A flower ball-shaped bi2o2(oH)(nO3) material, a preparation method thereof and application thereof in sodium / potassium ion batteries

Abstract

The application provides a flower-like Bi2O2(OH)(NO3) material and a preparation method and application thereof in a sodium / potassium ion battery. The preparation method comprises the following steps: adding a bismuth salt into a nitric acid solution, performing ultrasonic treatment, adding water for dilution, and then performing heating treatment to obtain a dilute solution; adding a urea solution into the dilute solution to perform a reaction; after the reaction is completed, centrifugation, washing and drying are performed to obtain an intermediate; the obtained intermediate is added into glacial acetic acid and uniformly dispersed by stirring; then, centrifugation is performed, the obtained solid is dissolved in water, and a hydrothermal reaction is performed; after the reaction is completed, filtration, washing and drying are performed, and the Bi2O2(OH)(NO3) material is obtained. The synthesized Bi2O2(OH)(NO3) material has a large crystal face spacing structure, can provide rich redox sites, and has uniform bismuth distribution; in combination with the large crystal face spacing of the material, the volume expansion problem of the material itself is effectively overcome, and the cycle stability of the material is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary sodium / potassium ion battery anode materials, specifically relating to a method for preparing a flower-shaped Bi2O2(OH)(NO3) material and its application in sodium / potassium ion batteries. Background Technology

[0002] With the rapid development of society and the increasing demand for carbon reduction and emission reduction, people's demand for batteries with high energy density and high stability is growing. The uneven distribution of lithium resources globally and the low reserves in the Earth's crust (Li 0.0017% vs K 2.09%) have inspired scientists to develop new rechargeable batteries that use other alkali metals as charge carriers. Sodium / potassium ion batteries, benefiting from low cost and a working principle similar to lithium ion batteries, have extremely high research value and development prospects.

[0003] Alloy-conversion mechanism metal compound materials are widely used in electrode materials due to their high theoretical specific capacity and simple preparation process. Among them, bismuth-based materials have attracted much attention due to their high theoretical specific capacity and diverse morphologies. However, these materials also have certain drawbacks: ① large volume changes accompany ion insertion / extraction, leading to reduced stability; ② poor conductivity. Existing technologies usually address these issues through carbon coating, carbon nanotube loading, etc., but the introduction of carbon materials often results in high pseudocapacitance, leading to a decrease in plateau specific capacity.

[0004] Therefore, finding a bismuth-based material that is simple to prepare, low in cost, and can effectively overcome the volume expansion problem of the material itself and improve the specific capacity is of great significance for improving the electrochemical performance of sodium / potassium ion batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flower-shaped Bi2O2(OH)(NO3) material, its preparation method, and its application in sodium / potassium ion batteries. This invention synthesizes Bi2O2(OH)(NO3) material via a hydrothermal method. The resulting material possesses a large interplanar spacing structure, providing abundant redox sites. Simultaneously, bismuth is uniformly distributed within the material, and the large interplanar spacing effectively overcomes the volume expansion problem, significantly improving the material's cycle stability. Electrode materials prepared using the Bi2O2(OH)(NO3) material of this invention exhibit excellent electrochemical performance.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a flower-shaped Bi2O2(OH)(NO3) material includes the following steps:

[0008] (1) Add bismuth salt to nitric acid solution, sonicate, dilute with water, and then heat to obtain a dilute solution;

[0009] (2) Add urea solution to the dilute solution obtained in step (1) and react; after the reaction is completed, centrifuge, wash and dry to obtain intermediate Bi6O5(OH)3(NO3)5·2H2O.

[0010] (3) The intermediate Bi6O5(OH)3(NO3)5·2H2O obtained in step (2) is added to glacial acetic acid and stirred to disperse evenly; then centrifuged, the obtained solid is dissolved in water and subjected to hydrothermal reaction; after the reaction is completed, the material is filtered, washed and dried to obtain flower-shaped Bi2O2(OH)(NO3) material.

[0011] According to a preferred embodiment of the present invention, the bismuth salt in step (1) is Bi(NO3)·5H2O or BiCl3.

[0012] According to a preferred embodiment of the present invention, the nitric acid solution in step (1) is obtained by mixing concentrated nitric acid with water, wherein the mass fraction of the concentrated nitric acid is 65-68% and the volume ratio of the concentrated nitric acid to water is 0.05-0.5:1.

