JPH10180118A - Fixed photocatalyst, preparation thereof, and method for decomposition-removing harmful substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixed photocatalyst which has high photocatalytic reaction efficiency and indicates good effects for the decomposition, etc., of dirt (sticking dirty substances) on the surface of solids and harmful substances in the air or drainage, a method for preparing the catalyst, and a method for decomposition-removing harmful substances using the catalyst. SOLUTION: In a fixed photocatalyst, a thin film of anatase-type titanium dioxide of 5-30nm average crystal size is fixed on the surface of a base material. Harmful substances in contact with the catalyst are decomposition-removed effectively by being irradiated with high energy light. The catalyst can be prepared by a method in which titania sol applied on the base material is heated at a prescribed temperature (250-800 deg.C) and burned for a short time (within 30min). The use of titania sol added with a prescribed quantity of zirconium dioxide and/or zirconium salt can alleviate the burning conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is effective for deodorization, antifouling (prevention of fouling of a solid surface), sterilization, etc., and acts to decompose and remove air pollutants or pollutants in wastewater. Further, the present invention relates to an immobilized photocatalyst which can be applied to photoelectrochemistry, organic synthesis, and the like, a method for producing the same, and a method for decomposing and removing harmful substances using the photocatalyst.

[0002]

2. Description of the Related Art When a semiconductor is irradiated with light, electrons having a strong reducing action and holes having a strong oxidizing action are generated on the irradiated surface, and molecules in contact with the semiconductor are decomposed by the redox action.

In recent years, such action of the semiconductor, i.e., a photocatalysis, degradation of air pollutants such as NO _x, deodorizing,
Attempts to apply to various environmental purification technologies such as antifouling, sterilization, and water purification have been made vigorously. However, at present, the efficiency of the photocatalytic reaction is low, and very few examples have been put to practical use.

Conventionally, semiconductor photocatalysts have been used in a state of being suspended in a solution in powder form or in a state of being fixed in a thin film form on a substrate. From the viewpoint of maintaining a high activity of the photocatalyst, it is desirable to use the suspension in a large surface area, but from a practical point of view, it is far more convenient to use in a fixed state that is easy to handle and has a wide range of applications. Promising.

[0005] Therefore, various methods have been proposed for increasing the activity of a photocatalyst in which a semiconductor having a photocatalytic action is fixed to a substrate (hereinafter, this is referred to as “immobilized photocatalyst”). The gazette discloses a titanium dioxide-immobilized photocatalyst comprising an anatase-type crystal. This photocatalyst is prepared by adding an alcoholamine to a sol of titanium dioxide used for coating on a substrate,
It is manufactured by slowly heating and raising the temperature to a firing temperature of 00 ° C. However, this immobilized photocatalyst does not provide sufficient photocatalytic activity, and has a problem that a large amount of energy is required during production because alcoholamine is not easily scattered.

Japanese Unexamined Patent Publication (Kokai) No. 6-293519 discloses a method for producing an immobilized photocatalyst in which titania sol used for coating is subjected to hydrothermal treatment in advance to grow titanium dioxide fine particles contained therein in a crystal form. Although this photocatalyst has a relatively high catalytic activity, the crystal-grown titania sol is difficult to apply uniformly to a substrate, and has a problem that it is easily peeled off after firing. Furthermore, hydrothermal treatment is a reaction under high temperature and high pressure,
Since it requires delicate control of solution concentration, temperature, pressure, etc., it is not suitable for mass production of photocatalysts.

[0007]

SUMMARY OF THE INVENTION The present invention has a high photocatalytic reaction efficiency under the above-described circumstances, and therefore has a deodorizing effect, an antifouling effect, an antibacterial effect, and a harmful substance contained in the atmosphere or wastewater. For example, an immobilized photocatalyst which shows an excellent effect on the decomposition and detoxification of NO _x , pesticides, organic halogen compounds, etc., and is also suitable from the viewpoint of economy, stability, safety and the like, and its production An object of the present invention is to provide a method and a method for decomposing and removing harmful substances using the photocatalyst.

[0008]

Means for Solving the Problems As a result of repeated studies to develop an immobilized photocatalyst using titanium dioxide and exhibiting high reaction efficiency, the titania sol was applied to a substrate, and then fired. By growing the crystal, an anatase-type titanium dioxide having an average crystallite size of 5 to 30 nm can be obtained, the specific surface area of the immobilized titanium dioxide increases, and a coordination unsaturated point, a lattice defect and the like can be increased. It has been found that the photocatalytic activity is significantly improved by increasing the number of reaction active sites and further increasing the oxidation-reduction power when the quantum size effect appears.

