Bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst as well as a preparation method and application thereof, the photocatalyst comprises a quantum dot self-modified imino covalent organic framework, and bismuth oxyiodide nanosheets are loaded on a cavity and the surface of the quantum dot self-modified imino covalent organic framework. The preparation method comprises the following steps: mixing bismuth oxyiodide, the quantum dot self-modified imino covalent organic framework and ethanol, carrying out electrostatic self-assembly, filtering, washing, drying and the like. In the invention, under the synergistic effect of the quantum dot self-modified imino covalent organic framework and the bismuth oxyiodide nanosheet, the heterojunction photocatalyst has higher photocatalytic activity, and has the advantages of wide photoresponse range, high carrier separation efficiency, good photocatalytic performance, strong environmental interference resistance, strong stability and the like; the method can be widely used for treating the pharmaceutical wastewater, can effectively purify the pharmaceutical wastewater, and has the advantages of high use value and good application prospect, and the preparation method has the advantages of simple process, convenience in operation, mild synthesis conditions and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental functional materials and relates to a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst and a preparation method and application thereof. Background Art

[0002] Antibiotics are commonly used in agricultural and medical industries such as medical treatment, animal husbandry and aquaculture, and crop disease prevention and control around the world. Therefore, the pharmaceutical wastewater generated in these industries has become an environmental problem that cannot be underestimated. In particular, the discharge of pharmaceutical wastewater will cause the antibiotics contained in it to spread and enrich in the environment and food chain, leading to the generation of drug-resistant genes and drug-resistant bacteria, ultimately endangering human health and affecting ecosystem functions. Take tetracycline (TC) as an example. At high concentrations, it can cause acute death or sublethal effects of aquatic organisms, inhibit the growth and reproduction of microorganisms in the soil, and destroy the structure of microbial communities. At present, a large number of researchers are trying new methods to control TC pollution in the ecological environment, including adsorption, advanced oxidation, microbial decomposition and membrane filtration. As an alternative to traditional physical, chemical and biological methods, photocatalytic technology is still the preferred strategy for green, efficient, low-cost and sustainable degradation of antibiotics.

[0003] So far, the semiconductor types of photocatalysts have experienced metal oxides based on TiO2, MXenes, two-dimensional materials based on black phosphorus, and polymer semiconductors. In particular, the graphene-like structure and suitable band gap of carbon nitride (g-C3N4) have shined in the photocatalytic degradation of antibiotics. For example, N-CQDs modified Sg-C3N4 nanotubes, β-In2S3 / g-C3N4 / WO3 double z-type photocatalysts, and g-C3N4 / WO3 / ZnS double s scheme heterojunctions all have stronger light response and redox capabilities. More notably, organic semiconductors with high crystallinity and porosity are becoming the preferred alternative to traditional non-polar semiconductors, among which framework materials based on metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have become new research hotspots.

[0004] As a new type of crystalline porous material, COFs have attracted a lot of attention in the fields of photocatalytic CO2 reduction, pollutant degradation, hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) due to their advantages such as easy modification, structural design and controllable synthesis, and high specific surface area. However, single COFs have the disadvantages of low separation efficiency of photogenerated carriers and poor redox activity generated by charge transfer, which leads to the need for further improvement of their photocatalytic activity. In order to improve the efficiency of photogenerated carrier separation, some researchers have proposed a strategy to construct heterojunction photocatalysts by combining COFs with other semiconductor materials. However, most covalent organic framework heterojunction photocatalysts still have the disadvantages of narrow photoresponse range, low separation efficiency of photogenerated electron-hole pairs, weak photocatalytic activity and poor stability, which makes it difficult for the catalysts to be adapted to the treatment of high-concentration organic wastewater and difficult to efficiently degrade organic pollutants in wastewater, thus greatly limiting the promotion and use of existing covalent organic framework heterojunction photocatalysts. For example, by loading silver phosphate particles on a covalent organic framework to construct a composite catalyst, although it can improve the separation efficiency of photogenerated electron-hole pairs, the composite catalyst still has defects such as a narrow light response range and poor stability, especially for high-concentration organic wastewater, the adaptability is very poor. In addition, the preparation method of the existing covalent organic framework heterojunction photocatalyst also has defects such as complex operation, harsh and difficult to control synthesis conditions, and high energy consumption, which makes the catalyst difficult to use on a large scale. Therefore, it is particularly important to develop a heterojunction photocatalyst based on an imine-based covalent organic framework material with a wide light response range, high carrier separation efficiency, good photocatalytic performance, strong resistance to environmental interference, and strong stability to achieve effective treatment of medical wastewater. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst with a wide light response range, high carrier separation efficiency, good photocatalytic performance, strong resistance to environmental interference and strong stability, as well as a preparation method and application thereof.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0007] A bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst comprises a quantum dot self-modified imine-based covalent organic framework, wherein the cavity and surface of the quantum dot self-modified imine-based covalent organic framework are loaded with bismuth iodide nanosheets.

