A method for preparing bismuth tungstate

Abstract

This invention relates to a method for preparing bismuth tungstate, characterized by the following steps: dissolving sodium tungstate dihydrate in a mixed solvent and sonicating it to form a solution A with a mass concentration of 0.1%–2.6%; dissolving bismuth nitrate pentahydrate in a mixed solvent and sonicating it to obtain a solution B with a mass concentration of 0.1%–5.5%; adding solution A dropwise to solution B and stirring magnetically to form solution C; transferring solution C to a microwave catalytic synthesis / extraction apparatus and heating it to 160–200°C for 20–180 min; filtering after the reaction and washing the product with anhydrous ethanol and deionized water, then drying the product, collecting the powder, and grinding it to obtain bismuth tungstate powder. Advantages of this invention: The preparation method of this invention is mild, quick, energy-efficient, green, and highly effective; the prepared product has uniform particles, small particle size, large specific surface area, high purity, and high photocatalytic activity; it exhibits good degradation rates for various dyes with different structures, such as crystal violet, water-soluble aniline blue, and Congo red.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst preparation technology, and relates to a method for preparing bismuth tungstate. Background Technology

[0002] Photocatalysis is a green and environmentally friendly new technology in environmental remediation, with significant potential for development in wastewater treatment. It can effectively degrade various organic pollutants in water. It can rapidly mineralize harmful organic or inorganic substances in water without selectivity, producing carbon dioxide water and simple mineral acids, or directly reducing them. It also boasts advantages such as low energy consumption, mild reaction conditions, and no secondary pollution problems such as waste residue or waste liquid. Therefore, it has become a highly promising and preferred technology for water pollution control.

[0003] Currently, widely studied visible light photocatalysts include WO3 (band gap approximately 2.7 eV), g-C3N4 (band gap approximately 2.7 eV), BiVO4 (band gap approximately 2.4 eV), and bismuth-based layered oxides. Among them, bismuth tungstate (Bi2WO6) has attracted considerable interest from researchers due to its unique layered structure and suitable band gap.

[0004] Common methods for preparing Bi₂WO₆ include hydrothermal synthesis, sol-gel synthesis, solid-state reaction, and solvothermal methods, but all have significant drawbacks. For example, the hydrothermal method, although widely used, typically requires reaction in a high-pressure reactor at 160-200℃ for tens of hours or even longer, resulting in high energy consumption, long preparation cycles, and product particle agglomeration and uneven particle size distribution. The sol-gel method also suffers from high calcination temperatures (typically 400-600℃) and the easy introduction of impurities. Solid-state reaction requires even higher temperatures (above 800℃), resulting in coarse product particles with small specific surface areas and very low photocatalytic activity. Currently, microwave-assisted synthesis has attracted considerable attention in nanomaterial preparation due to its uniform heating, fast reaction speed, and low energy consumption.

[0005] Currently, most preparation processes use pure water or single alcohols as reaction solvents, and rarely use mixed solvent systems. However, different solvent ratios can change the viscosity, solubility, polarity, and coordination of the system, thereby regulating the crystal growth and surface structure of the material and affecting the degradation effect of the product on organic pollutants. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing bismuth tungstate. This invention uses ethylene glycol (EG) and N,N-dimethylformamide (DMF) as a mixed solvent and employs a normal pressure microwave method to prepare pure phase Bi₂WO₆ in one step.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing bismuth tungstate, characterized by comprising the following steps: (1) Dissolve sodium tungstate dihydrate (Na2WO4·2H2O) in a mixed solvent and sonicate it (10~30min) to form a solution A with a mass concentration of 0.1% - 2.6%; (2) Dissolve bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) in a mixed solvent and sonicate (20~40min) to obtain a solution B with a mass concentration of 0.1% - 5.5%; (3) Add solution A dropwise to solution B, and stir magnetically (10~50min) to form solution C; (4) Transfer solution C to a microwave catalytic synthesis / extraction apparatus and heat it to 160-200℃ at a rate of 5-50℃ / min. React at this temperature for 20-180 min. After the reaction is completed, filter the product and wash it with anhydrous ethanol and deionized water. Then dry the product (dry at 60-120℃ for 10-24 h), collect the powder and grind it to obtain bismuth tungstate (Bi2WO6) powder.

[0008] Furthermore, the mixed solvent is prepared by mixing ethylene glycol (EG) and N,N-dimethylformamide (DMF) in a volume ratio of 1:1 to 5:1.

[0009] Furthermore, the mixed solvent is prepared by mixing ethylene glycol (EG) and N,N-dimethylformamide (DMF) in a volume ratio of 5:1.

[0010] Furthermore, the bismuth tungstate powder can be used to degrade water-soluble aniline blue, crystal violet, Congo red, rhodamine B, methyl orange, etc.

[0011] Furthermore, the bismuth tungstate powder exhibits a degradation rate of 92.6% for water-soluble aniline blue, 95.1% for crystal violet, and 90.3% for Congo red, as well as a degradation rate of 43.9% for Rhodamine B and 54.9% for methyl orange.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method of this invention is mild, quick, energy-efficient, green, and highly effective; 2. The product prepared by this invention has uniform particle size, small particle size, large specific surface area, high purity, and high photocatalytic activity; 3. The bismuth tungstate (Bi2WO6) powder prepared by this invention has a good degradation rate for various dyes with different structures, such as crystal violet, water-soluble aniline blue, and Congo red. It overcomes the limitations of traditional technology in product application and provides process technology and practical value for the efficient preparation of bismuth-based photocatalytic materials and the treatment of organic pollutant wastewater. Attached Figure Description

