JP2001246247A - Method for producing photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a photocatalyst which can be held stably in a particulate state even when it is pulverized and can develop a quantum size effect and a method for decomposing harmful substances using the photocatalyst. SOLUTION: When TiO2 is produced by hydrolyzing a titanium alkoxide as a TiO2 raw material, after the hydrolysis, the product is subjected to acid treatment or alkali treatment to form a TiO2 precursor, and TiO2 is pulverized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photocatalyst and a method for decomposing an organic compound using the photocatalyst.

[0002]

BACKGROUND OF THE INVENTION Exhaust gas or wastewater discharged from various incinerators such as municipal garbage incinerators, industrial waste incinerators, and sludge incinerators include, in addition to nitrogen oxides, Harmful halogenated aromatic compounds represented by dioxins and PCBs, highly condensed aromatic hydrocarbons,
In some cases, harmful substances such as environmental hormones are contained, causing damage to the human body, animals and plants, and destroying the natural environment, which has become a serious social problem.

A photocatalyst can oxidize and decompose various kinds of hydrocarbons adsorbed by using light such as ultraviolet light, so that there is no need to apply energy from the outside, and it is one of the earth-friendly environmental protection means. Particularly, in recent years, suppression of emission of environmental hormone substances such as dioxins has been called for, and various methods for detoxification by using a photocatalyst or the like have been studied.

However, as shown by the broken line in FIG. 2, anatase-type TiO ₂ generally used as a current photocatalyst has a large particle size of 200 ° or more.
It has not reached the particle size level with the quantum size effect. For this reason, attempts have been made to reduce the particle size of TiO ₂ to exhibit the quantum size effect and improve the catalytic activity. However, if the particle size is simply reduced, the problem that TiO ₂ is re-agglomerated and coarsened. is there. As a result, there is a demand for the development of a photocatalyst that does not become coarse due to re-aggregation or the like even if it is miniaturized and that can effectively exhibit the catalytic activity effect.

In view of the above problems, the present invention provides a photocatalyst capable of stably retaining fine particles even when the photocatalyst is further miniaturized and exhibiting a quantum size effect, and a method for decomposing harmful substances using the photocatalyst. That is the task.

[0006]

Means for Solving the Problems To solve the above problems, the invention of claim 1 is to produce a TiO ₂ by hydrolyzing a titanium alkoxide as a TiO ₂ raw material. To form a TiO ₂ precursor and to make TiO ₂ into fine particles.

The invention of claim 2 is characterized in that, in claim 1, the acid treatment is a nitric acid treatment or a hydrochloric acid treatment, and the alkali treatment is an ammonia water treatment.

According to a third aspect of the present invention, in the first aspect, at least one of organometallic compounds of Si, Al, Zr, P and B is added to the titanium alkoxide.

[0009] The invention of claim 4 is characterized in that the harmful substance in the gas phase or aqueous solution is brought into contact with the photocatalyst obtained by the production method of claims 1 to 3, and the harmful substance is decomposed. .

According to a fifth aspect of the present invention, in the fourth aspect, the harmful substance is at least one selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols, and halogenated toluenes. It is a halogenated aromatic compound, a highly condensed aromatic hydrocarbon, and an environmental hormone.

The invention of claim 6 is the invention according to claim 5, wherein the dioxins are polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polybrominated dibenzo-p-dioxins. (PBDDs), polybrominated dibenzofurans (PB
DFs), polyfluorinated dibenzo-p-dioxins (P
FDDs), polyfluorinated dibenzofurans (PFDF)
s), polyiodinated dibenzo-p-dioxins (PI
DDs), polyiodinated dibenzofurans (PIDFs)
It is characterized by being.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

[0013] The method for producing a photocatalyst according to the present invention comprises the steps of:
₂ Hydrolysis of raw material titanium alkoxide to TiO
Upon generating the _2, after hydrolysis, acid treatment or an alkali treatment to form a TiO ₂ precursor, in which the TiO ₂ was set to be fine particles. Here, the pore diameter of the photocatalyst is reduced to 100 ° or less (particularly preferably 50 ° or less). The condition of the fine particles depends on the reaction time pH, but it is sufficient to obtain a photocatalyst that does not exceed an average of 100 °. This is 100Å
This is because, as shown in FIG. 2, the quantum size effect does not effectively appear, and the catalytic activity is not good.