[0008] The above-mentioned bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is further improved in that the mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth oxyiodide nanosheets is 1-4:20.

[0009] The above-mentioned bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is further improved in that the mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth oxyiodide nanosheets is 1.6-3:20.

[0010] The above-mentioned bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is further improved in that the bismuth oxyiodide nanosheet is BiOI.

[0011] The above-mentioned bismuth iodide oxyhydroxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is further improved, wherein the quantum dot self-modified imine-based covalent organic framework is QDS-RTCOF; the quantum dot self-modified imine-based covalent organic framework is a dispersed particle block structure.

[0012] The above-mentioned bismuth oxide iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is further improved, and the bismuth oxide iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is in the form of porous microspheres; the particle size of the bismuth oxide iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is 2μm to 5μm.

[0013] As a general technical concept, the present invention also provides a method for preparing the above-mentioned bismuth iodide oxyhydroxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst, comprising the following steps:

[0014] The bismuth iodide, quantum dot self-modified imine-based covalent organic framework and ethanol are mixed for electrostatic self-assembly, filtered, washed and dried to obtain a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst.

[0015] The above preparation method is further improved, and the electrostatic self-assembly is: mixing bismuth iodide with ethanol, ultrasonically treating for 30min to 60min, adding quantum dot self-modified imine covalent organic framework, stirring for 8h to 10h, to obtain bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst.

[0016] The above preparation method is further improved, wherein the mass volume ratio of the bismuth iodide oxide to the ethanol is 4 mg: 1 mL to 4 mL; the mass ratio of the bismuth iodide oxide to the quantum dot self-modified imine-based covalent organic framework is 20: 1 to 4.

[0017] The above preparation method is further improved, and the preparation method of bismuth oxyiodide comprises the following steps:

[0018] (1.1) Mixing a bismuth salt with ethylene glycol and stirring for 1 h to 2 h to obtain a bismuth salt solution; mixing an iodine salt with ethylene glycol and stirring for 1 h to 2 h to obtain an iodine salt solution; the mass ratio of the bismuth salt to the iodine salt is 1.5 to 3:1; the mass volume ratio of the bismuth salt to the ethylene glycol in the bismuth salt solution is 2.43 g: 40 mL to 60 mL; the mass volume ratio of the iodine salt to the ethylene glycol in the iodine salt solution is 0.83 g: 40 mL to 60 mL; the bismuth salt is bismuth nitrate pentahydrate; and the iodine salt is potassium iodide;

[0019] (1.2) The bismuth salt solution and the iodine salt solution obtained in step (1.1) are mixed and subjected to a hydrothermal reaction to obtain bismuth iodide oxide; the temperature of the hydrothermal reaction is 160° C. to 180° C.; and the time of the hydrothermal reaction is 12 h to 6 h.

