Cafrrier for photocatalyst and photocatalyst using the same

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a carrier for a photocatalyst and a photocatalyst using the same. More specifically, the present invention comprises a low-cost and practical photocatalytic carrier made of a siliceous substrate capable of forming a photocatalytic active layer containing at least titanium dioxide particles with good adhesion, and at least titanium dioxide on the carrier. A photocatalyst active layer containing particles formed with good adhesion, which exhibits excellent photocatalytic function when irradiated with ultraviolet light or visible light, and is related to a photocatalyst which is suitably used for, for example, various water purification treatments. Is.

【0002】

[Conventional technology]

The so-called Honda-Fujishima effect, in which water is photodecomposed into hydrogen and oxygen by using a semiconductor such as titanium dioxide as a photoelectrode ["Industrial Chemistry Magazine", Vol. 72, pp. 108-113 (1968)) ] Has been actively researched for the development and practical application of photocatalysts since it was discovered. In this photocatalyst, when a photocatalytic active substance such as titanium dioxide is excited by light having an energy equal to or higher than the band gap, electrons are generated in the conduction band and holes are generated in the valence band, and this energy-rich electron- It uses a hole pair. When the photocatalytically active substance is photoexcited, electron-hole pairs are generated as described above, and the generated electrons reduce surface oxygen to superoxide anion ( O).₂^-), The holes oxidize the surface hydroxyl groups to generate hydroxyl radicals (.OH), and these reactive reactive oxygen species photodegrade organic substances with high efficiency. The photocatalyst exerts functions such as antibacterial, deodorant, antifouling, air purification, water purification, and superhydrophilicity by a strong oxidizing action derived from such a photocatalytic action.

【0003】

Various compounds such as titanium dioxide, zinc oxide, tungsten oxide, and barium titanate (BaTi) have been used as photocatalytic active substances.₄O₉), Strontium titanate (SrTiO)₃), Sodium titanate (Na₂Ti₆O₁₃), Zirconium dioxide, α-Fe₂O₃, Cadmium sulfide, zinc sulfide, etc. are known. Of these, titanium dioxide, especially anatase-type titanium dioxide, is useful as a practical photocatalyst. This titanium dioxide exhibits excellent photocatalytic activity by absorbing light of a specific wavelength in the ultraviolet region contained in everyday light such as sunlight. Utilizing the photocatalytic function of such a photocatalytic active substance such as titanium dioxide, for example, a wastewater treatment agent formed by coating silica gel particles with titanium dioxide fine powder, nitrogen oxides in the atmosphere are decomposed by the light energy of the sun. Building materials, antibacterial, lighting with deodorizing effect, deodorizing, antibacterial sheet, photocatalytic filter for environmental purification, antibacterial glass and antibacterial ceramics, antifouling wind film, etc. have been put into practical use. By the way, in titanium dioxide, which is a practical photocatalytically active substance, the anatase type having particularly high catalytic activity is photoexcited by ultraviolet light and exerts a photocatalytic function, so that the utilization efficiency of sunlight is low and visible light. Since it does not work, it has the disadvantage that its use is inevitably limited. Therefore, research on visible light-responsive titanium dioxide that exerts a photocatalytic function in visible light is being actively conducted. For example, titanium dioxide surface-treated by plasma, titanium dioxide having platinum ultrafine particles adhered to the surface, and rutile. Titanium dioxide fine particles in which metal ultrafine particles such as platinum are supported at high density on the surface of the titanium dioxide fine particles, titanium dioxide in which metal ions such as chromium and vanadium are injected, and the like have been developed.

