JP3538635B2 - Manufacturing method of harmful chemical substance removing material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent and porous porous material having a high adsorptive capacity and a photocatalytic ability, which can quickly adsorb harmful chemical substances in a house or the environment and can detoxify it by photolysis. The present invention relates to a method for preparing a high quality adsorptive photodecomposable material and an adsorptive photodecomposable material obtained by this method.

[0002]

2. Description of the Related Art Heretofore, as an example of using a photocatalyst such as titania for removing harmful chemical substances in combination with various materials having an adsorbing ability, a method of preparing a composite of a metal oxide sol and a photocatalyst (see, for example, Kaihei 9-299809), a method of compounding as a clay mineral (JP-A-9-29016)
4) There are many examples such as a method in which the silica gel is impregnated with a titanium-containing solution and then fired.

[0003]

It is known that titania photocatalyst has a high photocatalytic activity for decomposing harmful substances. However, crystalline titania catalyst does not have a large specific surface area and has a low surface activity. Therefore, there has been a problem that the adsorption process of the harmful substance often becomes a rate-determining process of the total decomposition process because of its low concentration. In addition, the crystalline titania catalyst is usually obtained as a fine powder and has difficulty in handling. For this reason, as in the above example, attempts have been made to combine the photocatalyst with a porous body having a high adsorptivity to increase the removal ability and to facilitate handling. However, these methods make it difficult to obtain a material with a high porosity, and especially when removing dilute harmful substances in the atmosphere, diffusion in the material is limited, so that the adsorption capacity and the adsorption speed are not sufficient. There were many. In addition, in order to increase the specific surface area and light absorption, they are often used after being formed into pellets, powders, or honeycombs, and the form of use is often limited.

Accordingly, the present invention provides a monolith having a highly porous and highly harmful substance adsorbing ability and a photocatalytic ability for detoxifying the adsorbed substance, having high transparency, and a highly fused photocatalyst and adsorbent. It is an object to obtain a harmful chemical substance removing material that can be prepared.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention impregnates a wet gel of silica with a titanium compound and impregnates the alcohol, which is liable to decompose, dissolve and reprecipitate the titanium compound, into a dry medium. Performing the critical point or supercritical drying using, or, using a non-combustible drying medium such as carbon dioxide, by performing the critical point or supercritical drying at a temperature at which the decomposition of the titanium compound proceeds, to obtain crystalline titania Disclosed is a method for producing a harmful chemical substance removing material, which is formed on a highly porous silica skeleton.

The type and preparation method of the silica wet gel body in the present invention are not particularly limited as long as it is a jelly-like substance containing silica as a main component and containing no solvent therein.
Specific examples include, for example, a silica wet gel obtained by hydrolysis using tetramethoxysilane in the presence of a base catalyst such as ammonia or an acid catalyst such as hydrochloric acid, and a solution of sodium silicate (water glass) with hydrochloric acid or the like. A silica wet gel obtained by adding an acid is used.

[0007] These silica wet gels are impregnated with a solvent dissolving the titanium compound or a solvent having an affinity for the titanium compound to replace the internal solvent. The solvent may be appropriately selected according to the properties of the titanium compound. For example, in the case of titanium alkoxide, an alcohol corresponding to the number of carbon atoms of the alkoxyl group is used.

Next, these silica wet gels are impregnated with a solvent containing a titanium compound to support the titanium compound on the surface of the skeleton. It is also possible to impregnate the drying medium containing the titanium compound more quickly and homogeneously at a critical point or supercritical state. The type of the titanium compound is not particularly limited as long as it is a substance that is supported by reacting or adsorbing with the silica wet gel. Specific examples include alkoxides such as titanium tetraisopropoxide, complexes obtained by modifying them with an appropriate ligand, titanium complexes such as titanylacetylacetonate and derivatives thereof, and the like.

The above silica wet gel supporting titanium compound is dried by a critical point or supercritical drying method using alcohols, or at a temperature not lower than the temperature at which the titanium compound is decomposed using carbon dioxide or the like. It is dried by a critical point or supercritical drying method. Since the drying is performed near the critical point or in a supercritical state, the silica wet gel skeleton is hardly affected by shrinkage due to interfacial tension and can be obtained in a very porous dry gel state.

[0010] In the critical point or supercritical drying method using alcohols, the type of alcohol is not particularly limited as long as it does not dissolve the silica wet gel and has an affinity for the titanium compound. Generally, ethanol, 1-propanol, 2-propanol and the like are used, but methanol is not preferred because it has a large effect of dissolving the silica wet gel.

