JP2018062442A - Process for producing porous titanium oxide fine particles and porous titanium oxide fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing porous titanium oxide fine particles that is capable of producing, in a simplified and inexpensive manner, porous titanium oxide fine particles that have high specific surface area due to the use of bubbles serving as a template that occur during the generation of the titanium oxide fine particles and that have high crystallinity due to a low temperature ranging from ordinary temperature to 200°C, and provide the porous titanium oxide fine particles.SOLUTION: The process comprises a mixing step where a fluorotitanic acid salt is mixed with an aqueous metal carbonate solution, and a generation step where a porous titanium oxide is generated by hydrothermal synthesis at a temperature ranging from ordinary temperature to 200°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing porous titanium oxide fine particles and porous titanium oxide fine particles.

  Titanium oxide fine particles are known as typical photocatalytic active substances, but not only pigments, UV screening agents, adsorbents, ion exchangers, fillers, reinforcing materials, ceramic raw materials, perovskite complex oxides It is used in various ways, such as precursors of complex oxides such as, and primer for magnetic tape.

  When the titanium oxide fine particles are used as a photocatalyst, it is necessary to increase the porosity of the specific surface area, improve the crystallinity, and improve the anatase phase ratio in order to enhance the photocatalytic function. Usually, in order to increase crystallinity, the specific surface area decreases when firing at a high temperature. Thus, it is difficult to achieve both the high specific surface area and the high crystallinity effect, and it is necessary to appropriately control as necessary.

  In Non-Patent Document 1, as a conventional industrial method for producing titanium oxide, an aqueous solution of purified titanium tetrachloride is sprayed in an oxygen atmosphere at a high temperature (800 to 1,000 ° C.) to oxidize titanium tetrachloride. In addition, a “gas phase method” for obtaining titanium oxide particles and a “liquid phase method” for producing a titanium oxide precursor having a hydroxyl group and heat-treating the titanium oxide precursor at a high temperature of 500 ° C. or higher are described. .

  As a method for producing titanium oxide having a high specific surface area, Non-Patent Document 2 describes a liquid phase method using an organic compound such as a surfactant or a polymer as a template. However, in these methods, the manufacturing process is very complicated, and in particular, the manufacturing process is very complicated, such as using a large amount of an organic solvent to remove the mold used and burning at a high temperature. It was. In addition, there is a problem that the specific surface area of the titanium oxide fine particles is reduced by performing a high-temperature heat treatment in order to improve crystallinity.

  As a method for producing titanium oxide at a lower temperature than the above technique using a simple production apparatus, “porous titanium oxide particles and production method thereof” described in Patent Document 1 are known. Specifically, it is a method for economically producing porous titanium oxide particles having a large specific surface area by reacting under normal pressure without using a special apparatus.

JP 2007-230824 A

Manabu Seino Published by Gihodo Publishing, “Titanium Oxide-Physical Properties and Applied Technology” p18-27 (1991.6.25) Hideaki Yoshitake, Tae Sugihara, Takashi Tsuji "Catalyst" published by the Catalysis Society of Japan Vol.44 No.6p480-482 (2002)

  According to the method described in Patent Document 1, since the reaction temperature is a low temperature of 100 ° C. or lower, the specific surface area is hardly reduced by heat, but the fluorination generated in the course of the reaction between fluorinated titanic acid and water. Expensive boric acid is used as a scavenger for hydrogen fluoride ions.

The specific surface area of titanium oxide produced using this method is about 120 (reaction at 90 ° C., 48 hours) to 140 (reaction at 60 ° C., 48 hours) m ² / g, but the photocatalytic activity of titanium oxide is specific surface area. Therefore, the development of titanium oxide having a higher specific surface area is desired. In addition, environmental standards for boron and boron compounds (February 1999 items added, 1 mg / L) and drainage standards (enforced in July 2001, 10 mg / L for non-sea areas and 230 mg / L for sea areas) were established respectively. The acid needs to be treated carefully as a waste liquid, which takes time and effort, and is difficult to use because it imposes a heavy burden on manufacturing costs. In addition, a long reaction time of 48 hours is required, and the production time is too long. Furthermore, in order to improve crystallinity, it is fired (crystal growth) at a high temperature of 500 ° C. or higher. Although there is no description of the specific surface area in that case, it is guessed that the specific surface area is decreasing.

  The present invention was devised in view of the above points, and has a high specific surface area using bubbles generated in the production process of titanium oxide fine particles as a mold, and also has a high crystallinity at low temperatures from room temperature to 200 ° C. It is an object to provide a method for producing porous titanium oxide fine particles and porous titanium oxide fine particles, which can be produced easily and inexpensively.

  In order to solve the above problems, the method for producing porous titanium oxide fine particles of the present invention comprises a mixing step of mixing a fluorinated titanate and a metal carbonate, and hydrothermal synthesis under conditions from room temperature to 200 ° C. And a production step for producing porous titanium oxide.

Here, in the mixing step, by mixing the fluorinated titanate and the metal carbonate, it is possible to react the hydrogen fluoride generated by the hydrolysis of the fluorinated titanate with the metal carbonate.
The production of an aqueous solution in which a fluorinated titanate and a metal carbonate are mixed may be performed in any of the following (1) to (3).
(1) An aqueous solution of a predetermined concentration of a fluorotitanate and an aqueous solution of a metal carbonate of a predetermined concentration are mixed at a predetermined ratio.
(2) The fluorinated titanate and the metal carbonate are dissolved in water as a solvent at a predetermined ratio.
(3) In the aqueous solution in which any one of the fluorinated titanate and the metal carbonate is dissolved, the other is added so that the molar ratio of the fluorinated titanate and the metal carbonate becomes a predetermined ratio. Mix and dissolve.

  In addition, in the production process, fine titanium oxide particles with a high specific surface area are produced by the reaction of fluorinated titanate and metal carbonate by producing porous titanium oxide by hydrothermal synthesis under conditions from room temperature to 200 ° C. Can be manufactured.

  Moreover, the porous titanium oxide microparticles | fine-particles which have a high specific surface area and high crystallinity can be manufactured by performing a hydrothermal synthesis in a production | generation process.

  In order to solve the above-mentioned problem, the method for producing porous titanium oxide fine particles of the present invention comprises a mixing step of mixing a fluorinated titanate and a metal carbonate, and hydrothermal generation, so that the condition is from room temperature to 100 ° C And a production step for producing porous titanium oxide.

  Here, by performing hydrothermal generation in the generation step, porous titanium oxide fine particles having a high specific surface area can be produced.

  In addition, when a crystal growth step of hydrothermally treating the porous titanium oxide fine particles under the conditions of 100 ° C. to 200 ° C. is provided, a porous material having higher crystallinity than the porous titanium oxide fine particles produced by hydrothermal generation Titanium oxide fine particles can be obtained. The purpose of hydrothermal treatment in an open system is to increase the crystallinity of the titanium oxide fine particles obtained by hydrothermal generation.

  In the case where a cleaning step of cleaning the fluorine compound generated by the reaction between the fluorinated titanate and the metal carbonate with water is provided, harmful fluorine compounds can be removed.

  Further, in order to solve the above-mentioned problems, the method for producing porous titanium oxide fine particles of the present invention comprises a mixing step of mixing a fluorinated titanate and a metal carbonate, and a condition of room temperature to 100 ° C. in an open system. In a closed system, the surface of the porous protruding nano-particles is formed from the outline of the fine bubbles of carbon dioxide generated by the reaction between the fluorotitanate and the metal carbonate under the conditions of room temperature to 200 ° C. A large number of protrusions and a hollow body formed by assembling the protruding nanoparticles on the surface of meso-sized or macro-sized carbon dioxide bubbles, or porous titanium oxide fine particles that are aggregates of the hollow bodies. A process is provided.

  Here, in the mixing step, by mixing the fluorinated titanate and the metal carbonate, it is possible to react the hydrogen fluoride generated by the hydrolysis of the fluorinated titanate with the metal carbonate. The generation of the aqueous solution in which the fluorinated titanate and the metal carbonate are dissolved at a predetermined ratio is the same as described above.

  In addition, in the production process, carbon dioxide generated by the reaction of a fluorotitanate and a metal carbonate under conditions of room temperature to 100 ° C. in an open system or from room temperature to 200 ° C. in a closed system. A hollow body or a hollow body in which a large number of porous protruding nanoparticles protrude from the surface using the outline of fine bubbles as a template, and protruding nanoparticles are assembled on the surface of meso-sized or macro-sized carbon dioxide bubbles By generating porous titanium oxide fine particles which are aggregates of bodies, crystals of titanium oxide fine particles having a high specific surface area can be generated.

