JP2007083146A - Method for preparing photocatalyst using ceramic foam, and photocatalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a photocatalyst comprising a titanium complex derived from titanium oxide using a dehydrated cake. <P>SOLUTION: The method for preparing a photocatalyst using a ceramic foam according to the present invention is characterized by comprising steps of preparing a slurry by adding a titanium complex solution, a carbonate, and hydrogen peroxide water to a dehydrated cake, filling a mold with the resulting slurry to form an article, releasing the molded article from the mold, drying the molded article under vacuum at a low temperature, and sintering the dried article at a temperature of 500°C to 700°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a photocatalyst using a foam ceramic and a photocatalyst using a foam ceramic that produces a titanium oxide composite foam ceramic mainly using a dehydrated cake generated in large quantities from a quarry.

  There have been many researches and developments regarding the effective use of dehydrated cake generated in large quantities from quarries, and there are also proposals for producing foam ceramics using the dehydrated cake as a raw material.

  It is also known to use ceramics as a catalyst carrier, and research on solidification of ceramics has been carried out. However, technology for making porous by firing with titanium for use in waste catalysts such as dehydrated cakes and low-temperature sintered bodies ( For example, sintering at 500 ° C. to 700 ° C. is not yet known.

In addition, the technology of using foam ceramics as a catalyst was also a research subject for photocatalyst titanium oxide.
JP 2001-269574 A JP 2003-210997 A JP 2001-205100 A JP 2001-198475 A

  Conventionally, dehydrated cakes generated in large quantities in quarries, etc., have been used as building materials as foam ceramics, but we have also studied to add more value and consume them in large quantities. I came up with it. However, when titanium oxide is used as a conventional photocatalyst, the dehydrated cake was sintered at 600 ° C. to 900 ° C., and titanium oxide was adhered thereto. However, further research was needed to improve the catalytic ability. .

  In addition, when glaze is put in ceramics, there is a problem that the catalytic ability is lowered.

  The invention described in the prior patent publication employs means for mixing ceramic, titanium oxide grains, molding, and sintering, but in the conventionally known manufacturing method, sintering is performed at 900 ° C. or lower. (Patent Documents 1 and 3).

  Moreover, the sintering temperature of the titanium oxide sintered body may be set to 500 ° C. to 1100 ° C. (Patent Document 2).

  Furthermore, there is also a proposal that the sintering of the titanium oxide porous ceramic body is 400 ° C. to 850 ° C. (Patent Document 4). However, many of the above are different in the ceramic component from the present invention, and there is an opening of 400 ° C. to 1100 ° C. about the sintering temperature. In sintering (for example, 800 ° C. or higher), the catalyst function may be lowered.

However, the present invention solves the above-mentioned conventional problems by allowing carbonate (low melting point substance) to be mixed in the dehydrated cake so that sintering can be performed at 500 ° C. to 700 ° C. When the sintering temperature is set to 400 ° C. to 500 ° C., it is recognized that the solidified foam ceramics collapses in water, and when it exceeds 700 ° C., the catalytic function of titanium oxide is reduced. Therefore, although variation may be considered depending on the material, in the case of the components shown in Table 1, it is considered that the sintering temperature should be higher than 500 ° C. and lower than 700 ° C.

  That is, in this invention, a titanium complex solution, carbonate and hydrogen peroxide solution are added to a dehydrated cake to form a slurry, and the slurry is put into a mold and molded, then demolded, and the molded product is dried at a low temperature under reduced pressure. Then, it is a manufacturing method of a photocatalyst using foam ceramics characterized by sintering at 500 ° C. to 700 ° C., and a titanium complex solution (Ti 1 mol / ml) is 20% to 40% wt with respect to the dehydrated cake. In addition, the carbonates are potassium carbonate, sodium carbonate, and calcium carbonate, and 5% to 30 wt% of each is used, and 10% to 30 wt% of 3% hydrogen peroxide is used.

  Further, the low-temperature low-pressure drying is performed at a pressure of −0.2 to −0.05 Pa and a temperature of 60 to 90 ° C., and the titanium complex solution is a citric acid solution, titanium (IV) sulfate, 3% hydrogen peroxide. The photocatalyst is produced by mixing equal amounts of water and aqueous ammonia. Another invention is a photocatalyst produced by the method according to claim 1.

  When the sintering temperature of the catalyst in the invention is less than 500 ° C., it collapses when the catalyst is put in water, and when it exceeds 700 ° C., a decrease in the photocatalytic ability is recognized, so the temperature is set to 500 ° C. to 700 ° C.

  Moreover, since the porosity becomes 70% or less in the normal pressure drying at the time of drying, the pressure is reduced to -0.2 to -0.05 Pa by drying. From the relationship of porosity, it was recognized that excessive decompression was unnecessary.

