Preparation method of W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF

Abstract

The invention discloses a preparation method of a W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF.The preparation method comprises the steps that bismuth nitrate pentahydrate and trimesic acid are added into an N, N-dimethylformamide / methyl alcohol mixed solvent, stirring is conducted, the mixture is poured into a high-pressure reaction kettle, and heat preservation and natural cooling are conducted; washing the precipitate, and drying in vacuum overnight; the preparation method comprises the following steps: dispersing Bi-MOF into deionized water, adding Na2WO4. 2H2O, carrying out ultrasonic treatment on the mixture, and stirring; and transferring into a microwave reactor, drying the precipitate, and then transferring into a porcelain boat for calcining to obtain the W-Bi-x photocatalyst. The preparation process is simple, the degradation effect is excellent, the degradation rate of MB reaches up to 98.9%, and excellent stability and reusability are shown; the defects that a traditional MOF-based photocatalyst is high in photon-generated carrier recombination rate, poor in stability, limited in pH adaptability and the like are overcome, and a new strategy is provided for efficient photocatalytic degradation of dye wastewater.

Description

Technical Field

[0001] The present invention relates to the field of efficient photocatalytic degradation of dye wastewater, and particularly to a preparation method of a W-Bi composite photocatalyst based on Bi-MOF for degrading methylene blue. Background Art

[0003] The main sources of wastewater pollution include industrial wastewater, agricultural drainage, urban domestic sewage, etc. In industrial production, a large amount of wastewater contains harmful substances such as heavy metals, organic substances, acids and alkalis, and direct discharge will cause water pollution. Agricultural drainage may contain chemical substances used in agricultural production such as pesticides and fertilizers. Urban domestic sewage contains various human excreta, detergents, food residues, etc., and there are also a large number of organic and inorganic pollutants. After these pollutants are discharged into water bodies, they have a negative impact on water bodies through processes such as dissolution, suspension, and sedimentation.

[0004] The impact of wastewater pollution on the environment and ecosystem is multi-faceted. First of all, the discharge of harmful substances will reduce the dissolved oxygen in the water body, thus causing harm to aquatic organisms and even leading to the collapse of the ecosystem. Secondly, the accumulation and enrichment of pollutants may trigger toxic effects and have a negative impact on the stability of the aquatic food chain. In addition, wastewater pollution may also cause soil and groundwater pollution, posing a threat to farmland and drinking water sources and threatening human health.

[0005] Among them, as a major source of water pollution, dye wastewater has become a major problem that needs to be solved urgently due to its large discharge volume and complex composition. Methylene blue (MB), as a refractory dye pollutant, has attracted people's attention due to its presence in dye wastewater. This compound is widely used due to its bright color, excellent coloring ability and low cost, but its potential harm to the environment cannot be ignored. In the context of the increasing awareness of environmental protection, how to effectively treat wastewater containing MB has become an urgent problem to be solved.

[0006] In order to solve the problem of dye wastewater treatment, a series of technologies and measures need to be taken. Among them, advanced wastewater treatment technologies and equipment are the key. At present, technologies such as adsorption, biodegradation, chemical oxidation, and photocatalytic degradation are widely used in the treatment of dye wastewater. The adsorption technology can effectively adsorb dye pigments, the biodegradation technology uses microorganisms to degrade organic substances in dye wastewater, the chemical oxidation technology can oxidize and decompose organic substances in dye wastewater through oxidants, and the photocatalytic degradation technology uses the photocatalytic activity of semiconductor materials to degrade organic substances in dye wastewater into harmless substances.

[0007] In the treatment of wastewater pollution, traditional wastewater treatment methods include physical treatment, chemical treatment, and biological treatment. Physical treatment mainly removes suspended solids and particulate matter in wastewater through means such as filtration, sedimentation, and adsorption. Chemical treatment uses chemical reactions to change the dissolved substances in wastewater, forming precipitates or sediments to achieve the purpose of purifying water quality. Biological treatment relies on the degradation of microorganisms, breaking down organic matter into harmless substances through organisms. Photocatalytic technology has attracted much attention because it does not require the addition of external energy and can efficiently degrade organic pollutants. Photocatalytic technology refers to the generation of highly active free radicals by semiconductor materials under light illumination to non-selectively degrade pollutants, which is a more thorough environmental remediation method. It can completely mineralize pollutants under mild conditions without secondary pollution, and the energy for photocatalytic degradation can come from sunlight, thus greatly reducing the energy cost.

