JP2000053421A - Titanium oxide sol and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to prepare a titanium oxide sol having superior dispersibility in a neutral pH range, also having good dispersion stability over a long period of time and maintaining its dispersion stability even under irradiation with light. SOLUTION: A titanium oxide sol is mixed with alkyl silicate as a dispersion stabilizer and the weight ratio (SiO2/TiO2) of the amt. expressed in terms of SiO2 of silicon in the alkyl silicate to the amt. expressed in terms of TiO2 of titanium in the titanium oxide ranges from 0.7 to 10. After the titanium oxide is mixed with the alkyl silicate, the resultant mixture is neutralized to prepare the objective titanium oxide sol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a titanium oxide sol which is stable at a neutral pH and is used for a photocatalyst, a catalyst, a catalyst carrier, an adsorbent, an ultraviolet absorber, a pigment, a filler, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Titanium oxide is used as a white pigment because it has a large refractive index for visible light, or as an ultraviolet absorber because it has an ultraviolet absorbing ability. Titanium oxide is also used as various adsorbents, catalysts, and catalyst carriers because of its excellent adsorption ability, catalytic ability, and large specific surface area. In recent years, attention has been paid to removing harmful substances by using the photocatalytic function of titanium oxide. When the titanium oxide is irradiated with light having energy equal to or greater than the band gap, holes and electrons are generated on the surface of the titanium oxide particles. In particular, holes generated on the surface of titanium oxide particles have a very strong oxidizing power, so they remove harmful substances such as harmful substances, odorous substances, irritants, environmental pollutants, molds, algae and bacteria. it can.

[0003] Titanium oxide used for the above-mentioned applications is used in the form of powders and compacts.
In many cases, titanium oxide is used in a sol state in which titanium oxide is dispersed. Such titanium oxide sols include those that are stable at an acidic pH, those that are stable at an alkaline pH, and those that are stable at a neutral pH.

[0004]

In the case of using a titanium oxide sol which is stable at an acidic range or an alkaline range, the pH of a reaction system for performing a photocatalytic reaction, an adsorption reaction or the like is similarly adjusted to an acidic range. There is a problem that it is necessary to maintain the temperature in an area or an alkaline area, and the use scene is limited. On the other hand, in a titanium oxide sol that is stable at a pH in a neutral range, p of a reaction system that performs a photocatalytic reaction, an adsorption reaction, etc.
It is preferable because there is no problem of H and there is no problem of corrosion.However, since titanium oxide is easily aggregated at a pH in a neutral range, to obtain a titanium oxide sol stable at a pH in a neutral range,
Conventionally, in order to maintain the dispersion stability of titanium oxide, a large amount of a polycarboxylic acid organic dispersant or the like is blended. However, this polycarboxylic acid organic dispersant is decomposed by the photocatalytic function of titanium oxide, and has a problem that the function as a dispersant is reduced and the dispersion stability of the titanium oxide sol is deteriorated. Further, when a hydrophilic organic solvent is added to a titanium oxide sol that is stable at a neutral pH, the titanium oxide is more likely to aggregate, and the dispersibility may be deteriorated.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have excellent dispersibility at a neutral pH, have good dispersion stability over a long period of time, and have a photocatalytic function. We studied diligently to obtain an excellent titanium oxide sol. As a result, they have found that a desired titanium oxide sol can be obtained by blending a specific amount of an alkyl silicate as a dispersion stabilizer, thereby completing the present invention. That is, an object of the present invention is to provide a titanium oxide sol which has excellent dispersion stability, is excellent in photocatalytic function, and is stable at a pH in a neutral range, and a method for producing the same.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a titanium oxide sol which is stable at a neutral pH and contains an alkyl silicate as a dispersion stabilizer, and converts silicon in the alkyl silicate into SiO ₂ . Weight ratio of the amount of titanium in titanium oxide to TiO ₂ (SiO ₂ / TiO _2)
2 ) is a titanium oxide sol, wherein 0.7 to 10 is used. In the present invention, the neutral pH refers to a range of about 5 to 9.

