WO2015122181A4

WO2015122181A4 - Manufacturing method for strontium titanate fine particles, and strontium titanate fine particles

Info

Publication number: WO2015122181A4
Application number: PCT/JP2015/000618
Authority: WO
Inventors: 佐々木　勉; 田中　淳; 鈴木　真之; 阿尻　雅文
Original assignee: 富士フイルム株式会社; 国立大学法人東北大学
Priority date: 2014-02-14
Filing date: 2015-02-10
Publication date: 2015-10-01
Also published as: JP6081936B2; WO2015122181A1; JP2015151304A

Abstract

[Problem] To provide: a manufacturing method for strontium titanate fine particles which enables the high yield manufacture of strontium titanate fine particles having a controlled shape; and strontium titanate fine particles. [Solution] A manufacturing method for strontium titanate fine particles comprising: step A1, in which an Sr-containing aqueous solution and a Ti-containing aqueous solution are prepared; step B1, in which the Sr-containing aqueous solution and the Ti-containing aqueous solution are mixed to prepare a mixed solution; step C1, in which a basic compound is added to the mixed solution to adjust the mixed solution so as to be basic, and a reaction solution is prepared; a step D1, in which the reaction solution is subjected to a sub-critical or super-critical reaction; and a step E1, in which, prior to the implementation of step D1, an amphipathic compound, which has a carboxyl group, and an organic basic compound, which does not contain a metallic element, are added to the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, or the reaction solution. The pH of the reaction solution used in step D1 is greater than 10.

Description

Method of producing strontium titanate fine particles and strontium titanate fine particles

The present invention relates to a method for producing shape-controlled strontium titanate fine particles suitable as a mother catalyst for dielectric materials and photocatalysts.

Strontium titanate (SrTiO ₃ ) is a composite oxide that is expected to be developed into various applications as functional materials, such as dielectric properties, thermoelectric properties, photocatalytic ability, and high refractive index properties. Photocatalytic activity has attracted attention from the viewpoints of energy and environmental problems in recent years, and strontium titanate produces hydrogen using only sunlight because of its high stability under light irradiation and the strength of photoreduction power. The expectation is growing as a photocatalyst that enables it.

As a hydrogen generation photocatalyst, it is preferable to have activity with respect to visible light which occupies a large proportion of sunlight. Strontium titanate with a metal such as Pt, Rh, or Cu supported as a co-catalyst as a strontium titanate photocatalyst capable of highly efficient hydrogen generation with visible light activity, and further, titanium oxide doped with Rh or Ir Strontium etc. are proposed (patent document 1, patent document 2 grade | etc.,).

On the other hand, among various functional materials, fine particle (nano particle) materials are expected to be capable of realizing high precision, miniaturization, and weight reduction of products because they can exhibit unique excellent properties and functions. Also, in the case of metal oxide materials, nanoparticulate technology is being studied. Patent Document 3 discloses high-temperature, high-pressure water in the coexistence of an organic substance as a method for producing ceria, which is known as an exhaust gas purification catalyst material, as cube-shaped nanocrystal particles having a high proportion of crystal faces with high catalytic activity. Methods have been proposed which are produced by thermal synthesis, preferably by supercritical synthesis.

Patent Documents 4 and 5 describe a method for producing titanium oxide fine particles or fine powder by high temperature, high pressure hydrothermal synthesis, and in an aqueous solution which is a hydrothermal synthesis or a subcritical / supercritical reaction site. It has been reported that nano-sized highly crystalline particles can be produced by suppressing aggregation by reacting fine particles synthesized while performing a synthesis reaction with an organic modifier. However, these documents do not describe controlling the shape so as to have a specific crystal face as in Patent Document 3, and an example actually manufactured is only a simple oxide, and a perovskite oxide There is no example about complex oxides, such as a thing.
Even for the same titanium oxide, the synthesis reaction mechanism is different between the simple oxide and the complex oxide, and it is usually difficult to apply the manufacturing method of the simple oxide to the complex oxide as it is.

There are solid phase method, flux method, sol-gel method, hydrothermal synthesis method etc. as the manufacturing method of the fine particles of strontium titanate, but similar to the patent documents 3-5, hydrothermal synthetic method also synthesizes nano order fine particles It is known that the method can be performed (Patent Documents 6 to 7).

Patent Document 6 discloses that strontium hydroxide and a water-soluble titanium compound such as ammonium titanium peroxolactate are strong at 200 ° C. in the presence of an amphiphilic compound such as oleic acid and a metal element-free basic compound such as hydrazine. It is described that by hydrothermal synthesis under alkaline conditions, it is possible to produce strontium titanate nanoparticles with controlled crystal shape without aggregation.

Further, Patent Document 7 discloses a method of aligning cubic strontium titanate nanocrystals on a substrate and a method of producing a film composed of nanocrystals, and in paragraph [0015], nano particles of strontium titanate are disclosed. In crystal synthesis, crystal growth proceeds with molecules of an organic carboxylic acid such as oleic acid adhering to the (111) plane, so crystal growth on the (111) plane proceeds without being interrupted by organic carboxylic acid molecules. It is described that the growth of all eight (111) planes proceeds to form a vertex and tends to have a cubic shape as a whole.

Patent No. 4076793 Patent No. 3440295 JP 2007-217265 A Patent No. 3925932 gazette Patent No. 4336856 gazette JP 2011-68500 A JP 2012-188335 A Patent No. 2709222 Japanese Examined Patent Publication 3-39016

According to Patent Document 6 and Patent Document 7, although it is possible to control the strontium titanate fine particles into a cubic shape and manufacture, the method of Patent Document 6 makes the hydrothermal reaction at 200 ° C. for 24 hours, and for Patent Document 7 It is necessary to carry out the hydrothermal reaction at 200 ° C. for 72 hours, and all have problems that the synthesis time is long and the productivity is very bad.