[0020] The above preparation method is further improved, and the preparation method of the quantum dot self-modified imine-based covalent organic framework comprises the following steps:

[0021] (2.1) Dissolving 1,3,5-tris(4-aminophenyl)benzene in an acetic acid solution to obtain a solution A; dissolving 1,3,5-benzenetricarboxaldehyde in an acetic acid solution to obtain a solution B; the mass ratio of the 1,3,5-tris(4-aminophenyl)benzene to 1,3,5-benzenetricarboxaldehyde is 50-80:23-46; the ratio of 1,3,5-tris(4-aminophenyl)benzene to the acetic acid solution in the solution A is 50 mg:7.0 mL-12.4 mL; the ratio of 1,3,5-benzenetricarboxaldehyde to the acetic acid solution in the solution B is 23 mg:7.0 mL-12.4 mL; the concentration of the acetic acid solution is 3 mol / L;

[0022] (2.2) Solution A and solution B obtained in step (2.1) are mixed to carry out quantum dot self-modification reaction, washed, and dried to obtain a quantum dot self-modified imine-based covalent organic framework; the time for the quantum dot self-modification reaction is 72h to 96h, and the drying time is 48h to 72h.

[0023] As a general technical concept, the present invention also provides an application of the above-mentioned bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst or the bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst prepared by the above-mentioned preparation method in treating medical wastewater.

[0024] The above application is further improved, and when using bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst to treat medical wastewater, the method includes the following steps: mixing the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst with the medical wastewater, stirring, and performing a photocatalytic degradation reaction under light conditions to complete the treatment of the medical wastewater; the addition amount of the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is 150 mg to 350 mg of the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst per liter of the medical wastewater.

[0025] The above application is further improved, wherein the antibiotic in the pharmaceutical wastewater is tetracycline; the concentration of the antibiotic in the pharmaceutical wastewater is 10 mg / L to 50 mg / L; the stirring time is 20 min to 80 min; the photocatalytic degradation reaction is carried out under visible light with a wavelength of >420 nm; and the photocatalytic degradation reaction time is 10 min to 60 min.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] (1) In view of the defects of existing covalent organic framework heterojunction photocatalysts, such as narrow light response range, low efficiency of separation of photogenerated electron-hole pairs, low photocatalytic activity, and poor stability, the present invention creatively provides a bismuth oxide iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst, including a quantum dot self-modified imine-based covalent organic framework, and the cavity and surface of the quantum dot self-modified imine-based covalent organic framework are loaded with bismuth oxide iodide nanosheets. Compared with conventional covalent organic frameworks, the quantum dot self-modified imine-based covalent organic framework used in the present invention has a rich pore structure and can provide a rich active site loading site. On this basis, with the quantum dot self-modified imine-based covalent organic framework as a carrier, the bismuth oxide iodide nanosheets can be firmly fixed on the cavity and surface of the quantum dot self-modified imine-based covalent organic framework to form a heterojunction photocatalyst. On the one hand, the bismuth oxide iodide nanosheets in the formed heterojunction photocatalyst are not easily corroded by light and are not easy to fall off from the carrier, so that the catalyst has better stability. On the other hand, under the promotion of the quantum dot self-modified imine-based covalent organic framework, the light absorption and utilization range of the bismuth oxide iodide nanosheets can be expanded, so that the heterojunction photocatalyst has a wider light response range. At the same time, under the action of the bismuth oxide iodide nanosheets, the columnar conductive channel formed by π-π stacking can improve the separation efficiency of electron-hole pairs, so that the heterojunction photocatalyst has a faster carrier separation efficiency, and thus under the synergistic effect of the quantum dot self-modified imine-based covalent organic framework and the bismuth oxide iodide nanosheets, the heterojunction photocatalyst has a higher photocatalytic activity. Therefore, the bismuth oxide iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst of the present invention has the advantages of wide light response range, high carrier separation efficiency, good photocatalytic performance, strong anti-environmental interference ability, strong stability, etc. As a new type of photocatalyst with excellent performance, it can be widely used in treating medical wastewater, can achieve effective purification of medical wastewater, has high use value, and has good application prospects.

[0028] (2) In the heterojunction photocatalyst of the present invention, the mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth iodide nanosheets is further optimized. By setting the mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth iodide nanosheets to 1 to 4:20, and in particular, when the mass ratio of the two is 1.6 to 3:20, it can be ensured that the catalyst has both very high photocatalytic performance and stability.

