JP2000227429A - Activity measuring method for photocatalyst thin film, and activity measuring film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate activity of a photocatalyst thin film formed on a surface of a tile or the like, using a simple method. SOLUTION: When a photcatalyst thin film 2 is irradiated with an ultra-violet ray, oxidation reaction and reduction reaction take place concurrently, and a pH of an alkali halide aqueous solution 3 rises by a hydroxyl ion generated by the reduction reaction. Activity is evaluated thereby by a pH difference between a pH before the ultra-violet ray irradiation and a pH after the ultra- vilolet ray irradiation. For example, since the alkali halide aqueous solution is dropped on a surface of the photocatalyst thin film 2 formed on a surface of a substrate such as a tile, the dropped alkali halide aqueous solution is irradiated with the ultra-violet ray for a prescribed time, and since a level of the activity of the photocatalyst thin film 2 is judged by the pH difference between the pH of the alkali halide aqueous solution before the irradiation and the pH of it after the irradiation, the activity of the photocatalyst thin film 2 is determined easily and quickly compared with a conventional method by a gas chromatograph or a conventional method wherein the number of annihilated bacteria is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the activity of a photocatalytic thin film formed on the surface of a substrate such as a tile and a measuring film used for measuring the activity.

[0002]

2. Description of the Related Art When irradiated with ultraviolet rays in the presence of air, adsorption or desorption of oxygen molecules occurs, which promotes the decomposition (oxidation) of organic organic compounds such as malodorous components. TiO _{2 and the} like are known as active substances, and proposals have been made to form a thin film of this photocatalyst on the surface of a tile or the like constituting a wall surface of a toilet or a kitchen to exhibit deodorization and antibacterial action.

When a photocatalytic thin film is formed on the surface of a substrate such as a tile as described above, it is necessary to evaluate the activity of the photocatalytic thin film when actually applying it to a toilet or a kitchen. Conventionally, as this evaluation method, a method of monitoring a temporal change in concentration of a gas (such as ammonia or methyl mercaptan) decomposed by the formed photocatalytic thin film is monitored by a gas chromatograph.

[0004]

In the method of monitoring with a gas chromatograph, a measuring apparatus is expensive and only one sample can be measured per apparatus, which is inefficient.
It is known that the photoactivity is improved by supporting a metal such as Pt on TiO _2. However, in a photocatalytic thin film having such a structure, the effect of gas adsorption by the metal causes
It is difficult to determine what the net photoactivity is. Furthermore,
Once a tile or the like is used as a wall surface, the activity of the photocatalytic thin film formed on the surface cannot be measured by gas chromatography.

[0005] On the other hand, as a method of evaluating photoactivity without using a gas chromatograph, a method of examining the survival rate of bacteria killed by a photocatalyst after irradiation with light can be considered. In such a photocatalytic thin film, the bacteria are also killed by the antibacterial power of the metal itself, so that it is difficult to determine the net photoactivity.

[0006]

According to a first aspect of the present invention, there is provided a method for measuring the activity of a photocatalytic thin film, comprising the steps of: providing potassium iodide or potassium chloride on the surface of a TiO ₂ -based photocatalytic thin film formed on a substrate surface; An alkali halide aqueous solution such as is dropped, and then the dropped alkali halide aqueous solution is irradiated with ultraviolet light for a predetermined time, and the magnitude of the activity of the photocatalytic thin film is determined from the difference between the pH of the alkali halide aqueous solution before irradiation and the pH after irradiation. I decided to judge.

The method for measuring the activity of a photocatalytic thin film according to the second invention is characterized in that a pH indicator is added to an aqueous solution of an alkali halide such as potassium iodide or potassium chloride on the surface of the photocatalytic thin film mainly composed of TiO ₂ formed on the substrate surface. The added mixed solution was dropped, and then the dropped mixed solution was irradiated with ultraviolet rays for a predetermined period of time, and the activity of the photocatalytic thin film was determined based on the change in color of the mixed solution.

The method for measuring the activity of a photocatalytic thin film according to the third invention is characterized in that the activity measuring film is brought into close contact with the surface of the photocatalytic thin film mainly composed of TiO ₂ formed on the surface of the substrate, UV irradiation was performed for a period of time, and the magnitude of the activity of the photocatalytic thin film was determined based on the change in the color of the activity measurement film.

Further, the activity measurement film of the photocatalytic thin film according to the present invention was formed by drying a mixed solution obtained by adding an aqueous solution of an alkali halide such as potassium iodide or potassium chloride and a pH indicator to an organic binder.

