JP2014201451A - Titania nanoparticle, dispersion liquid thereof, and titania paste using the titania nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide titania nanoparticles superior in dispersibility without using an inorganic strong acid or an organic dispersant or the like and to control the particle diameter of titania nanoparticles, and further to easily obtain a dispersion liquid having high transparency and a titania paste without using an inorganic strong acid or an organic dispersant or the like.SOLUTION: There are provided titania nanoparticles obtained by a method which comprises: (A) a step of obtaining a dispersion liquid by mixing a substance containing titanium, an organic acid and water; (B) a step of stirring the dispersion liquid obtained in the step (A) for 5 minutes or more; and (C) a step of heating the dispersion liquid obtained in the step (B) at 50°C or more for one hour or more, wherein in the step (A), in the mixing ratio between the substance containing titanium and the organic acid, the carboxyl group in the organic acid is 2 mol or more based on 1 mol of the titanium in the substance containing titanium.

Description

  The present invention relates to titania nanoparticles, a dispersion thereof, and a titania paste using the titania nanoparticles.

  Titania (titanium oxide) is used as a photocatalyst for decomposing toxic substances and dirt, and as a hydrophilic film, as well as various hydrogen and oxygen synthesis, anticorrosion, resin additives, negative electrodes for dye-sensitized solar cells, artificial photosynthesis, etc. Application is considered. Titania synthesized by a wet method using titanyl sulfate as a raw material or a gas phase method using titanium tetrachloride as a raw material is common and is sold as a powder.

J. Phys. Chem. B 2003, 107, 14336-14341

However, these photocatalytic titanias are insufficiently dispersible and agglomerate in water or alcohol, which is difficult to apply uniformly. On the other hand, when an organic dispersant is used, There is a problem that the activity of the titania surface is impaired. Further, when dispersed using a strong inorganic acid such as nitric acid or hydrochloric acid, the dispersibility is improved, but there is a problem that the surrounding apparatus is corroded by the volatilization of the acid.

  In addition, when used in dye-sensitized solar cells, etc., the dispersant is decomposed because it is fired at a high temperature after using the dispersant, but commercially available titania for photocatalyst is insufficient in transparency and excessive light scattering. There is a problem that energy is lost and sufficient performance cannot be obtained (titania for photocatalyst is in a strongly aggregated state, and aggregation cannot be avoided even if a dispersant is added).

  There is also a method of hydrothermal synthesis reaction using a titanium source such as titanium alkoxide and an inorganic strong acid such as nitric acid or hydrochloric acid (Non-Patent Document 1 etc.). In many cases, nitric acid or hydrochloric acid cannot be used because problems may occur. In the method of Non-Patent Document 1, crystallization is fast, particle formation is completed, and the particle size is saturated. Therefore, even if the reaction time is extended or the temperature is increased, the particle size is not so large. In particular, there is a problem that it is difficult to control the particle size during scale-up.

  Accordingly, an object of the present invention is to provide titania nanoparticles having extremely good dispersibility without using a strong inorganic acid, an organic dispersant, or the like, and to control the particle size of the titania nanoparticles. Another object of the present invention is to easily obtain a highly transparent dispersion or titania paste without using a strong inorganic acid or organic dispersant.