Further, the immobilized photocatalyst having such properties can be produced by shortening the firing time after coating the titania sol on the substrate surface.
It has been found that by adding a predetermined amount of zirconium dioxide or a salt of zirconium to the titania sol used for coating, it is possible to more easily produce the titania sol.

The present invention has been made based on these findings. The gist of the present invention is as follows: (1) an immobilized photocatalyst;
And (3) a method for producing the same, and (4) a method for decomposing and removing harmful substances using the immobilized photocatalyst.

(1) A photocatalyst wherein anatase-type titanium dioxide having an average crystallite size of 5 to 30 nm is fixed on the surface of a substrate in a thin film form.

(2) After applying the titania sol to the substrate,
The method for producing an immobilized photocatalyst according to the above (1), wherein a calcination treatment is carried out by heating to 250 to 800 ° C. and holding at that temperature for 30 minutes or less.

(3) After applying a titania sol to which one or both of zirconium dioxide and zirconium salt are added so that Zr / Ti (molar ratio) is less than 0.3, the substrate is heated to 300 to 1000 ° C. The method for producing an immobilized photocatalyst according to the above (1), wherein a calcination treatment is performed.

(4) Decomposition of the harmful substance, wherein the immobilized photocatalyst according to the above (1) is irradiated with light having an energy of a band gap or more under the condition that the harmful substance is in contact with the harmful substance. -Removal method.

[0015] The term "average crystallite size" is basically meant the crystal grain size observed directly by a transmission electron microscope, this value anatase by X-ray diffraction (d ₁₀₁₎
Since the peaks of the peaks well match the crystallite size calculated using the Scherrer equation, any of these values may be adopted as the average crystallite size in the present invention. In addition, there is no special meaning (limitation) in "average" and 5n
m, or slightly over 30 nm, the arithmetic average of a plurality of crystallite sizes is 5 to 3
What is necessary is just to be in the range of 0 nm.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention (the above (1) to
The invention (4) will be described in detail.

The invention of the above (1) is obtained by applying a titania sol to the surface of a base material and then sintering to grow a thin film of titanium dioxide crystal, the crystallite size of which is 5 to 30 nm on average. An immobilized photocatalyst characterized by being within the range (this is referred to as “immobilized photocatalyst of the present invention”).

In the immobilized photocatalyst of the present invention, first,
The crystal structure of titanium dioxide must be anatase type. This is because a photocatalyst having high photocatalytic activity cannot be obtained unless an anatase type is used, as will be described in Examples described later.

Further, it is necessary that the average crystallite size (hereinafter, simply referred to as “crystallite size”) is in the range of 5 to 30 nm. The fact that the crystallite size is less than 5 nm means that the average particle diameter of titanium dioxide contained in the titania sol is about 5 nm, and it is substantially difficult to produce such fine titanium dioxide particles. . On the other hand, when the crystallite size exceeds 30 nm, the photocatalytic activity is significantly reduced.

The base material to which titanium dioxide is fixed is a steel plate plated with stainless steel, carbon steel, zinc, or the like, or various metal materials such as an aluminum plate or a titanium plate, or an inorganic material such as ceramics, ceramics, or glass. Material, resin, wood, any material selected from organic materials such as activated carbon, or a composite material consisting of two or more of them,
A wide range of materials can be used. A member that has already been painted can also be used. The shape of the base material is not limited at all, and may be a plate shape such as a thick plate or a thin plate, a spherical shape such as a bead, or a complicated shape provided as a product as it is. Further, the surface may be porous or dense.

The thickness of the titanium dioxide is not particularly limited. In general, thicker films tend to exhibit higher photocatalytic activity. However, if the film thickness exceeds 2 μm, the effect of improving the photocatalytic activity is not recognized, and the film is liable to peel off. Therefore, the thickness is preferably 2 μm or less.

The immobilized photocatalyst exhibits a photocatalytic action by light from sunlight, fluorescent light, black light, mercury lamp, xenon lamp, etc., and is contained in antibacterial, deodorant, antifouling, and in the atmosphere or wastewater. Decomposition of harmful substances,
Excellent effect on detoxification. In addition, this immobilized photocatalyst is excellent in stability, safety (no toxicity), etc., and can be suitably used as interior materials, building materials, glass, decorative boards, tiles, etc., and requires some energy when used. It also has the advantage of being energy-saving and maintenance-free.