Although there is a report on the formation of nanoparticles of strontium titanate other than the hydrothermal synthesis method, there is no description or suggestion about a method of controlling the shape to a cubic (or rectangular parallelepiped) shape having a specific crystal face (patented) Literature 8, Patent Literature 9).

The present invention has been made in view of the above circumstances, and is a method of producing strontium titanate fine particles whose shape is controlled in a cube (or rectangular parallelepiped) shape having a specific crystal plane with high productivity, and obtained using the same. It is an object of the present invention to provide shape-controlled strontium titanate fine particles.

The first production method of the strontium titanate fine particles of the present invention is
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
A basic compound is added to the mixed solution to adjust the mixed solution to be basic to prepare a reaction solution C1;
A subcritical reaction or supercritical reaction of the reaction solution D1;
Prior to carrying out step D1, step E1 of adding an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group to an Sr-containing aqueous solution, a Ti-containing aqueous solution, a mixed solution or a reaction solution is The pH value of the reaction solution used in step D1 is more than 10.

In the step E1, “before performing the step D1” means all the steps and all the steps existing before the step D1 is performed. That is, it means between each process of process A1 to process C1 or between processes A1 to process D1. Step E1 may be performed only once or may be performed multiple times.

As used herein, "reacting the reaction solution" means reacting one or more components contained in the reaction solution.

Further, in the present specification, the term "fine particles" means particles having an average particle size of less than 1 μm, preferably nanoparticles. The nanoparticles may generally refer to those having an average particle size of 200 nm or less, preferably 200 nm or less. In some cases, the nanoparticles may be of a size with an average particle size of 100 nm or less, and in other cases with a size of 50 nm or less. Also preferably, the nanoparticles are of a size whose average particle size is 20 nm or less, and in other cases whose average particle size is 10 nm or less or 5 nm or less You may Also, in a preferred case, the particle size of the nanoparticles is preferably uniform, but in some cases, it may be preferable to mix particles having different particle sizes at a certain ratio.

The average particle size can be measured by a method known in the art, and can be measured by, for example, an electron microscope (TEM, SEM), an adsorption method, a light scattering method, X-ray small angle scattering (SAXS) or the like. In electron microscopy, when the particle size distribution is wide, it is necessary to pay attention to whether or not the particles within the field of view represent all particles.

In the present specification, water above the critical point of water (temperature 374 ° C., pressure 22 MPa) is supercritical water, and water at a temperature near 350 ° C. near critical point is subcritical water The reaction in supercritical water is a supercritical reaction, and the reaction in subcritical water is a subcritical reaction.

Moreover, you may have the process F1 which adds a basic substance or an acidic substance to Sr containing aqueous solution, Ti containing aqueous solution, mixed solution, or a reaction liquid, before implementing the process D1.

The pH of the reaction solution used in step D1 is preferably 11 or more.

The second production method of the strontium titanate fine particles of the present invention is
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
A basic compound is added to the mixed solution to adjust the mixed solution to be basic to prepare a reaction solution C1;
A subcritical reaction or supercritical reaction of the reaction solution D1;
Prior to carrying out step D1, step E1 of adding an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group to an Sr-containing aqueous solution, a Ti-containing aqueous solution, a mixed solution or a reaction solution is Have,
In the step C1, the ionization degree of the basic compound is 0.8 or more,
The concentration of the basic compound in the reaction solution used in step D1 is 0.60 mol / L or more.

In the second production method, the concentration of the basic compound in the reaction solution used in step D1 is preferably 0.70 mol / L or more.

In the first and second production methods of the strontium titanate fine particles of the present invention, the amphiphilic compound is preferably an organic acid having 2 to 20 carbon atoms, and is an organic acid having 10 to 20 carbon atoms. Is more preferred. Such amphiphilic compounds include at least one of oleic acid, decanoic acid, lauric acid, undecenoic acid, linoleic acid, and linolenic acid.

The organic basic compound is preferably at least one of an amine compound, ammonia, hydrazine, and derivatives thereof, and is at least one of hydrazine, hydrazine monohydrate, oleylamine, and hydrazine derivatives. Is more preferred.

The combination of an amphiphilic compound and an organic basic compound is preferably a combination of oleic acid and hydrazine.

In the reaction liquid used in step D1, the number of moles of Ti X, the number of moles of amphiphilic compound Y, and the number of moles of organic basic compound Z are 0 <Y / X ≦ 6 and 0 ≦ Z / X. It is preferable to satisfy ≦ 8, more preferably 1 ≦ Y / X ≦ 4, and most preferably 0 ≦ Z / X ≦ 4.

In the reaction liquid used in step D1, the concentration of the Ti component is preferably 0.1 mmol / L or more and 20 mol / L or less.

In the step A1 of preparing the Sr-containing aqueous solution and the Ti-containing aqueous solution, as the Sr-containing aqueous solution, a solution obtained by dissolving strontium acetate, hydroxide or nitrate in water is preferable. It is preferable that it is a titanium aqueous solution.

In the first production method and the second production method, the Ti-containing aqueous solution used in step B1 of preparing the mixed solution is preferably one not containing TiO ₂ as a main component of the Ti component, and in particular, rutile TiO 2 It is preferable not to contain ₂ .
In the present specification, the "main component" means a component having a content of 50% by mass or more.

In step B1, it is preferable to prepare a mixed solution so that the molar ratio Sr / Ti of Sr and Ti is 1 or more. In the step B1, it is preferable to use the Ti-containing aqueous solution not containing the rutile type TiO ₂ as the main component of a Ti component.

In the step C1, the basic compound is preferably sodium hydroxide or potassium hydroxide. Moreover, it is preferable to grind | pulverize the solid substance generate | occur | produced while adjusting a reaction liquid in process C1 to basicity.

The reaction solution used in step D1 is preferably a reaction solution containing Ti (OH) ₄ and / or HTiO ₃ ⁻ ions as the main component of the Ti component.
In addition, in step D1, the retention time of the reaction temperature in the subcritical reaction or supercritical reaction can be 10 minutes or less.

