Method for producing tantalum nitride material, and tantalum nitride material

Abstract

The present disclosure relates to a method for producing a tantalum nitride material, comprising: a nitriding step of heating a precursor containing a lithium-tantalum composite oxide in the presence of a nitrogen compound.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a tantalum nitride material and the tantalum nitride material. Background Art

[0002] Tantalum nitrides such as tantalum nitride and tantalum oxynitride can absorb light of longer wavelengths than conventional oxide photocatalysts (Non-Patent Documents 1 and 2). Therefore, tantalum nitrides are expected to be used as photocatalysts that absorb light of wavelengths in the visible light region and decompose water into hydrogen and oxygen.

[0003] As a method for producing tantalum nitride, for example, Patent Document 1 discloses a method in which potassium tantalate (KTaO3), which is a composite oxide of tantalum and a metal selected from sodium, potassium, etc., is used as a precursor and the precursor is heat-treated in an ammonia-containing gas. According to this production method, nitridation is completed in a relatively short heat treatment time, so tantalum nitride can be produced with less heat energy.

[0004] On the other hand, Patent Document 2 discloses a method for producing high-purity tantalum nitride by nitriding tantalum oxide (Ta2O5) at a temperature of 800 to 950°C with an ammonia gas flow rate of 0.05 to 0.8 L / min per 1 g of tantalum oxide. Patent Document 2 also discloses that there is a tendency to shift to the long wavelength side as the oxygen content decreases and the purity increases.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-037918

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-164732

[0009] Non-patent literature

[0010] Non-patent literature 1: Nature Catalysis, 2018, Vol. 1, p. 756-763

[0011] Non-patent literature 2: Angewandte Chemie International Edition, 2022, Vol.61, Issue17, e202116573 Summary of the invention

[0012] Problems to be solved by the invention

[0013] Therefore, there is a demand for the development of a method for producing tantalum nitride with high purity.

[0014] However, in the production method described in Patent Document 1, a large amount of metals such as Na and K derived from the precursor remain in the generated tantalum nitride, and it is not possible to achieve a sufficiently high purity of the tantalum nitride.

[0015] The technical problem of the present disclosure is to provide a method for producing a tantalum nitride material with high purity.

[0016] Furthermore, another technical problem of the present disclosure is to provide a tantalum nitride material with high purity.

[0017] Solutions for solving problems

[0018] The present inventors have conducted intensive research to solve the above technical problems. As a result, they have found that a high-purity tantalum nitride material can be obtained by using a precursor containing a lithium tantalum composite oxide as a precursor of a tantalum nitride material. That is, the gist of the present disclosure is as follows.

[0019] [1]

[0020] A method for producing a tantalum nitride material includes a nitriding step of heating a precursor containing a lithium tantalum composite oxide in the presence of a nitrogen compound.

[0021] [2]

[0022] The method for producing a tantalum nitride material according to [1], wherein the lithium tantalum composite oxide is amorphous.

[0023] 〔3〕

[0024] According to the method for manufacturing tantalum nitride material described in [2], before the nitriding process, it includes: a sintering process, in which a raw material mixture containing a lithium compound and a tantalum compound is sintered to obtain a sintered product; and an amorphization process, in which the sintered product is contacted with an acidic aqueous solution to obtain the lithium tantalum composite oxide.

[0025] [4]

[0026] The method for producing a tantalum nitride material according to [3], wherein the molar ratio of lithium in the lithium compound to tantalum in the tantalum compound in the raw material mixture is 3.00 or more and 3.50 or less.

[0027] 〔5〕

[0028] The method for producing a tantalum nitride material according to any one of [1] to [4], wherein the nitriding step is performed in the presence of a zirconium compound.

[0029] [6]

[0030] A tantalum nitride material, comprising: one or more nitrides selected from the group consisting of tantalum nitride, tantalum oxynitride, composite nitride of tantalum and other metals, and composite oxynitride of tantalum and other metals, wherein the content of the nitride is greater than 99.5% by weight and the content of lithium is greater than 0.1 ppm and less than 3000 ppm.

[0031] 〔7〕

[0032] A tantalum nitride material, comprising: a tantalum nitride material obtained by doping zirconium into the tantalum nitride material as described in [6], wherein the content of zirconium in the nitride material is 99.5% by weight or more, and the content of lithium is 0.1 ppm or more and 3000 ppm or less.

[0033] 〔8〕

[0034] A photocatalyst, wherein the photocatalyst is a photocatalyst in which one or more promoters selected from the group consisting of ruthenium, chromium oxide and iridium oxide are supported on the tantalum nitride material described in [7].

[0035] 〔9〕

[0036] The photocatalyst according to [8], wherein the photocatalyst shows water decomposition photocatalytic activity under visible light irradiation.

[0037] Effects of the Invention

[0038] According to the present disclosure, a method for producing a high-purity tantalum nitride material can be provided.

