Process for producing lead oxyfluorotitanate

Abstract

To provide a new method for producing a lead titanium oxyfluoride compound, which is completely different from conventional high-temperature dry synthesis and hydrothermal synthesis and can cause problems such as coarsening of particles due to sintering.SOLUTION: A method for producing an oxyfluoride titanium lead compound, comprising the steps of: (a) dissolving a compound containing a titanium (IV) fluoride complex ion or a combination of a compound containing a fluorine atom capable of forming a titanium (IV) fluoride complex ion and a compound containing a titanium atom, a compound containing a lead atom, and a compound containing a boron atom in an amine solution; and (b) heating the resulting solution to produce an oxyfluoride titanium lead compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a lead titanium oxyfluoride compound having excellent reducing ability such as hydrogen generation activity, the lead titanium oxyfluoride compound, and a photocatalyst containing the lead titanium oxyfluoride compound. [Background technology]

[0002] Metal oxyfluorides are used as photocatalytic materials, superconducting materials, secondary battery materials, etc. Because metal oxyfluorides contain fluorine, which has a high vapor pressure, their synthesis is generally carried out by a method in which a metal oxide and a metal fluoride are charged in a sealed environment in a stoichiometric ratio of the target composition and reacted (e.g., vacuum sealed tube or high-pressure synthesis) (Non-Patent Documents 1-2). However, this synthesis method is a dry reaction and requires high temperatures of about 400°C to 1,000°C to promote diffusion of the substances, which causes the particles of the resulting metal oxyfluoride to sinter and become coarse. In recent years, a method (topochemical reaction) has been developed in which a metal oxide having a crystalline structure similar to that of the target metal oxyfluoride is synthesized in advance and then reacted with a highly reactive fluorine source such as ammonium fluoride, xenon fluoride, or fluorine gas at a low temperature of 300°C or less (Non-Patent Document 3). However, the metal oxide precursor is limited to a compound having a layered structure that allows easy insertion and removal of fluoride ions, and when such a precursor is synthesized by a dry method, coarsening due to sintering is unavoidable.

[0003] Among metal oxyfluorides, titanium lead oxyfluoride compounds with a pyrochlore structure have photocatalytic functions that are activated under visible light. Visible-light-responsive photocatalysts are expected to be applied to artificial photosynthesis, such as hydrogen production via water photolysis and carbon dioxide reduction. The general method for producing lead titanium oxyfluoride compounds is high-temperature dry synthesis using a vacuum sealed tube (Non-Patent Document 4). In recent years, a method for producing lead titanium oxyfluoride compounds by hydrothermal synthesis using microwave heating (hydrothermal synthesis) has also been reported (Non-Patent Document 5). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] K.Oka et al., “Temperature-Independent, Large Dielectric Constant Induced by Vacancy and Partial Anion Order in the Oxyfluoride Pyrochlore Pb2Ti2O6-δF2δ”, Chem. Mater., 2016, 28, 5554-5559 [Non-patent document 2] R. Mizuochi et al., “A bifunctional lead-iron oxyfluoride, PbFeO2F, That functions as a visible-light-responsive photoanode and an electrocatalyst for water oxidation”, RSC Adv., 2021, 11, 25616-25623 [Non-patent document 3] PR Slater & RKB Gover, “Synthesis and structure of the new oxide fluoride Ba2ZrO3F2·xH2O”, J. Mater. Chem., 2001, 8, 2035-2038

