JP3496229B2 - Method for producing photocatalyst body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a photocatalyst used for water purification, deodorization, sterilization, wastewater treatment, water decomposition, various organic chemical reactions and the like.

[0002]

2. Description of the Related Art When a semiconductor is irradiated with light of an appropriate wavelength having an energy higher than its band gap, photoexcitation causes electrons to transit from the valence band to a conductor, and at the same time, holes are generated in the valence band. So-called charge separation occurs. Further, when the semiconductor is irradiated with light and brought into contact with water or a solution, a junction similar to a Schottky barrier is formed, and holes are emitted when the semiconductor is n-type and electrons are emitted when the semiconductor is p-type. It is well known that they gather on the surface of the semiconductor on the solid-liquid interface side. In the case of an n-type semiconductor, holes withdraw electrons from water or solution species, and as a result, water is decomposed or solutes in the solution are oxidized. In the case of a p-type semiconductor, electrons are
It is applied to adjacent water or solution species, and a reduction reaction of the water or solution species occurs. The semiconductor that promotes the photooxidation / reduction reaction is called a semiconductor photocatalyst or simply a photocatalyst.

Conventionally, as a redox reaction or a redox reaction operation using a photocatalyst, water decomposition reaction, microorganism killing reaction, deodorization reaction, sterilization reaction, water purification, deodorization, wastewater treatment, and other various organic chemical reactions Have been proposed.
Specifically, titanium oxide as an n-type semiconductor is most widely used as a photocatalyst because of its chemical stability. Titanium oxide may be used in the form of powder and suspended in a solution, or may be used in the form of being supported on some substrate. From the viewpoint of photocatalytic activity, the former is generally more active due to its large surface area, but from a practical standpoint, the latter should be used rather than the former because of its ease of handling. In many cases, it is unavoidable.

As a method of supporting a photocatalyst on a substrate, for example, a porous glass support is impregnated with an alcohol solution of titanium (IV) tetrabutoxyoxide and heated to form anatase-type titanium oxide. A method of holding and fixing to a transparent glass support has been proposed.

[0005]

When the coating is simply applied by the sol-gel method as described above, although there are fine pores,
Since these are very small holes, there was a problem that ultraviolet light could reach only the surface layer.

Further, in order to increase the mechanical strength of the formed photocatalyst layer, if it is fired at a higher temperature, the crystallization of the metal oxide will proceed, and such fine pores will become smaller, resulting in a dense film, There is a problem that the penetration of the ultraviolet light in the depth direction becomes more difficult.

[0007]

The present invention is a method of gelling a mixture of a powdery photocatalyst and a metal oxide sol acting as a binder for the powdery photocatalyst or a metal oxide sol as a starting material of the photocatalyst . After that, in hot water at 40-100 ° C
Immersion or contact with steam at 100-200 ° C
Also, a powdery photocatalyst and a binder for the powdery photocatalyst
Mixture with metal oxide sol that acts as
The metal oxide sol, which is the starting material of the medium, is used as a support for the photocatalyst.
After being loaded on and gelled, it is placed in hot water at 40 to 100 ° C.
Immerse or contact with steam at 100-200 ℃,
By heating at a temperature of 800 ° C. or lower , the above problems are solved.

[0008]

There are several known methods for synthesizing metal oxides in the form of thin films or films on various substrates. Among them, the so-called sol-gel method can synthesize metal oxides at low temperature. It is known as a method having a feature that a complex oxide can be easily manufactured. In the sol-gel technique, a method of obtaining a sponge-like alumina thin film by treating alumina gel in hot water has recently been proposed (Akira Hasegawa, Journal of the Chemical Society of Japan, 12, 1511).
(1992)).

Therefore, the inventors of the present invention use a metal oxide material used as a semiconductor photocatalyst or a metal oxide as a supporting / immobilizing agent for a powder photocatalyst because of its light transmittance, mass transfer effectiveness, and the like. Focusing on the possibility that a metal oxide can be a very effective structure as a photocatalyst layer by using the same method, the present invention has been achieved as a result of sincere research.

The photocatalyst composition or photocatalyst body according to the present invention is characterized in that the three-dimensional structure of the catalyst composition has large three-dimensional pores, or that the powdery catalyst carrying and immobilizing agent is three-dimensional. It has large pores, reflects little ultraviolet light and scatters it, and is extremely excellent in the transmittance of ultraviolet light in the depth direction.

Further, in these manufacturing methods, such an ideal structure as a photocatalyst can be simply and simply treated with a small amount of water which does not harm the environment or human body.

