Preparation method of nano-bismuth vanadate with different morphologies and application thereof

Abstract

The application discloses a preparation method of nano-bismuth vanadate with different morphologies and application thereof. The method specifically comprises the following steps: adding an ammonium metavanadate aqueous solution into a bismuth nitrate aqueous solution, and then performing a reaction under the condition that the pH value is 5-10, so that the nano-bismuth vanadate with different morphologies is prepared. The pH value of the reaction system is simply and effectively adjusted by using sodium hydroxide lye, and other organic reagents are not needed to be added, so that the nano-bismuth vanadate obtained not only has controllable appearance and large specific surface area, but also has peroxidase-like activity, and can be used for detecting melamine in a solution.

Description

Technical Field

[0001] This invention belongs to the field of bismuth-based material preparation technology, specifically relating to a method for preparing nano-bismuth vanadate with different morphologies and its application. Background Technology

[0002] Since its first synthesis in 1963, BiVO4 has attracted widespread attention. Bismuth vanadate is insoluble in water, exhibits good solvent resistance, and is soluble only in strong acids and alkalis. It is non-toxic and has a wide range of anticipated applications. Bismuth vanadate has four different crystal forms: orthorhombic bismuth vanadate, monoclinic scheelite, tetragonal scheelite, and tetragonal zirconium silicate. The orthorhombic form is brown, the tetragonal zirconium silicate form is a lighter yellow, and the monoclinic and tetragonal scheelite forms are yellow. Due to the growing global awareness of the harmful effects of lead, chromium, and cadmium pigments, developed countries have banned their use, leading to an increasing adoption of bismuth vanadate as a substitute for yellow pigments in industry. Furthermore, bismuth vanadate possesses a typical layered structure, giving it good photocatalytic properties. In addition, bismuth vanadate can be used in ferroelastic materials, reversible thermochromic materials, electrode materials, and ion conductor materials. Currently, the main methods for preparing bismuth vanadate include hydrothermal synthesis, coprecipitation, solid-state synthesis, and ultrasonic chemical synthesis. Increasing research has revealed that the various application properties of bismuth vanadate are greatly influenced by its morphology and specific surface area. Therefore, effective methods for adjusting the morphology of bismuth vanadate and increasing its specific surface area are extremely important.

[0003] Hydrothermal and coprecipitation methods are the most common and simplest methods for preparing bismuth vanadate. However, most of the methods developed in the past have used organic template agents (such as CATB) or added organic surfactants (such as PVP or P123), or directly used organic solvents (such as ethylene glycol, glycerol, etc.) as the reaction substrate to obtain bismuth vanadate with specific morphologies. These methods involve toxic chemicals and are inconvenient in operation; or, due to the nature of the preparation method, they cannot remove organic substances, thus compromising product purity. Therefore, a simple, easily replicable, and controllable method for preparing bismuth vanadate with specific morphologies is needed in both laboratory and industrial production. Summary of the Invention

[0004] To address the technical problem of requiring organic templates or organic surfactants to prepare bismuth vanadate with special morphologies in existing technologies, this invention provides a method for preparing nano-bismuth vanadate with different morphologies and large specific surface areas by controlling the pH value of the reaction system. Furthermore, the prepared bismuth vanadate exhibits peroxidase-like activity and can be used to detect melamine in solution.

[0005] The technical solution adopted in this invention is as follows:

[0006] A nano-bismuth vanadate is prepared using the following steps:

[0007] Step 1: Dissolve bismuth nitrate pentahydrate in water to obtain an aqueous solution of bismuth nitrate. Under heating and stirring conditions, add an equal volume of nitric acid solution dropwise to obtain a transparent and clear aqueous solution of bismuth nitrate.

[0008] Step 2: Dissolve ammonium metavanadate in water to obtain an aqueous solution of ammonium metavanadate. Under ultrasonic conditions, add an equal volume of sodium hydroxide solution to the solution to obtain a transparent and clear aqueous solution of ammonium metavanadate.

[0009] Step 3: Under heating and stirring conditions, add the aqueous solution of ammonium metavanadate to the aqueous solution of bismuth nitrate to obtain a suspension of bismuth vanadate precursor.

[0010] Step 4: Adjust the pH of the bismuth vanadate suspension from Step 3 to 5-7, 7-8, or 8-10, and then transfer it to a hydrothermal reactor for reaction. The reaction product is then vacuum filtered, washed, centrifuged, and dried to obtain bismuth vanadate with different morphologies.

[0011] Furthermore, in step 1, the ratio of bismuth nitrate pentahydrate to water is 3-5 g: 50 mL, the concentration of nitric acid solution is 0.01 mol / L, and the heating and stirring conditions are 60-80℃ and 300-800 rpm.

