Bismuth tungstate nanosheet as well as preparation method and application thereof
The synergistic effect of microwave heating and ionic liquids is synergistically synergistically, which solves the problems of high temperature, high pressure and large particle size in traditional methods, and achieves high-efficiency and low-energy consumption nanosheet preparation, improving photocatalytic performance.
Patent Information
- Application Number
- CN202510547355.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-28
- Publication Date
- 2025-08-15
AI Technical Summary
The traditional preparation method of bismuth tungstate has problems such as high temperature and high pressure and long time, and has large particle size and low specific surface area, resulting in the failure to fully utilize the photocatalytic efficiency.
Microwave heating is used to synergize bismuth tungstate nanosheets through template effect, and microwave heating is used to provide heat energy quickly and evenly, and the ionic liquid promotes uniform dispersion of reactants and nanosheet growth.
Synthesis of bismuth tungstate nanosheets with a thickness of 8-10 nm under low temperature and short-term conditions improves the separation efficiency of specific surface area and photogenerated carriers, significantly improves photocatalytic performance, simplifies the synthesis process and reduces energy consumption.
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Figure CN120483254A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of photocatalytic materials and relates to a bismuth tungstate nanosheet and a preparation method and application thereof. Background Art
[0002] With global environmental pollution becoming increasingly severe, particularly water and air pollution, the efficient and environmentally friendly removal of harmful substances from water and air has become a key research topic in environmental science and engineering. Among the numerous environmental protection and pollution remediation technologies, photocatalysis, due to its non-toxic, environmentally friendly, and renewable advantages, has become a highly sought-after solution in recent years.
[0003] Bismuth tungstate (Bi2WO6) is a tungstate semiconductor with good photocatalytic activity. Due to its wide light absorption range (especially in the visible light region), it has important applications in the fields of pollutant degradation and energy conversion. It can not only degrade organic pollutants in water, such as dyes and pesticide residues, but also effectively remove heavy metal ions in water, showing relatively excellent photocatalytic performance. However, despite the huge potential of Bi2WO6 in the field of photocatalysis, its traditional preparation methods (such as solution method, hydrothermal method, etc.) still face some problems. For example, there are difficulties such as high temperature, high pressure, and long time in the synthesis process, and the prepared Bi2WO6 particles are usually large in particle size and low in specific surface area, resulting in its photocatalytic efficiency not being fully utilized. In order to overcome these problems, developing a new efficient preparation method for Bi2WO6 and optimizing its structure have become a key to improving the photocatalytic performance of Bi2WO6. Summary of the Invention
[0004] The present invention provides a bismuth tungstate nanosheet and a preparation method and application thereof, which can effectively solve the above problems.
[0005] The present invention is achieved in that:
[0006] In one aspect, the present invention provides a method for preparing bismuth tungstate nanosheets, comprising:
[0007] (1) Precursor preparation: Dissolve Bi(NO3)3·5H2O in a certain amount of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) ionic liquid and stir at 50-70°C until dissolved;
[0008] (2) Introduction of tungsten source: Na2WO4·2H2O was dissolved in deionized water and added dropwise to the solution in step (1), followed by addition of polyvinyl pyrrolidone;
[0009] (3) Microwave reaction: Adjust the pH to acidic with dilute HNO3, transfer to microwave reactor, and react under microwave irradiation at 100-150°C;
[0010] (4) Post-treatment: centrifugal washing with ethanol and vacuum drying.
[0011] On the other hand, the present invention provides a bismuth tungstate nanosheet prepared by the above preparation method.
[0012] In another aspect, the present invention provides use of the above-mentioned bismuth tungstate nanosheets in a photocatalytic reaction.
[0013] The beneficial effects of the present invention are:
[0014] The present invention provides a method for preparing bismuth tungstate nanosheets. This method utilizes the synergistic effect of microwave heating and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) ionic liquid. During microwave heating, the ionic liquid, acting as a solvent, not only facilitates uniform dispersion of the reactants but also guides the layered growth of Bi2WO6 through a template effect (formed jointly by the ionic liquid and polyvinylpyrrolidone), optimizing the thickness and morphology of the nanosheets. Microwave heating rapidly and uniformly provides thermal energy, increasing the reaction rate and promoting the conversion of the reactants. The synergistic effect facilitates the synthesis of Bi2WO6 nanosheets with excellent photocatalytic properties under low-temperature, short-time reaction conditions.