[0039] Furthermore, it would be desirable to be able to provide tantalum nitride material of high purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 1 and 2 are powder XRD patterns of the tantalum nitride material obtained in Example 1 and the tantalum nitride material obtained in Example 2.

[0041] Figure 2 These are the evaluation results of the photocatalytic activity of the photocatalyst obtained in Example 7. DETAILED DESCRIPTION

[0042] The specific embodiments of the present disclosure are described in detail below. The present disclosure is not limited to each embodiment, and the constituent elements can be deformed and concretized within the scope of the main purpose. In addition, various inventions can be formed by appropriately combining multiple constituent elements disclosed in each embodiment. For example, several constituent elements can be deleted from all constituent elements shown in the embodiment. Moreover, the constituent elements of different embodiments can also be appropriately combined.

[0043] In addition, in this specification, when the combination of lower limits and upper limits of a plurality of numerical ranges is described, a numerical range in which the lower limit of one numerical range is combined with the upper limit of another numerical range may be employed.

[0044] 1) Method for manufacturing tantalum nitride material

[0045] The method for producing a tantalum nitride material according to the first embodiment of the present disclosure includes a nitriding step of heating a precursor containing a lithium tantalum composite oxide in the presence of a nitrogen compound. The production method according to this embodiment can produce high-purity tantalum nitride.

[0046] In this specification, "nitride" also includes oxynitride. Therefore, the tantalum nitride material in this embodiment includes one or more selected from the group consisting of tantalum nitride, tantalum oxynitride, composite nitride of tantalum and other metals, and composite oxynitride of tantalum and other metals. In addition, "high-purity" tantalum nitride material refers to a material having a high content ratio of the above-mentioned nitride and a low content of impurity elements.

[0047] Furthermore, in this specification, the compound to be nitrided is also referred to as a "precursor".

[0048] Lithium tantalum composite oxide is a composite oxide containing at least lithium and tantalum, and may contain metal atoms and hydrogen atoms other than lithium and tantalum in the oxide composition, and may be a hydrate. In addition, the lithium tantalum composite oxide may be crystalline or amorphous, but is preferably amorphous. By using amorphous lithium tantalum composite oxide as a precursor, nitridation is easily performed even at low temperatures and / or in a short time, so tantalum nitride materials can be manufactured with low energy and efficiency. In addition, by using amorphous lithium tantalum composite oxide as a precursor, lithium is easily removed from the tantalum nitride material in the nitridation process, so a tantalum nitride material with higher purity can be manufactured.

[0049] Lithium tantalum composite oxide can be prepared, for example, by performing a calcination process, in which a raw material mixture containing lithium compounds such as lithium carbonate (Li2CO3) and lithium chloride (LiCl) and tantalum compounds such as tantalum oxide (Ta2O5) is calcined. At this time, the molar ratio of lithium in the lithium compound to tantalum in the tantalum compound in the raw material mixture is preferably 3.00 or more and 3.50 or less, more preferably 3.10 or more and 3.40 or less, and further preferably 3.20 or more and 3.30 or less. The reason is that it is speculated that by making the molar ratio of tantalum and lithium in the raw material mixture within the above range, the generation of crystalline components that are difficult to amorphize in the amorphization process described later can be suppressed.

[0050] The firing conditions of the raw material mixture in the firing step are not particularly limited, but the firing temperature is usually 800° C. to 1000° C., and the firing time is 1 hour to 20 hours. The raw material mixture may be fired in air.

[0051] If an amorphization step of bringing the sintered product obtained in the sintering step into contact with an acidic aqueous solution is performed after the sintering step, then as the lithium tantalum composite oxide is amorphized, unreacted lithium compounds and other lithium-containing components are removed, which is preferred. Examples of the acidic aqueous solution include hydrochloric acid and sulfuric acid aqueous solutions. There are no particular limitations on the method of bringing the sintered product into contact with the acidic aqueous solution, and examples include a method of dispersing the sintered product in water and adding an acidic aqueous solution to the obtained dispersion. The amount of the acidic aqueous solution added at this time is an amount that allows the pH (25°C) of the dispersion to be greater than 1 and less than 4, and preferably an amount that allows the pH (25°C) of the dispersion to be greater than 1 and less than 3.

[0052] The calcined product is treated with an acidic aqueous solution and then recovered by filtration. At this time, the recovery of the acid-treated product of the calcined product by filtration and the washing of the filtrate by distilled water are set as one cycle, and the cycle is preferably performed multiple times, for example, 2 to 3 times. The reason is that the acid-treated product of the calcined product is washed, and the lithium-containing components are further removed, so that the purity of the amorphous lithium tantalum composite oxide is improved.