[0005] [Non-patent document 4] R. Kuriki et al., “A Stable, Narrow-Gap Oxyfluoride Photocatalyst for Visible-Light Hydrogen Evolution and Carbon Dioxide Reduction”, J. Am. Chem. Soc., 2018, 140, 6648-6655 [Non-Patent Document 5] K.Aihara et al., “Low-Temperature Microwave-Assisted Hydrothermal Synthesis of Pb2Ti2O5.4F1.2 Photocatalyst for Improved H2 Evolution under Visible Light”, ACS Materials Lett., 2023, 5, 2355-2360 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors have encountered problems when producing lead titanium oxyfluoride compounds using conventional methods, such as high-temperature dry synthesis (Non-Patent Document 4), in which the particles become coarse due to sintering, and when used as a photocatalyst, the surface area of ​​the photocatalyst that interacts with the object to be treated decreases, resulting in a decrease in photocatalytic activity; and in hydrothermal synthesis (Non-Patent Document 5), the particle diameter of the resulting particles is large and the specific surface area is insufficient. An object of the present invention is to provide a completely new method for producing a lead titanium oxyfluoride compound, which is different from the conventional high-temperature dry synthesis or hydrothermal synthesis that can cause the above-mentioned problems. [Means for solving the problem]

[0007] Through intensive research aimed at solving the above problems, the inventors have discovered that a lead titanium oxyfluoride compound can be produced by dissolving a compound containing a titanium fluoride (IV) complex ion, or a combination of a compound containing a fluorine atom capable of forming a titanium fluoride (IV) complex ion and a compound containing a titanium atom, a compound containing a lead atom, and a compound containing a boron atom in an amine solution, and then heating the resulting solution to produce the lead titanium oxyfluoride compound. Based on this finding, further research was carried out, and the present invention was completed.

[0008] That is, the present invention relates to the following: [1] A method for producing a lead titanium oxyfluoride compound, comprising the steps of: (a) a compound containing a titanium (IV) fluoride complex ion, or a combination of a compound containing a fluorine atom capable of forming a titanium (IV) fluoride complex ion and a compound containing a titanium atom; Compounds containing lead atoms, and Compounds containing boron atoms in an amine solution; (b) heating the resulting solution to form a lead titanium oxyfluoride compound; The method comprising: [2] The method according to [1], further comprising adjusting the pH of the resulting solution to 7 to 11 using a pH adjuster after step (a) and before step (b). [3] The method according to [2] above, wherein the pH adjuster is an organic acid or carbon dioxide. [4] The method according to [3] above, wherein the pH adjuster is an organic acid.

[0009] [5] The method according to any one of the above [1] to [4], wherein the compound containing a boron atom is boric acid. [6] The method according to any one of the above [1] to [5], wherein the amine solution is selected from the group consisting of 2-aminoethanol, triethanolamine, diethanolamine, 2-(2-aminoethylamino)ethanol, and ethylenediamine. [7] The method according to any one of [1] to [6] above, wherein the heating is carried out by irradiating with microwaves.

[0010] [8] D below 1000 nm 50 A lead titanium oxyfluoride compound having a particle size. [9] D of 1 to 100 nm 50 The lead titanium oxyfluoride compound according to [8], having a particle size.

[10] 3m 2 g -1 A lead titanium oxyfluoride compound having a specific surface area of ​​at least 10 ...

[11] Equation 1 below: Pb x Ti y O z Fw (Formula 1) where x is 1.5 to 2.5, y is 1.5 to 2.5, z is 4.0 to 6.0, and w is 1.0 to 2.0. The lead titanium oxyfluoride compound according to any one of [8] to

[10] above, which is represented by the following formula:

[12] x is 2.0, y is 2.0, z is 5.4, and w is 1.2; The lead titanium oxyfluoride compound according to

[11] .

[0011]

[13] A lead titanium oxyfluoride compound obtained by the method according to any one of the above [1] to [7].

[14] A photocatalyst comprising the lead titanium oxyfluoride compound according to any one of [8] to

[13] . [Effects of the Invention]

[0012] The method of the present invention can produce a lead titanium oxyfluoride compound through a new step that is neither a high-temperature dry synthesis nor a hydrothermal synthesis. According to the method of the present invention, coarsening of particles due to sintering does not occur. According to the method of the present invention, nano-order D 50 It is possible to produce a lead titanium oxyfluoride compound having a particle size. In one aspect, the method of the present invention adjusts the pH of the obtained solution to 7 to 11 using a pH adjuster at a predetermined timing, thereby obtaining nano-order D particles, which are much smaller than the conventional micro-order particle diameters. 50 It has a particle size and a much larger specific surface area, and when used as a photocatalyst, it is possible to produce a lead titanium oxyfluoride compound that has excellent reducing ability, such as hydrogen generation activity.