The strontium titanate fine particles of the present invention are produced by the method for producing strontium titanate fine particles of the present invention described above, and are cubic or rectangular in shape.
In the present specification, the “cubate or cuboid strontium titanate fine particle” also includes an incomplete shape in which the apex of the cube or cuboid is chamfered. At this time, the chamfering ratio is within 20% of the area in each face of a cube or a rectangular parallelepiped. The chamfer was defined from the length of the side. In the method, particles were observed directly by TEM, and the length of one side of the cubic particle and the length of the chamfer were measured, and the ratio to one side was calculated. In such strontium titanate fine particles, 85% or more of the crystal plane exposed on the surface of the cube or rectangular parallelepiped is preferably a {100} plane. The length of one side of a cube or a rectangular solid is preferably 10 nm or more and 500 nm or less.

The method for producing strontium titanate fine particles according to the present invention comprises a reaction liquid containing a basic compound having a pH of 10 or more and an ionization degree of 0.8 or more containing Sr-containing aqueous solution and Ti-containing aqueous solution of 0.60 mol / L or more. A subcritical or supercritical reaction method comprising the steps of adding an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group to a basic reaction solution before the reaction. ing. According to this configuration, by preferentially growing the (111) plane of the strontium titanate crystal, it is possible to manufacture strontium titanate fine particles whose shape is controlled so that the surface has a {100} plane with high productivity. .

Flow chart of the method for producing strontium titanate fine particles of the present invention The figure which shows the relationship between the number-of-moles of the amphiphilic compound contained in a reaction liquid, the ratio with respect to Ti mole number of an organic basic compound, and the manufacture availability of shape-controlled strontium titanate microparticles | fine-particles. Electron micrograph of the strontium titanate fine particles obtained in Example 1 Electron micrograph of amorphous strontium titanate fine particles obtained in Comparative Example 1 Magnified electron micrograph of the strontium titanate fine particles obtained in Example 1 Electron micrograph showing analysis results of crystal face of strontium titanate fine particles obtained in Example 1

"Production method of strontium titanate fine particles"
With reference to the drawings, a method of manufacturing strontium titanate particles according to an embodiment of the present invention will be described. FIG. 1 shows a flow diagram of the method for producing strontium titanate fine particles of the present embodiment.

As described above, as a method of controlling the strontium titanate fine particles into a cubic shape, a method of carrying out a hydrothermal reaction at 200 ° C. for 24 hours or more as in Patent Document 6 and Patent Document 7 is mentioned.
On the other hand, as described in Patent Document 4 and the like, it is described that titanium dioxide fine particles, which are simple oxides, can be obtained without aggregation of fine crystalline particles by a subcritical or supercritical reaction.
In Patent Document 3, ceria fine particles, which are simple oxides, are manufactured to be controlled into a cubic shape by a high temperature / high pressure hydrothermal synthesis method, preferably supercritical synthesis, in the coexistence of an organic substance.

In Patent Document 3, the ratio of cubic ceria fine particles having a (001) plane and a plane equivalent thereto in the produced fine particles by changing the reaction field from the hydrothermal reaction at 200 ° C. to supercritical. Is stated to rise from 70% to 80%. On the other hand, the reaction time is not changed between the hydrothermal reaction site and the supercritical reaction site, and it is neither described nor suggested that the reaction time can be shortened by the difference in the reaction site. In addition, since strontium titanate is a complex oxide, its crystal structure is complicated compared to simple oxides such as ceria and titanium dioxide, so the reaction does not proceed by the same mechanism as simple oxides, and is the same. Even in a supercritical reaction site, more severe conditions are considered to be required as production conditions for shape control of particles.

In Patent Documents 6 and 7, the inventors of the present invention are considered to cause the solubility of the material to rapidly decrease when the water of the reaction solution exceeds the critical point, and the formation of crystal nuclei and the growth thereof rapidly proceed. The particle synthesis was attempted with the reaction field as supercritical, and it was confirmed whether production of strontium titanate fine particles whose shape was controlled to a cubic shape (including a rectangular shape) in a short time was possible (Comparative Examples 4 and 5 described later). As a result, the obtained particles were indeterminate, and it was not possible to control the shape or to reduce the synthesis time.

As a result of intensive investigations by the inventors about the reason why shape control could not be performed in Comparative Examples 4 and 5, the Ti complex used as a Ti source is surrounded by a large complex ligand and a Ti atom is tightly enclosed. Since it exists in the following form, Ti is protected by the complex ligand, and it can not keep up with a high synthesis rate, and it is presumed that the complex oxide can not be formed well.

Therefore, in Patent Document 6 and Patent Document 7, manufacture of strontium titanate fine particles was tried using a titanium compound which is not a complex such as titanium tetrachloride as a titanium source. As a result, as described in the examples, the reaction field was made subcritical or supercritical, and it succeeded in manufacturing strontium titanate fine particles whose shape is controlled to a cubic shape (including a rectangular solid shape). In addition, the reaction time was as short as about 10 minutes, and a significant reduction in reaction time was realized as compared with the case where 24 hours was required in Patent Document 6.

That is, according to the first method for producing strontium titanate fine particles of the present invention,
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
A basic compound is added to the mixed solution to adjust the mixed solution to be basic to prepare a reaction solution C1;
A subcritical reaction or supercritical reaction of the reaction solution D1;
Prior to carrying out step D1, step E1 of adding an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group to an Sr-containing aqueous solution, a Ti-containing aqueous solution, a mixed solution or a reaction solution is The pH value of the reaction solution used in step D1 is more than 10.