Moreover, the titanium oxide fine particle which has moderate specific surface area and crystallinity can be obtained by making reaction time into 1 to 24 hours in a production | generation process.
When the reaction time is less than 1 hour, the reaction time is too short and the reaction does not proceed sufficiently, and amorphous titanium oxide fine particles are obtained. Such titanium oxide fine particles do not have photocatalytic activity, and thus are appropriate. is not. On the other hand, when the reaction time exceeds 24 hours, the specific surface area and the crystallite size are not significantly changed as compared with the case where the reaction time is less than 24 hours.

  In addition, the carbon dioxide bubbles generated in the production process include at least one carbon dioxide bubble of micro size, meso size, or macro size. Titanium oxide fine particles having at least one pore among three kinds of pore diameters of meso-sized pores and macro-sized pores can be generated. In addition, a pore means the fine hole formed in a titanium oxide inside.

Further, metal carbonates include sodium hydrogen carbonate (NaHCO ₃ ), lithium hydrogen carbonate (LiHCO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), cesium hydrogen carbonate (CsHCO ₃ ), sodium carbonate (Na ₂ CO ₃ ), lithium carbonate (Li ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), manganese carbonate (MnCO ₃ ), strontium carbonate (SrCO ₃ ), calcium carbonate (CaCO ₃ ), cesium carbonate (Cs ₂ CO ₃ ), magnesium carbonate (MgCO ₃ ), which is at least one selected from the group consisting of ammonium fluoride fluoride ([NH ₄ ] ₂ TiF ₆ ), sodium fluoride titanate (Na ₂ TiF ₆ ), fluoride fluoride by at least one selected from the group of potassium titanate (K 2 _{TiF 6)} It can also be generated carbon dioxide using either metal carbonate and titanium fluoride salts.

  Further, in the mixing step in which the metal carbonate is sodium hydrogen carbonate and the fluorinated titanate is ammonium fluoride titanate, the ammonium fluoride titanate and sodium bicarbonate are mixed at a molar ratio of 1: 2 to 1:18. By mixing at a ratio, the reaction can be advanced efficiently and crystals of titanium oxide fine particles can be generated stoichiometrically. In addition, when the molar ratio is lower than 1: 2 (particularly, sodium bicarbonate is less than 2), the yield is lowered, and the titanium oxide fine particles according to the present invention cannot be obtained with high yield. On the other hand, when the molar ratio is higher than 1:18 (that is, sodium bicarbonate exceeds 18), sodium titanate is produced in the open system.

  In the mixing step in which the metal carbonate is sodium carbonate and the fluorotitanate is ammonium fluoride titanate, ammonium fluoride titanate and sodium carbonate are mixed in a molar ratio of 1: 1 to 1: 9. Thus, the reaction proceeds efficiently and crystals of titanium oxide fine particles can be generated stoichiometrically. In addition, when the molar ratio is lower than 1: 1 (particularly, sodium carbonate is less than 1), the yield is lowered, and the titanium oxide fine particles according to the present invention cannot be obtained with a high yield. On the other hand, when the molar ratio is higher than 1: 9 (that is, sodium carbonate exceeds 9), sodium titanate is produced in the open system.

  In order to solve the above-mentioned problem, the porous titanium oxide fine particles of the present invention are a crystal body, a hollow body formed by agglomeration of protruding nanoparticles having a large number of pores, or an assembly of the hollow body Is the body.

Here, the projecting nanoparticles having a large number of pores are aggregated to form a porous hollow body or an aggregate of hollow bodies, and the fine particles of titanium oxide fine particles are maintained while maintaining a high specific surface area. The pore volume can be improved. The specific surface area refers to the BET specific surface area determined by the nitrogen adsorption method, and the pore volume is the volume per unit mass (cm ³ / g).

  Moreover, it can be set as the porous titanium oxide fine particle which has crystallinity by being a crystal body.

  Moreover, it can be set as the titanium oxide microparticles | fine-particles which have a pore by having at least one of a micropore, a mesopore, and a macropore.

Moreover, it can be set as the titanium oxide microparticles | fine-particles which have a high specific surface area per unit mass because a specific surface area is about 100-600 m < ² > / g.

  Moreover, it can be set as the titanium oxide microparticles | fine-particles of a higher specific surface area because the length of a protruding nanoparticle is 20-30 nm on average and a width | variety is 5-15 nm on average.

  Moreover, it can be set as the titanium oxide microparticles | fine-particles of a higher specific surface area because the hole diameter of the pore formed in the protruding nanoparticle is 6-10 nm.

  Further, when the band gap between the valence band and the conduction band is 3.2 to 3.4 eV, photocatalytic activity can be expressed mainly in the ultraviolet region.

  The method for producing porous titanium oxide fine particles and the porous titanium oxide fine particles according to the present invention have a high specific surface area using a bubble having a diameter of 0.5 nm to several hundreds of nm generated in the production process of the titanium oxide fine particles as a template, Highly crystalline titanium oxide fine particles can be easily and inexpensively produced by crystal growth at a low temperature of room temperature to 200 ° C.

It is the schematic explaining an example of the process of manufacturing the titanium oxide microparticles | fine-particles of this invention. 2 is a low magnification transmission electron microscope image of the product obtained in Example 1. FIG. 2 is a high magnification transmission electron microscope image of the product obtained in Example 1. FIG. It is the figure which compared the library data of the product obtained in Example 1, and a standard titanium oxide microparticle. It is the figure showing the pore distribution of the product of Example 1 and Example 5, and the product hydrothermally treated at 130 ° C. and 180 ° C. in Example 7. FIG. 3 is an explanatory diagram showing an enlarged process of producing titanium oxide fine particles obtained in Example 1. 4 is a transmission electron microscope image of a product obtained by hydrothermal synthesis at 180 ° C. in Example 3. FIG. It is the figure showing the relationship between the reaction time of the product obtained in Example 4, a specific surface area, and a crystallite size. Transmission electron microscope image (crystallinity can be confirmed) of a sample taken at the time of nucleation after mixing ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆₎ and sodium hydrogen carbonate (NaHCO ₃ ) for 5 minutes. It shows an amorphous state). 2 is a low magnification transmission electron microscope image of the product obtained in Example 5. FIG. 2 is a high magnification transmission electron microscope image of the product obtained in Example 5. FIG. 3 is an X-ray diffraction pattern of the product obtained in Example 5. 2 is a low-magnification transmission electron microscope image of a product obtained by hydrothermal treatment at 180 ° C. obtained in Example 7. FIG. 2 is a high-magnification transmission electron microscope image of a product obtained by hydrothermal treatment at 180 ° C. obtained in Example 7. FIG. In the performance comparison test 1, the product obtained in Example 5, the product obtained in Example 7 subjected to hydrothermal treatment at 130 ° C. and 180 ° C., and the photodecomposition of methylene blue by UV irradiation of P-25 were represented. FIG. In performance comparison test 1, the product obtained in Example 5, the product obtained in Example 7 hydrothermally treated at 130 ° C. and 180 ° C., and the pseudo-primary of photodegradation of methylene blue by UV irradiation of P-25 It is a figure showing the reaction rate plot. The graph of (a) is a figure showing the result of ultraviolet and visible light absorption, and the graph of (b) is a figure showing the calculation result of the band gap of the titanium oxide fine particles. It is a figure showing the photodegradation of the product obtained in Example 5, the product hydrothermally treated at 130 ° C. and 180 ° C. in Example 7, and methylene blue by light irradiation of a P-25 fluorescent lamp. The figure which represented the pseudo first-order reaction rate plot of the photolysis of the product obtained in Example 5, the product heat-heat-treated at 130 degreeC and 180 degreeC in Example 7, and the light irradiation of the fluorescent lamp of P-25. It is. FIG. 4 is a diagram showing nitrogen adsorption isotherms of the products of Example 1 and Example 5 and titanium oxide fine particles produced by hydrothermal treatment at 130 ° C. and 180 ° C. in Example 7. It is a figure showing the particle size distribution of the product of 1st, 3rd Embodiment, and the titanium oxide microparticles | fine-particles manufactured by hydrothermally treating at 130 degreeC and 180 degreeC in Example 7. FIG. It is a scanning electron microscope image of the product obtained in Example 8. 2 is an X-ray diffraction pattern of the product obtained in Example 8. It is a high magnification transmission electron microscope image of a product obtained from potassium fluorinated titanate (K ₂ TiF ₆ ). ₂ is an X-ray diffraction pattern of a product obtained from potassium fluorinated titanate (K ₂ TiF ₆ ).

