Preparation method of two-dimensional SnS2 nanosheet coupled Bi-MOF composite photocatalyst for degrading methylene blue

Abstract

The invention discloses a preparation method of a two-dimensional SnS2 nanosheet coupled Bi-MOF composite photocatalyst for degrading methylene blue. The preparation method comprises the following steps: gradually adding SnCl4 into an ethanol solution containing thioacetamide under stirring to prepare SnS2; the preparation method comprises the following steps: adding bismuth nitrate pentahydrate and trimesic acid into an N, N-dimethylformamide / methanol mixed solvent to prepare Bi-MOF; snS2 powder and Bi-MOF are scattered in water through ultrasonic treatment respectively; and mixing the two suspensions, and stirring to prepare the SnS < 2 >-Bi-MOF-x (SBM-x for short). The preparation process is simple, the degradation effect is excellent, through optimization of the initial concentration and pH, the degradation rate of the material to MB under the condition that the pH is equal to 11 reaches up to 99.8%, excellent stability and reusability are shown, and a new strategy is provided for efficient photocatalytic degradation of dye wastewater.

Description

Technical Field

[0001] This invention relates to the field of preparation of two-dimensional SnS2 nanosheet coupled Bi-MOF composite photocatalysts, and particularly to a method for preparing two-dimensional SnS2 nanosheet coupled Bi-MOF composite photocatalysts for degrading methylene blue. Background Technology

[0002] Energy and environmental challenges are among the most significant obstacles hindering global human progress and development. Rapid industrial development has also led to environmental pollution, posing a serious threat to human health and the natural environment. Water quality is a global concern. The Sustainable Development Goals aim to reduce pollution globally by 2030, eliminate or reduce the discharge and indiscriminate dumping of hazardous chemicals and materials, and ensure wastewater undergoes non-toxic and harmless treatment and is recycled as much as possible, thereby improving water quality. Due to improper wastewater treatment, many hazardous chemicals continue to be discharged into natural water resources, with synthetic dyes and antibiotics being particularly concerning pollutants.

[0003] Organic dyes are major water pollutants from papermaking, textile dyeing, cosmetics, paints, and food processing. The total annual production of synthetic dyes exceeds 700,000 tons, of which 15% is discharged into water. However, only 47% of synthetic dyes are biodegradable. These dyes are not only difficult to degrade naturally, but their rich content of azo compounds, heavy metal salts, and other toxic components can cause irreversible damage to the ecological environment and may also accumulate through the food chain, posing a direct threat to human health.

[0004] Traditional wastewater treatment methods (such as adsorption, flocculation, and biodegradation) can remove pollutants to some extent, but they suffer from problems such as low efficiency, high cost, and secondary pollution.

[0005] Methylene blue (MB) is a heterocyclic aromatic compound widely used as a chemical dye in many fields, including chemical indicators, dyes, biological stains, and pharmaceuticals. Its strong chemical stability and poor biodegradability lead to its long-term persistence in water bodies, causing not only water discoloration and reduced light transmittance, but also potential carcinogenic risks through bioaccumulation in the food chain.

[0006] Traditional treatment methods (such as adsorption, flocculation, and biodegradation) suffer from problems such as low efficiency, secondary pollution, or high cost. Therefore, developing new treatment technologies that combine high-efficiency degradation capabilities with environmentally friendly characteristics has become a top priority in overcoming the dilemma of organic pollution control in water bodies.

[0007] Traditional wastewater treatment methods include physical, chemical, and biological treatment. Physical treatment primarily removes suspended solids and particulate matter from wastewater through filtration, sedimentation, and adsorption. Chemical treatment utilizes chemical reactions to alter dissolved substances in wastewater, forming precipitates or sediments to purify the water. Biological treatment relies on the degradation by microorganisms, breaking down organic matter into harmless substances. Photocatalysis technology has attracted significant attention due to its ability to efficiently degrade organic pollutants without requiring external energy. Photocatalysis refers to the non-selective degradation of pollutants by semiconductor materials generating highly reactive free radicals under light irradiation, representing 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, significantly reducing energy costs.

[0008] However, existing technologies have the following drawbacks:

[0009] (1) Existing photocatalytic technologies for dye wastewater treatment suffer from problems such as rapid recombination of photogenerated carriers and low photocatalytic efficiency.