The invention of the above (2) is a method for producing an immobilized photocatalyst according to the above (1), wherein a titania sol is applied to a substrate,
This is a method of heating to 250 to 800 ° C. (firing temperature) and performing a firing process for maintaining the temperature for a short time (within 30 minutes).

The titania sol is prepared by suspending ultrafine titanium dioxide (5 to 10 nm) in water, titanium tetramethoxide, titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetra-i-propoxy. , Titanium tetraalkoxide such as titanium tetra-n-butoxide, titanium acetylacetonate, titanium tetrachloride and the like.
Further, an alcohol amine such as diethanolamine or triethanolamine, or a drying inhibitor such as 1,3 propanediol may be added to the sol.

The titanium dioxide contained in the titania sol thus obtained has an average particle size of about 5 to 10 nm. The titanium dioxide is applied to the surface of a base material, baked, and crystal-grown to obtain a desired crystallite size. (5 to 30 nm) titanium dioxide-immobilized photocatalyst.

The titania sol can be applied to the substrate by spin coating, dip coating, spray coating, bar coating or the like.

An immobilized photocatalyst can be obtained by applying the titania sol to a substrate and then sintering. However, sintering of a metal oxide such as titanium dioxide immobilized in a thin film on the surface of the substrate occurs very quickly. Since the crystal grains become large, the crystallite size described above is 5 to 30 n under normal firing conditions.
The immobilized photocatalyst of the present invention comprising titanium dioxide in the range of m cannot be obtained.

Therefore, firing is performed under the above-mentioned predetermined conditions.
That is, after applying the titania sol to the substrate, the substrate is heated to a firing temperature, held at that temperature for a predetermined time, and then cooled to perform a firing process. The sintering may be performed in a state of being applied (room temperature state), or may be performed after being dried at about 100 ° C. after the application.

The firing temperature is in a temperature range of 250 to 800 ° C. If the firing temperature is lower than 250 ° C., the titanium dioxide remains amorphous, while if it exceeds 800 ° C., crystal grains grow too large or rutile crystals appear, and an immobilized photocatalyst having high photocatalytic activity is obtained. I can't.

The heating to the firing temperature is preferably performed rapidly. If heating is not performed rapidly, sintering of titanium dioxide may progress too much before the above-mentioned firing temperature is reached, and the crystal grains may become coarse. A preferred heating rate is 30
° C / min or more. For rapid heating, it is preferable to use a method in which a heat treatment furnace is heated to a predetermined temperature in advance, and a substrate coated with titania sol is directly charged therein.

The holding time (firing time) after reaching the firing temperature is within 30 minutes. Since the firing temperature has a range, in practice, the firing time is set to be longer when the firing temperature is set to a lower temperature within the above temperature range, and shortened when the temperature is set to a higher temperature. . It is preferable to set the firing temperature in the range of 400 to 700 ° C. and the firing time within 10 minutes in order to obtain an immobilized photocatalyst having high photocatalytic activity.

After firing, cooling is performed, and it is desirable that cooling be performed rapidly. If the cooling rate is low, sintering may proceed too much as in the case of heating, and an immobilized photocatalyst made of anatase-type titanium dioxide having a desired crystallite size cannot be obtained. The cooling rate is preferably 20 ° C./min or more. In addition, as a method of rapidly cooling, a method such as air cooling or water cooling can be used.

The invention of the above (3) is the same as the invention of the above (2), wherein the method for producing an immobilized photocatalyst according to the above (1), wherein Zr / T
After applying a titania sol to which one or both of zirconium dioxide and a zirconium salt are added so that i (molar ratio) is less than 0.3, the substrate is treated with 300 to
This is a method of performing a baking treatment at 1000 ° C.

The zirconium dioxide added to the titania sol is dispersed inside the titanium dioxide crystal (in the crystal grains) or at the crystal grain boundaries, and as a result of a kind of pinning effect, an anatase during firing of the titanium dioxide. Crystal grain growth is suppressed. The addition of zirconium dioxide is also effective in suppressing the transition from anatase to rutile, which has low photocatalytic activity, which occurs during firing at a high temperature of 800 ° C. or higher. The zirconium salt also easily becomes an oxide at the time of firing, and thus has the same effect as the case where zirconium dioxide is added.

Therefore, by adding these zirconium dioxide and / or zirconium salt,
Even if the firing temperature or firing time slightly deviates from the firing temperature or the firing time specified in the invention (2), it is possible to produce an immobilized photocatalyst made of titanium dioxide having a small crystallite size. That is, the firing conditions can be relaxed, and the immobilized photocatalyst of the present invention can be manufactured more easily.

