Photocatalytic body, method for manufacturing the same, and photocatalytic body coating agent obtained by 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 photocatalyst, a method for producing the same, and a photocatalyst coating agent using the same. More specifically, the present invention relates to a photocatalyst that exhibits high activity by irradiation with visible light, a method for producing the same, and a photocatalyst coating agent used when imparting a photocatalytic function to a building material or the like.

【0002】

[Conventional technology]

When a semiconductor is irradiated with ultraviolet rays, electrons having a strong reducing action and holes having a strong oxidizing action are generated, and molecular species in contact with the semiconductor are decomposed by the redox action. Such an action is called a photocatalytic action, and by utilizing this photocatalytic action, an organic acid such as acetic acid in the work space can be decomposed and removed. Titanium oxide has attracted attention as a substance exhibiting a photocatalytic action, and a photocatalyst made of titanium oxide is commercially available.

【0003】

However, the photocatalysts currently on the market have not exhibited sufficient activity when irradiated with visible light.

【0004】

[Problems to be Solved by the Invention]

An object of the present invention is to provide a photocatalyst that exhibits high decomposition activity by irradiation with visible light, a method for producing the same, and a photocatalyst coating agent using the same.

【0005】

[Means for solving problems]

The present inventors have completed the present invention as a result of studying the improvement of the photocatalytic activity of titanium oxide.

【0006】

That is, the present invention uses anatase-type titanium oxide as a base material, has iron oxide on the surface thereof, and has a BET specific surface area of 55 m.²It provides a photocatalyst characterized by being / g or more.

【0007】

Further, in the present invention, an aqueous solution of a titanium compound and a base are reacted at 60 ° C. or lower, and the product is calcined to obtain titanium oxide, which is brought into contact with a solution or slurry of an iron compound and then heated. It provides a method for producing the photocatalyst.

【0008】

Furthermore, the present invention provides a photocatalyst coating agent containing the photocatalyst and a solvent.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. The photocatalyst of the present invention is based on titanium oxide. Titanium oxide, which is the base material, is TiO₂The crystal structure is anatase type. The crystal structure can be identified from the peak position of the X-ray diffraction spectrum. Further, the anatase crystallite diameter can be obtained from the peak position and its half-value width at this time. In the photocatalyst of the present invention, the anatase crystallite diameter is usually 10 nm or more. A photocatalyst having an anatase crystallite diameter of 10 nm or more exhibits high activity with respect to light irradiation.

【0010】

Further, the photocatalyst of the present invention has an iron oxide on the surface of titanium oxide as a base material. Examples of iron oxides include FeO and Fe.₂O₃, Fe₃O₄Or FeTiO₃Examples thereof include compounds indicated by. The greater the abundance of this iron oxide, the higher the activity of the photocatalyst, which is preferable. For example, Fe is relative to titanium oxide as a base material.₂O₃In terms of conversion, it is preferably 0.0005% by weight or more, more preferably 0.005% by weight or more. On the other hand, even if the amount of iron oxide is too large, the effect of improving the activity corresponding to the amount cannot be obtained. Therefore, it is preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 0.5% by weight or less. .. This iron oxide may be present so as to cover the entire surface of titanium oxide as a base material, or may be present so as to cover a part of the surface of titanium oxide. Photocatalysts in which a part of the surface of titanium oxide is coated with iron oxide include, for example, iron oxides that are discontinuously present on titanium oxide as dots, and iron oxides that are on titanium oxide. Some are continuous in a linear or lattice pattern. The iron oxide present on the surface of the base material, titanium oxide, usually has a Bronsted acid point or a Lewis acid point. Basic compounds such as amines tend to be selectively adsorbed on the Bronsted acid point of iron oxides, and oxygen-containing compounds and sulfur-containing compounds tend to be selectively adsorbed on the Lewis acid point. Therefore, depending on the target substance to be decomposed by the photocatalyst, the amount of Bronsted acid point or Lewis acid point of the iron oxide, or when both Bronsted acid point and Lewis acid point are present, these ratios are also appropriate. It is preferable to select. The total amount of each acid point can be adjusted by changing the amount of iron oxide. The ratio of the Bronsted acid point to the Lewis acid point in the iron oxide can be adjusted by, for example, steam treatment or vacuum degassing treatment. When the iron oxide on the surface of the base material has many Bronsted acid points, the iron oxide having the iron oxide on the surface may be subjected to steam treatment, while the iron oxide on the surface of the base material is Lewis acid. When the number of points is increased, titanium oxide having an iron oxide on the surface may be degassed under reduced pressure.

