JP2002159865A - Titanium oxide photocatalyst for basic gas removal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the capability of a titanium oxide photocatalyst for removing a basic gas. SOLUTION: This photocatalyst comprises titanium oxide particles having a photocatalytic activity as cores and silica hydrate covering the cores. The amount of the silica hydrate is adjusted so that a selectively adsorbed basic gas is efficiently supplied to the active sites of the cores to enhance the basic gas removal capability of the photocatalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally belongs to the field of titanium oxide photocatalyst, and more particularly to a titanium oxide photocatalyst for selectively removing basic gases such as ammonia gas and amine-based gas.

[0002]

It is well known that titanium oxide undergoes a photocatalytic reaction by photoexcitation with ultraviolet light in the presence of water and oxygen. Based on this reaction, the development of application fields for the purpose of removing malodorous substances, removing pollutants in the air, and sterilizing is rapidly progressing. Since the titanium oxide photocatalyst is a powder,
In order to use this for the above purpose, it is necessary to immobilize it using some kind of binder. In this case, when an organic binder is used, it is known that the photocatalyst is coated with an inert substance so that the photocatalyst particles do not come into direct contact with the binder because the strong photocatalytic activity of titanium oxide decomposes the binder itself.

For example, in JP-A-9-31335, a mixture of a titanium oxide photocatalyst and an inorganic deodorizing adsorbent such as zeolite is treated with silica sol, alumina sol, or the like.
A resin composition having a deodorizing function is obtained by blending an organic resin coated with a porous inorganic material.

[0004] Japanese Patent Application Laid-Open No. 11-226422 discloses that a core is composed of titanium dioxide in which primary particles having a particle size of 10 to 50 nm are aggregated to form aggregated particles, and this is microencapsulated in a matrix containing silica as a main component. The disclosed photocatalyst powder is disclosed. It is described that when the microencapsulated powder is dispersed in an organic resin to form a coating, deterioration of the coating film due to ultraviolet irradiation is hardly observed.

[0005] As represented by these prior arts, the purpose of coating a titanium oxide photocatalyst is to suppress decomposition (chalking) of an organic binder resin used for immobilizing the photocatalyst. This means that the original photocatalytic activity of the titanium oxide photocatalyst is partially sacrificed. The larger the degree, the smaller the degree of binder deterioration, but the lower the photocatalytic activity. Therefore, even if a sufficient supply of oxygen and water is present, these coated titanium oxide photocatalysts did not exhibit satisfactory photocatalytic activity under strong ultraviolet light such as black light (ultraviolet lamp). Further, silica or the like in the coating layer does not actively contribute to removal of harmful substances.

[0006] disclosure by contrast the present invention, the titanium oxide photocatalyst of the present invention have the ability to decompose and remove the basic gas even under weak ultraviolet light, such as fluorescent lamps, hydrated silica cover layer basic gas Is selectively adsorbed and supplied to the vicinity of the active site of titanium oxide to actively participate in its removal.

[0007] The titanium oxide phosphor of the present invention for removing basic gas
The medium has a core of titanium oxide particles having photocatalytic activity,
This is SiO_TwoAnd TiO_TwoSiO converted to_Two/ T
iO _TwoSilica so that the weight ratio becomes 0.01 to 0.5
It is coated with hydrate.

Since silica hydrate exhibits a weak acid property, it has a high ability to selectively adsorb a basic gas such as ammonia. However, the basic gas adsorption capacity of the uncoated titanium oxide photocatalyst is much lower than that of the coated photocatalyst. When comparing the basic gas reduction rate constants under ultraviolet irradiation, the former is several times larger than the latter. From this, it is clear that the high basic gas removing ability of the coated titanium oxide photocatalyst of the present invention is related to the basic gas adsorption ability of silica hydrate of the coating layer. However, the ability to adsorb basic gases can be increased by increasing the coverage of silica hydrate.
_{When the 2} / TiO ₂ weight ratio was set to 0.6, it was found that the decreasing rate constant under irradiation with ultraviolet rays was rather reduced, and was almost the same as that of the uncoated one. This suggests that the adsorption of the basic gas by the silica hydrate of the coating layer is important not only in its amount but also in the vicinity of the active site of the photocatalyst.

