JP2000070727A - Photocatalytic fine titanium particles and their production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain fine titanium particles having high photocatalytic activity in the visible light region as well as in the UV region. SOLUTION: The fine titanium particles have titanium dioxide crystal and contain 0.0001-10 wt.% divalent cobalt based on the total amt. of the fine titanium particles. The fine titanium particles contain the divalent cobalt preferably in the crystal structure of the titanium dioxide crystals. It is preferable that the titanium dioxide crystals are predominantly of anatase type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to titanium fine particles having photocatalytic activity.

[0002]

2. Description of the Related Art In recent years, research and development utilizing the photocatalytic activity of titanium oxide have been actively conducted. Titanium oxide induces a strong oxidizing effect by a photocatalytic reaction. That is, when the titanium oxide is irradiated with light having energy larger than its band gap energy, electrons are excited from the valence band, the electrons move to the conduction band, and holes are generated in the valence band. Since the holes have very reactive oxidizing ability, an oxidizing action is induced on the semiconductor surface, that is, the titanium oxide surface. Based on the strong oxidizing action induced by such a photocatalytic reaction, titanium oxide is capable of decomposing and removing harmful substances such as nitrogen oxides in the atmosphere,
For example, decomposition and removal of mercaptan, ammonia, amine, aldehyde, etc., decomposition and removal of plant growth substances such as ethylene, reduction of BOD and COD in wastewater, decolorization of wastewater, etc.
Can be used.

[0003]

Most of titanium oxides currently used as photocatalysts are anatase-type titanium oxides. The reasons include strong photocatalytic activity, chemical stability, high safety, white color, and colorless and transparent thin film.
However, anatase-type titanium oxide, like many other photocatalysts, induces a strong oxidizing effect when irradiated with ultraviolet light, but cannot induce a strong oxidizing effect when irradiated only with visible light. By the way, the titanium oxide currently used only uses 3 to 5% of the energy of sunlight. Therefore, there is a strong demand for titanium oxide having a higher photocatalytic activity in the ultraviolet region and a higher photocatalytic activity in the visible light region.

[0004] As a method for enhancing the photocatalytic activity of titanium oxide including the visible light region, a method of adding another metal to titanium oxide is known. For example, Chemical Review, Hoffman et al.
t al.) 1995, 95, 69-96, Fe ³⁺ , M
It is shown that the photocatalytic activity of titanium oxide can be increased by ^adding o ⁵⁺ , Ru ³⁺ , V ⁴⁺ , and the like. On the other hand, it is indicated that when Co ³⁺ is contained, the photocatalytic activity of titanium oxide decreases. Also, JP-A-63-225532
Japanese Patent Application Laid-Open Publication No. H11-163550 discloses that titanium oxide fine particles contain Co, V, Cr, M
It is shown that when a metal atom such as n or Cu is contained, the photocatalytic activity of titanium oxide can be suppressed.
It has been shown that the photocatalytic activity is suppressed by making the titanium oxide fine particles have a microcrystalline structure. As described above, it has been generally accepted that the inclusion of Co in titanium oxide has a function of suppressing photocatalytic activity.

The present invention provides titanium fine particles having high photocatalytic activity not only in the ultraviolet region but also in the visible light region, and manufactures such titanium fine particles with simple equipment and simple operation. To provide a method.

[0006]

According to the first aspect of the present invention,
Titanium fine particles having photocatalytic activity, comprising titanium oxide crystals, wherein the titanium fine particles contain 0.0001 to 10% by weight based on the total amount of the titanium fine particles. I have.

In the first aspect of the present invention, if the cobalt content is less than 0.0001% by weight, the photocatalytic activity in the visible light region is weak, and if it is more than 10% by weight, not only the visible light region but also the ultraviolet light region. Photocatalytic activity is extremely reduced.

According to a second aspect of the present invention, in the first aspect, divalent cobalt is contained in the crystal structure of the titanium oxide crystal.

In the second aspect of the present invention, the cobalt is present in a state where some atoms of the crystal structure of the titanium oxide crystal are substituted or confined between the crystal structures.

According to a third aspect of the present invention, in the first aspect, divalent cobalt is contained in the crystal structure of the titanium oxide crystal, and the divalent cobalt also exists as a cobalt titanate crystal. Is what you are doing.