[0013] According to a preferred embodiment of the present invention, the ratio of the number of moles of bismuth salt to the volume of nitric acid solution in step (1) is 0.2-0.5 mmol:1 mL.

[0014] According to a preferred embodiment of the present invention, the ultrasonic treatment time in step (1) is 20-40 min.

[0015] According to a preferred embodiment of the present invention, in step (1), after ultrasonic treatment, the ratio of the volume of water added to the molar number of bismuth salts is 10-50 mL: 1 mmol.

[0016] According to a preferred embodiment of the present invention, the temperature of the heating treatment in step (1) is 40-80°C, and the heating treatment time is 20-40 min.

[0017] According to a preferred embodiment of the present invention, the concentration of the urea solution in step (2) is 0.5-5 mmol / mL; and the molar ratio of urea to bismuth salt is 5-10:1.

[0018] According to a preferred embodiment of the present invention, the temperature of the reaction in step (2) is 40-80°C and the reaction time is 5-25 min.

[0019] According to a preferred embodiment of the present invention, the centrifugation step in step (2) is as follows: the obtained reaction solution is added to an equal volume of anhydrous ethanol, centrifuged, and the supernatant and precipitate are separated; the washing step is to wash the precipitate obtained by centrifugation with deionized water and anhydrous ethanol 3-5 times respectively; the drying step is to dry at 60-70℃ for 10-12 hours.

[0020] According to a preferred embodiment of the present invention, the mass ratio of the intermediate Bi6O5(OH)3(NO3)5·2H2O to the volume ratio of glacial acetic acid in step (3) is 1g:5-50mL; and the stirring time is 0.5-1h.

[0021] According to a preferred embodiment of the present invention, the volume ratio of water in step (3) to the mass ratio of intermediate Bi6O5(OH)3(NO3)5·2H2O is 50-300 mL: 1 g.

[0022] According to a preferred embodiment of the present invention, the temperature of the hydrothermal reaction in step (3) is 120-180°C, and the time of the hydrothermal reaction is 2-10h.

[0023] According to a preferred embodiment of the present invention, the washing in step (3) is washing with water and ethanol in sequence; the drying is drying the solid material obtained from washing at 60-70°C for 10-12 hours.

[0024] The present invention also provides a flower-shaped Bi2O2(OH)(NO3) material prepared by the above preparation method; the individual flower-shaped Bi2O2(OH)(NO3) material has a particle size of 400-600 nm.

[0025] According to the present invention, the above-mentioned flower-shaped Bi2O2(OH)(NO3) material is used as a negative electrode material for sodium-ion batteries or potassium-ion batteries; preferably, the specific application method is as follows:

[0026] The prepared flower-shaped Bi2O2(OH)(NO3) material, carbon material, binder, and conductive carbon black were mixed and thoroughly ground with water as a dispersant to prepare a negative electrode slurry. Subsequently, battery assembly and electrochemical performance testing were performed according to conventional sodium-ion or potassium-ion battery processes. The carbon material was reduced graphene oxide, carbon nanotubes, or carbon fibers, which played a role in constructing a stable conductive network. The binder was sodium carboxymethyl cellulose or PVDF. The mass ratio of the flower-shaped Bi2O2(OH)(NO3) material to the carbon material was 9:(1-9). The mass ratio of the total mass of the flower-shaped Bi2O2(OH)(NO3) material and carbon material to the binder was 8:1. The mass ratio of the total mass of the flower-shaped Bi2O2(OH)(NO3) material and carbon material to the conductive carbon black was 8:1. The volume ratio of water to the total mass of the flower-shaped Bi2O2(OH)(NO3) material, carbon material, binder, and conductive carbon black was 3-5 mL:100 mg.

