JP2013000724A - Method for producing photocatalyst solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a photocatalyst solution which has antibacterial properties even at a dim or lightless dark place and which can keep high antibacterial properties even when exposed to strong light.SOLUTION: The method for producing the photocatalyst solution comprises the steps of: hydrolyzing titanium alkoxide to obtain an amorphous titania fine particle; adding oxygenated water to the obtained amorphous titania fine particle to produce a peroxo titania gel; adding oxygenated water to the peroxo titania gel to form a titania gel 10; adding a silver-containing substance 11, which is obtained by depositing silver on titania, to the titania gel 10; and heating the substance 11 added titania gel for predetermined time at the temperature, for example at 120°C, to produce the photocatalyst solution 12 containing anatase titania.

Description

  The present invention relates to a method for producing a photocatalyst solution containing anatase-type titania fine particles and an antibacterial metal.

Titania [titanium oxide (TiO ₂ )], which is a typical photocatalyst, has antibacterial properties because it generates active oxygen when irradiated with light, but when used indoors, light is weak and the amount of active oxygen generated is small. Antibacterial properties are small. For this reason, a method of mixing titania with an antibacterial metal such as silver (Ag) has been attempted.

  For example, in Patent Document 1, titanium tetraisopropoxide is hydrolyzed to obtain titania fine particles, hydrogen peroxide water is added to form peroxo titania, and further heated to form one peroxo titania. The anatase-type titania obtained in this manner is disclosed as silver acetate, silver carbonate, silver formate, silver propionate, silver butyrate, silver citrate, or silver lactate. It is described that a photocatalytic solution exhibiting an antibacterial action can be produced without light by adding a silver component which is a dissolved substance or a copper component which is a dissolved substance of copper carbonate. However, the photocatalyst produced by this method has a phenomenon that the antibacterial property is lowered in a bright place as compared to a dark place, as described in Examples below.

JP 2009-154061 A

  The present invention has been made under such circumstances, and its purpose is to have antibacterial properties even in a dark place where light is weak or no light, and maintains high antibacterial properties even when exposed to strong light. Another object is to provide a method for producing a photocatalyst solution that can be used.

The method for producing a photocatalyst solution in the present invention includes:
Producing a sol in which fine particles containing peroxo-type titania are dispersed in a dispersion medium;
Adding a metal-containing substance containing an antibacterial metal to the sol;
Then, in order to obtain anatase type titania, the sol is heated to obtain a solution containing anatase type titania fine particles as a photocatalyst.

In addition, the manufacturing method of the photocatalyst solution in this invention may be as showing below.
1) The antibacterial metal is silver or copper.
2) The step of producing the sol includes a step of hydrolyzing titanium alkoxide to obtain amorphous titania fine particles, a step of adding hydrogen peroxide to the amorphous titania fine particles to produce a peroxo-type titania gel, Adding a dispersion medium to the gel.
3) The sol is formed by dispersing fine particles of a complex of peroxo-type titania and silica in a dispersion medium.

  According to the present invention, an antibacterial metal is added to the sol in which fine particles containing peroxo-type titania are dispersed in a dispersion medium before the heat treatment for anatase, and then the anatase Therefore, a photocatalyst solution having a high antibacterial property can be obtained even in a dark place where light is weak or no light, as will be understood from experimental examples described later.

It is a flowchart which shows the manufacturing method of the sol of the amorphous titania microparticles and titania-silica in this embodiment. It is a flowchart which shows the manufacturing method of the titania-silica solution containing the silver component and anatase type titanium crystal in this embodiment. It is a figure which shows the result of the antibacterial property test of the photocatalyst solution in a present Example. It is a figure which shows the result of the antibacterial property test of the photocatalyst solution in a present Example.