[0008] However, although the existing air annealing method can construct the BiOCl / ZnO heterojunction, it may involve high energy consumption or long reaction time, thus increasing the preparation cost of the material and being unfavorable for large-scale production and practical application promotion. ZnO may undergo self-corrosion in aqueous solution (ZnO + H2O → Zn 2+ + OH - ), resulting in a decrease in the long-term stability of the photocatalyst and affecting its reusability.

[0009] Therefore, to solve the technical problems existing in the prior art:

[0010] (1) There are problems of fast recombination of photo-generated carriers and low photocatalytic efficiency in the treatment of dye wastewater by existing photocatalytic technologies;

[0011] (2) Some catalysts have insufficient redox ability and are difficult to efficiently generate active free radicals, reducing the removal effect on refractory pollutants;

[0012] (3) The catalyst is vulnerable to photocorrosion or structural degradation during long-term operation, with poor stability and low recycling ability, increasing the treatment cost.

[0013] The present invention provides a new technical solution. The present invention anchors W atoms on Bi-MOF to form a photocatalyst for catalytic degradation of pollutants in wastewater. The preparation process is simple and the degradation effect is excellent. Moreover, the prepared W-Bi-0.06 has a unique rod-like morphology, and shows a scaly feature on the surface after calcination, which helps to provide a larger specific surface area and active sites, thereby improving the photocatalytic performance. The introduction of W atoms helps to regulate the electronic structure, improve the electron-hole separation efficiency, reduce recombination, and thus enhance the photocatalytic activity. This catalyst not only retains the catalytic activity of Bi-MOF, but also improves the light absorption ability of Bi-MOF and the separation efficiency of photogenerated carriers, thereby greatly improving the degradation effect of the catalyst. Summary of the Invention

[0014] In view of this, the present invention provides a preparation method of a W-Bi composite photocatalyst based on Bi-MOF for degrading methylene blue.

[0015] To solve the above technical problems, the present invention adopts the following technical solutions:

[0016] A preparation method of a W-Bi composite photocatalyst based on Bi-MOF for degrading methylene blue includes the following steps:

[0017] Step 1: Synthesis of Bi-MOF

[0018] Step 1.1: Add bismuth nitrate pentahydrate and trimesic acid to the N,N-dimethylformamide / methanol mixed solvent. After continuous stirring, pour the solution into a high-pressure reaction kettle, keep warm, and naturally cool to room temperature;

[0019] Step 1.2: Wash the white precipitate, and then dry it overnight in vacuum;

[0020] Step 2: Preparation of W-Bi-x

[0021] Step 2.1: Disperse Bi-MOF into deionized water, then add Na2WO4·2H2O, and ultrasonically treat and stir the mixture;

[0022] Step 2.2: Then transfer it to a microwave reactor, dry the obtained precipitate, and then transfer it to a porcelain boat for calcination to obtain a W-Bi-x photocatalyst.

[0023] Preferably, in step 1.1, the addition amount of the N,N-dimethylformamide / methanol mixed solvent is 30 mL, and the volume ratio of N,N-dimethylformamide to methanol is 1:2.

[0024] Preferably, in step 1.1, the concentration of bismuth nitrate pentahydrate is 98%, and the addition amount is 0.97 g; the concentration of trimesic acid is 98%, and the addition amount is 0.84 g.

[0025] Preferably, in step 1.1, the high-pressure reactor is specifically a Teflon-lined stainless-steel high-pressure reactor, which is kept at 120 °C for 24 h.

[0026] Preferably, in step 1.2, the white precipitate is washed three times with DMF and MeOH, and then dried overnight in vacuo at 60 °C.

[0027] Preferably, in step 2.1, the addition amount of Bi-MOF is 0.2 g, and the addition amount of deionized water is 20 mL.

[0028] Preferably, in step 2.1, 0.02 mM, 0.04 mM, 0.06 mM, and 0.08 mM of Na2WO4·2H2O are added respectively.