[0027] The technical features and beneficial effects of this invention are as follows:

[0028] 1. This invention proposes a novel method for the controllable synthesis of basic bismuth nitrate and the induction of self-assembly with glacial acetic acid as a soft template to prepare multi-level flower-shaped morphologies. First, this invention prepares the intermediate Bi6O5(OH)3(NO3)5·2H2O, a product of the incomplete hydrolysis of bismuth salts. Then, based on this intermediate and using glacial acetic acid as a soft template, a flower-shaped Bi2O2(OH)(NO3) material is obtained through a hydrothermal reaction. A specific amount of acetic acid is added in this invention; the acetic acid molecules not only adjust the pH during the preparation process but also react with [Bi2O2]. 2+ Bi atoms in the layers coordinate to suppress the layered stacking of the material, thereby optimizing the morphology and obtaining a flower-shaped Bi2O2(OH)(NO3) material composed of thinner nanosheets. The thinner nanosheets and larger interlayer spacing are more conducive to the excellent electrochemical performance of potassium-ion batteries. This invention controls the crystallinity of the material by inducing and regulating the morphology through acetic acid molecules, while simultaneously controlling the temperature and time in the hydrothermal process, thus obtaining a high-performance potassium-ion battery anode material. If the hydrothermal reaction temperature is too low, the crystallinity of the product is poor; if the hydrothermal temperature is too high, the morphology of the material cannot be maintained, and the performance is reduced; if the hydrothermal time is too short, a material with a perfect morphology cannot be obtained; if the hydrothermal time is too long, new impurities will be generated. Therefore, it is necessary to strictly control the hydrothermal conditions within the range of this invention.

[0029] 2. The Bi2O2(OH)(NO3) material prepared by this invention has the characteristics of chemical stability, easy storage, and safety. At the same time, the material has structural advantages such as large interlayer spacing, flower-shaped morphology and large specific surface area. When used to prepare secondary sodium-ion batteries / potassium-ion batteries, it has shown electrochemical performance far superior to traditional bismuth-based materials. Moreover, the application test of soft-pack batteries shows that the Bi2O2(OH)(NO3) material has practical application potential.

[0030] 3. The raw materials used in this invention, such as bismuth salt, urea, and glacial acetic acid, are simple and readily available, have low cost, and the preparation process is simple and environmentally friendly. Attached Figure Description

[0031] Figure 1 Scanning electron microscope image (a) and X-ray powder diffraction pattern (b) of the intermediate Bi6O5(OH)3(NO3)5·2H2O prepared in Example 1.

[0032] Figure 2 Scanning electron microscope (a), transmission electron microscope (b), and powder X-ray diffraction pattern (c) of the flower-shaped Bi2O2(OH)(NO3) material prepared in Example 1.

[0033] Figure 3 The specific capacity and efficiency-cycle graphs of the potassium-ion battery prepared by Bi2O2(OH)(NO3)-rGO anode in Example 1 at current densities of 100 mA / g (a) and 50 mA / g (b) are shown.

[0034] Figure 4 The constant current charge-discharge curves of the potassium-ion battery prepared by the Bi2O2(OH)(NO3)-rGO anode in Example 1 are shown at a current density of 50 mA / g.

[0035] Figure 5 The voltage-charge differential curves of the potassium-ion battery prepared by the Bi2O2(OH)(NO3)-rGO anode in Example 1 are shown.

[0036] Figure 6 The constant current charge-discharge curves of the sodium-ion battery prepared with the Bi2O2(OH)(NO3)-rGO negative electrode in Example 1 are shown at a current density of 25 mA / g.

[0037] Figure 7 The voltage-charge differential curves of the potassium-ion battery prepared by the Bi2O2(OH)(NO3)-rGO anode in Example 2 are shown.

[0038] Figure 8 Scanning electron microscope image of the flower-shaped Bi2O2(OH)(NO3) material prepared in Example 3.

[0039] Figure 9 The image shows the X-ray powder diffraction pattern of the bismuth oxide material prepared in Comparative Example 1.

[0040] Figure 10 This is a cycling diagram of a potassium-ion battery prepared from the bismuth oxide material obtained in Comparative Example 1 at a current density of 50 mA / g.

[0041] Figure 11 The transmission electron microscope scan image (a) of the bulk Bi2O2(OH)(NO3) obtained in Comparative Example 2 and the constant current charge-discharge performance of the potassium-ion battery prepared with it as the negative electrode at a current density of 50 mA / g are shown in (b, c, d). Detailed Implementation

[0042] The present invention will be specifically described below through embodiments, which are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described content.

[0043] The concentrated nitric acid used in the examples had a mass fraction of 65-68%; the nitric acid solution used was obtained by mixing concentrated nitric acid with water.

