JP4598704B2 - Method for producing titanium oxide precursor and method for producing titanium oxide - Google Patents

Description

  The present invention relates to a method for producing a titanium oxide precursor and a method for producing titanium oxide. More specifically, the present invention relates to a mixing reaction step in which an acidic aqueous solution of a titanium compound and a base are mixed and reacted to form a titanium oxide precursor slurry, and this mixing reaction. A method for producing a titanium oxide precursor having a step of filtering a reaction product obtained in the step and a step of drying a filtration residue obtained in the filtration step, and a titanium oxide precursor produced by this method were used. The present invention relates to a method for producing titanium oxide.

  In place of the conventional photocatalyst by ultraviolet irradiation, a photocatalyst exhibiting catalytic action was also discovered by irradiation with visible light, and various proposals have been made as methods for producing this photocatalyst. For example, Patent Document 1 describes a method of obtaining a photocatalyst by subjecting titanium oxide to hydrogen plasma treatment or rare gas element plasma treatment. However, this method has a problem that an expensive specific plasma processing apparatus including a vacuum vessel is required and the operation becomes complicated.

  Therefore, recently, a method for easily producing a titanium oxide photocatalyst has been proposed without using a specific apparatus equipped with a vacuum vessel. For example, a product obtained by hydrolyzing tetraisopropoxytitanium, heat-treating in ammonia gas and then firing in air (Patent Document 2), product obtained by hydrolyzing tetraisopropoxytitanium Is immersed in ammonia water and then calcined (Patent Document 3), titanium ammonium oxalate is calcined (Patent Document 4), titanium hydroxide is calcined in the presence of ammonia sulfate (Patent Document 5), A method in which titanium hydroxide is calcined in an ammonia gas atmosphere (Patent Document 6), a titanium compound such as titanium chloride, titanium oxychloride, titanium sulfate, titanium oxysulfate and a specific amount of ammonia are mixed, and the product obtained And the like (Patent Document 7).

  According to the method described in Patent Document 7, it is described that titanium oxide having a high photocatalytic action against visible light irradiation can be obtained.

WO00 / 10706 Publication JP 2001-278625 A JP 2001-278626 A JP 2001-278627 A JP 2001-302241 A JP 2001-354422 A JP 2002-47012 A

  However, when a film is formed using a coating liquid in which titanium oxide is dispersed in a solvent, the film can be thinned and the mechanical properties of the film can be improved. However, it is difficult to make titanium oxide fine particles by the above prior art method, and there is room for improvement.

  Accordingly, in view of the above-mentioned problems of the prior art, an object of the present invention is to produce titanium oxide for producing titanium oxide that can be easily formed into fine particles and has high photocatalytic activity by irradiation with visible light, without using a particularly expensive apparatus. An object of the present invention is to provide a method for producing a precursor and a method for producing titanium oxide using the same.

  The above-mentioned subject is achieved by the invention described in each claim. That is, the characteristic structure of the method for producing a titanium oxide precursor according to the present invention is obtained by mixing and reacting an acidic aqueous solution of a titanium compound and a base to form a titanium oxide precursor slurry, and this mixing reaction step. In the method for producing a titanium oxide precursor having a step of filtering the reaction product obtained and a step of drying the filtration residue obtained by the filtration step, the drying step is performed so that the maximum water vapor partial pressure in the furnace is 45 kPa or less. It is to dry in the atmosphere.

According to this configuration, it is possible to dry the nitrogen atoms in the titanium oxide precursor without escaping, and by firing, fine particles can be easily formed, the photocatalytic activity by irradiation with visible light is high, and the BET specific surface area is 70 m ² / g or more. A particulate anatase-type titanium oxide photocatalyst can be produced. Here, the titanium oxide precursor is an oxygen-containing titanium compound other than anatase-type titanium oxide, and can be a titanium oxide photocatalyst represented by the composition formula TiO ₂ when fired in air at 310 to 500 ° C. Say.

  As a result, it has been possible to provide a method for producing a titanium oxide precursor for producing titanium oxide that can be easily made into fine particles and has high photocatalytic activity by irradiation with visible light, without using a particularly expensive apparatus.

