JPH0649677A - Photocatalyst electrode, its production, method for promoting photocatalyst electrode reaction and method for cleaning the electrode - Google Patents

Abstract

PURPOSE:To produce a photocatalyst electrode stably held in a reactant, capable of uniformly irradiating the reactant with light and capable of efficiently absorbing a light energy, to promote the photocatalyst electrode reaction so that the reaction product is rapidly detached from the electrode surface and to easily clean off the contaminant stuck the electrode surface. CONSTITUTION:A porous photocatalyst electrode 21 is formed from a combination of a metal and a semiconductor. Both materials having a fine matrix structure are firmly joined to each other. The highly reductive material in the electrode 21 exhibits the polarity of an anode 22, and the highly oxidative material exhibits the polarity of a cathode 23. A cavity 24 is kept except in the joining region and used as a passage for the photocatalysis product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalytic electrode used in a photocatalytic reaction, a method for producing the same, a method for promoting a photocatalytic electrode reaction, and a method for cleaning a photocatalytic electrode.

[0002]

2. Description of the Related Art Of a pair of electrodes composed of a semiconductor and a metal, when the semiconductor part is irradiated with light, it is oxidized on the surface of the electrode.
It is generally known that a reduction reaction occurs (“ceramics” VOL21, NO4, P326-333 Tomoji Kawagoi, light energy conversion of titania). For example, a pair of electrodes made of titanium dioxide and platinum is placed in an electrolyte aqueous solution, and when titanium dioxide is irradiated with light, it has the action of decomposing water,
("Nature" VOL238, P37-38, A. Fujishima and K. Ho
nda, Electrochemical Photolysis of water ata semi
conductor electrode), such a phenomenon is known as the so-called Honda / Fujishima effect. In addition, platinum,
It has been confirmed that when titanium dioxide powder carrying palladium or ruthenium oxide is irradiated with light, water is decomposed and hydrogen and oxygen are generated. ("Chemical Physics Lette
r ”VOL72, P87-89 T.Kawai and T.Sakata, Photoca
talytic decomposition of gaseous water over Ti
O ₂ and TiO ₂ —RuO ₂ surfaces, 1980). It is known that by making the electrode fine powder, the light absorption area can be increased and at the same time the contact area with water can be increased.

Furthermore, the characteristic of the phenomenon surface due to the fine powder of the electrode is that the distribution of the energy level generated by the electric field gradient on the surface of titanium dioxide is limited by the particle size,
That is, electrons and holes can easily move. At the electrode surface, water decomposes into hydrogen and oxygen at room temperature.

The decomposition of water will be described below by taking a photocatalytic electrode using titanium dioxide as a semiconductor and platinum as a supporting metal as an example. FIG. 7 is a schematic view of a photocatalyst electrode 3 in which platinum 2 is supported on titanium dioxide 1 fine powder. The electrodes 3 are made of two kinds of materials, and form a pair.
It is a spherical fine powder having a diameter of m and has no lead portion. When the titanium dioxide 1 is irradiated with the light 4, the energy of the light 4 is absorbed by the titanium dioxide 1 and electrons 5 and holes 6 are generated inside the titanium dioxide 1. The situation is shown in FIG.
When the electrode 3 is placed in water 7 or in a water vapor atmosphere and irradiated with light 4, electrons 5 in the valence band 8 are excited into the conduction band 9 and holes 6 are generated in the valence band 8. Generated electron 5
And some of the holes 6 move to the surface of the semiconductor, the electrons 5 are used for the reduction reaction 10, and the holes 6 are used for the oxidation reaction 11. At this time, the platinum 2 acts as a catalyst electrode for promoting the reduction reaction 10.

FIG. 9 shows a schematic diagram of a photocatalytic electrode used for dispersing water. When the photocatalyst electrode 3 is put in a glass flask together with water 7 or an aqueous electrolyte solution and irradiated with light 4, gas (hydrogen 12 and oxygen 13) is generated from the electrode.

In addition, as a photocatalytic action, this electrode is considered to be applied to various fields. For example, separation of organic matter, sterilization and deodorization. Both are photocatalytic actions that utilize the strong oxidation / reduction reaction of the semiconductor-supported metal electrode.

[0007]

As described above, the photocatalytic electrode made of semiconductor and metal is used in the form of fine powder. In order to disperse water or water vapor by this photocatalyst electrode, the photocatalyst electrode must be placed in a light transmissive container and kept in water or water vapor.

In the decomposition of water, generally, a fine powder electrode is put together with water in a glass container and irradiated with light through the container. Since the specific gravity of the electrode is larger than that of water, it will accumulate on the bottom of the glass container. Therefore, the fine powder of the electrode is thick and easily deposited, and the entire electrode cannot efficiently absorb light.