[Method for Producing Titanium Oxide Fine Particles According to the Present Invention]
Terms used in the present invention are defined as follows.
“Closed system” refers to a system in which a series of reactions are performed in a sealed container, and “open system” refers to a system in which a series of reactions are performed in an unsealed container. In the open system, carbon dioxide generated during the reaction is released into the atmosphere, but in the closed system, there is a difference in that the release of carbon dioxide into the atmosphere is suppressed. In particular, the closed system has an advantage that the synthesis can be performed under a preset temperature condition without evaporation of water even at a reaction temperature of 100 ° C. or higher.

  “Hydrothermal synthesis” refers to compound synthesis or crystal growth performed in the presence of hot water of high temperature and high pressure, and is mainly performed in a closed vessel called an autoclave. Here, the autoclave refers to a process performed using a pressure-resistant apparatus or container capable of making the inside high pressure. The temperature and pressure in the autoclave are 1.00 atm below 100 ° C, 2.67 atm at 130 ° C, 4.70 atm at 150 ° C, 9.91 atm at 180 ° C, and 15.4 atm at 200 ° C.

  “Hydrothermal generation” refers to the generation of crystals in an open system and at a reaction temperature of 100 ° C. or less. “Hydrothermal treatment” refers to heating the slurry-like titanium oxide fine particles once hydrothermal generation is completed in an autoclave. It means processing.

  The method for producing titanium oxide fine particles according to the present invention will be described below with reference to FIG.

(S1 first step)
In the first step, a fluorinated titanate and a metal carbonate are mixed.
(S2 second step)
In the second step, the reaction is carried out in an aqueous solution under a predetermined temperature condition and a predetermined reaction time condition, and a crystal of titanium oxide fine particles is generated using the carbon dioxide bubbles generated thereby as a template.
(S3 3rd process)
In the third step, the aqueous solution obtained in the second step is washed with pure water (ion exchange water, distilled water, etc.) to obtain fine titanium oxide particles.

  In the first step (S1), this is a simple manufacturing method of generating crystals of titanium oxide fine particles using carbon dioxide bubbles produced by mixing fluorinated titanate and metal carbonate as a template. Such titanium oxide fine particles can be produced with a simple apparatus.

  In addition, since the organic solvent is not used as in the prior art, the means for suppressing the evaporation of the organic solvent in the production process and the appropriate treatment of the organic solvent that is industrial waste are unnecessary. Titanium fine particles can be easily produced.

  Moreover, since the expensive boric acid conventionally used as a scavenger for fluorine ions is not used, the production cost of the titanium oxide fine particles according to the present invention can be suppressed.

  In the second step, the method differs between an open system and a closed type. The former is hydrothermal generation with a reaction temperature of 100 ° C. or lower, and the latter is hydrothermal synthesis with a reaction temperature from room temperature to 200 ° C. Crystal growth in the former case is performed by hydrothermal treatment after the third step, but crystal growth in the latter case proceeds simultaneously during the hydrothermal synthesis step.

Crystals of titanium oxide are formed using the fine bubbles of carbon dioxide generated in the second step as a template. At this time, projecting nanoparticles are generated using a micro-sized carbon dioxide bubble having a diameter of several nanometers generated by the reaction of the fluorotitanate and the metal carbonate as a template. A hollow body or a hollow body formed by agglomeration of protruding nanoparticles on the surface of a meso-sized or macro-sized carbon dioxide bubble having a diameter of several tens to several hundreds of nanometers formed by collecting a large number of carbon dioxide Is formed.
The reaction at this time is represented by the following reaction formula.

  Further, in the second step (S2), the synthesis is performed in an environment from room temperature to 200 ° C., so that it is 800 to 1,000 ° C. in the conventional gas phase method and 500 ° C. or more in the liquid phase method. Unlike the case where the synthesis is performed at a high temperature, the specific surface area is hardly reduced, and titanium oxide fine particles having a high specific surface area can be produced.

  In the second step (S2), for example, the crystallinity and the specific surface area can be controlled by changing the reaction time.

  In the third step (S3), since the cleaning with pure water is performed, the waste liquid can be easily treated.

  Further, since the titanium oxide fine particles of the present invention have a large pore volume, it was confirmed that the aqueous solution has a higher buoyancy than those having a small pore volume, so that it is difficult to precipitate and has high dispersibility. Thus, the titanium oxide fine particles of the present invention can maintain high dispersibility without mixing additives such as surfactants. Since the dispersibility is high, it is considered to have hydrophilicity, so that it is not necessary to stir frequently and the handling is simple.

In the form 1 for carrying out the invention, the production of the titanium oxide fine particles in the first to third steps (S1 to S3) is carried out in a closed system, and in the form 2 for carrying out the invention, the first part is carried out. Production of titanium oxide microparticles by ~ 3 steps (S1-S3) is performed in an open system.
Each will be described in detail below.

(Mode 1 for carrying out the invention 1: closed system)
In Embodiment 1 for carrying out the invention, fine titanium oxide particles are produced in a closed system by the following steps (S11 to 13).
(S11 1st process)
An aqueous solution in which ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ), which is an example of a fluorotitanate, is dissolved, and an aqueous solution in which sodium bicarbonate (NaHCO ₃ ), which is an example of a metal carbonate, is dissolved at room temperature. Mix.
(S12 second step)
The container containing the aqueous solution is placed in a pressure resistant container (hereinafter referred to as autoclave) under a predetermined temperature condition and a predetermined reaction time condition, and hydrothermal synthesis is performed in a closed system.
(S13 third step)
The precipitate obtained in the second step is washed with pure water (ion exchange water, distilled water, etc.) to obtain titanium oxide fine particles.

In Embodiment 1 for carrying out the invention, when mixing an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) having a predetermined concentration, these two aqueous solutions are mixed. Since this is a simple method of using a container having a capacity capable of mixing and placing the container in an autoclave to perform hydrothermal synthesis, no large-scale equipment is required.

  In addition, since the titanium oxide fine particles are produced in a closed system, most of the carbon dioxide generated in the production process is present as extremely fine bubbles in the aqueous solution without being released out of the reaction vessel. For this reason, in the process of producing titanium oxide fine particles, it becomes easier for titanium oxide fine particles to be crystallized using carbon dioxide fine bubbles as a template, and high specific surface area titanium oxide fine particles with improved pore volume are produced. Can be manufactured.

For example, the pore volume of titanium oxide fine particles produced by a reaction for 8 hours in a closed system at 90 ° C. was about 0.84 m ³ / g by the BET method. On the other hand, the pore volume of titanium oxide fine particles produced in an open system under the same reaction conditions was about 0.70 m ³ / g. That is, the pore volume of titanium oxide fine particles produced in a closed system is generally about 20% larger than the pore volume of titanium oxide fine particles produced in an open system. This is probably because carbon dioxide in the aqueous solution remains in the aqueous solution without being released in the closed system, but carbon dioxide is released in the production process of the titanium oxide fine particles in the open system.

In addition, about 0.84m < ³ > / g of a closed system, it is a BET measurement result interlock | cooperated with the specific surface area 294m < ² > / g measured in 0.3 mol / L sodium hydrogencarbonate of (Table 1). In addition, the numerical value of about 0.70 m ³ / g of the open system is a BET measurement result linked to the specific surface area of 297 m ² / g measured in 0.3 mol / L sodium hydrogen carbonate in (Table 3).

  In addition, since it is a method for producing titanium oxide fine particles without using an organic solvent or the like, the treatment of waste liquid is simple, and titanium oxide fine particles can be produced without using expensive boric acid. Cost can be reduced.

Example 1
A first embodiment of the present invention will be described with reference to FIGS.
In Example 1, an aqueous solution of 0.05 mol / L ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) and 0.3 mol / L sodium bicarbonate (NaHCO ₃ ) was used, and the following steps were performed. Titanium oxide fine particles were produced in a closed system according to (S21 to S23).