[0010] (2) Some catalysts have insufficient redox capacity, making it difficult to generate active free radicals efficiently, which reduces the removal effect on recalcitrant pollutants;

[0011] (3) The catalyst is susceptible to photocorrosion or structural degradation during long-term operation, has poor stability, low recycling capacity, and increases treatment costs.

[0012] Compared with the literature (Inorganic Chemistry Communications, 2022, 140, 109445) on the degradation of methylene blue, Ni-MOF@BiOBr (NB-11) achieved a degradation rate of 92% for MB within 120 min.

[0013] This invention achieves a higher degradation rate (99%) within the same timeframe. By coupling SnS2 and Bi-MOF to prepare a heterojunction, this invention effectively improves electron-hole separation efficiency and optimizes catalytic performance. Furthermore, this invention delves into the effect of pH, confirming the broad applicability of the catalyst, and elucidates the photocatalytic mechanism through active species analysis.

[0014] Therefore, to address the shortcomings of existing technologies, this invention employs a hydrothermal method to prepare Bi-MOF and couples SnS2 and Bi-MOF to prepare a heterojunction. This heterojunction combines the advantages of SnS2 and Bi-MOF, possessing a unique structure and abundant modulating catalytic active sites, thereby enhancing photocatalytic performance and achieving photocatalytic oxidation-reduction of recalcitrant organic dye pollutants in wastewater. Summary of the Invention

[0015] In view of this, the present invention provides a method for preparing a two-dimensional SnS2 nanosheet coupled Bi-MOF composite photocatalyst for degrading methylene blue.

[0016] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0017] The preparation method of a two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue includes the following steps:

[0018] Step 1: Preparation of two-dimensional SnS2 nanosheets

[0019] Step 1.1: The precursor solution was prepared by gradually adding SnCl4 to an ethanol solution containing thioacetamide under stirring;

[0020] Step 1.2: After SnCl4 is completely dissolved, the solution is placed in a reaction vessel for reaction. After cooling to room temperature, the precipitate is obtained by centrifugation.

[0021] Step 1.3: Wash the product with water and ethanol, then dry it in a vacuum;

[0022] Step 2: Synthesis of Bi-MOF

[0023] Step 2.1: Add bismuth nitrate pentahydrate and trimesic acid to the N,N-dimethylformamide / methanol mixed solvent, stir continuously, and then pour the solution into a Teflon-lined stainless steel high-pressure reactor. Allow the reaction vessel to cool naturally to room temperature.

[0024] Step 2.2: The white precipitate was washed with DMF and MeOH, and then dried under vacuum;

[0025] Step 3: Synthesis of SnS2@Bi-MOF:

[0026] Step 3.1: Scatter SnS2 powder and Bi-MOF in water by ultrasonic treatment;

[0027] Step 3.2: Mix the two suspensions and stir, centrifuge the mixture, wash with water and ethanol and dry to prepare SnS2@Bi-MOF-x, abbreviated as SBM-x.

[0028] Preferably, in step 1.1, the amount of SnCl4 is 20 mmol, the amount of thioacetamide is 60 mmol, and the amount of ethanol solution added is 100 mL.

[0029] Preferably, in step 1.2, the reaction temperature in the reactor is 70°C, the reaction time is 6 hours, and the centrifugation rate is 8000 rpm.

[0030] Preferably, in step 2.1, the amount of N,N-dimethylformamide / methanol mixed solvent DMF / MeOH added is 60 mL, V / V = 1:2, the amount of bismuth nitrate pentahydrate Bi(NO3)3 added is 0.97 g, the amount of trimesic acid H3BTC added is 1.68 g, the volume of the Teflon-lined stainless steel high-pressure reactor is 50 mL, the reaction temperature is 120℃, and the reaction time is 24 h.

[0031] Preferably, in step 2.2, the white precipitate is washed three times with DMF and MeOH, dried at 60°C for 12 hours.

[0032] Preferably, in step 3.1, 0.50g, 0.75g, 1.00g, and 1.25g of SnS2 powder and 1.00g of Bi-MOF are subjected to ultrasonic treatment and scattering in water for 30 minutes.