As a result of intensive studies in view of the above object, the present inventors have found that all of the above problems can be solved by performing a hydrothermal synthesis reaction using a specific amount of an organic acid. Then, further research was conducted to complete the present invention. That is, the present invention includes the following configurations.
Item 1. (A) A step of mixing a substance containing titanium, an organic acid and water to obtain a dispersion,
(B) a step of stirring the dispersion obtained in the step (A) for 5 minutes or more, and (C) a step of heating the dispersion obtained in the step (B) at 50 ° C. or more for 1 hour or more. ,and,
In the step (A), the mixing ratio of the substance containing titanium and the organic acid is a titania nanoparticle obtained by a method in which the carboxyl group in the organic acid is 2 moles or more with respect to 1 mole of titanium in the substance containing titanium. .
Item 2. Item 2. The titania nanoparticles according to Item 1, wherein the step (A) is a step of adding a substance containing titanium to a mixed solvent of an organic acid and water while stirring.
Item 3. Item 3. The titania nanoparticles according to Item 1 or 2, wherein the heating temperature in the step (C) is 150 ° C or higher.
Item 4. Item 4. The titania nanoparticles according to any one of Items 1 to 3, wherein the heating pressure in the step (C) is 0.45 MPa or more.
Item 5. Item 1-4 is a step in which the step (C) is a step of bringing the dispersion obtained in the step (B) into contact with supercritical water at 374 ° C or higher and holding at 300 ° C or higher for 10 seconds or longer. The titania nanoparticle according to any one of the above.
Item 6. Item 6. The titania nanoparticles according to any one of Items 1 to 5, wherein the substance containing titanium is titanium alkoxide, titanium hydroxide, or titanium halide.
Item 7. Item 7. The titania nanoparticles according to any one of Items 1 to 6, wherein the concentrations of the N, Cl, and S elements in the dispersion prepared in the step (A) are each 0.01 mol / L or less.
Item 8. Item 8. The titania nanoparticles according to any one of Items 1 to 7, wherein the concentration of the inorganic acid in the dispersion produced in the step (A) is 0.01 mol / L or less.
Item 9. Item 9. The titania nanoparticles according to any one of Items 1 to 8, wherein the dispersion prepared in the step (A) has a pH of 2 or more and less than 6.
Item 10. Item 1-9, wherein the organic acid is at least one selected from the group consisting of a monocarboxylic acid having 1 to 12 carbon atoms, a dicarboxylic acid having 2 to 10 carbon atoms, and a hydroxycarboxylic acid having 1 to 6 carbon atoms. The titania nanoparticle according to any one of the above.
Item 11. Item 11. The titania nanoparticles according to any one of Items 1 to 10, wherein the organic acid is acetic acid.
Item 12. (A) A step of mixing a substance containing titanium, an organic acid and water to obtain a dispersion,
(B) a step of stirring the dispersion obtained in the step (A) for 5 minutes or more, and (C) a step of stirring the dispersion obtained in the step (B) at 50 ° C. or more for 1 hour or more. ,and,
In the step (A), the mixing ratio of the substance containing titanium and the organic acid is such that the carboxyl group in the organic acid is 2 mol or more per 1 mol of titanium in the substance containing titanium. .
Item 13. A titania dispersion containing 60% by weight or more of water and the titania nanoparticles according to any one of Items 1 to 11.
Item 14. Item 14. The titania dispersion according to Item 13, which does not contain an organic dispersant separately from the organic acid.

  According to the present invention, titania nanoparticles having high transparency during dispersion and coating can be produced by controlling the particle size without using an inorganic strong acid or an organic dispersant. Moreover, the titania dispersion liquid and titania paste with high transparency at the time of application | coating can be manufactured.

It is a photograph which shows the state of the reaction liquid of Example 2 (after 240 hours of ultrasonic dispersion) and the reaction liquid of Comparative Example 3 (after 1 hour of ultrasonic dispersion).

In this specification, “titanium oxide” or “titania” does not only refer to titanium dioxide (TiO ₂ ) but also titanium dioxide (Ti ₂ O ₃ ); titanium monoxide (TiO); Ti ₄ O. ₇ and those having a composition deficient in oxygen from titanium dioxide typified by Ti ₅ O _{9 and the} like. Further, as represented by terminal OH groups and COOH groups, groups other than Ti—O—Ti resulting from the synthesis of titanium oxide may be included.

1. Titania nanoparticles The titania nanoparticles of the present invention are:
(A) A step of mixing a substance containing titanium, an organic acid and water to obtain a dispersion,
(B) a step of stirring the dispersion obtained in the step (A) for 5 minutes or more, and (C) a step of heating the dispersion obtained in the step (B) at 70 ° C. or more for 1 hour or more. ,and,
In the step (A), the mixing ratio of the substance containing titanium and the organic acid is obtained by a method in which the carboxyl group in the organic acid is 2 moles or more with respect to 1 mole of titanium in the substance containing titanium.

<Process (A)>
In the step (A), a substance containing a specific amount of titanium, a specific amount of organic acid, and water are mixed to obtain a dispersion.

  The substance containing titanium to be used is not particularly limited as long as it is a substance that becomes titanium oxide by heating. That is, as the substance containing titanium, titanium oxide and / or a titanium oxide precursor are preferable. Specifically, titanium oxide; titanium hydroxide; titanium alkoxide; titanium halide such as titanium trichloride and titanium tetrachloride (especially Neutralized with a base); metal titanium and the like. Moreover, only 1 type of these may be used and 2 or more types may be used together. Among these, titanium alkoxide, titanium hydroxide or titanium halide (especially neutralized with a base) is preferable from the viewpoint of dispersibility of the obtained titania, and titanium alkoxide is particularly preferable from the viewpoint of purity and dispersibility. .