<Manufacturing process>
(S21 1st process)
A 0.05 mol / L ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution and a 0.3 mol / L sodium bicarbonate (NaHCO ₃ ) aqueous solution at a volume ratio of 1: 1 at room temperature To mix. Suspension began immediately in this aqueous solution, confirming the nucleation of titanium oxide fine particles.
(S22 second step)
Under the conditions of a reaction temperature of 90 ° C. and a reaction time of 8 hours, the container containing the aqueous solution was placed in an autoclave, and hydrothermal synthesis was performed in a closed system.
(S23 third step)
The precipitate obtained in the second step was washed with ion exchange water to obtain titanium oxide fine particles.

<Identification and performance evaluation of the product obtained in Example 1>
A low magnification transmission electron microscope image of the product obtained in Example 1 is shown in FIG. From FIG. 2, it was confirmed that the obtained product was a hollow body having a diameter of several tens to several hundreds nm. Moreover, the high magnification transmission electron microscope image of the product obtained in Example 1 is shown in FIG. From FIG. 3, it can be seen that the structure of the obtained product is a structure in which elongated projecting nanoparticles are densely packed on the surface of the hollow body.

FIG. 4 shows the X-ray diffraction pattern (a) of Example 1 and anatase-type titanium oxide fine particles obtained by using boric acid by the LPD method (calculated at 500 ° C. for 3 hours in Patent Document 1). X-ray diffraction pattern (b) is shown. By confirming a substantially similar waveform, it was revealed that the product of Example 1 was anatase-type titanium oxide fine particles.
The LPD method is a liquid phase deposition method, which is a conventional typical titanium oxide fine particle film forming method.

The titanium oxide fine particles of Example 1 were subjected to morphological analysis using a transmission electron microscope (JEM-3010, JEOL) and a scanning electron microscope (S-5200, Hitachi). The crystal structure of the product was determined by powder X-ray diffraction measurement (XRD, Smart lab, Rigaku). In XRD measurement, the crystal structure of the sample was determined by measuring the diffraction angle (θ) of the sample and comparing it with data (library) of known substances. Further, from the half width (β _1/2 ) of the peak of the diffraction angle (2θ = 23 °) corresponding to the crystal plane (101) of the titanium oxide fine particles, the crystallite size (D) of the titanium oxide fine particles is expressed by the following Scherrer equation: It was determined. Here, λ is the wavelength (= 1.5418A) in the CuKα ray, and K is the Scherrer constant (= 0.9).

With respect to the titanium oxide fine particles of Example 1, the crystallite size was calculated from the Scherrer equation, and was about 5.2 nm. The specific surface area was determined to be 294 m ² / g. Although the crystallite size is not so large, fine titanium oxide particles having a high specific surface area were obtained.

  The specific surface area and pore distribution of the titanium oxide fine particles obtained from the present invention are those of a nitrogen adsorption isotherm obtained using an automatic specific surface area / pore distribution measuring device (BELSORP-mini II, Nippon Bell). The measurement results were calculated using the BET method and nonlocal density functional theory.

FIG. 5 shows the pore distribution of titanium oxide fine particles (referred to as “90 ° C. (closed system)”) produced in the present embodiment (closed system).
It was confirmed that the hollow body of the titanium oxide fine particles of Example 1 had a distribution of micropores of 0.5 nm or more and less than 3.5 nm, mesopores of 3.5 nm or more and less than 30 nm, and macropores of 30 nm or more. The micropores are formed using microsize carbon dioxide as a template, the mesopores are formed using mesosize carbon dioxide as a template, and the micropores are formed using macrosize carbon dioxide as a template.

The production process of the titanium oxide fine particles obtained in Example 1 is shown in FIG.
In the production process of the titanium oxide fine particles of Example 1, the crystal formation of the titanium oxide fine particles and the generation of carbon dioxide are performed at the same time. At the same time as the particles are generated, the carbon dioxide that has become the template for the protruding nanoparticles is gathered and formed on the surface of the meso-sized or macro-sized carbon dioxide bubbles with a diameter of several tens to several hundreds of nanometers. The particles are aggregated to form hollow titanium oxide fine particles of a hollow body or an aggregate of hollow bodies. This generation process is the same in other embodiments.

  In particular, the hollow titanium oxide fine particles were formed as shown in FIG. 2 by forming a hollow body in which a crystal of titanium oxide fine particles was generated around carbon dioxide bubbles as a template.

  Moreover, it became clear from FIG. 3 that the protruding nanoparticles produced in Example 1 have a width average of about 5 to 15 nm and a length average of 20 to 30 nm. Furthermore, since the protruding nanoparticles are aggregated using carbon dioxide grown in a macro size as a template, the titanium oxide fine particles of Example 1 have a significantly high pore volume and a very high specific surface area.

Note that the generation of carbon dioxide (Formula 1) as shown in, ammonium fluoride titanate _{([NH 4] 2 TiF 6} ) aqueous solution and sodium hydrogen carbonate (NaHCO ₃₎ solution were mixed, acid-base reaction Is caused by the occurrence of

A mixture of an ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution and pure water, or an ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution and carbonated water (CO ₂ concentration of about 4000 ppm). The reaction did not progress. This is because pure water alone does not cause the formation reaction of titanium oxide shown in (Chemical Formula 1), and carbonic acid is weakly acidic, so that the reaction with ammonium fluoride titanate does not proceed. From this, it is understood that the production of carbon dioxide formed by mixing an aqueous solution of ammonium fluorotitanate ([NH ₄ ] ₂ TiF ₆ ) and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) is deeply related to the production of titanium oxide fine particles. I understand.

(Example 2)
A second embodiment of the present invention will be described based on Tables 1 and 2.
In Example 2, an ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution having a concentration of 0.05 mol / L and concentrations of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.6 mol / L, 0.9 mol / L sodium hydrogen carbonate (NaHCO ₃ ) aqueous solution was used to produce titanium oxide fine particles in a closed system by the following steps (S31 to S33).

<Manufacturing process>
(S31 1st process)
An aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L was prepared at concentrations of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.6 mol / L, 0 in .9Mol / sodium hydrogen carbonate each concentration was adjusted to L (NaHCO ₃₎ solution and room temperature, respectively 1 were mixed so that the 1 volume ratio. Suspension began immediately in this aqueous solution, confirming the nucleation of titanium oxide fine particles.
(S32 second step)
It carried out similarly to S22 of Example 1.
(S33 Third step)
It carried out similarly to S23 of Example 1.

<Identification and performance evaluation of the product obtained in Example 2>
Table 1 summarizes the results of evaluating the specific surface area, crystal phase, and crystallite size of this product in the same manner as in Example 1.
At all concentrations, the product of Example 2 was found to be anatase-type titanium oxide microparticles with a crystallite size of about 5.2 to 6.5 nm.
Moreover, although the width | variety of the change of the crystallite size by the density | concentration change of sodium hydrogencarbonate was small, the tendency for a specific surface area to increase remarkably as the density | concentration became large was confirmed. In particular, the specific surface area when produced at a concentration of 0.9 mol / L was 374 m ² / g. It can be said that this is a remarkably high value compared with the specific surface area of the commercial photocatalyst (titanium oxide fine particles) being about 50 m ² / g.

  In Example 2, it became clear that as the concentration of sodium bicarbonate increased, the specific surface area increased accordingly. By producing in a closed system, carbon dioxide produced in the production process of titanium oxide fine particles remains in the aqueous solution without escaping, and the amount of carbon dioxide produced increases as the concentration of sodium bicarbonate increases. It is considered that the shape of carbon dioxide was easily maintained when the protruding nanoparticles were collected using carbon dioxide bubbles as a template, and titanium oxide fine particles having a high specific surface area could be formed.

(Example 3)
A third embodiment of the present invention will be described with reference to FIG.
In Example 3, an ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution having a concentration of 0.05 mol / L and an aqueous solution of NaHCO ₃ having a concentration of 0.3 mol / L were used, and the following steps (S41 to S43) were performed. The performance evaluation test accompanying the temperature change of the titanium oxide fine particles was performed in a closed system.

<Manufacturing process>
In Example 3, the reaction temperature was set to 130 ° C., 150 ° C., and 180 ° C., and titanium oxide fine particles were obtained by hydrothermal synthesis.
(S41 1st process)
It carried out similarly to S21 of Example 1.
(S42 2nd process)
The reaction temperature was set to 130 ° C., 150 ° C., and 180 ° C. Under the conditions of each reaction time of 8 hours, the container containing the aqueous solution was placed in an autoclave, and hydrothermal synthesis was performed in a closed system.
(S43 3rd process)
It carried out similarly to S23 of Example 1.

