JP5666802B2 - Discharge type photocatalyst and method for producing the same - Google Patents

Description

  The present invention relates to a discharge photocatalyst having high photocatalytic performance and a method for producing the same, and more particularly to a discharge photocatalyst applicable to an environmental purification device such as air purification and water purification and a method for producing the same.

In recent years, photocatalysts have attracted attention in a wide range of fields such as air purification / deodorization, water purification / drainage treatment, antifouling, antibacterial / sterilization, and antifogging.
When light having a wavelength having energy equal to or greater than the band gap is given to the optical semiconductor particles, electrons existing in the valence band are photoexcited and moved to the conduction band. In addition, holes are generated in the valence band. The generated electron (e ⁻ ) reacts with oxygen (O ₂ ) to generate a superoxide anion (• O ₂ ⁻ ), and the hole (h ⁺ ) reacts with water to generate a hydroxy radical (• OH). Is generated. The generated superoxide anion (• O ₂ ⁻ ) exhibits a strong reducing power, and the hydroxy radical (• OH) exhibits a strong oxidizing power. Therefore, these reducing powers and oxidizing powers can be used for various environmental purification fields. Attempts have been made to apply it.

Photocatalysts are attracting attention because they have a very wide range of applications and can be directly used as energy sources such as sunlight or light from fluorescent lamps. However, since the catalytic reaction of the photocatalyst is not so powerful and rapid, how to increase the efficiency is an important issue.
For the purpose of improving the catalytic efficiency of the photocatalyst, many studies as described below have been made.
For example, in Japanese Patent Laid-Open No. 9-262482 (Patent Document 1), one or more kinds of metal ions selected from the group consisting of Cr, V, Cu, Fe, Mg, Ag, Pd, Ni, Mn, and Pt are 1 A photocatalyst contained inside from the surface of titanium oxide (TiO ₂ ) at a rate of × 10 ¹⁵ ions / g-TiO ₂ or more is described.

This photocatalyst is produced by using an ion implantation method used for impurity doping means in the semiconductor field. Specifically, the metal ions described above are accelerated to a high energy of 30 keV or more, and this is irradiated onto titanium oxide to dope metal ions into titanium oxide. The photocatalyst produced by such a manufacturing method absorbs light not only in the ultraviolet light region but also in the visible light region, which has been impossible in the past. It is possible to further improve the catalytic efficiency of the photocatalyst.
Japanese Patent Laid-Open No. 2-107339 (Patent Document 2) describes a catalyst structure applied to a refrigeration cycle apparatus such as a refrigerator and an air conditioner, and a method for manufacturing the catalyst structure. A catalyst structure in which a photocatalytically active component is supported on a base material having a three-dimensional network structure that allows a reaction gas and light to flow. According to this catalyst structure, a malodorous component contained in air is photocatalyzed. Can be removed more efficiently.

  Furthermore, Japanese Patent Laid-Open No. 8-103631 (Patent Document 3) describes a photocatalytic filter and a method for producing the same. Specifically, after coating a glass filter made by fusing spherical heat-resistant glass with a titania sol prepared from titanium alkoxide and alcohol amines, or with a polyethylene glycol or polyethylene oxide added thereto, room temperature The temperature is gradually raised from 600 ° C. to a final temperature of 700 ° C. to produce a photocatalytic filter.

  The photocatalyst obtained by this manufacturing method has a large surface area, and the titanium oxide covering the surface is transparent, and the incident light strikes the entire titanium oxide on the filter surface, so that contaminants can be adsorbed or decomposed efficiently.

JP-A-9-262482 Japanese Patent Laid-Open No. 2-107339 Japanese Patent Laid-Open No. 8-103631 JP 2000-140624 A

However, as described above, in order to improve the efficiency of the photocatalytic reaction, although various studies have been made, it is difficult to say that the efficiency is still sufficient in any case, and it is an effective measure for further improving the efficiency. Was demanded.
The inventors have also invented an invention that uses discharge light instead of a conventional lamp type as an excitation source of a photocatalyst (Japanese Patent Laid-Open No. 2000-140624 (Patent Document 4)).

  With the structure of the present invention, a photocatalyst having excellent performance was realized. However, since discharge light is used as a light source, recent research has revealed that the discharge state depends on humidity and the performance changes.

  The present invention has been made to solve such a problem, and provides a method for producing a discharge photocatalyst capable of mass production while reducing the cost while obtaining a discharge photocatalyst having greatly stabilized humidity dependency. The purpose is to provide.

