A metal-doped bismuth tungstate material for treating iodine-containing wastewater, a preparation method thereof and a method for treating iodine-containing wastewater

Abstract

The application belongs to the technical field of iodine-containing wastewater treatment, and specifically provides a method for treating iodine-containing wastewater, which comprises the following steps: mixing a metal-doped bismuth tungstate material for treating iodine-containing wastewater with a binder and a conductive agent to prepare a slurry, coating the slurry on a conductive substrate, and drying to obtain a membrane electrode, and using the obtained membrane electrode to treat iodine-containing wastewater; and a preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater, which comprises the following steps: 1) dissolving bismuth salt and iron salt in a solvent to prepare a mixed solution; 2) adding a tungstate solution to the mixed solution to form a suspension, and then performing a hydrothermal reaction, collecting the precipitate after cooling, and washing and drying to obtain the product. The metal-doped bismuth tungstate material prepared by the application has the advantages of high specific surface area and good photo-assisted electric adsorption performance.

Description

Technical Field

[0001] This application belongs to the field of iodine-containing wastewater treatment technology, and in particular relates to a metal-doped bismuth tungstate material for treating iodine-containing wastewater, its preparation method, and a method for treating iodine-containing wastewater. Background Technology

[0002] Iodine, as an indispensable strategic resource, has wide applications in medicine and health, new energy materials, chemicals, agriculture, and even aerospace and nuclear industries, with demand steadily increasing in recent decades. Iodine resources are mainly found in phosphate rock, seawater (seaweed), and oil and gas field brines, but extraction is difficult and its global distribution is uneven. Currently, methods for purifying iodine resources in seawater, salt lake brines, and oil and gas field brines include ashing, air blowing, activated carbon adsorption, and ion exchange. These methods generally face challenges such as environmental pollution, high energy consumption and cost, and the influence of coexisting ions. Therefore, developing green, environmentally friendly, energy-efficient, and highly selective separation technologies is of great significance.

[0003] Electro-controlled ion exchange (ESIX) technology is a novel ion recovery technology that selectively captures and releases target ions by controlling the redox state of membrane materials. It boasts advantages such as environmental friendliness, high selectivity, and large adsorption capacity, but suffers from high energy consumption. To save energy and reduce consumption, light energy is used to replace part of the electrical energy, leading to the development and research of photo-assisted electro-controlled ion exchange (P-ESIX) technology to achieve highly selective separation of iodide ions under low energy consumption conditions. Chinese invention patent CN201910651148.4 discloses "A photo-assisted electro-controlled ion exchange process and a method for treating anions in low-concentration wastewater," which can achieve Cl... - F - ,ClO 4- PO4 3- One type of anion. The key to P-ESIX technology is the development of ion exchange membranes that are both photoactive and electroactive. Bismuth-based materials have become the main research target because they have both photoactive and electroactive effects, and progress has been made in the field of iodine ion extraction.

[0004] Bismuth tungstate (Bi₂WO₆) is a typical Aurivillius-type layered structure, composed of [Bi₂O₂]. 2+Bi2WO6, composed of alternating layers of [WO6] octahedrons, exhibits a layered crystal structure highly similar to bismuth-based materials such as BiOI. Compared to traditional BiOI materials, Bi2WO6 has attracted widespread attention due to its superior structural stability, simpler synthesis process, and unique layered structure. These structural characteristics endow Bi2WO6 with a robust framework and ion transport pathways, making it a promising primary material for ion adsorption and electrochemical applications. Compared to traditional BiOI-based materials, Bi2WO6 exhibits higher adsorption capacity, better ion selectivity, and cycling stability, demonstrating good application potential as a novel functional membrane material for photo-assisted electrochemical iodine extraction. However, its band gap is typically wide (approximately 2.6-2.8 eV), only responding to short-wavelength visible light, and its high photogenerated electron-hole recombination rate limits further improvement in adsorption performance. Therefore, it is necessary to broaden the visible light response range of the material and suppress carrier recombination through modification strategies to improve the extraction efficiency of iodine ions from iodine-containing wastewater. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a metal-doped bismuth tungstate material for treating iodine-containing wastewater, its preparation method, and a method for treating iodine-containing wastewater.

