Preparation method and application of nanoflower-shaped bismuth tungstate copper oxide composite photocatalytic material

Abstract

The application discloses a preparation method and application of a nano-flower-shaped bismuth tungstate copper oxide composite photocatalytic material, and relates to the technical field of photocatalytic materials.The preparation method uses soluble tungstate and soluble bismuth salt as raw materials, and the nano-flower-shaped bismuth tungstate is prepared through hydrothermal reaction, centrifugal drying, mixing with soluble copper salt, hydrothermal reaction, separation of solid, calcination and cooling to room temperature, so as to obtain the nano-flower-shaped bismuth tungstate copper oxide composite photocatalytic material.The nano-flower-shaped bismuth tungstate copper oxide composite photocatalytic material prepared by the application is a gray powder, and has the advantages of simple preparation method, large specific surface area, small particle size, uniform dispersion, high photocatalytic activity and certain photocatalytic effect under visible light conditions.The photocatalytic composite material can be used for photocatalytic degradation of formaldehyde in air, and the degradation rate can reach 87%.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst preparation technology, specifically relating to a method for preparing and applying a nano-flower-shaped bismuth tungstate-copper oxide composite photocatalytic material. Background Technology

[0002] Formaldehyde is a common VOC, frequently used in the production of adhesives, paints, furniture, building materials, and home appliances. It easily volatilizes into indoor air. Long-term exposure to high concentrations of formaldehyde can harm human health, causing respiratory problems, eye irritation, and potential carcinogenic risks. Therefore, developing a simple, pollution-free gaseous formaldehyde degradation technology has broad prospects and a certain market potential.

[0003] Among the methods for purifying gaseous formaldehyde, there are physical or chemical adsorption methods, thermocatalytic oxidation methods, plasma technology, and photocatalytic technology. Physical and chemical adsorption methods are difficult to decompose under conditions where indoor furniture materials slowly release formaldehyde; they reach adsorption equilibrium after a period of time, making them unsuitable for formaldehyde degradation in indoor environments. Thermocatalytic oxidation and plasma technology are also unsuitable for indoor environments due to their operating conditions. Photocatalytic oxidation, however, can react at room temperature, producing carbon dioxide and water as oxidation products, which are non-toxic and harmless. It can also degrade pollutants at low concentrations, making it very suitable for indoor formaldehyde degradation.

[0004] Since Akira Fujishima and Honda first discovered the photocatalytic effect of TiO2 in 1972, various photocatalytic properties of TiO2 have become a hot research topic. As one of the most representative semiconductor photocatalytic materials, it has the advantages of being non-toxic, chemically stable, inexpensive, and having high photocatalytic and photoelectric performance.

[0005] However, TiO2 has a wide band gap (3.2 eV) and only responds under ultraviolet light, limiting its full utilization of sunlight. Therefore, research on photocatalysts under visible light conditions has gradually gained attention in recent years. Bismuth-based semiconductor materials, due to their unique electronic configuration, suitable band gap, and controllable surface structure, have become a popular material for novel visible-light-responsive semiconductors. The conduction band (CB) of Bi2WO6 is composed of W 5d orbitals, and the valence band (VB) is composed of hybridized O 2p and Bi 6p orbitals. This hybridization between orbitals results in a large number of dispersed valence bands, promoting the migration of photogenerated holes in the valence band and ultimately enhancing the photocatalytic performance of Bi2WO6. With a band gap of approximately 2.7 eV, it is a photocatalyst with a narrow band gap, thus exhibiting good performance in the visible light region. In addition to its photocatalytic performance, Bi2WO6 also possesses other desirable chemical and physical properties, including non-toxicity, good photoelectric stability, and ferroelectric voltage. Meanwhile, the surface of Bi2WO6 is loaded with a large number of hydrogen ions, which can increase the transfer efficiency of photogenerated electrons, holes and free radicals, thereby effectively increasing the adsorption and degradation efficiency of pollutants.