【0004】

However, these are not always sufficiently satisfactory because the photocatalytic function in visible light is not sufficiently exhibited and the manufacturing cost is high due to expensive raw materials and complicated processes. On the other hand, when a photocatalytic active layer mainly composed of titanium dioxide is provided on the surface of glass, ceramics, or other siliceous base material, when a thin film mainly composed of titanium dioxide is formed by the sol-gel method, the base material and the thin film are formed. Adhesion with the substrate is relatively good, but when a photocatalytic active layer mainly composed of titanium dioxide particles is provided, the adhesion with the substrate is poor, and as it is, the adhesive strength is practical on the surface of the substrate. There is a big problem that a photocatalytic active layer mainly composed of titanium dioxide particles cannot be formed. Powdered titanium dioxide is generally easy to manufacture, inexpensive, easy to handle, and highly efficient, and is therefore advantageous over a thin film produced by the sol-gel method. Practical photocatalysts are required to exhibit excellent photocatalytic functions in visible light, to prevent the photocatalyst active layer from peeling off from the substrate, to have good durability, and to be inexpensive.

【0005】

[Problems to be Solved by the Invention]

The present invention provides a low-cost and practical photocatalytic carrier made of a siliceous substrate capable of forming a photocatalytic active layer containing at least titanium dioxide particles with good adhesion under such circumstances, and a carrier for the photocatalyst. A photocatalytic active layer containing at least titanium dioxide particles is formed with good adhesion, and exhibits excellent photocatalytic function when irradiated with ultraviolet light or visible light, and is suitably used for, for example, various water purification treatments. It is an object of the present invention to provide a photocatalyst which is inexpensive and has good durability.

【0006】

[Means for solving problems]

As a result of intensive studies to achieve the above object, the present inventors have made a siliceous base material having a base layer composed of a specific substance and titanium dioxide particles on the surface as a carrier for a photocatalyst. And, a coating layer containing titanium dioxide particles or titanium dioxide particles and zinc chloride is provided on the surface of the carrier and fired at a specific temperature, which can be suitable for the purpose as a photocatalyst. I found that. The present invention has been completed based on such findings. That is, the present invention comprises (1) a carrier for a photocatalyst, characterized in that a base layer composed of water glass and / or an alkali-dispersed paste-like carbohydrate and titanium dioxide particles is provided on the surface of a siliceous base material. 2) A photocatalyst (hereinafter referred to as photocatalyst I) obtained by providing a coating layer containing titanium dioxide particles on the surface of the carrier and firing at a temperature of 500 to 900 ° C. Provided is a photocatalyst (hereinafter referred to as photocatalyst II) obtained by providing a coating layer containing titanium particles and zinc chloride and firing at a temperature of 500 to 900 ° C.

【0007】

BEST MODE FOR CARRYING OUT THE INVENTION

In the carrier for photocatalyst of the present invention, a siliceous base material is used as a base material. The shape of this siliceous base material is not particularly limited, and may be any of granular, columnar, honeycomb, fibrous, bead-like, wool-like, flake-like, sheet-like, plate-like, etc. It can be selected as appropriate. The material is also not particularly limited, and for example, a granular solid or a granular foam obtained by firing glass, glass fiber, glass beads, glass wool, glass balloon, silica gel, silica, silica alumina, or hedro granules. It can be appropriately selected from the translucent and non-translucent base materials according to the application. Among these siliceous substrates, granular solids and granular foams obtained by firing sludge granules are preferable from the viewpoint of environmental problems and resource problems, and in particular, the photocatalyst of the present invention is used for water purification treatment. When used, it is useful as a carrier thereof. The granular solid can be produced by a known method, for example, sludge is dried, granulated into a desired shape, and calcined in a calcining furnace at a temperature of about 950 to 1250 ° C. ( Patent No. 1452239). Further, the granular foam is an inorganic substance that generates gas by appropriately selecting the firing conditions in the above method and decomposing the organic substance in sludge to generate gas, or by decomposing or evaporating at the firing temperature. It can be produced by adding sludge or an organic substance and firing it. The specific gravity of the granular foam can be controlled by the degree of foaming.

【0008】

When the photocatalyst of the present invention is used for water purification treatment, the size of the granular base material is not particularly limited and is appropriately selected according to the purpose of the purification treatment, but usually has an average diameter in the range of 3 to 50 mm. Things are used. The specific gravity of the photocatalyst is appropriately selected depending on the type of use of the photocatalyst, for example, when it is suspended in water to be purified or when it is used by sedimentation. In the photocatalytic carrier of the present invention, a base layer is provided on the surface of the siliceous base material. In the photocatalyst, this base layer has good adhesion to the photocatalyst active layer containing at least titanium dioxide particles formed on the photocatalyst, and also has good adhesion to the siliceous base material. , Water glass and / or those consisting of alkali-dispersed paste-like carbohydrates and titanium dioxide particles are provided.