[0015] Furthermore, the method has a simple and intuitive reaction process and does not require complex equipment and tedious post-processing steps. The synthesis can be completed in only 30 minutes at a low temperature of 120°C. Compared with traditional methods, the synthesis process is simplified, the experimental operation difficulty is reduced, the synthesis time is greatly shortened, the energy consumption is reduced, and it has high economy and operability, making it suitable for large-scale production.
[0016] Furthermore, the Bi2WO6 nanosheets prepared by the method have a thickness of 8-10 nm, and the structure not only increases the specific surface area, but also significantly improves the separation efficiency of photogenerated carriers, providing more active sites for photocatalytic reactions. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.
[0018] Figure 1 This is a physical picture of the Bi2WO6 nanosheets prepared in Example 2 of the present invention.
[0019] Figure 2 This is the SEM spectrum of the Bi2WO6 nanosheets prepared in Example 2 of the present invention.
[0020] Figure 3 This is the XRD spectrum of the Bi2WO6 nanosheets prepared in Example 2 of the present invention.
[0021] Figure 4 This is the light response diagram of the Bi2WO6 nanosheets prepared in Example 2 of the present invention. DETAILED DESCRIPTION
[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.
[0023] An embodiment of the present invention provides a method for preparing bismuth tungstate nanosheets, comprising:
[0024] (1) Precursor preparation: Dissolve Bi(NO3)3·5H2O in a certain amount of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) ionic liquid and stir at 50-70°C until dissolved;
[0025] (2) Introduction of tungsten source: Na2WO4·2H2O was dissolved in deionized water and added dropwise to the solution in step (1), followed by addition of polyvinylpyrrolidone (PVP);
[0026] (3) Microwave reaction: Adjust the pH to acidic with dilute HNO3, transfer to microwave reactor, and react under microwave irradiation at 100-150°C;
[0027] (4) Post-treatment: centrifugal washing with ethanol and vacuum drying.
[0028] Dissolving at 50-70°C can significantly improve the solubility of the bismuth salt and increase the fluidity of the ionic liquid, thereby promoting the uniform dispersion of the bismuth salt, ensuring the uniformity of the solution, providing a stable reaction environment for subsequent reactions, and avoiding excessive local concentration leading to agglomeration of nanosheets or increased thickness.
[0029] The present invention uses Bi(NO3)3·5H2O because Bi(NO3)3·5H2O has a high solubility in ionic liquids and is not easily decomposed. In the synthesis process of Bi2WO6 nanomaterials, ionic liquids can not only provide a good dissolution environment, but also serve as a template to guide the growth of the material and regulate its size and morphology. Ionic liquids can act as templates in the synthesis process of nanomaterials to regulate the growth direction and morphology of nanomaterials. Ionic liquids can be adsorbed on the surface of nanoparticles to prevent their agglomeration, and through charge and spatial stabilization, they promote the orderly assembly of nanoparticles and increase the specific surface area of the material. The cations and anions in the ionic liquid can undergo electrostatic or chemical interactions with the reactants or the growing nanomaterial grains, changing their surface energy and growth dynamics, thereby achieving precise control of the growth direction and thickness of the nanomaterial.
[0030] As a further improvement, in some embodiments, the step of dissolving Bi(NO3)3·5H2O in a certain amount of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and stirring at 50-70°C until dissolved comprises:
[0031] The Bi(NO₃)₃·5H₂O and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid are used in a ratio of 1 mmol: 5-20 mL and stirred at 55-65°C until dissolved. The ionic liquid's interionic interactions and hydrogen bonding vary at different concentrations, affecting its templating effect. By adjusting the amount of ionic liquid in the reaction system, its templating effect can be further optimized. More preferably, the Bi(NO₃)₃·5H₂O and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid ratio is approximately 1 mmol: 10 mL, and stirred at 60°C until dissolved.
[0032] As a further improvement, the molar ratio of Bi(NO3)3·5H2O to Na2WO4·2H2O is 1:0.1~1.