[0029] (3) The present invention also provides a method for preparing a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst, using bismuth iodide and quantum dot self-modified imine covalent organic framework as raw materials, and ethanol as solvent. By utilizing the different solubility of bismuth iodide and quantum dot self-modified imine covalent organic framework in ethanol, bismuth iodide is dissolved in ethanol, and mixed with undissolved quantum dot self-modified imine covalent organic framework for electrostatic self-assembly. In the electrostatic self-assembly process, the abundant active sites in the quantum dot self-modified imine covalent organic framework can be utilized to uniformly and firmly load bismuth iodide on the cavity and surface of the quantum dot self-modified imine covalent organic framework. After filtering, washing, and drying, a heterojunction photocatalyst with a wide light response range, high carrier separation efficiency, good photocatalytic performance, strong anti-environmental interference ability, and strong stability is obtained. At the same time, the preparation method of the present invention also has the advantages of simple process, convenient operation, mild synthesis conditions, high preparation efficiency, low energy consumption, green and pollution-free, etc., is suitable for large-scale preparation, and is convenient for industrial application of catalysts.

[0030] (4) In the preparation method of the heterojunction photocatalyst of the present invention, the order of adding raw materials is also optimized. First, bismuth iodide and ethanol are mixed and ultrasonically treated for 30min to 60min, which can promote the dissolution of bismuth iodide and form a solution, and then the quantum dot self-modified imine covalent organic framework is added and stirred for 8h to 10h. Under this stirring condition, the adsorption of bismuth iodide by the quantum dot self-modified imine covalent organic framework is completed, and the bismuth iodide can be evenly and firmly dispersed on the quantum dot self-modified imine covalent organic framework, which is conducive to the preparation of a heterojunction photocatalyst with excellent photocatalytic performance and stability. More importantly, the subsequent addition of the quantum dot self-modified imine covalent organic framework can also effectively prevent its dissolution, which is conducive to the preparation of the heterojunction photocatalyst. At the same time, the mass volume ratio of bismuth iodide to ethanol is also optimized to 4mg: 1mL to 4mL in the present invention. By optimizing the amount of ethanol, the complete dissolution of bismuth iodide can be promoted, so as to facilitate the preparation of the heterojunction photocatalyst of the present invention.

[0031] (5) In the preparation method of the heterojunction photocatalyst of the present invention, the preparation method of the quantum dot self-modified imine-based covalent organic framework is adopted, using 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarboxaldehyde as raw materials, and preparing the quantum dot self-modified imine-based covalent organic framework by a room temperature solvent method. The quantum dot self-modified imine-based covalent organic framework presents a dispersed particle block structure, is an organic semiconductor material synthesized at room temperature, and has good biocompatibility. In particular, in the present invention, acetic acid is selected to replace 1,4-dioxane or 1,3,5-trimethylbenzene as a solvent, which can reduce the synthesis cost and harmfulness of the material, so that the covalent organic framework synthesized with acetic acid has better biocompatibility.

[0032] (6) In the preparation method of the heterojunction photocatalyst of the present invention, a preparation method of bismuth iodide is adopted, using bismuth nitrate pentahydrate and potassium iodide as raw materials, and a bismuth iodide semiconductor with a nanosheet structure is obtained by a solvent thermal synthesis method.

[0033] (7) The present invention provides an application of bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst in treating pharmaceutical wastewater, specifically, the bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst of the present invention is used to treat pharmaceutical wastewater, which has the advantages of simple process, convenient operation, low cost, high removal efficiency, good circulation performance, and no secondary pollution. Taking tetracycline pharmaceutical wastewater as an example, the bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is used to treat tetracycline in water, showing excellent photocatalytic performance, wherein the maximum degradation rate of tetracycline can reach 92.02%. It can be seen that the bismuth iodide oxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst of the present invention can be widely used in the harmless treatment and toxicity elimination of antibiotics in pharmaceutical wastewater, which not only opens up a new idea of ​​constructing heterojunction photocatalysts of bismuth iodide oxide and quantum dot self-modified imine covalent organic framework, but also promotes the application of quantum dot self-modified imine covalent organic framework heterojunction photocatalysts in environmental governance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0035] Figure 1 This is a scanning electron microscope image of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0036] Figure 2 This is a transmission electron microscopy image of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0037] Figure 3 This is the XPS energy spectrum of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0038] Figure 4 This is a scanning electron microscope image of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0039] Figure 5 This is a transmission electron microscope image of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0040] Figure 6This is the XPS energy spectrum of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0041] Figure 7 This is a scanning electron microscope image of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0042] Figure 8 This is a transmission electron microscope image of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0043] Fig. 9 XRD patterns of quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 5% QDS-RTCOF, BiOI / 10% QDS-RTCOF, BiOI / 20% QDS-RTCOF) prepared in Examples 1 to 3 of the present invention.