The manufacturing process, structure and meaning of the photocatalyst according to the present invention will be described in detail below. In the present invention
There are various methods in the manufacturing process of such a photocatalyst,
First, the metal oxide sol, which is the photocatalytically active component, is directly synthesized.
The method for doing so is shown in FIG.
When using a photocatalyst and a metal oxide as its binder
The manufacturing method of the combination is shown in FIG. 1 and 2
, 1 is a photocatalytically active component, 2 is a photocatalyst powder, and 3 is a binder.
The agent, 4 is a substrate, and 5 is a void portion.

First, as the material used as the substrate 4 , a metal oxide sol is carried by a method such as coating or impregnation,
Alternatively, any material can be applied as long as it can form a film by a method such as dip coating or spin coating. For example, ceramic mats obtained by dispersing glass or ceramic fibers in water and making paper in the manner of papermaking, porous glass, or nylon, acrylic,
Those having three-dimensional voids such as polyester and other textile products, or translucent plate-like, linear, tubular products such as glass and PMMA, ceramic, metal and plastic molded products. .

Next, as the photocatalyst active component 1 or the photocatalyst powder 2, TiO ₂ , ZnO, SrTiO ₃ and Cd are used.
S, GaP, InP, GaAs, BaTiO ₃ , K ₂ N
bO ₃ , Fe ₂ O ₃ , Ta ₂ O ₅ , WO ₃ , SnO ₂ ,
Bi ₂ O ₃ , NiO, Cu ₂ O, SiC, SiO ₂ , M
oS ₂ , InPb, RuO ₂ , CeO _2, etc., and Pt, Rh, RuO ₂ , Nb, Cu, S for these photocatalysts.
Conventionally known materials carrying metals such as n and NiO and metal oxides are all applicable.

There are various methods for producing the photocatalyst body according to the present invention . First , the method for directly synthesizing the sol of the metal oxide as the photocatalytically active component 1 will be described with reference to FIG .

A typical production method in this case is a method of supporting a metal oxide sol which becomes the photocatalytically active component 1 on the substrate 4 as described above by a method such as impregnation.

That is, first, an alcoholic solution of a metal organic compound such as a metal alkoxide, acetylacetonate, or carboxylate as employed in the sol-gel method or a chloride such as titanium tetrachloride is hydrolyzed in the presence of an acid or alkali catalyst. By preparing a sol of the metal oxide obtained by doing, coating method, spraying method,
The substrate is supported by a method such as a dip coating method. Next, the solvent component is volatilized and gelled to form a metal oxide gel. However, in this case, the final amount of money
Group oxides are limited to materials that become active as photocatalysts.

Next, the metal oxide gel layer thus obtained is immersed in hot water at 40 to 100 ° C. or 100 to 20.
Contact with 0 ° C. steam . Then, in order to increase the binding strength of the photocatalyst layer or to increase the mechanical strength thereof, by heating at a temperature of 800 ° C. or lower, preferably at a temperature of 200 to 600 ° C. To obtain a photocatalyst.

Next, a manufacturing method in which a powdery photocatalyst is used as the photocatalytically active component and a metal oxide is used as the binder will be described with reference to FIG .

There are various manufacturing methods in this case, but one typical manufacturing method is to use the optical method in advance.
The photocatalyst powder 2 which is the catalytically active component 1 is supported on the substrate 4 ,
Then, a method of impregnating a metal oxide sol which does not act as a photocatalyst or has little effect on the photocatalyst is used.

[0021] That is, first, in advance of the surface of the substrate 4, a spray spraying, dip coating,
A layer of the photocatalyst powder 2 is formed by a method such as a spin coating method. The photocatalyst powder carrier, to which the photocatalyst powder 2 has just been adhered, is adhered or impregnated with a sol of a metal oxide to be the binder 3 by a method such as a spray method or an impregnation method, and the solvent is removed to form a gel. , A photocatalyst-metal oxide gel layer. Since the metal oxide in this case does not need to have any activity as a photocatalyst, any material that can be applied to the sol-gel method can be used. Excellent materials are preferred. Further, it may be effective to mix two or more kinds of metal oxide sols to use as a gel of the metal composite oxide.

As another method, a mixed solution of a photocatalyst powder and a sol of a metal oxide is prepared, and instead of carrying only the semiconductor photocatalyst powder on a substrate, this mixed solution is impregnated, coated,
Alternatively, a photocatalyst-metal oxide gel layer may be used in a method of supporting and gelling by various coating methods.

