WO2015122181A1 - チタン酸ストロンチウム微粒子の製造方法およびチタン酸ストロンチウム微粒子 - Google Patents

チタン酸ストロンチウム微粒子の製造方法およびチタン酸ストロンチウム微粒子 Download PDF

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WO2015122181A1
WO2015122181A1 PCT/JP2015/000618 JP2015000618W WO2015122181A1 WO 2015122181 A1 WO2015122181 A1 WO 2015122181A1 JP 2015000618 W JP2015000618 W JP 2015000618W WO 2015122181 A1 WO2015122181 A1 WO 2015122181A1
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fine particles
strontium titanate
titanate fine
aqueous solution
reaction
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WO2015122181A4 (ja
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佐々木　勉
田中　淳
鈴木　真之
阿尻　雅文
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富士フイルム株式会社
国立大学法人東北大学
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C01G23/006—Alkaline earth titanates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/38—Particle morphology extending in three dimensions cube-like
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

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  • the present invention relates to a method for producing finely shaped strontium titanate fine particles suitable as a base material for dielectric materials and photocatalysts.
  • Strontium titanate is a complex oxide that is expected to be used in various applications as a functional material, such as dielectric properties, thermoelectric properties, photocatalytic properties, and high refractive index properties.
  • Photocatalytic activity has attracted attention from the viewpoint of energy problems and environmental problems in recent years, and strontium titanate is able to produce hydrogen using only sunlight because of its high stability under light irradiation and the strength of photoreduction power.
  • Expectation is increasing as a photocatalyst that enables it.
  • a hydrogen generation photocatalyst it is preferable to have an activity with respect to visible light which occupies a large proportion of sunlight.
  • strontium titanate photocatalyst capable of generating highly efficient hydrogen with visible light activity, strontium titanate with a metal such as Pt, Rh, Cu or the like supported thereon, and further titanic acid doped with Rh or Ir Strontium and the like have been proposed (Patent Document 1, Patent Document 2, etc.).
  • Nanoparticle materials are expected to realize high precision, downsizing, and weight reduction of products because they can express unique excellent properties and functions. Nanoparticle technology is also being studied for metal oxide materials.
  • Patent Document 3 as a method for producing ceria known as an exhaust gas purification catalyst material as cubic nanocrystal particles having a high ratio of crystal faces with high catalytic activity, high-temperature and high-pressure water in the presence of an organic substance is disclosed. A method of manufacturing by thermal synthesis, preferably supercritical synthesis has been proposed.
  • Patent Documents 4 and 5 describe methods for producing titanium oxide fine particles or fine powders by high-temperature, high-pressure hydrothermal synthesis, in an aqueous solution that is a hydrothermal synthesis or subcritical / supercritical reaction field. It has been reported that nano-sized highly crystalline particles can be produced while suppressing aggregation by reacting with fine particles synthesized with an organic modifier while carrying out a synthesis reaction. However, these documents do not describe the shape control so as to have a specific crystal plane as in Patent Document 3, and the actual manufactured example is only a simple oxide, and the perovskite type oxidation. There are no examples of complex oxides such as products. Even if the same titanium oxide is used, the synthesis reaction mechanism differs between the simple oxide and the complex oxide, and it is usually difficult to apply the production method of the simple oxide to the complex oxide as it is.
  • strontium hydroxide and a water-soluble titanium compound such as titanium peroxoammonium lactate are mixed at 200 ° C. in the presence of an amphiphilic compound such as oleic acid and a basic compound not containing a metal element such as hydrazine. It is described that strontium titanate nanoparticles whose crystal shape is controlled can be produced without agglomeration by hydrothermal synthesis under alkaline conditions.
  • Patent Document 7 discloses a method of aligning cubic strontium titanate nanocrystals on a substrate and a method of producing a film made of nanocrystals.
  • paragraph [0015] a nanostructure of strontium titanate nanocrystals is disclosed.
  • crystal growth proceeds with organic carboxylic acid molecules such as oleic acid adhering to the (111) plane, so the crystal growth on the (111) plane proceeds without obstruction by the organic carboxylic acid molecules. It is described that the growth of all eight (111) planes proceeds to form vertices, which tend to be cubic as a whole.