[0006] Bi2WO6 has been widely recognized as a novel photocatalyst with a narrow bandgap and visible light response, capable of absorbing visible light energy to degrade organic pollutants. However, Bi2WO6 itself still has many shortcomings: (1) Although it can absorb visible light, its absorption efficiency for visible light wavelengths greater than 450 nm is extremely poor due to the bandgap limitation; (2) It is difficult to reduce the recombination rate of photogenerated electrons and holes; (3) The surface has insufficient exposed reaction sites, limiting the adsorption and activation of reactants. Therefore, researchers at home and abroad have been continuously studying and exploring methods to modify Bi2WO6 photocatalysts, hoping to improve the photocatalytic activity of Bi2WO6 materials, and have made great progress. From a microscopic perspective, the main approaches and principles for modifying Bi2WO6 photocatalysts are: (1) broadening the spectral response range of the material through bandgap modulation measures; (2) promoting the migration and separation of electrons and holes in the material by forming a heterojunction structure through composite with other semiconductors; and (3) enhancing the adsorption and catalytic performance of the material by increasing the highly active exposed surface, thus promoting the separation of photoinduced charge carriers. Summary of the Invention

[0007] To address the problems of poor visible light absorption and high recombination rate of photogenerated electrons and holes in existing bismuth tungstate photocatalysts, the present invention aims to provide a method for preparing and applying a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material. The preparation method of this invention is simple and easy to operate. The prepared photocatalyst has a unique nano-flower-like morphology, a large specific surface area, and good adsorption properties. It forms a heterojunction with copper oxide, promoting the separation of photogenerated charges and exhibiting excellent photocatalytic activity.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material, comprising the following steps:

[0010] (1) Dissolve soluble tungstate in water to obtain solution A; dissolve soluble bismuth salt in a mixed solvent of water and acetic acid to obtain solution B; while stirring, add solution A dropwise to solution B and stir to mix to obtain the precursor solution;

[0011] (2) The precursor solution was subjected to a hydrothermal reaction. After the reaction was completed, the solid was separated by centrifugation, washed, dried, and ground to obtain nano-flower-shaped bismuth tungstate.

[0012] (3) Add nano-flower-shaped bismuth tungstate to a mixed solvent of ethanol and water, add soluble copper salt while stirring, stir, and sonicate; adjust the pH of the solution while stirring, let stand and carry out hydrothermal reaction, centrifuge to separate the solid after the reaction, wash, dry, grind and obtain bismuth tungstate copper oxide composite powder.

[0013] (4) The bismuth tungstate copper oxide composite powder was heated to 350-450℃ and calcined for 3-5 hours, and then cooled to room temperature to obtain nano-flower-shaped bismuth tungstate copper oxide composite photocatalytic material.

[0014] Furthermore, in step (1), the soluble tungstate is Na2WO4·2H2O; the soluble bismuth salt is Bi(NO3)3·5H2O;

[0015] Furthermore, in step (1), the volume ratio of water to acetic acid in the mixed solvent of water and acetic acid is 4:1 to 3:1;

[0016] Furthermore, in step (1), the concentration of soluble tungstate in solution A is 0.02 mol / L to 0.03 mol / L; and the concentration of soluble bismuth salt in solution B is 0.04 mol / L to 0.06 mol / L.

[0017] Furthermore, in step (1), the molar ratio of W element in solution A to Bi element in solution B is 1:6 to 1:5.

[0018] Furthermore, in step (2), the temperature of the hydrothermal reaction is 180℃~200℃, and the time is 2-4h;

[0019] Furthermore, in step (2), the washing is performed using anhydrous ethanol and deionized water.

[0020] Furthermore, in step (3), the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 1:1 to 1.5;

[0021] Furthermore, in step (3), the concentration of the nano-flower-shaped bismuth tungstate in the mixed solvent of ethanol and water is 2 g / L to 2.5 g / L;

[0022] Furthermore, in step (3), the soluble copper salt is Cu(CO2CH3)2·H2O;

[0023] Furthermore, in step (3), the stirring time is 30 min to 45 min;

[0024] Furthermore, in step (3), the ultrasound duration is 15 min to 30 min;

[0025] Furthermore, in step (3), Na2CO3 powder is added to adjust the pH of the solution;

[0026] Furthermore, in step (3), the settling time is 2h to 3h;

[0027] Furthermore, in step (3), the washing is performed using anhydrous ethanol and deionized water;

[0028] Furthermore, in step (3), the temperature of the hydrothermal reaction is 80℃~100℃ and the time is 10~12h.

[0029] Furthermore, in step (3), the amount of soluble copper salt added is 5% to 30% by mass ratio of CuO to nano-flower-shaped bismuth tungstate.

[0030] Preferably, in step (3), the amount of soluble copper salt added is 10% to 15% by mass ratio of CuO to nano-flower-shaped bismuth tungstate.

[0031] Furthermore, in step (3), the pH of the solution is adjusted to 10-11.

[0032] Furthermore, in step (4), the heating rate is 2 to 5 °C / min.