【0011】

Further, the photocatalyst of the present invention has a BET specific surface area of 55 m, which is obtained by the nitrogen adsorption method.²It is more than / g. BET specific surface area is 55m²With a photocatalyst of less than / g, it is difficult to obtain a photocatalyst that exhibits high activity with respect to visible light irradiation, even if the base material is titanium oxide and iron oxide is present on the surface thereof. The photocatalyst has a higher BET specific surface area, the higher the photocatalytic activity tends to be. However, if the BET specific surface area is too large, it becomes difficult to disperse the photocatalyst in the solvent when the coating agent is obtained by mixing with the solvent. BET specific surface area is 300m²/ G or less, and even 250m²Below / g, especially 200m²It is preferably / g or less.

【0012】

The photocatalyst of the present invention measures the ultraviolet-visible diffuse reflection spectrum, and when the integral value of the absorbance at a wavelength of 220 nm to 800 nm is A and the integral value of the absorbance at a wavelength of 400 nm to 800 nm is B, the formula (I) X = B / A (I) The index X calculated by is preferably 0.2 or more, more preferably 0.25 or more. The integrated value of absorbance indicates the area of the region surrounded by the horizontal axis and the diffuse reflection spectrum within the specified wavelength range in the ultraviolet-visible diffuse reflection spectrum with the absorbance on the vertical axis and the wavelength on the horizontal axis. ..

【0013】

It is based on titanium oxide, has iron oxide on its surface, and has a BET specific surface area of 55 m.²The photocatalyst having a value of / g or more can have an acidic metal oxide or a basic metal compound other than titanium oxide or the iron oxide shown above on the surface of titanium oxide as a base material. By having another acidic metal oxide in addition to the iron oxide, it is possible to obtain a photocatalyst having Bronsted acid points and Lewis acid points at various ratios. Further, by having a basic metal compound, it becomes a photocatalyst that exhibits an excellent decomposition action on substances such as hydrogen sulfide, isobutyric acid, and acetic acid.

【0014】

Examples of this acidic metal oxide include metal oxides having a Bronsted acid point, a Lewis acid point, or both, and examples thereof include zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, cobalt, and nickel. , Single-unit oxides of metals such as copper, aluminum, gallium, indium, tin, silicon-zinc, silicon-zirconium, silicon-magnesium, silicon-calcium, silicon-gallium, silicon-aluminum, silicon-lantern, silicon -Titanium, Titanium-Zinc, Titanium-Copper, Titanium-Zinc, Titanium-Aluminum, Titanium-Zyrinc, Titanium-Lead, Titanium-Bismus, Zinc-Magnet, Zinc-Aluminum, Zinc-Zyrosine, Zinc-Lead, Zinc-Antimon In addition to composite oxides of two types of metals such as, there are composite oxides of three or more types of metals that have acid points. Among these acidic metal oxides, the application of unidimensional oxides of metals such as zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum and tin is recommended. .. Examples of the above basic metal compound include metal oxides, metal hydroxides or metal carbonates having a Bronsted base point, a Lewis base point or both, and examples thereof include sodium oxide, potassium oxide and magnesium oxide. , Calcium oxide, barium oxide, lanthanum oxide, cerium oxide, zinc oxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lantern hydroxide, cerium hydroxide, zinc hydroxide, sodium carbonate , Potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, zinc carbonate, etc. The total amount of these acidic metal oxides and basic metal compounds is 0.05 mol% or more in terms of metal elements with respect to titanium oxide, which is the base material, and further 0. It is preferably 1 mol% or more. On the other hand, if the total amount of these is too large, the activity of the photocatalyst may decrease, so 50 mol% or less, more preferably 30 mol% or less, particularly 10 mol% or less is preferable. [0015]

One of these acidic metal oxides and basic metal compounds may be present on the surface of titanium oxide as a base material, or only one of them may be present in two or more kinds, or these There may be one or more of each. The acid point of an acidic metal oxide is sometimes called an acidic center, and its existence can be identified by measuring the amount of gaseous bases adsorbed on the surface of the metal oxide or the amount of bases adsorbed from the solution. it can. The acidity of the acidic metal oxide can also be identified by utilizing the discoloration of the indicator having various pKa values, and by this method, the acid strength of the acidity and the number of acidity in the acid strength are measured. it can. The base point of a basic metal compound can also be identified by utilizing the discoloration of an indicator having various pKa values.