Further, according to a second method of producing strontium titanate fine particles of the present invention,
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
A basic compound is added to the mixed solution to adjust the mixed solution to be basic to prepare a reaction solution C1;
A subcritical reaction or supercritical reaction of the reaction solution D1;
Prior to carrying out step D1, step E1 of adding an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group to an Sr-containing aqueous solution, a Ti-containing aqueous solution, a mixed solution or a reaction solution is Have,
In the step C1, the ionization degree of the basic compound is 0.8 or more,
The concentration of the basic compound in the reaction solution used in step D1 is 0.60 mol / L or more.

The first production method and the second production method are the same except that the definition of the basic compound used in step C1 and the definition of the basicity of the reaction liquid used in step D1 are different. In the first production method, the basic compound used in the step C1 is not particularly limited, but it is preferable to use a basic compound having an ionization degree of 0.8 or more as in the second production method.
Each step will be described below with reference to FIG.

<Step (A1)>
Step A1 is a step of preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution, respectively.
The aqueous solution containing Sr is not particularly limited, but hydroxides of Sr, oxides, chlorides, fluorides, halides such as iodide, inorganic salts such as nitrates, carbonates, sulfates, acetates, oxalic acid A salt, an organic acid salt such as a lactic acid salt, etc. may be dissolved in water, and an acetate, a hydroxide or a nitrate may be dissolved in water.

The method for preparing the Sr-containing aqueous solution is not particularly limited, and any known method depending on the substance can be adopted as appropriate.

The aqueous solution containing Ti is not particularly limited, but hydroxides of Ti, oxides, chlorides, fluorides, halides such as iodide, inorganic salts such as nitrates, carbonates, sulfates, acetates, oxalic acid A salt, an organic acid salt such as lactic acid salt and the like dissolved in water may be mentioned, and titanium tetrachloride which is a chloride is preferable.
The method for preparing the Ti-containing aqueous solution is not particularly limited, and any known method depending on the substance can be appropriately adopted.

Further, although the details will be described in the description of the next step, the Ti-containing aqueous solution is preferably used in the next step because the aqueous solution maintaining the state immediately after the preparation is used. In order to maintain the state immediately after, immediately after preparation, store the product in a light-shielded, refrigerated or frozen state.

<Step (B1)>
Step B1 is a step of mixing the Sr-containing aqueous solution prepared in step A1 and the Ti-containing aqueous solution. The method of mixing is not particularly limited, but the Ti-containing aqueous solution to be mixed with the Sr-containing aqueous solution in step B1 is preferably one that does not contain TiO ₂ as a main component of the Ti component.

In the synthesis of strontium titanate fine particles by subcritical synthesis or supercritical synthesis, the inventors of the present invention suppress the precipitation of titanium dioxide, which is an intermediate product, to produce strontium titanate fine particles with good crystallinity. I thought it was important to move forward.

The inventors focused on the instability of the Ti-containing aqueous solution and focused on the potential-pH diagram of Ti. According to the potential-pH diagram of Ti, at room temperature (25 ° C.), Ti is not in the ion dissociation state but in the hydrate of titanium dioxide (TiO ₂ · H ₂ O) in a weak acid to a weak alkaline environment of less than pH 12. From the stability, it is considered that, at room temperature, the conversion to the titanium dioxide hydrate is initiated soon after preparation of the Ti-containing aqueous solution when in a weak acid to a weak alkaline environment of less than pH 12.
On the other hand, in an alkaline environment at a pH of 12 or more, Ti is considered to be in the form of Ti hydroxide (Ti (OH) ₄ ) or HTiO ₃ ⁻ from the potential-pH diagram. Therefore, in a strong alkaline environment, it is considered that the aqueous solution state can be maintained without precipitation of titanium dioxide.

The present inventors have found that, as a reaction site for hydrothermal synthesis, subcritical water or the like in which the synthesis rate becomes faster by using a reaction liquid in which Ti in the reaction liquid maintains Ti (OH) ₄ or HTiO ₃ ^- ion state. It was considered that even in supercritical water, perovskite-type oxides having good crystallinity can be produced. Then, it was considered that by adding conditions that allow shape control to such a reaction liquid, it is possible to manufacture strontium titanate fine particles whose shape is controlled in a cubic shape (rectangular shape) with high productivity. The conditions under which the shape can be controlled will be described in detail in the item of step E1 described later.

In addition, after preparing the Ti-containing aqueous solution, the present inventors start to change to titanium dioxide hydrate due to temporal changes such as ultraviolet light and temperature conditions after the Ti ion in the aqueous solution, and then white crystals of titanium dioxide start to precipitate. Have confirmed that. Then, the crystal structure of titanium dioxide formed at this stage is mainly rutile type, and once crystals of rutile type nonuniform and large in particle diameter are precipitated, production of strontium titanate fine particles with uniform crystallinity is good. Confirmed that it was difficult. Accordingly, in step B1, it is preferable to use the Ti-containing aqueous solution not containing the rutile type TiO ₂ as the main component of a Ti component.

As a result, it is possible to produce strontium titanate having good crystallinity if the formation of skeleton or precipitation of large size titanium dioxide can be minimized at the stage of mixing the strontium-containing aqueous solution with the titanium-containing aqueous solution. Suggests that.

The inventors prepared a Ti-containing aqueous solution by setting the pH of the reaction solution to be subjected to a hydrothermal reaction to more than 10 (or, the concentration of an alkaline compound having an ionization degree of 0.8 or more in the reaction solution is 0.6 mmol or more). By mixing with the Sr-containing aqueous solution while keeping the state immediately after, it becomes possible to almost suppress the formation or precipitation of the framework of large size titanium dioxide in the mixed solution, and the crystallinity is high by the subsequent subcritical reaction or supercritical reaction. We believe that strontium titanate can be synthesized.