[0044] Example 1

[0045] A method for preparing a flower-shaped Bi2O2(OH)(NO3) material includes the following steps:

[0046] (1) Add 4 mmol Bi(NO3)·5H2O to 15 mL of nitric acid solution (the volume ratio of concentrated nitric acid to water in the nitric acid solution is 2:13), sonicate for 30 min, then add 80 mL of deionized water to dilute, and then heat in a water bath at 60 °C and stir for 30 min to obtain a dilute solution.

[0047] (2) Add urea solution (prepared by mixing 40 mmol of urea with 20 mL of deionized water) to the dilute solution obtained in step (1), and continue to heat and stir the reaction in a water bath at 60 °C for 15 min. After the reaction is completed, pour the resulting reaction solution into an equal volume of anhydrous ethanol, centrifuge, and separate the supernatant and precipitate. Wash the precipitate with deionized water and anhydrous ethanol three times in sequence, and dry the washed material at 60 °C for 10 h to obtain the intermediate Bi6O5(OH)3(NO3)5·2H2O.

[0048] (3) Weigh 0.4 g of the intermediate Bi6O5(OH)3(NO3)5·2H2O obtained in step (2) and add it to 5 mL of glacial acetic acid. Stir for 1 h to disperse it fully. Centrifuge the resulting suspension at 10000 rpm for 5 min, discard the glacial acetic acid, and add 30 mL of deionized water to the centrifuge tube to dissolve the solid at the bottom of the tube to obtain a clear solution. Transfer the obtained clear solution to a 40 mL Teflon-lined container and hydrothermally react it at 150 °C for 5 h in a high-pressure reactor. After the reaction is completed, cool it naturally to room temperature, filter it, wash the obtained solid with deionized water and ethanol, and then dry the obtained solid material at 60 °C for 10 h to obtain flower-shaped Bi2O2(OH)(NO3) material.

[0049] Figure 1 a is a scanning electron microscope image of the intermediate prepared in this embodiment. It can be seen that the material has a bulk morphology; and from its XRD characterization results ( Figure 1 b) It can be seen that the intermediate is Bi6O5(OH)3(NO3)5·2H2O (PDF#54-0627).

[0050] Figure 2 a, Figure 2 b shows scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the flower-shaped Bi₂O₂(OH)(NO₃) material obtained in this embodiment. It can be observed that the material has a multi-level flower-shaped structure and a large specific surface area; and based on its XRD characterization results (… Figure 2 c) It can be seen that the material has strong crystallinity and strong diffraction peaks at small angles, proving that its large interlayer spacing crystal planes account for a large proportion of the entire crystal structure, which is beneficial to its stability.

[0051] The flower-shaped Bi2O2(OH)(NO3) material prepared in this embodiment was used as the negative electrode material to prepare a potassium-ion battery, and its electrochemical performance was tested. The specific steps are as follows:

[0052] The prepared flower-shaped Bi₂O₂(OH)(NO₃) material, reduced graphene oxide, sodium carboxymethyl cellulose, and conductive graphite were mixed in a mass ratio of 4:4:1:1 and ground thoroughly in a mortar for 30 minutes with water as a dispersant to prepare a negative electrode slurry. The volume ratio of water to the total mass of the flower-shaped Bi₂O₂(OH)(NO₃) material, reduced graphene oxide, sodium carboxymethyl cellulose, and conductive graphite was 4 mL:100 mg. The slurry was then coated onto aluminum foil and scraped to obtain the negative electrode sheet. The loading of the flower-shaped Bi₂O₂(OH)(NO₃) material was 1.2 mg / mm². 2 .

[0053] Battery assembly and testing: The negative electrode sheet was pressed into an electrode sheet, with potassium metal as the positive electrode and 5 mol / L KFSI electrolyte as the electrolyte, and the battery was assembled in an argon-filled glove box. Charge-discharge cycle tests were conducted at room temperature and current densities of 50 mA / g and 100 mA / g, respectively.

[0054] Figure 3 The charge-discharge cycle diagrams in a and b demonstrate that the material exhibits extremely high specific capacity and cycle stability at different current densities. Figure 4 The constant current charge-discharge curves in the data demonstrate that the potassium-ion battery constructed based on Bi2O2(OH)(NO3) material has voltage plateaus that are consistent with theoretical values: the plateaus of 0.8V and 0.4V prove that Bi2O2(OH)(NO3) material participates in electrochemical potassium storage and that there are no charge-discharge plateaus corresponding to side reactions.