【0016】

Based on anatase-type titanium oxide, it has iron oxide on its surface and has a BET specific surface area of 55 m.²In the photocatalyst of the present invention having / g or more, for example, an aqueous solution of a titanium compound such as titanium oxysulfate, titanium sulfate, titanium oxychloride, or titanium chloride is reacted with a base, and the product is calcined to obtain titanium oxide. , This titanium oxide can be prepared by contacting with a solution or slurry of an iron compound and then heating.

【0017】

Examples of the base used at this time include ammonia, amines, amino acids, hydrazine derivatives, hydroxylamine derivatives and the like. The amount of this base is preferably 1.2 times or more, more preferably 2 times or more, and 20 times or less of the stoichiometric amount of the base required to convert the titanium compound in the aqueous solution into titanium hydroxide. , Furthermore, it is preferably 10 times or less. The reaction between the titanium compound and the base is usually carried out at 60 ° C. or lower, preferably 50 ° C. or lower. Firing of the product is usually carried out at 300 ° C. or higher, preferably 330 ° C. or higher, and 600 ° C. or lower, preferably 500 ° C. or lower, more preferably 450 ° C. or lower. Further, this firing can be performed under static conditions, in an air stream, or the like. Iron compounds that come into contact with titanium oxide include, for example, iron (III) nitrate, iron (II) sulfate, iron (III) sulfate, ammonium iron oxalate, iron (II) chloride, iron (III) chloride, and perchlorite. Examples thereof include iron, iron bromide, iron citrate, iron 4-cyclohexylbutyrate, iron naphthenate, triammonium triammonate triammonate and iron malate, which produce iron oxide by heating. Further, as an iron compound, iron sulfate produced by a method for producing titanium oxide (sulfuric acid method) by dissolving ilmenite in sulfuric acid, purifying this solution, hydrolyzing it, and then firing the hydrolyzate is used. You can also do it. Further, as the iron compound, an iron oxide colloid can be used in addition to a compound that produces an iron oxide by heating. These iron compounds may be one kind or a combination of two or more kinds. The heating after contact with the iron compound may be performed at a temperature at which the iron compound is converted into iron oxide, and is usually 200 ° C or higher, preferably 250 ° C or higher, and 600 ° C or lower, preferably 500 ° C. Hereinafter, it can be carried out more preferably in air at 400 ° C. or lower.

【0018】

The photocatalyst obtained in this manner is usually in the form of powder, but if necessary, a polymer resin, a binder, a molding aid, an antistatic agent, an adsorbent, or the like is added, and then the film is molded. , Honeycomb, pellet, ring or sheet.