As described above, the Ti-containing aqueous solution is considered to cause a change to the hydrate of titanium dioxide soon after preparation under conditions other than a strong alkaline environment of pH 12 or more at room temperature. Under other conditions of temperature and pH, the presence or absence and the rate of the change are considered to be different, so under the conditions where it is difficult to change titanium dioxide into hydrate, the mixed solution of the next step is not necessarily immediately after preparation. Although it is not necessary to carry out the preparation, if the mixed solution of the next step is prepared immediately after the preparation of the Ti-containing aqueous solution, the temperature condition and the pH condition can be achieved by carrying out the later steps. Regardless, highly crystalline strontium titanate fine particles can be formed.
Therefore, it is preferable to carry out step B1 immediately after preparation of the Ti-containing aqueous solution, or otherwise, using a Ti-containing aqueous solution stored immediately after preparation and protected from light by light and refrigerated or frozen.

In step B1, it is preferable to prepare a mixed solution so that the molar ratio Sr / Ti of Sr to Ti in the reaction liquid is 1 or more. In the case where the stability of the hydrate of titanium dioxide is high and the pH is adjusted to more than neutral pH 10 to less than 12, the Ti-containing aqueous solution is kept in the state immediately after preparation and mixed with the Sr-containing aqueous solution. The supercritical reaction is preferably performed in a Sr-rich state in which the amount of Sr in the reaction solution is larger than the number of moles of the amount of Ti. The molar ratio Sr / Ti of the Sr component and the Ti component in the mixed solution is preferably 1.3 or more, and more preferably 1.3 or more and 1.7 or less.

In the supercritical reaction beyond the critical point, the ions are destabilized because the water is in a nonpolar gas state, and the equilibrium of the metal salt aqueous solution is from the ion dissociation state to the hydroxide side and further to the oxide side. Shift very fast. In addition, in the presence of Ti ions, it is speculated that strontium titanate is more stable than oxides and Sr than hydroxides, and hydrothermal reaction is caused by forming an Sr-rich environment in the reaction liquid. Can be rapidly produced to produce fine crystalline strontium titanate fine particles with less heterophase.

In the step B1, in view of suppressing the formation of precipitates in the mixed solution as much as possible during the preparation of the mixed solution, it is preferable to well stir during the step B1. Moreover, it is more preferable to implement stirring until immediately before performing the next step C1.

<Step C1, Step D1, Step E1, Step F1>
Steps C1, E1 and F1 are reactions in which reaction is performed in step D1 so that strontium titanate fine particles whose shape is controlled to a cubic shape (rectangular shape) can be obtained in step D1 by a subcritical reaction or a supercritical reaction. The steps (C1, F1) of adjusting the basicity of the solution and the step (E1) of performing the reaction necessary for shape control.

The step E1 and the step F1 are steps which may be performed any time before the step D1 is carried out, but the basic substance or the acidic substance is added to the Sr containing aqueous solution, the Ti containing aqueous solution, the mixed solution or the reaction solution Since the process F1 is a process of adjusting the final basicity of the reaction liquid which implements the process D1, it is preferable to carry out just before performing the process D1. Examples of the basic substance used in step F1 include aqueous potassium hydroxide solution and aqueous sodium hydroxide solution, and examples of the acidic substance include nitric acid, hydrochloric acid and the like.
On the other hand, step E1 is preferably performed in the middle of step C1, and is preferably performed immediately after the addition of the basic compound in step C1. Step E1 and step F1 may be carried out only once or plural times, respectively.

The reaction liquid to be reacted in step D1 has a basicity of more than 10 when it is expressed by pH, and 0.60 mol / L or more when it is expressed by the molar concentration of the basic substance (the basic substance has an ionization degree of 0. The reaction solution is adjusted to 8 or more), preferably 11 or more when expressed by pH, or 0.70 mol / L or more when expressed by molar concentration of basic substance (basic substance is ionized In the case of a degree of 0.8 or more).

As the basicity of the reaction solution to be reacted in the step D1 is higher, the reaction temperature is likely to be higher, so that it is possible to produce perovskite-type strontium titanate fine particles even under low alkaline conditions.

The upper limit of the basicity of the reaction solution is not particularly limited as long as the reaction container storing the reaction solution is not corroded. In order to perform subcritical synthesis or supercritical synthesis under strongly alkaline conditions such as exceeding pH 13.5, alkali resistance is essential for the reaction vessel. As a reaction container having alkali resistance, ones made of Teflon (registered trademark) or those made of Hastelloy (registered trademark) are known, however, those made of Teflon (registered trademark) have limited heat resistance, so the reaction temperature is There is a limit and there is a problem that the product made of Hastelloy (registered trademark) is very expensive, resulting in high equipment cost. From the viewpoints of heat resistance and equipment cost, it is preferable that a reaction container made of SUS etc., which is excellent in heat resistance, is highly versatile and inexpensive, can be used as a reaction container, and for that purpose It is preferable to be able to manufacture on conditions.

In addition, the reaction liquid to be reacted in step D1 includes, before carrying out step D1, an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group up to before the steps A1 to B1. In the above, the step E1 is carried out by adding the Sr-containing aqueous solution or the Ti-containing aqueous solution to the mixed solution up to the completion of the steps B1 to C1 and adding it to the reaction solution after the completion of the step C1. Hereinafter, in order to make it easy to understand, the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, and the reaction liquid in which the step E1 and the step F1 are performed are collectively referred to as a liquid to be added.

First, the step (E1) of carrying out the reaction necessary for shape control will be described.
As described above, step E1 is preferably performed in the middle of step C1, and is preferably performed immediately after the addition of the basic compound in step C1. In step E1, the order of addition of the amphiphilic compound having a carboxyl group to be added to the liquid to be added and the basic compound containing no metal is not particularly limited. In some cases, the aqueous layer and the amphiphilic compound layer having a basic compound or a carboxyl group may be separated, but in such a case, it is preferable to stir well. For the stirring, the same method as in the case where a precipitate is generated in Step C1 described later can be used.

In the step E1, as a basic compound which does not contain a metal element to be added to the solution to be added, any known compound can be used without particular limitation as long as it exhibits basicity in an aqueous solution, for example, quaternary ammonium Examples thereof include basic organic compounds having no metal element such as compounds, amine compounds, ammonia, pyridine and derivatives thereof, and hydrazine and derivatives thereof.