  • Japanese Patent No. 4076793 Japanese Patent No. 3340295 JP 2007-217265 A Japanese Patent No. 3925932 Japanese Patent No. 4336856 JP 2011-68500 A JP 2012-188335 A Japanese Patent No. 2709222 Japanese Patent Publication No. 3-39016
  • the strontium titanate fine particles can be manufactured in a cubic shape, but in the method of Patent Document 6, hydrothermal reaction at 200 ° C. is performed for 24 hours. The hydrothermal reaction at 200 ° C. needs to be carried out for 72 hours, both of which have a problem that the synthesis time is long and the productivity is very poor.
  • Patent Document 9 Other than hydrothermal synthesis methods, there are reports on the formation of nanoparticles of strontium titanate, but there is no description or suggestion of a method for shape control to a cubic (or cuboid) shape having a specific crystal plane (patent) Document 8, Patent Document 9).
  • the present invention has been made in view of the above circumstances, and a method for producing strontium titanate fine particles whose shape is controlled to a cubic (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 a strontium titanate fine particle having a controlled shape.
  • Step A1 for preparing each of the Sr-containing aqueous solution and the Ti-containing aqueous solution Step B1 of preparing the mixed solution by mixing the prepared Sr-containing aqueous solution and the Ti-containing aqueous solution, A step C1 of preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic; A step D1 of causing the reaction liquid to undergo a subcritical reaction or a supercritical reaction; Before 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, Ti-containing aqueous solution, mixed solution or reaction solution And the pH of the reaction solution used in the step D1 exceeds 10.
  • “before performing the process D1” means all processes and all processes existing before the process D1 is performed. That is, it means during each step from step A1 to step C1 or between each step from step A1 to step D1.
  • Step E1 may be performed only once or a plurality of times.
  • reacting the reaction solution means reacting one or more components contained in the reaction solution.
  • the term “fine particles” means those having an average particle size of less than 1 ⁇ m, and preferably nanoparticles.
  • the nanoparticles may generally have a mean particle size of 200 nm or less, but preferably have a size of 200 nm or less.
  • the nanoparticles may have an average particle size of 100 nm or less, and in other cases the average particle size may be 50 nm or less.
  • the nanoparticles have an average particle size of 20 nm or less, and in other cases, the average particle size is 10 nm or less or 5 nm or less. It's okay.
  • the nanoparticles preferably have a uniform particle size, but may have a mixture of 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.
  • TEM electron microscope
  • SEM electron microscope
  • SAXS X-ray small angle scattering
  • water in a temperature and pressure region above the critical point of water is supercritical water
  • water in the region near the critical point near 350 ° C. is subcritical water.
  • the reaction in supercritical water is called supercritical reaction
  • the reaction in subcritical water is called subcritical reaction.
  • step D1 the step F1 of adding a basic substance or an acidic substance to the Sr-containing aqueous solution, Ti-containing aqueous solution, mixed solution, or reaction solution may be included.
  • the pH of the reaction solution used in step D1 is preferably 11 or more.
  • the second method for producing strontium titanate fine particles of the present invention is as follows. Step A1 for preparing each of the Sr-containing aqueous solution and the Ti-containing aqueous solution, Step B1 of preparing the mixed solution by mixing the prepared Sr-containing aqueous solution and the Ti-containing aqueous solution, A step C1 of preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic; A step D1 of causing the reaction liquid to undergo a subcritical reaction or a supercritical reaction; Before 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, Ti-containing aqueous solution, mixed solution or reaction solution Have In 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 concentration of the basic compound in the reaction solution used in step D1 is preferably 0.70 mol / L or more.
  • the amphiphilic compound is preferably an organic acid having 2 to 20 carbon atoms, and an organic acid having 10 to 20 carbon atoms. Is more preferable.
  • 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 amine compounds, ammonia, hydrazine, and derivatives thereof, and is at least one of hydrazine, hydrazine monohydrate, oleylamine, and hydrazine derivatives. It is more preferable.
  • the combination of the amphiphilic compound and the organic basic compound is preferably a combination of oleic acid and hydrazine.
  • the mole number X of Ti, the mole number Y of the amphiphilic compound, and the mole number Z of the organic basic compound are 0 ⁇ Y / X ⁇ 6 and 0 ⁇ Z / X.
  • ⁇ 8 is preferably satisfied, more preferably 1 ⁇ Y / X ⁇ 4, still more preferably 0 ⁇ Z / X ⁇ 4.
  • the concentration of the Ti component is preferably 0.1 mmol / L or more and 20 mol / L or less.