[0013] The present inventors have also found that if trivalent titanium is mixed in the resulting lead titanium oxyfluoride compound in addition to tetravalent titanium, the reduction ability, such as hydrogen generation activity, will decrease when used as a photocatalyst. In one aspect, the method of the present invention controls the valence of titanium to tetravalent by adjusting the pH of the resulting solution to 7 to 11 using a pH adjuster at a predetermined timing, thereby producing a lead titanium oxyfluoride compound that has excellent reduction ability, such as hydrogen generation activity, when used as a photocatalyst. The photocatalyst containing the lead titanium oxyfluoride compound having a high specific surface area of ​​the present invention enables large-scale hydrogen production with a small amount of photocatalyst. Furthermore, because the lead titanium oxyfluoride compound has CO2 reduction properties, it is expected that the lead titanium oxyfluoride compound having a high specific surface area of ​​the present invention can be used to produce large amounts of formic acid, which serves as an energy carrier, with a small amount of photocatalyst.

[0014] The present inventors presume that the reaction by which the method of the present invention can produce a lead titanium oxyfluoride compound, particularly one on the nano-order, through a step that is neither a high-temperature dry synthesis nor a hydrothermal synthesis is as follows. The present inventors have succeeded in producing titanium fluoride complex ions ([TiF6]) by using titanium fluoride (IV) complex ions or substances capable of forming titanium fluoride complex ions ([TiF6]) as a starting material. 2- ) hydrolysis reaction [TiF6] 2- +nH2O → [TiF 6-n (OH) n ] 2- We have found that it is possible to provide a method for producing a titanium oxyfluoride lead compound using +nHF. Here, by using a compound containing a boron atom as a starting material, the hydrolysis of titanium fluoride (IV) complex ions can be promoted. Furthermore, by adjusting the pH to 7-11, i.e., on the alkaline side, the hydrolysis of titanium fluoride (IV) complex ions can be further promoted, and a large amount of titanium oxyfluoride lead compound nuclei can be formed in a short period of time, thereby depleting the raw materials used for nucleus growth, and D 50 It is estimated that the particle size can be made much smaller.

[0015] As an example of the preparation of lead titanium oxyfluoride compound, ammonium titanium fluoride, lead(II) acetate trihydrate, and boric acid are dissolved in 2-aminoethanol, and the resulting solution is heated at 200 °C to give PbTiO. 5.4 F 1.2 When the above reaction is obtained, the reaction represented by the following reaction formula is thought to occur. [ka] [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a SEM image of the surface of a lead titanium oxyfluoride compound (Powder 2) wet-synthesized by the method of Example 2. [Figure 2] FIG. 1 is a SEM image of the surface of a lead titanium oxyfluoride compound (Powder 3) wet-synthesized by the method of Example 3. [Figure 3] FIG. 1 is a graph showing the cumulative amount of hydrogen produced by photocatalyst 0 (comparison) using the lead titanium oxyfluoride compound (powder 0) described in Non-Patent Document 5, and photocatalysts 1 to 3 using the lead titanium oxyfluoride compounds (powders 1 to 3) obtained in Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the present invention will be described in detail based on preferred embodiments of the present invention.

[0018] The present invention provides a method for preparing a lead titanium oxyfluoride compound, the method comprising the steps of: (a) a compound containing a titanium (IV) fluoride complex ion, or a combination of a compound containing a fluorine atom capable of forming a titanium (IV) fluoride complex ion and a compound containing a titanium atom; Compounds containing lead atoms, and Compounds containing boron atoms in an amine solution; (b) heating the resulting solution to form a lead titanium oxyfluoride compound; The present invention relates to the method comprising the steps of:

[0019] The method of the present invention includes, in step (a), dissolving a compound containing a titanium(IV) fluoride complex ion or a combination of a fluorine atom-containing compound and a titanium atom-containing compound capable of forming a titanium(IV) fluoride complex ion, a lead atom-containing compound, and a boron atom-containing compound in an amine solution.