[0010]

When a photocatalytic thin film is irradiated with ultraviolet rays, an oxidation reaction and a reduction reaction occur simultaneously, and the pH of an aqueous alkali halide solution or the like increases due to hydroxyl groups generated by the reduction reaction.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a diagram illustrating the activity measuring method of the photocatalytic film according to the present invention, reference numeral 1 denotes a substrate of the tile or the like, this substrate 1 surface photocatalytic film 2 mainly composed of TiO ₂ Is formed.

The photocatalytic thin film 2 can be formed by a method of forming a Ti sulfate film and thermally decomposing it, a method of forming a Ti alkoxide film and thermally decomposing the same, or a method of forming a Ti sol and then heating the film. There is a method obtained, further increasing the photoactive effect, uniformly Cu to TiO ₂ in the thin film, Ag, Fe, C
Metals such as o, Pt, Ni, and Pd may be immobilized.

To check whether or not the photocatalytic thin film 2 formed as described above has photoactivity, the photocatalytic thin film 2
An aqueous alkali halide solution 3 such as potassium iodide or potassium chloride is dropped on the surface, and then the dropped aqueous alkali halide solution 3 is irradiated with ultraviolet light by an ultraviolet lamp 4 for a predetermined time to adjust the pH of the aqueous alkali halide solution before irradiation. The magnitude of the activity of the photocatalytic thin film 2 is determined from the difference from the pH after irradiation.

FIG. 4 is a graph showing the relationship between the ultraviolet irradiation time and the amount of change in pH.
The test was performed with a concentration of 0.1 mol / l, a BLB fluorescent lamp 20W as the ultraviolet lamp 4, a distance between the photocatalytic thin film 2 and the ultraviolet lamp 4 of 20 cm, and an irradiation time of 60 minutes. As can be seen from this figure, regardless of the type of the photocatalytic thin film 2 of the anatase type, the metal-carrying type, and the rutile type, the pH of the aqueous alkali halide solution 3 is high until the irradiation time of the ultraviolet light becomes 30 minutes. Become.

[0015] The reason why the pH of an aqueous alkali halide solution 3 by the irradiation of ultraviolet rays is increased occurs following oxidation and reduction reactions simultaneously, OH by reduction reaction ^-
(Hydroxyl ion) is generated. Oxidation ^{reaction: 2I - + 2h + = I} 2 reduction ^{_{reaction: O 2 + 2H 2 O +}} 4e - = 4OH - Thus, the higher the pH of an aqueous alkali halide solution 3 by irradiation of ultraviolet rays, the photocatalytic film 2 has a photoactive It can be said that.

FIG. 5 is a graph showing the relationship between R30 and the amount of change in pH. Here, R30 is the ratio (%) of the gas (methyl mercaptan or the like) reduced 30 minutes after the irradiation of the ultraviolet rays. From this figure, it can be seen that there is a positive correlation between R30 and the amount of change in pH. That is, the amount of change in pH serves as an indicator of the presence or absence of photoactivity.

In the first aspect, the amount of change in pH is p
H-meter or pH measurement sheet 5
In the present invention, a mixed solution obtained by adding a pH indicator to an aqueous alkali halide solution 3 is dropped on the surface of the photocatalytic thin film 2, and then, the dropped mixed solution is irradiated with ultraviolet rays for a predetermined time, and the color of the mixed solution is changed by changing the color of the mixed solution. The magnitude of the activity of the thin film 2 is determined.

As the pH indicator, methyl red is suitable because the pH of the aqueous alkali halide solution 3 before UV irradiation is about 4.5 and the pH after UV irradiation is 5.5 to 6.5.

In the first and second aspects of the present invention, an aqueous alkali halide solution 3 or a mixed solution obtained by adding a pH indicator to the aqueous alkali halide solution 3 is dropped on the surface of the photocatalytic thin film 2. The spread of the liquid dropped on the substrate varies, and a constant liquid thickness cannot be ensured, and the reaction area may differ from substrate to substrate.

FIG. 2 shows a method for solving this problem. In this method, an alkali halide aqueous solution 3 is used.
After dripping such as on the surface of the photocatalytic thin film 2, the alkali halide aqueous solution 3 is pressed by a transparent plate 6 such as a glass plate to have a constant thickness and prevent drying.

Further, the liquid such as the aqueous alkali halide solution 3 requires that the surface of the substrate 1 be horizontal.
It is difficult to determine the activity of a photocatalytic thin film formed on a vertical surface such as an existing wall surface or a ceiling surface.

FIG. 3 shows a method for solving this problem. In this method, the activity measurement film 7 is brought into close contact with the surface of the photocatalytic thin film 2 formed on the surface of the substrate 1, and in this state, the activity measurement is performed. The film 7 is irradiated with ultraviolet light, and the magnitude of the activity of the photocatalytic thin film 2 is determined based on a change in the color of the activity measurement film 7. Here, the activity measurement film 7 is obtained by drying a mixed solution obtained by adding an aqueous solution of an alkali halide such as potassium iodide or potassium chloride and a pH indicator to an organic binder to form a film.