[0006] This application first provides a method for treating iodine-containing wastewater, which involves mixing a metal-doped bismuth tungstate material for treating iodine-containing wastewater with a binder and a conductive agent to form a slurry, coating it onto a conductive substrate, drying it to obtain a membrane electrode, and then using the obtained membrane electrode for treating iodine-containing wastewater. The preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater includes the following steps: 1) Prepare a mixed solution by dissolving bismuth salt and iron salt in a solvent; 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

[0007] This application provides a method for extracting iodide ions by photo-assisted electro-controlled ion exchange, using the above-mentioned membrane electrode as the working electrode to achieve the adsorption and desorption of iodide ions in iodine-containing wastewater in a photo-assisted electro-controlled ion exchange system.

[0008] Furthermore, a reduction potential of -0.6V to -0.4V is applied to the membrane electrode before adsorption, and a pre-desorption process is performed for 20min to 40min to activate the ion adsorption sites. And / or, selective adsorption of iodide ions is achieved under the synergistic effect of visible light introduction and oxidation potential of 0.4V-0.6V; desorption of iodide ions and electrode recycling can be achieved by applying reduction potential; And / or, the membrane electrode exhibits high adsorption capacity and high selectivity for iodine ions, and can be used in F - Cl - , Br- SO4 2- NO 3- Efficient separation of iodide ions under plasma coexistence conditions.

[0009] This application provides a method for preparing a metal-doped bismuth tungstate material for treating iodine-containing wastewater, comprising the following steps: 1) Prepare a mixed solution by dissolving bismuth salt and iron salt in a solvent; 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

[0010] Furthermore, the preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater includes the following steps: 1) Dissolve bismuth salt and iron salt in a solvent to prepare solution A; mix ferric nitrate, casein phosphopeptide and deionized water evenly to prepare a precursor solution, then add molybdate solution to the precursor solution and mix evenly to prepare solution B; mix solution A and solution B to prepare a mixed solution. 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

[0011] Furthermore, the bismuth salt is bismuth nitrate, and the iron salt is ferric nitrate; And / or, the solvent is an alcohol solvent, preferably, the solvent is ethylene glycol; And / or, the tungstate is one of sodium tungstate or potassium tungstate; And / or, the molybdate is one of ammonium molybdate, sodium molybdate, or potassium molybdate.

[0012] Furthermore, in step 1), the molar ratio of bismuth ions to iron ions in the mixed solution is 1:(0.005-0.015).

[0013] Furthermore, in step 2), the hydrothermal reaction is carried out at 150-200℃ for 10-15 hours.

[0014] Furthermore, in step 1), the volume ratio of solution A to solution B is 1:(0.1-0.25); And / or, in step 1), the mass fraction of casein phosphopeptide in solution A is 1-3%.

[0015] This application provides a metal-doped bismuth tungstate material for treating iodine-containing wastewater, which is prepared using the above-described method.

[0016] Compared with the prior art, this application has the following beneficial effects: 1. This application successfully incorporated metal elements into the crystal structure of Bi₂WO₆ via a hydrothermal method to prepare metal-doped bismuth tungstate material. Metal doping can effectively control the crystal structure of Bi₂WO₆, broaden the visible light response range of the material, improve its electronic conductivity, promote the separation and migration of photogenerated carriers, and significantly enhance its photoelectrochemical performance. Furthermore, using long-chain casein phosphopeptides as stabilizers for iron and molybdate ions can further improve the doping state, enhance assembly densification and specific surface area, and result in higher Ig. - Insertion and release capabilities.

[0017] 2. The mechanism of action of the metal-doped bismuth tungstate material prepared in this application for photo-assisted electro-controlled ion exchange extraction of iodide ions from iodine-containing wastewater is as follows: In the crystal structure of Bi2WO6, [Bi2O2]... 2+ The layers serve as electron transfer channels, while the interlayer space is I0 - The introduction of bimetallic elements effectively modulates the band structure of Bi₂WO₆, reducing the band gap and the energy required for electron transitions, thus significantly enhancing the absorption wavelength range of visible light. Under visible light irradiation, electrons on the material surface absorb light energy and transition from the valence band to the conduction band, forming photoelectrons. The reduced band gap makes it easier for electrons to transition into the electrochemical process, generating more free electrons under the same energy input, accelerating the electron migration rate of the system, increasing the number of free electrons, and driving more I₂... - Through the inter-floor passageway.