  • the Sr-containing aqueous solution is preferably one in which strontium acetate, hydroxide or nitrate is dissolved in water, and the Ti-containing aqueous solution is tetrachloride.
  • a titanium aqueous solution is preferred.
  • the Ti-containing aqueous solution used in Step B1 for preparing the mixed solution is preferably one containing no TiO 2 as a main component of the Ti component, and particularly rutile TiO. 2 is preferably not included.
  • the “main component” means a component having a content of 50% by mass or more.
  • 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.
  • Step B1 it is preferable to use a Ti-containing aqueous solution that does not contain rutile TiO 2 as the main component of the Ti component.
  • the basic compound is preferably sodium hydroxide or potassium hydroxide. Moreover, it is preferable to grind
  • the reaction solution used in the step D1 is preferably a reaction solution containing Ti (OH) 4 and / or HTiO 3 ⁇ ions as the main component of the Ti component. Moreover, in the process D1, the retention time of the reaction temperature in the subcritical reaction or supercritical reaction can be made within 10 minutes.
  • the strontium titanate fine particles of the present invention are produced by the method for producing strontium titanate fine particles of the present invention, and the shape is a cube or a rectangular parallelepiped.
  • the “strontium titanate fine particles that are a cube or a rectangular parallelepiped” include those having an incomplete shape in which the vertex of the cube or the rectangular parallelepiped is chamfered. At this time, the ratio of chamfering is within 20% of the area of each surface of the cube or cuboid. The chamfer was defined from the side length.
  • the particles were directly observed by TEM, the length of one side of the cubic particle and the length of the chamfered portion were measured, and the ratio to the one side was calculated.
  • 85% or more of the crystal planes exposed on the surface of the cube or rectangular parallelepiped are preferably ⁇ 100 ⁇ planes.
  • the length of one side of a cube or a rectangular parallelepiped is 10 nm or more and 500 nm or less.
  • the method for producing strontium titanate fine particles of the present invention comprises a reaction solution containing a basic compound having a pH of more than 10 including an Sr-containing aqueous solution and a Ti-containing aqueous solution, or a basic compound having an ionization degree of 0.8 or more and 0.60 mol / L or more.
  • a subcritical or supercritical reaction method comprising a step of adding an organic basic compound not containing a metal element and an amphiphilic compound having a carboxyl group in a basic reaction solution before the reaction. ing. According to this configuration, strontium titanate fine particles whose shape is controlled so that the (111) plane of the strontium titanate crystal has a ⁇ 100 ⁇ plane by preferential growth can be produced with high productivity. .
  • FIG. 1 shows a flow chart of the method for producing strontium titanate fine particles of the present embodiment.
  • Patent Document 4 As already described, as a method of controlling the strontium titanate fine particles into a cubic shape, a method of performing a hydrothermal reaction at 200 ° C. for 24 hours or more as described in Patent Document 6 and Patent Document 7 is cited.
  • Patent Document 4 As disclosed in Patent Document 4 and the like, it is described that titanium dioxide fine particles, which are simple oxides, can be obtained by aggregating fine crystalline fine particles by a subcritical or supercritical reaction.
  • Patent Document 3 ceria fine particles which are simple oxides are produced by controlling them in a cubic shape by a high-temperature and high-pressure hydrothermal synthesis method, preferably supercritical synthesis, in the presence of an organic substance.
  • Patent Document 3 discloses a ratio of cubic ceria fine particles having a (001) plane and an equivalent plane in the produced fine particles by changing the reaction field from a hydrothermal reaction at 200 ° C. to a supercritical state. Increases from 70% to 80%.
  • the reaction time is not changed between the hydrothermal reaction field and the supercritical reaction field, and there is no description or suggestion that the reaction time can be shortened by the difference in the reaction field.
  • strontium titanate is a complex oxide, its crystal structure is more complex than that of simple oxides such as ceria and titanium dioxide. Even in a supercritical reaction field, it is considered that more stringent conditions are required as manufacturing conditions for particle shape control.
  • the inventors have considered that when the water in the reaction solution exceeds the critical point, the solubility of the substance is drastically decreased, and the generation and growth of crystal nuclei proceed rapidly. Particle synthesis was attempted using the reaction field as supercritical, and it was confirmed whether or not strontium titanate fine particles whose shape was controlled to a cubic shape (including a rectangular parallelepiped shape) could be produced in a shorter time (Comparative Examples 4 and 5 below). As a result, the obtained particles were indefinite, and it was impossible to control the shape as well as shortening the synthesis time.