The embodiment of the present invention will be described by taking as an example a method for producing a titania-silica solution 12 carrying silver as a photocatalyst solution. The titania-silica solution 12 which is a photocatalyst solution in the present embodiment is manufactured using, for example, amorphous titania fine particles 4 as a raw material. The amorphous titania fine particles 4 are produced, for example, by the method shown in the flow of FIG. First, a titanium alkoxide such as titanium tetraisopropoxide (Ti (OC ₃ H ₇ ) ₄ : TIP) 1 and an alcohol corresponding to the alkoxide, such as isopropanol (iso-C ₃ H ₇ OH: IPA) 2, are added to a predetermined mole. The mixture is mixed at a ratio such as TIP / IPA / H ₂ O = 1/10/4, and a corresponding alcohol 3 such as a mixture 3 of isopropanol, water and ammonia is added and reacted. Reaction R1 shown in FIG. 1 is as follows.
(Reaction R1)
Ti (OC ₃ H ₇ ) ₄ + 4H ₂ O → Ti (OH) ₄ + 4C ₃ H ₇ OH
Ti (OH) ₄ → TiO (OH) ₂ + H ₂ O
Then, the white suspension obtained by this reaction is separated into solid and liquid by, for example, filtration, and amorphous titania fine particles 4 are obtained through steps of drying, pulverizing, and drying the solid content.

Next, amorphous titania fine particles 4 and an oxidizing agent such as hydrogen peroxide solution 5 are mixed with 1 g of amorphous titania fine particles in a ratio of, for example, 20 ml of 31% hydrogen peroxide solution, and further a silica precursor such as tetraethyl orthosilicate. ((C ₂ H ₅ O) ₄ Si: TEOS) 6 is mixed so that the Ti / Si molar ratio is 1/9 or more. When this mixed solution is stirred for 2 hours at a temperature of 293 K, for example, a titania-silica solution (red-orange transparent solution 7), which is a complex of peroxo titania and silica, is obtained. Further, when the molar ratio of Ti / Si is 1/1, for example, when this solution 7 is allowed to gel at room temperature, for example, at a temperature of 300 K, for example for 3 days to 10 days, the peroxo titania-silica is obtained. A yellow gel 8 containing is produced. Reaction R2 shown in FIG. 1 is as follows.
(Reaction R2)
TiO (OH) ₂ + 2H ₂ O ₂ → TiO (OOH) ₂ + 2H ₂ O
Si (OC ₂ H ₅ ) ₄ + 2H ₂ O → SiO ₂ + 4C ₂ H ₅ OH
2H ₂ O ₂ → 2H ₂ O + O ₂
For example, a predetermined amount of 31% hydrogen peroxide water 9 is added to the gel 8 as a dispersion medium and mixed. For example, when the gel 8 is allowed to stand at a temperature of 293 K for 3 days, the hydrogen peroxide is decomposed and a peroxo yellow translucent titania- A silica sol 10 is obtained.

Here, the oxidizing agent may be a solution using ozone, sodium hypochlorite, hypochlorous acid, sodium chlorate, chlorine dioxide, etc. in addition to the hydrogen peroxide solution described above. It is preferable to use a hydrogen peroxide solution or the like because it causes a problem in purity if it remains or impurities are mixed. Moreover, the silica precursor is a silicon component supply source, and if it is a silica precursor containing no metal, other than TEOS, for example, Si ₄ C ₈ H ₂₄ O ₄ or Si ₄ C ₄ H ₁₆ O ₄ is also used. be able to.

A method of supporting Ag on the yellow transparent titania-silica sol 10 obtained as described above will be described with reference to FIG. In the yellow transparent titania-silica sol 10, which is a sol in which fine particles containing peroxo-type titania are dispersed in a dispersion medium, a metal-containing substance containing an antibacterial metal such as a colloidal solution 11 of silver-carrying titania is used as silver. It is added and mixed so as to have a concentration of 25 ppm by weight, and left at, for example, 20 ° C. for 1 day. And this mixed solution is heat-processed. The heating conditions are not particularly limited, but it is preferable to heat at 100 ° C. or higher, for example, 150 Pa, 120 ° C. for 2 hours, or normal pressure, 100 ° C. for 7 hours to 8 hours. As a result, the peroxo compound is decomposed, and a titania-silica solution 12 supporting Ag and containing anatase type crystals is produced. Reaction R3 shown in FIG. 2 is as follows.
(Reaction R3)
TiO (OOH) ₂ → 2TiO ₂ + 4H ₂ O + O ₂