[0007] The dispersion of the particles in the medium takes place in principle in relation to the settling of the particles and the Brownian motion. That is, if the Brownian motion of the particles is dominant over the sedimentation, the dispersed state is maintained. In general, in a system in which particles are dispersed in a medium, as the particle diameter decreases, the interface free energy increases, the system becomes unstable, and the particles tend to aggregate. In particular, in a fine particle dispersion having a particle diameter of 100 nm or less, the tendency is remarkable, the dispersion state becomes unstable, and particle aggregation occurs. Particles thus aggregated have a larger apparent particle size,
Settling prevails. Therefore, in order to obtain a fine particle dispersion system, a large amount of a polycarboxylic acid organic dispersant is generally used to prevent agglomeration of the particles, and a high-viscosity medium is used to prevent sedimentation of the particles. Or The present invention is a titanium oxide sol containing an alkyl silicate as a dispersion stabilizer, and is stable even at a low viscosity of several mPas at room temperature.

[0008] The titanium oxide used in the present invention includes:
In addition to so-called titanium oxide, it includes what is referred to as hydrous titanium oxide, hydrated titanium oxide, metatitanic acid, orthotitanic acid, and titanium hydroxide. As can be understood from the fact that titanium oxide has a high refractive index and is used as a pigment, titanium oxide has high visible light scattering ability. However, it is known that the scattering ability decreases when the aggregate particle diameter becomes 100 nm or less, and the dispersion system becomes transparent. Since the titanium oxide sol of the present invention has excellent dispersion stability, it has a high transmittance in visible light. The transmittance in the visible light is represented by the spectral transmittance measured under the conditions that the titanium oxide concentration is 0.5% by weight, the optical path length of the quartz cell is 1 cm, the control sample is water, and the light wavelength is 550 nm. , Preferably 80-1
It has a high transmittance of 00%. Further, in the present invention, a titanium oxide sol having excellent dispersion stability can be obtained regardless of the particle size. However, in order to obtain excellent transmittance with respect to visible light and excellent photocatalytic function, the titanium oxide sol should have a particle size of 1%. -100 nm, preferably 1-50
It is more preferably in the range of nm, most preferably in the range of 1 to 10 nm. If the particle size is smaller than the above range, the dispersibility tends to decrease, and if the particle size is larger than the above range, the visible light transmittance and the photocatalytic function tend to decrease, which is not preferable.

The alkyl silicate used as a dispersion stabilizer in the present invention is represented by the general formula: Si _n O _n-1 (OR)
_{2n + 2} (where, Si represents silicon, O represents oxygen, and R represents an alkyl group), wherein n is 1 to 6, and R is an alkyl group having 1 to 4 carbon atoms. Some are more preferred in that the proportion of silicon is high. The content of the alkyl silicate is determined by converting silicon in the alkyl silicate to SiO _2.
The weight ratio (SiO ₂ / TiO ₂ ) between the amount converted to TiO ₂ and the amount of titanium in the titanium oxide converted to TiO ₂ is 0.7 to 1
0, preferably 0.9 to 2. If the amount of the alkyl silicate is less than the above range, the dispersion stability tends to decrease, and if the amount is more than the above range, the photocatalytic function tends to decrease, which is not preferable.

The titanium oxide sol of the present invention is a sol having excellent dispersion stability even when a hydrophilic organic solvent is blended. In the present invention, as the hydrophilic organic solvent, alcohols such as methanol, ethanol, 2-propanol and ethylene glycol, ketones, carboxylate esters and the like can be used without particular limitation as long as they are hydrophilic solvents. Alcohol is preferred in that the solubility of the silicate is good. The blending amount of the hydrophilic organic solvent can be appropriately set according to the application scene, but the hydrophilic organic solvent is used in an amount of 30 to 400 parts by weight per 100 parts by weight of water in the titanium oxide sol.
It is preferable to mix them in an amount of about part by weight because dispersion stability can be maintained.