As the cobalt titanate, Co ₂ Ti
O ₄ , CoTiO ₃ , CoTi ₂ O _{5 and the} like can be mentioned.

According to a fourth aspect of the present invention, in the first aspect, the titanium oxide crystal is mainly of an anatase type.

The crystal structure of titanium oxide includes rutile type and amorphous type. The band gap of rutile-type titanium oxide is 3.0 eV, while the band gap of anatase-type titanium oxide is 3.2 eV. When the energy corresponding to these band gaps is converted into light energy, they are 413 nm and 387 nm, respectively. . This indicates that rutile-type titanium oxide can use light of a longer wavelength than anatase-type titanium oxide, that is, has higher photocatalytic activity in the visible light region. However, the rutile-type titanium oxide has a lower oxidizing effect induced by a photocatalytic reaction due to the lower band gap than the anatase-type titanium oxide. Therefore, if the content of the rutile-type titanium oxide is too large, the overall photocatalytic activity becomes weak. Accordingly, the main crystal structure of titanium oxide is preferably an anatase type, particularly an anatase type having high crystallinity, and a rutile type may be contained but a small amount is preferable. Also,
Since amorphous titanium oxide has low photocatalytic activity, it is preferably not contained.

According to a fifth aspect of the present invention, in the first aspect, the titanium fine particles have an average particle diameter of 5 to 100 n.
m.

In the photocatalyst, it is generally better that the particle size of the fine particles is small, but if the particle size is too small, it becomes difficult to handle the particles during production or use. Therefore, the thickness is preferably 5 to 100 nm.

According to a sixth aspect of the present invention, there is provided a dissolving step of dissolving a titanium salt and a divalent cobalt salt in water or an alcohol or a mixed solution of water and an alcohol;
A hydroxide ion-containing, water, or alcohol, or a mixed solution of water and alcohol is dropped under stirring, a dropping step, and after completion of the dropping, the solution is heated to reflux, a reflux step, and filtration after reflux. The fine particles obtained by washing are
Baking at 00 ° C., and a baking step.

The molar amount of the cobalt salt is preferably set to 0.0002 to 15% based on the total molar amount of the titanium salt and the cobalt salt.

As the titanium salt, titanium sulfate, titanyl sulfate, titanium chloride and the like are preferably used.

As the divalent cobalt salt, a sulfate, a nitrate, a chloride, a carboxylate, an alkoxide, a complex salt and the like are preferably used. As the complex salt, an acetylacetone complex salt, an EDTA complex salt, an ammine complex salt, or the like is used. Particularly, among these, divalent cobalt salts are preferable. These salts are used alone or as a mixture.

As the alcohol, lower aliphatic alcohols such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol are preferably used.

In the dissolving step, for example, titanyl sulfate does not dissolve in alcohol, so that titanyl sulfate is preferably dissolved in a mixed solution of water and alcohol as follows. That is, water is added to titanyl sulfate to generate an aqueous solution of titanyl sulfate, an alcohol is added thereto, the aqueous solution of titanyl sulfate is dropped into alcohol, a mixed solution of water and alcohol is prepared first, and titanyl sulfate is added to this. . Regarding the cobalt salt, those that do not dissolve in alcohol dissolve in the same manner as titanyl sulfate.

If the molar amount of the cobalt salt is less than 0.0002%, the photocatalytic activity in the visible light region is weak, and
If it is larger, the photocatalytic activity not only in the visible light region but also in the ultraviolet region is extremely reduced.

As the hydroxide for generating hydroxide ions, NaOH, KOH, NH ₄ OH, H ₂ N ₄ .H ₂ O, etc. are preferably used.

The dropping speed is 10 minutes or more, preferably 15 minutes.
The dropping speed is set to be within 60 minutes.

The heating and refluxing are performed at a boiling point of water and alcohol for 10 minutes or more, preferably 30 to 120 minutes. If the reflux time is shorter than 10 minutes, the hydrolysis of the titanium salt and the cobalt salt does not completely proceed, and the yield decreases.