[0033] Preferably, in step 3.2, the two suspensions are mixed and stirred for 24 hours, and the mixture is centrifuged at a speed of 5000 rpm.

[0034] The present invention achieves the following technical effects compared to the prior art:

[0035] (1) The preparation process of this invention is simple and the degradation effect is excellent. After optimization of the initial concentration and pH, the material has a degradation rate of up to 99.8% of MB under pH=11 conditions, and exhibits excellent stability and reusability.

[0036] (2) Mechanism studies have shown that ·OH, h + and O2 - All of them play an important role in the degradation process, among which h + Dominant reaction: This invention overcomes the shortcomings of traditional MOF-based photocatalysts, such as high recombination rate of photogenerated carriers, poor stability, and limited pH adaptability, and provides a new strategy for efficient photocatalytic degradation of dye wastewater. Attached Figure Description

[0037] Figure 1 (a) XRD patterns of Bi-MOF, SnS2 and SBM composites with different ratios of the present invention; (b) FT-IR patterns of the present invention.

[0038] Figure 2 SEM images of (a,b)Bi-MOF, (c,d)SnS2 and (e,f)SBM-0.75 of the present invention;

[0039] Figure 3(a) is a graph showing the degradation curves of MB by different catalysts of the present invention; (b) is a graph showing the first-order kinetics of MB degradation by different catalysts of the present invention; (c) is a graph showing the distribution of the degradation kinetic constant k of MB by different catalysts of the present invention.

[0040] Figure 4 (a) is a photocatalytic degradation curve of MB at different pH values ​​according to the present invention; (b) is a first-order kinetic fitting curve of photocatalytic degradation of MB at different pH values ​​according to the present invention; (c) is a distribution of the kinetic constant k value of photocatalytic degradation of MB at different pH values ​​according to the present invention.

[0041] Figure 5 (a) is a diagram of the cyclic experiment of the present invention; (b) is a diagram of the capture experiment of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention discloses a method for preparing a two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue, comprising the following steps:

[0044] Step 1: Preparation of two-dimensional SnS2 nanosheets

[0045] Step 1.1: The precursor solution was prepared by gradually adding 20 mmol of SnCl4 to 100 mL of ethanol solution containing 60 mmol of thioacetamide under stirring.

[0046] In step 1.2, after SnCl4 is completely dissolved, the solution is loaded into a reaction vessel and kept at 70°C for 6 hours. After cooling to room temperature, the precipitate is obtained by centrifugation at 8000 rpm.

[0047] Step 1.3: Wash the product with water and ethanol, then dry it in a vacuum;

[0048] Step 2: Synthesis of Bi-MOF

[0049] Step 2.1: Add bismuth nitrate pentahydrate (Bi(NO3)3, 0.97g) and trimesic acid (H3BTC, 1.68g) to a mixed solvent of N,N-dimethylformamide / methanol (DMF / MeOH, 60mL, V / V = 1:2). After stirring continuously, pour the solution into a 50mL Teflon-lined stainless steel high-pressure reactor and keep it at 120℃ for 24h. Allow the container to cool naturally to room temperature.

[0050] Step 2.2: The white precipitate was washed three times with DMF and MeOH, and then dried in vacuum at 60°C for 12 hours.

[0051] Step 3: Synthesis of SnS2@Bi-MOF

[0052] Step 3.1: Sonicate SnS2 powder (x = 0.50, 0.75, 1.00, 1.25) and Bi-MOF (1.00 g) in water for 30 min.

[0053] Step 3.1: Mix the two suspensions and stir for 24 hours. Centrifuge the mixture at 5000 rpm, wash with water and ethanol and dry to prepare SnS2@Bi-MOF-x, abbreviated as SBM-x.

[0054] Example 1: Characterization of W-Bi-x photocatalyst

[0055] The crystal structure of the prepared sample was characterized using X-ray diffraction (XRD) analysis.