[0011] The present invention is a method for producing a titanium oxide sol which comprises an alkyl silicate as a dispersion stabilizer and is stable at a neutral pH, wherein the alkyl silicate and the titanium oxide sol are mixed. This is a method for producing a titanium oxide sol characterized by neutralization.

As the titanium oxide sol used in the present invention, a titanium oxide sol obtained by a conventional method can be used.
Titanium oxide sol that is stable in an acidic range and titanium oxide sol that is stable in an alkaline range are preferable.
It is more preferable to use a titanium oxide sol which is stable because it can provide a titanium oxide sol containing an alkyl silicate with excellent dispersibility and visible light transmittance.

In order to obtain a titanium oxide sol, for example, titanium oxide such as hydrous titanium oxide is peptized with a monobasic acid or a salt thereof, titanium tetrachloride is added to low-temperature water and dialyzed, or a hydrochloric acid aqueous solution is used. Or a titanium alkoxide. In the above method, the hydrous titanium oxide is, for example, titanium sulfate such as titanium sulfate, titanyl sulfate, or a water-soluble inorganic titanium compound such as titanium tetrachloride or the like. It can be obtained by adding an alkali such as aqueous ammonia and neutralizing the same. Hydrous titanium oxide obtained by hydrolysis is usually neutralized with alkali, solid-liquid separation, washing, dehydration,
After removing as much as possible the sulfate radicals remaining in the inside, a monobasic acid such as hydrochloric acid, nitric acid, acetic acid, chloric acid, or chloric acid or a salt thereof is added to the dehydrated product, and peptization is performed. Alternatively, a salt capable of reacting with a sulfate group to form an insoluble sulfate and simultaneously forming a monovalent acid, for example, barium chloride, in the hydrous titanium oxide without performing the desulfation group treatment by neutralization as described above. For peptization. The titanium oxide sol produced by peptization contains a monobasic acid or a salt thereof as a dispersion stabilizer, and usually shows an acidity of pH 3 or less. The particle diameter of the titanium oxide fine particles can be made finer by performing hydrolysis by heating, lowering the neutralization temperature, or slowing the neutralization reaction. When the pH is increased by gradually adding an alkali to the titanium oxide sol which is stable in the acidic range thus obtained, a titanium oxide sol which is stable in the pH in the alkaline range can be obtained. If necessary, impurities can be removed from the obtained titanium oxide sol in the alkaline region.

In the present invention, first, a titanium oxide sol and an alkyl silicate are mixed by an ordinary method. When mixing both, the titanium oxide aqueous sol may be diluted with a hydrophilic organic solvent, or the alkyl silicate may be diluted with a hydrophilic organic solvent. As the hydrophilic organic solvent, alcohols such as methanol, ethanol, 2-propanol, and ethylene glycol, ketones, carboxylic esters, and the like can be used without any particular limitation as long as they are hydrophilic. Alcohol is preferred in that it has good properties. The dilution ratio of the titanium oxide sol with the hydrophilic organic solvent is more preferably 1.2 to 5 times by weight ratio, while the dilution ratio of the alkyl silicate with the hydrophilic organic solvent is more preferably 1.5 to 5 times by weight ratio. preferable. It is more preferable to mix both the titanium oxide sol and the alkyl silicate after diluting them with a hydrophilic organic solvent since the two can be mixed without causing aggregation of the titanium oxide. It is not necessary to use the same compound as the hydrophilic organic solvent for diluting the titanium oxide sol and the hydrophilic organic solvent for diluting the alkyl silicate.

Next, the obtained mixture is neutralized to obtain the titanium oxide sol of the present invention. Neutralization can be performed by a conventional method, but is preferably performed by at least one method selected from a method by ion exchange, a method of adding a neutralizing agent, and a method by dialysis. In particular, after ion exchange, neutralizing by adding a neutralizing agent,
This is more preferable because the content of impurities can be reduced.