[0013] Figure 1 XRD patterns of Bi2WO6 prepared with different solvent ratios; Figure 2 The degradation rate of RhB by Bi2WO6 was obtained for different solvent ratios; Figure 3 This is a SEM image of the bismuth tungstate product obtained by the present invention. Detailed Implementation

[0014] A method for preparing bismuth tungstate, the specific implementation steps of which are as follows: Example 1

[0015] (1) Weigh 1.5 mmol Na2WO4·2H2O and dissolve it in 30 mL of mixed solvent (EG to DMF volume ratio is 5:1). After sonication for 20 min, solution A is formed. (2) Dissolve 3 mmol Bi(NO3)3·5H2O in 30 mL of mixed solvent (EG to DMF volume ratio is 5:1), and sonicate for 30 min to obtain solution B; (3) Add solution A dropwise to solution B, and stir magnetically for 30 min to form solution C; (4) Transfer solution C to a microwave catalytic synthesis / extraction instrument, set the heating time to 7 min, the heating rate to 20℃ / min, heat to 160℃, and the reaction time to 100 min; after the reaction, wash the product with anhydrous ethanol and deionized water, dry at 60℃ for 12 h, collect the powder and grind it to obtain 1.03 g of Bi2WO6 powder.

[0016] Weigh 0.05 g of the prepared Bi2WO6 product (EG to DMF volume ratio 5:1), add 25 mL of a 10 mg / L water-soluble aniline blue solution, and ultrasonically disperse for 3 min. Then, place a magnetic stir bar in the reactor and put it under a preheated xenon lamp light source. Turn on the magnetic stirring and start timing simultaneously. After 10 min of illumination, remove the magnetic stir bar, let stand for 5 min, and transfer the supernatant to a centrifuge tube. Centrifuge at 12000 r / min for 5 min. Finally, measure the absorbance of the supernatant at the maximum absorption wavelength using a spectrophotometer. Measure the initial absorbance of the water-soluble aniline blue using the same method. The results show that the Bi2WO6 product prepared by the method of this invention has a degradation rate of up to 92.6% for water-soluble aniline blue. Under the same conditions, the degradation rates of the prepared Bi2WO6 product for crystal violet, Congo red, and methyl orange are 95.1%, 90.3%, and 54.9%, respectively. Example 2

[0017] The same preparation steps as in Example 1 were used, except that the volume ratio of EG to DMF was 4:1, resulting in 0.95 g of Bi2WO6 powder. Example 3

[0018] The same preparation steps as in Example 1 were used, except that the volume ratio of EG to DMF was 3:1, and 0.91 g of Bi2WO6 powder was obtained. Example 4

[0019] The same preparation steps as in Example 1 were used, except that the volume ratio of EG to DMF was 2:1, and 0.67 g of Bi2WO6 powder was obtained. Example 5

[0020] The same preparation steps as in Example 1 were used, except that the volume ratio of EG to DMF was 1:1, and 0.19 g of Bi2WO6 powder was obtained. Example 6

[0021] The same preparation steps as in Example 2 were used, except that the prepared Bi2WO6 product (EG to DMF volume ratios of 1:1, 2:1, 3:1, 4:1, and 5:1, respectively), and a 5 mg / L Rhodamine B (RhB) solution were used. The absorbance of the solution was measured at 554 nm after 10 min of illumination, and the results are as follows. Figure 2 As shown in the figure, when the volume ratio of EG to DMF is 5:1, 4:1, 3:1, 2:1, and 1:1, the degradation rates of RhB by the prepared Bi2WO6 product are 43.9%, 41.5%, 39.6%, 27.7%, and 7.4%, respectively. As the proportion of ethylene glycol in the system gradually increases from 1:1 to 5:1, the degradation rate of RhB by the sample increases, indicating that the solvent ratio plays a positive role in regulating the viscosity, solubility, polarity, and formulation of the system.

Claims

1. A method for preparing bismuth tungstate, characterized in that... Includes the following steps: (1) Dissolve sodium tungstate dihydrate in a mixed solvent and sonicate to form a solution A with a mass concentration of 0.1% - 2.6%; (2) Dissolve bismuth nitrate pentahydrate in a mixed solvent and sonicate to obtain a solution B with a mass concentration of 0.1% - 5.5%; (3) Solution A is added dropwise to solution B, and after magnetic stirring, solution C is formed; (4) Transfer solution C to a microwave catalytic synthesis / extraction apparatus and heat it to 160-200℃ at a rate of 5-50℃ / min. React at this temperature for 20-180 min. After the reaction is completed, filter the product and wash it with anhydrous ethanol and deionized water. Then dry the product, collect the powder and grind it to obtain bismuth tungstate powder.

2. The method for preparing bismuth tungstate according to claim 1, characterized in that: The mixed solvent is prepared by mixing ethylene glycol and N,N-dimethylformamide in a volume ratio of 1:1 to 5:

1.

3. The method for preparing bismuth tungstate according to claim 1, characterized in that: The mixed solvent is prepared by mixing ethylene glycol and N,N-dimethylformamide in a volume ratio of 5:

1.

4. The method for preparing bismuth tungstate according to claim 1, characterized in that: The ultrasonic dissolution time in step (1) is 10~30 min.

5. The method for preparing bismuth tungstate according to claim 1, characterized in that: The ultrasound time in step (2) is 20~40 min.

6. The method for preparing bismuth tungstate according to claim 1, characterized in that: The magnetic stirring time in step (3) is 10~50 min.

7. The method for preparing bismuth tungstate according to claim 1, characterized in that: In step (4), the drying temperature is 60~120℃ and the drying time is 10~24 h.

8. A method for preparing bismuth tungstate according to any one of claims 1 to 7, characterized in that: The bismuth tungstate powder is suitable for the degradation of water-soluble aniline blue, crystal violet, Congo red, rhodamine B, and methyl orange.

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