The zirconium dioxide is prepared by suspending ultrafine zirconium dioxide (5 to 10 nm) in water, or zirconium such as zirconium tetra-n-propoxide, zirconium tetra-i-propoxide, zirconium tetra-n-butoxide. It can be prepared as a zirconia sol by hydrolyzing tetraalkoxide, zirconium tetrachloride or the like. As the zirconium salt, zirconium oxychloride, zirconyl nitrate and the like can be used.

Zirconium dioxide used for coating and / or
Alternatively, the preparation of the titania sol to which the zirconium salt is added may be such that the zirconia sol or the zirconium salt described above may be added to a separately prepared titania sol. Mixing can be easily performed.

The amount of zirconium dioxide and / or zirconium salt to be added to the titania sol is less than 0.3 (excluding 0) in Zr / Ti (molar ratio).
When Zr / Ti (molar ratio) becomes 0.3 or more (that is, the amount of Zr with respect to Ti is 30 mol%) or more, a composite oxide of titanium and zirconium, for example, ZrTi
Since the generation of O _{4 and the} like occurs preferentially, the photocatalytic activity is significantly reduced. Preferably it is 1 to 18 mol%, more preferably 12 to 18 mol%.

The firing temperature is 300 to 1000 ° C. If the firing temperature is lower than the lower limit of this temperature range, it becomes amorphous,
If the upper limit is exceeded, rutile crystals will be formed, and in either case, an immobilized photocatalyst having high photocatalytic activity cannot be obtained.

The heating up to the sintering temperature is considerably milder than the heating condition in the production method (2) because zirconium dioxide effectively suppresses the growth of anatase crystals during the sintering of titanium dioxide. It may be performed under conditions.
The conditions are not particularly limited, but the preferred heating rate is 3
° C / min or more.

The holding time (sintering time) after reaching the firing temperature is not particularly limited. However, if the time is excessively long, the production efficiency is reduced and the cost is increased.

Cooling after firing is the same as heating.
The reaction may be performed under milder conditions than the method (2), but a preferable condition is 3 ° C./min or more.

According to the methods (2) and (3),
The immobilized photocatalyst of the present invention can be easily manufactured at a relatively low cost without requiring any special means.

The invention of the above (4) is a method of decomposing and removing harmful substances by using the immobilized photocatalyst of the invention of (1), and under the condition that these immobilized photocatalysts and harmful substances come into contact with each other. A method of irradiating the photocatalyst with light having energy equal to or greater than a band gap. In other words, under the condition that the harmful substance can be catalyzed by the immobilized photocatalyst, a considerable number of electrons in the full band in the crystal constituting the photocatalyst pass through the forbidden band to the vacant band (conduction band). It emits light of energy.

The "harmful substance" as referred to herein is a substance which has a bad influence on the human body or a substance which may cause such a harmful effect, and specifically, NO _x , SO _x , chlorofluorocarbon, ammonia, hydrogen sulfide, etc. Substances contained in exhaust gas or air of the air, aldehydes, amines, mercaptans, alcohols, organic compounds such as BTX (benzene, toluene, xylene), phenols, and the like; and organic halogen compounds such as trihalomethane and trichloroethylene; Various pesticides such as herbicides, fungicides, insecticides, various substances with high biochemical oxygen demand (BOD) including proteins and amino acids, surfactants, inorganic compounds such as cyanide and sulfur compounds, various Heavy metal ions and the like, and also microorganisms such as bacteria, actinomycetes, fungi, and algae, and those mainly contained in wastewater. .

Further, the "harmful substance" includes an "adhering substance" which directly adheres to the surface of a photocatalyst or a multifunctional member using the same. For example, in addition to fungi such as Escherichia coli, staphylococci, green bacterium, and mold, there are oil, tobacco tar, fingerprints, rain dripping, and mud.

The above-mentioned “conditions under which the immobilized photocatalyst contacts the harmful substance” include, for example, the case where the above-mentioned harmful substance is directly attached to the immobilized photocatalyst. The immobilized photocatalyst is placed in air or other gas or water or other liquid, and the harmful substance is in a state where it can be catalyzed by the photocatalyst.

When the immobilized photocatalyst of the invention (1) is irradiated with light having an energy equal to or larger than the band gap under such conditions, a photocatalytic action is exhibited, and harmful substances are effectively decomposed and removed.

The light having an energy equal to or greater than the band gap is preferably light containing ultraviolet rays. Specifically, there are sunlight, light from fluorescent lamps, black lights, mercury lamps, xenon lamps and the like. Can be used. In particular, light containing near-ultraviolet light having a wavelength of 300 to 400 nm is preferable.