The above acid treatment is preferably a nitric acid treatment or a hydrochloric acid treatment, while the alkali treatment is preferably an ammonia water treatment.

[0015] By repeating the pH swing, the effect of micronization is exhibited. The width of the pH swing is
The pH is preferably in the range of 2 to 13.

The material of the photocatalyst metal alkoxide (ethyl, methyl, propyl, butyl group, etc.) a liquid phase is preferred using, as the TiO ₂ material, TiCl ₄
A solution such as a solution, a TiSO ₄ solution, a Ti (SO ₄ ) ₂ solution, or a titania sol may be used.

The titanium alkoxide includes Si,
Fine particles can also be obtained by using a composite oxide photocatalyst to which at least one of the organometallic compounds of Al, Zr, P and B is added. The addition of the organometallic compound is not particularly limited, but may be added first to the TiO ₂ raw material and mixed.

In the present invention, fine particle formation can also be promoted by using the above-mentioned acid or alkali treatment and complex oxide treatment together.

According to the present invention, the fine-particle TiO ₂ also has an increased specific surface area, so that the ability to adsorb organic substances and the like increases, and the quantum size effect acts, so that the photocatalytic action is dramatically improved.

The photocatalyst forms a hydroxyl radical from water using ultraviolet light, and the hydroxyl radical has a high-performance oxidizing ability, so that organic compounds and the like can be oxidatively decomposed at room temperature.

The effect of the photocatalyst according to the present invention is further enhanced by utilizing ultraviolet light. Further, the oxidizing ability is increased by adding ozone. Furthermore, a synergistic effect of decomposition of harmful substances of dioxins is exhibited by the combination of these.

The harmful substances decomposed by the photocatalyst of the present invention include nitrogen oxides, dioxins and PXB.
(X represents a halogen.) Hazardous substances such as harmful halogenated aromatic compounds and high-condensation degree aromatic hydrocarbons represented by the class. It is not limited to these if it is a hormone.

The aromatic halogen compound to be decomposed in the present invention is not limited to any harmful substances (for example, environmental hormones) represented by dioxins and PCBs. Here, the dioxins are polyhalogenated dibenzo-p-dioxins (P
XDDs) and polyhalogenated dibenzofurans (PX
DFs) (X represents halogen), and is said to be generated in a small amount when a halogen compound and a certain organic halogen compound are burned. Depending on the number of halogens, there are monohalides to octahalides, of which dibenzo-p-dioxin tetrachloride (T ₄ CDD) is particularly preferred.
Is known to be the most toxic. The harmful halogenated aromatic compounds include, in addition to dioxins, various organic halogen compounds which are precursors thereof (for example, aromatic compounds such as phenol and benzene (for example, halogenated benzenes, halogenated phenols and halogenated phenols). And halogenated alkyl compounds) and must be removed from the ash.
That is, dioxins represent not only chlorinated dioxins but also halogenated dioxins such as brominated dioxins. PXBs (polyhalogenated biphenyls) are a general term for compounds in which several halogen atoms are added to biphenyl, and there are isomers depending on the number and position of substitution of halogen, but in the case of PCB (polychlorinated biphenyl), , 2,6-dichlorobiphenyl, 2,2'-dichlorobiphenyl, 2,3,5-trichlorobiphenyl and the like are typical, are highly toxic, and may emit dioxins when incinerated. Known and need to be removed. Needless to say, the PXBs include the coplanar PXB.

The aromatic hydrocarbon having a high degree of condensation is a general term for polynuclear aromatic compounds, which may contain one or more OH groups, is recognized as a carcinogen, and needs to be decomposed and removed. .

Further, in many production processes, in addition to dust, exhaust gas containing, for example, gaseous organic compounds such as formaldehyde, benzene or phenol may be generated. Since these organic compounds are also environmental pollutants and significantly impair human health, they also need to be decomposed and removed.

The nitrogen oxide to be treated in the present invention usually means NO and NO ₂ , and also a mixture thereof.
It is also called NOx. However, the NOx often contains various oxidation numbers and unstable nitrogen oxides in addition to the above. Accordingly, x is not particularly limited, but is usually a value of 1 to 2. It becomes nitric acid, nitrous acid, etc. in rainwater or NO, or NO is said to be one of the main causes of photochemical smog, and is a harmful compound to the human body.

