A nitrogen-doped layered oxide, preparation method and application thereof

Abstract

The present invention relates to the technical field of material synthesis and renewable clean energy utilization, and in particular to a nitrogen-doped layered oxide, a preparation method and an application thereof. The method comprises preparing a first precursor, wherein the first precursor is AM2Ta3O 10 or ARTa2O7; then, the first precursor is subjected to molten salt treatment to prepare a second precursor; finally, the second precursor is subjected to molten salt-assisted, high-temperature nitridation to prepare a nitrogen-doped layered oxide. The nitrogen-doped layered oxide can reduce the low-valent defects of the central atom and improve its activity in decomposing water when used as a photocatalyst. The problem of low activity of photocatalyst water decomposition caused by low-valent metal element defects in layered nitrogen-doped compounds in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of material synthesis and renewable clean energy utilization, and in particular to a nitrogen-doped layered oxide, a preparation method and application thereof. Background Art

[0002] As the use of large amounts of fossil fuels has caused increasing energy consumption and environmental problems, decomposing water into hydrogen and oxygen through photocatalytic technology is one of the most important ways to solve the future shortage of fossil fuels and reduce environmental pollution associated with fossil fuel consumption.

[0003] The conduction band of traditional metal oxides is mainly composed of empty d orbitals or sp orbitals of metal cations, and the valence band is mainly composed of O 2p orbitals, which is roughly around 3.0 eV (vs. NHE, pH = 0). Generally, metal oxides have a wide band gap and can only absorb ultraviolet light. Considering that visible light accounts for 43% of the solar spectrum and ultraviolet light accounts for 4%, it is very helpful to adopt effective strategies to expand the absorption spectrum of known materials or synthesize new photocatalysts that respond to visible light. At present, more research is on introducing elements with lower electronegativity than oxygen to dope or participate in the composition of compounds, so as to increase the valence band and narrow the band gap, thereby expanding the absorption range of the catalyst.

[0004] In 2001, Professor R. Asahi's research group reported the first nitrogen-doped TiO2 photocatalytic material with visible light response. Since then, people have conducted a lot of exploration around the nitrogen-doped metal oxide system. However, the nitrogen-doped materials obtained by the traditional high-temperature nitridation method often have low doping content and are mainly distributed on the surface of the material, showing shoulder-shaped absorption. How to uniformly dope nitrogen atoms in space to red-shift the overall absorption spectrum of the material has received special attention. In recent years, some research groups have significantly expanded the absorption spectrum of layered or tunnel-like compounds by nitrogen doping. This is mainly because the layered or tunnel-like structure is conducive to the diffusion of ammonia, which increases the contact area between the oxide and ammonia and effectively increases the content of doped nitrogen atoms. Based on this guiding idea, Cs 0.68 Ti 1.83 O 4-x N, CsCa2Ta3O 10-x N x 、Sr5Ta4O 15-x N x A series of nitrogen-doped materials have been developed successively, all of which have good visible light absorption, and most of them have proton reduction and water oxidation reaction activity.

[0005] In addition to nitrogen-doped layered compounds, layered oxynitride compounds are also considered to be potential photocatalytic materials.

[0006] However, the nitrogen-doped layered oxides in the prior art generate a large number of low-valent metal element defects during the nitridation process, which easily leads to low activity of photocatalytic water decomposition, thus limiting the use of the nitrogen-doped layered oxides. Summary of the invention

[0007] In view of the problem in the prior art that the photocatalytic water decomposition activity of layered nitrogen-doped compounds is low due to defects in low-valent metal elements, the present invention provides a nitrogen-doped layered oxide, a preparation method and an application thereof.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for preparing a nitrogen-doped layered oxide, comprising the following steps:

[0010] Step 1) Prepare a first precursor, wherein the first precursor is AM2Ta3O 10 or ARTa2O7; wherein A is Cs or Rb, M is Ca, Sr or Ba, and R is La or Y;

[0011] Step 2) treating the first precursor with a molten salt to prepare a second precursor;

[0012] Step 3) The second precursor is prepared by a molten salt-assisted, high-temperature nitridation method to obtain a nitrogen-doped layered oxide.

[0013] Preferably, in step 1), the method for preparing the first precursor is a sol-gel method or a high-temperature solid phase method.