[0044] Fig.10 FTIR spectra of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0045] Fig.11 The UV-visible diffuse reflection absorption spectra of the quantum dot self-modified imine covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0046] Fig.12 The photogenerated surface photocurrent diagrams of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0047] Fig.13This is a relationship graph of the change in the residual rate of tetracycline degradation over time during the photoreaction stage for the quantum dot self-modified imine covalent organic framework (QDS-RTCOF), bismuth oxyiodide (BiOI), bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalysts (BiOI / 5% QDS-RTCOF, BiOI / 10% QDS-RTCOF and BiOI / 20% QDS-RTCOF) in Example 4 of the present invention.

[0048] Fig.14 This is a graph showing the relationship between the degradation residual rate of tetracycline at different concentrations and time of the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) in Example 5 of the present invention.

[0049] Fig.15 This is a diagram showing the cyclic degradation effect of tetracycline wastewater by the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) in Example 6 of the present invention.

[0050] Fig.16 This is a diagram showing the degradation effect of tetracycline wastewater by the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst prepared under different solvent conditions in Example 7 of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0052] Embodiment 1:

[0053] A bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst comprises a quantum dot self-modified imine-based covalent organic framework, and bismuth iodide nanosheets are loaded on the cavity and surface of the quantum dot self-modified imine-based covalent organic framework.

[0054] In this embodiment, the mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth oxyiodide nanosheets is 1:10.

[0055] In this embodiment, the bismuth oxyiodide nanosheets are BiOI, and the bismuth oxyiodide nanosheets are in the form of nanosheets stacked layer by layer.

[0056] In this embodiment, the quantum dot self-modified imine-based covalent organic framework is a quantum dot self-modified high molecular organic polymer, such as QDS-RTCOF, and the quantum dot self-modified imine-based covalent organic framework is a dispersed particle block structure.

[0057] In this embodiment, the bismuth iodide oxyhydroxide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is in the form of porous microspheres with a particle size of 2 μm to 5 μm.

[0058] A method for preparing the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst in the above-mentioned embodiment comprises the following steps:

[0059] S1. Preparation of quantum dot self-modified imine-based covalent organic frameworks

[0060] (1.1) Dissolve 100 mg of 1,3,5-tris(4-aminophenyl)benzene in 14.2 mL of 3 mol / L acetic acid solution and stir well to obtain solution A. Dissolve 46 mg of 1,3,5-benzenetricarboxaldehyde in 14.2 mL of 3 mol / L acetic acid solution and stir well to obtain solution B.

[0061] (1.2) Solution A and solution B obtained in step (1.1) were mixed to immediately form an orange gel, which was placed at room temperature for 72 hours for quantum dot self-modification reaction. The gel was then washed using Soxhlet extraction, and the purified solid was dried in an open atmosphere for 48 hours to obtain a quantum dot self-modified imine-based covalent organic framework, denoted as QDS-RTCOF.

[0062] Figure 1 This is a scanning electron microscope image of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0063] Figure 2 This is a transmission electron microscopy image of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0064] Figure 3 This is the XPS energy spectrum of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) prepared in Example 1 of the present invention.

[0065] Depend on Figure 1 to Figure 3 It can be seen that the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF) sample prepared by the present invention is an irregularly arranged staggered distribution of particle blocks, containing three elements of C, N and O, and its transmission electron microscope image shows a dispersed flaky structural ripple.