<Performance Evaluation of Titanium Oxide Fine Particles Obtained in Example 3>
Table 2 shows the performance evaluation of the titanium oxide fine particles obtained in Example 3.

  From Table 2, the product of Example 3 was anatase-type titanium oxide fine particles, and it was confirmed that the specific surface area decreased and the crystallite size increased as the temperature of hydrothermal synthesis increased. In the case of hydrothermal synthesis, it can be seen that the crystal growth proceeds with the generation of titanium oxide fine particles. A high magnification transmission electron microscope image of titanium oxide fine particles synthesized hydrothermally at 180 ° C. is shown in FIG. As can be seen from FIG. 7, it was confirmed that the titanium oxide fine particles synthesized hydrothermally at 180 ° C. were nanocrystals of dispersed titanium oxide fine particles of 20 nm or less.

(Mode for carrying out the invention 2: open system)
In Embodiment 2 for carrying out the invention, titanium oxide fine particles are produced in an open system by the following steps (S51 to 53).
(S51 1st process)
This is performed in the same manner as the first step (S11) of the closed system.
(S52 second step)
Under a predetermined temperature condition, a predetermined humidity, and a predetermined reaction time condition, the container containing the aqueous solution is heated and hydrothermal generation is performed in an open system.
(S53 3rd process)
Performed in the same manner as the third step (S13) of the closed system.

In Embodiment 2 for carrying out the invention, an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) having a predetermined concentration are mixed to generate hydrothermal energy.

  In the case of an open system, after the third step, hydrothermal treatment can be performed at 100 to 200 ° C. in order to improve crystallinity.

Since the titanium oxide fine particles are produced in an open system, carbon dioxide bubbles generated by the reaction of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) and sodium hydrogen carbonate (NaHCO ₃ ) are present in the aqueous solution. Are gradually released out of the reaction vessel. For this reason, in the process of producing titanium oxide fine particles, the production of titanium oxide fine particles using fine bubbles of carbon dioxide as a template occurs in the same manner as in the closed system, but the titanium oxide fine particles produced in the closed system have a pore volume. It is thought that it will not improve as much.
However, titanium oxide fine particles having a sufficiently higher specific surface area than commercially available titanium oxide fine particle products (specific surface area: 50 m ² / g) are produced.

Example 4
A fourth embodiment of the present invention will be described with reference to FIGS.
In Example 4, an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) having a concentration of 0.3 mol / L were used. Titanium oxide fine particles were produced in an open system by the steps (S61 to S63).

<Manufacturing process>
(S61 1st process)
It carried out similarly to S21 of Example 1.
(S62 second step)
The container containing the aqueous solution was heated at a reaction temperature of 90 ° C. for an arbitrary reaction time, and hydrothermal generation was performed in an open system.
(S63 third step)
It carried out similarly to S23 of Example 1.

FIG. 8 shows the relationship between reaction time, specific surface area, and crystallite size in an open system. From FIG. 8, it can be seen that the reaction proceeds gradually within 1 to 24 hours. In the closed system, since the production of carbon dioxide is suppressed, the reaction rate is slightly slower than in the open system, but almost the same result can be obtained. FIG. 9 is a transmission electron microscope image of a sample taken at the time of nucleation 5 minutes after mixing ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) and sodium bicarbonate (NaHCO ₃ ). Crystallinity could not be confirmed, and amorphous titanium oxide fine particles were obtained. Such titanium oxide fine particles have no photocatalytic activity.

(Example 5)
A fifth embodiment of the present invention will be described with reference to FIGS.
In Example 5, an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) having a concentration of 0.3 mol / L were used. The titanium oxide fine particles were produced in an open system by the steps (S71 to S73).

<Manufacturing process>
(S71 1st process)
It carried out similarly to S21 of Example 1.
(S72 2nd process)
Under the conditions of a reaction temperature of 90 ° C. and a reaction time of 8 hours, the vessel containing the aqueous solution was heated and hydrothermal generation was performed in an open system.
(S73 3rd step)
It carried out similarly to S23 of Example 1.

<Identification and performance evaluation of the product obtained in Example 5>
Transmission electron microscope images of the product of Example 5 are shown in FIGS.
FIG. 10 is a low-magnification transmission electron microscope image of the product obtained in Example 5. From FIG. 10, it can be seen that the product obtained in Example 5 is a particle having a diameter of about several tens to several hundreds of nanometers having protruding nanoparticles on the surface.

  FIG. 11 is a high-magnification transmission electron microscope image of the product obtained in Example 5. From FIG. 11, it was found that the protruding nanoparticles had an elongated shape having a width of about 5 to 15 nm and a length of about 30 to 40 nm. Further, it can be confirmed that the protruding nanoparticles have a large number of pores having a pore diameter of about 10 nm or less.

  Thus, the product obtained in Example 5 is a fine particle having a large number of protruding nanoparticles on the surface, and the protruding nanoparticles have a large number of pores. It became clear that the particles had a high surface area.

In addition, when the specific surface area of the product obtained in Example 5 was determined, a value of 297 m ² / g was obtained. This can be said to be a remarkably high value when the specific surface area of a commercial photocatalyst (titanium oxide fine particle) product is about 50 m ² / g.
The crystallite size of this product was about 5.7 nm.

  And the X-ray-diffraction pattern of the product obtained in Example 5 is shown in FIG. From this figure, it was revealed that the product of Example 5 was anatase type titanium oxide fine particles.

  Further, the yield obtained from the mass of the powdered titanium oxide fine particles obtained by drying under reduced pressure after (S73 third step) (relative to the theoretical value of the titanium oxide fine particles obtained by hydrolysis of ammonium fluoride titanate). The percentage) was almost 100%.

  Moreover, the pore distribution of the product obtained in Example 5 is shown in FIG. According to FIG. 5, in the case of the titanium oxide fine particles “90 ° C. (open system)” of Example 5, the macroscopic diameter of 30 nm or more is compared with the titanium oxide fine particles “90 ° C. (closed system)” of Example 1 (closed system). It was found that the pores were decreasing. This is considered that the titanium oxide particles of Example 5 were not able to grow into particles having macropores due to the release of carbon dioxide in the process of being produced in an open system.

  In general, the specific surface area of the titanium oxide fine particles is considered to be determined by the amount of micro-sized or meso-sized carbon dioxide bubbles. In micro size or meso size, since the pore distribution is almost the same as in Example 1, it is considered that the decrease in macro pores does not greatly affect the specific surface area.

(Example 6)
Example 6 of the present invention will be described with reference to Table 3.
Example 6 is an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L, and an aqueous solution of 0.3 mol / L and 0.9 mol / L sodium hydrogen carbonate (NaHCO ₃ ). The titanium oxide fine particles were produced in an open system by the following steps (S81 to S83).

<Manufacturing process>
(S81 1st process)
Ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L and aqueous sodium hydrogen carbonate (NaHCO ₃ ) solutions adjusted to concentrations of 0.3 mol / L and 0.9 mol / L, respectively, at room temperature. At a volume ratio of 1: 1. Suspension began immediately in this aqueous solution, confirming the nucleation of titanium oxide fine particles.
(S82 second step)
Under the condition of a reaction time of 90 hours at a reaction temperature of 90 ° C., the container containing each of the aqueous solutions was heated and hydrothermal generation was performed in an open system.
(S83 third step)
It carried out similarly to S23 of Example 1.

<Identification and performance evaluation of the product obtained in Example 6>
Obtained by using sodium bicarbonate (NaHCO ₃ ) concentrations of 0.3 mol / L and 0.9 mol / L against 0.05 mol / L ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ). Table 3 shows the results of evaluating the specific surface area (m ² / g), crystal phase, and crystallite size (nm) of the product obtained in the same manner as in Example 5. The crystalline phase of the product obtained using a sodium bicarbonate concentration of 0.9 mol / L was sodium titanate, and the specific surface area was greatly reduced to 153 mm ² / g.

  As a result, it became clear that titanium oxide fine particles were not generated when the concentration of sodium hydrogen carbonate was increased in an open system. It is conceivable that sodium is advantageously produced.