【0009】

There are three types of titanium dioxide, rutile type, anatase type and brookite type, depending on the crystal form, but the industrialized ones are rutile type and anatase type. The rutile type is more stable than the anatase type, and when the anatase type is heated at a high temperature, the crystal is transferred to the rutile type. From the viewpoint of photocatalytic activity, the anatase type of this titanium dioxide is preferable to the rutile type. The crystal form of the titanium dioxide particles used in the base layer is not particularly limited, and any crystal form can be used. However, the photocatalytic active layer provided on the base layer is anatase-type dioxide. Since titanium particles are preferably used, the anatase type is preferable in consideration of the adhesion to the photocatalytically active layer. The average particle size of the titanium dioxide particles is usually in the range of 0.005 to 0.5 μm, preferably 0.01 to 0.25 μm.

【0010】

On the other hand, water glass is an alkali silicate obtained by melting silicon dioxide and alkali, and there are soda water glass and potassium water glass, both of which can be used. In this case, soda water glass and potassium water glass may be used alone, or they may be mixed and used. Water glass is characterized by remaining as vitreous after firing. Alkali-dispersed paste-like carbohydrates are carbohydrates such as wheat starch, potato starch, rice starch, sweet starch, tapioca starch, and dextrin that have been heat-treated in an alkaline aqueous solution and transformed into a paste. Therefore, for example, a commercially available starch paste can be used. Of these, at least the carbohydrate component is characterized in that it does not remain unburned when fired in air. It is also possible to leave the carbon component by firing in a nonflammable gas such as nitrogen. In order to form an underlayer on the surface of a siliceous base material, first, the titanium dioxide particles are added and dispersed in an aqueous solution containing the water glass or an alkali-dispersed paste-like carbohydrate or a mixture thereof, and then coated. Prepare the liquid. The viscosity of this coating liquid is not particularly limited as long as it can be applied to the surface of a siliceous base material. The amount of titanium dioxide particles used is selected so as to be contained in the formed base layer in a range of preferably 5 to 99% by weight, more preferably 40 to 99% by weight.

【0011】

Next, the above coating liquid is applied to the surface of the siliceous base material by a known method such as a dip coating method, and dried at a temperature of about 500 to 900 ° C. to form a desired base layer. Will be done. If necessary, after the drying treatment, it may be further fired at a temperature of about 500 to 900 ° C. The thickness of this base layer is usually in the range of 1 to 500 μm, preferably 1 to 100 μm. In this way, a photocatalyst carrier having good adhesion to the photocatalyst active layer containing at least titanium dioxide particles provided on the photocatalyst active layer can be obtained. This carrier for photocatalyst has photocatalytic activity by itself due to the titanium dioxide particles existing on the surface of the base layer, but since the activity is very small, it is used as a carrier in the present invention, and at least on it. A photocatalyst active layer containing titanium dioxide particles is formed to form a photocatalyst. Next, in the photocatalyst I of the present invention, a coating layer containing titanium dioxide particles is provided on the surface of the carrier for photocatalyst and fired at a temperature of 500 to 900 ° C. to form a photocatalyst active layer. In Photocatalyst II, a coating layer containing titanium dioxide particles and zinc chloride is provided on the surface of the carrier and fired at a temperature of 500 to 900 ° C. to form a photocatalyst active layer.