  Examples of the titanium alkoxide include titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra n-propoxide, titanium tetraethoxide, and the like, from the viewpoint of cost and water solubility of by-products, titanium tetraisopropoxide. Is preferred.

  Depending on the combination of titanium alkoxide and organic acid, an ester compound that is hardly soluble in water may be liberated using the obtained titania as a catalyst, but titania itself has no problem (for example, titanium tetra-n-butoxide and acetic acid). However, from the viewpoint of obtaining a uniform dispersion, a combination of an organic acid and a titanium alkoxide is used from which a water-soluble organic acid alkoxide can be obtained. It is preferable.

  Titanium halide (titanium tetrachloride, titanium trichloride, etc.) is neutralized with a base from the viewpoint of impurities (halogen), corrosion of the reactor during mass production, and crystallinity control, and the precipitate is washed. Is preferably used. In that case, it is preferable to use without performing drying from a dispersible viewpoint of the titania obtained.

  In addition, when using solid, such as a titanium oxide and a metal titanium, an average particle diameter has preferable 100 nm or less, and 50 nm or less is more preferable. The lower limit is not particularly set, but is usually about 1 nm. When the particle size is large, the particles may be pulverized dry or wet using a planetary ball mill, paint shaker or the like. The average particle diameter can be measured, for example, by observation with an electron microscope (SEM or TEM).

  The concentration of the substance containing titanium in the dispersion is preferably from 0.01 to 5 mol / L, more preferably from 0.05 to 3 mol / L, from the viewpoint of productivity and the viscosity of the reaction solution.

The acid used in the reaction is an organic acid, a monocarboxylic acid represented by the chemical formula C _n H _{2n + 1} COOH (n = 0 to 11), a dicarboxylic acid represented by HOOCC _m H _2m COOH (m = 0 to 8), Examples thereof include hydroxycarboxylic acids having 1 to 6 carbon atoms.

  In the monocarboxylic acid, acetic acid with n = 1 is desirable from the viewpoint of solubility in water (especially n = 4 or less is easily dissolved in water) and odor (especially, n = 2 to 4 has a strong bad odor).

  As for the dicarboxylic acid, m = 0 to 2 is preferable from the viewpoint of solubility in water, but m = 1 or 2 is more preferable in consideration of dispersibility in titania.

  Examples of the hydroxycarboxylic acid include glycolic acid, lactic acid, malic acid, tartaric acid, citric acid and the like.

  Of these, acetic acid is particularly preferable.

  These organic acids may use only 1 type and may use 2 or more types together.

  From the viewpoint of dispersibility and cost, the amount of the organic acid used is preferably adjusted so as to contain 2 moles or more, preferably 4 to 10 moles of COOH groups with respect to 1 mole of titanium in the substance containing titanium. The more organic acid is used, the better the dispersibility and the larger the particle size.

  The concentration of the organic acid in the dispersion is preferably 0.02 to 10 mol / L and more preferably 0.1 to 7 mol / L from the viewpoints of dispersibility and cost.

  As the reaction solvent, an aqueous solvent such as water is preferably used as a main component (specifically, for example, 50% by weight or more), but may contain alcohols or esters during the reaction.

  For example, when titanium tetraisopropoxide is used as a raw material, isopropanol is produced by reaction with an organic acid. Moreover, the isopropyl ester of organic acid may be produced by heating. That is, alcohols or esters may be added to the dispersion obtained in the step (A) or may be generated in the system. The alcohols or esters may be removed by heating in an open system at 100 ° C. or lower, or may remain in the reaction solution.

  In addition, when alcohol is contained in a dispersion liquid, it exists in the tendency for a particle size to become small, and in order to control a particle size, you may add alcohol intentionally.

  In the present invention, inorganic acids (particularly strong inorganic acids) such as nitric acid, hydrochloric acid, and sulfuric acid that are often used for the hydrothermal synthesis reaction of titania nanoparticles usually have low transparency of the resulting titania nanoparticles. Do not use in principle from the viewpoint of corrosion, impurities, drainage, etc. However, when the dispersibility, uniformity, etc. of the raw materials are increased and handling is facilitated, they can be used supplementarily within a range not impairing the effect, for example, within a range of 0.01 mol / L or less. In this case, the concentrations of N, Cl, and S elements in the dispersion are all 0.01 mol / L.