As a result of intensive studies on the stabilization of the humidity dependence of the discharge photocatalyst, the present inventors have found that the primary constituent of the photocatalyst film used in the so-called discharge photocatalyst that uses the discharge light as the excitation source is the primary particle size. The particle size of the secondary particles that are 80 nm or less and in which the primary particles are aggregated is
The porosity is 5% or more and 48 % or less including the base material made of titanium oxide of 80 μm or less and made of insulating ceramics , and the specific surface area including the base material is 1.2 m ² / g.
It has been found that the photocatalytic performance can be greatly stabilized by the above process. Further, the present invention has been completed by finding a method for freely controlling such a photocatalytic film with good reproducibility.

That is, the present invention according to claim 1 is a discharge photocatalyst in which discharge light is used as an excitation source and a photocatalyst film is formed on the surface of a substrate, and the main component of the photocatalyst film has a primary particle diameter of 80 nm.
The porosity is 5% or more including a base material made of titanium oxide having a particle diameter of secondary particles in which the primary particles are aggregated of 80 μm or less and composed of insulating ceramics.
Provided is a discharge type photocatalyst having a specific surface area of not more than 48 % and a specific surface area including a substrate of not less than 1.2 m ² / g.

In the present invention, the photocatalyst film comprising titanium oxide as a main constituent is defined to have a porosity of 5% or more and 48 % or less including the base material. However, if the porosity is less than 5%, the photocatalyst film contributes in the thickness direction of the photocatalyst film. This is because when the porosity is less than 48 %, the photocatalyst film is peeled off or dropped due to insufficient strength of the photocatalyst film.

Furthermore, the specific surface area including the base material is defined as 1.2 m ² / g or more, but if it is smaller than 1.2, the chemical potential on the surface of the photocatalyst is lowered and the catalytic activity is lowered. The reason why the performance is stabilized by the porosity is considered to be because the discharge was stabilized by the moisture contained in the atmosphere being effectively adsorbed on the pores of the photocatalyst and the substrate.
Furthermore, in the present invention, the primary particle diameter of titanium oxide is 80 nm or less, and this
The particle size of the secondary particles in which the primary particles are aggregated is defined as 80 μm or less.
If the primary particles are larger than 80 nm, crystal defects such as vacancies and dislocations existing in the grains will increase and performance will increase.
If the secondary particle diameter is larger than 80 μm, the secondary particle diameter is too large.
This is because the performance of the titanium oxide at the center of the secondary particles is not exhibited.
Although the base material is limited to insulating ceramics, unwanted discharge between the discharge electrode and the base material is prevented.
It is for suppressing. In addition, ceramics have excellent corrosion resistance, so stable discharge is achieved.
This is because it can.

  According to a second aspect of the present invention, there is provided a discharge type photocatalyst characterized in that, in the photocatalytic film of the first aspect, the amount of titanium oxide supported is 10% or more relative to the substrate.

  In the present invention, the supported amount of titanium oxide is specified to be 10% or more with respect to the substrate. This is because if the amount is lower than 19%, the absolute amount of titanium oxide is insufficient and the performance is deteriorated.

The invention according to claim 3 provides the discharge photocatalyst according to claim 1 or 2, wherein a base material having a three-dimensional network structure is used as the base material.

  In the present invention, the base material having a three-dimensional network structure is limited to the base material supporting the photocatalyst. However, the base material having the three-dimensional network structure can form a photocatalyst film having a large amount of support, and is effective. This is because the catalyst performance is improved because it is possible to apply light that excites the photocatalyst.

The invention according to claim 4 is the discharge photocatalyst according to claim 1 or 2 , characterized in that a pore forming component that is decomposed and removed by heat treatment when the photocatalyst film is formed on the substrate is added. A method for producing a discharge-type photocatalyst is provided.

  In the present invention, it is defined that a pore-forming component that is decomposed and removed by heat treatment is added when forming the photocatalyst film. This is because it is effective.

  As described above, according to the present invention, in the discharge photocatalyst using discharge light as the excitation source of titanium oxide, the porosity and specific surface area of the photocatalyst film including the base material are defined, and the humidity dependency is greatly increased. It is possible to obtain a discharge photocatalyst stabilized in a stable manner, and to obtain a method for producing a discharge photocatalyst that can be mass-produced while reducing costs.

The graph which shows the relationship between the discharge type photocatalyst which changed the porosity of the titanium oxide explaining the Example 1 of embodiment of this invention, and photocatalyst efficiency. The graph which shows the relationship between the discharge-type photocatalyst which changed the specific surface area explaining Example 2 of embodiment of this invention, and photocatalyst efficiency. The graph which shows the relationship between the discharge type photocatalyst which changed the particle diameter of the titanium oxide explaining the Example 3 of embodiment of this invention, and photocatalyst efficiency. The graph which shows the relationship between the discharge type photocatalyst which changed the pore formation additive, and photocatalyst efficiency explaining the comparative example 1 of embodiment of this invention. The graph which shows the relationship between the discharge-type photocatalyst which changed the base material explaining the Example 4 of embodiment of this invention, and photocatalyst efficiency.