【0019】

The decomposition treatment of the organic acid using this photocatalyst is, for example, from the container 2 having the surface 1 through which light passes, the introduction port 3 for introducing the fluid into the container 2, and the container 2 as shown in FIG. An object to be treated using a reaction device 7 including a discharge port 4 for discharging a fluid, a photocatalyst body 5 fixed in a container 2, and a light source 6 for irradiating the photocatalyst body 5 with light through surface 1. Is introduced into the container 2 from the introduction port 3 and sealed, and then the light source 6 is turned on, or as shown in FIG. 2, the cylindrical container 9 whose inner surface is coated with the photocatalyst 8 and the inside of the container 9 Using the reaction device 13 including the installed light source 10, the introduction port 11 for introducing the fluid into the container 9, and the discharge port 12 for discharging the fluid from the container 9, the inner surface of the container 9 is provided by the light source 10. It can be carried out by a method of continuously introducing the object to be treated into the container 9 from the introduction port 11 while irradiating the photocatalyst body 8 in the above. In the former batch method, the object to be treated is treated and then discharged through the discharge port 4. In the latter method, the container 9 may be rotated by an electric motor (not shown) or the like. As the light source, a fluorescent lamp, a halogen lamp, a black light, a xenon lamp, a neon sign, a light emitting diode, an EL lamp, a mercury lamp, a sodium lamp, or the like can be applied. It is also possible to use the sun's rays, in which case the reactor is installed outdoors or a means (reflector, optical fiber, etc.) for introducing the sun's rays into the indoor reactor is provided. The irradiation time (in the continuous type, the average residence time of the object to be processed in the container) may be appropriately selected according to the light intensity of the light source and the type and concentration of the object to be processed. Although the decomposition treatment of organic acids has been shown here, according to the reactor using the photocatalyst of the present invention, NOx in the atmosphere, malodorous substances in living spaces and work spaces (for example, tobacco odors) or organic halogen-based compounds , Or it is also possible to decompose organic solvents or surfactants in water.

【0020】

The photocatalyst coating agent of the present invention contains the above-mentioned specific photocatalyst and solvent.

【0021】

The photocatalyst coating agent makes it easy to apply the photocatalyst to building materials, automobile materials, etc., and makes it possible to impart high photocatalytic activity to these materials. Solvents used to prepare the coating agent include, for example, water, acetic acid, propionic acid, oxalic acid, glutaric acid, succinic acid, malonic acid, maleic acid, adipic acid, carboxylic acids such as citric acid, ammonium acetate, ammonium oxalate, oxalic acid. Examples thereof include ammonium hydrogen, ammonium citrate, ammonium carboxylate such as ammonium hydrogen citrate, alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol, and ketones such as 2-butanone (methyl ethyl ketone) and acetone. In addition, an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid or an aqueous solution of sodium hydroxide is used in the solvent as long as the iron oxide on the surface of the substrate and any acidic metal oxide or basic metal compound are not substantially dissolved. , An alkaline aqueous solution such as a potassium hydroxide aqueous solution can also be used.

【0022】

[Example]

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto. The physical characteristics of the photocatalyst were measured by the following method.

【0023】

(1) BET specific surface area (m)²/ g): Obtained by the nitrogen adsorption method.

【0024】

(2) Anatase crystallite diameter (nm): After crushing the photocatalyst in a dairy pot, the X-ray diffraction spectrum was measured with an X-ray diffractometer (trade name "RAD-IIA", manufactured by Rigaku Denki), and (101) The half-value width β (radian) of the peak of the plane and the peak position 2θ (radian) of the (101) plane were obtained, and the crystallite diameter L (nm) was calculated by the following formula. L = K λ / (β cosθ) [In the equation, K represents the Scherrer constant 0.94 and λ (nm) represents the measured X-ray wavelength (CuK α-ray: 0.15406 nm).

【0025】

(3) Index X [= B / A]: Using an ultraviolet-visible spectrophotometer (trade name "UV-2500PC", manufactured by Shimadzu Corporation), measure the ultraviolet-visible diffuse reflection spectrum using barium sulfate as a standard white plate, and measure this spectrum. The integrated value A of the absorbance at a wavelength of 220 to 800 nm and the integrated value B of the absorbance at a wavelength of 400 to 800 nm were obtained from the above. Based on these values, the index X was calculated from the above equation (I).