[0018] 3. This application describes the fabrication of a film electrode using metal-doped bismuth tungstate material, applied to a photo-assisted electro-controlled ion exchange technology for iodine extraction from iodine-containing wastewater. This electrode exhibits excellent selectivity for iodine ions in the wastewater and can be used in F... - Cl - ,Br - SO4 2- NO3 - This invention enables the extraction of iodide ions in a multi-coexisting anionic environment. Simultaneously, the membrane electrode exhibits excellent cycling stability, maintaining a high adsorption capacity and structural stability even after 20 adsorption / desorption cycles. The preparation process of the metal-doped bismuth tungstate material is simple and controllable, requiring no complex equipment or expensive reagents. Furthermore, the iodine extraction process is environmentally friendly and produces no secondary pollution, making it suitable for the efficient resource recovery of iodine resources from low-concentration iodine-containing liquids in salt lake halogens, and possesses promising prospects for industrial application. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of SEM and TEM tests of the bismuth tungstate material in Example 2 of this application.

[0020] Figure 2This is a schematic diagram of the electrochemical characteristic test data of bismuth tungstate material in Example 2 and the control group of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0024] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0025] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0026] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0027] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0028] Unless otherwise specified, all steps of this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0029] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0030] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0031] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0032] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0033] Example 1 The preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater in this embodiment includes the following steps: 1) Dissolve 2.97 mmol Bi(NO3)3·5H2O and 0.03 mmol Fe(NO3)3·9H2O in 10 mL of ethylene glycol to prepare a mixed solution; dissolve 1.5 mmol Na2WO4·2H2O in 30 mL of deionized water to prepare a Na2WO4 solution; 2) Na₂WO₄ solution was added dropwise to the mixed solution to form a suspension, which was then sonicated for 1 hour. Finally, the resulting suspension was transferred to a high-pressure reactor and kept at 180°C for 12 hours. After naturally cooling to room temperature, the precipitate was collected and washed three times each with deionized water and anhydrous ethanol to thoroughly remove residues. The precipitate was then air-dried at room temperature for 12 hours to obtain D1-Bi₂WO₆ powder.

[0034] Example 2 The preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater in this embodiment includes the following steps: 1) Dissolve 2.97 mmol Bi(NO3)3·5H2O and 0.03 mmol Fe(NO3)3·9H2O in 10 mL of ethylene glycol to prepare solution A of Fe(NO3)3·9H2O and Bi(NO3)3; dissolve 2 mmol Na2WO4·2H2O in 40 mL of deionized water to prepare solution A of Na2WO4. 0.01 mol Fe(NO3)3·9H2O was dissolved in 25 mL of deionized water, and 0.5 g of casein phosphopeptide was added and mixed thoroughly to prepare a precursor solution; 2.6447 g of ammonium molybdate was dissolved in 25 mL of deionized water to prepare an ammonium molybdate solution; the ammonium molybdate solution was added to the precursor solution and mixed thoroughly by blowing and stirring to obtain solution B; 2) Mix solutions A and B at a volume ratio of 1:0.2 to obtain a mixed solution. Then, add Na₂WO₄ solution dropwise to the mixed solution to form a suspension, followed by sonication for 1 hour. Finally, transfer the resulting suspension to a high-pressure reactor and maintain it at 180°C for 12 hours. After naturally cooling to room temperature, collect the precipitate, wash it three times each with deionized water and anhydrous ethanol to thoroughly remove residues, and air-dry it at room temperature for 12 hours to obtain D₂-Bi₂WO₆ powder.

[0035] control group Preparation of Bi2WO6 powder: 3 mmol Bi(NO3)3·5H2O and 1.5 mmol Na2WO4·2H2O were dissolved in 10 mL ethylene glycol and 30 mL deionized water, respectively. The Na2WO4 solution was added dropwise to the Bi(NO3)3 solution with continuous stirring to form a white suspension, which was then sonicated for 1 hour. Finally, the resulting suspension was transferred to a high-pressure reactor and kept at 180 °C for 12 hours. After natural cooling to room temperature, the precipitate was collected, washed three times each with deionized water and anhydrous ethanol, and then air-dried at room temperature for 12 hours to obtain Bi2WO6 powder.