  • Patent Document 6 and Patent Document 7 an attempt was made to produce strontium titanate fine particles using a titanium compound that is not a complex such as titanium tetrachloride as a titanium source.
  • a titanium compound that is not a complex such as titanium tetrachloride as a titanium source.
  • the strontium titanate fine particles whose shape was controlled to a cubic shape (including a rectangular parallelepiped shape) with a reaction field of subcritical or supercritical were successfully produced.
  • the reaction time was as short as about 10 minutes, and the reaction time was significantly shortened as compared with the case where Patent Document 6 required 24 hours.
  • Step A1 for preparing each of the Sr-containing aqueous solution and the Ti-containing aqueous solution Step B1 of preparing the mixed solution by mixing the prepared Sr-containing aqueous solution and the Ti-containing aqueous solution, A step C1 of preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic; A step D1 of causing the reaction liquid to undergo a subcritical reaction or a supercritical reaction; Before 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, Ti-containing aqueous solution, mixed solution or reaction solution And the pH of the reaction solution used in the step D1 exceeds 10.
  • the second method for producing strontium titanate fine particles includes: Step A1 for preparing each of the Sr-containing aqueous solution and the Ti-containing aqueous solution, Step B1 of preparing the mixed solution by mixing the prepared Sr-containing aqueous solution and the Ti-containing aqueous solution, A step C1 of preparing a reaction solution by adding a basic compound to the mixed solution to adjust the mixed solution to be basic; A step D1 of causing the reaction liquid to undergo a subcritical reaction or a supercritical reaction; Before 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, Ti-containing aqueous solution, mixed solution or reaction solution Have In 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 basicity of the reaction solution used in step D1 are different.
  • the basic compound used in 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 with reference to FIG.
  • Step A1 is a step of preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution, respectively.
  • Halide such as Sr hydroxide, an oxide, chloride, fluoride, and iodide
  • Inorganic acid salts such as nitrate, carbonate, a sulfate, acetate, oxalic acid Examples include those obtained by dissolving organic acid salts such as salts and lactates in water, but those obtained by dissolving acetate, hydroxide or nitrate in water are preferred.
  • the method for preparing the Sr-containing aqueous solution is not particularly limited, and a known method according to the substance can be appropriately employed.
  • Ti-containing aqueous solution is not particularly limited, but Ti hydroxides, oxides, chlorides, fluorides, iodides and other halides, nitrates, carbonates, sulfates and other inorganic acid salts, acetates and oxalic acids Examples include salts obtained by dissolving organic acid salts such as salts and lactates in water, and titanium tetrachloride which is a chloride is preferable.
  • the method for preparing the Ti-containing aqueous solution is not particularly limited, and a known method corresponding to the substance can be appropriately employed.
  • the Ti-containing aqueous solution is preferably an aqueous solution that maintains the state immediately after preparation in the next step. Therefore, if the next step B1 is not performed immediately after the preparation, In order to maintain the state immediately after the preparation, it should be stored immediately after preparation and refrigerated or frozen.
  • Step B1 is a step of mixing the Sr-containing aqueous solution and the Ti-containing aqueous solution prepared in Step A1.
  • 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 preferably does not contain TiO 2 as a main component of the Ti component.
  • strontium titanate fine particles In the synthesis of strontium titanate fine particles by subcritical synthesis or supercritical synthesis, the present inventors have synthesized strontium titanate fine particles with good crystallinity by suppressing precipitation of titanium dioxide, which is an intermediate product. I thought it was important to proceed.
  • Ti is not an ion-dissociated state and hydrated titanium dioxide (TiO 2 ⁇ H 2 O) at room temperature (25 ° C.) in a weakly alkaline to weakly alkaline environment of less than pH 12. Because of its stability, it is considered that at room temperature, when it is in a weakly alkaline environment with a pH of less than 12, a change to titanium dioxide hydrate will start soon after the preparation of the Ti-containing aqueous solution.
  • Ti is, Ti hydroxide (Ti (OH) 4) or HTiO 3 - considered an ionic state. Therefore, it is considered that the aqueous solution state can be maintained without precipitation of titanium dioxide in a strong alkaline environment.