  Titanium oxide used in the present invention is a typical semiconductor material that is active by absorbing ultraviolet rays, and is effective in purifying water or air.

  In general, it is considered that the firing temperature of a ceramic carrier mainly composed of a dehydrated cake is 900 ° C. to 1000 ° C., but the firing temperature of the ceramic containing titanium oxide is preferably 500 ° C. or more and 700 ° C. or less.

  Therefore, in order to sinter a mixture of ceramics and titanium oxide, the strength that can withstand a catalyst such as ordinary water purification at a temperature at which the sintering temperature does not adversely affect the catalyst is preferable, and thus the temperature is 500 ° C to 700 ° C.

  In the invention, the effective use of the dehydrated cake generated in large quantities from the quarry is being studied, and the foam is mainly composed of dehydrated cake that is fine crushed stone for the purpose of agricultural horticulture, building materials and environmental purification. We are considering the production of ceramics. As a feature of this manufacturing process, by adding hydrogen peroxide as a foaming aid, the components contained in the dehydrated cake are foamed, which has the advantage of uniform air bubbles and is extremely simple and easy to manufacture. is there. Conventionally, a foam having a porosity of 50% to 60% can be produced by adding 3% hydrogen peroxide water to the foaming aid and adding glaze to the sintering aid and baking at 800 ° C. for 1 hour. Further, as an application to the environmental purification field, it is possible to impart photocatalytic properties to foam ceramics by utilizing the complex forming ability of titanium and hydrogen peroxide solution.

Further, by using a glaze as a conventional sintering aid, the amount of titanium oxide (TiO ₂ ) exposed on the surface is reduced and the photocatalytic property is reduced, and foam ceramics having a higher porosity The production conditions were studied, and photocatalytic properties were imparted by mixing a dehydrated cake and a titanium complex solution to study photomixing properties.

  In the present invention, a 3% hydrogen peroxide solution and water were mixed to form a slurry so that the total amount of water was 40 wt% with respect to the dehydrated cake. At this time, if the added amount of the hydrogen peroxide solution is small, foaming does not occur, and if the added amount is large, the pores are crushed by its own weight during foaming. This is the same even when the hydrogen peroxide concentration is increased. Therefore, the best slurrying condition was set to 40 wt% of the total water amount of 3% hydrogen peroxide water 10wt% and water 30wt% with respect to the dehydrated cake. After slurrying at this mixing ratio, the foamed ceramic of the present invention was produced by molding, drying, releasing, and firing in the air.

In this invention, a sintering aid was selected in place of the glaze for lowering the solidification temperature, and the influence of each component on the solidification temperature was studied, as well as the influence on the porosity.
In addition, for imparting photocatalytic properties, titanium sulfate (IV) and hydrogen peroxide water, and further complex forming agents, citric acid and ammonia water are added to form a titanium complex solution, and this titanium complex solution is added to a dehydrated cake as a slurry. A mixing method for producing foam ceramics was investigated. Further, EPMA analysis was performed to confirm the TiO _{2 on} the exposed surface.

The main components of the dehydrated cake are SiO ₂ and Al ₂ O ₃ as shown in the chemical composition of Table 1 above. The melting point of the dehydrated cake was between 1300 ° C and 1400 ° C. Therefore, the components that can lower the melting point were investigated based on the phase diagram. Consequently _{SiO 2 -Al 2 O 3 -CaO,} SiO 2 -Al 2 O 3 -K 2 O, that a low melting point composition in each state diagram of _{SiO 2 -Al 2 O 3 -Na 2} O was confirmed . Therefore, the possibility of low-temperature solidification was examined by adding CaCO ₃ , K ₂ CO ₃ , and Na ₂ CO ₃ as sintering aids. The effect of the addition of these carbonates on the porosity of the foam was also investigated. The mineral composition in this case is as shown in Table 2.

  The foam produced by adding 10 wt% of calcium carbonate to the dehydrated cake solidified at a baking temperature of 500 ° C., but collapsed as soon as it was put in water. Foams prepared by adding 10% by weight of potassium carbonate and sodium carbonate, respectively, produced at a firing temperature of 500 ° C. did not collapse even in water. Furthermore, in order to solidify at low temperature, the addition amount of potassium carbonate and sodium carbonate was increased to 20 wt% and 30 wt%, and the baking was carried out at 400 ° C, but it collapsed. Next, instead of 800 ° C. when glaze was used, it was possible to reduce the firing temperature to 500 ° C. by adding potassium carbonate, calcium carbonate, and sodium carbonate.