By using the photocatalyst obtained according to the present invention, the above-mentioned harmful substances such as nitrogen oxides, halogenated aromatic compounds, and highly condensed aromatic hydrocarbons and gaseous organic compounds can be eliminated. It can be detoxified by catalytically reducing or decomposing. Here, the halogenated aromatic compound, the precursor of the halogenated aromatic compound, the halogenated aromatic compound such as PXB, the highly condensed aromatic hydrocarbon, and the environmental hormone of the harmful substance of the present invention are contained in the exhaust gas of the present invention. By using the photocatalyst in the form of fine particles as described above, the oxidative decomposition effect is improved by the development of the quantum size effect, and the detoxification treatment is performed.

By forming a catalyst device in which the photocatalyst according to the present invention is immobilized on a carrier such as a glass substrate, and irradiating ultraviolet rays from an ultraviolet irradiation device, it is possible to decompose and remove harmful substances such as environmental hormones in wastewater. it can.

The photocatalyst of the present invention can exhibit an effective photocatalytic function not only in decomposing harmful substances in a liquid phase into a gas phase but also in decomposing harmful organic compounds such as dioxins in a gas phase. .

That is, by using the photocatalyst according to the present invention, after removing soot in exhaust gas discharged from various incinerators such as municipal garbage incinerator, industrial waste incinerator, sludge incinerator, etc. In addition, harmful substances such as nitrogen oxides, halogenated aromatic compounds, highly condensed aromatic hydrocarbons and environmental hormones in exhaust gas can be decomposed and removed.

Further, since the photocatalyst of the present invention can decompose dioxins and the like at ordinary temperature, it is not necessary to set the treatment temperature as high as 200 to 300 ° C. unlike the conventional oxidation catalyst. Therefore, the decomposition at room temperature does not generate dioxins due to resynthesis of the precursor of dioxins, which is a preferable treatment temperature.

In particular, a dust removing device (eg, a bag filter)
Exhaust gas is cooled when processing at low temperature (below 150 ° C)
Even when the above method is adopted, it becomes possible to treat harmful substances in the exhaust gas without reheating the sheet as in the related art.

Further, by providing the present catalyst device at the opening of the chimney, the photocatalyst can be activated by sunlight and decompose and remove harmful substances in exhaust gas without using an ultraviolet irradiation device separately. it can.

Furthermore, the photocatalyst according to the present invention is applied thinly directly to the surface of a fluorescent tube, so that harmful substances such as volatile gas in a room or in a tunnel can be decomposed and removed by photolysis from the fluorescent tube. it can.

[0035]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples.

<Example 1> [Preparation of powder photocatalyst 1] 25 cc of titanium isopropoxide (Ti (OC ₃ H ₇ ) ₄ ) was sampled, 25 cc of isopropanol was dropped at once, and the mixture was stirred at 400 rpm for 10 minutes at room temperature. Obtain solution A. Also, a solution B is obtained by mixing 100 cc of ion-exchanged water and 200 cc of isopropanol. Also, add solution B to solution A,
The mixture is stirred at 400 rpm for 2 hours at 60 ° C. to obtain a slurry in which titanium hydroxide is formed by hydrolysis. Also, 10 cc of concentrated nitric acid and 100 cc of ion-exchanged water were added to the slurry.
And the mixture is stirred at 60 ° C. for 2 hours. After that, it is washed with water, dried, and calcined at 400 ° C. for 3 hours.

[Preparation of Powder Photocatalyst 2] In the preparation of the photocatalyst 1, when preparing the solution A, 4 cc of titanium isopropoxide and silane ethoxide (Si (OC ₂ H ₅ ) ₄ ) were added dropwise to the solution A. did. Thereafter, the same operation as the method for adjusting the photocatalyst 1 was performed to obtain a photocatalyst 2 made of a TiO ₂ / SiO ₂ composite oxide.

[Adjustment of Powder Photocatalysts 3 and 4] The above photocatalyst 1
In the method of adjusting the concentration, concentrated hydrochloric acid (HCl: 35) was used instead of concentrated nitric acid as the liquid to be added to the titanium hydroxide slurry.
%) And concentrated aqueous ammonia (NH ₃ : 28%), respectively, and stirred at 60 ° C. for 2 hours. Thereafter, the same operation as that of the photocatalyst 1 was performed to obtain photocatalyst powders 3 and 4 made of TiO ₂ .