Specifically, hydrazine derivatives such as hydrazine, 1-monomethylhydrazine, 1,1-dimethylhydrazine, 1-ethyl-2-methylhydrazine and the like; primary amines such as methylamine, ethylamine, n-propylamine and ethanolamine; Examples include secondary amines such as dimethylamine and diethylamine; and tertiary amines such as trimethylamine and triethylamine. Above all, hydrazine, hydrazine monohydrate, oleylamine, and the like are relatively easy to handle and have a remarkable effect on shape control because they do not contain metal impurities that adversely affect the performance of the strontium titanate fine particles obtained. At least one of the hydrazine derivatives is preferred, with hydrazine being most preferred.
In particular, since hydrazine also has a function as a strong reducing agent, it is speculated that it also has a role of preventing oxidation or the like of an amphiphilic compound having a carboxyl group.

Two or more types of basic compounds not containing these metal elements can be used in combination, but using hydrazine or a derivative thereof as one of them can control the shape of the resulting composite oxide nanoparticles into a cube. Preferred for

As the amphiphilic compound having a carboxyl group (hereinafter referred to as an amphiphilic compound) added to the liquid to be added in step E1, the compound has a carboxyl group (hydrophilic group) and a hydrophobic group. For example, known compounds can be used without particular limitation. Such compounds include saturated fatty acids such as propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, etc. Examples include unsaturated fatty acids such as linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, oleic acid, elaidic acid, erucic acid, nervonic acid, etc. Be

Among them, organic acids having 2 to 20 carbon atoms are preferable, and organic acids having 10 to 20 carbon atoms are more preferable. Therefore, oleic acid, decanoic acid, lauric acid, undecenoic acid, linoleic acid, and At least one of the linolenic acids is preferred, with oleic acid being most preferred.

Strontium titanate is presumed to be synthesized as a minute amorphous form including various plane orientations at the initial stage of growth. In organic amphiphilic compounds such as oleic acid, carboxyl groups are easily adsorbed to the (100) plane. Therefore, when crystal growth proceeds in the presence of an organic amphiphilic compound, crystals grow in a state in which the amphiphilic compound is adsorbed to the (100) plane, so crystal growth on the (111) plane preferentially proceeds. become. As a result, the growth of all (111) planes proceeds to form a vertex, and a strontium titanate fine particle whose shape is controlled to a cubic shape as a whole is synthesized.

The blending amount of the amphiphilic compound and the basic compound not containing a metal element is not particularly limited, but if the blending amount is too small, the particle diameter of the obtained fine particles becomes large, and if too large, the target substance is obtained It disappears.

FIG. 2 shows the content of the amphiphilic compound on the horizontal axis, and the content of the basic compound not containing metal on the vertical axis, where the content of the Ti component is 100 in the reaction liquid to be reacted in step D1. It is the figure which described the-plot in the place where the strontium titanate by which shape control was carried out in cube shape (or rectangular parallelepiped shape) was obtained in the example mentioned below in the figure which carried out.
As illustrated, in the reaction liquid used in step D1, the number of moles X of Ti, the number Y of moles of the amphiphilic compound, and the number Z of moles of the organic basic compound containing no metal are 0 <Y /. It is preferable to satisfy X ≦ 6 and 0 ≦ Z / X ≦ 8, more preferably 1 ≦ Y / X ≦ 4, and most preferably 0 ≦ Z / X ≦ 4.
In the reaction liquid used in step D1, the concentration of the Ti component is preferably 0.1 mmol / L or more and 20 mol / L or less.

Next, step C1 and step F1 will be described. The step C1 and the step F1 are steps for adjusting the basicity of the reaction solution to be reacted in the step D1. Although adjustment of the basicity is usually sufficient only in the step C1, when fine adjustment of the basicity is required, such as when the step E1 is performed after the execution of the step C1, the step F1 is preferably performed. As described above, since the step F1 is a step of adjusting the final basicity of the reaction solution in which the step D1 is performed, it is preferably performed immediately before the step D1. Examples of the basic substance used in step F1 include aqueous potassium hydroxide solution and aqueous sodium hydroxide solution, and examples of the acidic substance include nitric acid, hydrochloric acid and the like.

The basic aqueous solution used in the step C1 is not particularly limited, but an aqueous solution of a basic compound having an ionization degree of 0.8 or more is desirable, and an aqueous solution of a strongly basic compound near 1 is preferably used. As such a basic compound, sodium hydroxide or potassium hydroxide is preferably exemplified.

The dropwise addition of the basic aqueous solution is preferably carefully added drop by drop. Immediately after the addition of the basic compound in step C1, a gel-like precipitate is generated. There is no problem in producing such precipitates, but if the variation in the size of the precipitates is large or if the precipitates themselves are large in units of milli units or more even if the variation is small, the crystallinity is good at the end of the next step It is presumed that the yield of strontium titanate is likely to be low. Therefore, when a precipitate is produced, it is preferable to carry out stirring or grinding so as to be as fine as possible. The means for stirring or pulverizing is not particularly limited, and may be carried out manually using a stirring rod or the like, or may be dispersed by a stirrer or ultrasonic treatment.

As already described, in step D1, the basicity is more than 10 when expressed in pH, or 0.60 mol / L or more in the molar concentration of the basic substance (the basic substance has an ionization degree of 0.8 or more) Subcritical reaction or supercritical reaction of the reaction solution prepared in

In step D1, the holding time of the reaction temperature is not particularly limited, but in the case of supercritical conditions, as described in the examples, the shape was controlled to a cubic shape (cuboid shape) with a holding time of 10 minutes or less. Strontium titanate fine particles can be produced.