  • the present inventors as a reaction field of the hydrothermal synthesis, Ti in the reaction solution, Ti (OH) 4 or HTiO 3 - by using a reaction liquid was maintained ionic state, subcritical water Ya synthesis rate becomes faster We thought that perovskite oxides with good crystallinity could be produced even in supercritical water. Then, it was considered that the strontium titanate fine particles whose shape was controlled in a cubic shape (cuboid shape) could be produced with high productivity by adding conditions capable of shape control to the reaction solution. The conditions under which the shape can be controlled will be described in detail in the item of step E1 described later.
  • the present inventor begins to change titanium ions in the aqueous solution into titanium dioxide hydrate due to changes over time such as ultraviolet rays and temperature conditions, and then white crystals of titanium dioxide begin to precipitate. I have confirmed that.
  • the crystal structure of titanium dioxide formed at this stage is mainly rutile, and once a rutile-type non-uniform crystal with a large particle size is precipitated, production of strontium titanate fine particles with uniform and good crystallinity is produced. Confirmed that it was difficult. Therefore, in step B1, it is preferable to use a Ti-containing aqueous solution that does not contain rutile TiO 2 as the main component of the Ti component.
  • strontium titanate with good crystallinity can be produced if the skeleton formation or precipitation of large-sized titanium dioxide can be minimized at the stage of mixing the strontium-containing aqueous solution and the titanium-containing aqueous solution. It is suggested that.
  • the present inventor prepared a Ti-containing aqueous solution by setting the pH of the reaction solution to be hydrothermally reacted 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).
  • 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.
  • the Ti-containing aqueous solution is considered to cause a change to titanium dioxide hydrate soon after preparation in a state other than a strong alkaline environment having a pH of 12 or more at room temperature.
  • the presence or speed of the change and the speed are considered to be different under other temperature and pH conditions. Therefore, under conditions where the change to titanium dioxide hydrate is unlikely to occur, the mixed solution in the next step is not necessarily prepared immediately after preparation.
  • the subsequent step is carried out by the method described later, so that the temperature and pH conditions Regardless, strontium titanate fine particles having high crystallinity can be formed. Therefore, the step B1 is preferably carried out immediately after the preparation of the Ti-containing aqueous solution, or if not, it is preferably carried out using the Ti-containing aqueous solution that is immediately shielded and stored after refrigeration or freezing.
  • step B1 it is preferable to prepare a mixed solution so that the molar ratio Sr / Ti of Sr and Ti in the reaction solution is 1 or more.
  • the pH is more than 10 and less than 12
  • the molar ratio Sr / Ti between 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.
  • step B1 it is preferable to stir well during step B1 from the viewpoint of suppressing the generation of precipitates in the mixed solution as much as possible during preparation of the mixed solution. Moreover, it is more preferable to implement stirring until just before implementing the next process C1.
  • Steps C1, E1, and F1 are reactions in which the strontium titanate fine particles whose shape is controlled in a cubic shape (cuboid shape) in Step D1 are reacted in Step D1 so that they can be obtained by a subcritical reaction or a supercritical reaction.
  • This is a step (C1, F1) for adjusting the basicity of the liquid and a step (E1) for carrying out a reaction necessary for shape control.
  • Step E1 and Step F1 may be performed at any time before step D1, but a basic substance or acidic substance is added to an Sr-containing aqueous solution, Ti-containing aqueous solution, mixed solution, or reaction solution. Since the process F1 is a process for adjusting the final basicity of the reaction solution for performing the process D1, it is preferably performed immediately before the process D1. Examples of the basic substance used in Step F1 include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution, and examples of the acidic substance include nitric acid and hydrochloric acid. On the other hand, the step E1 is preferably performed in the middle of the step C1, and is preferably performed immediately after the addition of the basic compound in the step C1. Each of the process E1 and the process F1 may be performed only once or a plurality of times.
  • the reaction solution to be reacted in the step D1 has a basicity of more than 10 when expressed in pH, and 0.60 mol / L or more when expressed in molar concentration of the basic material (the basic material has an ionization degree of 0.1. 8 or more), preferably 11 or more when expressed in pH, 0.70 mol / L or more when expressed in molar concentration of basic substance (basic substance is ionized)
  • the reaction solution is adjusted to a degree of 0.8 or more.
  • the basicity of the reaction solution to be reacted in the step D1 is likely to be able to produce perovskite-type strontium titanate fine particles even under low alkaline conditions as the reaction temperature is higher.
