JP3940393B2 - Method for producing photocatalytic titanium oxide - Google Patents

Description

The present invention relates to a method for producing titanium oxide used as a photocatalyst, and more particularly to a method for producing photocatalytic titanium oxide that can easily produce photocatalytic titanium oxide in which the ratio of anatase type crystals and rutile type crystals is controlled .

In recent years, as an environmental purification material for decomposing and removing bad odors and harmful substances scattered in the air, or for performing wastewater treatment, water purification treatment, etc., it has excellent hydrophilicity on the surface of various substrates. Titanium oxide (titania) with photocatalytic activity as a hydrophilicity-imparting agent for imparting photocatalytic activity because it has few restrictions on reaction conditions such as temperature, pH value, gas atmosphere and toxicity, and is highly active and easy to handle. ) are focused, for example, aldehydes, mercaptans, ammonia, decomposition deodorizing malodorous substances such as various amines, NO _X, SO _X, PCB, dioxins, organic halogen compounds, organic phosphorus compounds, such as a surfactant It has been applied to many uses such as decomposing and removing harmful substances, sterilizing various kinds of fungi and algae and treating algae, and hydrophilic treatments such as building materials and civil engineering materials.

  And about the method of manufacturing such a titanium oxide industrially, if it divides roughly, the aqueous solution of refined titanium tetrachloride will be sprayed in a high-temperature (800-1,000 degreeC) oxygen atmosphere, and titanium tetrachloride will be oxidized. The vapor phase method for obtaining titanium oxide particles and the liquid phase method for producing a titanium oxide precursor having a hydroxyl group and heat-treating the titanium oxide precursor are known (Titanium oxide- Physical properties and applied technology "pp18-27 (1991.6.25)).

  However, in the former gas phase method, the product obtained is already titanium oxide particles, so when using it as a photocatalyst, so-called secondary processing, which is processed into various dosage forms and forms according to its purpose, is compared. In the liquid phase method, it can be processed into various dosage forms and forms in the state of a titanium oxide precursor, and secondary processing is relatively easy, but 500 ° C. or higher. When firing at a high temperature, the crystal form of titanium oxide in the titanium oxide precursor transitions from the anatase type with relatively high photocatalytic activity to the rutile type with relatively low photocatalytic activity, and the presence of these anatase type crystals and rutile type crystals There is a problem that the ratio changes and the photocatalytic activity decreases during firing.

By the way, the cause of the high photocatalytic activity of titanium oxide is not necessarily clear, but pure anatase-type titanium oxide and pure rutile-type titanium oxide were used, and the mixing ratio was changed for each catalyst composition. As a result of preparing and evaluating photocatalytic activity, it has been reported that anatase-type titanium oxide and rutile-type titanium oxide are mixed, and the mixed state is an important factor governing photocatalytic activity (Catalyst Vol. 45, No. 1, pp35-37 (2003)).
However, there is no known method for industrially producing titanium oxide with a controlled ratio of anatase type crystal and rutile type crystal by a wet method.

Manabu Seino, published by Gihodo Publishing, "Titanium Oxide-Physical Properties and Applied Technology" pp18-27 (1991.6.25) Catalyst Vol.45, No.1, pp35-37 (2003)

  Therefore, the present inventors are relatively easy to perform secondary processing when processing into various dosage forms and forms, and even when firing at a temperature of 500 ° C. or higher, anatase type crystals and rutile types As a result of intensive investigations on means for easily producing photocatalytic titanium oxide with a controlled ratio to the crystal, after adding a basic aqueous solution to a titanium-containing acidic aqueous solution to precipitate a titanium oxide precursor having a hydroxyl group In the obtained titanium oxide precursor slurry, an operation of adding an acidic raw material aqueous solution to lower the pH value to the dissolution region of the titanium oxide precursor and adding the raw material, and the titanium content obtained by this operation By repeating a pH swing operation consisting of adding an aqueous basic solution to an acidic aqueous solution and raising the pH value to the precipitation region of the titanium oxide precursor at least three times, In addition to easy secondary processing, a titanium oxide precursor capable of easily producing titanium oxide in which the ratio of anatase type crystal and rutile type crystal is controlled when baked at a high temperature of 500 ° C. or higher is obtained. The present invention has been completed.