【0012】

The titanium dioxide particles used in the photocatalysts I and II are preferably anatase type particles from the viewpoint of photocatalytic activity, and the average particle size is usually selected in the range of 0.005 to 0.5 μm, preferably 0.01 to 0.25 μm. Is done. In addition, zinc chloride in the coating layer of Photocatalyst II has physical properties with a boiling point of 313 ° C and a boiling point of 732 ° C, and is considered to partially evaporate during firing. The photocatalytically active layer becomes porous, and the photocatalytic activity is improved. Moreover, it has the effect that the photocatalytic function is exhibited by visible light. The amount of zinc chloride is preferably in the range of 5 to 40 parts by weight per 100 parts by weight of titanium dioxide particles. If the amount of zinc chloride is less than 5 parts by weight, the effect of adding zinc chloride is not sufficiently exhibited, and if it exceeds 40 parts by weight, the effect is not improved for the amount, but rather the amount of evaporation increases. Not preferable for environmental hygiene. For these reasons, more preferred amounts of zinc chloride are in the range of 10-30 parts by weight.

【0013】

In the photocatalysts I and II of the present invention, if the firing temperature is less than 500 ° C, the firing is insufficient and the photocatalytic activity is not sufficiently exhibited, and if the firing temperature exceeds 900 ° C, the titanium dioxide particles tend to be rutile type. , Photocatalytic activity decreases. From the viewpoint of photocatalytic activity, the preferred firing temperature is in the range of 500 to 600 ° C. In order to form a coating layer on the surface of the photocatalytic carrier, first, a coating liquid prepared by adding a small amount of an organic binder such as starch paste, polyvinyl alcohol, or carboxymethyl cellulose to an aqueous dispersion of titanium dioxide particles. Prepare a coating solution (for photocatalyst I) or a coating solution (for photocatalyst II) to which zinc chloride is further added. The viscosity of these coating liquids is not particularly limited as long as it can be applied to the surface of the carrier. Next, the coating liquid is applied to the surface of the photocatalyst carrier by a known method such as a dip coating method to form a coating layer, and then calcined at the temperature to form a photocatalyst active layer. , The desired photocatalysts I and II are obtained.

【0014】

In the present invention, for the purpose of improving the photocatalytic activity of the coating layer before firing in the photocatalysts I and II, if desired, a known cocatalyst, for example, platinum group such as platinum, palladium, rhodium, ruthenium derived from each colloid, etc. Ultrafine particles of metal, ultrafine particles of gold derived from gold colloid, and particles such as NiOx, RuOx, and RhOx are contained in a range of preferably 0.1 to 20% by weight based on the total weight with the titanium dioxide particles and fired. can do. Alternatively, an aqueous solution containing a water-soluble inorganic metal compound for forming a cocatalyst is applied onto the photocatalyst active layer formed by firing, and then light is irradiated to irradiate the photocatalyst active layer with the metal of the cocatalyst. The metal of the co-catalyst may be supported on the photocatalyst active layer by a photodeposition method of depositing the metal, or a method of further applying a reducing agent to precipitate the metal of the co-catalyst. The thickness of the photocatalyst active layer in the photocatalysts I and II of the present invention is preferably in the range of 1 to 500 μm, more preferably 1 to 100 μm. In the photocatalysts I and II thus obtained, since the photocatalyst active layer is provided on the surface of the siliceous base material via the base layer, the adhesion between the photocatalyst active layer and the base material is maintained. Very good and durable. In particular, in the photocatalyst II, the photocatalytic active layer contains a chloride subsalt together with titanium dioxide particles, has excellent photocatalytic activity, and exhibits a photocatalytic function by visible light.

【0015】

[Example]

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. Example 1 30 parts by weight of commercially available anatase-type titanium dioxide (manufactured by Wako Pure Chemical Industries, Ltd.) powder, 60 parts by weight of water and 25 parts by weight of commercially available starch paste were mixed to prepare a coating liquid. The above coating liquid was applied to a glass plate (45 × 15 × 1 mm) used for a microscope preparation, and dried at 110 ° C. for 60 minutes. This glass plate was fired in an electric furnace at 580 ° C for 5 hours. After slowly cooling to room temperature, it was washed with water, and the titanium dioxide that had fallen off was removed by an ultrasonic cleaner, and the mixture was dried at 110 ° C. When the X-ray diffraction of the titanium dioxide adhering surface of this glass substrate was measured, a main peak with a lattice constant of 3.51 Å was observed, and it was confirmed that the transition to the rutile type did not occur under the conditions used in this example. .. Example 2 60 parts by weight of commercially available surfactant-dispersed titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd., STS-21, amorphous) and 25 parts by weight of commercially available starch paste were mixed to prepare a coating liquid. This coating liquid was applied to a glass plate in the same manner as in Example 1, and dried, fired, cooled, washed with water, irradiated with ultrasonic waves, and dried. A main peak with a lattice constant of 3.51 Å was also observed in the X-ray diffraction of this glass substrate, and it was confirmed that the transition from the amorphous to the anatase type occurred under these conditions and the transition to the rutile type had not yet occurred.