The ion exchange is performed using an ion exchange resin. For example, a cation exchange resin or an anion exchange resin is added to the mixture to remove cations and anions, and then the ion exchange resin is separated. As the ion exchange resin, there is no distinction between strongly acidic and weakly acidic, and as the anion exchange resin, there is no distinction between strongly basic and weakly basic. Both of them are, for example, commercially available Urbanlite (manufactured by Organo), Ions (manufactured by Mitsubishi Chemical Corporation) or the like can be used.

Examples of the neutralizing agent include alkalis such as sodium hydroxide, potassium hydroxide and aqueous ammonia, or monobasic acids such as hydrochloric acid, nitric acid, acetic acid, chloric acid and chloric acid or salts thereof, sulfuric acid and hydrofluoric acid. An acid such as an acid or a salt thereof can be used.

The titanium oxide sol thus obtained can be adjusted to a desired solid content concentration depending on its use,
It may be adjusted to a desired pH.

The titanium oxide sol of the present invention is particularly useful as a photocatalyst. By irradiating light with a wavelength having energy equal to or greater than the band gap of titanium oxide, harmful substances such as toxic substances, odorous substances, irritants, environmental pollutants, bacteria, molds, algae, and bacteria that exist around it can be removed. Can be removed. Examples of the light to be irradiated include light containing ultraviolet light, such as sunlight, a fluorescent light, a black light,
Light from a halogen lamp, a xenon flash lamp, a mercury lamp, or the like can be used. In particular, 300-400n
Light containing m near-ultraviolet light is preferred. The light irradiation amount, irradiation time, and the like can be set as appropriate depending on the amount of the substance to be treated.

[0020]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 (A) Preparation of Aqueous Sol of Acidic Titanium Oxide To 1 liter of an aqueous solution of titanium tetrachloride having a concentration of 50 g / l as TiO ₂ , 20% aqueous ammonia was added over 60 minutes to neutralize titanium tetrachloride. did. Immediately after filtration and dehydration of the hydrous titanium oxide slurry obtained by the neutralization, repulping was performed to obtain a hydrous titanium oxide slurry, and then 80 g of concentrated sulfuric acid was added to the slurry, followed by heat treatment at 95 to 100 ° C for 3 hours. Thereafter, a 5% aqueous solution of sodium hydroxide was added thereto over 10 hours to neutralize, followed by filtration and washing. Concentrated nitric acid and water were added to the obtained dehydrated cake to peptize the mixture, the pH was adjusted to 1, and the mixture was stirred for 7 hours to reduce the titanium oxide concentration to Ti.
An acidic titanium oxide aqueous sol (sample a) was obtained at 20.1% by weight in terms of O ₂ .

(B) Preparation of neutral titanium oxide sol Aqueous sol of acidic titanium oxide obtained in (A) (sample a) 2
While stirring 5 g at room temperature, gradually add 45.4 ethanol.
g, followed by gradually adding 2-propanol (10 g) to obtain an acidic titanium oxide sol diluted with alcohol. The dilution ratio was 3.2 times by weight. Then
Methyl silicate (Methyl silicate 51: General formula Si
_{n O n-1 (OCH 3} ) 2n + 2 ( where n is 3-5), manufactured by Colcoat Co., Ltd.) to obtain a methyl silicate diluted with methanol and diluted to 50% methanol. The dilution ratio was 2 times by weight. 80.4 g of the acidic titanium oxide sol diluted with the obtained alcohol and 19.6 g of methyl silicate diluted with methanol were mixed, and 396 g of a wet anion exchange resin (Amberlite IRA-910: manufactured by Organo Corporation) was added thereto. It was added with stirring and neutralized by ion exchange. Next, the ion exchange resin was filtered to obtain a neutral titanium oxide sol of the present invention (sample A) having a pH of 5.7 and a solid content of 5.7% by weight. This sample A had a weight ratio (S) of the amount of silicon in methyl silicate converted to SiO ₂ and the amount of titanium in titanium oxide converted to TiO _2.
iO ₂ / TiO ₂ ) was 1.

