JP2003190811A - Photocatalyst, method for producing the same, and photocatalyst coating using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalyst exhibiting high activity upon irradiation with visible light, a method for producing the same, and a photocatalyst coating agent using the same. SOLUTION: Anatase type titanium oxide is used as a base material, and iron oxide (FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe
TiO ₃ ) and a BET specific surface area of 55 m ² /
g or more, and an aqueous solution of a titanium compound and a base are reacted at 60 ° C. or less, and the product is calcined to obtain titanium oxide. This titanium oxide is converted to an iron compound (iron (III) nitrate) , Iron (II) sulfate, iron (III) sulfate, iron oxalate, iron (II) chloride, iron (III) chloride, etc.) solution or slurry, and then heating the photocatalyst.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a photocatalyst body, a method for producing the same, and a photocatalyst body coating agent using the same. More specifically, the present invention relates to a photocatalyst that exhibits high activity upon 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]

2. Description of the Related Art When a semiconductor is irradiated with ultraviolet rays, electrons having a strong reducing action and holes having a strong oxidizing action are generated, and a molecular species in contact with the semiconductor is decomposed by the redox action. Such an action is called a photocatalytic action, and by utilizing this photocatalytic action, organic acids 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 photocatalyst bodies made of titanium oxide are commercially available.

However, currently available photocatalysts do not exhibit sufficient activity when irradiated with visible light.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photocatalyst which exhibits a high decomposition activity upon irradiation with visible light, a method for producing the same and a photocatalyst coating agent using the same.

[0005]

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

That is, the present invention is based on anatase type titanium oxide, has iron oxide on its surface, and has BET.
The present invention provides a photocatalyst having a specific surface area of 55 m ² / g or more.

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

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

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The photocatalyst body of the present invention is based on titanium oxide. Titanium oxide, which is a base material, is represented by a composition formula of TiO ₂ , and has a crystal structure of 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 determined from the peak position and the half width at that time. In the photocatalyst of the present invention, the anatase crystallite size is usually 10 nm.
That is all. A photocatalyst having an anatase crystallite diameter of 10 nm or more exhibits high activity against light irradiation.

Further, the photocatalyst of the present invention has a base material of oxidation.
It has iron oxide on the surface of titanium. As iron oxide,
For example, FeO, Fe₂O₃, Fe₃O_FourOr FeTiO
₃And the like. Of this iron oxide
As the abundance increases, the activity of the photocatalyst increases, so
Preferably, for example, Fe with respect to titanium oxide as a base material ₂
O₃Converted to 0.0005% by weight or more, and even 0.0
It is preferably at least 05% by weight. On the other hand, iron oxide
Even if the amount is too large, the effect of improving the activity commensurate with the amount
5% by weight or less, further 3% by weight
It is preferable that it is below, especially 0.5% by weight or less.
Yes. This iron oxide is the entire surface of titanium oxide which is the base material.
May be present to cover the surface of titanium oxide
May be present so as to cover a part thereof. Of titanium oxide
The photocatalyst body whose part of the surface is coated with iron oxide,
For example, iron oxide is discontinuous as dots on titanium oxide.
What is present, iron oxide is linear or on the titanium oxide
There are things that continuously exist in a grid pattern. It is a base material
Iron oxides present on the surface of titanium oxide are usually
It has a Steadic acid point or a Lewis acid point. Blur of iron oxide
Basic compounds such as amines are selected as the acid point
Tend to be adsorbed, and the Lewis acid sites are oxygenated.
Compounds and sulfur-containing compounds tend to be selectively adsorbed
Therefore, depending on the target substance to be decomposed by the photocatalyst,
Of Bronsted acid point or Lewis acid point of iron oxide
Volume, or both Bronsted and Lewis acid points
If present, it is preferable to select these ratios appropriately.
Good The total amount of each acid point depends on the amount of iron oxide.
Can be adjusted more. Brence in iron oxide
The ratio of Ted acid point and Lewis acid point is, for example, steam treatment.
Alternatively, it can be adjusted by vacuum degassing. Base material
Surface iron oxides with many Bronsted acid points
When using water vapor on titanium oxide with iron oxide on the surface
The iron oxide on the surface of the substrate should be treated with Lewis.
If you want to have many acid points, iron oxide on the surface
The titanium oxide may be subjected to degassing under reduced pressure.