[0029] Preferably, in step 2.1, the ultrasonic treatment time of the mixture is 30 min, and the stirring time is 2 h.

[0030] Preferably, in step 2.2, the material of the microwave reactor is Teflon-lined, and it is kept at 150 °C for 30 min in the microwave reactor; the obtained precipitate is dried at 60 °C.

[0031] Preferably, in step 2.2, the heating temperature in the porcelain boat is 550 °C, the heating time is 2 h, and the heating rate is 5 °C / min.

[0032] The present invention has achieved the following technical effects compared with the prior art:

[0033] (1) The preparation process of the present invention is simple, and the degradation effect is excellent. After the optimization of the initial concentration and pH, the degradation rate of this material for MB is as high as 98.9% under the condition of pH = 11, and it shows excellent stability and reusability;

[0034] (2) The research of the present invention shows that ·OH, h + and ·O2 - all play important roles in the degradation process, among which ·OH dominates the reaction;

[0035] (3) The present invention overcomes the disadvantages of traditional MOF-based photocatalysts, such as high recombination rate of photo-generated carriers, poor stability, and limited pH adaptability, and provides a new strategy for the efficient photocatalytic degradation of dye wastewater. Description of the Drawings

[0036] Figure 1 XRD patterns of Bi-MOF, Bi@C, and W-Bi-x;

[0037] Figure 2 (a) SEM image of Bi-MOF;

[0038] Figure 2 (b) is the SEM image of W-Bi-0.06;

[0039] Figure 2 (c) is the SEM image of Bi@C;

[0040] Figure 2 (d-f) are the HRTEM images of W-Bi-0.06;

[0041] Figure 2 (g) is the mapping image;

[0042] Figure 2 (h) is the distribution map of C element in the whole sample;

[0043] Figure 2 (i) is the distribution map of O element in the whole sample;

[0044] Figure 2 (j) is the distribution map of W element in the whole sample;

[0045] Figure 2 (K) is the distribution map of Bi element in the whole sample;

[0046] Figure 3 (a) is the degradation curve of MB by different catalysts;

[0047] Figure 3 (b) is the first-order kinetic curve of MB by different catalysts;

[0048] Figure 3 (c) is the kinetic constant analysis chart of MB by different catalysts;

[0049] Figure 4 (a) is the degradation curve of MB by W-Bi-0.06 at different pH values;

[0050] Figure 4 (b) is the first-order kinetic curve of MB by W-Bi-0.06 at different pH values;

[0051] Figure 4 (c) is the kinetic constant analysis chart of MB by W-Bi-0.06 at different pH values;

[0052] Figure 5 (a) is the cyclic experiment chart;

[0053] Figure 5 (b) is the capture experiment chart. Specific implementation manners

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] The present invention discloses a preparation method of a W-Bi composite photocatalyst for degrading methylene blue based on Bi-MOF, comprising the following steps:

[0056] Step 1: Synthesis of Bi-MOF

[0057] Step 1.1: Add 0.97 g of bismuth nitrate pentahydrate with a concentration of 98% and 0.84 g of trimesic acid with a concentration of 98% into 30 mL of N,N-dimethylformamide / methanol mixed solvent, wherein the volume ratio of N,N-dimethylformamide to methanol is 1:2. After continuous stirring, pour the solution into a Teflon-lined stainless steel autoclave, keep it at 120 °C for 24 h, and naturally cool to room temperature;

[0058] Step 1.2: Wash the white precipitate three times with DMF and MeOH, and then dry it overnight in vacuo at 60 °C;

[0059] Step 2: Preparation of W-Bi-x

[0060] Step 2.1: Disperse 0.2 g of Bi-MOF into 20 mL of deionized water, and then add 0.02 mM, 0.04 mM, 0.06 mM, and 0.08 mM of Na2WO4·2H2O respectively. Ultrasonically treat the mixture for 30 min and stir for 2 h;

[0061] Step 2.2: Then transfer it to a microwave reactor with a Teflon lining, keep it at 150 °C for 30 min. Dry the obtained precipitate at 60 °C, then transfer it to a porcelain boat, heat at a temperature of 550 °C for 2 h, and the heating rate is 5 °C / min to obtain the W-Bi-x photocatalyst.