Therefore, an object of the present invention is to easily perform secondary processing into various dosage forms and forms required when used as a photocatalyst, and calcinate at a high temperature of 500 ° C. or higher to form anatase type crystals and rutile type crystals It is an object of the present invention to provide a photocatalytic titanium oxide production method capable of producing a photocatalytic titanium oxide with a controlled ratio.

Another object of the present invention is to produce a photocatalytic titanium oxide in which the titanium oxide precursor is secondarily processed into a shape necessary for use as a photocatalyst before firing when producing the photocatalytic titanium oxide. Is to provide.

That is, the present invention provides a titanium oxide precursor having a hydroxyl group by adding a basic aqueous solution to a titanium-containing acidic aqueous solution, and then calcining the titanium oxide precursor at a high temperature to produce a photocatalytic titanium oxide. At the time of manufacturing the titanium oxide precursor, a basic aqueous solution is added to the titanium-containing acidic aqueous solution to precipitate a titanium oxide precursor having a hydroxyl group, and then the acidic raw material aqueous solution is added to the obtained titanium oxide precursor slurry. Then, the pH value is lowered to the dissolution region of the titanium oxide precursor and an additional raw material is added, and a basic aqueous solution is added to the titanium-containing acidic aqueous solution obtained by this operation to change the pH value of the titanium oxide precursor. the pH swing operation consisting of operations and to increase the deposition region at least repeated 3 times or more and 7 times or less in the range and, during firing of the titanium oxide precursor Anatase-type crystals (AnT) are produced by controlling the number of times of pH swing operation during the production of the titanium oxide precursor and the temperature and time during the firing of the titanium oxide precursor, under the conditions of a firing temperature of 500 ° C. to 600 ° C. ) And rutile-type crystals (Ru) (An / Ru) in the range of 1.7 to 11.5, and a photocatalytic titanium oxide having a BET surface area of 42 m ² / g or more is produced. This is a method for producing photocatalytic titanium oxide .

In addition, the present invention is a method for producing photocatalytic titanium oxide, in which the titanium oxide precursor is secondarily processed into a shape necessary for use as a photocatalyst before firing when producing the photocatalytic titanium oxide .

Further, in the production of the photocatalytic titanium oxide , the present invention has a value of 3.5 or less when the pH value is lowered to the dissolution region during the production of the titanium oxide precursor, and the precipitation region of the titanium oxide precursor. Is a method for producing photocatalytic titanium oxide synthesized with a pH value of 7 or more .

  In the present invention, the titanium raw material used for producing the titanium oxide precursor is not particularly limited. For example, titanium chloride, fluoride, bromide, iodide, nitrate, sulfate, carbonate, acetate , Phosphates, borates, oxalates, fluorides, silicates, iodates, and other titanium salts, titanic acid, titanium oxoacid salts, and titanium alkoxides. For example, titanium tetrachloride, titanium sulfate, titanyl sulfate, titanium trichloride, titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium tetraisopropoxide, titanium tetrabutoxide, orthotitanic acid, metatitanium Acid, titanium tetrabromide, titanium tetrafluoride, titanium trifluoride, potassium titanate, sodium titanate, barium titanate It can be mentioned. These titanium raw materials can be used alone or in a mixture of two or more.

  Examples of the acidic aqueous solution and basic aqueous solution used for the production of the titanium oxide precursor include titanium tetrachloride, titanium sulfate, titanyl sulfate, titanium trichloride, titanium tetrabromide, titanium tetrafluoride, titanium trifluoride. In addition to acid aqueous solutions such as nitric acid, hydrochloric acid, sulfuric acid, etc., basic aqueous solutions such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc. can be mentioned, These acidic aqueous solutions and basic aqueous solutions can also be used alone or in a mixture of two or more. These acidic aqueous solution and basic aqueous solution are used together with the titanium raw material to optimally control the pH value when the above-mentioned titanium raw material alone cannot be controlled to a predetermined pH value.

  Furthermore, the solvent used in producing the titanium oxide precursor is basically water, but is not particularly limited, and examples thereof include water-soluble organic substances such as methanol, ethanol, propanol, tetrahydrofuran, acetone, and dioxane. An aqueous solution of a solvent can also be used.

  Here, regarding the reaction conditions for producing the titanium oxide precursor, the titanium concentration in the aqueous solvent at the time of production is usually 0.1 to 15 wt%, preferably 0.5 to 10 wt% in terms of titanium oxide. In addition, the reaction temperature is from room temperature to 300 ° C., preferably from room temperature to 180 ° C., more preferably from room temperature to 100 ° C., and the reaction pressure is basically normal pressure (0 MPa), and the solvent used It is sufficient to have a pressure that maintains the liquid phase under the conditions of the system and reaction temperature.