[0055] Figure 5 The differential voltage-charge curves of a potassium-ion battery prepared with Bi₂O₂(OH)(NO₃)-rGO as the negative electrode were obtained. Cyclic voltammetry tests were performed at a rate of 50 mV / s, with a voltage range of 0–3 V. Figure 5 It can be seen that the redox process of Bi2O2(OH)(NO3) material during potassium storage is similar to... Figure 4 The voltage plateaus of the constant current charge-discharge curves corroborate each other.

[0056] The flower-shaped Bi₂O₂(OH)(NO₃) material prepared in this embodiment was used as the negative electrode material to prepare a sodium-ion battery, and its electrochemical performance was tested. The specific steps are as follows: The preparation of the negative electrode sheet is the same as that of the potassium-ion battery; Battery assembly and testing: The negative electrode sheet was pressed into an electrode sheet, with metallic sodium as the positive electrode, 5 mol / L sodium hexafluorophosphate electrolyte, and a conventional sodium battery separator (glass fiber separator) as the separator. The battery was assembled in an argon-filled glove box. Charge-discharge cycle tests were conducted at a current density of 25 mA / g at room temperature.

[0057] Figure 6 The sodium-ion battery prepared with Bi2O2(OH)(NO3)-rGO as the negative electrode was subjected to constant current charge-discharge at a current density of 25 mA / g, and it was found that it also has high reversibility and specific capacity.

[0058] Example 2

[0059] A method for preparing a flower-shaped Bi2O2(OH)(NO3) material includes the following steps:

[0060] (1) Add 4.8 mmol Bi(NO3)·5H2O to 15 mL of nitric acid solution (the volume ratio of concentrated nitric acid to water in the nitric acid solution is 3:12), sonicate for 30 min, then add 85 mL of deionized water to dilute, and then heat in a water bath at 80 °C and stir for 30 min to obtain a dilute solution.

[0061] (2) Add urea solution (prepared by mixing 30 mmol urea and 20 mL deionized water) to the dilute solution obtained in step (1), and continue to heat and stir the reaction in a water bath at 80°C for 15 min. After the reaction is completed, pour the resulting reaction solution into an equal volume of anhydrous ethanol, centrifuge, and separate the supernatant and precipitate. Wash the obtained precipitate three times with deionized water and anhydrous ethanol respectively, and dry the washed material at 60°C for 10 h to obtain the intermediate Bi6O5(OH)3(NO3)5·2H2O.

[0062] (3) Weigh 0.4 g of the intermediate Bi6O5(OH)3(NO3)5·2H2O obtained in step (2) and add it to 10 mL of glacial acetic acid. Stir for 1 h to disperse it fully. Centrifuge the resulting suspension at 10000 rpm for 5 min, discard the glacial acetic acid, and add 30 mL of deionized water to the centrifuge tube to dissolve the solid at the bottom of the tube to obtain a clear solution. Transfer the obtained clear solution to a 40 mL Teflon-lined container and hydrothermally react it at 150 °C for 5 h in a high-pressure reactor. After the reaction is completed, cool it naturally to room temperature, filter it, wash the obtained solid with deionized water and ethanol, and then dry the obtained solid material at 60 °C for 10 h to obtain flower-shaped Bi2O2(OH)(NO3) material.

[0063] The battery assembly was performed as described in Example 1. Cyclic voltammetry tests were conducted at a rate of 50 mV / s, with a voltage range of 0–3 V. Figure 7 The differential curves of its charge and voltage are given.

[0064] Example 3

[0065] A method for preparing a flower-shaped Bi2O2(OH)(NO3) material is as described in Example 1, except that in step (3), a hydrothermal reaction is carried out at 180°C for 5 hours to obtain the flower-shaped Bi2O2(OH)(NO3) material.

[0066] Scanning electron microscope images of the flower-shaped Bi2O2(OH)(NO3) material obtained in this embodiment are as follows: Figure 8 As shown, by Figure 8 It can be seen that, compared with Example 1, the product obtained at this temperature is larger in size and has a slightly worse morphology.

[0067] Comparative Example 1

[0068] A method for preparing a bismuth oxide material is as described in Example 1, except that in step (3), a hydrothermal reaction is carried out at 60°C for 5 hours to obtain the bismuth oxide material.

[0069] The XRD pattern of the bismuth oxide material obtained in this comparative example is as follows: Figure 9 As shown, by Figure 9 It can be seen that the crystallinity of the material has deteriorated.