[0056] like Figure 1 (a) XRD patterns of Bi-MOF, SnS2, and SBM photocatalysts composed of the two in different proportions are shown. In the XRD pattern of Bi-MOF, the characteristic diffraction peaks of the synthesized sample are consistent with those mentioned in the literature, proving the successful synthesis of Bi-MOF. In the XRD pattern of SBM-x, all the main characteristic peaks of Bi-MOF and SnS2 are retained, and no significant shift or new impurity peaks are generated at different mass ratios. This phenomenon indicates that no crystal phase reconstruction or formation of new crystal structure types occurs between the two materials during the composite process, and the original crystal structure is effectively preserved. In addition, the sharpness of the peaks also shows that the composite material still has a high degree of crystallinity, indicating that the composite of Bi-MOF and SnS2 has not damaged the integrity of their respective crystal structures, laying the foundation for building a stable heterojunction interface.

[0057] To further verify the formation of the composite material and the chemical interactions between the components, the changes in functional groups and chemical bonds of each sample were analyzed by Fourier transform infrared spectroscopy (FT-IR).

[0058] The results are as follows Figure 1 As shown in (b). Between 1380-1600 cm -1 Within this range, characteristic absorption bands of the carboxylate group (-COO-) in Bi-MOF can be clearly observed. These vibrational peaks are generally attributed to asymmetric and symmetric stretching vibrations, indicating that the carboxyl group in the organic ligand of the MOF structure successfully participates in coordination. At 765 cm⁻¹ -1 The absorption peak detected at 765 cm⁻¹ is attributed to the stretching vibration of the Bi-O bond in Bi-MOF. SBM-0.75 and Bi-MOF show similar absorption peaks at 765 cm⁻¹. -1 The good matching of characteristic peaks indicates that the Bi-O framework structure in the synthesized material is maintained.

[0059] However, the intensity of this peak decreased in the SBM-0.75 sample, which may be related to the change in the local environment of the Bi-O bond or the perturbation of the crystal field caused by the introduction of SnS2, suggesting that there is a certain degree of interaction between the two materials.

[0060] In addition, 3400cm -1 The broad peak at 612 cm⁻¹ can be attributed to the OH stretching vibration of water molecules, which may originate from water adsorbed on the material surface or in the pores, and may also reflect that the composite material has a certain degree of hydrophilicity and open pore structure. In the FT-IR spectrum of the SBM-0.75 sample, a peak at 612 cm⁻¹ was also observed. -1 The characteristic absorption peak corresponds to the stretching vibration of the Sn-S bond in SnS2 and is a typical fingerprint region of the SnS2 structure. The appearance of this peak further confirms the successful introduction of SnS2 into the composite system.

[0061] The surface morphology and microstructure of two-dimensional SnS2 nanosheets, Bi-MOF and SBM composites were captured by SEM.

[0062] like Figure 2 (ab)Bi-MOF has a regular three-dimensional polyhedral structure with abundant mesoporous structures on the surface. The crystal surface is smooth and the edges are distinct, indicating that the solvothermal method successfully constructed a highly crystalline Bi-MOF framework.

[0063] like Figure 2 The SnS2 sample in (cd) exhibits a typical two-dimensional sheet structure with a smooth surface and clear edges, and less interlayer stacking, indicating that the aggregation of nanosheets was effectively suppressed by surfactant regulation during the hydrothermal synthesis process.

[0064] like Figure 2(ef) is the SEM image of SBM-0.75. It can be seen that SnS2 nanosheets are uniformly loaded on the Bi-MOF surface without obvious agglomeration, indicating that the electrostatic adsorption method has achieved effective coupling of the two phases and the SnS2 nanosheets are tightly attached to the Bi-MOF surface.

[0065] Example 2: Performance of SnS2@Bi-MOF photocatalyst in degrading RhB

[0066] Photocatalysis was used to determine the reaction rate of the catalyst. Under suitable temperature and humidity conditions, 100 mL of MB solution was poured into the photocatalytic reactor and irradiated with a xenon lamp as a simulated light source. Then, a certain mass of photocatalyst was added to the MB solution and sonicated for 3 min. Finally, the reactor was sealed with tin foil, stirred (500 r / min), and allowed to adsorb in the dark for 60 min before the light source was turned on. Every half hour, 4 mL of solution was drawn from the reactor using a syringe and filtered twice using a disposable syringe filter. The absorbance at 664 nm was then measured using a UV meter and compared with blank water. The measurements were repeated three times, and the average value was calculated.