[0014] Furthermore, the first precursor AM2Ta3O was prepared by a sol-gel method. 10 The method comprises: adding a salt or oxide of A, a salt or oxide of M, and tantalum chloride or tantalum ethoxide to methanol or ethanol, mixing them evenly, adding citric acid and ethylene glycol as binders, heating to form a sol-gel, and then calcining to obtain a first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3;

[0015] The method for preparing the first precursor ARTa2O7 by the sol-gel method is as follows: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and added into methanol or ethanol and mixed evenly, and citric acid and ethylene glycol are added as binders, heated to form a sol-gel, and then calcined to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:2.

[0016] Preferably, the conditions for preparing the first precursor by the sol-gel method are: heating temperature of 200-300° C., calcination temperature of 500-800° C., and calcination time of 1-4 h.

[0017] Furthermore, the first precursor AM2Ta3O is prepared by a high temperature solid phase method. 10 The method is as follows: the salt or oxide of A, the salt or oxide of M, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and then calcined at high temperature to obtain the first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3;

[0018] The method for preparing the first precursor ARTa2O7 by a high-temperature solid phase method is: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and calcined at a high temperature to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:2.

[0019] Preferably, the conditions for preparing the first precursor by the high temperature solid phase method are: the high temperature calcination temperature is 800 to 1100° C., and the high temperature calcination time is 2 to 10 h.

[0020] Preferably, the conditions for the molten salt treatment in step 2) are: the temperature of the molten salt treatment is 300-400°C, the treatment time is 24-48h, and the molten salt is KNO3, LiNO3 or NaNO3.

[0021] Furthermore, the specific operation of step 3) is: mixing the second precursor with auxiliary molten salt KCl, NaCl or LiCl in a molar ratio of 1: (0.5-5), and then nitriding; wherein the nitriding temperature is 800-900° C., and the nitriding is performed in a 200-300 mL / min ammonia gas flow for 0.15-1 h.

[0022] The present invention also provides a nitrogen-doped layered oxide prepared by the above-mentioned method for preparing the nitrogen-doped layered oxide, wherein the absorption spectrum of the nitrogen-doped layered oxide is 500-600 nm.

[0023] Application of the nitrogen-doped layered oxide as mentioned above as a water decomposition photocatalyst.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a method for preparing a nitrogen-doped layered oxide, wherein the method comprises preparing a first precursor, wherein the first precursor is AM2Ta3O 10or ARTa2O7; then, the first precursor is treated with molten salt to prepare the second precursor; finally, the second precursor is subjected to molten salt-assisted, high-temperature nitridation to prepare nitrogen-doped layered oxides. First, the first precursor undergoes an ion exchange reaction to obtain a layered perovskite oxide with a small interlayer ion radius; then, the second precursor is subjected to molten salt-assisted treatment to reduce the low-valent defects of the central atom and improve its activity in decomposing water as a photocatalyst. In addition, the molten salt ions after the molten salt-assisted treatment replace the volatile alkali metal cesium, thereby reducing the low-valent metal element defects generated during the nitridation process and improving its activity in decomposing water as a photocatalyst.

[0026] Furthermore, the molten salt uses one or more of KNO3, LiNO3 and NaNO3. Compared with cesium and rubidium, alkali metals lithium, sodium and potassium are less volatile, which can further reduce the low-valent defects of the central atom and improve the activity of catalytic water decomposition.

[0027] The nitrogen-doped layered oxide prepared by the method has an absorption spectrum of 500-600 nm and has very good photocatalytic water decomposition activity.

[0028] The nitrogen-doped layered oxide is used as a water decomposition photocatalyst. It has been tested that a large amount of hydrogen and oxygen can be decomposed during the catalytic decomposition of water, showing high catalytic decomposition activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process of preparing a nitrogen-doped layered oxide according to the present invention.

[0030] Figure 2 The structure diagram and XRD diagram of the nitrogen-doped layered oxide prepared in Example 1 of the present invention, wherein a is the structure diagram of the prepared layered oxide, and b is the structure diagram of KCa2Ta3O prepared in Example 1 10 and nitrogen-doped layered oxide KCa2Ta3O 10-x N x XRD pattern of .

[0031] Figure 3 KCa2Ta3O prepared by the present invention 10 and nitrogen-doped layered oxide KCa2Ta3O 10-x N x SEM image of KCa2Ta3O 10 SEM image, b is nitrogen-doped layered oxide KCa2Ta3O 10-x N x SEM image of .

[0032] Figure 4 KCa2Ta3O prepared in Example 1 of the present invention 10and nitrogen-doped layered oxide KCa2Ta3O 10-x N x Absorption spectrum of .