  According to the above-described embodiment, as shown in the examples described later, the colloidal solution of silver-supporting titania having a silver component before the heat treatment for anatase formation is performed on the peroxo titania-silica sol 10. 11 is added, followed by heat treatment (anatase formation) to obtain a photocatalyst solution that has antibacterial properties in a dark place and, for example, a room that is not so bright, such as indoors, and that can maintain antibacterial activity in a light place. Can do.

  In the above-described embodiment, the sol to which silver is added is a sol in which fine particles of a composite of titania and silica are dispersed in a dispersion medium, but the substance forming the composite with titania is not limited to silica. For example, alumina may be used. The sol may be one in which fine particles of titania simple substance are dispersed in a dispersion medium.

  In the above embodiment, the colloidal solution 11 of silver-supporting titania is used as the Ag component to be added, but the present invention is not limited to this, and an Ag salt such as silver acetate, silver carbonate, silver formate, Silver propionate, silver butyrate, silver citrate or silver lactate may be used. The antibacterial metal is not limited to Ag but may be copper (Cu). In this case, for example, Cu-supporting titania or Cu salt such as copper carbonate is added to the sol.

Next, examples performed for confirming the effects of the present invention will be described.
[Sample manufacturing method]
Example 1
In Example 1, silver-supporting titania was added at a silver concentration of 50 ppm by weight to the peroxo yellow transparent titania-silica solution in the above-described embodiment, and then heat-treated in the same manner as in the above-described embodiment. A titania-silica solution containing the anatase-type crystal was obtained. This solution is referred to as Example 1.

(Comparative Example 1)
The yellow and transparent titania-silica solution in the same peroxo form as in Example 1 described above was heat-treated under the same conditions as in Example 1, and then silver-supported titania was used in Example 1 for the titania-silica solution containing the anatase-type crystals. To obtain a titania-silica solution carrying the Ag component. This solution is referred to as Comparative Example 1. That is, Example 1 and Comparative Example 1 differ in the timing of adding Ag.
(Comparative Example 2)
A titania-silica solution was obtained in the same manner as in Example 1 except that the Ag component was not added. This solution is referred to as Comparative Example 2.

[Antimicrobial test]
In this example, according to JIS R 1702 (Fine ceramics-Antibacterial test method / antibacterial effect of photocatalyst antibacterial processed product under light irradiation), antibacterial test was conducted on Example 1, Comparative Example 1 and Comparative Example 2. . The outline of this antibacterial test is that after inoculating a predetermined amount of bacterial cells on a test piece coated with a photocatalyst solution as a specimen, the cells are cultured under the determined conditions, and the number of viable bacteria before and after the culture is measured. To evaluate antibacterial properties. In this example, Staphylococcus aureus and Escherichia coli were used and the test was conducted by the film adhesion method. As for the light irradiation conditions, ultraviolet rays were irradiated at 0.01 mW / cm ² for 8 hours, assuming a room in the daytime. In addition, the antibacterial activity of each specimen (photocatalyst solution) in this example is evaluated by calculating the antibacterial activity value described in JIS R 1702 and the effect of light irradiation from the test results, and comparing these as indicators. It was.