[Adjustment of Powder Photocatalyst 5] In the method of adjusting the photocatalyst 1, an aqueous nitric acid solution was added to the titanium hydroxide slurry, and the mixture was stirred at 60 ° C. for 2 hours. Thereafter, the same operation as that of the photocatalyst 1 was performed, and the photocatalyst powder 5 made of TiO ₂ was used.
I got

[Adjustment of Powdered Photocatalysts 6, 7, 8, 9] In the above-mentioned method of adjusting the photocatalyst 2, aluminum propoxide (Al (OC) was used instead of silane ethoxide.
₃ H _{7) 3),} zirconium propoxide (Zr (OC
₃ H ₇ ) ₄ ), boron propoxide (B (OC ₃ H ₇ )
₃ ) and phosphorus propoxide (P (OC ₃ H ₇ ) ₃ ) were added dropwise in an amount of 4 cc to prepare solution A. Thereafter, the same operation as in the case of the photocatalyst 2 was performed to obtain a TiO ₂ .Al ₂ O ₃ composite oxide, a TiO ₂ .Zr ₂ O ₃ composite oxide, and a TiO ₂ .B ₂
Photocatalyst powders 6, 7, 8, and 9 composed of an O ₃ composite oxide and a TiO ₂ .P ₂ O ₃ composite oxide were obtained.

[Adjustment of Powder Photocatalyst 10] In the method for adjusting the photocatalyst 1, the solution A used was a solution of 23 g of titanyl sulfate and 200 cc of ion-exchanged water. As the solution B, a solution of 30 cc of concentrated ammonia water and 200 cc of ion-exchanged water was used. The solution A and the solution B were mixed to obtain a titanium hydroxide slurry. Concentrated sulfuric acid 10c in the obtained slurry
A solution of c and 100 cc of ion-exchanged water was added, and the same operation as in photocatalyst 1 was performed to obtain photocatalyst powder 10 made of TiO ₂ .

[Adjustment of Comparative Catalysts 1 and 2]
In the adjusting method, the solution A is obtained by mixing the solution A and the solution B.
Without adding nitric acid solution to the titanium hydroxide slurry
TiO adjusted in the same manner as Catalyst 1 _TwoComparative catalyst 1 consisting of
Obtained. In addition, ordinary anatase TiO_Two(Ishihara Sangyo
And “MC-50” (product name) as Comparative 2
It was subjected to a sex evaluation test.

The specific surface area of the obtained photocatalyst and the crystallite diameter of TiO ₂ determined by the X-ray diffraction method are shown in Table 1 below.

<Activity Evaluation Test> The photocatalyst activity was evaluated using the photocatalysts 1 to 10 and the comparative catalysts 1 and 2. The test method is a liquid phase decomposition test of dibenzofuran, which is a simulated substance of dioxins. The raw material dibenzofuran aqueous solution was prepared by the following method. First, dibenzofuran 0.0
5 g was dispersed in 1 cc of methanol for 3 minutes using an ultrasonic water washer, and 60 μL of a dibenzofuran methanol solution was dissolved in 250 cc of pure water. The powdered photocatalyst was added at 0.5 g / L and the tank reactor was stirred at 23 ° C. and 600 rpm. UV light having a UV output of 20 W was used.

FIG. 1 shows an outline of the test apparatus. As shown in FIG. 1, the test apparatus controls a reaction vessel 12 provided in a constant temperature water tank 11, an ultraviolet lamp 13 whose periphery is protected by a protective tube 12 in the reaction vessel, and controls the temperature of the constant temperature water tank 11. A constant temperature water tank control means 14 and an ultraviolet lamp control means 15 for controlling the ultraviolet lamp 13, and a dibenzofuran aqueous solution 16 containing a photocatalyst in the constant temperature water tank 11.
And stirring the dibenzofuran aqueous solution 16 with a stirrer 17 using a stirring means 17.

For the analysis, the dibenzofuran solution concentration was analyzed after 15 minutes and 30 minutes of light irradiation. The analysis method was such that after irradiation with light for a predetermined time, the slurry was sampled, and the dibenzofuran concentration was determined by gas chromatography analysis using the supernatant separated by a centrifuge. The results are shown in Table 1 below.

