supported on an inorganic or organic granular material. There is no limitation as a granular inorganic substance, and it is selected depending on the application. Examples thereof include silica such as silica gel having a particle diameter of 1 mm or more. As the granular organic material, the above-mentioned resin granular material can be applied.

The particle diameter of the granular material is preferably 1 mm to 20 mm, more preferably 2 mm to 10 mm. These porous bodies are preferred.
The surface area of the granular material is preferably 20 m ² / g or more, more preferably 50 m ² / g or more, particularly preferably 100 m ² / g or more, and most preferably 200 m ² / g or more. The specific surface area can be obtained from an adsorption isotherm obtained by measuring the amount of adsorption of a gas (for example, nitrogen gas) by a calculation formula, for example, the BET method.
The supported amount of the photocatalyst is preferably 0.1 to 100 mg, more preferably 1 to 50 mg with respect to 1 g of the carrier.

As a method for supporting the photocatalyst of ultrafine particles of the present invention on these granular materials, for example,
(1) Simply mixing the photocatalyst of ultrafine particles and the above granular material (hereinafter referred to as both) with a known mixing device,
(2) After both are mixed in the liquid material, the liquid material is removed.
(3) Mix while grinding both,
(4) Hydrogen fluoride treatment after being supported on the particulate matter during the synthesis of silica.
(5) The method of carrying | supporting during a hydrogen fluoride process is mentioned, However It is not limited to these, The optimal method is used at any time according to a use.

The photocatalyst of the present invention removes environmental pollutants by oxidative decomposition by irradiation with light. Examples of environmental pollutants include nitrogen oxides NO _x that cause air pollution such as nitrous oxide N ₂ O, nitric oxide NO, dinitrogen trioxide N ₂ O ₃ , nitrogen dioxide NO ₂ , trichloroethane, Organic halogen compounds that cause environmental pollution such as tetrachloroethylene, dichlorodifluoromethane, tribromomethane, polychlorobiphenyl (PCB), aldehydes that cause sick house such as formaldehyde, acetaldehyde, benzene, toluene, xylene Examples thereof include sulfur-containing compounds that cause malodor such as aromatic hydrocarbons, mercaptans, and ethanedithiols.

In order to decompose and detoxify an environmental pollutant using the photocatalyst of the present invention, it is preferable to mix oxygen or nitrogen with the environmental pollutant and contact the photocatalyst while irradiating the mixture with irradiation light.
Conventional semiconductor photocatalysts such as TiO ₂ and ZnO show their decomposing ability only in the light absorption region of environmental pollutants, but they do not exhibit catalytic ability with light of other wavelengths, so that they are like sunlight. When natural light is used, the light utilization efficiency is unavoidable. However, the photocatalyst of the present invention can decompose environmental pollutants even with light having a wavelength that hardly exhibits light absorption. Irradiation light in the wavelength region, for example, ultraviolet light or visible light can be used.

  That is, the wavelength region of ultraviolet light is 200 to 400 nm and the wavelength region of visible light is 400 to 800 nm, but the photocatalyst of the present invention can use irradiation light in a wide wavelength region of 200 to 800 nm. In the case of decomposing an organic halogen compound with high efficiency, it is preferable to use irradiation light in a wavelength region of 240 to 500 nm.

  Examples of the light source that artificially generates the irradiation light include an ultraviolet lamp, a xenon lamp, a fluorescent lamp, and an incandescent lamp that are commonly used as the irradiation light source.

  When the photocatalyst of the present invention is used for continuous photodegradation of environmental pollutants, the environmental pollutants are transported together with oxygen in a fluid such as gas or liquid and brought into contact with the photocatalyst. The fluid is not particularly limited as long as it does not inhibit the photolysis of environmental pollutants. However, nitrogen gas is preferable as the gas and water is preferable as the liquid because it is available in large quantities and does not cause environmental pollution.

In the photolysis of environmental pollutants, the oxygen concentration of the fluid to be mixed is not particularly limited. However, the higher the concentration, the higher the decomposition efficiency of environmental pollutants. When the fluid is a gas, it is preferable to use air in terms of cost, so the oxygen concentration is about 20% by volume. In the case of a liquid, since water is used for the same reason, the oxygen concentration is 4.9% by volume (standard state).
On the other hand, the ratio of oxygen to environmental pollutants is preferably a ratio of at least two oxygen molecules to one carbon atom contained in the molecules of the environmental pollutants, but is not particularly limited.

In the present invention, as a method of bringing a mixture of an environmental pollutant and oxygen into contact with the photocatalyst, a batch processing method in which both are enclosed in a sealed container and the fluid and the surface of the photocatalyst are brought into contact with each other by thermal motion of the fluid, and a fluid Any of the flow treatment methods in which the fluid and the photocatalyst surface are brought into contact with each other by forcible flow can be used.
When the environmental pollutant is nitrogen oxide, the nitrogen oxide is nitrated and rendered harmless when the above-mentioned photooxidation reaction is performed in the presence of oxygen and water using the photocatalyst of the present invention. The amount of oxygen used in this case is not particularly limited, but the oxygen is selected in a range of at least 1 mole, preferably 2 moles or more per mole of nitrogen oxide.

  The fused quartz described in Japanese Patent Application Laid-Open No. 2004-290747 does not have a high decomposition rate with respect to harmful substances other than nitric oxide such as toluene, acetaldehyde, ethanedithiol, etc., but contains silica treated with hydrogen fluoride of the present invention. The photocatalyst characterized in that the average particle diameter of primary particles is composed of ultrafine particles having a diameter of 1 nm or more and less than 1 μm can efficiently remove environmental pollutants.