In the critical point or supercritical drying method performed at a temperature higher than the temperature at which the titanium compound decomposes, the drying medium is not particularly limited as long as it is stable at the decomposition temperature of the titanium compound and does not impair the silica wet gel body. . For example, carbon dioxide, chlorofluorocarbon, acetone, and mixtures thereof, or mixtures of these and alcohols are used.

The titanium compound supported on the silica wet gel body is precipitated on the silica skeleton as crystalline titania through processes such as dissolution, hydrolysis or thermal decomposition, reprecipitation due to a decrease in solubility, and crystallization during drying. I do. This crystalline titania is usually obtained as an anatase type having high photocatalytic activity.

[0013] The optimum drying conditions are determined by the critical point of the drying medium and the properties of the titanium compound. For example, when titanium tetraisopropoxide-acetylacetonate is used as the titanium compound and ethanol is used as the drying medium, the conditions at 250-280 ° C. and about 90-110 atm are used, and titanium tetraisopropoxide-acetylacetonato is used as the titanium compound. When carbon dioxide is used as a drying medium, the conditions are preferably 280-310 ° C. and 90-160 atm.

The dried gel obtained by the critical point or supercritical drying is usually at 500 ° C. in air to remove organic residues.
Heat treatment is performed for about 1-2 hours. High heat treatment temperature,
Alternatively, if the time is long, the porosity decreases due to the shrinkage of the gel body. Therefore, it is desirable to perform the treatment at a temperature as low as possible for a short time.

The dry gel thus obtained has a remarkable porosity in which more than 90% of the total volume is voids, a huge specific surface area, and has the photocatalytic activity of titania. Further, this gel body has extremely high transparency and does not inhibit light absorption of titania. Depending on the preparation method, titania is number 1
Fine crystals with a size of 0 nm or less can be obtained, and since they are highly dispersed in the silica skeleton, problems such as peeling do not occur. Further, this gel body can be easily obtained as a transparent monolithic shape, and can be given an arbitrary shape.

The dried gel body can adsorb harmful substances on the surface of its skeleton by bringing it into contact with air containing harmful substances. Since the porosity and critical area of the obtained gel body are large, the adsorption speed and adsorption capacity of harmful substances are very large. The adsorbed harmful substances can be decomposed into carbon dioxide by light irradiation. Therefore, for example, it is installed in a place exposed to light in a living space, and used as an air purifier that permanently absorbs and decomposes harmful substances that cause sick house syndrome, or uses harmful chemical substances released in high concentrations due to accidents etc. The present invention can be applied to uses such as a contamination treatment material which is quickly adsorbed and fixed and then rendered harmless by light irradiation.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention are as follows. (1) A harmful effect of impregnating a wet gel body of silica with a titanium compound solution and then using a drying medium at a critical point or supercritical of the drying medium to form crystalline titania on the silica skeleton. A method for producing a porous gel for a chemical substance removing material. (2) wet gel of silica to the titanium compound solution is impregnated in a critical point or supercritical solvent and then titanium
Mixture using a solvent and drying medium compound solution, the
A method for producing a porous gel for a harmful chemical substance removing material, wherein crystalline titania is formed on a silica skeleton by drying at a critical point or supercritical of a mixture . (3) The method for producing a porous gel for a toxic chemical substance removing material according to the above (1) or (2), wherein the porous gel is dried at a temperature not lower than a temperature at which a decomposition reaction of a titanium compound proceeds and at a critical point or supercritical of a drying medium. (4) The method for producing a porous gel for a harmful chemical substance removing material according to any one of (1) to (3) above, wherein a step of heating and removing organic substances is provided after the drying step. (5) A titanium compound is a metal alkoxide represented by titanium tetraisopropoxide, titanium tetraethoxide, titanium tetramethoxide, a complex obtained by modifying them with a ligand, a metal acetyl represented by titanyl acetylacetonate A method for producing a material for removing airborne harmful chemical substances corresponding to any one of the above items 1 to 4, which is any one of acetonate and derivatives thereof. (6) The drying medium is ethanol, 1-propanol, 2
One or more of alcohols represented by propanol and / or carbon dioxide,
The method for producing a harmful chemical substance removing material according to any one of the above. (7) The material for removing harmful chemical substances according to any one of (1) to (4) above, wherein the solvent of the titanium compound solution is one or more of alcohols represented by ethanol, 1-propanol and 2-propanol. Manufacturing method.
(8) The method for producing a harmful chemical substance removing material as described in any one of (1) to (7) above, wherein the silica wet gel is an alcogel. (9) The material for removing harmful chemical substances according to any one of the above-mentioned items 1 to 8.