[0053] More specifically, lithium orthotantalic acid lithium (Li3TaO4) can be prepared by calcining lithium carbonate and tantalum oxide, and used as a lithium tantalum composite oxide. In addition, Li orthotantalic acid lithium can be prepared by contacting lithium orthotantalic acid with an aqueous sulfuric acid solution. 3－x H x An amorphous body represented by TaO4 (1.6<x≤2.7) is used as a lithium tantalum composite oxide.

[0054] In the above, the method for preparing the lithium tantalum composite oxide is described. However, the lithium tantalum composite oxide may be a commercially available product or may be a product obtained by amorphizing a commercially available product.

[0055] In addition to the lithium tantalum composite oxide, the precursor may also contain oxides of other metals, that is, it may contain oxides of metals other than lithium and tantalum. By nitriding the precursor containing oxides of other metals, a tantalum nitride material containing a nitride selected from a composite nitride of tantalum and other metals and a composite oxynitride of tantalum and other metals can be manufactured. Among these nitrides, composite oxynitrides such as barium tantalum oxynitride (BaTaO2N) and strontium tantalum oxynitride (SrTaO2N) have been studied for use as photocatalysts. Therefore, in order to obtain a tantalum nitride material containing the composite oxynitride, the oxide of the other metal is preferably selected from barium oxide and strontium oxide.

[0056] The nitrogen compound used in the nitriding process is a nitrogen source that supplies the nitrogen required for nitriding to the precursor. As the nitrogen compound, for example, ammonia, zinc nitride and carbon nitride, etc. can be listed, preferably ammonia. When ammonia is used as the nitrogen compound, the nitriding process is preferably carried out under the circulation of an ammonia-containing gas. The ammonia-containing gas can be ammonia gas or a mixed gas of ammonia gas and nitrogen gas. The flow rate of the ammonia-containing gas is greater than 100 mL / min and less than 300 mL / min. By setting the flow rate of the ammonia-containing gas to more than 100 mL / min, a sufficient amount of nitrogen can be supplied to the precursor, and the nitriding time can be shortened. In addition, by setting the flow rate of the ammonia-containing gas to less than 300 mL / min, the amount of ammonia gas that is not consumed by nitriding is reduced, which can suppress the manufacturing cost.

[0057] The heating temperature in the nitriding process is preferably 800°C or higher and 950°C or lower, and more preferably 850°C or higher and 920°C or lower. By setting the heating temperature to 800°C or higher, nitriding can be fully performed. In addition, by setting the heating temperature to 950°C or lower, the release of nitrogen from the generated tantalum nitride (Ta3N5) and the conversion to nitrogen-deficient nitride (Ta3N5) can be suppressed. x , 0≤x<5).

[0058] The heating time of the precursor in the nitriding process is determined according to the heating temperature and the composition of the target tantalum nitride material. The heating time at the above heating temperature is usually 0.5 hours or more and 30 hours or less. In the case of increasing the proportion of various nitrides other than oxynitride in the tantalum nitride material, the heating time can be extended within the above range. In the case of increasing the proportion of oxynitride, the heating time can be shortened within the above range.

[0059] The reaction apparatus used in the nitriding step may be any apparatus as long as it can withstand the above-mentioned heating temperature, and for example, a tubular furnace, an electric furnace, a batch kiln, a rotary kiln, etc. can be used.

[0060] In the nitridation step, the nitridation of the precursor is preferably carried out in the presence of a zirconium compound such as zirconium oxychloride (ZrOCl2). Thus, zirconium is doped in various nitrides, which can improve the photocatalytic activity when the tantalum nitride material is used as a photocatalyst.

[0061] The charge amount of the zirconium compound in the nitriding process is not particularly limited. It is preferred that the molar ratio of the total amount of tantalum in various nitrides to zirconium is 5 or more and 25 or less, more preferably the molar ratio of the total amount of tantalum in various nitrides to zirconium is 10 or more and 20 or less, and further preferably the molar ratio of the total amount of tantalum in various nitrides to zirconium is 15 or more and 20 or less.

[0062] In the manufacturing method of the present embodiment, it is preferred that after the nitriding process, preferably after the nitriding process in the presence of a zirconium compound, a reaction process is included, in which the nitride obtained in the nitriding process is reacted with one or more compounds selected from the group consisting of ruthenium compounds, chromium compounds and iridium compounds. In other words, the reaction process is a loading process, in which one or more components selected from the group consisting of ruthenium, chromium oxide and iridium oxide are loaded on the nitride obtained in the nitriding process. These components act as co-catalysts when the tantalum nitride material is used as a photocatalyst, and can improve the photocatalytic activity of the tantalum nitride material. It should be noted that as chromium oxides, for example, chromium oxide (Cr2O3) can be listed, and as iridium oxides, for example, iridium oxide (IrO2) can be listed.

[0063] The reaction step may be a step of reacting one or more compounds selected from the group consisting of a ruthenium compound, a chromium compound, and an iridium compound with the nitride one by one. That is, for example, the reaction step may be a step of first reacting a ruthenium compound to support ruthenium on the nitride obtained in the nitriding step, then reacting a chromium compound to support chromium oxide on the nitride obtained in the above step, and finally reacting an iridium compound to support iridium oxide on the nitride obtained in the above step.