[0033] This invention provides a nano-flower-like bismuth tungstate copper oxide composite photocatalytic material, which is prepared by the above-described preparation method.

[0034] This invention provides an application of the above-mentioned nano-flower-shaped bismuth tungstate-copper oxide composite photocatalytic material in the photocatalytic degradation of gaseous formaldehyde.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. The bismuth tungstate prepared by this invention has a unique nano-flower-like morphology, which increases its specific surface area, improves its adsorption capacity for formaldehyde, and enhances the photocatalytic reaction sites.

[0037] 2. This invention enables bismuth tungstate and copper oxide to form a heterojunction, which promotes the separation efficiency of photogenerated charges, has good photocatalytic activity, and has a high degradation rate of formaldehyde.

[0038] 3. The present invention is simple to operate and has low cost. Attached Figure Description

[0039] Figure 1 The images show the XRD patterns of the nano-flower-shaped bismuth tungstate and copper oxide composite photocatalysts prepared in Examples 1-4, and the nano-flower-shaped bismuth tungstate and copper oxide in Comparative Example 1.

[0040] Figure 2 The images show SEM images of the nano-flower-like bismuth tungstate-copper oxide composite photocatalysts prepared in Examples 1-4.

[0041] Figure 3 The image shows a SEM image of the nano-flower-shaped bismuth tungstate prepared in Comparative Example 1.

[0042] Figure 4 The UV-Vis absorption spectra of the photocatalysts in Examples 1-4 and Comparative Example 1 are shown. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0044] Example 1

[0045] A method for preparing a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material includes the following steps:

[0046] (1) Dissolve 0.08 g Na₂WO₄·2H₂O in 10 mL of deionized water; this is solution A. Dissolve 0.72 g Bi(NO₃)₃·5H₂O in 30 mL of a mixed solvent of deionized water and acetic acid in a volume ratio of 4:1; this is solution B. The molar ratio of Na₂WO₄·2H₂O to Bi(NO₃)₃·5H₂O is 1:6. While stirring, slowly add solution A to solution B and mix thoroughly to obtain the precursor solution.

[0047] (2) The precursor solution was placed in a reaction vessel for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol and deionized water, dried, and ground to obtain nano-flower-shaped bismuth tungstate.

[0048] (3) Add 0.1g of nano-flower-shaped bismuth tungstate to a mixed solvent of 20mL anhydrous ethanol and 20mL deionized water, and add 0.016g of Cu(CO2CH3)2·H2O while stirring. Stir for 30min, sonicate for 10min, and then add Na2CO3 powder while stirring to adjust the pH of the solution to 10. After standing for 2h, place it in a reaction vessel for hydrothermal reaction at a temperature of 80℃ for 12h. After the reaction, centrifuge to separate the solid, wash it three times with anhydrous ethanol and deionized water respectively, dry it, and grind it to obtain bismuth tungstate copper oxide composite powder.

[0049] (4) The bismuth tungstate copper oxide composite powder is heated to 350℃ in a muffle furnace and calcined for 3h (heating rate is 2℃ / min), and then cooled to room temperature to obtain the product, which is called BWC-1.

[0050] Example 2

[0051] A method for preparing a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material includes the following steps:

[0052] (1) Dissolve 0.08g Na₂WO₄·2H₂O in 10mL of deionized water; this is solution A. Dissolve 0.72g Bi(NO₃)₃·5H₂O in 30mL of a mixed solvent of deionized water and acetic acid in a volume ratio of 4:1; this is solution B. The molar ratio of Na₂WO₄·2H₂O to Bi(NO₃)₃·5H₂O is 1:6. While stirring, slowly add solution A to solution B and mix thoroughly to obtain the precursor solution.

[0053] (2) The precursor solution was placed in a reaction vessel for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol and deionized water, dried, and ground to obtain nano-flower-shaped bismuth tungstate.

[0054] (3) Add 0.1g of nano-flower-shaped bismuth tungstate to a mixed solvent of 20mL anhydrous ethanol and 20mL deionized water, and add 0.031g of Cu(CO2CH3)2·H2O while stirring. Stir for 30min, sonicate for 10min, and then add Na2CO3 powder while stirring to adjust the pH of the solution to 10. After standing for 2h, place it in a reaction vessel for hydrothermal reaction at a temperature of 80℃ for 12h. After the reaction, centrifuge to separate the solid, wash it three times with anhydrous ethanol and deionized water respectively, dry it, and grind it to obtain bismuth tungstate copper oxide composite powder.