[0009]

[Detailed description] Titanium oxide having photocatalytic activity includes titanium dioxide, hydrous titanium oxide, metatitanic acid, orthotitanic acid,
It is selected from low titanium oxide and the like. The crystal form may be any of an amorphous form, an anatus form, a rutile form, and a brookite form, but an anatase form having high photocatalytic activity is preferable. The particle diameter is preferably in the range of 1 to 300 nm, particularly preferably 5 to 100 nm. In order to further improve the photocatalytic activity of titanium oxide itself, V, Fe, Co, Ni, Cu, Zn, Ru, Rh,
Titanium oxide carrying or doping a metal or metal compound such as Pt, Pd, Ag or the like may be used.

The coating with silica hydrate is performed by a wet method. It starts with an aqueous slurry of metatitanic acid obtained by the thermal hydrolysis of titanium tetrachloride or titanyl sulphate or an aqueous slurry of ready-made uncoated titanium oxide. A water-soluble silicon compound is added to the slurry, the pH is adjusted to a value at which silica hydrate is precipitated with an acid or a base, and the precipitated silica hydrate is used to coat the titanium oxide particles. Examples of the water-soluble silicon compound include sodium silicate, potassium silicate, and silicon tetrachloride. Sodium silicate such as sodium metasilicate, sodium orthosilicate, sodium disilicate, sodium tetrasilicate, and mixtures thereof are easily available and convenient to handle. As the acid or base, sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, aqueous ammonia or the like is used. The pH of the slurry after neutralization with an acid or a base may be within a range where silica hydrate is precipitated, and is generally in a range of pH 2 to 9.5,
Is the best.

The amount of the water-soluble silicon compound to be added to the slurry, and therefore the coating amount of the silica hydrate, depends on the amount of SiO ₂ and Ti
The weight ratio of SiO ₂ / TiO ₂ converted to O ₂ is 0.01
To 0.5, preferably 0.1 to 0.2. As described above, the basic gas adsorption capacity of the coated titanium oxide photocatalyst increases in proportion to the amount of the coating, but in order for most of it to be adsorbed near the active site of the photocatalyst and decomposed efficiently, The coverage should not be too high. For example SiO ₂ / TiO ₂ weight ratio 0.6 basic gas reduction rate constant of the photocatalyst was coated, even during the black light irradiation SiO ₂ / TiO ₂ weight ratio of 0.1
Of the photocatalyst at the time of irradiation with a fluorescent lamp. In contrast, in order to coat the silica so as to suppress the deterioration of the binder resin of the paint, the weight ratio of SiO ₂ / TiO ₂ must be 1.0 or more.

After coating with silica hydrate, the slurry is filtered and washed with water, and the obtained cake is dried, and then pulverized using a pulverizer such as a sample mill or a steam-flow energy mill to obtain the silica of the present invention. A hydrate-coated titanium oxide photocatalyst is obtained. According to a preferred embodiment, the slurry p
After adjusting the H to 4.0, the slurry is aged for at least 30 minutes before filtration. The coated photocatalyst thus obtained has a specific surface area larger than that of titanium oxide before coating, for example, 100 m ² / g or more. This fact also explains that the silica hydrate of the coating layer contributes to the removal of the basic gas by efficiently supplying the adsorbed basic gas to the active site of the photocatalyst.

The basic gas removing photocatalyst of the present invention has an ability to remove basic gases, such as ammonia and amines, which are sources of unpleasant odors generated in a living environment as long as ultraviolet rays, water and oxygen are continuously supplied. Have. In particular, the ability can be sufficiently exerted even under weak ultraviolet light such as a fluorescent lamp, so that it can be carried or immersed in, for example, wallpaper, curtain, shoji paper, etc., and can be used for deodorizing basic gas. Of course, under strong ultraviolet light such as black light, the effect is more strongly exerted, so that it can be carried on a filter or the like of an air purifier equipped with black light to help remove basic gas. However, it will be necessary to devise a supporting method so that gas adsorption is not hindered.

[0014]

The present invention will be specifically described with reference to the following examples and comparative examples. These are for illustrative purposes and should not be construed as limiting.