[0062] Example 1: Characterization of the W-Bi-x photocatalyst

[0063] As Figure 1As shown, the XRD (X-ray diffraction) patterns of Bi-MOF, Bi@C, and W-Bi-x of the present invention are presented. The XRD pattern of Bi-MOF shows distinct characteristic diffraction peaks corresponding to its original crystal structure. However, after the calcination treatment, Bi-MOF transforms into Bi@C, and significant changes occur in its XRD diffraction peaks, indicating that the crystal phase structure of the material has been reshaped. This change may be due to the reorganization of the organic framework of MOF during high-temperature calcination and the formation of the Bi@C composite structure accompanied by carbonization.

[0064] Further comparing the XRD patterns of Bi@C and W-Bi-x, it can be found that their characteristic diffraction peaks are almost identical, indicating that the introduction of W does not significantly change the crystal phase structure of Bi@C.

[0065] In addition, in the XRD pattern of W-Bi-x, there are no characteristic peaks related to the W element, such as oxides and nitrides, indicating the high dispersion of W atoms. This highly dispersed state may contribute to optimizing the photocatalytic performance. The high dispersion of W can effectively regulate the electronic structure of Bi@C, improve the separation efficiency of photo-generated carriers, and thus inhibit electron-hole recombination. Although no obvious W-related characteristic peaks (such as WO3 or WN) are detected by XRD, W atoms may partially replace certain sites in Bi@C or be embedded in the lattice, causing changes in the long-range order of the crystal. This may lead to the enhancement of certain characteristic diffraction peaks and even slight peak position shifts.

[0066] The morphologies and microstructures of Bi-MOF, W-Bi-0.06, and Bi@C were systematically characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to deeply explore their morphological evolution and the microcharacteristics of the materials.

[0067] As Figure 2 (a) shows, the SEM image of Bi-MOF clearly shows a smooth and regular rod-like morphology.

[0068] As Figure 2 (b) shows, after calcination and the anchoring of W atoms, the morphology of Bi-MOF has changed significantly, with its surface becoming rough and showing a scaly structure.

[0069] In contrast, as Figure 2 (c) shows, although Bi@C has also undergone the calcination process without the introduction of W elements, no obvious scaly morphology appears on its surface. The scaly characteristics of W-Bi-0.06 may be closely related to the anchoring process of W atoms, and this structure helps to increase the specific surface area and provide more active sites, thus enhancing the catalytic performance of the material.

[0070] As Figure 2As shown in Figs. (d)-2(f), in order to more deeply analyze the crystal structure and composition distribution of the sample, high-resolution transmission electron microscopy (HRTEM) images were taken. It is worth noting that in the HRTEM image of the W-Bi-0.06 sample, the fringes of the Bi(012) and C(002) crystal planes can be clearly observed, and their interplanar spacings are 0.32 nm and 0.36 nm respectively. This result indicates that the W-Bi-0.06 sample was successfully synthesized, and at the same time, the Bi and carbon phases were formed, further proving the composite structure of the material.

[0071] In addition, as Figure 2 shown in Fig. (g), in order to confirm the successful incorporation of the W element and its distribution state, energy-dispersive X-ray spectroscopy (EDS) analysis and elemental mapping imaging were performed on W-Bi-0.06.

[0072] As Figure 2 shown in Figs. (h)-(k), the results show that the C, O, W, and Bi elements are uniformly distributed throughout the sample, and no element aggregation or segregation phenomenon appears, indicating that the W atoms are uniformly anchored on the Bi-MOF matrix.