  In the present invention, after adding a basic aqueous solution to a titanium-containing acidic aqueous solution to precipitate a titanium oxide precursor having a hydroxyl group, the acidic aqueous solution is added to the resulting titanium oxide precursor slurry to adjust the pH value. An operation of lowering the titanium oxide precursor to the dissolution region and adding an additional raw material and an operation of adding a basic aqueous solution to the titanium-containing acidic aqueous solution obtained by this operation to raise the pH value to the precipitation region of the titanium oxide precursor It is necessary to repeat the pH swing operation consisting of: at least 3 times or more, preferably 5 times or more, more preferably 7 times or more. As the number of repetitions of this pH swing increases, the transition from the anatase type crystal to the rutile type crystal when fired at 500 ° C. or higher is suppressed, and the anatase type crystal (An) and the rutile type crystal ( The ratio (An / Ru) to Ru) increases, and the particle size tends to increase and the pore volume tends to increase.

  Here, a specific method of pH swing operation is to add a basic aqueous solution to a titanium-containing acidic aqueous solution to precipitate a titanium oxide precursor having a hydroxyl group, and in the obtained titanium oxide precursor slurry, The addition of the basic aqueous solution and the addition of the basic aqueous solution are alternately performed to have a pH of 3.5 or less, preferably 0.5 ≦ pH ≦ 2.0, which is a dissolution region of the titanium oxide precursor, and a pH of 7 which is a precipitation region of the titanium oxide precursor. As mentioned above, Preferably it is made to swing between 7.0 <= pH <= 8.5. Also, after the addition of the acidic aqueous solution, it is held for a time sufficient for dissolution and disappearance of fine particles, usually 3 to 60 minutes, preferably 5 to 20 minutes, and after the addition of the basic aqueous solution, an aging time sufficient for particle growth, Usually, the aging time is set by holding for 3 to 30 minutes, preferably 5 to 15 minutes.

  The titanium oxide precursor of the present invention is obtained by filtering the titanium oxide precursor slurry obtained by the above pH swing operation, dehydrating and drying if necessary, and washing if necessary. When the titanium oxide precursor is dehydrated or dried to a water content of 10 to 200 wt%, preferably 50 to 100 wt% on a solid basis, and if necessary, the wet cake is dispersed again in water and filtered. Can be washed by repeating the above. In washing, this operation is preferably repeated 1 to 3 times to remove compounds other than titanium hydroxide produced during the synthesis. The titanium oxide precursor thus obtained is then subjected to secondary processing into various dosage forms and forms required for use as a photocatalyst.

  The secondary processing of the titanium oxide precursor is not particularly limited. For example, the wet cake is molded into a desired shape and fired, or the wet cake is dissolved in a solvent such as water to a desired concentration. Examples of the method of firing after being dispersed and applied can be exemplified, and these usage forms can be used in various forms according to the needs of the products to be applied.

  The titanium oxide precursor for photocatalyst thus obtained by secondary processing is then further heated at a temperature of 40 to 350 ° C., preferably 80 to 120 ° C. for 0.5 to 24 hours, preferably 0.5 to 5 After drying for a period of time, it is calcined at a temperature of 120 to 1,000 ° C., preferably 500 to 800 ° C. for 0.5 to 48 hours, preferably 1 to 5 hours, to obtain titanium oxide used as a photocatalyst. About this firing temperature, the higher the anatase type crystal (An), the more the anatase type crystal (An) is transferred to the rutile type crystal (Ru), and the lower the ratio (An / Ru) of the anatase type crystal (An) to the rutile type crystal (Ru). Therefore, it is preferable to select an appropriate firing temperature and time according to the ratio (An / Ru) of anatase type crystal (An) and rutile type crystal (Ru) desired as photocatalytic titanium oxide.

  According to the present invention, when producing titanium oxide having a high photocatalytic activity at a ratio (An / Ru) of anatase type crystal (An) to rutile type crystal (Ru) of 50% or more, the number of repetitions of pH swing is set. 5 times or more, preferably 7 times or more, and the firing temperature is more preferably 550 to 800 ° C.