The firing temperature is 400 to 800 ° C.
Especially 500-700 degreeC is preferable. The firing temperature is 400 ° C
If the temperature is lower, crystallization becomes insufficient and photocatalytic activity cannot be obtained. If the temperature is higher than 800 ° C., rutile-type titanium oxide becomes a main component, and the photocatalytic activity decreases.

When a titanium salt and a divalent cobalt salt are dissolved in water or an alcohol or a mixed solution of water and an alcohol, and then added with hydroxide ions and heated, the titanium oxide and the divalent cobalt salt have titanium oxide crystals and are dissolved. Titanium fine particles containing monovalent cobalt ions are obtained. When dissolved in water, hydrolysis and agglomeration proceed rapidly, and the resulting titanium fine particles become large having a particle diameter of several tens of nm. On the other hand, when dissolved in a mixed solution of water and alcohol, the presence of water in the solution is diluted, and therefore, the progress of hydrolysis is controlled and aggregation is suppressed. It has a small particle size of nm. The same applies to the case of dissolving only in alcohol.

According to a seventh aspect of the present invention, in the invention of the sixth aspect, in the dissolving step or the dropping step, the ratio of water and alcohol in the mixed solution is arbitrarily set.

Since the progress of the hydrolysis is limitedly controlled in accordance with the amount of the alcohol, the particle size of the obtained titanium fine particles is controlled.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1-3) titanyl sulfate _{(TiOSO 4 · 5H 2 O)} 30mmol cobalt acetate _{(Co (CH 3 COO) 2} · 4H 2 O) 0.09mmol
Was dissolved in 50 ml of water, and 150 ml of ethanol was added thereto with stirring (dissolution step). In this case, Co /
(Co + Ti) was 0.3%. Next, an ethanol solution in which 60.2 mmol of sodium hydroxide was dissolved was added dropwise to the solution over 1 hour with stirring (dropping step). After completion of the dropwise addition, the solution was heated and refluxed at the boiling point for 1 hour (reflux step). After the reflux, the fine particles obtained by filtration and washing were centrifuged, washed with methanol, dried, and baked at various temperatures for 1 hour (baking step). The various temperatures were 400 ° C., 600 ° C., and 800 ° C.

(Comparative Embodiment 1) The sintering temperature was set to 1000 ° C., and the other conditions were the same as in Embodiment 1.

(Comparative Embodiment 2) The same treatment as in Embodiment 1 was carried out except that firing was not performed.

(Evaluation) Embodiments 1 to 3 and Comparative Embodiment 1
Photocatalytic activity of the titanium fine particles obtained in Step 2 was evaluated, and the average particle diameter was determined. Table 1 shows the results.

[0034]

[Table 1]

The photocatalytic activity was evaluated as follows. That is, first, 0.2 g of a sample was set in a sample holder, placed in a reaction vessel (capacity: 700 ml), and evacuated to about 1.1 ± 0.1 Torr by a vacuum pump. Next, an acetaldehyde standard gas (Neriki Gas, 508 ppm) was injected until the pressure reached 300 Torr, and then air was introduced to normal pressure. Then, 0.5 ml every 30 minutes until the concentration of acetaldehyde becomes constant.
Each sample was collected and analyzed by gas chromatograph. When the concentration became constant, the sample was irradiated with a xenon lamp for 10 minutes.
0.5 ml was sampled every 30 minutes, and the acetaldehyde concentration was measured. The obtained result was analyzed by the following first-order rate equation (1), and the acetaldehyde decomposition rate constant k was used as an index of the photocatalytic activity.

In (Cs / Ct) = kt (1) Cs: initial concentration of acetaldehyde Ct: acetaldehyde concentration after t minutes k: rate constant t: irradiation time of xenon lamp

The photocatalytic activity was evaluated by irradiation with ultraviolet light and visible light (ie, λ> 300 nm) and irradiation with only visible light (ie, λ> 400 nm). When irradiating ultraviolet light and visible light, the light amount is 3.7 mW / cm ² at λ> 254 nm and λ> 4.
0.9 mW / cm ² at 50 nm, and 0.7 mW / cm ² at λ> 450 nm when irradiating only visible light.
²

The average particle diameter was determined as the specific surface area diameter Ds from the following equation (2). Sw = 6 / (ρp · Ds) (2) Sw: specific surface area ρp: density of titanium fine particles Ds: specific surface area diameter