[0064] As the ruthenium compound used in the reaction process, ruthenium chloride (RuCl3) can be listed. As the chromium compound used in the reaction process, potassium chromate (K2CrO4) can be listed. In addition, as the iridium compound used in the reaction process, sodium hexachloroiridate (IV) hexahydrate (Na2IrCl6·6H2O) can be listed.

[0065] As the reaction conditions of these compounds and the nitride obtained in the nitriding step, known reaction conditions used when supporting ruthenium, chromium oxide, or iridium oxide on a photocatalyst can be appropriately adopted.

[0066] 2) Tantalum nitride materials

[0067] The tantalum nitride material of the second embodiment of the present disclosure is a tantalum nitride material obtained by the manufacturing method of the first embodiment, and includes one or more nitrides selected from the group consisting of tantalum nitride, tantalum oxynitride, composite nitride of tantalum and other metals, and composite oxynitride of tantalum and other metals. In addition, the tantalum nitride material of the third embodiment of the present disclosure includes a nitride material obtained by doping zirconium into the tantalum nitride material of the second embodiment.

[0068] In the method of nitriding a composite oxide of sodium and a metal including tantalum as described in Japanese Patent Application Publication No. 2019-037918, a large amount of metal elements such as sodium derived from the precursor remain in the produced nitride, and a high-purity tantalum nitride material cannot be obtained.

[0069] On the other hand, the tantalum nitride materials according to the second and third embodiments of the present disclosure are produced by the production method of the first embodiment described above, and therefore the residual amount of lithium derived from the precursor is small, and the materials are high-purity materials.

[0070] The content of the nitride in the tantalum nitride material according to the second embodiment of the present disclosure is 99.5 wt % or more, preferably 99.8 wt % or more, more preferably 99.9 wt % or more, and is usually less than 100 wt %.

[0071] The content of the nitride material in the tantalum nitride material of the third embodiment of the present disclosure is 99.5 wt % or more, preferably 99.8 wt % or more, more preferably 99.9 wt % or more, and is usually less than 100 wt %.

[0072] The lithium contained in the tantalum nitride materials of the second and third embodiments of the present disclosure is an impurity element derived from the lithium tantalum composite oxide as a precursor. The lithium content in these tantalum nitride materials is 0.1 ppm or more and 3000 ppm or less, preferably 1 ppm or more and 3000 ppm or less, more preferably 3 ppm or more and 2500 ppm, further preferably 5 ppm or more and 2000 ppm or less, and particularly preferably 8 ppm or more and 1000 ppm or less.

[0073] In the conventional production method that does not use a precursor containing lithium tantalum composite oxide, the tantalum nitride material may contain lithium derived from impurity lithium in the raw material and lithium inevitably mixed in during other production stages. However, as shown in the examples described below, the tantalum nitride material obtained by the conventional production method does not contain lithium more than 0.1 ppm, and even if it contains lithium, its content is a minute amount that cannot be detected by a conventional analysis method such as GD-MS analysis.

[0074] On the other hand, in the conventional production method using a composite oxide of a metal selected from sodium and tantalum instead of lithium tantalum composite oxide as a precursor, a large amount of the metal remains in the obtained tantalum nitride material. 8－y H y Ta6O 19 The tantalum nitride material obtained by using H2O as a precursor contains a large amount of sodium, 7300 ppm. In contrast, although the tantalum nitride materials of the second and third embodiments of the present disclosure use lithium tantalum composite oxide as a precursor, the lithium content is less than the above lower limit.

[0075] Therefore, containing lithium within the above range is unique to the tantalum nitride materials of the second and third embodiments of the present disclosure.

[0076] The impurity elements other than lithium contained in the tantalum nitride materials of the second and third embodiments of the present disclosure are: elements other than tantalum, the other metals mentioned above, oxygen, nitrogen and zirconium, for example: metal elements such as sodium, aluminum, silicon, potassium, calcium, chromium, iridium and iron; non-metallic elements such as chlorine and phosphorus; etc.

[0077] 3) Method for determining the purity of tantalum nitride materials

[0078] The purity of the tantalum nitride material of the second embodiment of the present disclosure, that is, the content of nitride in the tantalum nitride material, is obtained as the following value: the content of impurity elements contained in the tantalum nitride material is measured by glow discharge mass spectrometry (GD-MS), and the total content of each impurity element is subtracted from 100 weight %. The purity of the tantalum nitride material of the third embodiment of the present disclosure, that is, the content of nitride material in the tantalum nitride material, is also obtained by the same method as the purity of the tantalum nitride material of the second embodiment of the present disclosure. Among them, for impurity elements with a content less than the measurement limit of GD-MS, it is regarded as substantially not contained and the purity is calculated. As the measurement conditions of GD-MS, the conditions described in the examples described later can be adopted.