Alternatively, before obtaining the metal oxide sol, the photocatalyst powder is first mixed with an alcohol solution of the above-mentioned metal organic compound or chloride, and the photocatalyst powder is obtained by hydrolysis in the presence of an acid or alkali catalyst. A similar photocatalyst-metal oxide gel layer can also be obtained by a method in which a metal oxide mixed sol is impregnated into a substrate, coated, or supported by various coating methods and gelled.

Next, the metal oxide gel layer or the photocatalyst layer containing the metal oxide gel thus obtained is mixed with 40 to 1
Immerse in hot water at 00 ° C or 100-200 ° C
Contact with water vapor . Next, in order to increase the binding strength of the photocatalyst layer or to increase the mechanical strength thereof , a temperature of 800 ° C. or lower, preferably 2
The desired photocatalyst is obtained by heating at a temperature of 00 to 600 ° C.

In the process of producing the photocatalyst according to the present invention, a metal oxide layer as a photocatalytically active component or a photocatalyst-metal oxide layer as a mixed layer of a semiconductor photocatalyst powder and a binder is preferably used. This is the most important point, and not only the material, shape, and physical properties of the substrate used, but also the raw material of the photocatalytically active component and the photocatalyst powder-carrying and immobilizing agent 3 itself, the handling method, etc. are limited. Not something to do.

Here, it is considered that the good constitution of the photocatalyst powder and the supporting / immobilizing agent and its significance are as follows. That is, the metal oxide sol, which is supported and gelled on the substrate by a method such as a spray method, a coating method, an impregnation method, or a dip coating method, is a film-like metal oxide gel layer having fine pores on the substrate, Alternatively, it forms a network of porous metal oxide gel that has entered between the photocatalyst powder particles and the substrate on the substrate to form a film-shaped photocatalyst-metal oxide gel layer. When this is treated with hot water or steam, water enters the pores of the gel where the solvent has escaped and swells,
It becomes a relatively large hole. Next, this is baked to form a metal oxide layer having three-dimensional large pores. However, since the metal oxide itself generated in this way is not large enough to scatter or reflect ultraviolet light,
The irradiated ultraviolet light can also excite the photocatalytically active component located "behind" it, that is, function as a photocatalyst. That is, the ultraviolet light can penetrate deeper in the depth direction than the metal oxide obtained by the so-called sol-gel method. This is a point that is significantly different from the case of manufacturing by a method such as a sol-gel method. Furthermore, it is considered that such a configuration improves the inflow and outflow of the reactant.

An ideal structure as such a photocatalyst body is immersed in hot water in the manufacturing process of the sol-gel method .
Another feature is that it can be realized only by adding a step of contacting with steam.

There is a point that the present inventors have not been able to elucidate the action mechanism of the present invention. However, according to the present invention, a photocatalyst having excellent catalytic activity and constant mechanical strength, which has not been obtained by a conventionally known production method, can be obtained.
For the first time, it was possible to obtain it.

[0029]

<Example 1> 4 g of tetraethoxysilane was dissolved in 50 ml of ethanol, and 20 ml of ethanol was added thereto.
A mixed solution of 2 ml of water and 0.3 ml of concentrated hydrochloric acid was added to obtain a silica sol. 5 g of anatase-type titanium oxide (particle diameter 0.03 μm), which had been preliminarily heat-treated at 350 ° C. for 2 hours, was dispersed in this, a photocatalyst layer was formed on a glass plate having a diameter of 36 mm by a dip coating method, and the solvent was removed , Gelled. Then 1
It was immersed in hot water at 00 ° C for 1 hour and baked at 400 ° C for 1 hour to obtain a photocatalyst. The amount of titanium oxide supported at this time was 2.5 mg. For comparison, it was prepared which do not immersed in hot water in the same fabrication process.

The resulting photocatalyst was placed on the bottom of a 130 ml beaker. 100 ml of an aqueous phenol solution having a concentration of 0.02 mmol / l was put into the beaker, and 400 nm-300 n of a 1 kW high pressure mercury lamp from the bottom of the beaker.
m of ultraviolet light was irradiated, and the change with time of the phenol concentration with respect to the light irradiation time of this aqueous solution was examined. The ultraviolet intensity at this time was 11 mW / cm2 (365 nm).

As a result, the concentration of phenol was halved about 20 minutes after the start of light irradiation, and it was decomposed below the detection limit in about 2 hours. For comparison, was subjected to the same examination for those manufactured without immersion in hot water during, for those manufactured without immersion in hot water in the completely even after light irradiation for 3 hours degradation Was not done.