The irradiation amount and irradiation time of light may be appropriately determined depending on the amount of harmful substances to be decomposed and removed.

[0051]

【Example】

(Example 1) 40.5 g of titanium tetra-n-butoxide
(0.12 mol) was added to 75 ml (milliliter) of dehydrated ethanol, and the mixture was stirred at room temperature for 30 minutes.
Cool using an ice bath. Then, ethanol (75 ml), water (2.6 ml), nitric acid (2 ml) were added to this mixture.
Was slowly added dropwise, and the mixture was stirred for 1 hour, taken out of the ice bath, returned to room temperature, and stirred for 12 hours to obtain a transparent titania sol solution.

Further, this sol was subjected to a mirror-polished stainless steel substrate (SUS304: 4 cm × 4) using a spin coater at a rotation speed of 300 rpm and a holding time of 1 minute.
cm × 1 mm thick). Immediately thereafter, the substrate was placed in an electric furnace having a furnace temperature set to 550 ° C. in advance, fired for 3 minutes, taken out, and cooled in air. By repeating this sol solution application and firing operation four times, an immobilized photocatalyst having titanium dioxide formed in a thin film on the surface of stainless steel was produced.

The titanium dioxide of this photocatalyst was examined by X-ray diffraction. As a result, only an anatase crystal pattern was observed as shown in FIG. Also, Scherre
The crystallite size (d ₁₀₁ ) determined from the equation for r is 15.5 n
m and the crystal grain size (about 1 μm) observed with a transmission electron microscope.
5 nm). Table 1 shows the firing temperature, firing time, and crystallite size.

Using this titanium dioxide-immobilized photocatalyst as a sample, an acetic acid decomposition experiment was performed.

First, a quartz reaction cell (with an internal capacity of 100 c)
In c), the sample and 70 ml of an acetic acid aqueous solution having a concentration of 6.6 mM (mmol) (acetic acid content: 462 μmol) were put, and oxygen was passed for 20 minutes. Next, light irradiation was performed for 4 hours through a UV filter (UV-31 manufactured by Toshiba) from a 250 W ultra-high pressure mercury lamp while stirring the ceramic at 25 ° C. Thereafter, the amount of acetic acid contained in the aqueous solution was analyzed by ion chromatography.
It was 0 μmol (shown in the same table).

Example 2 A mixture obtained by adding 80 g of titanium tetra-i-propoxide to 50 ml of isopropanol was dropped into 500 ml of vigorously stirred distilled water, and then nitric acid (60%, hereinafter referred to as nitric acid). 5 g of 60% nitric acid) were added. Then, the mixture was stirred at 80 ° C. for 24 hours,
The solution was concentrated under vacuum to obtain a titania sol solution containing 15% by weight of titanium dioxide, and a 2-fold amount of ethanol was added to obtain a sol solution for application.

This sol solution was applied to a stainless steel base material (SUS304: 4 cm × 4 cm × 1 mm thick) in the same manner as in Example 1, and then dried in air for 30 minutes. C., placed in an electric heating furnace, baked for 30 minutes, taken out, and cooled in air. The application and baking operations of this sol solution were repeated four times to produce a titanium dioxide-immobilized photocatalyst.

The titanium dioxide of this photocatalyst was anatase type as a result of examination by X-ray diffraction, and its crystallite size (d ₁₀₁ ) was about 6.0 nm. Table 1 shows the firing temperature, firing time, and crystallite size.

Using this titanium dioxide-immobilized photocatalyst as a sample, an acetic acid decomposition experiment was performed in the same manner as in Example 1. The results are shown in Table 1, and the amount reduced by the decomposition of acetic acid was 54.5 μmol.

(Examples 3 to 10) A titanium dioxide-immobilized photocatalyst was obtained in the same manner as in Example 1 except that the calcination conditions (calcination temperature and calcination time) were as shown in Table 1.
Similarly, an experiment for decomposing acetic acid was performed in the same manner as in Example 1. The results were as shown in Table 1.

Comparative Example 1 A titanium dioxide-immobilized photocatalyst was produced in the same manner as in Example 1 except that the firing time was changed to 60 minutes. As a result of X-ray diffraction, the titanium dioxide of this photocatalyst showed only an anatase crystal peak as shown in FIG. 1. However, the crystallite size (d ₁₀₁ ) determined from the Scherrer equation was 32.5 nm (transmission type). When observed with an electron microscope, the value was 33.0 nm), which was out of the range specified in the present invention.