[0033] As a further improvement, the ratio of Bi(NO₃)₃·5H₂O to polyvinylpyrrolidone is: 1 mmol: 0.1 g to 0.5 g. Polyvinylpyrrolidone is a nonionic surfactant whose molecular structure consists of a hydrophilic pyrrolidone moiety and a hydrophobic alkyl moiety. This amphiphilic nature enables it to adsorb on the surface of nanoparticles, where it prevents nanoparticle aggregation through the steric hindrance effect generated by the hydrophobic carbon chain, thereby stabilizing the nanostructure. Furthermore, by adsorbing on the crystal surface, PVP selectively inhibits the growth of certain crystal faces, further enhancing the template effect of the ionic liquid and ensuring the formation of nanosheets.
[0034] Compared with traditional heat source heating methods, microwave heating has more significant advantages. Microwave radiation can directly act on the molecules or atoms of the material, which greatly increases the reaction rate and makes the temperature distribution of the reaction process more uniform, which helps to achieve rapid and uniform synthesis of the material. Microwave heating can effectively shorten the synthesis time while avoiding the high temperature and high pressure problems common in traditional methods. The fast and uniform heating characteristics of microwave heating are particularly important for the synthesis of Bi2WO6 nanomaterials. Microwave heating can reduce the problems of overreaction and particle aggregation, thereby obtaining Bi2WO6 nanomaterials with smaller particle size and larger specific surface area.
[0035] Therefore, microwave-assisted synthesis can not only improve the reaction efficiency, but also optimize the crystal structure of the material and further enhance its photocatalytic performance.
[0036] Microwave heating can quickly and evenly heat the reaction system. Preferably, the reaction can be promoted at a relatively low temperature of 100-150°C, achieving the effect of traditional high-temperature methods without the need for higher temperatures. More preferably, the microwave radiation reaction is carried out at 110-120°C for 30-40 minutes. The method is synthesized at a relatively low temperature, which can reduce energy consumption while avoiding the occurrence of side reactions and excessive grain growth or structural damage caused by high temperatures. Lower synthesis temperatures help to form thinner nanosheets and avoid excessive crystal growth at high temperatures that leads to increased thickness. If the temperature is too high, the ordered structure of the ionic liquid may be destroyed, thereby losing its guiding effect on the layered growth of Bi2WO6, resulting in uncontrolled material morphology.
[0037] In some embodiments, placing the reaction solution in a microwave reactor comprises:
[0038] Adjust the pH to 2.5-3.5 with dilute HNO3.
[0039] Under acidic conditions, ionic liquids and PVP can better play their role as templates and surfactants, guiding the growth of nanosheets along specific crystal planes to form structures. If the pH is too high or too low, it may cause particle agglomeration or irregular morphology.
[0040] Under acidic pH, the electrostatic interaction between the cations of the ionic liquid, such as the imidazole group of BMIMBF4, and the bismuth ions is enhanced, precisely guiding the growth of Bi2WO6 along specific crystal planes to form a nanosheet structure.
[0041] PVP is adsorbed on the crystal surface under acidic conditions, selectively inhibiting the growth of certain crystal faces and further promoting the formation of the structure.
[0042] In some embodiments, the power of the microwave reactor is 200-400W.
[0043] Microwave heating at this power can avoid local overheating, ensure that the reaction system heats up quickly and evenly, and synthesize at the preset reaction temperature, avoiding agglomeration or grain coarsening of Bi2WO6 due to high temperature.
[0044] The present invention further discloses a bismuth tungstate nanosheet prepared by the above-mentioned preparation method. The thickness of the bismuth tungstate nanosheet is 8-10 nm.
[0045] The embodiment of the present invention further discloses an application of the bismuth tungstate nanosheets in a photocatalytic reaction.
[0046] The instrument used in the present invention is as follows:
[0047] (1) X-ray diffractometer (XRD) uses German Bruker D8 ADVANCE wide-angle X-ray diffractometer with Cu target. Scanning range 0-10°.
[0048] (2) The scanning electron microscope (SEM) used was JEM2100PLUS (Jeolus).
[0049] (3) The electrochemical workstation used was Chenhua CHI760E.
[0050] The chemical reagents used in the present invention were purchased from Sinopharm Chemical Reagent Co., Ltd.
[0051] Example 1
[0052] (1) Precursor preparation: Dissolve 1 mmol of Bi(NO3)3·5H2O in 5 mL of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and stir at 60°C until transparent;
[0053] (2) Introduction of tungsten source: 0.5 mmol Na2WO4·2H2O was dissolved in 10 mL deionized water and added dropwise to the above solution, followed by the addition of 0.2 g polyvinylpyrrolidone (PVP);
[0054] (3) Microwave reaction: Adjust the pH to 3 with dilute HNO3, transfer to a microwave reactor, and irradiate with microwaves (320W) at 120°C for 30 min;
[0055] (4) Post-treatment: Wash with ethanol by centrifugation 5 times, and vacuum dry at 60℃ for 6h. The actual photo is as follows Figure 1 shown.