From the results of the performance evaluation of the titanium oxide fine particles produced in Examples 1 to 6, when sodium bicarbonate (NaHCO ₃ ) with a concentration of 0.3 mol / L was compared between the closed system and the open system in terms of specific surface area. No major difference could be confirmed. Therefore, in the case of sodium bicarbonate having a concentration of 0.3 mol / L, when obtaining anatase-type titanium oxide fine particles having a specific surface area of about 300 m ² / g, both a closed system and an open system are suitable production methods. It became clear that there was.

In the case of sodium bicarbonate (NaHCO ₃ ) with a concentration of 0.9 mol / L, anatase-type titanium oxide fine particles having a specific surface area of 374 m ² / g in the closed system and high photocatalytic activity were produced.
In contrast, in the case of 0.9 mol / L sodium hydrogen carbonate (NaHCO ₃ ) in the open system, the specific surface area was 153 m ² / g, and sodium titanate having a low photocatalytic activity was also produced in terms of the crystal phase. .
Therefore, in order to obtain highly crystalline titanium oxide fine particles having a specific surface area of 300 m ² / g or more, it is necessary to increase the concentration of sodium hydrogen carbonate (NaHCO ₃ ) in a closed system.

(Example 7)
Example 7 will be described with reference to FIGS. 13 and 14 and Table 4. FIG.
Example 7 uses an aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L and an aqueous solution of sodium bicarbonate (NaHCO ₃ ) having a concentration of 0.3 mol / L, as follows. Titanium oxide fine particles were produced in an open system by the steps (S91 to S94).
In Example 7, the titanium oxide fine particles produced in Example 5 (open system) were subjected to hydrothermal treatment to produce titanium oxide fine particles.

<Manufacturing procedure>
(S91 1st process)
It carried out similarly to S21 of Example 1.
(S92 2nd step)
Under the conditions of a reaction time of 90 hours at a reaction temperature of 90 ° C., the vessel containing the aqueous solution was heated and hydrothermal synthesis was performed in an open system.
(S93 3rd step)
It carried out similarly to S23 of Example 1.
(S94 4th step)
The slurry-like titanium oxide fine particles obtained in the third step were placed in an autoclave and hydrothermally treated for 6 hours under each temperature condition of 130 ° C, 150 ° C and 180 ° C.

<Performance Evaluation of Titanium Oxide Fine Particles Obtained in Example 6>
Table 4 shows the results of evaluating the specific surface area, the crystal phase, and the crystallite size in the same manner as in Example 4 when hydrothermal treatment was performed under the conditions of each temperature (130 ° C., 150 ° C., 180 ° C.). It is a representation. From Table 4, at all hydrothermal treatment temperatures, the product of Example 7 is anatase-type titanium oxide fine particles having a specific surface area of 124 to 145 m ² / g and a crystallite size of about 9.4 to 12.0 nm. It turns out to have. Moreover, the specific surface area decreased and the crystallite size increased as the hydrothermal treatment temperature increased. It was found that crystal growth was promoted by hydrothermal treatment.

  FIG. 13 is a low-magnification transmission electron microscope image of titanium oxide fine particles hydrothermally treated at 180 ° C. in Example 7. 14 is a high-magnification transmission electron microscope image of titanium oxide fine particles hydrothermally treated at 180 ° C. in Example 7. FIG.

  From FIG. 13, it was confirmed that the obtained titanium oxide fine particles were a hollow body having a diameter of 300 to 500 nm and an aggregate of hollow bodies. Further, from FIG. 14, the projecting nanoparticles formed on the surface of the hollow body of the titanium oxide fine particles have a size of about 40 to 60 nm, and further have pores with a pore diameter of several nm inside. I was able to confirm.

In Example 7, when the titanium oxide fine particles produced in an open system were placed in an autoclave and subjected to hydrothermal treatment, the specific surface area decreased with increasing temperature, but the crystal phase had an extremely high photocatalytic activity. It was found that a single crystal of the type was formed. Further, as shown in FIG. 14, pores having a pore diameter of several nm are confirmed inside the single crystal. These pores maintain a high specific surface area of 124 to 145 m ² / g.

From the above, Example 6 is a method suitable for the production of anatase-type titanium oxide fine particles having a specific surface area of about 150 m ² / g or less, and particularly about 120 to 150 m ² / g by changing the temperature of hydrothermal treatment. It was revealed that a large crystallite size of 9.0 to 12.0 nm can be controlled at the same time as the specific surface area of N is formed.

  Further, as shown in FIG. 13, the titanium oxide fine particles in Example 7 are excellent in thermal stability because they maintain a hollow shape even after hydrothermal treatment at about 180 ° C. Became clear.

  Moreover, the pore distribution of the product obtained in Example 5 is shown in FIG. From FIG. 5, when the titanium oxide fine particles “90 ° C. (open system)” obtained in Example 5 were hydrothermally treated at 130 ° C., the distribution of micropores and mesopores was greatly reduced, and the hydrothermal treatment at 180 ° C. Then, the peak value of the pore distribution converged around 2.6 nm with crystallization. The distribution of mesopores decreased and the distribution of macropores hardly changed.

(Performance comparison test 1)
The titanium oxide fine particle performance comparison test 1 of the present invention will be described with reference to FIGS. 15 and 16.
Here, the titanium oxide fine particles produced in Example 5 are referred to as “90 ° C. (open system)”, and 90 ° C. (open system) is obtained by performing hydrothermal treatment at 130 ° C. in Example 7 as “90 ° C. (open system)”. The titanium oxide fine particles that were hydrothermally treated at 180 ° C. in Example 7 were referred to as “90 ° C. (open system) → 130 ° C.”.

  The performance comparison test 1 used these to perform a performance evaluation test on the decomposition of methylene blue by ultraviolet irradiation. The following procedure 1 to procedure 3 (T1 to T3) were performed using “P-25” (Sigma-Aldrich), which is a commercially available titanium oxide fine particle known to have high photocatalytic activity, as a comparative substance. Was used for photolysis of methylene blue in the ultraviolet region.

<Performance evaluation test procedure>
(T1 procedure 1)
Titanium oxide fine particles were added to a methylene blue aqueous solution having a concentration of 40 μM as a catalyst at a concentration of 1 mg / mL.
(T2 procedure 2)
After adsorbing methylene blue for 30 minutes, the methylene blue aqueous solution was irradiated with ultraviolet rays (UV (wavelength 365 nm)).
(T3 procedure 3)
The absorption spectrum of the methylene blue aqueous solution collected during the decomposition experiment was measured using an ultraviolet-visible spectrophotometer (V-570, JASCO Corporation).

As a measurement result, the result of photodegradation by UV irradiation of methylene blue by photocatalytic reaction of titanium oxide fine particles is shown in FIG. FIG. 16 shows a quasi-first order reaction rate plot obtained using Here, k is a pseudo first-order rate constant, t is the reaction time, C ₀ is the initial concentration of the reactant, and C is the concentration of the reactant at an arbitrary reaction time t.

Here, since C ₀ and C are proportional to the absorbance of the absorption spectrum, they can be replaced with the absorbance.

<Performance evaluation of the obtained titanium oxide fine particles>
From FIG. 15, “90 ° C. open system” shows much higher methylene blue adsorption than P25, but “90 ° C. (open system) → 130 ° C.” and “90 ° C. (open system) → 180 ° C.” are slightly higher. It was confirmed to show adsorptivity.

  In addition, “90 ° C. (open system) → 180 ° C.” decomposes about 80% in about 15 minutes from the start of ultraviolet irradiation, and “90 ° C. (open system)” and “90 ° C. (open system) → 130 ° C.” Then, about 60% was disassembled. P25 has a decomposition ability of about 40% in 15 minutes, and all showed higher decomposition ability in a shorter time than P25.

  Further, from FIG. 16, “90 ° C. (open system) → 180 ° C.” showed the fastest reaction rate of about 3 times P-25. “90 ° C. (open system) → 130 ° C.” showed a fast reaction rate of about 1.3 times P-25. “90 ° C. (open system)” also showed almost the same reaction rate although slightly inferior to P-25.

  From this, in terms of the adsorptivity of methylene blue in the ultraviolet region, photodecomposition ability and reaction rate, the titanium oxide fine particles of Example 5 have performance superior to P-25 in adsorbability and photodecomposition ability, It was revealed that the titanium oxide fine particles obtained in Example 7 had performance superior to P-25 in all of the adsorptivity, the photolysis ability and the reaction rate.