[0055] (4) The bismuth tungstate copper oxide composite powder is heated to 350℃ in a muffle furnace and calcined for 3h (heating rate is 2℃ / min), and then cooled to room temperature to obtain the product, which is called BWC-2.

[0056] Example 3

[0057] A method for preparing a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material includes the following steps:

[0058] (1) Dissolve 0.08g Na₂WO₄·2H₂O in 10mL of deionized water; this is solution A. Dissolve 0.72g Bi(NO₃)₃·5H₂O in 30mL of a mixed solvent of deionized water and acetic acid in a volume ratio of 4:1; this is solution B. The molar ratio of Na₂WO₄·2H₂O to Bi(NO₃)₃·5H₂O is 1:6. While stirring, slowly add solution A to solution B and mix thoroughly to obtain the precursor solution.

[0059] (2) The precursor solution was placed in a reaction vessel for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol and deionized water, dried, and ground to obtain nano-flower-shaped bismuth tungstate.

[0060] (3) Add 0.1g of nano-flower-shaped bismuth tungstate to a mixed solvent of 20mL anhydrous ethanol and 20mL deionized water, and add 0.058g of Cu(CO2CH3)2·H2O while stirring. Stir for 30min, sonicate for 10min, and then add Na2CO3 powder while stirring to adjust the pH of the solution to 10. After standing for 2h, place it in a reaction vessel for hydrothermal reaction at a temperature of 80℃ for 12h. After the reaction, centrifuge to separate the solid, wash it three times with anhydrous ethanol and deionized water respectively, dry it, and grind it to obtain bismuth tungstate copper oxide composite powder.

[0061] (4) The bismuth tungstate copper oxide composite powder is heated to 350℃ in a muffle furnace and calcined for 3h (heating rate is 2℃ / min), and then cooled to room temperature to obtain the product, which is called BWC-3.

[0062] Example 4

[0063] A method for preparing a nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material includes the following steps:

[0064] (1) Dissolve 0.08g Na₂WO₄·2H₂O in 10mL of deionized water; this is solution A. Dissolve 0.72g Bi(NO₃)₃·5H₂O in 30mL of a mixed solvent of deionized water and acetic acid in a volume ratio of 4:1; this is solution B. The molar ratio of Na₂WO₄·2H₂O to Bi(NO₃)₃·5H₂O is 1:6. While stirring, slowly add solution A to solution B and mix thoroughly to obtain the precursor solution.

[0065] (2) The precursor solution was placed in a reaction vessel for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol and deionized water, dried, and ground to obtain nano-flower-shaped bismuth tungstate.

[0066] (3) Add 0.1g of nano-flower-shaped bismuth tungstate to a mixed solvent of 20mL anhydrous ethanol and 20mL deionized water, and add 0.075g of Cu(CO2CH3)2·H2O while stirring. Stir for 30min, sonicate for 10min, and then add Na2CO3 powder while stirring to adjust the pH of the solution to 10. After standing for 2h, place it in a reaction vessel for hydrothermal reaction at a temperature of 80℃ for 12h. After the reaction, centrifuge to separate the solid, wash it three times with anhydrous ethanol and deionized water respectively, dry it, and grind it to obtain bismuth tungstate copper oxide composite powder.

[0067] (4) The bismuth tungstate copper oxide composite powder is heated to 350℃ in a muffle furnace for 3h (heating rate is 2℃ / min) and cooled to room temperature to obtain the product, which is called BWC-4.

[0068] Comparative Example 1

[0069] A method for preparing a nano-flower-like bismuth tungstate photocatalytic material includes the following steps:

[0070] (1) Dissolve 0.08 g Na₂WO₄·2H₂O in 10 mL of deionized water; this is solution A. Dissolve 0.72 g Bi(NO₃)₃·5H₂O in 30 mL of a mixed solvent of deionized water and acetic acid in a volume ratio of 4:1; this is solution B. The molar ratio of Na₂WO₄·2H₂O to Bi(NO₃)₃·5H₂O is 1:6. While stirring, slowly add solution A to solution B and mix thoroughly to obtain the precursor solution.

[0071] (2) The precursor solution was placed in a reaction vessel for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol and deionized water, dried, and ground to obtain nano-flower-shaped bismuth tungstate photocatalytic material, called BW.