[0056] Example 2-4:
[0057] Example 2-4 is basically the same as Example 1, except that: in step (1) of Example 2-4, 10 mL [BMIM] BF4 ionic liquid, 15 mL [BMIM] BF4 ionic liquid and 20 mL [BMIM] BF4 ionic liquid were used respectively.
[0058] Comparative Example 1-2:
[0059] Comparative Example 1-2 is substantially the same as Example 1, except that in step (1) of Comparative Example 1-2, 1 mL [BMIM] BF4 ionic liquid and 25 mL [BMIM] BF4 ionic liquid were used, respectively.
[0060] Images of the Bi2WO6 nanosheet samples prepared in Examples 1-4 were taken, and their thicknesses were all around 8-10 nm. However, images of the sample prepared in Comparative Example 1 showed that its thickness distribution was uneven and agglomerated, with a thickness between 20 and 40 nm. Images of the sample prepared in Comparative Example 2 also showed that its thickness distribution was uneven, with a thickness between 10 and 20 nm.
[0061] Furthermore, the experimental results of the samples in Example 2 are analyzed as follows:
[0062] The actual picture of the Bi2WO6 nanosheet sample prepared in Example 2 is as follows Figure 1 shown.
[0063] Figure 2 Shown is an SEM image of the Bi2WO6 nanosheet sample obtained in Example 2. It can be seen from the figure that the sample has a typical nanosheet morphology, with the long side size of the nanosheet being about 50-70nm and the thickness being 8-10nm. This is attributed to the combined effects of ionic liquid solvent, pH adjustment, microwave heating power, surface regulation of PVP, suitable reaction temperature and time, etc., which control the growth rate, morphology and size of the bismuth tungstate nanosheets, so that the final product forms a structure with a typical two-dimensional nanosheet. The nanosheet structure indicates that the material has a large specific surface area and can effectively provide more reaction sites, thereby improving its catalytic activity in the photocatalytic reaction. The thinner sheet structure helps to reduce the recombination of photogenerated electrons and holes and promote the effective separation and migration of photogenerated carriers, which is crucial to improving the photocatalytic performance of the material.
[0064] In addition, the nanosheets have a flat surface that facilitates the adsorption of pollutants or reactants, further enhancing their efficiency in photocatalytic reactions. Overall, the optimized morphology of the material is conducive to improving the selectivity and stability of photocatalytic reactions.
[0065] Figure 3 This is the XRD spectrum of the Bi2WO6 nanosheet sample prepared in Example 2.
[0066] Results showed that the diffraction peaks of the synthesized Bi2WO6 material closely matched those of a standard card (PDF#26-1044), demonstrating typical cubic crystal structure characteristics and confirming the sample's crystal structure and high crystallinity. The XRD pattern lacked significant impurity peaks, indicating high purity and perfect crystallization of the target product, with no significant impurities or byproducts. The concentrated distribution of diffraction peaks and narrow half-height width indicate the material's large grain size and excellent crystallinity, enabling stable photocatalytic performance.
[0067] Combined with the position and intensity analysis of the diffraction peak, the lattice constant and structural stability of the Bi2WO6 material were further confirmed, which provides a favorable physical basis for its subsequent application in photocatalytic reactions.
[0068] Example 5
[0069] 10 mg of the Bi2WO6 nanosheet sample prepared in Example 2 was dissolved in 1 mL of ethanol and ultrasonicated for 1 h. The completely ultrasonically dispersed solution was dropped onto a 1 cm×3 cm FTO sheet to prepare an FTO photoelectrode as the anode.
[0070] Use 300W xenon lamp (PLS-SXE300C, wavelength range: 420nm≤λ≤780nm, light intensity: 300mW / cm 2 ) as the light source, using 0.5M Na2SO4 electrolyte, a three-electrode system, a Pt sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The test was conducted at a voltage of 0.7V vs.Ag / AgCl for 120s, with the light source blocked at intervals of 10s to determine the material's photoresponse and to test the sample's photoresponse current.