  Hereinafter, the discharge type photocatalyst of the present invention and the manufacturing method thereof will be described with reference to FIGS.

Example 1
As shown in FIG. 1, in Example 1, a method for producing a discharge photocatalyst is shown below, and a discharge photocatalyst made of titanium oxide and having a porosity of 5% or more and 48 % or less including a base material is produced. Then, the photocatalyst outlet side ammonia concentration for obtaining the photocatalytic efficiency was measured.
In Example 1, a titanium oxide sol having a concentration of 30% and a crystal particle diameter of 6 nm was used, and the substrate was impregnated with the sol, dried, and then heat-treated in the atmosphere at 600 ° C. for 1 hour to form a titanium oxide film on the substrate. A photocatalytic module was prepared. At this time, activated carbon was added to the titanium oxide sol, and its concentration was changed to produce photocatalytic films having different porosity, and the average particle diameter was controlled by adjusting the concentration of the activated carbon.

A silicate having a three-dimensional network structure with cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ) as a main component and an open porosity of 85% was used as the base material.
The specific surface area was controlled by changing the supported amount of titanium oxide to 5 to 20%.

  When the obtained catalyst was observed with a scanning electron microscope, it was confirmed that titanium oxide particles were present, and the average particle diameter was 30 nm.

Moreover, the specific surface area was measured using the physical adsorption method of nitrogen.
The photocatalytic performance of the obtained photocatalyst was evaluated by measuring the decomposition efficiency of ammonia while sandwiching electrodes between both ends and discharging between them. In this example, ammonia was used as an evaluation of the photocatalytic performance, but it was used as a representative odor substance that can be easily experimented. Of course, the same evaluation can be obtained with other gases.

  Specifically, a stainless steel electrode was placed on the photocatalyst including the obtained base material so as to sandwich the base material. The electrode spacing at this time is about 7 mm. While discharging between the electrodes, ammonia gas having an ammonia concentration of 100 ppm and a flow rate of 0.5 l / min was introduced from one of the photocatalyst modules.

  And the ammonia concentration in the exit side opposite to the inflow side was measured. At this time, the result of carrying out the same evaluation by changing the humidity is shown in FIG.

  As a comparative example, a photocatalyst film made of only titanium oxide with no porosity added and 3% porosity was prepared in the same manner.

  As shown in FIG. 1, in the case of the comparative example in which the porosity of titanium oxide is 3%, the ammonia concentration on the outlet side exceeded 60 ppm and the photocatalytic efficiency was lowered, but the porosity was between 5% and 55%. In this case, the ammonia concentration on the outlet side was lower than 40 ppm, and the photocatalytic efficiency was good.

  Further, an attempt was made to produce a material having a porosity of more than 55%, but the titanium oxide was largely removed after the heat treatment, and a satisfactory photocatalytic film could not be obtained.

  In addition, although the example of activated carbon was shown as a pore formation component decomposed | disassembled and removed by heat processing in a present Example, an organic binder which does not contain chlorine, such as polyethyleneglycol and a phenol resin, can form a pore similarly.

Further, in this embodiment, as an insulating ceramic, an example of a silicate having cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ) as a main component and having a three-dimensional network structure with an open porosity of 85% has been described. However, alumina, silicon carbide, silicon nitride, silicon oxide, zirconia, and composite materials thereof can be used as substrates having similar performance.

Example 2
Next, Embodiment 2 of the present invention will be described with reference to FIG.

  FIG. 2 shows the measurement of the ammonia concentration on the outlet side opposite to the inflow side for the photocatalyst having a changed loading ratio and specific surface area by changing the titanium oxide concentration.

  Specifically, a stainless steel electrode was placed on the photocatalyst containing the base material obtained in Example 1 so as to sandwich the base material. The electrode spacing at this time is about 7 mm. While discharging between the electrodes, ammonia gas having an ammonia concentration of 100 ppm and a flow rate of 0.5 l / min was introduced from one of the photocatalyst modules.

  And the ammonia concentration in the exit side opposite to the inflow side was measured. At this time, the same evaluation was performed by changing the humidity.

As shown in FIG. 2, when the titanium oxide loading was 3% and the specific surface area was 0.8 m ² / g, the ammonia concentration on the outlet side exceeded 60 ppm, and the photocatalytic efficiency decreased. When the loading rate was 10% and the specific surface area was 1.2 m ² / g or more, the ammonia concentration on the outlet side was lower than 40 ppm and the photocatalytic efficiency was good.