  The pH of the dispersion obtained in the step (A) is preferably 2 or more and less than 6 and more preferably 2.4 to 5 from the viewpoints of corrosion of the apparatus, safety of handling, and dispersibility.

  In the step (A), a method for producing the dispersion is not particularly limited, and a substance containing titanium, an organic acid, and water (solvent) may be mixed simultaneously or sequentially. In particular, from the viewpoint of preventing agglomeration and forming a large lump so that stirring can be continued, it is preferable to add a substance containing titanium while stirring after mixing the organic acid and water (solvent). In addition, when water is dripped after mixing the substance containing titanium and the organic acid, it tends to aggregate on the contrary.

<Process (B)>
In the step (B), the dispersion obtained in the step (A) is stirred for 5 minutes or more.

  There is no restriction | limiting in particular in the method of stirring, What is necessary is just to follow a conventional method. The stirring time is 5 minutes or more, preferably 15 minutes or more, from the viewpoint of sufficiently reacting the substance containing titanium, the organic acid and water. The upper limit of the stirring time is not particularly limited, but is usually about 240 hours.

<Process (C)>
In the step (C), the dispersion obtained in the step (B) is heated at 70 ° C. or higher for 1 hour or longer.

  Step (C) may be performed under normal pressure, or may be performed under pressure in a sealed container. When performed under pressure, it may be performed under supercritical conditions. More specifically, the pressure during heating is preferably 0.45 MPa or more and more preferably 1 to 30 MPa from the viewpoint of increasing the particle size. However, when the particle size may be small, it is easier to carry out under normal pressure.

  The heating temperature is 50 ° C. or higher, preferably 70 to 450 ° C., more preferably 150 to 400 ° C. When the heating temperature is less than 50 ° C., highly active titania nanoparticles cannot be obtained.

  In addition, when performing reaction under a normal pressure, 50-120 degreeC is preferable and 70-110 degreeC is more preferable from a viewpoint from which a titania nanoparticle with a smaller average particle diameter is obtained.

  Moreover, when performing reaction under pressurization (not supercritical), 120-370 degreeC is preferable and 150-300 degreeC is more preferable from a viewpoint from which a titania nanoparticle with a larger average particle diameter than normal pressure is obtained. In this case, you may heat at low temperature (for example, 50-120 degreeC) first, and then you may heat to high temperature (for example, 120-370 degreeC).

  Even under pressure, when the process is performed under supercritical conditions, the dispersion obtained in step (B) is mixed with supercritical water in a flow reactor, for example, so that the particle size can be reduced in a very short time. It is possible to synthesize all the titania nanoparticles and a titania dispersion with extremely high dispersibility. In this case, the dispersion obtained in step (B) at 50 ° C. or lower is mixed with supercritical water at 374 ° C. or higher, and 300 ° C. or higher (especially 375 to 450 ° C.) for 1 second or longer (especially 5 to 600 seconds). ) It is preferable to hold. When contacting with supercritical water, the reaction can be completed in a very short time.

  The titania nanoparticles of the present invention thus obtained have greatly improved dispersibility compared to conventional titania nanoparticles.

The titania nanoparticles of the present invention have an average particle size of about 3 to 50 nm, particularly about 4 to 40 nm. Moreover, the titania nanoparticle of the present invention has a specific surface area of 30 to 500 m ² / g, particularly 40 to 350 m ² / g. Furthermore, the titania nanoparticles of the present invention can be obtained in which the concentrations of N, Cl and S elements are all 0 to 5000 ppm, particularly 0 to 1000 ppm.

  Thereafter, the titania nanoparticles of the present invention can be recovered by precipitation and centrifugation of the titania nanoparticles of the present invention by a conventional method.

  Thus, the titania nanoparticles of the present invention can adjust the average particle diameter and specific surface area, and are excellent in dispersibility, so that they are not only for photocatalysts (superhydrophilic, organic / inorganic decomposition, hydrogen production, etc.) , For dye-sensitized solar cells, for transparent conductive films, for catalyst carriers, for heat-resistant coatings, for high refractive coatings, for thermal barrier coatings, etc.

2. Titania Dispersion The titania dispersion of the present invention can be prepared as a uniform dispersion by adding a dispersion step such as ultrasonic dispersion using the reaction solution that has undergone the steps (A) to (C). At this time, in the conventional titania dispersion, since a uniform dispersion could not be obtained unless a dispersant was used, in the present invention, a dispersant may be added, but a dispersant is not added. However, a dispersion having far better dispersibility than ordinary titania nanoparticles can be obtained. As a result of good dispersibility, the coating has excellent crack resistance. Further, as a result of not having to add a dispersant, a dense titania coating is possible.