Further, the photocatalyst of the present invention has a BET specific surface area of 55 m ² / g or more as determined by the nitrogen adsorption method. With a photocatalyst having a BET specific surface area of less than 55 m ² / g, a photocatalyst having high activity for visible light irradiation is obtained even if titanium oxide is used as a base material and iron oxide is present on the surface. Becomes difficult. The photocatalyst is B
The higher the ET specific surface area, the higher the photocatalytic activity tends to be. However, when the BET specific surface area is too large, when the BET specific surface area is mixed with a solvent to obtain a coating agent, it may be difficult to disperse it in the solvent. Therefore, the BET specific surface area is 300 m ² / g or less, further 250 m ² / g or less,
It is particularly preferably 200 m ² / g or less.

In the photocatalyst of the present invention, when the ultraviolet-visible diffuse reflectance spectrum is measured and the integrated value of the absorbance at the wavelength of 220 nm to 800 nm is A and the integrated value of the absorbance at the wavelength of 400 nm to 800 nm is B, the formula ( I) The index X calculated by X = B / A (I) is 0.2 or more, further 0.2
It is preferably 5 or more. The integrated value of the absorbance indicates the area of the region surrounded by the horizontal axis and the diffuse reflectance spectrum within the specified wavelength range in the ultraviolet-visible diffuse reflectance spectrum with the absorbance on the vertical axis and the wavelength on the horizontal axis. .

The photocatalyst body having titanium oxide as a base material, having iron oxide on the surface thereof, and having a BET specific surface area of 55 m ² / g or more, has a titanium oxide surface or a titanium oxide surface. It is possible to have an acidic metal oxide or a basic metal compound other than the iron oxides shown in. By having other acidic metal oxides in addition to iron oxide, a photocatalyst having Bronsted acid points and Lewis acid points in various ratios can be obtained. 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.

Examples of the acidic metal oxides include metal oxides having Bronsted acid points, Lewis acid points or both of them. For example, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, One of metals such as cobalt, nickel, copper, aluminum, gallium, indium, tin
Original oxide, silicon-zinc, silicon-zirconium, silicon-
Magnesium, silicon-calcium, silicon-gallium, silicon-aluminum, silicon-lanthanum, silicon-titanium, titanium-zinc, titanium-copper, titanium-zinc, titanium-aluminum, titanium-zirconium, titanium-lead, titanium-bismuth, In addition to complex oxides of two metals such as zinc-magnesium, zinc-aluminum, zinc-zirconium, zinc-lead and zinc-antimony, 3 having an acid site
There are complex oxides of one or more metals. Among these acidic metal oxides, especially zirconium, vanadium,
It is recommended to use a single-element oxide of a metal such as niobium, tantalum, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum or tin. Examples of the above basic metal compound include metal oxides, metal hydroxides or metal carbonates having Bronsted base points, Lewis base points or both of them, 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, lanthanum hydroxide, cerium hydroxide, zinc hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, Examples include lanthanum carbonate, cerium carbonate and zinc carbonate. The total amount of these acidic metal oxides and basic metal compounds is preferably 0.05 mol% or more, and more preferably 0.1 mol% or more in terms of metal element with respect to titanium of titanium oxide as the base material. 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, and further 3
0 mol% or less, especially 10 mol% or less is preferable

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

Anatase-type titanium oxide is used as a base material, iron oxide is present on the surface, and the BET specific surface area is 55 m ^2.
/ G or more, the photocatalyst of the present invention, for example, by reacting an aqueous solution of a titanium compound such as titanium oxysulfate, titanium sulfate, titanium oxychloride, titanium chloride with a base and calcining the product to obtain titanium oxide. The titanium oxide can be prepared by bringing the titanium oxide into contact with a solution or slurry of an iron compound and then heating.