  • the upper limit of the basicity of the reaction solution is not particularly limited as long as the reaction vessel storing the reaction solution is not corroded.
  • alkali resistance is essential for the reaction vessel.
  • reaction vessels having alkali resistance those made of Teflon (registered trademark) or made of Hastelloy (registered trademark) are known, but those made of Teflon (registered trademark) are limited in heat resistance, so the reaction temperature is limited.
  • Hastelloy registered trademark
  • reaction vessel made of SUS or the like that is excellent in heat resistance, versatility, and inexpensive, and for that purpose, it is possible to use a low alkali as neutral as possible. It is preferable that it can be manufactured under conditions.
  • the reaction liquid to be reacted in the step D1 contains an organic basic compound not containing a metal element and an amphiphilic compound having a carboxyl group before carrying out the step D1 before carrying out the step A1 to the step B1.
  • a step E1 of adding an Sr-containing aqueous solution or a Ti-containing aqueous solution to the mixed solution before the completion of the steps B1 to C1 and adding the reaction solution after the completion of the step C1 is performed.
  • the Sr-containing aqueous solution, the Ti-containing aqueous solution, the mixed solution, and the reaction solution in which the step E1 and the step F1 are performed are collectively referred to as an addition target solution.
  • step E1 which performs reaction required for shape control is demonstrated.
  • the step E1 is preferably performed in the middle of the step C1, and is preferably performed immediately after the addition of the basic compound in the step C1.
  • the addition order of the amphiphilic compound having a carboxyl group added to the liquid to be added and the basic compound not containing a metal is not particularly limited.
  • the aqueous layer may be separated from the basic compound or amphiphilic compound layer having a carboxyl group, but in that case, it is preferable to stir well. About stirring, the method similar to the case where the precipitate generate
  • the basic compound not containing a metal element added to the liquid to be added is not particularly limited as long as it shows basicity in an aqueous solution, and a known compound can be used, for example, quaternary ammonium.
  • a known compound can be used, 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.
  • hydrazine derivatives such as hydrazine, 1-monomethylhydrazine, 1,1-dimethylhydrazine and 1-ethyl-2-methylhydrazine; primary amines such as methylamine, ethylamine, n-propylamine and ethanolamine; Examples include secondary amines such as dimethylamine and diethylamine; tertiary amines such as trimethylamine and triethylamine.
  • hydrazine, hydrazine monohydrate, oleylamine, and hydrazine which do not contain metal impurities that adversely affect the performance of the obtained strontium titanate fine particles, are relatively easy to handle, and have a more remarkable effect on shape control.
  • At least one of the hydrazine derivatives is preferred, and hydrazine is most preferred.
  • hydrazine also has a function as a strong reducing agent, and thus is presumed to play a role in preventing oxidation of an amphiphilic compound having a carboxyl group.
  • Two or more basic compounds not containing these metal elements can be used in combination, but the use of hydrazine or a derivative thereof as one of them can control the shape of the resulting composite oxide nanoparticles into a cube. Therefore, it is preferable.
  • amphiphilic compound having a carboxyl group added to the liquid to be added may have a carboxyl group (hydrophilic group) and a hydrophobic group in the compound. Any known compound can be used without particular limitation.
  • Such compounds include propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid and other saturated fatty acids, ⁇ - Listed are unsaturated fatty acids such as linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, ⁇ -linolenic acid, dihomo- ⁇ -linolenic acid, arachidonic acid, oleic acid, elaidic acid, erucic acid, nervonic acid, etc. It is done.
  • an organic acid having 2 to 20 carbon atoms is preferable, and an organic acid having 10 to 20 carbon atoms is more preferable. Therefore, oleic acid, decanoic acid, lauric acid, undecenoic acid, linoleic acid, and At least one of linolenic acids is preferred, and oleic acid is most preferred.
  • strontium titanate is synthesized as a minute indefinite shape including various plane orientations in the early stage of growth.
  • an organic amphiphilic compound such as oleic acid
  • the carboxyl group is easily adsorbed on the (100) plane. Therefore, when crystal growth proceeds in the presence of an organic amphiphilic compound, the crystal grows with the amphiphilic compound adsorbed on the (100) plane, and therefore the crystal growth on the (111) plane preferentially proceeds. become.
  • growth of all (111) planes proceeds to form vertices, and strontium titanate fine particles whose shape is controlled in a cubic shape as a whole are synthesized.