[0036] Performance testing 1. D2-Bi2WO6 powder was taken and its morphology and structure were analyzed using scanning electron microscopy and transmission electron microscopy, respectively. The test results are as follows: Figure 1 As shown, D2-Bi2WO6 exhibits a flower-like structure formed by the self-assembly of nanosheets, indicating that the doping of bimetallic elements did not significantly alter its basic morphological characteristics.

[0037] 2. Select common coexisting anions (F) in low-concentration iodine-containing wastewater systems. - Cl - ,Br - SO4 2- NO3 - Using D1-Bi2WO6 membrane electrodes, D2-Bi2WO6 membrane electrodes, and Bi2WO6 membrane electrodes as competing ions, respectively, the research objects were determined when each competing anion (F... - Cl - ,Br - SO4 2- NO3 - ) and I - At a molar ratio of 1:1, competitive adsorption experiments were conducted to determine the separation factor and compare the selective adsorption performance of the two materials for iodide ions. - After 20 adsorption and desorption cycles in the solution, the adsorption rate was measured. The adsorption rate (%) was calculated as (adsorption capacity at 21 cycles / initial adsorption capacity) × 100%. The test results are shown in Table 1. Table 1. Results of Selectivity and Stability Tests

[0038] Table 1 shows that the D2-Bi2WO6 membrane electrode exhibits good selectivity for iodide ions. This indicates that the D2-Bi2WO6 membrane electrode possesses optimal adsorption selectivity for iodide ions, especially for achieving efficient and specific extraction of iodide ions in complex wastewater systems. After 20 consecutive adsorption and desorption cycles, I... -The adsorption capacity remains above 75% of the initial value, demonstrating excellent cycle stability.

[0039] 3. Take D1-Bi2WO6 powder, D2-Bi2WO6 powder and Bi2WO6 powder, mix them thoroughly with PVDF and conductive carbon black in a mass ratio of 8:1:1, grind for 10 minutes, then add an appropriate amount of NMP and stir for 6 hours. Finally, coat them evenly on the pretreated FTO conductive glass and vacuum dry for 12 hours to obtain the test membrane electrode for later use.

[0040] The electrochemical characteristics of Bi₂WO₆ and D₂-Bi₂WO₆ membrane electrodes were tested using cyclic voltammetry. The test results are as follows: Figure 2 As shown (where D represents the black element and L represents the lighting), it can be seen that... Figure 2 The left side shows the CV curves of the conductive substrate, Bi₂WO₆, and D₂-Bi₂WO₆ in 0.1M KI solution under light and dark conditions at a scan rate of 200 mV / s. Notably, except for the conductive substrate, Bi₂WO₆ and D₂-Bi₂WO₆ both exhibited a pair of distinct redox peaks under both light and dark conditions, with the oxidation and reduction peaks corresponding to I₂ and I₂, respectively. - Adsorption and desorption. Figure 2 The right side shows that the electrochemical active area and peak current of D2-Bi2WO6 under dark conditions are significantly higher than those of Bi2WO6, indicating that bimetallic doping significantly improves the electrochemical response of Bi2WO6. This also suggests that the D2-Bi2WO6 membrane electrode has a higher Ig. - The insertion and release capabilities are likely related to the excellent electron conduction ability of the doped metal. Furthermore, compared to dark conditions, the peak current and electrochemical active area of ​​both membrane electrodes significantly increased after the introduction of an external light field, indicating that the introduction of the external light field significantly enhanced photoelectric activity. Meanwhile, the increase in peak current and electrochemical active area of ​​the D2-Bi2WO6 membrane electrode under illumination was much greater than that of Bi2WO6, suggesting that bimetallic doping may allow a greater number of free electrons to enter the electrochemical system under illumination. When visible light is applied, the photocurrent intensity of both increases sharply. In addition, bimetallic doping further improved the photocurrent density, thus improving the photocurrent response capability of the membrane electrode.