[0023]

As described above, according to the method for measuring the activity of a photocatalytic thin film according to the first invention, an aqueous alkali halide solution is dropped on the surface of a photocatalytic thin film formed on the surface of a substrate such as a tile. The alkali halide aqueous solution is irradiated with ultraviolet light for a predetermined time, and the magnitude of the activity of the photocatalytic thin film is determined from the difference between the pH of the alkali halide aqueous solution before irradiation and the pH after irradiation, so that it is monitored by a conventional gas chromatograph. The presence or absence of the activity of the photocatalytic thin film can be determined easily and quickly as compared with the method of performing the method and the method of measuring the number of dead bacteria.

According to the method for measuring the activity of a photocatalytic thin film according to the second aspect of the present invention, a mixed solution obtained by adding a pH indicator to an aqueous solution of an alkali halide is dropped on the surface of the photocatalytic thin film. The activity of the photocatalytic thin film can be measured by using a change in the color of the mixed solution itself without using a sheet, which is more convenient.

In particular, if a transparent plate such as a glass plate is placed on the surface of the substrate after the above-mentioned aqueous alkali halide solution or a mixture of the aqueous alkali halide solution and the pH indicator is dropped, the aqueous alkali halide solution or the like can be obtained. As the thickness of the film becomes constant and drying becomes difficult, more accurate judgment can be made.

Further, an aqueous solution of an alkali halide such as potassium iodide or potassium chloride and pH
If the activity of the photocatalytic thin film is determined by measuring the activity of the photocatalytic thin film formed by drying the mixed solution containing the indicator and forming it into a film, the tile after the construction, specifically the ceiling or The activity of the photocatalytic thin film formed on the tile on which the measuring solution is not easily dropped can be easily measured because the vertical surface is formed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for measuring the activity of a photocatalytic thin film according to the first invention and the second invention.

FIG. 2 is a diagram illustrating a method for measuring the activity of a photocatalytic thin film according to another example.

FIG. 3 is a diagram illustrating a method for measuring the activity of a photocatalytic thin film using the activity measurement film according to the third invention.

FIG. 4 is a graph showing the relationship between ultraviolet irradiation time and the amount of change in pH.

FIG. 5 is a graph showing the relationship between R30 and the amount of change in pH.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... photocatalytic thin film, 3 ... alkali halide aqueous solution, 4 ... ultraviolet lamp, 5 ... pH measurement sheet, 6 ... glass plate, 7 ... activity measurement film.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Toshiya Watanabe 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu-shi, Fukuoka

Claims (5)

[Claims] An aqueous solution of an alkali halide such as potassium iodide or potassium chloride is dropped on the surface of a photocatalytic thin film mainly composed of TiO ₂ formed on the surface of a substrate. A method for measuring the activity of a photocatalytic thin film, wherein the magnitude of the activity of the photocatalytic thin film is determined from the difference between the pH of the aqueous alkali halide solution before the irradiation and the pH after the irradiation. 2. A mixed solution obtained by adding a pH indicator to an aqueous solution of an alkali halide such as potassium iodide or potassium chloride is dropped on the surface of a photocatalytic thin film mainly composed of TiO ₂ formed on the surface of the substrate, and then the mixed solution is dropped. A method for measuring the activity of a photocatalytic thin film, comprising irradiating a liquid with ultraviolet light for a predetermined time and determining the magnitude of the activity of the photocatalytic thin film based on a change in color of the mixed liquid. 3. The method for measuring the activity of a photocatalytic thin film according to claim 1, wherein an aqueous solution of an alkali halide or a mixture of an aqueous solution of an alkali halide and a pH indicator is dropped on the surface of the substrate, and then the surface of the substrate is transparent. Place the board,
A method for measuring the activity of a photocatalytic thin film, wherein ultraviolet light is irradiated through the transparent plate. 4. An activity measurement film is brought into close contact with the surface of a photocatalytic thin film mainly composed of TiO ₂ formed on the surface of a substrate, and in this state, the activity measurement film is irradiated with ultraviolet rays for a predetermined time to change the color of the activity measurement film. A method for measuring the activity of a photocatalytic thin film, wherein the magnitude of the activity of the photocatalytic thin film is determined. 5. A photocatalytic thin film activity measurement film obtained by drying a mixture obtained by adding an aqueous solution of an alkali halide such as potassium iodide or potassium chloride and a pH indicator to an organic binder to form a film.