Example 2 Titanium tetraisopropoxide (10 g) was dissolved in 50 ml of ethanol, and a mixed solution of 20 ml of ethanol, 2 ml of water and 0.3 ml of concentrated hydrochloric acid was added to the solution for oxidation. A titanium sol was obtained.
A photocatalyst layer was formed on a 30 mm × 30 mm square glass plate by a dip coating method, the solvent was removed, and the mixture was gelled. Then, it was immersed in hot water at 100 ° C. for 1 hour and baked at 400 ° C. for 1 hour to obtain a photocatalyst. For comparison, the same manufacturing method without hot water treatment was prepared.

The obtained photocatalyst was placed inside a glass tube having a diameter of 50 mm to form a closed system, and acetaldehyde 20 p
300 W on the photocatalyst while circulating air containing pm
40-300nm UV light from the xenon lamp
When irradiated with mW / cm 2 (365 nm), acetaldehyde was almost decomposed about 15 minutes after the start of light irradiation.
For comparison, titanium oxide prepared by the sol-gel method 1.
When the same examination was carried out for 1 mg, it was not decomposed even after irradiation with light for 4 hours.

Example 3 The titanium oxide-silica sol layer used in Example 1 was
It was formed on glass beads having a diameter of 1.5 mm. afterwards,
It was immersed in hot water at 100 ° C. for 1 hour and baked at 450 ° C. for 3 hours to obtain a photocatalyst-supporting filling material. For comparison, the same manufacturing method without hot water treatment was prepared.

This photocatalyst-supporting packing was applied to a high silicate glass reactor 8 (hollow structure, internal volume 5 as shown in FIG.
0 ml, was charged into an ultraviolet light receiving area 100 cm @ 2) in, was flushed with water containing geosmin concentration of 500ppt continuously from the processing water inlet 6 at a space time of 50 seconds, the processing
The geosmin concentration at the water outlet 7 was treated to about 100 ppt, which continued for 24 hours or more. For comparison, a similar experiment was conducted using a photocatalyst filler that had not been subjected to hydrothermal treatment. As a result, the space time was about 100 seconds in order to obtain the same reaction rate.

[0036]

As described above in detail, the present invention is based on the sorge.
A method for producing a photocatalyst by the method of claim 1, wherein a mixture of a powdery photocatalyst and a metal oxide sol acting as a binder for the powdery photocatalyst or a metal oxide sol as a starting material of the photocatalyst is gelled. After that, in hot water of 40-100 ° C
Immersion or contact with steam at 100-200 ° C
And a method for producing a photocatalyst.
The present invention also provides a powder photocatalyst and a binder for the powder photocatalyst.
Mixture if Ku light between the metal oxide sol which acts as agent
Support the photocatalyst of metal oxide sol, which is the starting material of the catalyst
After being supported on the body and gelling, hot water at 40-100 ° C
Or contact it with steam at 100-200 ° C.
Furthermore, the present invention relates to a method for producing a photocatalyst, characterized in that the metal oxide gel is made into a foam-like metal oxide by heating at a temperature of 800 ° C. or lower . According to this, a photocatalyst having a certain mechanical strength and a high photocatalytic activity can be produced by a very simple and environmentally friendly production method. The industrial value of the present invention is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a photocatalyst according to the invention.

FIG. 2 is a schematic cross-sectional view for explaining a photocatalyst body according to the present invention.

FIG. 3 is a diagram showing an appearance of a photocatalytic reactor according to a third embodiment of the present invention.

[Explanation of symbols]

1 Photocatalytically Active Component 2 Photocatalyst Powder 3 Binder 4 Base 5 Hole 6 Treated Water Inlet 7 Treated Water Outlet 8 Reactor

Claims (2)

(57) [Claims] 1. A method for producing a photocatalyst body by a sol-gel method, comprising a powdery photocatalyst and a binder for the powdery photocatalyst.
Mixture with working metal oxide sol or release of photocatalyst
The metal oxide sol serving as originating materials, after gelation, 40
Immerse in hot water at ~ 100 ° C or water at 100 ~ 200 ° C
A method for producing a photocatalyst body, which comprises contacting with steam . 2. A mixture of a powdery photocatalyst and a metal oxide sol which acts as a binder for the powdery photocatalyst or a metal oxide sol which is a starting material of the photocatalyst is supported on a photocatalyst support and gelled. After that, in hot water at 40-100 ° C
A method for producing a photocatalyst, characterized in that the metal oxide gel is made into a foam-like metal oxide by immersing it or bringing it into contact with water vapor of 100 to 200 ° C. and further heating at a temperature of 800 ° C. or lower.