  At this time, in the titania dispersion of the present invention, the content of water as a solvent is preferably 60% by weight or more, particularly 75% by weight or more from the viewpoint of easy coating and film properties of the coating.

  It is also possible to take out titania nanoparticles from the reaction solution and change the solvent. Water may be removed from the reaction solution by centrifugation, filtration membrane, or the like, and replaced with an organic solvent. In that case, it is preferable not to dry the titania nanoparticles from the viewpoint of dispersibility, transparency and the like.

  Examples of the organic solvent used in the dispersion include alcohols. Examples of the alcohol include aliphatic alcohols having 1 to 6 carbon atoms such as methanol, ethanol and isopropanol, and non-aliphatic alcohols such as α-terpineol; butyl carbitol (diethylene glycol monobutyl ether), hexylene glycol ( 2-methyl-2,4-pentanediol), glycol solvents such as ethylene glycol-2-ethylhexyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, 1,4-butanediol, 1,5-pentanediol, And diols such as 6-hexanediol.

  Moreover, even if it does not have an OH group, it only needs to have an affinity with titania and other solvents (water, alcohol, etc.), diethylene glycol butyl methyl ether, tripropylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, Examples include triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol diacetate, triethylene glycol diacetate, and tetraethylene glycol diacetate. Of these, diethylene glycol monobutyl ether acetate, tetraethylene glycol dimethyl ether and the like are preferable from the viewpoint of boiling point and the like.

  The titania dispersion of the present invention adjusts the viscosity according to the application, for example, low viscosity when used for spin coating, dip coating, spraying, etc., and higher viscosity when used for brush coating, squeegee method, etc. And when using for screen printing, it is preferable to adjust viscosity further and to suppress fluidity | liquidity.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Example 1]
Acetic acid 120 g (2 mol) was added to titanium tetraisopropoxide 142.1 g (0.5 mol), and the mixture was stirred for 15 minutes, and 550 g of water was added. The pH of this dispersion was 2.5. Although a large amount of translucent precipitate was generated, heating was performed after stirring for 60 minutes, and all the precipitate was dissolved at 60 ° C.

  Then, after stirring at 80 ° C. for 5 hours at normal pressure (0.1 MPa), water was added to the reaction solution to prepare a total of 800 g, and then subjected to ultrasonic waves, it was translucent without using an inorganic strong acid. A uniform titania dispersion was obtained. When this dispersion was applied to glass by spin coating and dried, a transparent coating film was obtained.

Aqueous ammonia was added to this dispersion, and the mixture was precipitated to pH 6. The titania nanoparticles were collected by centrifugation, and the average particle size was calculated from the BET specific surface area (300 m ² / g). .

  Further, when the crystallinity was analyzed by X-ray diffraction, it was 100% anatase.

[Example 2]
200 g of the titania dispersion obtained in Example 1 was placed in a titanium autoclave, and further reacted in a hot air oven at 9 MPa and 300 ° C. for 12 hours.

  The resulting reaction solution had a white precipitate, but by ultrasonic dispersion, it was evenly dispersed without using an inorganic strong acid, and no precipitate was formed after 240 hours. When this dispersion was applied to glass and dried, a translucent coating film was obtained.

The dispersion was centrifuged to collect titania nanoparticles, and the average particle size was calculated from the BET specific surface area (60 m ² / g), which was 25 nm.

  Further, when the crystallinity was analyzed by X-ray diffraction, it was 100% anatase.

[Example 3]
To a mixture of 60 g (1 mol) of acetic acid and 600 g of water, 142.1 g (0.5 mol) of titanium tetraisopropoxide was slowly added dropwise. The dispersion had a pH of 2.6. Thereafter, when the mixture was stirred for 60 minutes, a large amount of white precipitate was generated. Thereafter, heating was performed at 60 ° C. for 3 hours and at 80 ° C. for 5 hours at normal pressure (0.1 MPa) with stirring, and a cloudy liquid was obtained.

  Water was added to this solution to prepare 800 g, and then ultrasonic dispersion was performed to obtain a uniform titania dispersion without using an inorganic strong acid, and precipitation did not occur after 240 hours. When this dispersion was applied to glass and dried, a translucent coating film was obtained.