Example 2 Pure water and an aqueous solution of sodium hydroxide having a concentration of 0.1 N were added to the neutral titanium oxide sol (sample A) obtained in Example 1 to obtain a solution having a pH of 7.3 and a solid content of 5% by weight. A neutral titanium oxide sol of the present invention (sample B) was obtained.

Example 3 (A) Preparation of Acidic Titanium Oxide Aqueous Sol A titanium ore and sulfuric acid were reacted, and the resulting titanium sulfate solution was hydrolyzed by heating to produce metatitanic acid. The obtained metatitanic acid was converted into an aqueous slurry of 30% by weight in terms of TiO ₂ , this slurry was neutralized to pH 7 with aqueous ammonia, and then washed by filtration to remove sulfate groups. Concentrated nitric acid and water are added to the obtained dehydrated cake to perform peptization and HNO
₃ containing 2.0% by weight and titanium oxide concentration of TiO
_An aqueous sol of acidic titanium oxide (sample b) having a pH of 1.5 at 30% by weight in terms of ₂ was obtained.

(B) Preparation of neutral titanium oxide sol In place of sample a in Example 1 (B), ion-exchanged water was added to sample b to reduce the titanium oxide concentration to 20% by weight.
A neutral titanium oxide sol of the present invention (sample C) was obtained in the same manner as in Example 1 except that the sample described above was used. Sample C had a pH of 6.4 and a solid content of 5.3% by weight.
Met. Further, silicon in methyl silicate is converted to SiO
The weight ratio between the amount of the titanium Amount of oxide in the titanium in terms in terms of TiO ₂ to ₂ (SiO ₂ / TiO ₂₎ was 1.

Example 4 (A) Preparation of Acidic Titanium Oxide Aqueous Sol (Sample b)
Was used.

(B) Preparation of Neutral Titanium Oxide Sol The ion exchanged water was added to sample b to reduce the titanium oxide concentration to 28.
While stirring 49 g of the acidic titanium oxide aqueous sol of 6% by weight at room temperature, 8 g of methanol was gradually added, and then 6.5 g of 2-propanol was gradually added to obtain an acidic titanium oxide sol diluted with alcohol. . The dilution ratio was 1.3 times by weight. Then, methyl silicate (methyl silicate 51: general formula Si _n O _n-1 (OCH
₃ ) _{2n + 2} (where n is 3 to 5; manufactured by Colcoat) was diluted to 50% with methanol to obtain methyl silicate diluted with methanol. The dilution ratio was 2 times by weight. 63.5 g of the acidic titanium oxide sol diluted with the obtained alcohol and 38.6 g of methyl silicate diluted with methanol were mixed, and the mixture was wetted with an anion exchange resin (Amberlite IRA-910: manufactured by Organo Corporation).
34 g was added with stirring and neutralized by ion exchange. Next, the ion-exchange resin was filtered, and pH 6.1,
A neutral titanium oxide sol of the present invention (sample D) having a solid content of 13.3% by weight was obtained. This sample D has a weight ratio (SiO ₂ / Ti) of the amount of silicon in methyl silicate converted to SiO ₂ and the amount of titanium in titanium oxide converted to TiO _2.
O ₂ ) was 0.70.