As can be seen from Table 1, the firing temperature was 600
In the case of ° C., compared with the case of 400 ° C. and 800 ° C., in the case of irradiating ultraviolet light and visible light, and in the case of irradiating only visible light, the acetaldehyde decomposition rate constant k is large, that is, Strong photocatalytic activity. 4
Even at 00 ° C., the constant k is larger than at 1000 ° C. and unfired. In the case of unfired, there was almost no photocatalytic activity when irradiated with ultraviolet light and visible light, and no photocatalytic activity was shown when irradiated only with visible light.

(Results of X-ray diffraction) When the sintering temperature was 1000 ° C., only the peak of rutile type titanium oxide was observed,
At 0 ° C., a peak of highly crystalline anatase-type titanium oxide was observed. FIG. 1 is an X-ray diffraction diagram of titanium fine particles obtained with an excessively large amount of cobalt in Embodiment 2 and Comparative Embodiment 2 to clearly show a peak based on cobalt. As can be seen from FIG. 1, when unfired, it is amorphous, and at 600 ° C., there are a peak of highly crystalline anatase-type titanium oxide and a peak of rutile-type titanium oxide. Are present more than rutile titanium oxide. CoTiO _{3 is} also present.

[0041] The (Embodiment 4-10) molar ratio of cobalt sulfate to the total molar amount of titanyl sulfate and cobalt sulfate _{(CoSO 4 · 7H 2 O)} , 0.0002,0.00
1, 0.01, 0.1, 1, 5, and 15% were used, and the other processing was the same as in the first embodiment. However, the firing temperature is 600
° C.

Comparative Example ₃ The molar ratio of cobalt sulfate to the total molar amount of titanyl sulfate and cobalt sulfate (CoSO ₄ .7H ₂ O) was set to 20%.
The same treatment was performed.

(Comparative Embodiments 4 and 5) As Comparative Embodiment 4, a commercially available photocatalytic titanium oxide, trade name "ST-01" (manufactured by Ishihara Sangyo Co., Ltd.), and as Comparative Embodiment 5, the trade name "P-25" (Manufactured by Nippon Aerosil Co., Ltd.).

(Evaluation) Embodiments 4 to 10 and Comparative Embodiment 3
The photocatalytic activity was similarly evaluated for ~ 5,
The average particle diameter was determined, and the cobalt content of Examples 4 to 10 and Comparative Example 3 was also determined. Table 2 shows the results.
Shown in

[0045]

[Table 2]

As can be seen from Table 2, Embodiments 4 to 10
The titanium fine particles obtained in Comparative Examples 3 to 5 are:
Excellent photocatalytic activity was exhibited in both cases of irradiation with ultraviolet and visible light and irradiation of only visible light. Comparative Example 3 showed only a slight photocatalytic activity when irradiated with ultraviolet light and visible light, but did not exhibit photocatalytic activity when irradiated with visible light.

(Embodiment 11) Titanium (VI) sulfate solution 30
mmol and cobalt citrate (Co ₃ (C ₆ H ₅ O ₇ ) _2.
(14H ₂ O) 0.55 mmol was dissolved in 200 ml of water (dissolution step). At this time, Co / (Co + Ti) is 1.
8%. Next, sodium hydroxide 6 was added to the solution.
An aqueous solution in which 1.1 mmol was dissolved was added dropwise with stirring over 1 hour (dropping step). After completion of the dropwise addition, the solution was heated and refluxed at the boiling point for 1.5 hours (reflux step). Then, after reflux, the fine particles obtained by filtration and washing were centrifuged, washed with methanol, dried, and fired at 650 ° C. for 2 hours (firing step).

Embodiment 12 Titanium tetrachloride (TiCl
₄₎ 30 mmol with cobalt nitrate _{(Co (NO 3) 2 ·} 6
The H ₂ O) 0.04 mmol was dissolved in methanol 200 ml (dissolution step). At this time, Co / (Co + Ti) was 0.14%. Next, a methanol solution in which 60.1 mmol of potassium hydroxide was dissolved was added dropwise to the solution over 1 hour with stirring (dropping step). After dropping,
The solution was heated to reflux at the boiling point for 30 minutes (reflux step). Then, after reflux, the fine particles obtained by filtration and washing,
The mixture was centrifuged, washed with methanol, dried, and baked at 550 ° C. for 40 minutes (baking step).