[0041] Further analysis reveals that Fe and Mo were successfully doped into Bi₂WO₆, resulting in superior photoelectric properties and adsorption performance. The material exhibits a lower band gap, and the relative positions of the valence and conduction bands change due to the introduction of bimetallic ions. The valence band shifts to a more negative position, and the conduction band shifts to a more positive position, reducing the energy required for electron transitions. This allows the material to absorb lower-energy light, leading to a significantly enhanced absorption wavelength range. Under visible light irradiation, electrons on the surface of D₂-Bi₂WO₆ absorb light energy and transition from the valence band to the conduction band, becoming photoelectrons. The reduced band gap makes it easier for electrons to transition into photoelectrons and enter the electrochemical process. Absorbing the same amount of energy allows a greater number of free electrons to enter the reaction system, accelerating the electron migration rate and increasing the number of free electrons, thereby further improving the I₂-VIX process. - Adsorption performance.

[0042] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for treating iodine-containing wastewater, characterized in that: A slurry was prepared by mixing a metal-doped bismuth tungstate material for treating iodine-containing wastewater with a binder and a conductive agent. The slurry was coated onto a conductive substrate and dried to obtain a membrane electrode. The membrane electrode was then used for the treatment of iodine-containing wastewater. The preparation method of the metal-doped bismuth tungstate material for treating iodine-containing wastewater includes the following steps: 1) Prepare a mixed solution by dissolving bismuth salt and iron salt in a solvent; 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

2. A method for extracting iodide ions by photo-assisted electro-controlled ion exchange, characterized in that: Using the membrane electrode described in claim 1 as the working electrode, the adsorption and desorption of iodide ions in iodine-containing wastewater are realized in a photo-assisted electro-controlled ion exchange system.

3. The method according to claim 2, characterized in that: Before adsorption, a reduction potential of -0.6V to -0.4V is applied to the membrane electrode for a pre-desorption process of 20min to 40min to activate the ion adsorption sites. And / or, selective adsorption of iodide ions is achieved under the synergistic effect of visible light introduction and an oxidation potential of 0.4V-0.6V; Applying a reduction potential enables the desorption of iodide ions and the recycling of the electrode; And / or, the membrane electrode exhibits high adsorption capacity and high selectivity for iodine ions, and can be used in F - Cl - , Br - SO4 2- NO 3- Efficient separation of iodide ions under plasma coexistence conditions.

4. A method for preparing a metal-doped bismuth tungstate material for treating iodine-containing wastewater, characterized in that: Includes the following steps: 1) Prepare a mixed solution by dissolving bismuth salt and iron salt in a solvent; 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

5. The method for preparing metal-doped bismuth tungstate material for treating iodine-containing wastewater according to claim 4, characterized in that: Includes the following steps: 1) Dissolve bismuth salt and iron salt in a solvent to prepare solution A; mix ferric nitrate, casein phosphopeptide and deionized water evenly to prepare a precursor solution, then add molybdate solution to the precursor solution and mix evenly to prepare solution B; mix solution A and solution B to prepare a mixed solution. 2) Add tungstate solution to the mixed solution to form a suspension, then carry out a hydrothermal reaction, collect the precipitate after cooling, and wash and dry it to obtain the final product.

6. The method for preparing metal-doped bismuth tungstate material for treating iodine-containing wastewater according to claim 4 or 5, characterized in that: The bismuth salt is bismuth nitrate, and the iron salt is ferric nitrate; And / or, the solvent is an alcohol solvent, preferably, the solvent is ethylene glycol; And / or, the tungstate is one of sodium tungstate or potassium tungstate; And / or, the molybdate is one of ammonium molybdate, sodium molybdate, or potassium molybdate.

7. The method for preparing metal-doped bismuth tungstate material for treating iodine-containing wastewater according to claim 4, characterized in that: In step 1), the molar ratio of bismuth ions to iron ions in the mixed solution is 1:(0.005-0.015).

8. The method for preparing metal-doped bismuth tungstate material for treating iodine-containing wastewater according to claim 4 or 5, characterized in that: In step 2), the hydrothermal reaction is carried out at 150-200℃ for 10-15 hours.

9. The method for preparing metal-doped bismuth tungstate material for treating iodine-containing wastewater according to claim 5, characterized in that: In step 1), the volume ratio of solution A to solution B is 1:(0.1-0.25); And / or, in step 1), the mass fraction of casein phosphopeptide in solution A is 1-3%.

10. A metal-doped bismuth tungstate material for treating iodine-containing wastewater, characterized in that: It is prepared by any one of the preparation methods described in claims 4-9.

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