[0033] Figure 5 The nitrogen-doped layered oxide KCa2Ta3O prepared in Example 1 of the present invention 10-x N x Hydrogen production activity under different sacrificial agents or redox sites, where a is 150 mg 0.5 wt% Pt-loaded KCa2Ta3O 10-x N x Sample, 120mL H2O, 30mL CH3OH solution, hydrogen production activity under 300W xenon lamp light source (λ≥420nm), 4b is 150mg 0.5wt% Pt-loaded KCa2Ta3O 10-x N x Sample, 150 mL NaI aqueous solution (2 mM), adjusted to pH = 2.0 with sulfuric acid solution, hydrogen production activity diagram under 300 W xenon lamp light source (λ ≥ 420 nm).

[0034] Figure 6 The nitrogen-doped layered oxide KCa2Ta3O prepared in Example 1 of the present invention 10-x N x Oxygen generation activity under sacrificial agent, condition of 100 mg 1.0 wt% CoO x / KCa2Ta3O 10-x N x Sample, 100 mL of 10 mM AgNO3 aqueous solution, 300 W xenon lamp light source (λ ≥ 420 nm). DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0039] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0040] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0042] See also Figure 1 The present invention discloses a method for preparing a nitrogen-doped layered oxide, comprising the following steps:

[0043] Step 1) Prepare a first precursor, wherein the first precursor is AM2Ta3O 10 Or ARTa2O7; wherein A is Cs or Rb, M is Ca, Sr or Ba, and R is La or Y; wherein the method for preparing the first precursor is a sol-gel method or a high-temperature solid-phase method.

[0044] Preparation of the first precursor AM2Ta3O by sol-gel method 10The method is as follows: a salt or oxide of A, a salt or oxide of M, and tantalum chloride or tantalum ethoxide are mixed and added to methanol or ethanol to mix evenly, and citric acid and ethylene glycol are added as binders, and heated at 200-300°C to form a sol-gel, and then calcined at 500-800°C for 1-4h to obtain a first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3;

[0045] The method for preparing the first precursor ARTa2O7 by the sol-gel method is as follows: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and added into methanol or ethanol and mixed evenly, and citric acid and ethylene glycol are added as binders, and heated at 200-300° C. to form a sol-gel, and then calcined at 500-800° C. for 1-4 hours to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:2.

[0046] The first precursor AM2Ta3O was prepared by high temperature solid phase method. 10 The method is as follows: the salt or oxide of A, the salt or oxide of M, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and then calcined at 800-1100°C for 2-10 hours to obtain the first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3;

[0047] The method of preparing the first precursor ARTa2O7 by high-temperature solid phase method is: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and high-temperature calcined at 800-1100°C for 2-10 hours to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:2.

[0048] Preferably, the salt or oxide of A is one or more of the carbonate of A, the oxide of A, the oxalate of A and the nitrate of A; the salt or oxide of M is one or more of the carbonate of M, the oxide of M, the oxalate of M and the nitrate of M; the salt or oxide of R is one or more of the carbonate of R, the oxide of R, the oxalate of R and the nitrate of R.

[0049] Preferably, the heating temperature in preparing the first precursor by the sol-gel method is 200°C, 220°C, 235°C, 260°C, 270°C, 285°C or 300°C; the calcination temperature is 500°C, 550°C, 580°C, 600°C, 660°C, 700°C, 750°C or 800°C; and the calcination time is 1h, 1.5h, 2h, 2.5h, 3h or 4h.

[0050] Preferably, the high-temperature calcination temperature in preparing the first precursor by the high-temperature solid phase method is 800°C, 850°C, 880°C, 900°C, 950°C, 1000°C or 1100°C; the high-temperature calcination time is 2h, 4h, 6h, 7h, 8h, 9h or 10h.

[0051] Step 2) treating the first precursor with molten salt to prepare a second precursor; wherein the conditions for the molten salt treatment are: the temperature of the molten salt treatment is 300-400°C, the treatment time is 24-48h, and the molten salt is KNO3, LiNO3 or NaNO3.

[0052] Preferably, the temperature of the molten salt treatment is 300°C, 320°C, 350°C, 380°C or 400°C; the molten salt treatment time is 24h, 28h, 30h, 36h, 40h, 45h or 48h.

[0053] Step 3) The second precursor is prepared by a molten salt-assisted, high-temperature nitridation method to obtain a nitrogen-doped layered oxide. The specific operation is: the second precursor is mixed with an auxiliary molten salt KCl, NaCl or LiCl in a molar ratio of 1: (0.5-5), and then nitrided; wherein the nitridation temperature is 800-900°C, and the nitridation is carried out in a 200-300 mL / min ammonia gas flow for 0.15-1h.