Example 1 An aqueous solution of titanyl sulfate was thermally hydrolyzed to give a crystal particle diameter of 6 nm.
Was prepared. This metatitanic acid slurry (100 g / l in terms of TiO ₂ ) 5,000 m
The temperature was raised to 40 ° C. l, sodium silicate as SiO ₂ 200 g / l aqueous solution of 250ml (SiO ₂ / TiO ₂
(Weight ratio = 0.1) was added at a constant rate over 10 minutes. After the addition, the pH is adjusted to 4.0 with sodium hydroxide, and 4
The mixture was stirred for 30 minutes while maintaining 0 ° C. Thereafter, the slurry was filtered and washed with water, and the obtained cake was dried at 110 ° C. for 12 hours and pulverized using a sample mill. Table 1 summarizes the general characteristics of the obtained powder.

Example 2 In Example 1, the addition amount of a sodium silicate solution having a concentration of 200 g / l as SiO ₂ was 25 ml (SiO ₂ /
TiO ₂ weight ratio = 0.01), and otherwise the same processing as in Example 1 was performed. Table 1 summarizes the general characteristics of the obtained powder.

Example 3 In Example 1, the same treatment as in Example 1 was performed except that the slurry was changed to a metasilicate slurry having a crystal particle diameter of 30 nm. Table 1 summarizes the general characteristics of the obtained powder.

Comparative Example 1 The same treatment as in Example 1 was performed, except that the aqueous solution of sodium silicate was not added. Table 1 summarizes the general characteristics of the obtained powder.

[0019] In Comparative Example 2 Example 1, the amount of sodium silicate solution 200 g / l concentration as SiO ₂ 750 ml (SiO ₂
/ TiO ₂ weight ratio = 0.6), except that the same treatment as in Example 1 was performed. Table 1 summarizes the general characteristics of the obtained powder.

Comparative Example 3 Titanium dioxide P-25 manufactured by Nippon Aerosil Co., Ltd.
2 nm) was used as is.

[0021]

[Table 1]

Evaluation of Performance of Removing Odor Gas from Powder The powders of Examples and Comparative Examples were evaluated for the performance of removing ammonia as a base gas and the performance of removing methyl mercaptan as an acid gas for reference.

1. The target gas diluted with air in advance is injected into a 3 L capacity bag, and the gas concentration is confirmed by a gas detection tube. 2. Spread the powder evenly on the sample table in the smell bag, taking care not to let the injected gas escape. 3. The odor bag is left in a dark place at a temperature of 30 ° C. and a relative humidity of 50%. 4. Confirm that the gas concentration in the odor bag has reached the adsorption equilibrium, and record the gas concentration A after adsorption. 5. Place the odor bag directly under the black light (40W) or fluorescent light (40W) and use the UV intensity (TOPCON
UVR-2, measured by the light receiving unit UD-25, UD-36) is the case of the black light 1.0 mW / cm ^2, in the case of fluorescent lamp adjusted to be 0.03 mW / cm ^2. 6. The light irradiation is started, and the residual gas concentrations B at 1 hour, 2 hours and 3 hours are measured by a gas detector tube. 7. From the gas concentration A (ppm) before the light irradiation after adsorption and the residual gas concentration B (ppm) after the light irradiation, 1n (A / B) at each irradiation time is calculated, and the horizontal axis is represented by the time coordinate. Plot, connect with a first-order approximation straight line passing through the origin,
The slope of this straight line is defined as a decreasing rate constant. The higher the constant, the greater the rate of gas reduction by the photocatalytic reaction.

Table 2 shows test conditions for each target gas in the above test method, and Table 3 shows the results.

[0025]

[Table 2]

[0026]

[Table 3]

[0027] Discussion reduction rate constant towards numbers in shows the decreasing rate of the gas by the photocatalytic activity is high has a high photocatalytic activity. When comparing the reduction rate constants of ammonia gas, which is a basic gas, in the evaluation of the photocatalyst with powder, the results of Example 1 were obtained under both the conditions of strong ultraviolet light of black light and weak ultraviolet light of fluorescent light.
To 3 show higher values than Comparative Examples 1 to 3. Further, in Comparative Examples 1 to 3, the removal effect developed under strong ultraviolet light of black light was obtained under weak ultraviolet light of the fluorescent lamps of Examples 1 to 3.

Further, from the results of the concentration after adsorption of ammonia gas, it was confirmed that Examples 1 to 3 have much higher ammonia gas adsorption ability than Comparative Examples 1 to 3.