Example 5 (A) Preparation of Acidic Titanium Oxide Aqueous Sol (Acid Titanium Oxide Aqueous Sol Obtained in Example 1) (Sample a)
Was used. (B) Preparation of Neutral Titanium Oxide Sol While stirring 25 g of the acidic titanium oxide aqueous sol of sample a at room temperature, 15.5 g of ethanol was gradually added to obtain an acidic titanium oxide sol diluted with ethanol. The dilution ratio was 1.6 times by weight. Then, ethyl silicate (ethyl silicate 28: general formula Si _n O _n-1 (OC
₂ H _{5) 2n + 2} (where n is 1), to obtain a diluted ethyl silicate with ethanol and diluted to 80% by Colcoat Co., Ltd.) was dissolved in ethanol. The dilution ratio was 2.3 times by weight. 40.5 g of the obtained acidic titanium oxide sol diluted with ethanol and 59.5 g of ethyl silicate diluted with ethanol were mixed, and an anion exchange resin (Amberlite IRA-910: manufactured by Organo Corporation) was wetted.
303 g was added with stirring and neutralized by ion exchange. Then, the ion exchange resin was filtered, and the pH5.
4. A neutral titanium oxide sol of the present invention (sample E) having a solid content of 3.4% by weight was obtained. This sample E has a weight ratio (SiO ₂ / Ti) of the amount of silicon in ethyl silicate converted to SiO ₂ and the amount of titanium in titanium oxide converted to TiO _2.
O ₂ ) was 1.

The particle diameters of titanium oxide in Samples A, B and E were all 1 to 2 nm. The particle diameter of titanium oxide in each of Samples C and D was 10 nm.

Comparative Example 1 Aqueous sol of acidic titanium oxide obtained in Example 3 (sample b)
Was diluted to 15% by weight with ion-exchanged water, and then added to a wet anion-exchange resin (Amberlite IRA-9).
10: manufactured by Organo Corporation) with stirring, and neutralized to pH 7 by ion exchange. Next, the ion-exchange resin was filtered and subjected to ultrasonic irradiation for 3 hours to obtain a neutral titanium oxide aqueous sol (sample F) of a comparative sample. This sample F
SiO ₂ / TiO ₂ was 0.

Comparative Example 2 Example 3 was repeated except that 19.6 g of methyl silicate diluted with methanol was changed to 9.8 g.
To obtain a neutral titanium oxide sol of a comparative sample (sample G). Sample G had a pH of 6.8 and a solid content of 5.7% by weight. Also, the weight ratio (SiO ₂ / Ti) of the amount of silicon in methyl silicate converted to SiO ₂ and the amount of titanium in titanium oxide converted to TiO _2.
O ₂ ) was 0.5.

The neutral titanium oxide sols of the present invention (samples A, B, C, D, and E) and the comparative sample neutral titanium oxide sols (samples F and G) obtained in the examples were each adjusted to a titanium oxide concentration of 0.5. %, And water was used as a control sample in a quartz cell having an optical path length of 1 cm, and the spectral transmittance at a wavelength of 550 nm was measured. Table 1 shows the obtained results.

[0033]

[Table 1]

As shown in Table 1, the transmittance of the neutral titanium oxide sol of the present invention at a wavelength of 550 nm is 90% or more.
It turned out that it was excellent in transparency.

Next, using the neutral titanium oxide sol of the present invention (samples A, C and D) obtained in the examples, samples A and C were used.
5% solids for C, 1 solids for sample D
After dilution with ion-exchanged water to 0%, the spectral transmittance was measured at the initial stage and after 20 days by the above method. Table 2 shows the obtained results.

[0036]

[Table 2]

As can be seen from Table 2, the transmittance of the neutral titanium oxide sol of the present invention hardly changed even after standing for 20 days. On the other hand, it was found that Comparative Sample F gelled after 20 days and had poor dispersion stability.