[0054] Preferably, in the molten salt assisted treatment, the molar ratio of KCl, NaCl and LiCl is 1:0.5, 1:1, 1:2, 1:4 or 1:5; the nitriding temperature is 800°C, 820°C, 850°C or 900°C; the ammonia flow rate is 200mL / min, 220mL / min, 250mL / min or 300mL / min; and the nitriding time is 0.15h, 0.25h, 0.35h, 0.45h, 0.55h or 1h.

[0055] Example 1

[0056] Synthesis of the first precursor RbCa2Ta3O by high temperature solid phase method 10

[0057] According to the molar ratio of Rb, Ca and Ta ions of 0.75:2:1.5, Rb2CO3, CaCO3 and Ta2O5 were ground and uniformly mixed, and calcined at 900 °C for 6 h to obtain the first precursor RbCa2Ta3O 10 .

[0058] The first precursor RbCa2Ta3O 10 Perform molten salt treatment, select KNO3 as the molten salt, the heating temperature of the molten salt treatment is 400°C, the treatment time is 48h, and the second precursor is obtained;

[0059] The second precursor was mixed with KCl at a molar ratio of 1:1 and nitrided at 850 °C in a 250 mL / min ammonia flow for 1 h to generate a nitrogen-doped layered oxide, denoted as KCa2Ta3O 10-x N x .

[0060] See also Figure 2 and Figure 4 , the first precursor RbCa2Ta3O prepared in Example 1 10 and nitrogen-doped layered oxide, denoted as KCa2Ta3O 10-x N x Characterization shows that the synthesized nitrogen-doped layered oxide KCa2Ta3O 10-x N x With KCa2Ta3O 10 Similar XRD peaks, no phase change, and KCa2Ta3O 10 With KCa2Ta3O 10-x N x The absorption spectrum of KCa2Ta3O shows that nitrogen is successfully doped into KCa2Ta3O 10 middle.

[0061] See also Figure 5 and Figure 6 , the nitrogen-doped layered oxide KCa2Ta3O prepared in Example 1 10-x N x Evaluation of the activity of photocatalyst for photocatalytic water splitting:

[0062] Pt-supported KCa2Ta3O 10-x N x Sample preparation: 150 mg KCa2Ta3O 10-x N x The powder was added to a 20% methanol solution, followed by a certain amount of H2PtCl6·6H2O solution. After being stirred and dispersed evenly, it was illuminated under a 300W xenon lamp with full spectrum for one hour. After the precious metal Pt was photodeposited, the system was evacuated for half an hour, and then a hydrogen production half-reaction test was performed under a visible light filter (λ>420nm).

[0063] After the catalyst was photodeposited with precious metal Pt, the solution was centrifuged to remove the supernatant, and the catalyst was placed in an oven at 80 °C for drying. Subsequently, 150 mg of 0.5 wt% Pt-loaded KCa2Ta3O 10-x N x The sample was placed in 150 mL of NaI aqueous solution (2 mM) for testing.

[0064] CoO x The catalyst CoO was reduced by ammonia x Loaded on the sample. Typically, 200 mg KCa2Ta3O 10- x N x The sample powder was dispersed in 2 mL of Co(NO3)2 aqueous solution, ultrasonically dispersed for five minutes, and then evaporated to dryness in a water bath at 80 °C. The resulting powder was then -1 The ammonia gas flow was heated to 700℃ and kept for one hour. It was found that compared with the first precursor KCa2Ta3O 10 The nitrogen-doped layered oxide prepared by the present invention is denoted as KCa2Ta3O 10-x N x It has higher hydrogen and oxygen production activity, indicating that the device has better catalytic water decomposition activity.

[0065] Example 2

[0066] The first precursor is prepared by a sol-gel method.

[0067] The ion molar ratio of Rb2CO3, CaCO3 and TaCl5 was 0.75:2:3. 0.0075 mol Rb2CO3, 0.02 mol CaCO3 and 0.03 mol TaCl5 were weighed and added into 75 mL methanol. Then 40 g citric acid and 40 mL ethylene glycol were added. The mixture was heated and stirred at 250 °C to turn into a brown viscous sol-gel liquid. The mixture was calcined at 600 °C for 2 h to obtain the first precursor RbCa2Ta3O with a smaller particle size. 10 .

[0068] The first precursor RbCa2Ta3O 10 Perform molten salt treatment, select KNO3 as the molten salt, and treat for 48 hours at 400°C to obtain a second precursor;

[0069] The second precursor was mixed with KCl in a molar ratio of 1:1 and nitrided at 850 °C in a 250 mL / min ammonia flow for 1 h to generate KCa2Ta3O 10-x N x .