[0079] 4) Photocatalyst

[0080] The fourth embodiment of the present disclosure is a photocatalyst in which the tantalum nitride material of the third embodiment is loaded with one or more promoters selected from the group consisting of ruthenium, chromium oxide, and iridium oxide. The photocatalyst of this embodiment is manufactured by the following method, which is the manufacturing method of the first embodiment including the above-mentioned reaction step.

[0081] As chromium oxides serving as promoters, for example, chromium oxide (Cr2O3) can be cited. In addition, as iridium oxides serving as other promoters, for example, iridium oxide (IrO2) can be cited.

[0082] The amount of the promoter supported in the tantalum nitride material is usually 0.1 parts by weight or more and 8.0 parts by weight or less, and preferably 0.5 parts by weight or more and 4.0 parts by weight or less, based on 100 parts by weight of the nitride material in the tantalum nitride material.

[0083] The photocatalyst of the present embodiment preferably exhibits water-splitting photocatalytic activity under visible light irradiation, that is, preferably exhibits photocatalytic activity (water-splitting activity) of absorbing light in the visible light region to decompose water into hydrogen and oxygen.

[0084] Example

[0085] Hereinafter, the embodiments of the present disclosure will be described in more detail using examples, but the present disclosure is not limited to these examples.

[0086] [Measurement conditions of glow discharge mass spectrometry (GD-MS)]

[0087] · Apparatus: Astrum (manufactured by Nu Instruments).

[0088] Discharge current: 2.0mA.

[0089] Discharge voltage: 1.0V.

[0090] Discharge time: about 60 minutes.

[0091] Discharge gas: Ar.

[0092] Discharge gas flow rate: 300sccrm.

[0093] [Measurement conditions of powder X-ray diffraction (XRD)]

[0094] · Device: MiniFlex300 (manufactured by Rigaku Corporation).

[0095] ·X-ray source: Cu (Kα) line

[0096] Tube voltage: 30kV.

[0097] Tube current: 10mA.

[0098] ·Measurement range: 2θ = 10° to 80°.

[0099] Scanning speed: 10° / min.

[0100] Scanning step: 0.01°.

[0101] Divergence slit: 1.25°.

[0102] Scattering slit: 1.25°.

[0103] · Light receiving slit: 13mm.

[0104] [Example 1]

[0105] (Precursor production)

[0106] 4.42 g of Ta2O5 (manufactured by RARE METALLIC Co., Ltd., purity 99.99%) and 2.22 g of Li2CO3 (manufactured by Kanto Chemical Co., Ltd.) were placed in an agate mortar and crushed with a pestle to obtain a raw material mixture. The raw material mixture was placed in an alumina crucible and calcined at 850°C for 6 hours in an atmospheric atmosphere using a muffle electric furnace to obtain a calcined product containing Li3TaO4. The calcined product was dispersed in 500 mL of ultrapure water to obtain a Li3TaO4 dispersion having a pH (25°C) of about 12. A 10% aqueous sulfuric acid solution was added little by little to the obtained Li2CO3 dispersion. The addition of the 10% aqueous sulfuric acid solution was stopped when the pH (25°C) of the dispersion reached 3, and the dispersion was filtered using a membrane filter with a pore size of 1 μm to recover the solid substance. The solid substance was vacuum dried at 40°C for more than 12 hours and then crushed to obtain an amorphous Li 3－x H x TaO4 (1.6<x≤2.7). 3－x H x TaO 4 contains a small amount of crystalline lithium tantalate (LiTaO 3 ). Table 1 shows the main production conditions of the precursor and the components contained in the precursor.

[0107] (Nitriding)

[0108] 169 μL of a 2 mol / L ZrOCl2 aqueous solution and 6 mL of ethanol were placed in an agate mortar and mixed. 1.2 g of Li was weighed so that the molar ratio of Ta to Zr in the raw material mixture was 15. 3－x H x TaO4 was mixed with the obtained solution, and further mixed for 1 minute while ultrasonically dispersing using an ultrasonic disperser. The obtained mixture was heated at 150°C while vigorously stirring to completely dry and solidify, thereby obtaining a raw material mixture.

[0109] The raw material mixture is transferred to a combustion boat made of alumina. The combustion boat containing the raw material mixture is placed in an alumina tube, and the alumina tube is set in an electric tube furnace with an open and closed vacuum furnace body. The atmosphere in the alumina tube is replaced with nitrogen, and then the nitrogen in the alumina tube is replaced with ammonia. Next, while circulating ammonia at a flow rate of 200 mL / min in the alumina tube, the raw material mixture is heated at 900°C for 1 hour and then naturally cooled. The powder obtained is washed with water, filtered using a membrane filter with a pore size of 1 μm, and the solid substance is recovered. The solid substance is vacuum dried at 40°C for more than 2 hours and then crushed to obtain a tantalum nitride material.