[0012] Furthermore, in step 2, the ratio of ammonium metavanadate to water is 0.6-1.5g:50mL, and the concentration of sodium hydroxide solution is 0.01mol / L.

[0013] Furthermore, in step 3, the volume ratio of ammonium metavanadate aqueous solution to bismuth nitrate aqueous solution is 1:1, and the heating and stirring conditions are 60-80℃ and 300-800rpm.

[0014] Furthermore, in step 4, sodium hydroxide solution is used to adjust the pH of the reaction system, and the concentration of the sodium hydroxide solution is 0.01 mol / L.

[0015] Furthermore, in step 3, the hydrothermal reaction temperature of the bismuth vanadate precursor suspension is 140-200℃, and the reaction time is 8-24h.

[0016] In one embodiment of the present invention, the prepared nano-bismuth vanadate has a specific surface area of ​​up to 240 m². 2 / g.

[0017] The aforementioned nano-bismuth vanadate exhibits peroxidase-like activity and can be used to detect melamine in solution.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention provides a method for preparing bismuth vanadate with different morphologies by controlling the pH value of the reaction system. This method allows for simple and effective control of the pH value of the reaction system using sodium hydroxide alkaline solution, enabling the preparation of nano-sized bismuth vanadate without the addition of other organic reagents. Specifically, when the pH value of the reaction system is weakly acidic (pH = 5.5), the product bismuth vanadate is composed of micron-sized spheres (2 μm in size, 40 m² in specific surface area) formed by the aggregation of small flakes. 2 / g); when the reaction system is neutral (pH=7.6), the product bismuth vanadate appears as dispersed fishbone-like particles with micropores on the surface (size 3μm, specific surface area 150m²). 2 / g); When the reaction system is weakly alkaline (pH=9), the product bismuth vanadate appears as a two-ended bouquet, composed of short, thin rods bonded together at the bottom (size 4μm, specific surface area 240m²). 2 / g).

[0020] The nano-bismuth vanadates with various morphologies (especially bouquet-like structures) prepared by this invention have the characteristics of narrow band gap (approximately 2.4 eV), strong and extensive visible light response, large specific surface area, and controllable morphology. They also exhibit peroxidase-like activity and can be used to detect melamine. Attached Figure Description

[0021] Figure 1 This is a scan of bismuth vanadate prepared at pH 5.5 in Example 1.

[0022] Figure 2 This is a scan of bismuth vanadate prepared at pH 7.6 in Example 2.

[0023] Figure 3 This is a scan of bismuth vanadate prepared at pH 9 in Example 3.

[0024] Figure 4 The image shows the XRD pattern of bismuth vanadate prepared in Example 3.

[0025] Figure 5 The image shows the ultraviolet-diffuse reflectance spectrum of the bismuth vanadate prepared in Example 3.

[0026] Figure 6 This is a morphological scan of bismuth vanadate prepared at pH 4 in Comparative Example 1.

[0027] Figure 7 This is a morphological scan of bismuth vanadate prepared at pH 12 in Comparative Example 2.

[0028] Figure 8 This is a photograph of the bismuth vanadate peroxidase activity prepared in Example 3.

[0029] Figure 9 Comparison photos of the bismuth vanadate sample prepared in Example 3 for detecting melamine and the blank sample. Detailed Implementation

[0030] This invention provides a method for preparing nano-bismuth vanadate with different morphologies and their applications by controlling the pH value of the reaction system, comprising the following steps:

[0031] Step S1: Prepare a transparent and clear aqueous solution of bismuth nitrate with uniform dispersion.

[0032] S1-1, Bismuth nitrate pentahydrate is dissolved in pure water to form solution a, and nitric acid is dissolved in pure water to form solution b; wherein the mass of bismuth nitrate pentahydrate is 3-5g, the volume of pure water is 50mL, and the concentration of solution b is 0.01mol / L;

[0033] S1-2, under heating and stirring, solution b is added dropwise to solution a, wherein the heating temperature of the water bath or oil bath is 60-80℃ and the stirring rate is 300-800rpm, to obtain a transparent and clear bismuth nitrate aqueous solution;

[0034] Step S2: Prepare a transparent and clear aqueous solution of ammonium metavanadate with uniform dispersion.

[0035] S2-1, ammonium metavanadate is dissolved in pure water to form solution c, and sodium hydroxide is dissolved in pure water to form solution d; wherein the mass of ammonium metavanadate is 0.6-1.5g, the volume of pure water is 50mL, and the concentration of solution d is 0.01mol / L;

[0036] S2-2, under ultrasonic conditions, solution d is added dropwise to solution c to obtain a transparent and clear aqueous solution of ammonium metavanadate;

[0037] Step S3: Add the aqueous solution of ammonium metavanadate to the aqueous solution of bismuth nitrate to obtain a suspension of bismuth vanadate precursor; wherein the solution is added dropwise under the conditions of heating at 60-80℃ and stirring at 300-800rpm.