[0020] The compound containing titanium (IV) fluoride complex ions used in the present invention is free in solution to form titanium (IV) fluoride complex ions [TiF6] 2- There are no particular limitations on the compound that produces this, but examples include ammonium fluoride titanium (IV), sodium fluoride titanium (IV), potassium fluoride titanium (IV), and fluoride titanium (IV) acid, and from the viewpoint of solubility in an amine solution, ammonium fluoride titanium (IV) is preferred. One or more compounds containing titanium (IV) fluoride complex ions can be used. The concentration of the titanium (IV) fluoride complex ion in the amine solution is not particularly limited, but can be, for example, 10 to 500 mM, and preferably 50 to 200 mM.

[0021] The combination of the fluorine atom-containing compound and the titanium atom-containing compound used in the present invention is not particularly limited as long as it can form a titanium(IV) fluoride complex ion in solution. Examples of the fluorine atom-containing compound include ammonium fluoride, potassium fluoride, lead(II) fluoride, and hydrofluoric acid. From the viewpoint of solubility in an amine solution, ammonium fluoride is preferred. Examples of the titanium atom-containing compound include titanium(IV) isopropoxide and titanium(IV) oxide bis(acetylacetone). From the viewpoint of solubility in an amine solution, titanium(IV) isopropoxide is preferred. One or more types of compounds containing fluorine atoms and two or more types of compounds containing titanium atoms can be used.

[0022] The concentration of fluorine in the amine solution is not particularly limited, but can be, for example, 60 to 3,000 mM, and preferably 300 to 1,200 mM. The concentration of titanium in the amine solution is not particularly limited, but can be, for example, 10 to 500 mM, and preferably 50 to 200 mM.

[0023] The lead atom-containing compound used in the present invention is not particularly limited, but examples include organic acid lead salts such as lead(II) acetate trihydrate, lead(II) formate, lead(II) bis(2-ethylhexanoate)lead(II), lead(II) nitrate, and lead halides such as lead fluoride and lead(II) chloride. From the viewpoint of solubility in an amine solution, organic acid lead salts are preferred, and lead(II) acetate trihydrate and lead(II) formate are more preferred. One or more lead atom-containing compounds can be used. The concentration of lead in the amine solution is not particularly limited, but can be, for example, 10 to 500 mM, and preferably 50 to 200 mM. The lead atom-containing compound of the present invention forms a complex with the amine solution and can suppress the formation of insoluble lead acetate.

[0024] The compound containing a boron atom used in the present invention is not particularly limited, but examples thereof include boric acid, sodium tetraborate, lithium tetraborate, diboron trioxide, and boron. From the viewpoint of solubility in an amine solution, boric acid and sodium tetraborate are preferred. One or more boron atom-containing compounds can be used. The content of boron in the amine solution is not particularly limited, but can be, for example, 20 to 1,000 mM, and preferably 100 to 400 mM.

[0025] In the present invention, the use of a compound containing a boron atom can promote the formation of a lead titanium oxyfluoride compound. Specifically, when a compound containing boron atoms reacts with fluoride ions, it breaks down the titanium(IV) fluoride complex ions and produces tetrafluoroborate ions (BF4 - ) and is thought to contribute to the formation of lead titanium oxyfluoride compounds. In addition, if the compound containing boron atoms is boric acid, it can also serve as an oxygen source, so (formula)H 3BO3+4H + +4F - →It is thought that water is generated as in HBF4 + 3H2O, which promotes the hydrolysis of titanium (IV) and contributes to the generation of titanium lead oxyfluoride compounds.

[0026] The amine solution used in the present invention is not particularly limited, but examples thereof include alkanolamines such as 2-aminoethanol, diethanolamine, triethanolamine, 2-(2-aminoethylamino)ethanol, ethylenediamine, and choline chloride (deep eutectic solvent ethaline) dissolved in a solvent such as polyethylene glycol. From the viewpoint of suppressing hydrolysis of divalent lead ions and the generation of insoluble lead fluoride, alkanolamines are preferred, and 2-aminoethanol and diethanolamine are more preferred. One or more types of amine solutions can be used. The concentration of the amine in the amine solution is not particularly limited, but can be, for example, 1,000 to 20,000 mM, and preferably 5,000 to 20,000 mM.