[0070] The battery assembly is as described in Example 1, and it operates at 50 mA·g. -1 Cyclic curves at current density are as follows Figure 10 As shown, by Figure 10 It can be seen that as the crystallinity of the material deteriorates, the capacity of the prepared battery decreases significantly and its stability is reduced.

[0071] Comparative Example 2

[0072] A method for preparing a bulk Bi2O2(OH)(NO3) material includes the following steps:

[0073] 1 mmol Bi(NO3)·5H2O was added to 30 mL of water, sonicated for 30 min, and stirred for 30 min. The uniformly dispersed solution was then poured into a 40 mL Teflon-lined container. The container was then placed in a high-temperature and high-pressure reactor and hydrothermally heated at 150 °C for 5 h. The resulting precipitate was washed three times each with deionized water and anhydrous ethanol. The washed material was then dried at 60 °C for 10 h to obtain a bulky Bi2O2(OH)(NO3).

[0074] Figure 11 (a) shows the TEM characterization results of the material, which reveals that the product obtained without intermediates and acetic acid regulation has a bulky morphology.

[0075] Battery assembly and testing are as described in Example 1. Figure 11 (b) The specific capacity-cycle number curve shows that the capacity of the material continuously decreases. Figure 11 The charge-discharge curves (c-d) show that the bulk Bi2O2(OH)(NO3) completely lost its plateau capacity after ten cycles and was no longer usable, highlighting the crucial role of intermediate processing and acetic acid regulation.

Claims

1. A method for preparing a flower-like Bi2O2(OH)(NO3) material, comprising the following steps: (1) adding a bismuth salt into a nitric acid solution, then adding water to dilute after ultrasonic treatment, and then performing a heating treatment to obtain a dilute solution; the bismuth salt is Bi(NO3)·5H2O or BiCl3; the nitric acid solution is obtained by mixing concentrated nitric acid and water, the mass fraction of the concentrated nitric acid is 65-68%, and the volume ratio of the concentrated nitric acid to water is 0.05-0.5:1; after the ultrasonic treatment, the volume ratio of water to the number of moles of the bismuth salt is 10-50 mL:1 mmol; (2) adding a urea solution into the dilute solution obtained in step (1) to perform a reaction; after the reaction is completed, centrifugation, washing, and drying are performed to obtain an intermediate Bi6O5(OH)3(NO3)5·2H2O; the molar ratio of the urea to the bismuth salt is 5-10:1; (3) adding the intermediate Bi6O5(OH)3(NO3)5·2H2O obtained in step (2) into glacial acetic acid to uniformly stir and disperse; then centrifuging, dissolving the obtained solid in water, and performing a hydrothermal reaction; after the reaction is completed, filtering, washing, and drying are performed to obtain the flower-like Bi2O2(OH)(NO3) material; the mass ratio of the intermediate Bi6O5(OH)3(NO3)5·2H2O to the volume of the glacial acetic acid is 1 g:5-50 mL; and the temperature of the hydrothermal reaction is 120-180°C.

2. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (1), the ratio of the number of moles of the bismuth salt to the volume of the nitric acid solution is 0.2-0.5 mmol:1 mL.

3. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (1), the ultrasonic treatment time is 20-40 min.

4. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, The heating treatment temperature is 40-80°C, and the heating treatment time is 20-40 min.

5. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (2), the concentration of the urea solution is 0.5-5 mmol / mL.

6. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (2), the reaction temperature is 40-80°C, and the reaction time is 5-25 min. The centrifugation step is: adding the obtained reaction liquid into an equal volume of anhydrous ethanol, centrifuging, and separating the supernatant from the precipitate; the washing is: sequentially washing the centrifuged precipitate with deionized water and anhydrous ethanol for 3-5 times, respectively; and the drying is: drying at 60-70°C for 10-12 h.

7. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (3), the stirring time is 0.5-1 h.

8. The method for preparing the flower-shaped Bi2O2(OH)(NO3) material according to claim 1, characterized in that, In step (3), the volume ratio of water to the mass of the intermediate Bi6O5(OH)3(NO3)5·2H2O is 50-300 mL:1 g; The hydrothermal reaction time is 2-10 h; the washing is: sequentially using water and ethanol; and the drying is: drying the washed solid material at 60-70°C for 10-12 h.

Images