[0038] Step S4: Adjust the pH of the reaction system with 0.01 mol / L sodium hydroxide solution; wherein, the pH of the reaction system can be adjusted to 5-7, 7-8, or 8-10;

[0039] Step S5: Transfer the reaction solution to a hydrothermal reactor for hydrothermal reaction; wherein the temperature of the hydrothermal reaction is 140-200℃ and the reaction time is at least 8 hours.

[0040] Step S6: Vacuum filter the obtained product and wash it several times with pure water and anhydrous ethanol, respectively, and centrifuge.

[0041] Step S7: Place the washed product in a vacuum oven to dry.

[0042] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0044] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0045] Examples 1-3

[0046] Step S1: Dissolve 5g of bismuth nitrate pentahydrate in 50mL of purified water to form solution a. Prepare 50mL of 0.01mol / L nitric acid solution as solution b. Add solution b to solution a in a 60℃ water bath with stirring. After addition, the solution slowly becomes clear and transparent. Continue stirring for 5 minutes to obtain a uniformly dispersed bismuth nitrate aqueous solution.

[0047] Step S2: Take 1g of ammonium metavanadate and add it to 50mL of purified water to form a suspension c. Separately prepare 50mL of sodium hydroxide solution d with a concentration of 0.01mol / L. Under ultrasonic conditions, slowly add solution d to solution c until the solution is completely transparent and clear, and obtain an aqueous solution of ammonium metavanadate that is evenly dispersed.

[0048] Step S3: Continue to add ammonium metavanadate aqueous solution dropwise to bismuth nitrate aqueous solution under the conditions of 60°C water bath and stirring.

[0049] In step S4, the pH of the reaction solution was adjusted to 5.5 (Example 1), 7.6 (Example 2), and 9 (Example 3) respectively using 0.01 mol / L sodium hydroxide solution, and a pale yellow reaction solution was obtained in all cases.

[0050] Step S5: Transfer the reaction solution to a hydrothermal reactor, set the temperature to 160℃, and perform a hydrothermal reaction for 8 hours.

[0051] Step S6: After the reaction is complete and cooled, the product is filtered through a vacuum filter and washed several times by centrifugation with pure water and ethanol, respectively.

[0052] Step S7: Place the washed product in a vacuum oven to dry overnight, and then perform morphology inspection.

[0053] Figure 1 , 2Images 3 are SEM images of bismuth vanadate products in reaction systems with pH values ​​of 5.5, 7.6, and 9, respectively. As can be seen from the images, the morphology of bismuth vanadate products differs under different pH values ​​in the reaction systems.

[0054] Figure 4 The image shows the XRD pattern of bismuth vanadate prepared at pH 9. The characteristic diffraction peaks at 2θ of 18.7°, 28.9°, 30.5°, 34.5°, 35.2°, and 39.8° correspond to the crystal planes (110), (121), (040), (200), (002), and (211), respectively, which are consistent with the positions of the monoclinic bismuth vanadate diffraction peaks, proving that the synthesis of bismuth vanadate was successful.

[0055] Figure 5 The figure shows the ultraviolet-diffuse reflectance spectrum of the bismuth vanadate sample prepared at a reaction system pH of 9. As can be seen from the figure, strong light absorption occurs in both the ultraviolet and visible light regions, indicating that the sample is monoclinic scheelite type BiVO4, and also indicating that the sample has a good response to visible light.

[0056] Comparative Examples 1-2

[0057] The difference between this embodiment and embodiments 1-3 is that in step S4, the pH value of the reaction solution is adjusted to 4 (Comparative Example 1) and 12 (Comparative Example 2), while the other conditions are the same as in embodiments 1-3.

[0058] like Figure 6 As shown, when the pH of the reaction system is less than 5, bismuth vanadate consists of irregular clusters and lumps; as Figure 7 As shown, when the pH of the reaction system is greater than 10, the reaction product bismuth vanadate can be rod-shaped or plate-shaped.

[0059] As can be seen from the test results in Table 1, the BET results of Comparative Examples 1 and 2 are significantly lower than those of Examples 1-3. This is mainly due to the morphology of Comparative Examples 1 and 2, which also results in fewer active sites compared to Examples 1-3, thus affecting their activity.

[0060] Table 1 BET Detection Results

[0061] Example 1 5.5 40 Example 2 7.6 150 Example 3 9 240 Comparative Example 1 4 21 Comparative Example 2 12 13

[0062] The results above show that the bismuth vanadate product has good morphology and a large specific surface area under the neutral to slightly alkaline pH reaction system of this invention.