[0027] The method of the present invention includes, as step (b), heating the resulting solution to produce a lead titanium oxyfluoride compound. The heating temperature is not particularly limited as long as it is a temperature at which a lead titanium oxyfluoride compound can be produced, but may be, for example, 50 to 300°C, preferably 100 to 300°C, and more preferably 200 to 240°C.

[0028] The heating means is not particularly limited as long as it can achieve the desired temperature in a short time (preferably instantaneously), but examples include microwave irradiation, steam bath heating, and oil bath heating. From the viewpoint of uniformly heating the solution, microwave irradiation is preferred. The heating time is not particularly limited, but may be, for example, 5 to 240 minutes, preferably 30 to 180 minutes, and more preferably 100 to 150 minutes.

[0029] The method of the present invention may further include the steps of heating the resulting solution, filtering the resulting precipitate, washing the filtrate, and drying. By filtering the resulting precipitate and washing the filtrate, by-products other than lead titanium oxyfluoride can be removed. The solvent used for washing is not particularly limited, but one or more of water, ethanol, acetone, an aqueous solution of nitric acid, an aqueous solution of sulfuric acid, etc. may be used. The drying method is not particularly limited, but examples include vacuum drying, air drying, and fluidized bed drying, and vacuum drying is preferred from the viewpoint of removing residual solvent. The temperature during drying is not particularly limited, but may be 80 to 200°C, and preferably 100 to 150°C.

[0030] The method of the present invention may further comprise adjusting the pH of the obtained solution to 7 to 11 using a pH adjuster after step (a) and before step (b). By adjusting the pH to 7 to 11, the valence of titanium can be controlled to tetravalent, which functions as the conduction band of the photocatalyst and improves the hydrogen generation activity. Trivalent titanium causes heat loss of absorbed photons due to dd transition absorption, so it is preferable to have a low amount of trivalent titanium. The above pH range allows for the reduction of trivalent titanium, which results in the Ti content of the obtained lead titanium oxyfluoride compound in the UV-vis diffuse reflectance spectrum. 3+ 3d 1 This can be confirmed by observing the dd transition absorption. Also, lead oxyfluoride titanium compound D 50The particle size can be controlled from the microscale to the much smaller nanoscale, and the specific surface area can be dramatically increased, resulting in a dramatic improvement in hydrogen generation activity.

[0031] pH is related to the valence of titanium and D 50 From the viewpoint of controlling the particle size, it is preferably 7 or more and less than 11, more preferably 8 or more and less than 11, even more preferably 9.5 or more and 10.5 or less, and most preferably 10. Examples of pH adjusters include organic acids and carbon dioxide. Examples of organic acids include carboxylic acids such as formic acid, acetic acid, propionic acid, and 2-ethylhexanoic acid. The pH adjuster is D 50 From the viewpoint of controlling the particle size, formic acid and acetic acid are preferred.

[0032] The present invention also provides a method for producing a D 50 The present invention also relates to a lead titanium oxyfluoride compound having a particle size. 50 The particle diameter is measured by photographing the target titanium oxyfluoride lead compound particles using a field emission scanning electron microscope (SEM) (Regulus (registered trademark) 8230, manufactured by Hitachi High-Technologies Corporation) and analyzing the image using Image J. Specifically, the target particles are photographed at a predetermined magnification (D 50 Particles expected to have a diameter of approximately 20 to 100 nm are photographed at 100,000x magnification, those expected to have a diameter of approximately 100 nm to 1 μm at 30,000x magnification, and those expected to have a diameter of 1 μm to 30 μm at 2000x magnification. The image is imported into Image J, and 50 titanium oxyfluoride lead compound particles are randomly selected from the image. The area of ​​each particle is calculated, and the circle equivalent diameter is calculated from that area. The particle size distribution is obtained based on the calculated circle equivalent diameter. The horizontal axis of the particle size distribution graph is the circle equivalent diameter, and the vertical axis is the area frequency. The area frequency is number frequency x area. In the particle size distribution curve obtained in this way, the number cumulative particle size at 50 number % of the cumulative number is defined as D 50 It is defined as:

[0033] The lead titanium oxyfluoride compound obtained by the method of the present invention has nanoscale D 50 The method of the present invention, in particular, includes adjusting the pH to 7 to 11 using a pH adjuster after step (a) and before step (b), to produce a much smaller nanoscale D 50 It can have a particle size. D of the titanium oxyfluoride compound of the present invention 50 From the viewpoint of reducing ability such as hydrogen generation activity when used as a photocatalyst, the particle size is preferably 1 to 100 nm, more preferably 10 to 100 nm, and even more preferably 20 to 60 nm. The present invention also provides a 3m 2 g -1 Specific surface area of ​​3 to 50 m or more, preferably 2 g -1 , more preferably 5 to 50 m 2 g -1 More preferably, the specific surface area is 30 to 50 m 2 g -1 The present invention also relates to a lead titanium oxyfluoride compound having a specific surface area of In this specification, the specific surface area is measured by the BET method, in which nitrogen (N2) molecules with a known adsorption area are adsorbed onto the powder particle surface at the temperature of liquid nitrogen, and the surface area of ​​the sample is determined from the amount of adsorption.

[0034] The lead titanium oxyfluoride compound of the present invention has the following formula 1: Pb x Ti y O z F w (Formula 1) where x is between 1.0 and 3.0, y is between 1.0 and 5.0, z is between 2.0 and 10.0, and w is between 0.1 and 3.0; Preferably, x is 1.5 to 2.5, y is 1.5 to 2.5, z is 4.0 to 6.0, and w is 1.0 to 2.0. It is expressed as:

[0035] Titanium oxyfluoride lead compounds include, for example, Pb 2.0 Ti 2.0 O 5.5F 1.2 (x=2.0, y=2.0, z=5.4, w=1.2), Pb 2.0 Ti 2.0 O 5.0 F 2.0 (x=2.0, y=2.0, z=5.0, w=2.0), Pb 2.0 Ti 4.0 O 9.0 F 2.0 (x=2.0, y=4.0, z=9.0, w=2.0), etc., and preferably Pb 2.0 Ti 2.0 O 5.5 F 1.2 (x=2.0, y=2.0, z=5.4, w=1.2).

[0036] The present invention further relates to lead titanium oxyfluoride compounds obtainable by the process of the present invention. The present invention also relates to a photocatalyst containing the lead titanium oxyfluoride compound of the present invention. 50 Photocatalysts containing lead titanium oxyfluoride compounds with particle sizes controlled to the nanoscale have higher reduction capabilities, such as higher hydrogen generation activity, compared to those produced by conventional methods. Furthermore, because lead titanium oxyfluoride compounds have CO2 reduction properties, the lead titanium oxyfluoride compounds of the present invention with a high specific surface area are expected to be able to produce large amounts of formic acid, which serves as an energy carrier, with a small amount of photocatalyst. [Example]

[0037] The method for producing a lead titanium oxyfluoride compound of the present invention will be explained in more detail below with reference to the following examples, but the present invention is not limited to these.

[0038] Comparative Example 1: Dry synthesis of lead titanium oxyfluoride compound As described in Non-Patent Document 5, lead oxide (PbO) powder, lead fluoride (PbF2) powder, and titanium oxide (TiO2) powder were mixed in a molar ratio of 1.4:0.6:2, and then the mixture was vacuum sealed in a glass tube and heated at 600°C to obtain Pb2Ti2O. 5.4 F 1.2Powder 0 (comparison) was used. From the SEM image of Powder 0 (magnification 2000 times), D was obtained using the above method. 50 The particle size was measured to be 20 μm (i.e., 20,000 nm). 5.4 F 1.2 The specific surface area of ​​is 0.5m 2 ·g -1 is.