Further, when decomposing water vapor, the fine powder electrode must be held in the water vapor. For example,
A method of putting the electrode fine powder in a light transmissive container and filling the water vapor or placing the electrode fine powder on a light transmissive dish and holding it in the water vapor is adopted. Even in such a case, the electrode fine powder easily deposits on the bottom, and it becomes difficult for the electrode as a whole to efficiently absorb light.

The same can be said for many reaction systems utilizing photocatalysis. That is, the powder of the photocatalyst electrode is deposited or spread thinly in the reaction system, but it is extremely difficult to maintain a uniform thickness due to variation in thickness due to the powder. Therefore, it is not possible to uniformly irradiate the electrode with light and efficiently absorb the light energy in the electrode.

Further, it is not preferable that the dispersion product stays around the electrode in terms of progress of the reaction. In order to allow the reaction to proceed rapidly, it is necessary to promptly remove the decomposition product generated on the electrode surface and replace it with the reaction product.

Further, if the photocatalytic electrode is contaminated by dust or a substance having a high boiling point, the light absorbing ability is deteriorated. Therefore, it is necessary to remove the pollutant from time to time. However, it is difficult to separate the contaminants and the photocatalyst electrode by cleaning the photocatalyst electrode which is a powder. For example, it is difficult to distinguish dust from photocatalytic electrodes.

Therefore, an object of the present invention is to provide a photocatalyst electrode which can be stably held in a reactant and irradiated with light so as to reach the whole and to efficiently absorb light energy, and a method for producing the same. Another object of the present invention is to provide a photocatalytic electrode reaction accelerating method capable of rapidly separating reaction products from the electrode surface. Another object of the present invention is to provide a photocatalyst electrode cleaning method capable of easily removing contaminants that adhere to the electrodes and deteriorate the reaction.

[0014]

The photocatalyst electrode according to the present invention forms a bonded body composed of a semiconductor and a metal while keeping voids inside, and determines the polarity according to the reducing property or oxidizing property of both materials. It was done.

Further, in the method for producing the photocatalyst medium electrode, the semiconductor fine powder and the metal fine powder are mixed, and then the fine powder mixture is formed into a desired shape, and thereafter, the formed shape is maintained and fired. It was done in this way.

According to another method of manufacturing a photocatalyst electrode, a semiconductor fine powder and a metal fine powder are mixed with a binder, and then the fine powder mixture is molded into a desired shape. Is kept and fired, and at this time, the binder is volatilized.

The photocatalyst electrode reaction promoting method according to the present invention is such that the fluid is caused to flow when the photocatalyst electrode is placed in a fluid which causes a photocatalytic action and the reaction proceeds.

Furthermore, a reaction promoting method according to another invention is to vibrate the photocatalyst electrode when the photocatalyst electrode is placed in a fluid which causes a photocatalytic action and the reaction proceeds. A cleaning method according to another invention is one in which a cleaning gas or a cleaning liquid is sprayed on a photocatalyst electrode to remove electrode contaminants.

[0019]

The photocatalyst electrode according to the present invention can be stably retained in the reaction product by firing the powder. That is, semiconductor and metal powders are mixed, placed in a mold, and baked in a heating furnace to be baked and solidified into a porous body having a high porosity. As a result, the specific weight is lowered, and it can be easily floated and held in the reaction product.

Further, in particular, it becomes possible to efficiently irradiate light by baking the thin sheet. That is, semiconductor and metal powders are mixed and formed into a thin plate shape,
Light can be spread to the inside of the electrode.

Further, by flowing the reactant so as to pass through the pores of the photocatalyst electrode according to the present invention, the reaction product can be promptly released from the electrode surface. further,
By vibrating the photocatalytic electrode in the reactant, the electrode surface can be kept clean. Further, the photocatalyst electrode according to the present invention can easily wash away dust and other pollutants in the cleaning gas or cleaning liquid.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a porous photocatalytic electrode 21 which is a combination of a metal and a semiconductor. The fine metal and the fine semiconductor are combined in a matrix structure. Due to the combination of the metal and the semiconductor, the one having a strong reducing property becomes the anode 22, and the one having a strong oxidizing property becomes the cathode 23.
In this figure, the anode 22 is integrated with the cathode 23 in a dispersed state. When the photocatalyst electrode 21 is held in the fluid reactant, the reactant can freely flow in the voids 24 having the matrix structure. When the photocatalyst electrode 21 is irradiated with light, a reduction reaction is repeated on the anode 22 and an oxidation reaction is repeated on the cathode 23 to cause a photocatalytic action. The products of this photocatalytic reaction can also freely flow in the voids 24 of the matrix structure. For example, when the photocatalyst electrode 21 is irradiated with light in water or water vapor, oxygen is produced on the anode 22 and hydrogen is produced on the cathode 23 at the same time.