  200 g of this dispersion was placed in a titanium autoclave and further reacted in a hot air oven at 9 MPa and 300 ° C. for 12 hours.

  The resulting reaction solution had a white precipitate, but by carrying out ultrasonic dispersion, a uniform titania dispersion was obtained without using an inorganic strong acid, and no precipitate was formed after 240 hours. When this dispersion was applied to glass and dried, a translucent coating film was obtained.

The dispersion was centrifuged to recover titania nanoparticles, and the average particle size was calculated from the BET specific surface area (70 m ² / g), which was 22 nm.

[Example 4]
The experiment was conducted in the same manner as in Example 2 except that the reaction time at 300 ° C. in the hot stove was changed to 60 hours instead of 12 hours.

  The obtained titania dispersion had a white precipitate, but was uniformly dispersed by ultrasonic dispersion, and no precipitate was formed after 240 hours. When this titania dispersion was applied to glass and dried, a translucent coating film was obtained.

The titania nanoparticles were recovered by centrifuging the dispersion, and the average particle size was calculated from the BET specific surface area (38 m ² / g) to be 40 nm.

[Example 5]
The experiment was performed in the same manner as in Example 2 except that the reaction temperature in the hot stove was changed to 250 ° C. instead of 300 ° C.

  The obtained titania dispersion had a white precipitate, but was uniformly dispersed by ultrasonic dispersion, and no precipitate was formed after 240 hours. When this titania dispersion was applied to glass and dried, a transparent coating film was obtained.

The dispersion was centrifuged to collect titania nanoparticles, and the average particle size was calculated from the BET specific surface area (90 m ² / g), and was 17 nm.

[Example 6]
The experiment was conducted in the same manner as in Example 2 except that the reaction temperature in the hot stove was changed to 250 ° C. instead of 300 ° C., and the reaction time was changed to 60 hours instead of 12 hours.

  The obtained titania dispersion had a white precipitate, but was uniformly dispersed by ultrasonic dispersion, and no precipitate was formed after 240 hours. When this titania dispersion was applied to glass and dried, a translucent coating film was obtained.

The dispersion was centrifuged to recover titania nanoparticles, and the average particle size was calculated from the BET specific surface area (65 m ² / g), which was 24 nm.

[Example 7]
The titania nanoparticles obtained in Example 5 were centrifuged to collect titania nanoparticles, and ethanol washing, ultrasonic dispersion, and centrifugation were repeated three times, taking care not to dry them.

  100 g of ethanol, 40 g of terpineol and 5 g of ethyl cellulose (10 cp) were added to 10 g of the titania nanoparticles obtained (wet with 25 g of ethanol), and stirred for 3 hours. After ultrasonic dispersion, ethanol and terpineol were mixed. A dispersed uniform titania dispersion was obtained, and no precipitation occurred after 240 hours. When this titania dispersion was applied to glass and dried, a transparent coating film was obtained.

[Example 8]
Aqueous titanium hydroxide was obtained by adding ammonia water to the titanium tetrachloride aqueous solution and adjusting the pH to 10 (16 wt% in terms of titania).

  To 100 g of this hydrous titanium hydroxide (corresponding to 0.2 mol of titania), 60 g (1 mol) of acetic acid and 160 g of water were added. The pH of this dispersion was 2.4. After stirring for 60 minutes and heating at 80 ° C. for 5 hours at normal pressure (0.1 MPa), water was added to prepare 320 g.

  200 g of this solution was placed in a titanium autoclave and reacted at 9 MPa and 300 ° C. for 12 hours.

  The resulting reaction solution had a white precipitate, but by ultrasonic dispersion, it was uniformly dispersed without using an inorganic strong acid, and no precipitate was formed after 48 hours. When this dispersion was applied to glass and dried, a translucent coating film was obtained.

The dispersion was centrifuged to collect titania nanoparticles, and the average particle size was calculated from the BET specific surface area (42 m ² / g), which was 37 nm.

  100 g of ethanol, 40 g of terpineol, 2.5 g of ethyl cellulose (10 cp) and 2.5 g of ethyl cellulose (50 cp) are added to 10 g of titania nanoparticles (but wet with 20 g of ethanol), and stirred for 3 hours to perform ultrasonic dispersion. As a result, a uniform dispersion dispersed in ethanol and terpineol was obtained, but no precipitation occurred after 48 hours, although not as much as in Examples 1-8 above. When this titania dispersion was applied to glass and dried, a translucent coating film was obtained.