By drying the silica wet gel at a critical point or by supercritical drying, shrinkage due to interfacial tension can be avoided, and a remarkably porous transparent skeleton having a high specific surface area can be obtained. This silica skeleton has a high surface activity and has a high adsorption capacity for harmful substances. The titanium compound supported on the silica wet gel is dissolved in a solvent contained in the drying medium or the wet gel in the vicinity of the silica skeleton by selecting appropriate conditions during drying, undergoes hydrolysis or thermal decomposition, and has a solubility of By lowering, it precipitates as crystalline titania on the silica skeleton. Since the silica skeleton functions as a carrier for preventing aggregation of the titanium component, titania is dispersed in an extremely fine state, exhibits high photocatalytic activity, and does not impair the transparency or adsorption ability of the obtained gel. The harmful substances in the air adsorbed on the silica skeleton move to the titania surface by surface diffusion or the like, and are completely decomposed into carbon dioxide by light irradiation.

In the present invention, it is important to set conditions under which the process of dissolving and reprecipitating the titanium compound functions properly during the drying process. For example, if the drying medium has a large effect of dissolving the silica skeleton, the titania peels off from the skeleton. If the titanium compound is not decomposed in the drying process,
The titanium compound is retained as it is on the silica skeleton. Although it is possible to crystallize by heat treatment after drying, the rearrangement of atoms in the solid state is difficult to proceed, so processing at a high temperature is required, and the porosity is significantly reduced due to shrinkage of the silica skeleton. . When alcohols are used as a medium for supercritical drying, crystalline titania is effectively produced because the critical conditions and properties as a solvent are suitable for the progress of the above-mentioned dissolution-reprecipitation process. In addition, even when a drying medium other than alcohol, such as carbon dioxide, is used, if the conditions under which the decomposition of the titanium compound proceeds during the drying process, the process of dissolution-reprecipitation due to the action of the solvent that slightly remains in the wet gel can be reduced. proceed.

[0020]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention should not be limited by these. <Example 1> Tetramethoxysilane, methanol, 0.1.
0135 mol / l aqueous ammonia solution in a volume ratio of 2: 4:
1 at 20 ° C., 30 mm inner diameter, 10 depth
It was poured into a vessel having a diameter of 2 mm and allowed to stand to obtain a wet gel of silica. The gel was sealed and aged at 60 ° C. for 48 hours. Then, it was impregnated with 2-propanol for 24 hours to replace the internal solvent.

This silica wet gel was added at 1.24 mol /
l of titanium tetraisopropoxide-acetylacetonate in 2-propanol for 24 hours to support the titanium compound. Next, in a 500 ml pressure vessel, the above three silica wet gel bodies and 210 ml of an ethanol solution were added.
And sealed and heated to a supercritical state of 280 ° C. and 110 atm.

Next, while maintaining the temperature inside the pressure vessel,
Ethanol was gradually removed so that the pressure was reduced to 1 atm per minute, the pressure was returned to normal pressure, and the mixture was cooled to obtain a dried gel. The dried gel body was calcined at 500 ° C. in air to remove organic substances to obtain a sample A.

Example 2 Three titanium compound-impregnated silica wet gels prepared in the same manner as in Example 1 were mixed with 50 ml
Into a pressure vessel together with 25 ml of a 2-propanol solution.
A two-component supercritical state at ℃. The pressure in the pressure vessel was kept constant with a pressure regulator. Subsequently, supercritical carbon dioxide was allowed to flow at 2 ml per minute for 3 hours to remove the remaining 2-propanol and the titanium compound from the inside of the vessel, and the pressure vessel was made to contain only supercritical carbon dioxide. From this state, raise the temperature to 280 ° C, and while maintaining this temperature,
Carbon dioxide was gradually removed so that the pressure was reduced to 1 atm per minute, and the pressure was reduced to normal pressure to obtain a dried gel. Thereafter, heat treatment was performed in the same manner as in Example 1 to obtain Sample B.

<Comparative Example 1> In Example 2, after the pressure vessel was made to contain only supercritical carbon dioxide, the temperature was increased to 8%.
In the same manner as in Example 2 except that the pressure was reduced at 0 ° C,
Sample C was obtained. At this temperature, titanium tetraisopropoxide-acetylacetonato is stable.

Comparative Example 2 Crystalline titania P-25 manufactured by Degussa, which is commercially available for photocatalytic reaction, was added at 150 ° C.
Sample D was obtained by vacuum drying for 4 hours.