  The reaction product is preferably titanium hydroxide or titanium peroxide.

According to this arrangement, when fired titanium oxide precursor after drying at from 310 to 500 ° C. in air, it tends reliably titanium oxide photocatalyst represented by the composition formula TiO _2.

  The reaction product is preferably amorphous.

  According to this structure, when a titanium oxide precursor is baked in the air of 310-500 degreeC, it can pulverize more reliably after baking. That is, the fine particles are remarkably progressed when the transition from the amorphous state to the anatase type crystal is performed by the firing at the above temperature.

The BET specific surface area after drying is preferably 45 m ² / g or less.

  According to this configuration, fine particles of anatase-type titanium oxide can be reliably obtained when fired.

  It is preferable to mix hydrogen peroxide with an acidic aqueous solution of the titanium compound and to react with the base at 65 ° C. or lower.

  According to this configuration, the titanium compound is hydrolyzed with hydrogen peroxide efficiently, and a titanium peroxide constituting the titanium oxide precursor can be obtained. The reaction temperature is preferably 60 ° C. or lower, more preferably 55 ° C. or lower.

  It is preferable that the amount of hydrogen peroxide mixed with the titanium compound is usually 0.1 mol times or more and 5 mol times or less with respect to titanium of the titanium compound.

  A larger amount of hydrogen peroxide is preferable because the particle diameter of the finally obtained titanium oxide becomes smaller. However, when the hydrogen peroxide exceeds 5 mol times, the photocatalytic activity of the titanium oxide obtained by firing is lowered. Sometimes. More preferably, they are 1 mol times or more and 5 mol times or less.

  The titanium compound is preferably selected from titanium chloride, titanium oxychloride, titanium sulfate, and titanium oxysulfate.

  According to this configuration, when the titanium oxide precursor formed of these titanium compounds is baked at 310 to 500 ° C., anatase-type titanium oxide can be reliably generated.

  Moreover, the characteristic structure of the manufacturing method of the titanium oxide which concerns on this invention is the titanium oxide precursor manufactured by the manufacturing method of the titanium oxide precursor of any one of Claims 1-7 at 310-500 degreeC. There is in firing.

  According to this configuration, it is possible to provide a method for producing titanium oxide that can be easily formed into fine particles and has high photocatalytic activity by irradiation with visible light, without using a particularly expensive apparatus.

  Hereinafter, embodiments of the present invention will be described in detail. The method for producing a titanium oxide precursor according to the present embodiment includes producing a raw material complex from an acidic aqueous solution of at least an oxygen-containing titanium compound, and mixing and reacting this with a base to form titanium oxide mainly composed of titanium hydroxide. A mixing reaction step for preparing a precursor slurry, a filtration step for filtering the titanium oxide precursor slurry, a washing step for cleaning the titanium oxide precursor as a filtration residue obtained by this filtration step, a drying step, and a necessity The process of crushing according to and the baking process are included. It is also preferable to mix a foaming component such as hydrogen peroxide into the titanium compound aqueous solution.

  In the present embodiment, the drying step is characterized by drying in an atmosphere having a maximum steam partial pressure in the furnace of 45 kPa or less. That is, a titanium oxide precursor capable of producing highly active titanium oxide is obtained by drying at 200 ° C. or more and 300 ° C. or less while maintaining an atmosphere having a maximum steam partial pressure in the furnace of 45 kPa or less. By adopting such a drying process, an anatase-type titanium oxide photocatalyst can be produced by firing without escaping nitrogen atoms in the titanium oxide precursor, which can be easily atomized and has high photocatalytic activity by irradiation with visible light. Can do.

  Further, the drying process may be a two-stage process in which preliminary drying and subsequent main drying are performed. That is, a titanium oxide precursor capable of producing a highly active titanium oxide may be obtained by preliminary drying at a temperature of 200 ° C. or lower and then performing main drying at a temperature exceeding 200 ° C. and not higher than 300 ° C. By adopting such a drying process, an anatase-type titanium oxide photocatalyst can be produced by firing without escaping nitrogen atoms in the titanium oxide precursor, which can be easily atomized and has high photocatalytic activity by irradiation with visible light. Can do.