Since step D1 is a subcritical reaction or supercritical reaction, the reaction container storing the reaction liquid is installed in a closed heating apparatus such as an autoclave (hereinafter referred to as an autoclave), and the subcritical condition and the supercritical condition It carries out by heating so that it may become. At this time, although the reaction vessel may be gradually heated after being placed in the autoclave at room temperature, it is better to place the autoclave in an environment previously controlled to a temperature atmosphere of subcritical condition or supercritical condition, It is preferable because the heating rate is fast and the progress of the hydrothermal reaction can be suppressed as much as possible.
As described above, strontium titanate fine particles can be obtained.

Strontium titanate fine particles
According to the method for producing strontium titanate fine particles of the present invention, strontium titanate fine particles having a cube or rectangular parallelepiped shape can be produced with high productivity (see Example 3 described later).

In strontium titanate, the most stable crystal structure is a cubic crystal, and in the case of a cubic crystal, the original crystal shape is a cube, and the crystal plane exposed on the surface is a {100} plane. As shown in Example 1 (FIG. 3, FIGS. 5A and 5B), according to the method for producing strontium titanate fine particles of the present invention, 85% or more of the crystal plane exposed on the surface of a cube or a rectangular solid is obtained. Strontium titanate fine particles having a {100} plane can be produced.

In addition, it is preferable that the length of one side of the cubic or rectangular solid particle is 10 nm or more and 500 nm or less.

Strontium titanate is a perovskite-type oxide that exhibits photocatalytic activity by sunlight irradiation, as described in the background art. Strontium titanate is a fine particle formed by supporting a metal promoter such as Pt, Rh, Cu, etc. on the surface as described in Patent Document 1 and Patent Document 2 as an embodiment giving more efficient photocatalytic ability. It is known to be preferred.

Strontium titanate fine particles supporting a metal promoter suppress electron recombination with holes because electrons excited in the strontium titanate by light irradiation move rapidly to the surface due to the presence of the metal promoter on the surface. And enable highly efficient reduction reaction. Hydrogen can be efficiently generated because the reduction reaction is efficiently performed.

However, as a method of supporting a metal promoter, a method of supporting a water-soluble metal salt by an impregnation method, an optical electrodeposition method or the like, and then reducing and attaching a metal ion is generally used. These metals tend to cause electron trapping between the mother catalyst strontium titanate (interface).

In order to make the electron trap difficult to occur, it is preferable that the strontium titanate fine particles have a crystal face that is as lattice-matched as possible with the supported metal. The lattice constant of cubic strontium titanate whose shape is controlled as described above is 0.3905 nm. The lattice constant of this lattice constant and the lattice constant of the supported metal, Pt, Ir, Pd, Rh, Ru, Cu, Ni, Co, has a mismatch rate of 10% or less, and Ir, Rh is 5% or less, Pt, Pd Is less than 0.5%, it is possible to realize a highly efficient photocatalyst with few electron traps at the interface with the supported metal by using cubic strontium titanate fine particles with a high {100} surface fraction of the surface . Furthermore, such cubic shaped strontium titanate fine particles have a cubic shape that is the original shape of cubic crystal particles, as described also in Patent Document 6 and Patent Document 7 other than for photocatalyst application. It has various advantages such as being easy to form, forming a dense film, and so on.

"Design changes"
The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the scope of the present invention.

(Examples 1 to 7)
Strontium titanate fine particles were produced under the conditions described in Table 1 as follows.
First, a required amount of purified water was collected as an Sr-containing aqueous solution, and strontium nitrate was weighed to prepare a strontium nitrate aqueous solution. Moreover, titanium tetrachloride aqueous solution was prepared as Ti containing aqueous solution. Ampoule-like TiCl ₄ is slowly added dropwise to purified water. At that time, it is carried out with stirring and cooling, and immediately after adjustment to the designated concentration, it is shielded from light and stored refrigerated. As a solvent water, purified water was used unless otherwise stated.
The aqueous solution of titanium tetrachloride was shielded from light, and immediately after preparation, it was stored in a refrigerator to maintain the state immediately after preparation, and then mixed with an aqueous solution of strontium nitrate to obtain a mixed solution. At the time of mixing, the molar ratio Sr / Ti of the Sr component to the Ti component in the mixed solution was mixed so as to be 1.

Next, the mixed solution is stored in a beaker, potassium hydroxide aqueous solution (15 mol / L) is dropped dropwise into the mixed solution, and then hydrazine is further dropped into the mixed solution, followed by oleic acid. It dripped. Immediately after the addition of the aqueous potassium hydroxide solution, a gel-like white precipitate was produced, so while stirring and crushing the precipitate, the aqueous potassium hydroxide solution and hydrazine, oleic acid were added dropwise, and finally the mixed solution The reaction mixture was adjusted to have a pH of 12.

The resulting reaction solution was charged into a reaction vessel, and the autoclave was charged into a 400 ° C. atmosphere to carry out a supercritical reaction. The synthesis of strontium titanate fine particles was carried out. The reaction conditions are shown in Table 1.
According to each temperature, the reaction solution is put into a designated volume of Hastelloy (registered trademark) container (made by AKICO) having an inner volume of about 5 cm ³ , and it is sealed in a stainless steel pressure container. The reaction was carried out for 10 minutes under the temperature conditions described in Table 1 and a pressure of 30 MPa, and then quenched.

The shape of the obtained strontium titanate fine particles was all cubic. FIG. 3 shows a micrograph of the microparticles obtained in Example 1, and FIG. 4 shows a micrograph of the microparticles obtained in Comparative Example 1.

Also, as described above, FIG. 2 shows the relationship between the number of moles of amphiphilic compound contained in the reaction liquid and the ratio of the organic basic compound to the number of Ti moles and whether or not the shape controlled strontium titanate fine particles can be produced Is shown.

5A is an enlarged electron micrograph of the strontium titanate fine particles obtained in Example 1, and FIG. 5B is an electron micrograph showing an analysis result of the crystal plane of the strontium titanate fine particles. As shown in FIG. 5B, the non- {100} -plane portion of the obtained particle is 2.2 nm at one end of one side, and calculated from the fact that the length of one side is 37.6 nm, It will be 2x2 / 37.6 = 0.116. Therefore, the {100} rate of the obtained particles was confirmed to be 88.4%.