The porosity of the specific surface area of 1.2 m ² / g was 30%, and the porosity of 2.0 m ² / g was 48%.

Example 3
Next, Embodiment 3 of the present invention will be described with reference to FIG.

  In Example 3, a photocatalyst in which the primary particle diameter was changed by changing the heat treatment temperature in Example 1 and a photocatalyst in which the degree of aggregation of primary particles was changed by changing the sol pH were prepared.

  About the obtained photocatalyst, the ammonia concentration in the exit side opposite to the inflow side was measured.

Specifically, a stainless steel electrode was placed on the photocatalyst containing the base material obtained in Example 1 (porosity 5%, specific surface area 1.2 m ² / g) so as to sandwich the base material. The electrode spacing at this time is about 7 mm. While discharging between the electrodes, ammonia gas having an ammonia concentration of 100 ppm and a flow rate of 0.5 l / min was introduced from one of the photocatalyst modules.

  And the ammonia concentration in the exit side opposite to the inflow side was measured. At this time, the same evaluation was performed by changing the humidity.

  As shown in FIG. 3, in the case of a photocatalytic film having a primary particle diameter exceeding 80 nm and a secondary particle diameter exceeding 80 μm, the ammonia concentration at the outlet exceeds 60 ppm, but the primary particle diameter is 80 nm or less. Thus, when a photocatalyst film having a secondary particle diameter of 80 μm or less was used, the ammonia concentration at the outlet was lower than 40 ppm and the photocatalytic efficiency was good.

Comparative example 1 according to the invention of claim 2
In this Comparative Example 1, a photocatalyst having a porosity of 55% was prepared in the same manner as in Example 1 except that silica gel that was not decomposed by heat was used in the titanium oxide sol shown in Example 1 instead of activated carbon.

  About the obtained catalyst, the ammonia concentration on the outlet side opposite to the inflow side was measured.

  Specifically, a stainless steel electrode was placed on the photocatalyst containing the base material obtained in Comparative Example 1 so as to sandwich the base material. The electrode spacing at this time is about 7 mm. While discharging between the electrodes, ammonia gas having an ammonia concentration of 100 ppm and a flow rate of 0.5 l / min was introduced from one of the photocatalyst modules.

  And the ammonia concentration in the exit side opposite to the inflow side was measured. At this time, the same evaluation was performed by changing the humidity.

  As shown in FIG. 4, in the case of Comparative Example 1 in which silica gel was added, the ammonia concentration on the outlet side was 50 ppm or more, and the photocatalytic efficiency was lower than that in Example 1.

Comparative Example 2 according to the invention of claim 5 (FIG. 5)
In this example, the base material used in Example 1 was ceramic (a silicate having a three-dimensional network structure with cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ) as a main component and an open porosity of 85%). A photocatalytic film was prepared in the same manner as in Example 1 except that conductive stainless steel was used.

  About the obtained catalyst membrane, the ammonia concentration on the outlet side opposite to the inflow side was measured.

  Specifically, a stainless steel electrode was placed on the photocatalyst containing the base material obtained in Comparative Example 1 so as to sandwich the base material. The electrode spacing at this time is about 7 mm. While discharging between the electrodes, ammonia gas having an ammonia concentration of 100 ppm and a flow rate of 0.5 l / min was introduced from one of the photocatalyst modules.

  And the ammonia concentration in the exit side opposite to the inflow side was measured. At this time, the same evaluation was performed by changing the humidity.

  As shown in FIG. 5, when stainless steel is used for the substrate, the discharge is unstable, and the ammonia concentration at the outlet shows 50 ppm or more compared to the case where ceramic is used for the substrate. Compared with 1, the photocatalytic efficiency decreased.

Claims (4)

In the discharge photocatalyst in which the photocatalyst film is formed on the surface of the substrate using the discharge light as the excitation source,
The main constituent of the photocatalyst film has a primary particle diameter of 80 nm or less, and the primary particles are
The aggregated secondary particles are made of titanium oxide having a particle size of 80 μm or less ,
And a porosity including a substrate composed of insulating ceramics is 5% or more and 48 % or less, and a specific surface area including the substrate is 1.2 m ² / g or more. Type photocatalyst. The discharge photocatalyst according to claim 1, wherein the photocatalyst film has a titanium oxide loading of 10% or more with respect to the base material. The base material is a base material having a three-dimensional network structure.
The discharge-type photocatalyst described. The discharge photocatalyst according to claim 1 or 2, wherein the photocatalytic film is formed on the substrate.
Discharge-type photocatalyst characterized by adding pore-forming components that are decomposed and removed by heat treatment
Manufacturing method.

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