[0073] Example 2: Performance of NFO@MIL-101(Cr) photocatalyst in degrading RhB

[0074] The photocatalytic technology was used to measure the reaction rate of the catalyst. Under suitable temperature and humidity conditions, 100 mL of RhB solution was poured into the photocatalytic reaction device, and a xenon lamp was used as a simulated light source for irradiation. Then, a certain mass of the photocatalyst was put into the MB solution and ultrasonically treated for 3 min. Finally, the reaction device was sealed with tin foil paper, stirred at a rate of 500 r / min, and after dark adsorption for 60 min, the light source was turned on. Every half hour, 4 mL of the solution was aspirated from the reactor with a syringe, screened twice with a disposable needle filter, and then the absorbance at 664 nm was measured using a UV meter, and compared with blank water. The measurement was repeated three times, and finally their average value was calculated. According to the formula, the degradation rate of MB can be estimated:

[0075] Degradation=(C0 - C t ) / C0×100%

[0076] Degradation represents the degradation rate of MB; at time t and the initial time, C t and C0 represent the residual amount and the initial concentration of MB respectively.

[0077] As Figure 3 shown in Figs. (a)-3(c), the photocatalytic degradation and degradation kinetics diagrams of MB by the Bi-MOF, Bi@C, and W-Bi-x of the present invention are shown.

[0078] AsFigure 3 As shown in (a), when 30 mg of photocatalyst was added and the adsorption equilibrium was reached after 60 min, after 180 min of visible light irradiation, W-Bi-0.06 exhibited the best photocatalytic performance, and the degradation rate of MB reached 97.59%. Then, according to the degradation kinetics, the first-order degradation kinetic line was obtained.

[0079] As Figure 3 As shown in (b), the slope of the first-order kinetic line of W-Bi-0.06 was the largest, indicating that the degradation efficiency of W-Bi-0.06 was the highest. In order to more intuitively observe the change of the slope, a bar chart of kinetic constants was made.

[0080] As Figure 3 As shown in (c), it can be seen that the kinetic constant of W-Bi-0.06 was the largest, 0.02035 min -1 , which was much larger than that of the monomer catalyst.

[0081] As Figure 4 As shown in (a), the degradation performance and degradation kinetics of W-Bi-0.06 for methylene blue (MB) under different pH conditions were shown. The results showed that with the increase of pH, the degradation efficiency was significantly improved. Especially when pH = 11, the degradation rate was as high as 98.9% within 90 min and then tended to be stable.

[0082] As Figure 4 As shown in (b)-(c), the pseudo-first-order kinetic rate constant was the highest (0.0278 min -1 ) under this condition, indicating the strongest photocatalytic activity. This phenomenon was mainly attributed to the increase in the concentration of OH- in the alkaline environment, which promoted the generation of hydroxyl radicals (·OH) and increased the degradation rate of MB. At the same time, the MB molecule was more easily ionized under alkaline conditions, which was beneficial to the reaction with the catalyst surface. In addition, under alkaline conditions, the surface of W-Bi-0.06 might be negatively charged, while the MB molecule was usually a cationic dye. This electrostatic interaction would enhance the adsorption of MB on the catalyst surface and improve the degradation rate.

[0083] To verify the stability of the catalyst for degrading MB, its performance was evaluated through a recycling experiment. At room temperature, with pH = 7, 30 mg of the NM-70 heterojunction catalyst was weighed and added to a MB solution with a concentration of 10 mg / L. After 60 min of dark adsorption, the solution was irradiated for 180 min. About 4 mL of the solution was taken every 30 min, and the transmittance was measured using a UV-visible spectrophotometer, and then five recycling experiments were carried out.

[0084] As Figure 5As shown in (a), the photocatalytic activity of W-Bi-0.06 did not show obvious inactivation, and the removal efficiency remained at 92.78%, indicating that the catalyst had significant photocatalytic stability under visible light irradiation. The slight decrease in photocatalytic activity was mainly attributed to the mass loss of the catalyst during the recycling and filtration processes. In addition, the photocatalytic degradation efficiency of MB did not decrease significantly, which further demonstrated the good reusability and stability of W-Bi-0.06 in the actual wastewater purification.

[0085] In the present invention, in order to deeply explore the main active species during the photocatalytic degradation of methylene blue (MB) by W-Bi-0.06, benzoquinone (BQ), isopropyl alcohol (IPA), and triethanolamine (TEOA) were used as the quenchers of superoxide radical (·O2 - ), hydroxyl radical (·OH), and hole (h + ), respectively, and their effects on the degradation efficiency were analyzed.