【0026】

Example 1 [Preparation of photocatalyst] 3388 g of titanium oxysulfate (manufactured by Teika) was dissolved in 2258 g of water to prepare an aqueous solution of titanium oxysulfate. Ion exchange in a reaction vessel equipped with a pH electrode and a pH controller connected to this pH electrode and having a mechanism for supplying 25 wt% aqueous ammonia (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) to adjust the pH to a constant level. I put 4700g of water. The pH setting of the pH controller was set to 4, and the pH of water was adjusted to the set value using dilute sulfuric acid. The speed at which ammonia water was supplied was set to 18 ml / min. In this reaction vessel, when the pH of the liquid in the vessel becomes lower than the set value, ammonia water starts to be supplied, and is continuously supplied at the above rate until the pH reaches the set value. The above titanium aqueous solution of oxysulfate was added to this reaction vessel at 12 ml / min while stirring at 117 rpm, and the mixture was reacted with aqueous ammonia supplied to the reaction vessel by a pH controller to obtain a product. The reaction temperature at this time was in the range of 23 ° C to 35 ° C. The obtained product was held for 1 hour with stirring, and then 25 wt% aqueous ammonia (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) was supplied to obtain a slurry. The total amount of ammonia water supplied to the reaction vessel was twice the amount required to convert titanium oxysulfate to titanium hydroxide. The slurry obtained above was filtered, and the obtained solid matter was washed with ion-exchanged water and dried to obtain a powder. This powder was calcined in air at 425 ° C for 1 hour under standing, and then cooled to room temperature to obtain particulate anatase-type titanium oxide having a water content of 15% by weight.

【0027】

Iron (III) Nitrate 9 Hydrate (Fe (NO)₃)₃ 9H₂O, manufactured by Wako Pure Chemical Industries, Ltd.) 0.0458 g was dissolved in 100 g of ion-exchanged water to prepare an iron nitrate aqueous solution. This iron nitrate aqueous solution and 20.2 g of the above particulate anatase-type titanium oxide were mixed and stirred at normal temperature and pressure for 20 minutes. The mixture was then kept at 55 ° C. under reduced pressure with stirring to evaporate the water and then calcined in air at 300 ° C. for 1 hour to give a photocatalyst. This photocatalyst is Fe to titanium oxide.₂O₃It has 0.1% by weight of iron oxide in terms of conversion, and has a BET specific surface area of 67 m.²It was / g and the crystallite diameter was 12 nm. In addition, this photocatalyst has an integral value A of the absorbance at a wavelength of 220 nm to 800 nm of 330.4 and an integral value of the absorbance of a wavelength of 400 nm to 800 nm of 92.5 when the ultraviolet-visible diffuse reflection spectrum is measured, and has an index X (=). B / A) was 0.28.

【0028】

[Evaluation of photocatalyst activity] A glass petri dish with a diameter of 5 cm was installed in a closed glass container with a diameter of 8 cm, a height of 10 cm, and a capacity of about 0.5 liter, and the photocatalyst 0.3 obtained above was placed on the petri dish. Placed g. The inside of the container was filled with a mixed gas consisting of 20% by volume of oxygen and 80% by volume of nitrogen, 13.4 μmol of formic acid was sealed, and visible light was irradiated from the outside of the container. For visible light irradiation, a 500W xenon lamp (trade name "Official Modularx SX-UI500XQ", "Lamp UXL-500SX", manufactured by Ushio Denki) is used with a filter (product) that blocks ultraviolet rays with a wavelength of about 430 nm or less. Name "Y-45", made by Asahi Techno Glass) and a filter that cuts infrared rays with a wavelength of about 830 nm or more (trade name "Super Gold") A filter equipped with a filter (manufactured by Ushio, Inc.) was used as the light source. When carbon dioxide is decomposed by irradiation with visible light, carbon dioxide is generated, so the concentration of carbon dioxide is measured by the photoacoustic multi-gas monitor (model number "1312 type"). , INNOVA), and the photodegradation effect of the photocatalyst on formic acid was evaluated by the carbon dioxide production rate calculated from the concentration change. The carbon dioxide production rate in this example is 10.3 μmol per 1 g of the photocatalyst. It was / h.

【0029】

[Effect of the invention]

The photocatalyst of the present invention exhibits a high photocatalytic action when irradiated with visible light, and efficiently decomposes various organic substances including organic acids such as formic acid. The photocatalyst coating agent of the present invention facilitates application of a photocatalyst to building materials, automobile materials and the like, and imparts a high photocatalytic action to these materials. Further, according to the method for producing a photocatalyst of the present invention, the above-mentioned photocatalyst can be easily produced.

[Simple explanation of drawings]

[Figure 1]

A reactor using the photocatalyst of the present invention.

[Figure 2]

Another reactor using the photocatalyst of the present invention.

[Explanation of symbols]

2, 9 containers 3, 11 inlet 4, 12 outlets 5, 8 photocatalyst 6, 10 light sources 7, 13 reactor