The titanium oxide precursor is an oxygen-containing titanium compound (including amorphous) other than anatase-type titanium oxide, and a titanium oxide photocatalyst represented by a composition formula TiO ₂ when fired in air at 310 to 500 ° C. A compound that can form a body, specifically, an oxygen-containing inorganic titanium compound such as titanium hydroxide or titanium peroxide.

Specific examples of the titanium hydroxide include Ti (OH) ₂ , Ti (OH) ₃ , Ti (OH) ₄ , and TiO (OH) ₂ . In addition, as the titanium peroxide, a part of the Ti—O—H bond of titanium hydroxide is replaced with a Ti—O—O bond, and a part of the Ti—O bond of titanium oxide is Ti—O—. The thing replaced with O coupling | bonding, or these mixtures, for example, what is shown by Formula (1) is mentioned.

Ti (O ₂ ) _x O _y (OH) _z (1)
[In Formula (1), 0 <x <4, 0 <= y <2, 0 <= z <4. ]
One of these may be sufficient as a titanium oxide precursor, and these mixtures may be sufficient as it.

Furthermore, the titanium oxide obtained by this production method preferably has a BET specific surface area of 70 m ² / g or more. A small BET specific surface area indicates a large primary particle size. Conversely, a large BET specific surface area indicates that the primary particle diameter is small, and it can be a highly active titanium oxide photocatalyst and a particulate titanium oxide photocatalyst that is fine and excellent in dispersibility.

  The drying equipment is not particularly limited as long as the atmosphere can have a maximum water vapor partial pressure of 45 kPa or less. For example, a tubular electric furnace, a box electric furnace, a tunnel furnace, a far infrared furnace, a microwave heating furnace, Using a dryer such as a shaft furnace, a reflection furnace, a rotary furnace, or a roller hearth furnace, gas can be discharged from the machine or gas can be introduced.

  The anatase-type titanium oxide obtained by firing may be surface-coated with an acidic metal oxide or a basic metal compound as necessary. The acidic metal oxide for surface coating may be any having Bronsted acid point, Lewis acid point or both, for example, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron , One-component oxides of metals such as cobalt, nickel, copper, aluminum, gallium, indium, tin, silicon-zinc, silicon-zirconium, silicon-magnesium, silicon-calcium, silicon-gallium, silicon-aluminum, silicon -Lanthanum, silicon-titanium, titanium-zinc, titanium-copper, titanium-zinc, titanium-aluminum, titanium-zirconium, titanium-lead, titanium-bismuth, titanium-iron, zinc-magnesium, zinc-aluminum, zinc-zirconium Like zinc-lead, zinc-antimony A composite oxide species metal. Moreover, as long as it is a metal oxide having an acid point, the surface may be coated with a composite oxide of three or more metals. Among these metal oxides, one-component oxides of metals such as zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, aluminum, and tin are particularly preferable.

  The basic metal compound that covers the surface may be any of those having a Bronsted base point, a Lewis base point, or both, such as sodium oxide, potassium oxide, magnesium oxide, calcium oxide, barium oxide, and lanthanum oxide. , Cerium oxide, zinc oxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lanthanum hydroxide, cerium hydroxide, zinc hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate , Barium carbonate, lanthanum carbonate, cerium carbonate, and zinc carbonate.

  Further, the surface of the titanium oxide may be coated with both the acidic metal oxide and the basic metal compound. Furthermore, you may mix and use what was surface-coated with an acidic metal oxide, and what was surface-coated with a basic metal compound. The amount of the acidic metal oxide or basic metal compound to be coated on the surface is 30 mol% or less, preferably 10 mol% or less, more preferably 5 mol% or less in terms of metal element with respect to titanium of titanium oxide as a base material. It is.

  This titanium oxide can be mixed with a polymer resin, a binder, a molding aid, an antistatic agent, an adsorbent, etc., and molded into pellets, fibers or sheets, but has excellent dispersibility in liquids. Therefore, it is recommended to use as a coating agent obtained by mixing with a solvent.