[0072] Comparative Example 2

[0073] A method for preparing copper oxide material includes the following steps:

[0074] Add 0.1g Cu(CO2CH3)2·H2O to a mixed solvent of 20mL anhydrous ethanol and 20mL deionized water, stir for 30min, sonicate for 10min, and then add 0.04g Na2CO3 powder while stirring to adjust the pH of the solution to 10. After standing for 2h, place it in a reaction vessel for hydrothermal reaction at 80℃ for 12h. After the reaction, centrifuge to separate the solid, wash it three times with anhydrous ethanol and deionized water respectively, dry it, grind it, and calcine it in a muffle furnace at 350℃ for 3h (heating rate of 2℃ / min). Cool it to room temperature to obtain CuO.

[0075] 1. X-ray diffraction (XRD) test

[0076] The composition and crystal structure of the sample were determined using a Cu-target Kα radiation source on a Bruker D8 Advance. The test results are shown in [Figure number missing]. Figure 1 .

[0077] from Figure 1 The characteristic peaks of composite materials BWC1-4 and BW at 28°, 32° and 47°, 55° are observed. These peaks are attributed to the (131), (200), (202), and (133) crystal planes of Bi2WO6 (JCPDS standard card 39-0256). The peak at 32° coincides with the (110) crystal plane of CuO (JCPDS standard card 89-5896), resulting in a larger peak. Furthermore, the high CuO content in the BWC-4 composite material leads to characteristic peaks at 35° and 38°, which belong to the (002) and (111) crystal planes of CuO, confirming the successful composite material formation.

[0078] 2. Scanning electron microscopy (SEM) testing

[0079] The microstructure of the samples was observed using a scanning electron microscope (SU8220), and the results are shown in [Figure number missing]. Figure 2 and Figure 3 , Figure 2 The four sets of images from top to bottom are BWC1-4. Figure 3 For BW.

[0080] Depend on Figure 3 It is evident that the nanoflower-like bismuth tungstate photocatalyst BW has a nanoflower-like structure composed of nanosheets, possessing a high specific surface area. Figure 2 It can be seen that the nano-flower-shaped bismuth tungstate copper oxide composite photocatalyst BWC uses the nano-flower-shaped bismuth tungstate photocatalyst BW as the substrate, and copper oxide is attached to the surface of bismuth tungstate nanosheets in the form of rhombic nanorods. Among them, BWC-4 shows a scattering single-phase CuO with a special morphology, which is consistent with the XRD results.

[0081] 3. Photocatalytic formaldehyde degradation performance test

[0082] A nano-flower-shaped bismuth tungstate-copper oxide composite photocatalyst was used for the degradation of gaseous formaldehyde. The application method was as follows: 0.15g of the nano-flower-shaped bismuth tungstate-copper oxide composite photocatalyst was evenly distributed in a petri dish, placed in a Tedlar gas bag, and 3μL of formaldehyde solution was injected. 4L of fresh air was then introduced, and the gas bag was placed in a 60℃ oven for 20 minutes to ensure complete vaporization. The entire degradation process was first carried out under dark conditions for 1.5 hours of dark adsorption. A xenon lamp equipped with a 420nm cutoff filter was used for photocatalytic reaction. 5mL of gas was collected from the gas bag every 30 minutes, and the formaldehyde concentration was detected using phenol reagent spectrophotometry. The formaldehyde removal rate was calculated using the following formula, indicating the formaldehyde degradation performance of the reaction catalyst material.

[0083] Removal efficiency (%) = (C0-C) / C0×100%

[0084] Where C0 is the concentration of gaseous pollutants at adsorption equilibrium, in ppm; C is the concentration of gaseous pollutants at each sampling, in ppm. The test results are shown in Table 1.

[0085] As shown in Table 1, formaldehyde hardly degrades under blank conditions and under copper oxide only conditions. The formaldehyde degradation rate of BW nano-flower bismuth tungstate photocatalyst is only 28% after 5 hours of light irradiation. After being combined with copper oxide, the formaldehyde degradation rate is greatly improved. Among them, BWC-2 has the best effect, reaching 89%. BWC-3 may have a lower formaldehyde degradation rate than BWC-2 and BWC-4 because too much copper oxide is attached to its surface, which affects the adsorption of formaldehyde molecules on the surface of bismuth tungstate nanosheets.

[0086] Table 1

[0087]

[0088]

[0089] 4. Ultraviolet-vis diffuse reflectance spectra (UV-vis DRS) test

[0090] UV-Vis diffuse reflectance spectroscopy was used to measure the catalyst's absorption capacity for light in different wavelengths within the UV-Vis range, and its band gap was calculated accordingly. A Hitachi U-3900 spectrophotometer was used to characterize the sample's absorption of UV and visible light using UV-Vis diffuse reflectance spectroscopy (with BaSO4 as the reflectance standard). The test results are shown below. Figure 4 .