When the samples A, B, and C were evaluated by the powder X-ray diffraction method, A and B contained crystals of anatase having high photocatalytic activity. A prepared by ethanol supercritical drying, which has a large contribution to the dissolution-reprecipitation mechanism, had a higher crystallinity than B prepared by carbon dioxide supercritical drying.
On the other hand, Sample C was amorphous despite being heat-treated at 500 ° C. This indicates that the production method of the present invention is effective for obtaining a harmful substance remover having high photocatalytic activity.

Table 1 summarizes the specific surface area of each of Samples A, B, C and D measured by the nitrogen adsorption method and the benzene adsorption capacity at 30 ° C. measured by the vapor adsorption method. Samples A, B, and C show a specific surface area and a benzene adsorption capacity of 10 times or more as compared with commercially available crystalline titania, and the harmful substance remover of the present invention has a high effect of removing harmful substances by adsorption. I understood.

[0028]

[Table 1]

The ability to remove harmful substances by photocatalysis was evaluated according to the following procedure. Sample A, B, C 0.2g each
After crushing, the mixture was mixed with 20 g of glass beads having a diameter of 0.5 mm and held in a glass reaction tube, and humid air containing 100 ppm of benzene was passed at a flow rate of 30 ml / min to completely saturate the benzene on the sample surface and to adsorb the sample. Eliminated effects. In this state, the reaction tube was irradiated with 4 W of black light, the benzene concentration was measured by gas chromatography at the inlet side and the outlet side of the reaction tube, and the benzene decomposition rate was calculated from the ratio between the two. On the outlet side, the concentration of carbon dioxide generated by the decomposition of benzene is measured,
This is also summarized in Table 2. For sample D, 0.06 g of the sample was taken so that the total amount of titania was equal to that of samples A to C, and the other samples were evaluated in the same manner as samples A to C.

[0030]

[Table 2]

As shown in Table 2, Samples A and B containing crystalline anatase show a high benzene decomposition rate and a high carbon dioxide concentration, and the photodegradation ability of the harmful substance removing agent obtained in the present invention was confirmed. did it. From the above results, it was found that the harmful substance removing agent of the present invention has an excellent ability to remove harmful substances.

[0032]

According to the present invention, it is possible to obtain a transparent and easy-to-shape removing material for harmful chemical substances, which is extremely porous and has both a high adsorptivity for harmful substances and optical resolution.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B01J 20/30 B01J 20/30 35/02 ZAB 35/02 ZABJ 37/02 101 37/02 101E C07B 37/06 C07B 37/06 C07C 15/04 C07C 15/04 (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53 / 86,53 / 94

Claims (9)

(57) [Claims] 1. A wet gel body of silica is impregnated with a titanium compound solution, and then dried using a drying medium at a critical point or supercritical of the drying medium to produce crystalline titania on a silica skeleton. Of producing a porous gel for a harmful chemical substance removing material. 2. A wet gel body of silica is impregnated with a titanium compound solution at a critical point or supercritical point of a solvent.
Using a mixture of a solvent of a titanium compound solution and a drying medium, drying at the critical point or supercritical point of the mixture to form crystalline titania on a silica skeleton. Manufacturing method. 3. At a temperature not lower than the temperature at which the decomposition reaction of the titanium compound proceeds and at a critical point or supercritical of the drying medium,
The method for producing a porous gel for a harmful chemical substance removing material according to claim 1 or 2, wherein the porous gel is dried. 4. The method for producing a porous gel for a harmful chemical substance removing material according to claim 1, wherein a step of removing organic substances by heating is provided after the drying step. 5. A titanium compound represented by a metal alkoxide represented by titanium tetraisopropoxide, titanium tetraethoxide and titanium tetramethoxide, a complex obtained by modifying the metal alkoxide with a ligand, and titanyl acetylacetonate. The method for producing a material for removing atmospheric harmful chemical substances according to any one of claims 1 to 4, which is one of metal acetylacetonate and a derivative thereof. 6. The method according to claim 1, wherein the drying medium is one or more alcohols represented by ethanol, 1-propanol and 2-propanol, and / or carbon dioxide. Manufacturing method of the used harmful chemical substance removing material. 7. The solvent of the titanium compound solution is ethanol,
The method for producing a harmful chemical substance removing material according to any one of claims 1 to 4, which is one or more of alcohols represented by 1-propanol and 2-propanol. 8. The method for producing a harmful chemical substance removing material according to claim 1, wherein the wet gel of silica is an alcogel. 9. A material for removing harmful chemical substances according to any one of claims 1 to 8.