  • the combination of the amphiphilic compound and the organic basic compound is preferably a combination of oleic acid and hydrazine.
  • the blending amount of the amphiphilic compound and the basic compound not containing the metal element is not particularly limited, but if the blending amount is too small, the particle size of the resulting fine particles becomes large, and if it is too large, the target substance is obtained. Disappear.
  • FIG. 2 shows the content of the amphiphilic compound in the reaction liquid to be reacted in Step D1 when the content of Ti component is 100, and the amount of the basic compound not containing metal is the vertical axis.
  • the figure it is the figure which described the ⁇ plot in the place where the strontium titanate shape-controlled in the cubic shape (or rectangular parallelepiped shape) was obtained in the examples described later.
  • the number of moles of Ti, the number of moles of amphiphilic compounds, the number of moles of organic basic compounds not containing metal, Z are 0 ⁇ Y / X ⁇ 6 and 0 ⁇ Z / X ⁇ 8 are preferably satisfied, more preferably 1 ⁇ Y / X ⁇ 4, still more preferably 0 ⁇ Z / X ⁇ 4.
  • the concentration of the Ti component is preferably 0.1 mmol / L or more and 20 mol / L or less.
  • Step C1 and Step F1 are steps for adjusting the basicity of the reaction solution reacted in Step D1. Adjustment of basicity is usually sufficient only in step C1, but when fine adjustment of basicity is necessary, such as when step E1 is performed after step C1, step F1 is preferably performed.
  • the process F1 is a process for adjusting the final basicity of the reaction solution for performing the process D1, it is preferably performed immediately before the process D1.
  • the basic substance used in Step F1 include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution, and examples of the acidic substance include nitric acid and hydrochloric acid.
  • the basic aqueous solution used in 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 in the vicinity of 1 is preferably used.
  • a basic compound sodium hydroxide or potassium hydroxide is preferably exemplified.
  • step C1 a gel-like precipitate is generated immediately after the addition of the basic compound.
  • a precipitate is generated immediately after the addition of the basic compound.
  • the means for stirring and pulverization are not particularly limited, and may be performed manually using a stirring bar or the like, or a method of dispersing by a stirrer or ultrasonic treatment may be used.
  • 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).
  • the reaction liquid prepared in step (3) is a subcritical reaction or supercritical reaction.
  • the reaction temperature holding time is not particularly limited. However, as long as it is supercritical, the shape is controlled to a cubic shape (cuboid shape) with a holding time of 10 minutes or less as described in the examples. Strontium titanate fine particles can be produced.
  • a reaction vessel in which the reaction solution is stored is placed in a closed heating apparatus such as an autoclave (hereinafter referred to as an autoclave), and subcritical and supercritical conditions are set. It heats so that it may become.
  • the reaction vessel may be gradually heated after being installed in the autoclave at room temperature, but it is preferable to install the autoclave in an environment adjusted to a subcritical or supercritical temperature atmosphere in advance. This is preferable because the rate of temperature rise is fast and the progress of the hydrothermal reaction can be suppressed as much as possible.
  • 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 cubic shape or a rectangular parallelepiped shape can be produced with high productivity (see Example 3 in the following description).
  • the most stable crystal structure of strontium titanate is a cubic crystal.
  • the original crystal shape is a cube, and the crystal plane exposed on the surface is a ⁇ 100 ⁇ plane.
  • Example 1 (FIGS. 3, 5A, and B) to be described later, according to the method for producing strontium titanate fine particles of the present invention, 85% or more of crystal planes exposed on the surface of a cube or a rectangular parallelepiped. Can produce strontium titanate fine particles having a ⁇ 100 ⁇ plane.
  • the length of one side of the cubic or rectangular parallelepiped particles is 10 nm or more and 500 nm or less.
  • the method for producing strontium titanate fine particles of the present invention comprises a reaction solution containing a basic compound having a pH of more than 10 including an Sr-containing aqueous solution and a Ti-containing aqueous solution, or a basic compound having an ionization degree of 0.8 or more and 0.60 mol / L or more.
  • a subcritical or supercritical reaction method comprising a step of adding an organic basic compound not containing a metal element and an amphiphilic compound having a carboxyl group in a basic reaction solution before the reaction. ing. According to this configuration, strontium titanate fine particles whose shape is controlled so that the (111) plane of the strontium titanate crystal has a ⁇ 100 ⁇ plane by preferential growth can be produced with high productivity. .