(Performance comparison test 2)
The performance comparison test 2 of the titanium oxide fine particles of the present invention will be described with reference to FIG.
In the performance comparison test 2, the titanium oxide fine particles “90 ° C. (open system)” produced in Example 5 and the titanium oxide fine particles “90 ° C. (open system) → 130 ° C.” and “90” obtained in Example 7 were used. The performance evaluation test for ultraviolet and visible light absorption and band gap was performed using “° C. (open system) → 180 ° C.”. In addition, the performance evaluation test of an ultraviolet-ray and visible light absorption spectrum was done using "P-25" (Degussa) which is a commercially available titanium oxide fine particle which shows high photocatalytic activity as a comparative substance.

<Performance evaluation test procedure>
The ultraviolet and visible light absorption spectra of the titanium oxide fine particles produced in Example 5 and the titanium oxide fine particles obtained in Example 7 were measured.

<Performance evaluation of the obtained titanium oxide fine particles>
The results of ultraviolet and visible light absorption are shown in FIG. 17A, and the band gap calculation results of the respective titanium oxide fine particles are shown in FIG. 17B.
In the case of P-25, since it is a composite crystal titanium oxide fine particle of anatase (80%) and rutile (20%), it clearly absorbs a wavelength of 400 nm or less, but the anatase type titanium oxide fine particle according to the present invention is 380 nm. It became clear that only the following ultraviolet light was absorbed. Moreover, the band gap of these titanium oxide fine particles was 3.2 to 3.4 eV, and it became clear that the band gap decreased as the hydrothermal treatment temperature increased.

  From FIG. 17, since the titanium oxide fine particles produced in Example 5 and the titanium oxide fine particles obtained in Example 7 have a large band gap, these titanium oxide fine particles hardly absorb visible light, but only ultraviolet rays. It became clear that it was absorbing.

(Performance comparison test 3)
A performance comparison test 3 of the titanium oxide fine particles of the present invention will be described with reference to FIGS.
In the performance comparison test 3, the titanium oxide fine particles “90 ° C. (open system)” produced in Example 5 and the titanium oxide fine particles “90 ° C. (open system) → 130 ° C.” and “90” obtained in Example 7 were used. Decomposition of methylene blue with visible light was performed using “° C. (open system) → 180 ° C.”. The results are shown in FIGS. In addition, the photocatalytic activity of titanium oxide fine particles was obtained by the following procedure 1 to procedure 3 (T1 to T3) using “P-25” which is a commercially available titanium oxide fine particle known to have high photocatalytic activity as a comparative substance. A performance evaluation test was conducted.

<Performance evaluation test procedure>
The photocatalytic activity of the titanium oxide fine particles produced in Example 4 and the titanium oxide fine particles obtained in Example 7 were evaluated.
(T1 procedure 1)
Titanium oxide fine particles were added to a methylene blue aqueous solution having a concentration of 40 μM as a catalyst at a concentration of 1 mg / mL.
(T2 procedure 2)
After adsorbing for 30 minutes, light from a fluorescent lamp (5000 lux) was irradiated.
(T3 procedure 3)
The absorption spectrum of the methylene blue aqueous solution collected during the decomposition experiment was measured using an ultraviolet-visible spectrophotometer (V-570, JASCO Corporation).

<Performance evaluation of the obtained titanium oxide fine particles>
After 1800 minutes from FIG. 18, P-25 shows about 70% of photolytic activity, but the titanium oxide fine particles (“90 ° C. open system”, “90 ° C. open system → 130 ° C.” and “90” C. open system → 180 ° C. ”) show higher photocatalytic activity than P-25.

  Further, from FIG. 19, the “90 ° C. open system” decomposes methylene blue at a rate about 1.2 times that of P-25, and “90 ° C. open system → 130 ° C.” and “90 ° C. open system → It was revealed that “180 ° C.” decomposes methylene blue at a rate about 2.3 times that of P-25.

  However, in performance comparison test 2, it is clear that the anatase-type titanium oxide fine particles according to the present invention absorb only ultraviolet light of 380 nm or less. From this, it is considered that in the performance comparison test 3, methylene blue was photodegraded in response to a very small amount of ultraviolet rays contained in the visible light region. And even if this very small amount of ultraviolet rays, it became clear that it has performance higher than P-25 in terms of adsorptivity and photolytic ability.

  And since fluorescent lamps and LED bulbs are known to emit a trace amount of ultraviolet rays, the titanium oxide fine particles according to the present invention react with a trace amount of ultraviolet rays emitted from fluorescent lamps and LED bulbs and have a high photocatalytic activity. It became clear to express.

  Titanium oxide fine particles are materials having various functions such as photocatalysts and wet solar cells, but one of the major features is that the refractive index is as large as 2.5 or more. A large scattering effect is expected if spherical particles having a size of about the wavelength of light can be produced with a material having such characteristics. This is considered to be one reason why the titanium oxide fine particles obtained in the present invention exhibit high photocatalytic activity.

  In addition, the titanium oxide microparticles | fine-particles which react with the wavelength of visible light region and express photocatalytic activity can also be manufactured by doping nitrogen, a sulfur atom, iron ion, and copper ion.

(Performance comparison test 4)
The performance comparison test 4 of the titanium oxide fine particles of the present invention will be described with reference to FIG.
In the performance comparison test 4, the nitrogen adsorption isotherms of the titanium oxide fine particles obtained in Example 1, Example 5 and Example 7 were compared.

<Performance evaluation test procedure>
In FIG. 20, Example 1 “90 ° C. (closed system)”, Example 5 “90 ° C. (open system)” and Example 7 “90 ° C. (open system) → 130 ° C.” and “90 ° C. (open system)” The measurement result of the nitrogen adsorption isotherm of the titanium oxide fine particles obtained at “→ 180 ° C.” is shown.

<Performance evaluation of the obtained titanium oxide fine particles>
From FIG. 20, it was revealed that the titanium oxide fine particles obtained in Example 1 and Example 5 have substantially the same adsorptivity.

(Performance comparison test 5)
The titanium oxide fine particle performance comparison test 5 of the present invention will be described with reference to FIG.
In performance comparison test 5, Example 1 “90 ° C. (closed system)”, Example 5 “90 ° C. (open system)” and Example 7 “90 ° C. (open system) → 130 ° C.” and “90 ° C. (open) The particle size distributions of the titanium oxide fine particles obtained at “system) → 180 ° C.” were compared.

<Performance evaluation test procedure>
The particle size distribution of the titanium oxide fine particles obtained in Example 1, Example 5 and Example 7 was measured using a zeta potential / particle size measuring device (ELSZ-1000, Otsuka Electronics Co., Ltd.). The obtained results are shown in FIG.

<Performance evaluation of the obtained titanium oxide fine particles>
From FIG. 21, it can be seen that the obtained titanium oxide fine particles have a particle size distribution of several hundred nm to several μm. This is a large value compared to titanium oxide P-25 having a particle distribution of 20-25 nm.

  The reason why such particle distribution was obtained was due to the aggregation of several hundred nm hollow nanoparticles having protruding nanoparticles on the surface, compared with titanium oxide fine particles obtained in an open system at 90 ° C. The closed titanium oxide fine particles at 90 ° C. have a larger particle size, and the titanium oxide fine particles obtained in the open system at 90 ° C. are hydrothermally treated at 130 ° C. and 180 ° C. to increase the size of the aggregate. I understand that.

  Further, as can be seen from the transmission microscope photograph in FIG. 13, another feature of the titanium oxide fine particles obtained in the present invention is a cloud of several μm (clouds) in which nano-sized nanoparticles of several hundred nm are connected. ) Can be formed. Moreover, it is clear that these nanoparticles are hollow because of their bright central part, and they produce a relatively large buoyancy in the solution, and exhibit high dispersibility despite being a size of several μm.

(Embodiment 3 for carrying out the invention)
A third embodiment for carrying out the invention will be described with reference to FIGS.
(Example 8)
In Embodiment 3 for carrying out the invention, titanium oxide fine particles are produced using sodium carbonate in a closed system by the following steps (S91 to 93).
Form 3 for carrying out the invention comprises a 0.05 mol / L ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) aqueous solution and a 0.015 mol / L sodium carbonate (Na ₂ CO ₃ ) aqueous solution. The titanium oxide fine particles used were produced in an open system by the following first to third steps (S101 to S103).