[0110] The obtained tantalum nitride material was subjected to powder XRD measurement. As a result, it was found that the tantalum nitride material was a mixture of Zr-doped Ta3N5 and Zr-doped TaON (hereinafter sometimes referred to as "Ta3N5 / TaON:Zr"). The XRD pattern of the tantalum nitride material is shown in Figure 1 .

[0111] In addition, the impurity element content and purity of the tantalum nitride material were measured by GD-MS analysis. The results are shown in Table 2.

[0112] [Example 2]

[0113] (Precursor production)

[0114] In the preparation of the raw material mixture, except that the amount of Li2CO3 used was set to 2.4 g, an amorphous Li 3－x H x TaO4.Li 3－x H x TaO 4 does not contain crystalline LiTaO 3. Table 1 shows the main production conditions of the precursor and the components contained in the precursor.

[0115] (Nitriding)

[0116] Use the obtained Li 3－x H x A tantalum nitride material was obtained in the same manner as in Example 1 except that TaO 4 was used as a precursor.

[0117] The obtained tantalum nitride material was subjected to powder XRD measurement. As a result, it was found that the tantalum nitride material was Ta3N5 / TaON:Zr. The XRD pattern of the tantalum nitride material is shown in Figure 1 .

[0118] In addition, the impurity element content and purity of the tantalum nitride material were measured by GD-MS analysis. The results are shown in Table 2.

[0119] [Example 3]

[0120] (Precursor production)

[0121] Amorphous LiCO3 was obtained in the same manner as in Example 2 except that a 10% aqueous sulfuric acid solution was added to the Li2CO3 dispersion until the pH (25°C) of the dispersion reached 1. 3－x H x TaO4.Li 3－x H x TaO 4 does not contain crystalline LiTaO 3. Table 1 shows the main production conditions of the precursor and the components contained in the precursor.

[0122] (Nitriding)

[0123] Use the obtained Li 3－x H x A tantalum nitride material was obtained in the same manner as in Example 1 except that TaO 4 was used as a precursor.

[0124] The obtained tantalum nitride material was subjected to powder XRD measurement, and the result showed that the tantalum nitride material was Ta3N5 / TaON:Zr.

[0125] In addition, the impurity element content and purity of the tantalum nitride material were measured by GD-MS analysis. The results are shown in Table 2.

[0126] [Example 4]

[0127] (Precursor production)

[0128] After adding 10% sulfuric acid aqueous solution to the Li2CO3 dispersion until the pH (25°C) of the dispersion becomes 1, the solid matter recovered by filtration and the filtrate washed with 500 mL of distilled water were recycled three times to obtain a washed solid matter. In addition, an amorphous Li 3－x H x TaO4.Li 3－x H x TaO 4 does not contain crystalline LiTaO 3. Table 1 shows the main production conditions of the precursor and the components contained in the precursor.

[0129] (Nitriding)

[0130] Use the obtained Li 3－x H x A tantalum nitride material was obtained in the same manner as in Example 1 except that TaO 4 was used as a precursor.

[0131] The obtained tantalum nitride material was subjected to powder XRD measurement, and the result showed that the tantalum nitride material was Ta3N5 / TaON:Zr.

[0132] In addition, the impurity element content and purity of the tantalum nitride material were measured by GD-MS analysis. The results are shown in Table 2.

[0133] [Comparative Example 1]

[0134] (Precursor production)

[0135] 4.4 g of Ta2O5 (manufactured by RARE METALLIC Co., Ltd., purity 99.99%) and 4.42 g of NaOH (FUJIFILM WakoPure Chemical Co., Ltd.) were placed in an agate mortar and crushed with a pestle to obtain a raw material mixture. The raw material mixture was placed in an alumina crucible and calcined at 350°C for 12 hours in an atmospheric atmosphere using a muffle electric furnace to obtain a calcined product containing Na3TaO4 and NaOH. The calcined product was added to 500 mL of ultrapure water to obtain a Na3TaO4 aqueous solution with a pH (25°C) of 13. A 10% aqueous sulfuric acid solution was added little by little to the obtained Na3TaO4 aqueous solution, and when the pH (25°C) of the solution reached 5, a white precipitate was precipitated. After decantation 5 times, the precipitate was filtered using a membrane filter with a pore size of 1 μm to recover the solid substance. The solid substance was vacuum dried at 40°C for more than 12 hours and then crushed to obtain Na 8－y H y Ta6O 19 ·H2O(7.0<y≤7.5).

[0136] (Nitriding)

[0137] 172.6 μL of a 2 mol / L ZrOCl2 aqueous solution and 6 mL of ethanol were placed in an agate mortar and mixed. 1.2 g of Na2O3 was weighed so that the molar ratio of Ta to Zr in the raw material mixture was 15. 8－y H y Ta6O 19 The obtained solution was mixed with H2O, and further mixed for 1 minute while ultrasonically dispersing using an ultrasonic disperser. The obtained mixture was heated at 150°C while vigorously stirring to completely dry and solidify, thereby obtaining a raw material mixture.