  • strontium titanate is a perovskite oxide that exhibits photocatalytic activity when irradiated with sunlight.
  • Strontium titanate has fine particles formed by supporting metal promoters such as Pt, Rh, and Cu on the surface, as described in Patent Document 1 and Patent Document 2, as a mode for providing a more efficient photocatalytic ability. It is known to be preferred.
  • Strontium titanate microparticles carrying a metal cocatalyst suppress the recombination with holes because electrons excited in the strontium titanate by light irradiation move to the surface quickly due to the presence of the metal cocatalyst on the surface. And enables a highly efficient reduction reaction. Since it suppresses and raise
  • a method for supporting a metal promoter is generally a method in which a water-soluble metal salt is supported by an impregnation method, a photo-deposition method, or the like, and then reduced and attached to a metal ion.
  • the obtained metal tends to trap electrons between (interfacial) the strontium titanate which is the mother catalyst.
  • the strontium titanate fine particles have a crystal plane that has as much lattice matching 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 the lattice constants of Pt, Ir, Pd, Rh, Ru, Cu, Ni, and Co, which are supported metals, is 10% or less, Ir and Rh are 5% or less, Pt, Pd Is 0.5% or less, and by using cubic strontium titanate fine particles with a high ⁇ 100 ⁇ surface ratio on the surface, a highly efficient photocatalyst with few electron traps at the interface with the supported metal can be realized. . Further, the cubic strontium titanate fine particles are not only used for photocatalysts, but also described in Patent Document 6 and Patent Document 7, the cubic shape is the original shape of cubic particles, It has various advantages such as being easy to be formed and being easy to form a dense film.
  • strontium titanate fine particles were prepared as follows. First, a necessary amount of purified water was collected as an Sr-containing aqueous solution, and strontium nitrate was weighed to prepare an aqueous strontium nitrate solution. Moreover, titanium tetrachloride aqueous solution was prepared as Ti containing aqueous solution. Ampoule-like TiCl 4 is slowly added dropwise to purified water drop by drop. At that time, it is carried out with stirring and cooling. Unless otherwise specified, purified water was used as the solvent water.
  • the titanium tetrachloride aqueous solution was shielded from light, stored in a refrigerator immediately after preparation, and mixed with a strontium nitrate aqueous solution while maintaining the state immediately after adjustment to obtain a mixed solution. During the mixing, the mixture was mixed so that the molar ratio Sr / Ti of the Sr component and the Ti component in the mixed solution was 1.
  • the mixed solution is stored in a beaker, and an aqueous potassium hydroxide solution (15 mol / L) is dropped dropwise into the mixed solution. Thereafter, hydrazine is further dropped into the mixed solution, and oleic acid is continuously added. It was dripped. Since a gel-like white precipitate was generated immediately after the potassium hydroxide aqueous solution was dropped, the potassium hydroxide aqueous solution, hydrazine, and oleic acid were dropped while stirring and pulverizing the precipitate, and finally the mixed solution The pH was adjusted to 12 to prepare a reaction solution.
  • the obtained reaction liquid was put into a reaction vessel, and an autoclave was put into a 400 ° C. atmosphere to carry out a supercritical reaction. Synthesis of strontium titanate fine particles was carried out.
  • the reaction conditions are shown in Table 1.
  • a specified amount of the reaction solution is put into a Hastelloy (registered trademark) container (made by AKICO) with an internal volume of about 5 cm 3 according to each temperature, and it is sealed in a stainless steel pressure vessel, 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 a cubic shape.
  • FIG. 3 shows a photomicrograph of the fine particles obtained in Example 1
  • FIG. 4 shows a photomicrograph of the fine particles obtained in Comparative Example 1.
  • FIG. 2 shows the relationship between the number of moles of the amphiphilic compound and the ratio of the organic basic compound to the number of Ti moles in the reaction solution and whether or not the shape-controlled strontium titanate fine particles can be produced. Is shown.
  • FIG. 5A is an enlarged electron micrograph of the strontium titanate fine particles obtained in Example 1
  • FIG. 5B is an electron micrograph showing the analysis result of the crystal plane of the strontium titanate fine particles.
  • the present invention can be applied to the production of strontium titanate fine particles suitable as photocatalysts, functional materials for electronic parts such as thermoelectric materials and dielectric materials, and lens materials.

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