(Comparative Examples 1 to 5)
As shown in Table 1, the strontium titanate fine particles were manufactured by changing the conditions of the example. In each of Comparative Examples 1, 3, 4 and 5, cubic particles were not obtained. In Comparative Example 2, although cubic-shaped fine particles were obtained, the reaction time was as long as 24 hours.

The present invention can be applied to the production of photocatalysts, functional materials for electronic parts such as thermoelectric materials and dielectric materials, and fine particles of strontium titanate fine particles suitable as lens materials.

Claims

Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing a mixed solution by mixing the Sr-containing aqueous solution and the Ti-containing aqueous solution;
Preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic, and C1.
A subcritical reaction or a supercritical reaction of the reaction solution D1;
Before carrying out the step D1, an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group are added to the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, or the reaction solution And step E1;
The method for producing strontium titanate fine particles, wherein the pH of the reaction solution used in step D1 is more than 10.
The process for producing strontium titanate fine particles according to claim 1, comprising the step F1 of adding a basic substance or an acidic substance to the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, or the reaction solution before carrying out the step D1. Method.
The method for producing strontium titanate fine particles according to claim 1, wherein the pH of the reaction solution used in the step D1 is 11 or more.
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing a mixed solution by mixing the Sr-containing aqueous solution and the Ti-containing aqueous solution;
Preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic, and C1.
A subcritical reaction or a supercritical reaction of the reaction solution D1;
Before carrying out the step D1, an organic basic compound containing no metal element and an amphiphilic compound having a carboxyl group are added to the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, or the reaction solution And step E1;
In the step C1, the ionization degree of the basic compound is 0.8 or more,
The manufacturing method of strontium titanate microparticles | fine-particles whose density | concentrations of the said basic compound of the said reaction liquid used at the said process D1 are 0.60 mol / L or more.
The method for producing strontium titanate fine particles according to claim 4, wherein the concentration of the basic compound in the reaction liquid used in the step D1 is 0.70 mol / L or more.
The method for producing strontium titanate fine particles according to any one of claims 1 to 5, wherein the amphiphilic compound is an organic acid having 2 to 20 carbon atoms.
The method for producing strontium titanate fine particles according to claim 6, wherein the amphiphilic compound is an organic acid having 10 to 20 carbon atoms.
The method for producing strontium titanate fine particles according to claim 7, wherein the amphiphilic compound is at least one of oleic acid, decanoic acid, lauric acid, undecenoic acid, linoleic acid and linolenic acid.
The method for producing strontium titanate fine particles according to any one of claims 1 to 8, wherein the organic basic compound is at least one of an amine compound, ammonia, hydrazine and derivatives thereof.
10. The method for producing strontium titanate fine particles according to claim 9, wherein the organic basic compound is at least one of hydrazine, hydrazine monohydrate, oleylamine, and hydrazine derivatives.
The method for producing strontium titanate fine particles according to any one of claims 1 to 8, wherein the amphiphilic compound is oleic acid and the organic basic compound is hydrazine.
In the reaction liquid used in the step D1, the number of moles X of Ti, the number Y of moles of the amphiphilic compound, and the number Z of moles of the organic basic compound are
The method for producing strontium titanate fine particles according to any one of claims 1 to 11, wherein 0 <Y / X ≦ 6 and 0 ≦ Z / X ≦ 8 are satisfied.
The method according to claim 12, wherein the X, the Y and the Z further satisfy 1 前記 Y / X ≦ 4.
The method according to claim 13, wherein the X, the Y and the Z further satisfy 0 前記 Z / X04.
The method for producing strontium titanate fine particles according to any one of claims 1 to 14, wherein the concentration of the Ti component in the reaction liquid used in the step D1 is 0.1 mmol / L or more and 20 mol / L or less.
The method for producing strontium titanate fine particles according to any one of claims 1 to 15, wherein the mixed solution is prepared such that the molar ratio Sr / Ti of Sr and Ti is 1 or more in the step B1.
The method for producing strontium titanate particles according to any one of claims 1 to 16, wherein the Ti-containing aqueous solution containing no rutile TiO 2 as a main component of the Ti component is used in the step B1.
The method for producing strontium titanate fine particles according to any one of claims 1 to 17, wherein in the step A1, the Sr-containing aqueous solution is obtained by dissolving an acetate, hydroxide or nitrate of strontium in water. .
The method for producing strontium titanate fine particles according to any one of claims 1 to 18, wherein the reaction liquid used in the step D1 contains Ti (OH) 4 and / or HTiO 3 - ions as a main component of the Ti component. .
The method for producing strontium titanate fine particles according to any one of claims 1 to 19, wherein an aqueous titanium tetrachloride solution is prepared as the Ti-containing aqueous solution in the step A1.
The method for producing strontium titanate particles according to any one of claims 1 to 20, wherein in the step C1, the basic compound is sodium hydroxide or potassium hydroxide.
The method for producing strontium titanate fine particles according to any one of claims 1 to 21, wherein solid matter generated during the preparation is pulverized in the step C1.
The method for producing strontium titanate fine particles according to any one of claims 1 to 22, wherein the holding time of the reaction temperature in the subcritical reaction or the supercritical reaction in the step D1 is within 10 minutes.
A strontium titanate particle manufactured by the method for manufacturing a strontium titanate particle according to any one of claims 1 to 23, and having a cube or rectangular parallelepiped shape.
25. The strontium titanate particles according to claim 24, wherein 85% or more of the crystal faces exposed on the surface of the cube or rectangular solid are {100} faces.
The strontium titanate particles according to any one of claims 24 or 25, wherein a length of one side of the cube or rectangular solid is 10 nm or more and 500 nm or less.