[0039] 1. Production of lead titanium oxyfluoride [Example 1: Wet synthesis of titanium oxyfluoride lead compound] 20 mL of a 0.25 mol / L ammonium hexafluorotitanate solution in 2-ethanolamine, 10 mL of a 0.5 mol / L lead acetate trihydrate solution in 2-ethanolamine, and 10 mL of a 1.0 mol / L boric acid solution in 2-ethanolamine were mixed, and then the mixture was sealed in a Teflon inner tube under atmospheric pressure, double-sealed with a pressure-resistant ceramic outer tube, and heated at 400 W for 2 hours using a microwave pretreatment device (Anton Paar, Model: Multiwave Pro) to produce PbTiO. 5.4 F 1.2 Precipitate 1 was prepared. This precipitate was filtered and washed with ethanol, water, 0.1 mol / L aqueous nitric acid solution, and acetone to remove by-products such as ammonium acetate, ammonium fluoride, and tetrafluoroboric acid (2-ethanol salt). It was then dried under reduced pressure at 110 °C to obtain Pb2Ti2O 5.4 F 1.2 Powder 1 was obtained. 50 The particle diameter was measured using an SEM (magnification 30,000 times) by the above-mentioned method and was found to be 920 nm. The specific surface area of ​​Powder 1 was measured by the BET method and was found to be 4 m 2 g -1 It was.

[0040] Example 2: Wet synthesis of lead titanium oxyfluoride compound 20 mL of a 0.25 mol / L solution of ammonium hexafluorotitanate in 2-ethanolamine, 10 mL of a 0.55 mol / L solution of lead acetate trihydrate in 2-ethanolamine, and 10 mL of a 1.0 mol / L solution of boric acid in 2-ethanolamine were mixed and adjusted to pH 10 with acetic acid. The mixture was then sealed in a Teflon inner tube under atmospheric pressure, double-sealed with a pressure-resistant ceramic outer tube, and heated at 400 W for 2 hours using a microwave pretreatment device (Anton Paar, Model: Multiwave Pro) to produce PbTiO. 5.4 F 1.2 Precipitate 2 was prepared. This precipitate 2 was filtered and washed with ethanol, water, 0.1 mol / L aqueous nitric acid solution, and acetone to remove by-products such as ammonium acetate, ammonium fluoride, and tetrafluoroboric acid (2-ethanol salt). It was then dried under reduced pressure at 110 °C to obtain Pb2Ti2O 5.4 F 1.2 Powder 2 was obtained. 50 The particle diameter was determined by the above-mentioned method based on SEM observation (magnification 100,000 times) and was found to be 76 nm. The specific surface area of ​​Powder 2 was measured by the BET method and found to be 15 m 2 g -1 It was.

[0041] Example 3: Wet synthesis of lead titanium oxyfluoride compound 20 mL of a 2-ethanolamine solution of 0.25 mol / L ammonium hexafluorotitanate, 10 mL of a 2-ethanolamine solution of 0.55 mol / L lead acetate trihydrate, and 10 mL of a 2-ethanolamine solution of 1.0 mol / L boric acid were mixed, and the pH was adjusted to 10 using formic acid. The mixture was then sealed in a Teflon inner tube under atmospheric pressure, and then double-sealed with a pressure-resistant ceramic outer tube. The mixture was heated at 400 W for 2 hours using a microwave pretreatment device (Anton Paar, Model: Multiwave Pro) to obtain PbTiO. 5.4 F 1.2Precipitate 3 was prepared. This precipitate 2 was filtered and washed with ethanol, water, 0.1 mol / L aqueous nitric acid solution, and acetone to remove by-products such as ammonium acetate, ammonium fluoride, and tetrafluoroboric acid (2-ethanol salt). It was then dried under reduced pressure at 110 °C to obtain Pb2Ti2O 5.4 F 1.2 Powder 3 was obtained. 50 The particle diameter was determined by the above-mentioned method based on SEM observation (magnification: 100,000 times) and was found to be 34 nm. The specific surface area of ​​Powder 3 was measured by the BET method and found to be 37 m 2 g -1 It was.