However, when evaluated with methyl mercaptan gas, which is an acid gas, under strong ultraviolet light of black light,
Under both conditions under the weak ultraviolet light of a fluorescent lamp, although better than P-25 of Comparative Example 3, there was no great difference between Examples 1 to 3 and Comparative Example 1.

From these results, it was confirmed that the titanium oxide of the present invention exhibited extremely high photocatalytic activity and adsorption ability with respect to basic gases, particularly ammonia gas.

Example 4 The photocatalyst powder obtained in Example 1 was rubbed into paper by the following method to prepare a paper containing titanium oxide.

1. Pulp 18 in 300ml beaker
g and 80 ml of water were added and stirred for 3 minutes to obtain a pulp slurry. 2. 7.2 g of a 1% diluted solution of Carterentin F (cationic fixing agent) was added, followed by stirring for 2 minutes. 3. 18 g of a 5% slurry of the photocatalyst powder of Example 1 was added and stirred for 1 minute. 4. EPINOX WS-500 (paper strength improver) 1%
7.2 g of the diluted solution was added and stirred for 1 minute. 5. 1.8 g of a 2% sulfuric acid band slurry was added and stirred for 1 minute. 6. The suspension was diluted to 1500 ml with water, paper-made using a sheet machine, and dried in a dryer for 1 hour.

Comparative Example 4 A titanium oxide-containing paper was prepared in the same manner as in Example 4, except that the powder of Comparative Example 1 was used instead of the powder of Example 1.

Comparative Example 5 A titanium oxide-containing paper was prepared in the same manner as in Example 4 except that the powder (P-25) of Comparative Example 3 was used instead of the powder of Example 1. Created.

Evaluation of the Odor Gas Removal Performance of the Titanium Oxide-Containing Paper The odor gas removal performance of the titanium oxide-containing paper was evaluated according to the test method previously performed on the powder. However, in this case, the sample was cut into a size of 5 × 10 cm, placed directly in an odor bag, and the initial injection amounts of ammonia and methyl mercaptan gas were both set to 30 ppm. No. 3L was prepared as No. 3 for methyl mercaptan gas. 71 (both manufactured by GASTEC) were used. Table 4 shows the results.

[0036]

[Table 4]

Discussion The same results as the test results for the powders shown in Table 3 were obtained for the paper containing titanium oxide.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenichi Konoji 1-3-47, Funamachi, Taisho-ku, Osaka City, Osaka Prefecture F-term (reference) 4C080 AA07 BB02 CC08 CC09 HH05 JJ04 KK08 LL03 MM02 NN06 QQ20 4D048 AA17 BA06X BA06Y BA07X BA07Y BA41X BA41Y BB17 BC07 EA01 EA04 4G069 AA02 AA03 AA08 BA02A BA02B BA04A BA04B BA48A CA11 EC03X EC03Y EE01

Claims (6)

[Claims] 1. A core comprising titanium oxide particles having photocatalytic activity, and a coating layer of silica hydrate surrounding the core. The coating layer selectively adsorbs a basic gas to form a titanium oxide core. A titanium oxide photocatalyst for removing basic gas, characterized in that it functions to enhance the basic gas removing ability of the entire photocatalyst by efficiently supplying the active site to an active site. 2. Core comprising titanium oxide particles having photocatalytic activity
And this is replaced by SiO_TwoAnd TiO _TwoSiO converted to
_Two/ TiO_TwoSo that the weight ratio becomes 0.01 to 0.5
Silica hydrate coated titanium oxide for removal of basic gas
Photocatalyst. 3. The titanium oxide photocatalyst according to claim 1, wherein the specific surface area is at least 100 m ² / g. 4. The method for removing a basic gas according to claim 1, wherein the coating of the silica hydrate is carried out by decomposing a silicon compound dissolved in an aqueous slurry of titanium oxide particles into a silica hydrate with an acid or a base. Titanium oxide photocatalyst. 5. The photocatalyst according to claim 1, wherein said photocatalyst is in the presence of oxygen and water.
Contact with basic gas in the presence _TwoBand gap
Characterized by irradiating with light having higher energy
Basic gas removal method. 6. A photocatalytic reaction element for removing a basic gas, comprising a substrate carrying the photocatalyst according to claim 1.