As a result of the actual measurement, the initial dibenzofuran concentration was 4.0 mg / L, only UV (no photocatalyst),
It has been confirmed that dibenzofuran is hardly decomposed by the photocatalyst alone (no UV).

Table 1 shows the dibenzofuran concentration (C) at each time as C / C _{0 with} respect to the initial (C ₀ ).
Indicated by.

[0049]

[Table 1]

As shown in Table 1, all of the photocatalysts according to the present invention had a primary particle diameter of 50 ° or less, a quantum particle size effect was exhibited, and it was confirmed that the photocatalyst had a high performance.

[0051]

As described above, according to claim 1 of the present invention, when hydrolyzing titanium alkoxide as a TiO ₂ raw material to form TiO ₂ , an acid treatment or an alkali treatment is performed after the hydrolysis. As a result, a TiO ₂ precursor is formed and TiO ₂ is finely divided, so that a fine particle photocatalyst can be produced.

According to the invention of claim 2, the photocatalyst in the form of fine particles can be manufactured by treating the acid treatment with nitric acid treatment or hydrochloric acid treatment and the alkali treatment with ammonia water treatment.

According to a third aspect of the present invention, there is provided a photocatalyst in the form of fine particles, wherein the photocatalyst is a composite oxide obtained by adding at least one of organometallic compounds of Si, Al, Zr, P and B to titanium alkoxide. Can be manufactured.

According to the invention of claim 4, the harmful substance can be decomposed by bringing the harmful substance in a gas phase or an aqueous solution into contact with the photocatalyst obtained by the production method of claims 1 to 3. .

According to the invention of claim 5, at least one halogenated aromatic compound selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols, and halogenated toluenes; Harmful substances such as aromatic hydrocarbons and environmental hormones can be decomposed.

According to the invention of claim 6, polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polybrominated dibenzo-
p-Dioxins (PBDDs), polybrominated dibenzofurans (PBDFs), polyfluorinated dibenzo-p-dioxins (PFDDs), polyfluorinated dibenzofurans (PFDFs), polyiodinated dibenzo-p-dioxins (PIDDs) ), Polyiodinated dibenzofurans (P
Dioxins such as IDFs) can be decomposed.

[Brief description of the drawings]

FIG. 1 is a schematic view of a powder photocatalyst test apparatus.

FIG. 2 is a diagram showing the relationship between the particle size of TiO ₂ and the catalytic activity.

[Explanation of symbols]

 Reference Signs List 11 constant temperature water tank 12 reaction vessel 13 ultraviolet lamp 13a protective tube 14 constant temperature water tank control means 15 ultraviolet lamp control means 16 dibenzofuran aqueous solution 17a stirrer 17 stirring means

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Claims (6)

[Claims] In producing TiO ₂ by hydrolyzing a titanium alkoxide as a TiO ₂ raw material, it is preferable to form an TiO ₂ precursor by performing an acid treatment or an alkali treatment after the hydrolysis to form TiO ₂ into fine particles. A method for producing a photocatalyst characterized by the following. 2. The method according to claim 1, wherein the acid treatment is a nitric acid treatment or a hydrochloric acid treatment, and the alkali treatment is an ammonia water treatment. 3. The titanium alkoxide according to claim 1, wherein Si, Al, Zr, P and B are added to the titanium alkoxide.
A method for producing a photocatalyst, comprising adding at least one of the organometallic compounds of the above. 4. A harmful substance in a gas phase or an aqueous solution is brought into contact with a photocatalyst obtained by the production method according to claim 1;
A method for decomposing harmful substances, comprising decomposing harmful substances. 5. The method according to claim 4, wherein the harmful substance is at least one halogenated aromatic compound selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols and halogenated toluenes. A method for decomposing harmful substances characterized by being aromatic hydrocarbons and environmental hormones. 6. The method of claim 5, wherein the dioxins are polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polybrominated dibenzo-p-dioxins (PBDDs), polyodors. Dibenzofurans (PBD
Fs), polyfluorinated dibenzo-p-dioxins (PF
DDs), polyfluorinated dibenzofurans (PFDFs),
Polyiodinated dibenzo-p-dioxins (PIDD
s), a method for decomposing harmful substances, which is polyiodinated dibenzofurans (PIDFs).