  Here, the antibacterial activity value and the effect of light irradiation will be described in a little more detail. First, as shown in Formula 1, the antibacterial activity value is a logarithmic value of the survival rate of bacterial cells inoculated on a test piece not subjected to photocatalytic antibacterial processing (test piece not coated with a photocatalyst solution) under light irradiation conditions. Is a value obtained by subtracting the logarithmic value of the survival rate of the bacterial cells inoculated on the photocatalyst antibacterial processed test piece (test piece coated with the photocatalyst solution). Therefore, this antibacterial activity value reflects not only the antibacterial effect due to the photocatalytic action but also the antibacterial action such as silver contained in the photocatalyst solution. Further, the higher the antibacterial property of the photocatalyst solution, the higher the antibacterial activity value. In JIS R 1702, when the antibacterial activity value is 2.0 or more, the photocatalytic antibacterial processed product is determined to have antibacterial properties. That is, the antibacterial activity value of a specimen having no antibacterial property, for example, a specimen not containing Ag and containing no photocatalyst becomes zero.

  The effect of light irradiation, which is another evaluation index, will be described. First, the cells inoculated on the test piece are cultured in the dark, and the difference in logarithmic value of the cell viability according to the presence or absence of application of the photocatalyst solution is determined for the test piece as in the case of the antibacterial activity. The effect of light irradiation is a value obtained by subtracting the difference value in this dark place from the antibacterial activity value, as shown in Equation 2. The value of the effect of light irradiation is a value obtained by subtracting the antibacterial effect other than the photocatalytic action such as the antibacterial action by silver from the antibacterial activity value, and can be considered as an index reflecting only the antibacterial effect by the photocatalytic action.

（式２）

The test result in a present Example is shown in FIG.3 and FIG.4.
(Formula 1)

(Formula 2)

[Discussion]
3 and 4 are the antibacterial test results inoculated with Escherichia coli and Staphylococcus aureus, respectively. First, the antibacterial activity value is compared. Example 1 and Comparative Example 1, which are titania-silica solutions carrying a silver component, both have higher antibacterial activity values than Comparative Example 2 that does not contain a silver component. From this, it can be estimated that the contribution of the silver component in antibacterial properties is large under the illuminance conditions assuming the room. Further, when Example 1 and Comparative Example 1 are compared, Example 1 shows a slightly higher antibacterial activity value.

Next, looking at the effect of light irradiation, Comparative Example 1 shows a negative value. This means that the antibacterial activity value in the dark place is higher than that in the light place, and it can be said that the antibacterial property is suppressed by light irradiation. About this result, the present inventors are estimating as follows. In Comparative Example 1, active oxygen generated when light hits a photocatalyst containing an Ag component reacts with the Ag component contained in the photocatalyst, so that silver oxide (Ag ₂ O) having a weak antibacterial power compared to Ag is produced. Therefore, it is considered that the antibacterial activity of the photocatalyst containing the Ag component is lowered in the light. On the other hand, in Example 1, Ag is added at the sol stage of the titania fine particles, and then undergoes a heating process. Therefore, Ag is attracted to the titania crystal at the stage of the heating process, so that Ag is not easily oxidized. I guess that is formed. As described above, Example 1 confirms that high antibacterial properties are maintained even when exposed to strong light.

4 Amorphous titania fine particles 10 Titania-silica sol (peroxo)
11 Silver-supported titania solution 12 Silver-supported titania-silica solution (anaters type)

Claims (4)

Producing a sol in which fine particles containing peroxo-type titania are dispersed in a dispersion medium;
Adding a metal-containing substance containing an antibacterial metal to the sol;
Then, in order to obtain anatase-type titania, the sol is heated to obtain a solution containing anatase-type titania fine particles as a photocatalyst, and a method for producing a photocatalyst solution.   2. The method for producing a photocatalyst solution according to claim 1, wherein the antibacterial metal is silver or copper. The step of generating the sol includes:
Hydrolyzing titanium alkoxide to obtain amorphous titania fine particles;
Adding a hydrogen peroxide solution to the amorphous titania fine particles to produce a peroxo-type titania gel;
The method for producing a photocatalyst solution according to claim 1, further comprising a step of adding a dispersion medium to the gel.   The method for producing a photocatalyst solution according to any one of claims 1 to 3, wherein the sol is formed by dispersing fine particles of a composite of peroxo-type titania and silica in a dispersion medium. .

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