  A film formed from fine particulate titanium oxide obtained by the method of the present embodiment or a coating liquid prepared using this titanium oxide is a high photocatalyst for irradiation with visible light (light having a wavelength of about 430 to 600 nm). Expresses activity. Irradiation with visible light can usually be performed with a fluorescent lamp, a halogen lamp, a black light, a xenon lamp, a neon sign, an LED, a mercury lamp, a sodium lamp, or the like, and sunlight can also be used. The fine particulate titanium oxide thus obtained or the film formed from the coating liquid prepared using this titanium oxide is not only used outdoors but also used indoors and other indoor arrangements. It can also be applied widely.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these. The physical properties of the titanium oxide precursor and titanium oxide were measured by the following method.

BET specific surface area (m ² / g): Determined by a nitrogen adsorption method using an automatic specific surface area measuring device (trade name “Monosorb”, manufactured by Yuasa Ionics). At this time, desorption was performed under a condition of holding at 200 ° C. for 30 minutes under vacuum, and adsorption was performed under a temperature condition of 77K.

<Example 1>
(Precursor synthesis)
75 kg of titanium oxysulfate was dissolved in 50 kg of ion-exchanged water to prepare a titanium oxysulfate aqueous solution. Under cooling, 30 kg of 35% hydrogen peroxide water (corresponding to 1 mol times with respect to titanium) was added to this aqueous solution of titanium oxysulfate. 30 kg of ion-exchanged water was placed in a reaction vessel equipped with a pH electrode and a pH controller connected to the pH electrode and having a mechanism for supplying a 25 wt% aqueous ammonia to adjust the pH to a constant level. The pH setting of the pH controller was 4. In this reaction vessel, when the pH of the liquid in the vessel becomes lower than the set value, ammonia water starts to be supplied and is continuously supplied at the rate until the pH reaches the set value. While stirring at 42 rpm, the mixed solution obtained above was added to the reaction vessel at 530 ml / min and reacted with ammonia water supplied to the reaction vessel by a pH controller to obtain a product. The reaction temperature at this time was in the range of 20 ° C to 30 ° C. The resulting product was held for 1 hour with stirring, and then 25 wt% aqueous ammonia was supplied to obtain a slurry. The total amount of ammonia water supplied to the reaction vessel was 90 kg, which was twice the amount necessary to change titanium oxysulfate to titanium hydroxide. The upper slurry was filtered and rinsed as it was to obtain a solid (cake).

[Dry]
2.3 kg of the cake obtained above was placed in a 30 cm × 40 cm stainless steel vat. Twelve of these vats were placed in a box-type dryer (internal volume: 216 liters, trade name “Super Temp Oven HP-60”, manufactured by Asahi Kagaku Co., Ltd.), and dried at 115 ° C. for 5 hours under a flow of 40 m ³ / h. After holding, drying was continued at 250 ° C. for 5 hours. The maximum water vapor partial pressure in the furnace at this time was 27.4 kPa. Moreover, the BET surface area of the dry powder was 18.0 m ² / g.

[Baking]
The dried powder obtained above was calcined in an air atmosphere at 350 ° C. for 2 hours and then cooled to room temperature to obtain a particulate titanium oxide photocatalyst.

[Evaluation of photocatalytic activity]
A glass petri dish having a diameter of 5 cm was placed in a sealed glass container having a diameter of 8 cm, a height of 10 cm, and a capacity of about 0.5 liter, and 0.3 g of the photocatalyst obtained above was placed on the petri dish. . The inside of the container was filled with a mixed gas composed of 20 volume% oxygen and 80 volume% nitrogen, and the relative humidity was adjusted to 50%. Here, 13.4 μmol of acetaldehyde is enclosed, and 27 watt fluorescent lamp (daylight, three wavelengths, trade name “BB Parallel”, manufactured by Mitsubishi Electric Corporation) is set so that the illuminance immediately above the photocatalyst becomes 7200 lux from the outside of the container. Was irradiated. When acetaldehyde is decomposed by irradiation with a fluorescent lamp, carbon dioxide is generated, so the concentration of carbon dioxide is measured over time with a photoacoustic multi-gas monitor (model number “1312”, manufactured by INNOVA), and carbon dioxide calculated from the concentration change. The photodegradation action of the photocatalyst against acetaldehyde was evaluated based on the production rate. The production rate of carbon dioxide in this example was 2.0 ppm / min.