The thus formed photocatalyst electrode 21 has sufficient rigidity between the metal and the semiconductor and has sufficient rigidity. Since this can be floated and held in the air, light can be absorbed from all directions of the photocatalyst electrode, and at the same time, the reactant can be completely flowed in all directions of the photocatalyst electrode 21. Therefore, the photocatalyst electrode 21 can be efficiently supplied with light and a reactant. In addition, by flowing the reactant from one direction of the photocatalyst electrode 21, the removal of the product and the supply of the reactant are accelerated,
A photocatalytic reaction can be efficiently generated. For example, in water dispersion by photocatalysis, fresh water or water vapor is always supplied to the photocatalyst electrode 21 by holding the photocatalyst electrode 21 in water or water vapor and deciding a certain direction to flow the water or water vapor. To be done. Hydrogen and oxygen generated by the photocatalytic reaction are quickly removed from the electrode surface.

A preferred method for producing a photocatalytic electrode having a matrix structure is a method in which metal powder and semiconductor powder are mixed and fired in a heating furnace. The metal powder and the semiconductor powder are mixed at an appropriate mixing ratio, both powders are placed in a mold, and then heated in a sintering furnace. At this time, the metal powder and the semiconductor powder are sintered while being dispersed. Therefore, the photocatalytic electrode having an arbitrary shape can be finished.

Next, a manufacturing method different from that described above will be described. Mixing multiple types of metals and heating, reacting any type of metal with a specific gas to turn it into a semiconductor,
Bake the mixture. Also by this method, a porous photocatalytic electrode composed of a metal and a semiconductor can be obtained.

Further, another manufacturing method will be described. After mixing the semiconductor powder and the metal powder with the binder, the binder is volatilized by heating to produce a porous photocatalytic electrode composed of the semiconductor and the metal. The photocatalyst electrode manufactured by this method has a void portion in the binder portion at the time of mixing, and can be made into a porous and strong bonded body.

Further, another manufacturing method will be described. After mixing a plurality of kinds of metal powders with a binder, the binder is volatilized by heating and at the same time any kind of metal is reacted with a specific gas to be converted into a semiconductor.
A void is formed in the portion where the binder is volatilized, and the semiconductor and the metal are sintered to obtain a porous and strong photocatalytic electrode.

Each of the photocatalytic electrodes manufactured by the above different manufacturing methods has a matrix structure, and the reactants and products can freely flow in the voids thereof, and photocatalytic reaction occurs on the metal and the semiconductor by light irradiation. Can be made.

Next, the shape of the electrode and the method for manufacturing the electrode will be described so that the electrode can be efficiently irradiated with light. FIG. 2 shows the appearance of the photocatalytic electrode. The photocatalyst electrode 21 is formed in a thin flat plate shape so that light can be transmitted to the inside of the electrode.
Since the above-mentioned photocatalyst electrode is porous and has fine voids, by forming it into a thin flat plate, the irradiation light can reach from the surface to the inside through the voids and efficiently absorb the light energy.

A method of manufacturing the photocatalyst electrode 21 in the shape of a thin plate will be described below with reference to the drawings. FIG. 3 shows an embodiment in which a mixture of semiconductor fine powder and metal fine powder is molded into a thin plate shape. In the process of moving the table 27 that can be driven by the motor 25 and the feed screw 26 from left to right, fine powder is formed in a thin plate shape on the heat-resistant plate 28 placed on the table 27. First, as the first step, the fine powder 29 of the photocatalyst electrode component is sprinkled on the heat-resistant plate 28 on the left side of the drawing.
Next, the cutter 30 scrapes off the surface of the fine powder 29 scattered in the center of the drawing. At the same time, the cutter 30
The fine powder adhered to is sucked by the nozzle 31 and collected. The cutter 30 rotates in the A direction, and the excess fine powder 29
Scoop up. Next, the dispersion thickness of the fine powder 29 is measured on the right side of the figure. The laser displacement meter 32 moves in the B direction, performs laser irradiation and reflected light detection from above the fine powder 29 on the heat resistant plate 28, and measures the thickness at this time.

In order to obtain a photocatalyst electrode by firing, as shown in FIG. 4, the fine powder 29 molded on the heat-resistant plate 28 is placed in a sintering furnace 33 and heated to an appropriate temperature, as shown in FIG.
The photocatalyst electrode 21 shown in can be obtained.

Photocatalyst electrode 21 produced through the above steps
Has a uniform thickness and at the same time has a high porosity. Therefore, the irradiation light reaches the inside of the photocatalytic electrode 21 and can effectively perform the photocatalytic action.