[0066] S2. Preparation of bismuth iodide

[0067] (2.1) Mix 2.43 g Bi(NO3)3·5H2O with 40 mL ethylene glycol and stir at room temperature for 1 h to obtain a bismuth salt solution; mix 0.83 g KI with 40 mL ethylene glycol and stir at room temperature for 1 h to obtain an iodine salt solution.

[0068] (2.2) The bismuth salt solution and the iodine salt solution obtained in step (2.1) are mixed and transferred to a 100 mL reactor, and a hydrothermal reaction is carried out at 160° C. for 12 h. The mixture is cooled to room temperature, and the reaction product is washed three times with deionized water. The yellow-brown solid after centrifugation is dried in a vacuum drying oven at 70° C. to obtain bismuth oxide iodide, which is referred to as BiOI.

[0069] Figure 4 This is a scanning electron microscope image of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0070] Figure 5 This is a transmission electron microscope image of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0071] Figure 6 This is the XPS energy spectrum of bismuth oxyiodide (BiOI) prepared in Example 1 of the present invention.

[0072] Depend on Figures 4 to 6 It can be seen that the bismuth iodide (BiOI) sample prepared by the present invention is in the form of stacked nanosheets, containing three elements of Bi, O and I, indicating that the prepared BiOI is consistent with the morphological characteristics of bismuth iodide semiconductors reported in the literature.

[0073] S3. Preparation of Bismuth Oxyiodide / Quantum Dot Self-Modified Imine-Based Covalent Organic Framework Heterojunction Photocatalyst

[0074] Weigh 200 mg of the bismuth iodide obtained in step S2 and mix it with 50 mL of ethanol, and ultrasonically treat it for 30 minutes to form a BiOI solution; weigh 20 mg of the quantum dot self-modified imine covalent organic framework obtained in step S1, add it to the BiOI solution and stir it continuously for 8 hours, and finally repeatedly filter and wash it with ultrapure water, and dry the material in a vacuum drying oven to obtain a yellow-brown solid powder, which is a bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst, recorded as BiOI / 10%QDS-RTCOF.

[0075] Figure 7 This is a scanning electron microscope image of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0076] Figure 8 This is a transmission electron microscope image of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention.

[0077] Depend on Figure 7 and Figure 8It can be seen that in the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst of the present invention, BiOI nanosheets are unevenly distributed in the cavity and surface of QDS-RTCOF, in the form of porous microspheres with a particle size of 2 μm to 5 μm.

[0078] Example 2

[0079] A bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst is basically the same as the bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 1, except that the mass ratio of the quantum dot self-modified imine covalent organic framework to the bismuth oxide iodide nanosheets in the bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 2 is 1:20.

[0080] A method for preparing the bismuth iodide oxide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in the above-mentioned embodiment is basically the same as the method for preparing the bismuth iodide oxide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 1, except that the amount of the quantum dot self-modified imine covalent organic framework used in step S3 of Example 2 is 10 mg.

[0081] The bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst prepared in Example 2 is labeled BiOI / 5%QDS-RTCOF.

[0082] Example 3

[0083] A bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst is basically the same as the bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 1, except that: in the bismuth oxide iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 3, the mass ratio of the quantum dot self-modified imine covalent organic framework to the bismuth oxide iodide nanosheets is 1:5.

[0084] A method for preparing the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in the above-mentioned embodiment is basically the same as the method for preparing the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in Example 1, except that the amount of the quantum dot self-modified imine covalent organic framework heterojunction used in step S3 of Example 3 is 40 mg.

[0085] The bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst prepared in Example 3 is labeled BiOI / 20% QDS-RTCOF.

[0086] Fig. 9The XRD patterns of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 5% QDS-RTCOF, BiOI / 10% QDS-RTCOF, BiOI / 20% QDS-RTCOF) prepared in Examples 1 to 3 of the present invention are shown in FIG. Fig. 9 It can be seen that BiOI has crystal diffraction peaks of (102), (110), (200), (212), (220) and (302) at 28.88°, 31.64°, 45.32°, 55.28°, 66.28° and 75.26°, respectively. QDS-RTCOF has diffraction peaks at 2θ values ​​of 5.78°, 15.12° and 25.34°, corresponding to the (001), (210) and (101) lattice planes, respectively. Based on the composite of QDS-RTCOF and BiOI at different doping ratios, the crystal diffraction peaks (200), (212), (220) and (302) representing BiOI become less obvious as the doping ratio increases when the QDS-RTCOF doping ratio is 20%, while the crystal diffraction peaks (210) and (101) representing QDS-RTCOF become more obvious as the doping ratio increases, which indicates that QDS-RTCOF and BiOI are successfully combined.