According to the manufacturing method of the titanium oxide photocatalyst of the present invention, not only it is easy to be fabricated into a variety of dosage forms and forms are required when used as a photocatalyst, the repetition of pH swing operation at the time of manufacture The photocatalytic titanium oxide in which the ratio of the anatase type crystal and the rutile type crystal is controlled according to the number and the temperature when firing at a high temperature of 500 ° C. or higher can be easily produced industrially, and thus has a desired photocatalytic activity. The titanium oxide having it can be easily produced industrially.

  Hereinafter, preferred embodiments of the present invention will be specifically described based on examples (experimental examples and test examples).

[Experimental Examples 1 to 27]
Ice made with pure water is crushed and placed in a container, 500 g of titanium tetrachloride (TiCl ₄ ) is added to this container and mixed with crushed ice, and pure water is further added to the container to complete the entire solution. The solution was made up to 1,000 ml, and an aqueous titanium tetrachloride solution (solution A) was prepared.
Further, 28 wt% -ammonia water was diluted with the same amount of pure water to prepare 14 wt% -ammonia water (solution B).

Next, 20 L of pure water was put into a 35 L reaction vessel and heated to 75 ° C., and 500 ml of the above solution A was added and mixed with stirring. The pH value of the obtained solution was 1.1.
Subsequently, 710 ml of the above solution B was added to the reaction vessel at a time with stirring. The resulting solution had a pH value of 8.5. By this operation, a titanium oxide precursor was precipitated in the solution, and the solution became a slurry.

  To the titanium oxide precursor slurry thus obtained, 500 ml of solution A is added under stirring, the pH value is lowered to 1.1 and held for 5 minutes, and then 720 ml of solution B is added under stirring. Then, the pH swing operation in which the pH value was raised to 8.5 and held for 5 minutes was repeated as many times as shown in Table 1 to obtain a titanium oxide precursor slurry.

The titanium oxide precursor slurry of each experimental example 1 to 27 was filtered to obtain a wet cake of the titanium oxide precursor, then each wet cake was dispersed in 20 L of pure water, stirred for 30 minutes, and then filtered again. The washing operation was performed three times to remove ammonium chloride remaining in the wet cake.
The obtained wet cakes of Experimental Examples 1 to 27 were dried at 120 ° C. for 3 hours to obtain titanium oxide precursors of Experimental Examples 1 to 27.

[Test Example 1]
About each titanium oxide precursor obtained in the said Experimental Examples 1-27, it baked on the conditions of the temperature and time which are respectively shown in Table 1 under air circulation, cooled, and it grind | pulverized, and obtained titanium oxide powder.

The obtained photocatalytic titanium oxides of Experimental Examples 1 to 27 were measured for BET surface area (m ² / g) by nitrogen adsorption and pore distribution measurement by mercury porosimetry (pore volume (cc / g)). And the average pore diameter (nm)], and then measuring the X-ray diffraction (XRD) pattern using an X-ray diffractometer (XPERT SYSTEM / APD-1700 manufactured by PHLIPS), and anatase crystals in each titanium oxide powder the content of anatase-type crystal from the strongest interference intensity peak I _Ru intensity I _an and rutile-type crystal of the strongest interference peaks (Ru), typically from the following used (1) of the (an) (wt%) The content of the rutile crystal was determined by taking the sum of the content of the anatase crystal and the content of the rutile crystal as 100. From these, the ratio of anatase type crystals (An / Ru) was calculated.
Anatase type crystal content (wt%) = 100 / [1 + 1.265 (I _Ru / I _An )] …… (1)
These results are shown in Table 1. From this, it can be seen that no rutile crystals are observed in the 120 ° C. dried product and the 400 ° C. fired product, but the rutile crystals are detected at a firing temperature of 500 ° C. or higher.

[Test Example 2]
[Suppression effect of crystal transition due to the number of swings at 500 ° C. and 600 ° C. during firing for 3 hours]
FIG. 1 shows the X-ray diffraction pattern of the precursor gel synthesized with the number of swings of 7 times (Experimental Example 22), 10 times (Experimental Example 23), and 15 times (Experimental Example 24) at 500 ° C. for 3 hours. Show. As the number of swings increases, the peak intensity of the rutile crystal decreases, indicating that the crystal transition is suppressed. FIG. 2 shows X when the precursor gels were baked at 600 ° C. for 3 hours (7 swings (Experiment 25), 10 (Experiment 26), and 15 (Experiment 27)). A line diffraction pattern is shown. As in the case of 500 ° C. firing in FIG. 1, the peak intensity of the rutile crystal decreases as the number of swings increases, and the crystal transition is suppressed, but the firing temperature is 600 ° C. compared to 500 ° C. It is observed that the peak intensity of the rutile crystal is higher than that in FIG. 1 due to the high temperature.