Using this titanium dioxide-immobilized photocatalyst as a sample, an acetic acid decomposition experiment was performed in the same manner as in Example 1. As a result, as shown in Table 1, the decrease due to the decomposition of acetic acid was 0.3 μmol, which was significantly lower than that in Example 1 described above.

Comparative Example 2 A titanium dioxide-immobilized photocatalyst was obtained in the same manner as in Example 1 except that the firing temperature was 850 ° C. As a result of X-ray diffraction, this photocatalyst was in a state in which an anatase crystal having a crystallite size of 35.5 nm and a rutile crystal having a crystal grain size of 70 to 80 nm were mixed.

Using this titanium dioxide-immobilized photocatalyst as a sample, an acetic acid decomposition experiment was performed in the same manner as in Example 1. As a result, as shown in Table 1, the decomposition amount of acetic acid was 0.

Example 11 0.561 g of a 2-propanol solution containing 40.5 g (0.12 mol) of titanium tetra-n-butoxide and 70% zirconium tetra-n-propoxide (1.2 × 10 ^-3 mol)
Was added to 75 ml of dehydrated ethanol.
After stirring for minutes, the mixture was cooled using an ice bath. Thereafter, ethanol (75 ml) and water (2.6 m
l), a mixed solution of nitric acid (2 ml) was slowly dropped, and 1
After stirring for an hour, remove from the ice bath and return to room temperature.
Stirring was continued for 2 hours to obtain a mixed sol solution of titania sol and zirconia sol (Zr / Ti = 1 mol%).

Further, this sol solution was applied to a stainless steel substrate (SUS304:
4cm x 4cm x 1mm thickness)
Baking was performed at 0 ° C. for 60 minutes. By repeating the application and firing operations of the sol solution four times, an immobilized photocatalyst based on stainless steel was produced.

FIG. 2 shows an X-ray diffraction diagram of the photocatalyst (titanium dioxide containing zirconium dioxide) formed on the substrate surface. As shown, the titanium dioxide was of the anatase type. On the other hand, no diffraction pattern based on zirconium dioxide was observed. Also, Scherre
The crystallite size (d ₁₀₁ ) of the titanium dioxide anatase crystal determined from the equation for r was 20.1 nm. This crystallite size is clearly smaller than the crystallite size (32.5 nm) of the sample of Comparative Example 1 prepared under the same firing conditions, and the addition of zirconium dioxide suppresses the sintering of titanium dioxide, and It can be seen that the coarsening of the grains was prevented.

Using this immobilized photocatalyst as a sample, Example 1
An experiment for decomposing acetic acid was performed in the same manner as described above. The results were as shown in Table 1.

Example 12 A mixture obtained by adding 80 g of titanium tetra-i-propoxide to 50 ml of isopropanol was dropped into 500 ml of vigorously stirred distilled water.
Thereafter, 5 g of nitric acid (60%) was added. Then, at 80 ° C
For 24 hours and concentrated under vacuum to remove titanium dioxide in 1 part.
A titania sol solution containing 5% by weight was obtained. 2.73 g of zirconium oxychloride was added to the sol solution (Zr / Ti =
3 mol%), and after sufficiently stirring, a 2-fold amount of ethanol was added to obtain a coating sol solution.

This sol solution was applied on a stainless steel base material (SUS304: 4 cm × 4 cm × 1 mm thick) in the same manner as in Example 1, and baked at 500 ° C. for 60 minutes in air. The immobilized photocatalyst was produced by repeating the application and firing operations of the sol solution four times. The photocatalyst on this substrate was composed of anatase crystals, and its crystallite size (d ₁₀₁ ) was 19.5 nm.

Using this immobilized photocatalyst as a sample, Example 1
An experiment for decomposing acetic acid was performed in the same manner as described above. The results were as shown in Table 1.

Examples 13 to 17 The amount of a 2-propanol solution containing zirconium tetra-n-propoxide (concentration: 70%) was 1.69 g, 3.37 g, 6.73.
g, 10.1 g, 13.48 g, and 13.48 g, respectively, to produce an immobilized photocatalyst based on stainless steel in the same manner as in Example 11. X-ray diffraction of the photocatalyst (titanium dioxide containing zirconium dioxide) formed on the surface of the substrate showed only an anatase crystal peak as shown in FIG. 2 and a diffraction peak based on zirconium dioxide was observed. Did not.

Using these immobilized photocatalysts as samples, acetic acid decomposition experiments were performed in the same manner as in Example 1.
The results are shown in Table 1. The decomposition amount of acetic acid was much higher than that of Comparative Example 3 (immobilized photocatalyst in which zirconium dioxide exceeds the amount specified in the present invention).