[0087] Fig.10 The FTIR spectra of the quantum dot self-modified imine-based covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention are shown in FIG. Fig.10 It can be seen that BiOI / 10% QDS-RTCOF is at 1620cm -1 、1700cm -1 、3030cm -1 The absorption peaks of C=N, CH-O and NH bonds appeared at 774 cm-1, which correspond to the imine bond outside the benzene ring of QDS-RTCOF and the functional groups of the synthetic raw materials. -1 、1630cm -1 and 3420cm -1 The Bi-O asymmetric vibration absorption peak, the hydroxyl groups of physically adsorbed water molecules and the interlayer OH groups appeared at the wavenumber.

[0088] Fig.11The UV-visible diffuse reflection absorption spectra of the quantum dot self-modified imine covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention are shown in FIG. Fig.11 It can be seen that compared with BiOI monomer, the longest absorption wavelength of BiOI / 10% QDS-RTCOF has a red shift, indicating that the doping of QDS-RTCOF expands the light absorption edge of the composite material in the visible light range.

[0089] Fig.12 The photogenerated surface photocurrent diagram of the quantum dot self-modified imine covalent organic framework (QDS-RTCOF), bismuth oxyiodide semiconductor (BiOI), and bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1 of the present invention. Fig.12 It can be seen that the photocurrent generated by BiOI / 10% QDS-RTCOF under visible light irradiation is significantly higher than that of monomer BiOI and QDS-RTCOF, which indicates that the composite of BiOI and QDS-RTCOF improves the photogenerated charge transfer and separation efficiency of the material, thereby having better photocatalytic activity.

[0090] Example 4

[0091] An application of a bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst in coupled adsorption-photocatalytic treatment of pharmaceutical wastewater, specifically using the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst prepared in Examples 1 to 3 to treat tetracycline wastewater, comprising the following steps:

[0092] Weigh 20 mg of the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalysts (BiOI / 5% QDS-RTCOF, BiOI / 10% QDS-RTCOF and BiOI / 20% QDS-RTCOF) prepared in Examples 1 to 3, the bismuth iodide (BiOI) in Example 1, and the quantum dot self-modified imine covalent organic framework (QDS-RTCOF), respectively, and add them to 100 mL of a 10 mg / L tetracycline (TC) aqueous solution, stir magnetically for 1 hour in the dark to reach adsorption equilibrium, place under a xenon lamp, and irradiate under visible light with a wavelength of >420 nm for 60 minutes to perform a photocatalytic degradation reaction on the tetracycline (TC) aqueous solution, thereby completing the adsorption-photocatalytic treatment of the tetracycline aqueous solution.

[0093] The reaction solution obtained after the photocatalytic degradation was filtered through a 0.22 μm filter membrane, and the tetracycline content in the filtrate was determined by ultraviolet spectrophotometry at a wavelength of 358.3 nm. The adsorption of tetracycline by different materials and the residual rate of photocatalytic degradation were calculated. The results are as follows: Fig.13 shown.