Next, a method different from the above method for forming a thin plate-shaped photocatalyst electrode will be described. FIG. 5 shows a general method for manufacturing a green sheet, and can be applied to a method for manufacturing a photocatalytic electrode. A slurry 34 in which fine powder of an electrode component is mixed with a binder is poured on a mount 35. At that time, the slurry 34 is squeezed through the cutter 36, and the sheet 37 is formed on the mount 35.

The sheet 37 formed by this method is placed on the heat-resistant plate 28 and heated in a sintering furnace 33 as shown in FIG.
The photocatalyst medium electrode manufactured by this method has a high porosity because the electrode components of the fine powder are bound together in the state where voids are formed by volatilization of the binder. Therefore, the irradiation light reaches the inside of the photocatalytic electrode and can effectively perform the photocatalytic action.

Next, the method for promoting the photocatalytic electrode reaction will be described. Since the photocatalyst electrode baked through the above steps has sufficient rigidity, it can be retained in the reaction product. FIG. 6 shows an example of water dispersion by photocatalysis. The photocatalytic electrode 21 is held in the middle of the transparent container 38, and water is supplied from below the transparent container 38. As the water flows, the water on the surface of the photocatalyst electrode 21 is constantly replaced and contributes to the photocatalytic reaction.
0 and oxygen 41 rapidly leave the surface of the photocatalytic electrode 21. This allows the reaction to proceed rapidly. The same effect can also be obtained by vibrating the fired photocatalyst electrode 21 in the reaction product.

Next, the photocatalyst electrode cleaning method will be described. When the photocatalytic electrode is contaminated with dust, organic substances, inorganic substances, etc., the electrode cannot absorb the light energy and cannot efficiently perform the photocatalytic action. By injecting a cleaning gas or a cleaning liquid onto the photocatalyst electrode, contaminants such as dust can be washed away. Further, the cleaning can be effectively performed by vibrating the photocatalytic electrode in the cleaning liquid.

[0038]

As described above, according to the present invention, since a porous photocatalyst electrode made of a semiconductor and a metal is molded, it can be easily floated and held in the reaction product. Therefore, it is possible to irradiate light from a wide range of the surroundings, and particularly by forming it into a thin flat plate, the irradiation light reaches the inside of the photocatalyst electrode, and the electrode can efficiently absorb the light energy. become. Also,
By supplying only the reactant to the electrode, the reactant can be supplied and the product can be quickly removed. Further, contaminants such as dust can be easily washed away using the cleaning gas or the cleaning liquid.

[Brief description of drawings]

FIG. 1 is a microscopic enlarged view of a photocatalytic electrode according to the present invention.

FIG. 2 is a perspective view showing an embodiment of a photocatalytic electrode according to the present invention.

FIG. 3 is a diagram for explaining a manufacturing process of the photocatalytic electrode according to the present invention.

FIG. 4 is a view for explaining the manufacturing process of the photocatalytic electrode according to the present invention.

FIG. 5 is a view for explaining the manufacturing process of the photocatalytic electrode according to the present invention.

FIG. 6 is a diagram for explaining a method of using the photocatalytic electrode according to the present invention.

FIG. 7 is a schematic diagram of a conventional photocatalytic electrode.

FIG. 8 is a diagram for explaining a photocatalytic action in the photocatalytic electrode.

FIG. 9 is a schematic diagram showing an application example of photocatalytic action.

[Explanation of symbols]

 21 ... Photocatalyst electrode 22 ... Anode 23 ... Cathode 24 ... Void

Claims (7)

[Claims] 1. A photocatalyst electrode in which a void is kept inside to form a combined body of a semiconductor and a metal, and the polarity is determined according to the reducing property or oxidizing property of both materials. 2. A semiconductor fine powder and a metal fine powder are mixed,
Next, a method for producing a photocatalyst electrode, in which the fine powder mixture is molded into a desired shape, and then the molded shape is maintained and fired. 3. A semiconductor fine powder and a metal fine powder are mixed together with a binder, and then the fine powder mixture is formed into a desired shape, and thereafter, the formed shape is maintained and fired at this time. A method for producing a photocatalytic electrode, which is adapted to volatilize. 4. The method for producing a photocatalytic electrode according to claim 2, wherein the fine powder mixture is formed into a flat plate shape. 5. A method for promoting a photocatalytic electrode reaction in which a fluid is caused to flow when a photocatalytic electrode is placed in a fluid which causes a photocatalytic action to proceed a reaction. 6. A method of promoting a photocatalytic electrode reaction, which comprises vibrating the photocatalytic electrode when the photocatalytic electrode is placed in a fluid which causes a photocatalytic action to proceed the reaction. 7. A photocatalyst electrode cleaning method in which a cleaning gas or a cleaning liquid is sprayed on the photocatalyst electrode to remove electrode contaminants.