<Example 2>
(Precursor synthesis)
A solid (cake) was obtained in the same manner as in Example 1.

[Dry]
2.3 kg of the cake obtained above was placed in a 30 cm × 40 cm stainless steel vat. Twelve of these vats are placed in a box-type dryer (internal volume: 216 liters, trade name “Super Temp Oven HP-60”, manufactured by Asahi Kagaku Co., Ltd.) for 5 hours at 115 ° C. under a flow of dry air of 20 m ³ / h. After holding, drying was continued at 250 ° C. for 5 hours. The maximum steam partial pressure in the furnace at this time was 36.5 kPa. The BET surface area of the dry powder was 27.3 m ² / g.

[Baking]
In the same manner as in Example 1, a particulate titanium oxide photocatalyst was obtained.

[Evaluation of photocatalytic activity]
The activity of the photocatalyst obtained above was evaluated under the same conditions as in Example 1. The production rate of carbon dioxide in this example was 1.8 ppm / min.

<Comparative Example 1>
(Precursor synthesis)
A solid (cake) was obtained in the same manner as in Example 1.

[Dry]
2.3 kg of the cake obtained above was placed in a 30 cm × 40 cm stainless steel vat. Twelve of these bats are placed in a box-type dryer (internal volume: 216 liters, trade name “Super Temp Oven HP-60”, manufactured by Asahi Kagaku Co., Ltd.) for 5 hours at 250 ° C. under a flow of dry air of 40 m ³ / h. Drying was performed. The maximum water vapor partial pressure in the furnace at this time was 49.6 kPa. The BET surface area of the dry powder was 47.3 m ² / g.

[Baking]
In the same manner as in Example 1, a particulate titanium oxide photocatalyst was obtained.

[Evaluation of photocatalytic activity]
About the obtained photocatalyst body, activity evaluation was performed on the same conditions as Example 1. FIG. The production rate of carbon dioxide in this example was 1.5 ppm / min.

  As described above, in Examples 1 and 2, the production rate of carbon dioxide produced by photolysis of acetaldehyde is about 33% and 20% faster than Comparative Example 1, respectively. It turns out that it is excellent.

Claims (7)

A mixing reaction step of mixing and reacting an acidic aqueous solution of a titanium compound and a base to form a titanium oxide precursor slurry, a step of filtering the reaction product obtained by this mixing reaction step, and a filtration obtained by the filtration step In the method for producing a titanium oxide precursor having a step of drying the residue,
Drying the drying step in an atmosphere having a maximum steam partial pressure in the furnace of 45 kPa or less ; and
A method for producing a titanium oxide precursor, wherein the BET specific surface area after drying is 45 m ² / g or less . The method for producing a titanium oxide precursor according to claim 1 , wherein the reaction product is titanium hydroxide or titanium peroxide. The method for producing a titanium oxide precursor according to claim 1, wherein the reaction product is amorphous. The hydrogen peroxide is mixed with an acidic aqueous solution of the titanium compound, the manufacturing method of the titanium oxide precursor according to claim 1 which in the reaction of a base at 65 ° C. or less. 5. The method for producing a titanium oxide precursor according to claim 4, wherein the amount of hydrogen peroxide mixed with the titanium compound is usually 0.1 mol times or more and 5 mol times or less with respect to titanium of the titanium compound. The titanium compound is titanium tetrachloride, titanium oxychloride, a manufacturing method of the titanium oxide precursor according to any one of claims 1 to 5, which has been selected from titanium sulfate, from titanium oxysulfate. Titanium oxide precursor produced by the method of the titanium oxide precursor according to any one of claims 1 to 6 production method of titanium oxide is calcined at 310-500 ° C..