[0070] The present invention also provides a nitrogen-doped layered oxide prepared by the above-mentioned method for preparing the nitrogen-doped layered oxide, wherein the absorption spectrum of the nitrogen-doped layered oxide is 500-600 nm.

[0071] The above-mentioned nitrogen-doped layered oxide is used as a photocatalyst for decomposing water. According to tests, a large amount of hydrogen and oxygen can be decomposed in the process of catalytic decomposition of water, showing high catalytic decomposition activity.

[0072] In summary, the present invention provides a nitrogen-doped layered oxide, a preparation method and an application thereof. First, a first precursor is prepared by a sol-gel method or a high-temperature solid-phase method, and then the precursor is subjected to a molten salt treatment, and then a molten salt-assisted high-temperature nitridation treatment is performed to finally obtain a nitrogen-doped layered oxide. The oxide reduces the low-valent defects of the central atom and exhibits high photocatalytic water decomposition activity.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A method for preparing a nitrogen-doped layered oxide, characterized in that: The following steps are involved: Step 1) Prepare a first precursor, wherein the first precursor is AM2Ta3O 10 or ARTa2O7; wherein A is Cs or Rb, M is Ca, Sr or Ba, and R is La or Y; Step 2) treating the first precursor with a molten salt to prepare a second precursor; wherein the temperature of the molten salt treatment is 300 to 400° C., the treatment time is 24 to 48 hours, and the molten salt is KNO3, LiNO3 or NaNO3; Step 3) Prepare the nitrogen-doped layered oxide from the second precursor by a molten salt-assisted, high-temperature nitridation method; wherein the auxiliary molten salt in the molten salt-assisted process is KCl, NaCl or LiCl, and the specific operation is: mix the second precursor and the auxiliary molten salt in a molar ratio of 1: (0.5-5), and then perform high-temperature nitridation at a temperature of 800°C to 900°C for 0.15-1h; the nitridation is performed in a 200-300mL / min ammonia gas flow.

2. The method for preparing nitrogen-doped layered oxide according to claim 1, characterized in that: In step 1), the method for preparing the first precursor is a sol-gel method or a high-temperature solid phase method.

3. The method for preparing nitrogen-doped layered oxide according to claim 2, characterized in that: Preparation of the first precursor AM2Ta3O by sol-gel method 10 The method comprises: adding a salt or oxide of A, a salt or oxide of M, and tantalum chloride or tantalum ethoxide to methanol or ethanol, mixing them evenly, adding citric acid and ethylene glycol as binders, heating to form a sol-gel, and then calcining to obtain a first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3; The method for preparing the first precursor ARTa2O7 by the sol-gel method is as follows: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and added into methanol or ethanol and mixed evenly, and citric acid and ethylene glycol are added as binders, heated to form a sol-gel, and then calcined to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:

2.

4. The method for preparing nitrogen-doped layered oxide according to claim 3, characterized in that: The conditions for preparing the first precursor by the sol-gel method are: a heating temperature of 200 to 300° C., a calcination temperature of 500 to 800° C., and a calcination time of 1 to 4 hours.

5. The method for preparing nitrogen-doped layered oxide according to claim 1, characterized in that: The first precursor AM2Ta3O was prepared by high temperature solid phase method. 10 The method is as follows: the salt or oxide of A, the salt or oxide of M, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and then calcined at high temperature to obtain the first precursor AM2Ta3O 10 ; Wherein, the molar ratio of A, M and Ta ions is: (1-1.8):2:3; The method for preparing the first precursor ARTa2O7 by a high-temperature solid phase method is as follows: the salt or oxide of A, the salt or oxide of R, and tantalum chloride or tantalum ethoxide are mixed and ground evenly, and calcined at a high temperature to obtain the first precursor ARTa2O7; wherein the molar ratio of A, R and Ta ions is: (1-1.8):1:

2.

6. The method for preparing nitrogen-doped layered oxide according to claim 5, characterized in that: The conditions for preparing the first precursor by the high-temperature solid phase method are as follows: the high-temperature calcination temperature is 800 to 1100° C., and the high-temperature calcination time is 2 to 10 hours.

7. A nitrogen-doped layered oxide prepared by the method for preparing a nitrogen-doped layered oxide according to any one of claims 1 to 6, characterized in that: The absorption spectrum of the nitrogen-doped layered oxide is 500-600 nm.

8. Use of the nitrogen-doped layered oxide as claimed in claim 7 as a water decomposition photocatalyst.

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