Comparative Example 3 Example 11 was repeated except that the amount of the 2-propanol solution containing zirconium tetra-n-propoxide (concentration: 70%) was changed to 16.84 g.
An immobilized photocatalyst using stainless steel as a base material was produced in the same manner as described above. As a result of X-ray diffraction of the photocatalyst (titanium dioxide containing zirconium dioxide) formed on the surface of the substrate, no diffraction pattern based on anatase crystals was observed as shown in FIG.

Using this immobilized photocatalyst as a sample, Example 1
An experiment for decomposing acetic acid was performed in the same manner as described above. The results are as shown in Table 1, and acetic acid was hardly decomposed. Although this was not observed by X-ray diffraction, it is because a composite oxide of titanium and zirconium (such as ZrTiO ₄ ) was mainly produced, and the photocatalytic activity was significantly reduced.

Example 18 Using the sol liquid (Ti / Zr = 18 mol%) prepared in Example 16, the firing temperature was 9
Example 1 except that the sintering time was 3 minutes at 00 ° C.
In the same manner as in Example 1, an immobilized photocatalyst based on stainless steel was produced. The photocatalyst formed on the surface of the substrate was composed of anatase crystals having a crystallite size of 25.5 nm, and did not include rutile crystals.

Using this immobilized photocatalyst as a sample, Example 1
An experiment for decomposing acetic acid was performed in the same manner as described above. The results were as shown in Table 1.

[0078]

[Table 1]

Example 19 In order to confirm the deodorizing effect of the immobilized photocatalyst, a decomposition experiment was performed on the assumption that acetaldehyde was a malodorous component.

The immobilized photocatalyst prepared in Example 16 was placed in a quartz reaction cell (internal volume 100 cc), and connected to a closed circulation line (total internal volume 350 ml). Acetaldehyde (5000 ppm) diluted with air was introduced into the system, and light was irradiated from a 250 W ultra-high pressure mercury lamp through a dimming filter and a UV filter (UV-31 manufactured by Toshiba) while circulating (ultraviolet intensity 15 mW / cm ^2). ). In addition, the amount reduced by the decomposition of acetaldehyde was measured using a gas chromatograph connected to a line.

As a result, as shown in FIG. 3, acetaldehyde decreased with time, and reached an undetectable level (10 ppm or less) after 120 minutes.

Comparative Example 4 Using the immobilized photocatalyst prepared in Comparative Example 1, an acetaldehyde decomposition experiment was performed in the same manner as in Example 19.

As shown in FIG. 3, the residual concentration of acetaldehyde after 120 minutes was about 3500 ppm.
Thus, the amount of decomposition of acetaldehyde was much smaller than that of Example 19.

Example 20 To confirm the antibacterial effect of the immobilized photocatalyst, Escherichia coli (Escherichiacol) was used.
i W3110 strain).

Using the immobilized photocatalyst prepared in Example 1 as a sample, its surface was previously sterilized with 70% ethanol, and then 0.2 ml of physiological saline containing 2.5 × 10 ⁵ cells / ml (number of E. coli) : 5 × 10 ⁴ ) to 0.0
Eight drops of 25 ml each were dropped on the surface. Next, under a condition of a relative humidity of 95%, light irradiation was performed from above using a 250 W ultra-high pressure mercury lamp through a dimming filter and a UV filter (UV-35 manufactured by Toshiba) for 15 minutes (ultraviolet intensity: 1 mW / cm ² ). .

Thereafter, the bacterial solution on the sample was added to physiological saline 9.
Rinse with 8 ml, dilute and spread on standard agar medium,
After culturing at 35 ° C. for 48 hours, the number of viable bacteria was measured by counting the grown colonies. Evaluation of antibacterial properties
Under the same conditions, a physiological saline solution containing Escherichia coli was added to a substrate (SUS30) on which titanium dioxide was not formed (coated).
4) The number of viable cells measured in the same manner as described above for the one that was dropped on the surface and irradiated with light for 15 minutes and the one that was dropped on the surface of the immobilized photocatalyst prepared in Example 1 and kept in a dark place for 15 minutes ( 4.8 × 10 ⁵ and 4.7 × 10 ^{5 respectively}
Number).

As a result, the number of surviving Escherichia coli became 1.6 × 10 ³ by light irradiation, and excellent antibacterial activity was recognized.