[Test Example 3]
[Suppression effect of crystal transition due to the number of swings at 600 ° C. during firing for 40 hours]
FIG. 3 shows an X-ray diffraction pattern of the precursor gel synthesized with 3 swings (Experimental Example 19), 5 (Experimental Example 20), and 7 (Experimental Example 21) when calcined at 600 ° C. for 40 hours. . Even when it is baked for 40 hours, the precursor synthesized by the 7th swing compared with the precursor synthesized by the 3rd or 5th swing has a large anatase-type crystal peak, and the crystal transition is suppressed. I understand that.

[Test Example 4]
[2-propanol photocatalytic degradation test (liquid phase test)]
Moreover, about each said titanium oxide powder, the following 2-propanol photocatalytic decomposition reaction test (liquid phase test) was done, and photocatalytic activity was investigated.
In a quartz glass reaction cell having a diameter of 2 cm and a length of 20 cm excellent in heat resistance and light transmittance, 50 mg of the photocatalytic titanium oxide of each of the above experimental examples 1 to 21 and 25 ml of 2-propanol aqueous solution or 2-hexanol aqueous solution 65 μmol) was added, and oxygen was bubbled for 30 minutes (in an oxygen atmosphere), followed by light irradiation at room temperature for 1 hour while stirring and suspending to determine the reduction rate (%) of 2-propanol. At this time, a rubber septum (diameter 2.1 cm) is attached to the top of the reaction cell, and light irradiation is performed by separating a high-pressure mercury lamp (100 W) as a light source from the reaction cell [Digital illuminometer (Tokyo Kodensha LX-1330) manufactured in parallel with a high-pressure mercury lamp, and the illuminance when measured was about 6150 Lux].
Table 1 shows the decomposition rate (%) of 2-propanol one hour after the start of the reaction.

[Test Example 5]
[NO photocatalytic decomposition reaction test (gas phase test)]
Moreover, about the said each titanium oxide powder, the following NO photocatalyst decomposition reaction test (gas phase test) was done, and photocatalytic activity was investigated.
In a reaction cell similar to the above (capacity: 73.3 cm ³ ), 100 mg of the photocatalytic titanium oxide of each of the above experimental examples 1 to 21 was gradually heated up to 523 K from which most of the adsorbed water was desorbed in the atmosphere. The temperature was raised to 723 K, and then evacuated at the same temperature for 3 hours. Oxygen treatment was performed at 723 K for 2 hours by introducing 20 Torr or more of oxygen purified by a liquid nitrogen trap into the contact portion. Thereafter, the temperature was returned to room temperature, the temperature was slowly raised again to 473 K, and evacuation was performed at the same temperature for 2 hours.

After the above pretreatment, NO, which is a reaction gas, is introduced into the reaction cell until a pressure of 5 Torr is reached, and photocatalytic titanium oxide is irradiated with ultraviolet light (using a UV-27 filter; λ> 270 nm) at 275K. Unreacted NO and reaction product N ₂ O are trapped with liquid nitrogen and qualitatively and quantified by gas chromatography (Shimadzu Corporation GC-12A, 14A; Porapack Q + S, 2m + 2m) Further, N ₂ and O ₂ of the reaction product which is not trapped are qualitatively and quantitatively analyzed by gas chromatography (GC-12A, 14A, manufactured by Shimadzu Corporation; molecular sieve 5A, 6m), and N ₂ and N ₂ produced in 1 μmol. The amount of O was determined.
The results are shown in Table 1.

[Test Example 6]
Using the titanium oxide powder obtained from each titanium oxide precursor of Experimental Examples 3 and 7, 2-propanol was completely decomposed into carbon dioxide (CO ₂ ) in the 2-propanol photocatalytic decomposition reaction test (liquid phase test). The time-dependent change until this time was measured and compared with a commercially available photocatalytic titanium oxide powder [JRC-TIO-4 (P-25)] (Comparative Example 1).
The results are shown in FIGS.