  By baking this coating film at 500 degreeC, the coating film which consists only of translucent titania nanoparticle was obtained.

[Example 9]
200 g of the titania dispersion obtained in Example 1 was diluted with 800 g of water to obtain 1000 g. A translucent and uniform dispersion was obtained.

  Using a flow-type supercritical reaction apparatus, a volume of 450 ° C. supercritical water was mixed with this dispersion in a metal tube and held at 400 ° C. for about 60 seconds.

  The reaction liquid discharged from the reactor was already a translucent dispersion (titania dispersion). When this dispersion was applied to glass and dried, a translucent coating film was obtained.

[Comparative Example 1]
While stirring 650 g of an aqueous nitric acid solution having a pH of 0.7, 142.1 g (0.5 mol) of titanium tetraisopropoxide was added. The pH of this dispersion was 1.0. After stirring for 1 hour, the temperature was raised to 80 ° C. at normal pressure (0.1 MPa) and maintained for 8 hours to synthesize a translucent titania dispersion. The final weight was adjusted to 800 g.

  This dispersion was applied onto a glass substrate by spin coating, but when dried, titania peeled off from the substrate.

The obtained dispersion was dried, and the average particle size of the nanoparticles was calculated from the BET specific surface area (220 m ² / g) by calculation.

  Further, when the raw titania dispersion was observed after 48 hours, precipitation occurred and gelation progressed to increase the viscosity.

[Comparative Example 2]
200 g of the titania dispersion obtained in Comparative Example 1 was sealed in a titanium pressure vessel and reacted in a hot air oven at 4 MPa and 250 ° C. for 12 hours to synthesize titania nanoparticles.

  The obtained reaction solution had a white precipitate and was subjected to ultrasonic dispersion, but the precipitate was formed after 1 hour and was in a non-uniform state.

Moreover, it was 12 nm when the average particle diameter of the obtained nanoparticle was computed from the BET specific surface area (126 m < ² > / g) by calculation.

[Comparative Example 3]
Acetic acid (30 g, 0.5 mol) was added to titanium tetraisopropoxide (142.1 g, 0.5 mol) and stirred for 15 minutes, and water (630 g) was added. The pH of this dispersion was 3.0. Although a large amount of translucent precipitate was generated, 4 ml of 65% nitric acid was added and heated with stirring for 60 minutes. All precipitates were dissolved at 50 ° C.

  Thereafter, water was added to the liquid stirred at 80 ° C. for 5 hours at normal pressure (0.1 MPa) to prepare a total of 800 g, and ultrasonic waves were applied to obtain a translucent uniform titania dispersion. When applied to glass and dried, the coating film cracked and dropped out of the glass.

Ammonia water was added to the titania dispersion and the precipitate was adjusted to pH 6. The titania nanoparticles were collected by centrifugation, and the average particle size was calculated from the BET specific surface area (280 m ² / g) to be 5.5 nm. Met.

  Thereafter, 200 g of this titania dispersion was sealed in a titanium pressure vessel and reacted in a hot air oven at 4 MPa and 250 ° C. for 12 hours to synthesize titania nanoparticles.

  The obtained reaction solution had a white precipitate and was subjected to ultrasonic dispersion, but the precipitate was formed after 1 hour and was in a non-uniform state.

The titania nanoparticles were recovered by centrifuging this dispersion, and the average particle diameter of the obtained titania nanoparticles was calculated from the BET specific surface area (128 m ² / g), and was 12 nm.

[Comparative Example 4]
The experiment was performed in the same manner as in Comparative Example 3 except that the reaction time in the hot stove was changed to 24 hours instead of 12 hours.

  The obtained reaction solution had a white precipitate and was subjected to ultrasonic dispersion, but the precipitate was formed after 1 hour and was in a non-uniform state.

The titania nanoparticles were recovered by centrifuging this dispersion, and the average particle diameter of the obtained nanoparticles was calculated from the BET specific surface area (120 m ² / g), which was 13 nm, which increased the reaction time. Therefore, the particle size could not be increased.

[Comparative Example 5]
The experiment was conducted in the same manner as in Comparative Example 3 except that the reaction temperature in the hot stove was changed to 300 ° C. instead of 250 ° C.

  The obtained reaction solution had a white precipitate and was subjected to ultrasonic dispersion, but the precipitate was formed after 1 hour and was in a non-uniform state.

The dispersion was centrifuged to collect titania nanoparticles, and the average particle size of the obtained nanoparticles was calculated from the BET specific surface area (96 m ² / g). The result was 16 nm, and the reaction temperature was increased. As a result, the particle size could not be increased dramatically.