For Examples 11 and 12, the photocatalytic activity was similarly evaluated, and the average particle size was determined. Table 3 shows the results.

[0050]

[Table 3]

As can be seen from Table 3, Embodiments 11 and 1
The titanium fine particles obtained in Example 2 exhibited excellent photocatalytic activity both when irradiated with ultraviolet light and visible light and when irradiated only with visible light.

(Embodiments 13-16) The ratio of water to ethanol was 10 ml: 190 ml and 50 ml:
150ml, 100ml: 100ml, 150ml: 5
The processing was performed in the same manner as in Embodiment 1 except that the volume was 0 ml. However, the firing temperature was 600 ° C. Table 4 shows the results.

[0053]

[Table 4]

As can be seen from Table 4, by controlling the ratio of water to alcohol, the particle size of the titanium fine particles is controlled.

[0055]

According to the present invention, not only in the ultraviolet region but also in the visible region,
Can exhibit strong photocatalytic activity.

According to the fourth aspect of the present invention, since a high-crystalline anatase-type titanium oxide is a main component and the content of the rutile-type titanium oxide is small, a strong photocatalytic activity can be exhibited.

According to the fifth aspect of the present invention, the photocatalytic activity can be satisfactorily exhibited, and at the time of manufacture and use can be easily performed.

According to the invention of claim 6, titanium fine particles capable of exhibiting a strong photocatalytic activity not only in the ultraviolet region but also in the visible region can be obtained with simple equipment and simple operation.

According to the seventh aspect of the invention, the particle size of the titanium fine particles can be controlled.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of titanium fine particles obtained in Example 2 and Comparative Example 2 with an excessive amount of cobalt.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Onaka 3-9-39 Mikunihonmachi, Yodogawa-ku, Osaka-shi, Japan Inside Nippon Aluminum Co., Ltd. (72) Inventor Seiji Hagino 3 Mikunihoncho, Yodogawa-ku, Osaka-shi, Osaka No. 9-39 F-term in Nippon Aluminum Co., Ltd. (Reference) 4G069 AA02 AA08 BA04A BA36C BA48A BB06A BB06B BC50B BC67A BC67B CA02 CA03 CA05 CA10 CA11 CA13 CA17 EB19 EC22X EC25 FA01 FB09 FB30 FB31 FC03 FC07 FC08 FC10

Claims (7)

[Claims] 1. Titanium fine particles having photocatalytic activity, comprising titanium oxide crystals, wherein divalent cobalt is contained in the titanium fine particles in an amount of 0.0001 to 1 with respect to the total amount of the titanium fine particles.
Photocatalyst titanium fine particles containing 0% by weight. 2. Photocatalytic titanium fine particles according to claim 1, wherein divalent cobalt is contained in the crystal structure of the titanium oxide crystal. 3. The photocatalytic titanium fine particles according to claim 1, wherein divalent cobalt is contained in the crystal structure of the titanium oxide crystal and divalent cobalt is also present as a cobalt titanate crystal. 4. The photocatalytic titanium fine particles according to claim 1, wherein the titanium oxide crystal is mainly of an anatase type. 5. The titanium fine particles having an average particle size of 5 to 100.
The photocatalyst titanium fine particles according to claim 1, wherein the particle diameter is in nm. 6. A dissolving step of dissolving a titanium salt and a divalent cobalt salt in water or an alcohol or a mixed solution of water and an alcohol, and dissolving the solution containing hydroxide ions in water or Dropping an alcohol or a mixed solution of water and an alcohol under stirring, a dropping step, heating the solution after the completion of the dropping, a reflux step, and, after refluxing, filtering and washing, to obtain fine particles of 400. ~ 800
A method of producing titanium fine particles of a photocatalyst, comprising a step of firing at a temperature of ° C. 7. The method for producing photocatalyst titanium fine particles according to claim 6, wherein in the dissolving step or the dropping step, the ratio between the water and the alcohol in the mixed solution is arbitrarily set.