<Manufacturing procedure>
(S101 1st process)
An aqueous solution of ammonium fluoride titanate ([NH ₄ ] ₂ TiF ₆ ) having a concentration of 0.05 mol / L and an aqueous solution of Na ₂ CO ₃ having a concentration of 0.15 mol / L were mixed at a volume ratio of 1: 1 at room temperature. Suspension began immediately in this aqueous solution, confirming the nucleation of titanium oxide fine particles.
(S102 second step)
Under the condition of a reaction temperature of 90 ° C. for 12 hours, the vessel containing the aqueous solution was heated and hydrothermal generation was performed in an open system.
(S103 third step)
The same operation as in Example 1 was performed.

<Identification and performance evaluation of the product obtained in the form 3 for carrying out the invention>
A scanning electron microscope image of the product of Example 8 is shown in FIG. 22, and an X-ray diffraction pattern is shown in FIG. The product obtained by adding 0.15 mol / L sodium carbonate (Na ₂ CO ₃ ) shows almost the same shape as the product obtained using sodium bicarbonate (NaHCO ₃ ) from FIG. It was confirmed that the crystallite size was 5.8 nm and the specific surface area was 254 m ² / g. Moreover, it became clear from FIG. 23 that it is a titanium oxide fine particle which has an anatase type.
From this, it was found that substantially the same titanium oxide fine particles can be obtained even if the titanium oxide fine particles are produced using sodium carbonate (Na ₂ CO ₃ ) as the metal carbonate.

(Embodiment 4 for carrying out the invention)
Embodiment 4 for carrying out the invention will be described with reference to FIGS. 24 (a) and 24 (b) and FIG.
Example 9
In Example 9, an aqueous solution of 0.05 mol / L of potassium fluorinated titanate (K ₂ TiF ₆ ) and 0.3 mol / L of sodium bicarbonate (NaHCO ₃ ) was used. According to the process, titanium oxide fine particles were produced in an open system.

<Manufacturing process>
(S111 1st process)
A 0.05 mol / L potassium fluoride titanate (K ₂ TiF ₆ ) aqueous solution and a 0.3 mol / L sodium bicarbonate (NaHCO ₃ ) aqueous solution were mixed at a room temperature so that the volume ratio was 1: 1. did. Suspension began immediately in this aqueous solution, confirming the nucleation of titanium oxide fine particles.
(S112 second step)
Under the conditions of a reaction time of 90 hours at a reaction temperature of 90 ° C., the vessel containing the aqueous solution was heated and hydrothermal generation was performed in an open system.
(S113, third step)
It carried out similarly to S23 of Example 1.

<Identification and performance evaluation of the product obtained in Example 8>
Transmission electron microscope images of the product of Example 9 are shown in FIGS.
FIG. 24 (a) is a high magnification transmission electron microscope image of the product obtained in Example 9. FIG. FIG. 24A shows that the product obtained in Example 9 is a protruding nanoparticle.
FIG. 24B is an enlarged crystal image of the square part of FIG. 24A, and the crystal plane of anatase-type titanium oxide can be confirmed.

FIG. 25 is an X-ray diffraction pattern of the obtained product. According to FIG. 25, the product of Example 9 was anatase-type titanium oxide fine particles, and the crystallite size estimated from Scherrer's formula (Equation 1) was 7.1 nm. The specific surface area was confirmed to be 197 m ² / g.
From this, it was found that substantially the same titanium oxide fine particles can be obtained even when the titanium oxide fine particles are produced using potassium fluorinated titanate (K ₂ TiF ₆ ) as the fluorinated titanate.

  As described above, the method for producing porous titanium oxide fine particles to which the present invention is applied and the porous titanium oxide fine particles include micro to macro-sized bubbles having a diameter of 0.5 nm to several hundreds of nanometers that are generated in the production process of the titanium oxide fine particles. And a high specific surface area and a highly crystalline titanium oxide fine particle at a low temperature from room temperature to 200 ° C. can be produced easily and inexpensively.

<Manufacturing process>
(S61 1st process)
It carried out similarly to S21 of Example 1.
(S62 second step)
The container containing the aqueous solution was heated at a reaction temperature of 90 ° C. for a predetermined reaction time, and hydrothermal generation was performed in an open system.
(S63 third step)
It carried out similarly to S23 of Example 1.

Claims (16)

A mixing step of mixing the fluorotitanate and the metal carbonate;
A production process for producing porous titanium oxide under a condition of normal temperature to 200 ° C. by hydrothermal synthesis. A mixing step of mixing the fluorotitanate and the metal carbonate;
A production method of producing porous titanium oxide under a condition from room temperature to 100 ° C. by hydrothermal generation. The method for producing porous titanium oxide fine particles according to claim 2, further comprising a crystal growth step in which the porous titanium oxide fine particles are hydrothermally treated under conditions of 100 ° C to 200 ° C. The manufacturing method of the porous titanium oxide microparticles | fine-particles of Claim 1, Claim 2 and Claim 3 equipped with the washing | cleaning process which carries out the water washing | cleaning of the fluorine compound produced by reaction of the said fluorotitanate and the said metal carbonate. A mixing step of mixing the fluorotitanate and the metal carbonate;
Outline of fine bubbles of carbon dioxide generated by the reaction of fluorinated titanate and metal carbonate under the condition of room temperature to 100 ° C. in the open system or from room temperature to 200 ° C. in the closed system. A hollow body or aggregate of hollow bodies formed by agglomerating the protruding nanoparticles on the surface of a large number of porous protruding nanoparticles as a template and projecting on the surface of meso-sized or macro-sized carbon dioxide bubbles And a production step for producing porous titanium oxide fine particles. A method for producing porous titanium oxide fine particles. In the said production | generation process, reaction time shall be 1 to 24 hours. The manufacturing method of the porous titanium oxide microparticles | fine-particles of Claim 1, Claim 2, Claim 3, Claim 4 or Claim 5. The carbon dioxide bubbles generated in the generating step include at least one microsize, mesosize, or macrosize carbon dioxide bubbles. 1, 2, 3, 4, 4. The manufacturing method of the porous titanium oxide microparticles | fine-particles of Claim 5 or Claim 6. The metal carbonate is sodium hydrogen carbonate (NaHCO ₃ ), lithium hydrogen carbonate (LiHCO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), cesium hydrogen carbonate (CsHCO ₃ ), sodium carbonate (Na ₂ CO ₃ ), lithium carbonate ( li ₂ CO _3), potassium carbonate _(K 2 _CO 3), manganese carbonate (MnCO _3), strontium carbonate (SrCO _3), calcium carbonate (CaCO _3), cesium carbonate _(Cs 2 _CO 3), magnesium carbonate (MgCO ₃ ) At least one selected from the group of
The fluorinated titanate is selected from the group consisting of ammonium fluorinated titanate ([NH ₄ ] ₂ TiF ₆ ), sodium fluorinated titanate (Na ₂ TiF ₆ ), and potassium fluorinated titanate (K ₂ TiF ₆ ). The method for producing porous titanium oxide fine particles according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, or claim 7. In the mixing step in which the metal carbonate is sodium hydrogen carbonate and the fluorinated titanate is ammonium fluoride titanate, the molar ratio of the ammonium fluoride titanate and the sodium bicarbonate is 1: 2-1. The method for producing porous titanium oxide fine particles according to claim 1, 2, 3, 4, 5, 6, or 7. In the mixing step in which the metal carbonate is sodium carbonate and the fluorinated titanate is ammonium fluorinated titanate, the ammonium fluoride titanate and the sodium carbonate are mixed at a molar ratio of 1: 1 to 1: 9. The method for producing porous titanium oxide fine particles according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, or claim 7. A porous titanium oxide fine particle, which is a hollow body formed by agglomerating protruding nanoparticles having a large number of pores, or an aggregate of the hollow bodies. The porous titanium oxide fine particles according to claim 11, which have at least one of micropores, mesopores, and macropores. Porous titanium oxide fine particles according to claim 11 or claim 12 having a specific surface area of 100~600m ² / g. The porous titanium oxide fine particles according to claim 11, wherein the protruding nanoparticles have an average length of 20 to 30 nm and an average width of 5 to 15 nm. The porous titanium oxide fine particles according to claim 11, 12, 13, or 14, wherein the pore diameter of the pores formed in the protruding nanoparticles is 6 to 10 nm. The porous titanium oxide fine particles according to claim 11, claim 12, claim 13, claim 14, or claim 15, wherein a band gap between the valence band and the conduction band is 3.2 to 3.4 eV.