[0042] 2. Photocatalyst Production and Evaluation Photocatalyst 0 (comparison), photocatalyst 1, photocatalyst 2 and photocatalyst 3 were obtained by supporting 0.5 wt % of platinum on each of powder 0, powder 1, powder 2 and powder 3 by photoelectrodeposition. 100 mg of each photocatalyst was suspended in 140 mL of 10 mmol / L ethylenediaminetetraacetic acid disodium aqueous solution and irradiated with visible light of wavelengths longer than 400 nm after removing the ultraviolet light from the white light of a 300 W xenon lamp (Ceramax, model number: PE300BF, output current 20 A) using a cold mirror (Eagle Engineering, model number: CM-1) and a long-pass filter (HOYA, model number: L42). The generated gas was collected and the hydrogen concentration was quantified. Figure 5 shows the cumulative hydrogen production over the visible light irradiation time for photocatalysts 0 to 3.

[0043] 5, it was confirmed that the photocatalysts using the lead titanium oxyfluoride compound obtained by the method of the present invention (Photocatalysts 1 to 3) were able to generate more hydrogen than the photocatalyst using the lead titanium oxyfluoride compound obtained by conventional high-temperature dry synthesis (Photocatalyst 0), and were therefore superior as photocatalysts. In particular, it was confirmed that the photocatalysts using the lead titanium oxyfluoride compound obtained by the method of the present invention, which involves pH adjustment (Photocatalysts 2 to 3), were able to generate significantly more hydrogen than the photocatalyst using the lead titanium oxyfluoride compound obtained by conventional high-temperature dry synthesis (Photocatalyst 0).

Claims

1. 1. A method for producing a lead titanium oxyfluoride compound, comprising the steps of: (a) a compound containing a titanium (IV) fluoride complex ion, or a combination of a compound containing a fluorine atom capable of forming a titanium (IV) fluoride complex ion and a compound containing a titanium atom; Compounds containing lead atoms, and Compounds containing boron atoms in an amine solution; (b) heating the resulting solution to form a lead titanium oxyfluoride compound; The method comprising:

2. 10. The method of claim 1, further comprising adjusting the pH of the resulting solution to between 7 and 11 using a pH adjuster after step (a) and before step (b).

3. 3. The method of claim 2, wherein the pH adjuster is an organic acid or carbon dioxide.

4. The method of claim 3 , wherein the pH adjuster is an organic acid.

5. The method according to any one of claims 1 to 4, wherein the compound containing a boron atom is boric acid.

6. The method of any one of claims 1 to 4, wherein the amine solution is selected from the group consisting of 2-aminoethanol, triethanolamine, diethanolamine, 2-(2-aminoethylamino)ethanol and ethylenediamine.

7. The method according to any one of claims 1 to 4, wherein the heating is carried out by microwave irradiation.

8. D less than 1000 nm ５０ A lead titanium oxyfluoride compound having a particle size.

9. D of 1 to 100 nm ５０ 9. The lead titanium oxyfluoride compound of claim 8 having a particle size.

10. 3 m ２ g －１ A lead titanium oxyfluoride compound having a specific surface area of ​​at least 10 ...

11. Formula 1 below: Pb ｘ Ti ｙ O ｚ F ｗ (Equation 1) wherein x is 1.5 to 2.5, y is 1.5 to 2.5, z is 4.0 to 6.0, and w is 1.0 to 2.

0. The lead titanium oxyfluoride compound according to any one of claims 8 to 10, wherein the compound is represented by the formula:

12. x is 2.0, y is 2.0, z is 5.4, and w is 1.2; 12. The lead titanium oxyfluoride compound of claim 11.

13. A lead titanium oxyfluoride compound obtainable by the method according to any one of claims 1 to 4.

14. A photocatalyst comprising the lead titanium oxyfluoride compound according to any one of claims 8 to 10.

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