【0016】

Example 3 A plurality of granular solids having an average particle size of about 1 cm and an average specific gravity of 0.9 formed from sludge were immersed in the coating liquid of Example 1 and taken out. This was dried, fired, cooled, washed with water, irradiated with ultrasonic waves and dried in the same manner as in Example 1 to prepare a photocatalyst A. Example 4 Using the coating solution of Example 2, the same granular solid as in Example 3 was dried, calcined, cooled, washed with water, irradiated with ultrasonic waves and dried in the same manner as in Example 3 to prepare a photocatalyst B.

【0017】

Example 5 A coating liquid for the base layer was prepared by mixing 30 parts by weight of titanium dioxide fine particle dispersion (manufactured by Ishihara Sangyo Co., Ltd., trade name: STS-21), 25 parts by weight of water glass No. 1, and 50 parts by weight of water. The above coating liquid is applied to the surface of a plurality of granular solids formed from sludge with an average particle size of about 10 mm and an average specific gravity of about 2.0 by the dip coating method, and then dried at 110 ° C. for 60 minutes to make the thickness. A base layer having a size of about 100 μm was formed to prepare a carrier for a photocatalyst. To 100 parts by weight of the titanium dioxide fine particle dispersion liquid, 25 parts by weight of commercially available starch paste (manufactured by Mitsue Glue Co., Ltd.) was added to prepare a coating liquid, which was applied to the surface of the photocatalyst carrier by a dip coating method. Then, the photocatalyst C was prepared by firing at 550 ° C. for 5 hours to form a photocatalyst active layer having a thickness of about 200 μm.

【0018】

Example 6 A carrier for a photocatalyst was prepared in the same manner as in Example 5. To 100 parts by weight of the titanium dioxide fine particle dispersion used in Example 5, 10 parts by weight of zinc chloride and 25 parts by weight of the starch paste used in Example 1 were added to prepare a coating liquid, and the same as in Example 1. A photocatalyst D was prepared by forming a photocatalyst active layer having a thickness of about 300 μm. Example 7 A coating liquid for an underlayer was prepared by mixing 100 parts by weight of the titanium dioxide fine particle dispersion used in Example 5, 25 parts by weight of starch paste used in Example 5, and 50 parts by weight of water. Hereinafter, the same procedure as in Example 2 was carried out to prepare a carrier for a photocatalyst, and further to prepare a photocatalyst E. The photocatalysts A to E obtained as described above were evaluated for their photocatalytic activity due to sunlight on a sunny day according to the method shown below. <Evaluation of photocatalytic activity> The photocatalyst was unified into 5 grains, each placed in a 100 ml beaker, 50 ml each of 0.001% methylene blue aqueous solution was added, and the decolorization test was performed. As a result, the time at which the absorbance at 660 nm was halved under the same sunlight was 8 hours, 7.5 hours, 7 hours, 7 hours and 6.5 hours, respectively, for photocatalysts A to E, respectively. Although the amount of ultraviolet rays in sunlight is not so large, this photocatalyst is considered to be effective.

【0019】

[Effect of the invention]

The carrier for a photocatalyst of the present invention is a practical carrier having excellent adhesion to a photocatalyst active layer containing at least titanium dioxide particles and having a low manufacturing cost. Further, the photocatalyst of the present invention is an inexpensive and highly durable photocatalyst active layer containing at least titanium dioxide particles formed on the carrier with good adhesion. It can be applied for sterilization and mold prevention of pools, hydroponics, cooling towers, circulating baths, etc.