[0038]

According to the present invention, an alkyl silicate is blended as a dispersion stabilizer, and the amount of silicon in the alkyl silicate is calculated as SiO ₂ and the amount of titanium in the titanium oxide is calculated as TiO ₂ . Weight ratio (SiO ₂ / TiO
₂ ) is a titanium oxide sol characterized by having 0.7 to 10 and having excellent dispersibility even in a neutral pH range,
It has excellent dispersion stability even under light irradiation,
Furthermore, it has excellent dispersion stability even when the pH of the sol is changed, and can be used for applications such as white pigments, ultraviolet absorbers, photocatalysts, catalysts, catalyst carriers, and adsorbents. Further, the titanium oxide sol of the present invention has an advantage that it is difficult to aggregate even when a hydrophilic organic solvent is blended. Titanium oxide sol blended with a hydrophilic organic solvent has the advantages of lower surface tension, better wetting, white pigments, and improved compatibility with other raw materials when used as an ultraviolet absorber. Yes, and can be used for a wider range of applications. Further, the present invention is a method for producing a titanium oxide sol which is obtained by blending an alkyl silicate as a dispersion stabilizer and is stable at a pH in a neutral region, wherein the alkyl silicate and the titanium oxide sol are mixed and then neutralized. This is a method for producing a titanium oxide sol, which is industrially advantageous in producing a titanium oxide sol that is stable at a neutral pH.

Continued on front page F-term (reference) 4D077 AA03 AA09 AB04 AB11 AB20 AC05 BA07 BA20 CA02 CA12 CA14 DB06X DB06Z DC02Y DC19Y DC70X DD55X DE02Y DE07Y 4G047 CA02 CA10 CB05 CC01 CC03 4G065 AA06 AB28Y BA07 BA03 EA01 003 FA10

Claims (13)

[Claims] 1. A titanium oxide sol which is stable at a pH in a neutral range, comprising an alkyl silicate as a dispersion stabilizer, wherein silicon in the alkyl silicate is converted into SiO ₂ and the the weight ratio of the converted amount of titanium _{TiO 2 (SiO 2 / TiO 2} ) is 0.7 to 10
A titanium oxide sol, which is: 2. The spectral transmittance measured under the following conditions is 80 to
The titanium oxide sol according to claim 1, wherein the sol is 100%. Measurement conditions: titanium oxide concentration 0.5% by weight,
Quartz cell optical path length 1cm, control sample water, light wavelength 550
nm 3. The titanium oxide sol according to claim 1, wherein the particle diameter of the titanium oxide is 1 to 100 nm. 4. The method according to claim 1, wherein the alkyl silicate is Si _n O _n-1 (O
The titanium oxide sol according to claim 1, wherein R) _{2n + 2} (where n is 1 to 6, and R is an alkyl group having 1 to 4 carbon atoms). 5. The titanium oxide sol according to claim 1, wherein the sol medium comprises water and a hydrophilic organic solvent. 6. The titanium oxide sol according to claim 5, wherein the hydrophilic organic solvent is an alcohol. 7. A method for producing a titanium oxide sol which is compounded with an alkyl silicate as a dispersion stabilizer and is stable at a neutral pH, wherein the alkyl silicate and the titanium oxide sol are mixed and then neutralized. A method for producing a titanium oxide sol. 8. The method for producing a titanium oxide sol according to claim 7, wherein a titanium oxide sol and an alkyl silicate which are stable at a pH in an acidic range are mixed. 9. The method for producing a titanium oxide sol according to claim 7, wherein the titanium oxide sol and the alkyl silicate each diluted with a hydrophilic organic solvent are mixed. 10. The method for producing a titanium oxide sol according to claim 9, wherein the hydrophilic organic solvent is an alcohol. 11. A method comprising diluting an aqueous sol of titanium oxide 1.2 to 5 times with a hydrophilic organic solvent, diluting an alkyl silicate 1.5 to 5 times with a hydrophilic organic solvent, and mixing. A method for producing the titanium oxide sol according to claim 9. 12. The method for producing a titanium oxide sol according to claim 7, wherein the neutralization is performed by at least one method selected from a method by ion exchange, a method of adding a neutralizing agent, and a method by dialysis. 13. The method for producing a titanium oxide sol according to claim 12, wherein neutralization is performed by adding a neutralizing agent after the ion exchange.