[0138] The raw material mixture is transferred to an alumina combustion boat. The combustion boat containing the raw material mixture is placed in an alumina tube, and the alumina tube is set in an electric tube furnace with an open and closed vacuum furnace body. The atmosphere in the alumina tube is replaced with nitrogen, and then the nitrogen in the alumina tube is replaced with ammonia. Next, while circulating ammonia at a flow rate of 200 mL / min in the alumina tube, the raw material mixture is heated at 900°C for 3 hours and then naturally cooled. The powder obtained is washed with water, filtered using a membrane filter with a pore size of 1 μm, and the solid substance is recovered. The solid substance is vacuum dried at 40°C for more than 2 hours and then crushed to obtain a tantalum nitride material.

[0139] The obtained tantalum nitride material was subjected to powder XRD measurement, and the result showed that the tantalum nitride material was Ta3N5 / TaON:Zr.

[0140] In addition, the impurity element content and purity of the tantalum nitride material were measured by GD-MS analysis. The results are shown in Table 2.

[0141] [Table 1]

[0142]

[0143] [Table 2]

[0144]

[0145] *1: “Purity” refers to the total proportion of Zr-doped Ta3N5 and Zr-doped TaON in the tantalum nitride material.

[0146] *2: "Hf" is a metal element derived from Hf inevitably contained in ZrOCl2.

[0147] According to Table 1, it is believed that there is a tendency that, in the production of the precursor, as the molar ratio of lithium in Li2CO3 to tantalum in Ta2O5 increases from 3.00, crystalline LiTaO3 is not generated, but only amorphous Li 3－x H x TaO4.

[0148] According to Table 2, it can be seen that when the precursor containing lithium is used (Examples 1 to 4) compared with the case of using the precursor containing sodium (Comparative Example 1), there is a tendency that the metal element derived from the precursor is less likely to remain in the tantalum nitride material, and a tantalum nitride material with high purity can be obtained. One of the reasons for this is that lithium is more likely to volatilize in the nitriding process than sodium, and is less likely to remain in the tantalum nitride material.

[0149] [Example 5]

[0150] 0.05 g of RuCl3·3H2O (manufactured by Kanto Chemical Co., Ltd.) was mixed with 2 mL of distilled water to prepare a RuCl3 aqueous solution. 165 mg of Ta3N5 / TaON:Zr obtained in Example 1, 683 μL of RuCl3 aqueous solution and 1.317 mL of distilled water were placed in an evaporating dish to fully disperse Ta3N5 / TaON:Zr, thereby obtaining a mixture. The obtained mixture was heated while being vigorously stirred to completely dry and solidify, thereby obtaining a raw material mixture.

[0151] The raw material mixture was transferred to an alumina combustion boat. The combustion boat containing the raw material mixture was placed in an alumina tube, and the alumina tube was set in an electric tube furnace with a vacuum furnace body opening and closing type, and the atmosphere in the alumina tube was replaced with nitrogen. Then, the raw material mixture was heated at 250°C for 1 hour under the flow of nitrogen / hydrogen mixed gas (N2:H2=200mL / min:20mL / min), and the reduction treatment was performed, and then naturally cooled to obtain Ta3N5 / TaON:Zr loaded with 4 wt% Ru.

[0152] [Example 6]

[0153] 2.5 g of K2CrO4 (FUJIFILM Wako Pure Chemical Co., Ltd.) was mixed with 50 mL of distilled water to prepare a K2CrO4 aqueous solution. 130 mL of distilled water, 20 mL of methanol, and 493 μL of the K2CrO4 aqueous solution were mixed in a PYREX (registered trademark) reactor, and the Ru-loaded Ta3N5 / TaON:Zr obtained in Example 5 was dispersed in the obtained mixture to obtain a reaction solution.

[0154] The reactor was placed in a closed gas circulation reaction test device (manufactured by Makuhari Glass Co., Ltd.), and the inside of the reactor and the device were fully vented. Then, the reaction solution was irradiated with light for 2 hours using a Xe lamp (λ≥420nm) equipped with a cold mirror (CM1) and a cutoff filter (L42), thereby allowing 4 wt% of Cr2O3 to be loaded on Ta3N5 / TaON:Zr loaded with Ru. The crude product was thoroughly washed and filtered using a membrane filter with a pore size of 1μm to recover the solid material. The solid material was vacuum dried at 40°C for more than 30 minutes, thereby obtaining Ta3N5 / TaON:Zr loaded with Ru and Cr2O3.