[0091] Depend on Figure 4 It is evident that compared to the nano-flower-shaped bismuth tungstate photocatalyst BW, the nano-flower-shaped bismuth tungstate-copper oxide composite photocatalyst BWC exhibits higher absorbance across the overall spectral band, indicating better photocatalytic activity. Furthermore, its longer cutoff wavelength signifies the absorption of more visible light. The combination of bismuth tungstate and copper oxide broadens the absorption spectrum and increases visible light utilization. The absorbance of BWC-3 in the ultraviolet band is slightly lower than that of BWC1-2, possibly due to excessive copper oxide on the bismuth tungstate surface obscuring the light source. However, BWC-4 forms a single-phase copper oxide, mitigating this problem. Figure 2 This can be verified.

[0092] Contents not described in detail in this specification are prior art known to those skilled in the art. Although specific embodiments of this invention have been described above, it should be understood that this invention is not limited to the scope of those embodiments. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of the claims.

Claims

1. A preparation method of a nanoflower-shaped bismuth copper oxide tungstate composite photocatalytic material, characterized in that, The method comprises the following steps: (1) dissolving a soluble tungstate in water to obtain solution A; dissolving a soluble bismuth salt in a mixed solvent of water and acetic acid to obtain solution B; under stirring, solution A is added dropwise into solution B, and the mixture is stirred to obtain a precursor solution; the soluble tungstate is Na2WO4·2H2O; the soluble bismuth salt is Bi(NO3)3·5H2O; the volume ratio of water to acetic acid in the mixed solvent of water and acetic acid is 4:1-3:1; the concentration of the soluble tungstate in solution A is 0.02-0.03 mol / L; the concentration of the soluble bismuth salt in solution B is 0.04-0.06 mol / L; the molar ratio of W in solution A to Bi in solution B is 1:6-1:5; (2) performing hydrothermal reaction on the precursor solution, centrifuging the solid obtained after the reaction, washing, drying, and grinding to obtain nano-flower-like bismuth tungstate; (3) adding the nano-flower-like bismuth tungstate into a mixed solvent of ethanol and water, adding a soluble copper salt under stirring, stirring, and ultrasonic treatment; adjusting the pH of the solution under stirring, standing, performing hydrothermal reaction, centrifuging the solid obtained after the reaction, washing, drying, and grinding to obtain bismuth tungstate / copper oxide composite powder; the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 1:1-1.5; the concentration of the nano-flower-like bismuth tungstate in the mixed solvent of ethanol and water is 2-2.5 g / L; the soluble copper salt is Cu(CO2CH3)2·H2O; the stirring time is 30-45 min; the ultrasonic treatment time is 10-30 min; the pH of the solution is adjusted by adding Na2CO3 powder; the standing time is 2-3 h; the washing is performed with anhydrous ethanol and deionized water; the hydrothermal reaction temperature is 80-100 ℃, and the time is 10-12 h; (4) calcining the bismuth tungstate / copper oxide composite powder at 350-450 ℃ for 3-5 h to obtain nano-flower-like bismuth tungstate / copper oxide composite photocatalytic material. 2.The method for preparing the nanoflower-like Bi2WO6 / Cu2O composite photocatalytic material according to claim 1, characterized in that, In step (2), the hydrothermal reaction temperature is 180-200 ℃, and the time is 2-4 h; In step (2), the washing is performed with anhydrous ethanol and deionized water.

3. The preparation method of the nano-flower-like bismuth tungstate-copper oxide composite photocatalytic material according to claim 1, characterized in that, In step (3), the mass ratio of the soluble copper salt (calculated as CuO) to the nano-flower-like bismuth tungstate is 10%-15%; In step (3), the pH of the solution is adjusted to 10-11. 4.The method for preparing the nanoflower-like Bi2WO6 / Cu2O composite photocatalytic material according to claim 1, characterized in that, In step (4), the heating rate is 2-5 ℃ / min.

5. Nano-flower-like bismuth tungstate / copper oxide composite photocatalytic material prepared by the method of any one of claims 1-4.

6. Application of the nano-flower-like bismuth tungstate / copper oxide composite photocatalytic material of claim 5 in photocatalytic degradation of gaseous formaldehyde.

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