[0071] The results are as follows Figure 4 As shown, the photocurrent value is 0.37mA / cm 2 , reflecting the charge separation and transport capabilities of the material under light conditions. The existence of photocurrent indicates that the material can effectively respond to light and generate photogenerated carriers, and has a certain photogenerated charge separation efficiency. The amplitude of the photocurrent is relatively moderate, indicating that the migration and transport process of photogenerated carriers in the material is relatively efficient. A higher photocurrent value usually indicates a lower electron-hole recombination rate, which is crucial to the reaction rate of the photocatalytic reaction. This result shows that the Bi2WO6 nanosheets prepared in the embodiment of the present invention have strong photocatalytic activity, and can effectively promote electron transfer under ultraviolet or visible light irradiation, thereby enhancing the photocatalytic effect.
[0072] In summary, XRD characterization of the Bi2WO6 nanosheets prepared in this embodiment of the present invention confirmed that the material has high purity and excellent crystal structure. SEM images show that the nanosheet morphology of the material has a high specific surface area and excellent electron separation properties. The photoresponse diagram reveals that the material has strong photocatalytic activity. These characterization results collectively demonstrate the potential of this material as a photocatalytic material and provide strong support for its application in fields such as photocatalysis, environmental pollution control, and energy conversion.
[0073] The method described in the embodiment of the present invention is based on the synergistic effect of microwave heating and ionic liquid, which can achieve more efficient and low-energy synthesis of Bi2WO6 nanosheets. During the microwave heating process, the ionic liquid as a solvent not only helps to uniformly disperse the reactants, but also can guide the growth direction of the material through the template effect. Microwave heating can increase the reaction rate and promote the conversion of the reactants by rapid heating. The interaction between the two helps to synthesize Bi2WO6 nanosheets with excellent photocatalytic performance under low temperature and short reaction conditions. The thickness of the Bi2WO6 nanosheets can be controlled at 8-10nm. The structural optimization of the Bi2WO6 nanosheets greatly increases the specific surface area of the material and significantly improves the separation efficiency of photogenerated carriers, thereby improving the photocatalytic performance. Compared with traditional methods, this synthesis method not only has lower energy consumption and operation difficulty, but also improves the quality and performance of the product, showing great application potential.
[0074] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.
Claims
1. A method for preparing bismuth tungstate nanosheets, characterized in that: include: (1) Precursor preparation: Dissolve Bi(NO3)3·5H2O in a certain amount of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and stir at 50-70°C until dissolved; (2) Introduction of tungsten source: Na2WO4·2H2O was dissolved in deionized water and added dropwise to the solution in step (1), followed by addition of polyvinyl pyrrolidone; (3) Microwave reaction: Adjust the pH to acidic with dilute HNO3, transfer to microwave reactor, and react under microwave irradiation at 100-150°C; (4) Post-treatment: centrifugal washing with ethanol and vacuum drying.
2. The preparation method according to claim 1, wherein In step (1), Bi(NO3)3·5H2O is dissolved in a certain amount of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and stirred at 50-70°C until dissolved, comprising: The ratio of Bi(NO3)3·5H2O to 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid is 1 mmol:5-20 mL, and the mixture is stirred at 55-65°C until dissolved.
3. The preparation method according to claim 2, wherein The molar ratio of Bi(NO3)3·5H2O to Na2WO4·2H2O is 1:0.1~1.
4. The preparation method according to claim 3, wherein The ratio of Bi(NO3)3·5H2O to polyvinyl pyrrolidone is: 1mmol:0.1g~0.5g.
5. The preparation method according to claim 4, wherein The method comprises adjusting the pH to acidic with dilute HNO3, transferring the mixture into a microwave reactor, and subjecting the mixture to microwave radiation reaction at 100-150°C, specifically comprising: Adjust the pH to 2.5-3.5 with dilute HNO3, transfer to a microwave reactor, and react under microwave irradiation at 110-120°C for 30-40 minutes.
6. The preparation method according to claim 5, wherein The power of the microwave radiation reaction is 200-400W.
7. A bismuth tungstate nanosheet, wherein the bismuth tungstate nanosheet is prepared according to the preparation method according to any one of claims 1 to 6. The bismuth tungstate nanosheet according to claim 7 , wherein the thickness of the bismuth tungstate nanosheet is 8-10 nm.
9. Use of the bismuth tungstate nanosheets according to claim 7 in a photocatalytic reaction.