[0155] [Example 7]

[0156] 0.0162 g of Na2IrCl6·6H2O (produced by Kanto Chemical Co., Ltd.) was mixed with 100 mL of distilled water, and a 1 mol / L NaOH aqueous solution was added to the obtained mixed solution to prepare a solution with a pH (25°C) of 5. The solution was heated in a water bath at 80°C for 30 minutes while stirring, cooled in ice water for 10 minutes, and then a 0.1 mol / L HNO3 aqueous solution was added until the pH (25°C) became 9. The obtained solution was heated in a water bath at 80°C for 30 minutes while stirring, and then cooled in ice water for 10 minutes, thereby obtaining an IrO2 colloidal solution.

[0157] The Ta3N5 / TaON:Zr loaded with Ru and Cr2O3 obtained in Example 6 was dispersed in 400 mL of distilled water to obtain a dispersion. 15 mL of IrO2 colloidal solution was added dropwise to the dispersion at 60 mL / h using a cylinder pump and stirred for 20 minutes, thereby loading 0.6 wt% of IrO2 on the Ta3N5 / TaON:Zr loaded with Ru and Cr2O3. The obtained crude product was thoroughly washed and filtered using a membrane filter with a pore size of 1 μm to recover the solid material. The solid material was vacuum dried at 40°C for more than 30 minutes to obtain Ta3N5 / TaON:Zr loaded with Ru, Cr2O3 and IrO2 (referred to as "the photocatalyst obtained in Example 7").

[0158] 〔Evaluation of photocatalytic activity〕

[0159] 150 mL of distilled water and 36 μL of 0.1 mol / L NaOH (produced by Kanto Chemical Co., Ltd.) were placed in a reactor and mixed, and 150 mg of the photocatalyst obtained in Example 7 was dispersed in the obtained mixed solution to prepare a reaction solution. The reactor was set in a closed gas circulation reaction test device, and after the inside of the reactor and the inside of the device were fully exhausted, 5 kPa of Ar was introduced into the device. Then, the reaction solution was irradiated with light using a Xe lamp (λ ≥ 420 nm) equipped with a cold mirror (CM1) and a cutoff filter (L42), thereby performing water decomposition. The generated gas was analyzed over time using a gas chromatograph connected to the closed gas circulation reaction test device to evaluate the photocatalytic activity. The evaluation results are shown in Figure 2 .

[0160] according to Figure 2 , it was confirmed that the photocatalyst obtained in Example 7 showed photocatalytic activity for decomposing water into hydrogen and oxygen under visible light irradiation.

[0161] Industrial Applicability

[0162] As described in the present disclosure, the tantalum nitride material produced by the method including the step of nitriding a precursor containing a lithium tantalum composite oxide has a small amount of residual impurity elements derived from the precursor and is of high purity. In addition, the tantalum nitride material has a photocatalytic activity of decomposing water into hydrogen and oxygen under visible light irradiation. Therefore, based on the high purity of the tantalum nitride material, it is expected to be used as a photocatalyst that decomposes water by absorbing light in the visible light region with a large number of photons in sunlight, especially light near 600nm.

Claims

1. A method for manufacturing a tantalum nitride material, wherein: include: In the nitriding step, a precursor containing a lithium tantalum composite oxide is heated in the presence of a nitrogen compound.

2. The method for producing a tantalum nitride material according to claim 1, wherein: The lithium tantalum composite oxide is amorphous.

3. The method for producing a tantalum nitride material according to claim 2, wherein: Before the nitriding process, the method comprises: a calcining step of calcining a raw material mixture containing a lithium compound and a tantalum compound to obtain a calcined product; and In the amorphization step, the sintered product is brought into contact with an acidic aqueous solution to obtain the lithium tantalum composite oxide.

4. The method for producing a tantalum nitride material according to claim 3, wherein: In the raw material mixture, a molar ratio of lithium in the lithium compound to tantalum in the tantalum compound is 3.00 or more and 3.50 or less.

5. The method for producing a tantalum nitride material according to any one of claims 1 to 4, wherein: The nitriding step is performed in the presence of a zirconium compound.

6. A tantalum nitride material, wherein: Include: One or more nitrides selected from the group consisting of tantalum nitride, tantalum oxynitride, composite nitride of tantalum and other metals, and composite oxynitride of tantalum and other metals, The content of the nitride is 99.5% by weight or more, The content of lithium is 0.1 ppm or more and 3000 ppm or less.

7. A tantalum nitride material, wherein: Include: A nitride material obtained by doping zirconium into the tantalum nitride material according to claim 6, The content of the nitride material is 99.5% by weight or more, The content of lithium is 0.1 ppm or more and 3000 ppm or less.

8. A photocatalyst, wherein: The photocatalyst is a photocatalyst in which one or more promoters selected from the group consisting of ruthenium, chromium oxide, and iridium oxide are supported on the tantalum nitride material according to claim 7 .

9. The photocatalyst according to claim 8, wherein The photocatalyst exhibits water splitting photocatalytic activity under visible light irradiation.

Images