  As is clear from the results shown in Table 1, as the number of repetitions of the pH swing increases, the anatase type crystal (An) and the rutile type crystal (Ru) in the photocatalytic titanium oxide obtained by baking at 500 ° C. or higher are obtained. The ratio (An / Ru) increases and a relatively high photocatalytic activity is exhibited. Further, as the firing temperature is increased, the anatase type crystal (An) is transferred to the rutile type crystal (Ru), the ratio of the rutile type crystal is increased, and the photocatalytic activity tends to be decreased.

According to the method for producing photocatalytic titanium oxide of the present invention, it is not only easy to secondary-process into various dosage forms and forms required when used as a photocatalyst, but also calcined at a high temperature of 500 ° C. or higher. Thus, the ratio of the anatase type crystal to the rutile type crystal is controlled, and as a result, the photocatalytic titanium oxide with controlled photocatalytic activity can be easily produced industrially.

FIG. 1 is an X-ray diffraction pattern when the precursor gels of Experimental Example 22, Experimental Example 23, and Experimental Example 24 were baked at 500 ° C. for 3 hours.

FIG. 2 is an X-ray diffraction pattern when the precursor gels of Experimental Example 25, Experimental Example 26, and Experimental Example 27 were baked at 600 ° C. for 3 hours.

FIG. 3 is an X-ray diffraction pattern when the precursor gels of Experimental Example 19, Experimental Example 20, and Experimental Example 21 were baked at 600 ° C. for 40 hours.

FIG. 4 shows that in 2-propanol photocatalytic decomposition reaction test (liquid phase test) conducted using the titanium oxide powder obtained from the titanium oxide precursor of Experimental Example 3, 2-propanol is completely carbon dioxide (CO ₂ ). It is a graph which shows a time-dependent change until it decomposes | disassembles into.

FIG. 5 is a graph similar to FIG. 4 that was obtained using the titanium oxide powder obtained from the titanium oxide precursor of Experimental Example 7.

FIG. 6 is a graph similar to FIG. 4 which was obtained using the commercially available photocatalytic titanium oxide powder [JRC-TIO-4 (P-25)] of Comparative Example 1.

Claims (6)

When a basic aqueous solution is added to a titanium-containing acidic aqueous solution to produce a titanium oxide precursor having a hydroxyl group, and then the titanium oxide precursor is calcined at a high temperature to produce a photocatalytic titanium oxide, the above titanium oxide precursor is produced. sometimes, oxidized after precipitation of the titanium oxide precursor having a hydroxyl group by adding a basic aqueous solution to a titanium-containing acidic aqueous solution, titanium oxide precursor slurry obtained, the pH value by adding the raw material acid aqueous solution An operation of lowering the titanium precursor to the dissolution region and adding an additional raw material, and an operation of adding a basic aqueous solution to the titanium-containing acidic aqueous solution obtained by this operation to raise the pH value to the precipitation region of the titanium oxide precursor repeated at least 3 times more than 7 times the range of the pH swing operation consisting of, also, at the time of calcination of the titanium oxide precursor firing temperature 500 ° C. or less Performed under the conditions of 600 ° C. or less, by controlling the temperature and time during the count and the titanium oxide precursor firing pH swing operation when the titanium oxide precursor prepared, anatase type crystal (An) and rutile-type crystal (Ru) and the ratio of (an / Ru) is in the range of 1.7 to 11.5, photocatalyst titanium oxide BET surface area is characterized by producing the titanium oxide photocatalyst is 42m ² / g or more Manufacturing method . The method for producing photocatalytic titanium oxide according to claim 1, wherein the titanium oxide precursor is secondarily processed into a shape necessary for use as a photocatalyst before firing . In the production of the titanium oxide precursor, the value when the pH value is lowered to the dissolution region is 3.5 or less, and the pH value of the precipitation region of the titanium oxide precursor is 7 or more. The manufacturing method of the photocatalytic titanium oxide of description . The method for producing photocatalytic titanium oxide according to any one of claims 1 to 3, wherein the titanium-containing acidic aqueous solution is a titanium tetrachloride aqueous solution . The method for producing photocatalytic titanium oxide according to any one of claims 1 to 4, wherein the basic aqueous solution used to increase the pH value in the titanium oxide precursor precipitation region by adding to the titanium-containing acidic aqueous solution is an aqueous ammonia solution . The photocatalytic oxidation according to any one of claims 1 to 5, wherein the number of repetitions of the pH swing operation is in the range of 5 to 7 and the ratio of the anatase-type crystal in the produced photocatalytic titanium oxide is 50% or more. A method for producing titanium .

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