  Hereinafter, the present invention will be described by way of examples, but is not limited thereto.

Example 1
100 g of the artificial quartz was pulverized with an Eiger mill (Crusher manufactured by Eiger Japan) and sieved to obtain 55 g of ultrafine particles having a volume average particle diameter of about 300 nm. Next, it is immersed in 200 g of a 10 wt% aqueous hydrogen fluoride solution at room temperature, treated by stirring for 5 minutes, taken out, left at room temperature for 5 hours, and then dried in a dryer at 50 ° C. for 3 hours to give the photocatalyst (1). Obtained.

Implementation column 2
In Example 1, a fused silica ultrafine photocatalyst (2) having a volume average particle diameter of about 700 nm was obtained in the same manner as in Example 1 except that 100 g of fused silica was used instead of 100 g of artificial quartz.

Example 3
100 g of artificial quartz was pulverized by changing the pulverization conditions of Eiger Mill (Eiger Japan Co., Ltd.) more strongly than in Example 1 and sieved to obtain 35 g of ultrafine particles having a volume average particle diameter of about 100 nm. This and 100 g of zeolite having an average particle size of about 1 mm are immersed in 200 g of a hydrogen fluoride aqueous solution having a concentration of 15% by weight at room temperature, treated with stirring for 5 minutes, and taken out. The mixture was filtered at 5 and allowed to stand at room temperature for 5 hours, and then dried at 50 ° C. for 3 hours to obtain a photocatalyst (3) supported on zeolite.

Example 4
In Example 3, a fused silica ultrafine photocatalyst (4) supported on zeolite and having a volume average particle diameter of about 210 nm was used in the same manner as in Example 3 except that 100 g of fused quartz was used instead of 100 g of artificial quartz. )

Example 5
10 g of colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name Snowtex 50, solid content 50%, volume average particle size 20 nm) and 90 g of zeolite are immersed in 120 g of a 25 wt% hydrogen fluoride aqueous solution at room temperature. Treated for a minute and removed. The mixture was filtered at 5 and allowed to stand at room temperature for 5 hours, and then dried at 50 ° C. for 3 hours to obtain a photocatalyst (5) supported on zeolite.

Comparative Example 1
100 g of fused quartz was pulverized with a ball mill and sieved to a fraction of 1 to 2 mm to obtain 50 g. Next, 200 g of an aqueous hydrogen fluoride solution having a concentration of 10% by weight is immersed at room temperature, treated by stirring for 5 minutes, taken out, left at room temperature for 5 hours, and then dried in a dryer at 50 ° C. for 1 hour to give a photocatalyst (6). Obtained.

Comparative Example 2
A commercially available porous supported titanium oxide photocatalyst was used as the photocatalyst (7).

Test Example 1 (Nitrogen oxide nitrification experiment)
Using the apparatus shown in FIG. 1, a nitric oxide nitrification experiment using photocatalysts (1) to (7) was performed.
A glass plate of 10 mm × 50 mm × 2 mm is placed on the bottom of a rectangular parallelepiped container of 20 mm × 100 mm × 10 mm, and 2 g of a photocatalyst is placed thereon, and a mixture of nitric oxide and oxygen (volume ratio 1: 1) is usually used. Nitrogen monoxide (NO) is nitrated under the conditions shown in Table 1 while filling the container with pressure and irradiating light from a low-pressure mercury lamp or fluorescent lamp through a 15 mm x 50 mm quartz glass light irradiation window. went. The results are shown in Table 1.
Note that the amount of nitric oxide filled with oxygen in the dry air of the rectangular parallelepiped container is 3.60 μmol. Moreover, the light intensity of the light source was measured under the following conditions using a detector dedicated to the measurement wavelength of an ultraviolet intensity meter (product name “UVR-400”, manufactured by Seiei Inoue).
Toshiba FL6M: 6W
Visible light output: 736 mW
Distance to sample surface: 130mm

Test example 2
A part of the same photocatalyst is placed in the same apparatus as used in Test Example 1, and air that has been passed through acetaldehyde or benzene at 15 ° C. is introduced therein, and a low-pressure mercury lamp (line special light source UVL−) is used as a light source. 10 and a light intensity of 230 nm or more and a light intensity of 0.15 mW / cm ^{2 on the} surface of the sample was used for photodecomposition reaction. Table 2 shows the filling amount, irradiation time, and decomposition rate of the sample at that time.

  Since the ultrafine photocatalyst of the present invention can efficiently remove various environmental pollutants, it removes the environmental pollutants as they are, or in a particulate form or dispersed in a resin. It can be suitably applied to devices and the like.

Claims (8)

A photocatalyst comprising an ultrafine silica particle having an average particle diameter of less than 1 μm treated with hydrogen fluoride. The photocatalyst according to claim 1, wherein the silica has a purity of 99.9% or more. 3. The photocatalyst according to claim 1, wherein the silica is artificial silica. The photocatalyst according to any one of claims 1 to 3, wherein the ultrafine silica particles are supported on an inorganic substance or an organic substance. A coating agent comprising a resin dispersed with a photocatalyst comprising ultrafine silica particles having an average particle diameter of less than 1 μm treated with hydrogen fluoride. The photocatalyst according to claim 5, wherein the silica has a purity of 99.9% or more. The photocatalyst according to claim 5, wherein the silica is artificial silica. The photocatalyst according to any one of claims 5 to 7, wherein the silica ultrafine particles are supported on an inorganic substance or an organic substance.