[0063] Example 4

[0064] Determination of peroxidase activity

[0065] Step S1: Prepare 100 mL of acetate-sodium acetate buffer solution (pH 5) and store it in a 4°C refrigerator for later use;

[0066] Step S2, H2O2 solution preparation: Dilute with 30% H2O2 solution to prepare 100mL of 1.5% H2O2 solution, and store in a sealed container at 4℃.

[0067] Step S3, TMB colorimetric solvent preparation: Dissolve 0.1g TMB in a small amount of DMSO and bring the volume up to 100mL. Store in a sealed container at room temperature, protected from light. Prepare and use immediately.

[0068] Step S4: Weigh 10 mg of the bismuth vanadate sample prepared in Example 3;

[0069] Step S5: Prepare two beakers, A and B, and add 3 mL of pH 5 buffer solution, 2 mL of H2O2 solution, and 1 mL of TMB solvent to each beaker. Continue to add the bismuth vanadate sample prepared in step S4 to beaker A, and add the blank sample to beaker B. After sonicating at 700 W for 10 min, disperse the sample and wait for the reaction to proceed for 10 min. Observe the color change.

[0070] Figure 8 Image a shows the color of the solution after adding the bismuth vanadate prepared in Example 3. Figure 8 Photob is a blank sample solution. As can be seen from the photo, the solution turns blue after the addition of bismuth vanadate, and the color is darker than that of the blank sample, indicating that the bismuth vanadate prepared in Example 3 has peroxidase activity.

[0071] Example 5

[0072] Step S1: Prepare 100 mL of acetate-sodium acetate buffer solution (pH 5) and store it in a 4°C refrigerator for later use;

[0073] Step S2, H2O2 solution preparation: Dilute with 30% H2O2 solution to prepare 100mL of 1.5% H2O2 solution, and store in a sealed container at 4℃.

[0074] Step S3, TMB colorimetric solvent preparation: Dissolve 0.1g TMB in a small amount of DMSO and bring the volume up to 100mL. Store in a sealed container at room temperature, protected from light. Prepare and use immediately.

[0075] Step S4: Mix 30 mg of the bismuth vanadate sample prepared in Example 3, 50 mL of pH 5 buffer solution, 30 mL of H2O2 solution, 15 mL of TMB solvent, and 10 mL of 6 mM melamine aqueous solution. Incubate the mixture at 45°C for 20 min, then store it in an ice-water bath for 10 min to completely stop the reaction. The preparation of the control sample remained unchanged except that 10 mL of purified water was used instead of the melamine aqueous solution.

[0076] like Figure 9 As shown, after the reaction was completed, the color of the solution with added melamine gradually changed from blue to colorless, while the color of the control group without added melamine remained blue. Therefore, the presence of melamine in the test solution can be determined based on the color change. If the color remains unchanged, it means there is no melamine; if the color becomes significantly lighter, it means there is melamine.

[0077] The above embodiments are merely preferred examples of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. Use of nanosized bismuth vanadate for the detection of melamine, characterized in that, The nano-bismuth vanadate is prepared by the following steps: Step S1: Dissolve 5g of bismuth nitrate pentahydrate in 50mL of purified water to form solution a, and prepare 50mL of 0.01mol / L nitric acid solution as solution b. Add solution b to solution a in a water bath at 60℃ with stirring to obtain a uniformly dispersed bismuth nitrate aqueous solution. Step S2: Take 1g of ammonium metavanadate and add it to 50mL of purified water to form a suspension c. Prepare another 50mL of sodium hydroxide solution d with a concentration of 0.01mol / L. Under ultrasonic conditions, slowly add solution d to solution c to obtain a uniformly dispersed aqueous solution of ammonium metavanadate. Step S3: Continue to add ammonium metavanadate aqueous solution dropwise to bismuth nitrate aqueous solution under the conditions of 60°C water bath and stirring; Step S4: Adjust the pH of the reaction solution to 9 with 0.01 mol / L sodium hydroxide solution to obtain a pale yellow reaction solution; Step S5: Transfer the reaction solution to a hydrothermal reactor, set the temperature to 160℃, and perform the hydrothermal reaction for 8 hours. Step S6: After the reaction is completed and cooled, the product obtained is filtered through a vacuum filter and washed several times by centrifugation with pure water and ethanol, respectively. Step S7: Place the washed product in a vacuum oven to dry, and obtain the nano-bismuth vanadate; The application process is as follows: Mix 30 mg of bismuth vanadate, 50 mL of pH 5 acetic acid-sodium acetate buffer solution, 30 mL of 1.5% H2O2 solution, 15 mL of 0.1% TMB solution and the sample to be tested. Then incubate the mixture at 45°C for 20 min, and then keep it in an ice-water bath for 10 min to completely stop the reaction. The presence of melamine in the test solution is determined by the color change. If the color does not change, it means that there is no melamine. If the color becomes significantly lighter, it means that there is melamine.

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