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, and more preferably 2 times or more the stoichiometric amount of the base necessary for converting the titanium compound in the aqueous solution into titanium hydroxide. Less than twice, or even 1
It is preferably 0 times or less. The reaction between the titanium compound and the base is usually performed at 60 ° C or lower, preferably 50 ° C or lower. The product is usually calcined at 300 ° C or higher, preferably 330 ° C or higher, and 600 ° C or lower, preferably 500 ° C.
Hereinafter, it is more preferably performed at 450 ° C. or lower. Also,
This firing can be performed while standing or in an air stream. Examples of the iron compound to be contacted with titanium oxide include iron nitrate (III), iron sulfate (II), iron sulfate (III), ammonium iron oxalate, iron chloride (II), iron chloride (III), and perchloric acid. Iron, iron bromide, iron citrate, iron 4-cyclohexylbutyrate,
Examples thereof include iron naphthenate, iron triammonium trioxalate, iron malate, and the like that generate iron oxides by heating. Further, as the iron compound, iron sulfate by-produced by a method for producing titanium oxide (sulfuric acid method) by dissolving ilmenite in sulfuric acid, purifying the solution, hydrolyzing the solution, and then firing the hydrolyzate is used. You can also Further, as the iron compound, iron oxide colloid can be used in addition to the one that produces iron oxide by heating. These iron compounds may be used alone or in combination of two or more. The heating after the contact with the iron compound may be carried out at a temperature at which the iron compound is converted to an iron oxide, and usually 200
℃ or more, preferably 250 ℃ or more, and 600 ℃ or less,
It can be carried out preferably in air at 500 ° C or lower, more preferably 400 ° C or lower.

The photocatalyst body thus obtained is usually in the form of powder, but after addition of a polymer resin, a binder, a molding aid, an antistatic agent, an adsorbent, etc., if necessary,
It can also be formed into membranes, honeycombs, pellets, rings or sheets.

The decomposition treatment of an organic acid using this photocatalyst, for example, as shown in FIG. 1, a container 2 having a surface 1 through which light passes, an inlet 3 for introducing a fluid into the container 2, Using a reaction device 7 including a discharge port 4 for discharging a fluid from the container 2, a photocatalyst body 5 fixed in the container 2, and a light source 6 for irradiating the photocatalyst body 5 with light through the surface 1,
A method of turning on the light source 6 after introducing the object to be processed into the container 2 through the introduction port 3 and sealing the container 2, or as shown in FIG.
A cylindrical container 9 whose inner surface is coated with the photocatalyst 8, and a container 9
The light source 10 is used for the container 9 by using the reaction device 13 including the light source 10 installed therein, the inlet 11 for introducing the fluid into the container 9, and the outlet 12 for discharging the fluid from the container 9. While irradiating the photocatalyst 8 on the inner surface of the
It can be performed by a method of continuously introducing the object to be treated into the container 9 through the introduction port 11. In the former batch method, the object to be processed is discharged through the discharge port 4 after being processed. 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 or a sodium lamp can be applied. It is also possible to use sunlight, and in this case, the reaction device is installed outdoors, or means for introducing the sunlight to the indoor reaction device (reflecting mirror, optical fiber, etc.) is provided. The irradiation time (in the continuous method, the average residence time in the container of the object to be treated) may be appropriately selected according to the light intensity of the light source and the type and concentration of the object to be treated. Although the decomposition treatment of the organic acid is shown here, according to the reaction device using the photocatalyst of the present invention, NOx in the air, a malodorous substance (for example, a cigarette odor) in the living space or the working space, or an organic halogen-based compound is used. It is also possible to decompose an organic solvent or a surfactant in water.