[Comparative Example 6]
100 g of ethanol, 40 g of terpineol, and 5 g of ethylcellulose (10 cp) were added to 10 g of titania nanoparticles obtained in Comparative Example 3 (wet with 45 g of ethanol), and the mixture was stirred for 3 hours and subjected to ultrasonic dispersion.

  When this dispersion was applied onto a glass substrate and baked at 500 ° C., cracks occurred, and the titania film dropped from the glass.

[Comparative Example 7]
Add titania nano particles ST-21: 10 g (Ishihara Sangyo Co., Ltd., specific surface area 50 m ² / g, equivalent to 31 nm) 100 g ethanol, 40 g terpineol, 2.5 g ethyl cellulose (10 cp), 2.5 g ethyl cellulose (50 cp), The mixture was stirred for 3 hours and subjected to ultrasonic dispersion.

  When this dispersion was applied onto a glass substrate and baked at 500 ° C., fine cracks were produced, and the titania film was completely opaque.

[Comparative Example 8]
95 g of water was added to the titania nanoparticle ST-21: 5 g, and ultrasonic dispersion was added. However, precipitation occurred immediately and a dispersion could not be obtained.

  Further, even when 1 ml of 65% nitric acid was added, precipitation similarly occurred, and a uniform dispersion could not be obtained.

  For reference, the states of the reaction solution of Example 2 (after 240 hours of ultrasonic dispersion) and the reaction solution of Comparative Example 3 (after 1 hour of ultrasonic dispersion) are shown in FIG.

Claims (14)

(A) A step of mixing a substance containing titanium, an organic acid and water to obtain a dispersion,
(B) a step of stirring the dispersion obtained in the step (A) for 5 minutes or more, and (C) a step of heating the dispersion obtained in the step (B) at 50 ° C. or more for 1 hour or more. ,and,
In the step (A), the mixing ratio of the substance containing titanium and the organic acid is a titania nanoparticle obtained by a method in which the carboxyl group in the organic acid is 2 moles or more per 1 mole of titanium in the substance containing titanium. . The titania nanoparticles according to claim 1, wherein the step (A) is a step of adding a substance containing titanium to a mixed solvent of an organic acid and water while stirring. The titania nanoparticle according to claim 1 or 2, wherein the heating temperature in the step (C) is 150 ° C or higher. The titania nanoparticle according to any one of claims 1 to 3, wherein the heating pressure in the step (C) is 0.45 MPa or more. The step (C) is a step of bringing the dispersion obtained in the step (B) into contact with supercritical water at 374 ° C or higher and holding at 300 ° C or higher for 10 seconds or longer. The titania nanoparticle according to any one of the above. The titania nanoparticle according to any one of claims 1 to 5, wherein the substance containing titanium is titanium alkoxide, titanium hydroxide, or titanium halide. The titania nanoparticles according to any one of claims 1 to 6, wherein the concentrations of the N, Cl and S elements in the dispersion liquid produced in the step (A) are each 0.01 mol / L or less. The titania nanoparticle according to any one of claims 1 to 7, wherein the concentration of the inorganic acid in the dispersion produced in the step (A) is 0.01 mol / L or less. The titania nanoparticles according to any one of claims 1 to 8, wherein the pH of the dispersion prepared in the step (A) is 2 or more and less than 6. The organic acid is at least one selected from the group consisting of a monocarboxylic acid having 1 to 12 carbon atoms, a dicarboxylic acid having 2 to 10 carbon atoms, and a hydroxycarboxylic acid having 1 to 6 carbon atoms. 9. The titania nanoparticle according to any one of 9. The titania nanoparticle according to any one of claims 1 to 10, wherein the organic acid is acetic acid. (A) A step of mixing a substance containing titanium, an organic acid and water to obtain a dispersion,
(B) a step of stirring the dispersion obtained in the step (A) for 5 minutes or more, and (C) a step of stirring the dispersion obtained in the step (B) at 50 ° C. or more for 1 hour or more. ,and,
In the step (A), the mixing ratio of the substance containing titanium and the organic acid is such that the carboxyl group in the organic acid is 2 mol or more per 1 mol of titanium in the substance containing titanium. . A titania dispersion containing 60% by weight or more of water and the titania nanoparticles according to any one of claims 1 to 11. The titania dispersion according to claim 13, which does not contain an organic dispersant separately from the organic acid.

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