  When the change in the porosity due to these carbonates was examined, the porosity of the foam ceramic produced without adding the sintering aid was 60% to 70%. When the glaze is added, the glaze melts and the pores are blocked, so the porosity is reduced by nearly 10%. However, it has been found that the addition of carbonate increases the porosity to around 80% due to the generation of carbon dioxide. FIG. 3 and FIG. 4 show the pore state observed with a stereomicroscope and SEM. There are continuous pores. In addition, the surface of the foam was very uneven by SEM observation, and small pores could be confirmed. It was confirmed that the foam ceramic added with these sintering aids greatly improved the porosity and floated on water.

  According to this invention, a dehydrated cake, a titanium complex solution, a carbonate, and a hydrogen peroxide solution were added to form a slurry. Since the mixture of this slurry and titanium oxide powder was molded, dried, and sintered, titanium oxide adhered to the catalyst carrier reliably and over a wide area, so that decolorization and other catalytic effects were significantly increased.

  Moreover, since sintering temperature was 500 degreeC-700 degreeC, even if it puts in water, catalyst efficacy can also be maintained, without collapsing. Therefore, when this catalyst is used, there is an effect that a decolorization rate (effect) of 70% to 80% can be achieved upon irradiation with ultraviolet rays (sunlight).

  In the present invention, a citric acid solution is added as a complex-forming agent to a mixed solution of titanium sulfate and 3% hydrogen peroxide water, and ammonia water is added thereto to prepare a yellow titanium complex solution. A dehydrated cake and 20 wt% potassium carbonate, sodium carbonate and calcium carbonate were added to the titanium complex solution to form a slurry, which was put into a mold and molded. Then, after drying in a reduced pressure atmosphere of −0.05 MPa at 80 ° C. for 1 hour, heat treatment was carried out at 500 ° C. for 5 hours to obtain a photocatalyst of the present invention in which a foam ceramic having a porosity of 80% and titanium oxide were combined.

  In the above, the porosity was 70% in the normal pressure drying, but the porosity was 80% in the vacuum drying in the atmosphere of -0.05 MPa.

  In the present invention, the photocatalytic property is imparted by adding 10 ml (1 mol / l) of citric acid solution as a complexing agent to a mixed solution of 10 ml of commercially available titanium sulfate (IV) and 10 ml of 3% hydrogen peroxide solution, and further adding 10 ml of aqueous ammonia. In addition, a yellow titanium complex solution was prepared.

  As a photocatalytic property imparting method using this complex, a mixing method was examined. FIG. 5 shows the application method.

  As a mixing method, a foam was prepared by adding a titanium complex and carbonate to a dehydrated cake. Even when only the titanium complex was added to the dehydrated cake, foaming did not occur and the porosity was around 30%. Therefore, 3% hydrogen peroxide solution and titanium complex were added, mixed and stirred, and fired as a slurry to produce foam ceramics. The porosity at this time was about 80%, and a foam having a high porosity was obtained. As the carbonate, 20 wt% of potassium carbonate, sodium carbonate and calcium carbonate were used.

The foam prepared by mixing the titanium sulfate and hydrogen peroxide water complex using glaze as a sintering aid described above showed a decolorization rate of about 40% in 20 hours. On the other hand, the foam obtained by mixing and stirring the complex added with citric acid and solidifying at a low temperature showed a decolorization rate of about 70% in 20 hours. As a result of EPMA analysis of the foam surface, the presence of TiO ₂ was confirmed throughout.

Next, considering that the foam was crushed and used, the foam was cut to expose TiO ₂ inside, and the cross section was irradiated with black light to evaluate photocatalytic properties. As a result, the color removal rate was about 70%.

The microscope picture of the state which coat | covered the pore of the molded object of the ceramic foam of this invention. A photomicrograph with the pores open. Photomicrograph Similarly, a partial SEM photograph of FIG. The block diagram of an Example similarly.

Claims (5)

  A titanium complex solution, carbonate and hydrogen peroxide solution are added to the dehydrated cake to form a slurry. After the slurry is put in a mold and molded, the mold is removed, and the molded product is dried at a low temperature under reduced pressure. A method for producing a photocatalyst using foam ceramics, characterized by sintering at 700 ° C.   Titanium complex solution (Ti 1 mol / ml) is added to the dehydrated cake in an amount of 20% to 40 wt%, and the carbonates are potassium carbonate, sodium carbonate and calcium carbonate. The method for producing a photocatalyst using the foamed ceramic according to claim 1, wherein water is used in an amount of 10% to 30 wt%.   The method for producing a photocatalyst according to claim 1, wherein the low-pressure drying under reduced pressure is performed at a pressure of -0.2 to -0.05 Pa and a temperature of 60 ° C to 90 ° C.   The method for producing a photocatalyst according to claim 1, wherein the titanium complex solution is produced by mixing equal amounts of citric acid solution, titanium (IV) sulfate, 3% hydrogen peroxide water and ammonia water.   A photocatalyst produced by the method according to claim 1.