[0067] The degradation rate of MB can be estimated using the formula:

[0068] Degradation = (C0 - C t ) / C0×100%Degradation represents the degradation rate of MB; at time t and the initial time, C t C0 and C0 represent the residual amount and initial concentration of MB, respectively.

[0069] The photocatalytic performance of the prepared composite catalyst was evaluated by degrading MB under visible light irradiation. Before the experiment, all photocatalysts were subjected to adsorption-desorption equilibrium in a dark environment to eliminate the influence of non-photocatalytic factors on the experimental results.

[0070] like Figure 3 As shown in (a), the degradation effect of MB after 1 hour of dark reaction is minimal, while the degradation effect is significant after 3 hours of visible light irradiation. SBM-0.75 exhibits the best degradation effect, reaching a degradation rate of 96%, which is significantly higher than that of single components and other composite samples. In the photocatalytic process of pure SnS2 and pure Bi-MOF, photogenerated electrons and holes easily recombine, resulting in a limited number of active species participating in the degradation reaction, thus affecting the degradation efficiency. However, when SnS2 and Bi-MOF are coupled and composited, a heterojunction or gap is formed between them. This structure can effectively promote the separation and transfer of photogenerated electrons and holes.

[0071] Moreover, Bi-MOF itself usually has a regular pore structure. When combined with SnS2, this pore structure can provide a good channel for the penetration and diffusion of methylene blue solution, enabling methylene blue molecules to reach the surface active sites of the catalyst more quickly, increasing the contact probability between reactants and catalyst, and thus accelerating the photocatalytic degradation reaction.

[0072] Linear regression analysis was performed on the data of photocatalytic degradation of MB using the first-order kinetic equation.

[0073] like Figure 3 (b) Clearly demonstrates the different ratios of -ln(C) t The good linear relationship between / C0) and time conforms to the first-order kinetic experimental model. The magnitude of the fitted k value reflects the degradation rate.

[0074] Depend on Figure 3 (c) It can be seen that SBM-0.75 has the fastest degradation rate, with a maximum k value of 0.0134 cm⁻¹. -1 .

[0075] The pH value of the pollutant solution is a key factor affecting the adsorption behavior and surface chemical properties of photocatalysts. The experiment explored the effect of different pH values ​​on the degradation of MB.

[0076] like Figure 4 (a) shows the performance of SBM-0.75 in degrading MB at different pH values.

[0077] As shown in the figure, the photocatalytic degradation efficiencies of SBM-0.75 on MB were 96%, 98.2%, and 99.8% at pH values ​​of 7, 9, and 11, respectively.

[0078] This demonstrates that the degradation efficiency significantly increases with increasing pH. This is because pH affects the separation efficiency of photogenerated electrons and holes in the two-dimensional SnS2 nanosheets coupled with the Bi-based metal-organic framework. Under suitable pH conditions, the effective separation of photogenerated electrons and holes can be promoted, reducing their recombination probability and thus enhancing photocatalytic activity.

[0079] For example, under acidic conditions, h+ in the solution may affect the band structure and charge transport processes of a material, while under alkaline conditions, OH-... - It may participate in related reactions, altering charge transfer paths and separation efficiency.

[0080] The results showed that the optimal conditions for SBM-0.75 to remove pollutants were a neutral or alkaline environment. The degradation of MB by SBM-0.75 under visible light irradiation followed pseudo-first-order kinetics.

[0081] like Figure 4As shown in (c), the reaction rate constant increases with increasing pH. The maximum reaction rate constant is 0.025 min when the pH is 11. -1 .

[0082] Chemical stability is one of the key indicators for evaluating the performance of a catalyst. To assess the cycling stability of the SBM-0.75 heterojunction under visible light, a degradation cycle experiment was conducted on MB. At pH 7, SBM-0.75 was used to degrade 10 mg / L methylene blue, repeated five times.

[0083] like Figure 5 As shown in (a), after the cyclic experiment, the degradation efficiency of MB by SBM-0.75 did not decrease significantly, indicating that the composite photocatalyst has good stability.