(Example 21) A quartz plate (4 cm
Example 1 except that (× 4 cm × 1 mm thick) was used.
An immobilized photocatalyst in which titanium dioxide was formed in a thin film on the surface of a quartz plate was produced in the same manner as described above. As a result of examining the crystal structure of this photocatalyst by X-ray diffraction, titanium dioxide was composed of anatase crystals, and the crystallite size was 1
It was 4.5 nm.

Using this titanium dioxide-immobilized photocatalyst as a sample, an experiment of decomposing tetrachloroethylene was performed. In addition, tetrachloroethylene is used as a solvent for detergents, fats, resins, and the like, and is a substance that has been regarded as a problem as one of the pollution factors of groundwater.

First, a quartz reaction cell (internal volume 100c)
In c), 40 ml of an aqueous solution of tetrachloroethylene having a concentration of 30 ppm was put, and the sample was immersed in the solution. Oxygen was bubbled for 20 minutes.
Light irradiation was performed for 4 hours through a filter (UV-29 manufactured by Toshiba). Thereafter, the amount of tetrachloroethylene contained in the aqueous solution was quantified using a gas chromatograph. As a result, the concentration of tetrachloroethylene was reduced to 3.2 ppm.

Example 22 A coated steel sheet (5 cm × 5 cm × 1 mm thick) was used as a substrate, and the surface of the coated steel sheet was produced in the same manner as in Example 2 except that the firing time was 2 minutes. An immobilized photocatalyst was prepared by forming titanium dioxide in a thin film. As a result of examining the crystal structure of this photocatalyst by X-ray diffraction, titanium dioxide was composed of anatase crystals, and its crystallite size was 5.8 nm.

Using this photocatalyst as a sample, a test for removing the tar of tobacco adhered to the sample surface was performed in the following manner.

After forcing one cigarette tar on the surface of the sample, light irradiation (ultraviolet intensity 5 mW / cm ² ) from a 250 W ultra-high pressure mercury lamp through a neutral density filter and a UV filter (UV-35 manufactured by Toshiba). ) Was measured by using a color difference meter to measure the change in the b value, which was a measure of yellow color, to thereby evaluate the reduction in tan.

As a result, the b value was reduced from 16.5 before light irradiation to almost 0 after 2 hours of light irradiation, and the color (white) of the coating used as the substrate was apparently restored. Was confirmed to be effectively removed. On the other hand, when a similar test was performed using a coated steel sheet that had not been subjected to the above treatment, the b value was 13.4 before light irradiation.
The light irradiation for 2 hours resulted in only 8.2, and much of the tar remained on the sample surface.

[0095]

The immobilized photocatalyst of the present invention has a high reaction activity and has an excellent effect on decomposing and removing harmful substances and dirt adhering substances in the air or wastewater. Therefore,
If metal, glass, ceramic, or the like is used as the base material, it is possible to easily provide members such as interior materials and building materials to which the effects of antibacterial, odor-proof, mud-proof, mold-proof, and decomposition of environmental pollutants are imparted. it can. In particular, according to the method for decomposing and removing harmful substances of the present invention, it is possible to effectively decompose and remove harmful substances that have a bad effect on the human body or have a possibility of causing harmful effects, including various attached substances.

According to the production method of the present invention, this photocatalyst uses relatively inexpensive raw materials, does not require any special equipment and operation, requires a short calcination time, and can be compared with a conventional immobilized photocatalyst. And can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a sample used in Example 1 and Comparative Example 1.

FIG. 2 is an X-ray diffraction diagram for the samples used in Examples 11 and 15 and Comparative Example 3.

FIG. 3 is a graph showing the change over time of the decomposition of acetaldehyde in the experimental results of Example 19 and Comparative Example 4.

Claims (4)

[Claims] 1. A photocatalyst comprising an anatase type titanium dioxide having an average crystallite size of 5 to 30 nm fixed on a surface of a substrate in a thin film form. 2. After the titania sol is applied to the substrate, 250
The method for producing an immobilized photocatalyst according to claim 1, wherein a baking treatment is performed in which the material is heated to ８００800 ° C. and held at that temperature for 30 minutes or less. 3. A titania sol to which one or both of zirconium dioxide and a zirconium salt is added so that Zr / Ti (molar ratio) is less than 0.3, is applied to a base material, and then heated at 300 to 1000 ° C. The method for producing an immobilized photocatalyst according to claim 1, wherein a calcination treatment is performed. 4. A method for decomposing and removing harmful substances, wherein the immobilized photocatalyst according to claim 1 is irradiated with light having an energy equal to or greater than a band gap under the condition that the harmful substances are in contact with the immobilized photocatalysts. Method.