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

The photocatalyst coating agent makes it easy to apply the photocatalyst to building materials, automobile materials and the like, and makes it possible to impart high photocatalytic activity to these materials. Examples of the solvent used for preparing the coating agent include 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, and oxalic acid. Examples thereof include ammonium hydrogen, ammonium citrate, ammonium carboxylates such as ammonium hydrogen citrate, alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol, 2-butanone (methyl ethyl ketone) and ketones such as acetone. Further, the solvent is an inorganic acid such as hydrochloric acid, sulfuric acid, phosphoric acid or an aqueous sodium hydroxide solution as long as it does not substantially dissolve the iron oxide and any acidic metal oxide or basic metal compound on the surface of the base material. It is also possible to use an alkaline aqueous solution such as an aqueous potassium hydroxide solution.

[0022]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto. The physical properties of the photocatalyst were measured by the following methods.

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

(2) Anatase crystallite diameter (nm): After crushing the photocatalyst in a mortar, an X-ray diffraction spectrum was measured with an X-ray diffractometer (trade name "RAD-IIA", manufactured by Rigaku Denki). The half-value width β (radian) of the peak of the (101) 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 · cos θ) [In the formula, K represents the Scherrer constant of 0.94, and λ (nm) represents the measured X-ray wavelength (CuKα line: 0.15406 nm). ]

(3) Index X [= B / A]: An ultraviolet-visible spectrophotometer (trade name "UV-2500PC", manufactured by Shimadzu Corporation) was used to measure the ultraviolet-visible diffuse reflectance spectrum using barium sulfate as a standard white plate. , From this spectrum, wavelengths 220-8
An integral value A of absorbance at 00 nm and an integral value B of absorbance at 400 to 800 nm were obtained. The index X was calculated from the formula (I) based on these values.

Example 1 [Preparation of photocatalyst] Titanium oxysulfate (manufactured by Teika) 33
88 g was dissolved in 2258 g of water to prepare an aqueous titanium oxysulfate solution. A pH electrode and a mechanism connected to the pH electrode and having a mechanism for adjusting the pH to a constant value by supplying 25 wt% ammonia water (special grade reagent, manufactured by Wako Pure Chemical Industries)
Deionized water 47 in a reaction vessel equipped with a controller
00g was added. The pH of the pH controller was set to 4, and the pH of water was adjusted to the set value using dilute sulfuric acid. The rate of supplying ammonia water is 18 ml / min.
Set to. In this reaction container, when the pH of the liquid in the container becomes lower than the set value, ammonia water starts to be supplied,
It is continuously supplied at the above speed until the pH reaches the set value.
While stirring at 117 rpm, the above titanium oxysulfate aqueous solution was added to this reaction vessel at 12 ml / min, and p
The product was obtained by reacting with ammonia water supplied to the reaction vessel by the H controller. The reaction temperature at this time was in the range of 23 ° C to 35 ° C. The obtained product was maintained for 1 hour with stirring, and then 25% by weight aqueous ammonia (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) was supplied to obtain a slurry. The total amount of aqueous ammonia supplied to the reaction vessel was twice the amount required to convert titanium oxysulfate to titanium hydroxide. Filtering the slurry obtained above,
The obtained solid substance was washed with ion-exchanged water and dried to obtain a powder. This powder was allowed to stand for 1 hour in air at 425 ° C while standing.
After baking for an hour, it is cooled to room temperature and the water content is 15% by weight.
To obtain particulate anatase type titanium oxide.

The iron nitrate (III) 9 hydrate _{(Fe (NO 3) 3 ·} 9H
0.045 g of ₂ O, manufactured by Wako Pure Chemical Industries, Ltd. was dissolved in 100 g of ion-exchanged water to prepare an iron nitrate aqueous solution. This iron nitrate aqueous solution and the above particulate anatase type titanium oxide 20.
2 g were mixed and stirred at room temperature and normal pressure for 20 minutes. Then, this mixture was kept under reduced pressure at 55 ° C. with stirring to evaporate water and then calcined in air at 300 ° C. for 1 hour to obtain a photocatalyst. This photocatalyst had 0.1% by weight of iron oxide in terms of Fe ₂ O ₃ with respect to titanium oxide, had a BET specific surface area of 67 m ² / g, and had a crystallite diameter of 12 nm. In addition, this photocatalyst has a wavelength of 220 nm when an ultraviolet-visible diffuse reflection spectrum is measured.
The integrated value A of the absorbance at 800 nm is 330.4, and the integrated value B of the absorbance at wavelengths of 400 nm to 800 nm is 92.
5, and the index X (= B / A) was 0.28.