[0084] This study investigated the main active species of the SBM-0.75 heterojunction in the photocatalytic degradation process using free radical and hole trapping experiments, employing p-benzoquinone, isopropanol, and ethylenediaminetetraacetic acid as superoxide anions. Hydroxyl radicals (·OH) and holes (h + The free radicals generated during photocatalysis were detected by electron paramagnetic resonance (EPR) using a scavenger. This analysis aimed to identify the main active substances in the degradation of the SBM-0.75 heterojunction.

[0085] Based on the experimental results, such as Figure 5 As shown in (b), when BQ, IPA, and EDTA were added to the reaction solution, the degradation rates were 73.35%, 62.49%, and 30.09%, respectively. These results indicate that... h + Both ·OH and ·OH play important roles in the degradation process, but their influence on SBM differs. Specifically, the order of influence is as follows:

[0086] The above experimental results indicate that during the SBM-0.75 catalytic degradation of MB, h + It is the most important active species, capable of directly oxidizing MB or reacting with water to generate ·OH, further promoting degradation. ·OH and ·O2 - It can effectively disrupt the chemical structure of MB, thereby achieving efficient degradation. This result reflects that SBM-0.75 may follow the following mechanism in the photocatalytic degradation process: First, SBM-0.75 is excited by light, causing electrons in its valence band (VB) to jump to the conduction band (CB), generating photogenerated electrons (e electrons) on the surface. - ) and holes (h + ), then h + It can directly oxidize MB, or react with H2O / OH -The reaction generates highly oxidizing ·OH, further promoting the degradation of MB. Simultaneously, e - It can react with O2 to produce ·O2 - This discovery allows for the degradation of MB. This finding provides a theoretical basis for optimizing the photocatalytic performance of SBM-0.75.

[0087] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue, characterized in that, Includes the following steps: Step 1: Preparation of two-dimensional SnS2 nanosheets Step 1.1: The precursor solution was prepared by gradually adding SnCl4 to an ethanol solution containing thioacetamide under stirring; Step 1.2: After SnCl4 is completely dissolved, the solution is placed in a reaction vessel for reaction. After cooling to room temperature, the precipitate is obtained by centrifugation. Step 1.3: Wash the product with water and ethanol, then dry it in a vacuum; Step 2: Synthesis of Bi-MOF Step 2.1: Add bismuth nitrate pentahydrate and trimesic acid to the N,N-dimethylformamide / methanol mixed solvent, stir continuously, and then pour the solution into a Teflon-lined stainless steel high-pressure reactor. Allow the reaction vessel to cool naturally to room temperature. Step 2.2: The white precipitate was washed with DMF and MeOH, and then dried under vacuum; Step 3: Synthesis of SnS2@Bi-MOF: Step 3.1: Scatter SnS2 powder and Bi-MOF in water by ultrasonic treatment; Step 3.2: Mix the two suspensions and stir, centrifuge the mixture, wash with water and ethanol and dry to prepare SnS2@Bi-MOF-x, abbreviated as SBM-x.

2. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 1.1, the amount of SnCl4 is 20 mmol, the amount of thioacetamide is 60 mmol, and the amount of ethanol solution added is 100 mL.

3. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 1.2, the reaction temperature in the reactor is 70°C, the reaction time is 6 hours, and the centrifugation rate is 8000 rpm.

4. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 2.1, the amount of N,N-dimethylformamide / methanol mixed solvent DMF / MeOH added is 60 mL, V / V = 1:2, the amount of bismuth nitrate pentahydrate Bi(NO3)3 added is 0.97 g, the amount of trimesic acid H3BTC added is 1.68 g, the volume of the Teflon-lined stainless steel high-pressure reactor is 50 mL, the reaction temperature is 120℃, and the reaction time is 24 h.

5. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 2.2, the white precipitate is washed three times each with DMF and MeOH, and dried at 60°C for 12 hours.

6. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 3.1, 0.50g, 0.75g, 1.00g, and 1.25g of SnS2 powder and 1.00g of Bi-MOF are respectively subjected to ultrasonic treatment and scattering in water for 30min.

7. The method for preparing the two-dimensional SnS2 nanosheet-coupled Bi-MOF composite photocatalyst for degrading methylene blue according to claim 1, characterized in that, In step 3.2, the two suspensions are mixed and stirred for 24 hours, and the mixture is centrifuged at a speed of 5000 rpm.

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