[0086] As Figure 5 shown in (b), in the absence of quenchers, W-Bi-0.06 could efficiently degrade MB, while when different quenchers were added, the degradation rate decreased to varying degrees. Among them, after adding IPA (the quencher of ·OH), the degradation rate of MB decreased significantly to 26.35%, indicating that ·OH played a dominant role in the degradation process. In contrast, after adding TEOA (the quencher of h + ), the degradation rate decreased to 69.4%, indicating that h + was also an important active species in the degradation process, but its role was secondary to ·OH. In addition, after adding BQ (the quencher of ·O2 - ), the degradation rate decreased to 76.26%. Although it still had a relatively high degradation ability, it indicated that ·O2 - contributed less to the degradation process.

[0087] The above experimental results showed that during the catalytic degradation of MB by W-Bi-0.06, ·OH was the most important active species, and its high oxidation ability could effectively destroy the chemical structure of MB, thus achieving efficient degradation.

[0088] And h + , as a secondary active species, could also directly oxidize MB or react with water to generate ·OH, further promoting the degradation. In contrast, the oxidation ability of ·O2 - was relatively weak, so its contribution to the degradation was small.

[0089] This result reflected that W-Bi-0.06 might follow the following mechanism during the photocatalytic degradation process:

[0090] First, light irradiation excites W-Bi-0.06, causing electrons in its valence band (VB) to jump to the conduction band (CB), generating photo-generated electrons (e - ) and holes (h + ) on the surface.

[0091] Subsequently, h + can directly oxidize MB or react with H2O / OH - to generate strongly oxidizing ·OH, further promoting the degradation of MB. At the same time, e - can react with O2 to generate ·O2 - , but its oxidation ability is relatively low, so its contribution to the degradation of MB is small.

[0092] This discovery provides a theoretical basis for optimizing the photocatalytic performance of W-Bi-0.06. For example, by regulating the surface properties of the catalyst or introducing co-catalysts to further improve the generation efficiency of ·OH, thereby enhancing the ability of photocatalytic degradation of pollutants.

[0093] The above description is only a preferred embodiment of the present invention and does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF, characterized in that: The steps include: Step 1: Synthesis of Bi-MOF Step 1.1: Add bismuth nitrate pentahydrate and trimesic acid to a N,N-dimethylformamide / methanol mixed solvent, and after continuous stirring, pour the solution into a high-pressure reactor, keep warm, and cool naturally to room temperature; Step 1.2: Wash the white precipitate and then dry it in vacuum overnight; Step 2: Preparation of W-Bi-x Step 2.1: Disperse Bi-MOF in deionized water, then add Na2WO4·2H2O, and ultrasonicate the mixture and stir. Step 2.2: Then transfer to a microwave reactor, dry the obtained precipitate, and then transfer to a porcelain boat for calcination to obtain a W-Bi-x photocatalyst.

2. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 1.1, the amount of N,N-dimethylformamide / methanol mixed solvent added is 30 mL, and the volume ratio of N,N-dimethylformamide to methanol is 1:

2.

3. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 1.1, the concentration of bismuth nitrate pentahydrate is 98%, and the added amount is 0.97 g; the concentration of trimesic acid is 98%, and the added amount is 0.84 g.

4. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 1.1, the autoclave is specifically a Teflon-lined stainless steel autoclave, which is kept warm at 120° C. for 24 hours.

5. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In step 1.2, the white precipitate was washed three times with DMF and MeOH, and then dried in vacuo at 60°C overnight.

6. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 2.1, the amount of Bi-MOF added is 0.2 g, and the amount of deionized water added is 20 mL.

7. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 2.1, 0.02 mM, 0.04 mM, 0.06 mM, and 0.08 mM Na2WO4·2H2O were added respectively.

8. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 2.1, the mixture is ultrasonically treated for 30 minutes and stirred for 2 hours.

9. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 2.2, the microwave reactor is lined with polytetrafluoroethylene and maintained at 150° C. for 30 min in the microwave reactor; the obtained precipitate is dried at 60° C.

10. The method for preparing the W-Bi composite photocatalyst capable of degrading methylene blue based on Bi-MOF according to claim 1, characterized in that: In the step 2.2, the heating temperature in the porcelain boat is 550° C., the heating time is 2 h, and the heating rate is 5° C. / min.

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