[Evaluation of photocatalyst activity] A glass petri dish having a diameter of 5 cm was placed in a closed glass container having a diameter of 8 cm, a height of 10 cm, and a volume of about 0.5 liter. 0.3 g of the obtained photocatalyst was placed.
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 enclosed, and visible light was irradiated from the outside of the container. 5 for visible light irradiation
00W Xenon lamp (Product name "Optical Modulex SX-UI"
"500XQ", "Lamp UXL-500SX", made by Ushio Inc.), and a filter (Product name "Y-45", made by Asahi Techno Glass) that blocks ultraviolet rays with a wavelength of about 430 nm or less and a wavelength of about 830 nm
A light source was equipped with the above infrared ray-cutting filter (trade name "Super Gold Filter", manufactured by Ushio Inc.). When formic acid is decomposed by irradiation with visible light, carbon dioxide is generated, so the concentration of carbon dioxide can be measured by a photoacoustic multi-gas monitor (model number "1312 type", INNOVA).
The photodecomposition effect of the photocatalyst on formic acid was evaluated by the production rate of carbon dioxide calculated from the change in concentration. The production rate of carbon dioxide in this example was 10.3 μmol / h per 1 g of the photocatalyst.

[0029]

INDUSTRIAL APPLICABILITY The photocatalyst of the present invention exhibits a high photocatalytic action upon irradiation with visible light, and efficiently decomposes various organic substances including organic acids such as formic acid. The photocatalyst coating agent of the present invention makes it easy to apply 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 photocatalyst can be easily produced.

[Brief description of drawings]

FIG. 1 is a reactor using the photocatalyst of the present invention.

FIG. 2 is another reactor using the photocatalyst of the present invention.

[Explanation of symbols]

2, 9 containers 3, 11 Inlet 4, 12 outlet 5, 8 Photocatalyst 6, 10 light source 7, 13 Reactor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C01G 23/053 B01D 53/36 J C09D 1/00 B01J 23/74 301M F term (reference) 4D048 AA17 AB03 BA07X BA36X BA41X EA01 4G047 CA02 CB05 CC03 CD03 CD07 4G069 AA03 AA08 BA04A BA04B BA48A BB04A BB04B BC66A BC66B CA01 CA11 DA05 EA02Y EC01X EC02Y EC22X EC22Y EC27 FA01 FB08 FB15 FB16 OA16 AFB06 FB16 038A FC08

Claims (6)

[Claims] 1. A base material of anatase-type titanium oxide, which has iron oxide on its surface and has a BET specific surface area of 55 m.
^A photocatalyst body having a content of ² / g or more. 2. The amount of iron oxide is Fe relative to titanium oxide.
_The photocatalyst body according to claim 1, which is 0.0005% by weight or more in terms of ₂ O ₃ . 3. The photocatalyst body according to claim 1, which has a BET specific surface area of 300 m ² / g or less. 4. The ultraviolet-visible diffuse reflectance spectrum is measured, and the integrated 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 index X calculated by the formula (I) X = B / A (I) is 0.2 or more.
3. The photocatalyst body according to any one of 3 above. 5. An aqueous solution of a titanium compound is reacted with a base at 60 ° C. or lower, the product is calcined to obtain titanium oxide, and the titanium oxide is brought into contact with a solution or slurry of an iron compound and then heated. 1. The method for producing a photocatalyst body according to 1. 6. A photocatalyst coating agent containing the photocatalyst according to any one of claims 1 to 4 and a solvent.