[0094] Fig.13 The relationship between the residual rate of tetracycline degradation and time change of quantum dot self-modified imine covalent organic framework (QDS-RTCOF), bismuth oxyiodide (BiOI), bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 5% QDS-RTCOF, BiOI / 10% QDS-RTCOF and BiOI / 20% QDS-RTCOF) in Example 4 of the present invention during the photoreaction stage is shown in FIG. Fig.13 It can be seen that the degradation residual rates of tetracycline by BiOI, QDS-RTCOF, BiOI / 5%QDS-RTCOF, BiOI / 10%QDS-RTCOF and BiOI / 20%QDS-RTCOF under visible light are 27.2%, 46.6%, 14.1%, 11.7% and 16.9%, respectively, and the corresponding degradation rates are 72.8%, 53.4%, 85.9%, 88.3% and 83.1%, respectively. The degradation rates in the photoreaction stage are 0.017min, respectively. -1 、0.012min -1 、0.027min -1 、0.029min -1 and 0.024min -1 , which indicates that the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst of the present invention has good photocatalytic performance, among which the degradation rate of BiOI / 10% QDS-RTCOF in the photoreaction stage is 2.42 times that of the monomer QDS-RTCOF. This shows that when the mass ratio of QDS-RTCOF and BiOI is 1:10, the prepared bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst has the highest degradation efficiency for tetracycline in the photoreaction stage, which is the most suitable ratio.

[0095] Example 5

[0096] An application of a bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction in coupled adsorption-photocatalytic treatment of pharmaceutical wastewater, specifically using the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst prepared in Example 1 to treat tetracycline wastewater of different concentrations, comprising the following steps:

[0097] Weigh 4 portions of bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction (BiOI / 10% QDS-RTCOF) prepared in Example 1, 20 mg each, and add them into 100 mL of tetracycline aqueous solution with concentrations of 10 mg / L, 20 mg / L, 30 mg / L and 40 mg / L, respectively. Stir magnetically in the dark for 1 hour to reach adsorption equilibrium and place under a xenon lamp. Irradiate with visible light with a wavelength of >420 nm for 60 minutes to perform photocatalytic degradation reaction on the tetracycline (TC) aqueous solution, thereby completing the adsorption-photocatalytic treatment of the tetracycline aqueous solution.

[0098] The reaction solution obtained after the photocatalytic degradation was filtered through a 0.22 μm filter membrane, and the tetracycline content in the filtrate was determined by ultraviolet spectrophotometry at a wavelength of 358.3 nm. The adsorption and photocatalytic degradation residual rates of tetracycline at different concentrations on the bismuth oxyiodide / quantum dot self-modified imine covalent organic framework heterojunction (BiOI / 10% QDS-RTCOF) were calculated. The results are shown in FIG. Fig.14 shown.

[0099] Fig.14 This is a graph showing the relationship between the degradation residual rate of tetracycline at different concentrations and the time change of the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) in Example 5 of the present invention. Fig.14 It can be seen that when the tetracycline concentration changes from 10 mg / L to 40 mg / L, the removal efficiency of BiOI / 10%QDS-RTCOF for TC first decreases and then tends to be flat. Among them, BiOI / 10%QDS-RTCOF can still achieve a photocatalytic degradation effect of 74.38% for 40 mg / L TC, which is not much different from the degradation rate of 30 mg / L TC (76.45%), indicating that the increase in TC concentration does not significantly affect the photocatalytic activity of BiOI / 10%QDS-RTCOF.

[0100] Example 6

[0101] The stability of the bismuth iodide oxyhydroxide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst of the present invention is investigated, comprising the following steps:

[0102] (1) Weigh 20 mg of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) prepared in Example 1, add it to 100 mL of a 10 mg / L tetracycline aqueous solution, stir it magnetically in the dark for 1 h to reach adsorption equilibrium, and place it under a xenon lamp and irradiate it with visible light of a wavelength >420 nm for 60 min to complete the adsorption-photocatalytic treatment of the tetracycline aqueous solution.

[0103] (2) After completing the treatment in step (1), the bismuth iodide oxide / imine covalent organic framework heterojunction photocatalyst is collected by a suction filtration device, washed with ethanol and ultrapure water, and dried in a vacuum at 70°C.

[0104] (3) Using the same treatment method as step (1), the bismuth iodide oxide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst obtained after drying in step (2) was repeatedly used to treat the tetracycline aqueous solution, and a total of 4 repeated experiments were performed.

[0105] The reaction solution obtained after each photocatalytic degradation was filtered through a 0.22 μm filter membrane, and the tetracycline content in the filtrate was determined by ultraviolet spectrophotometry at a wavelength of 358.3 nm. The coupled adsorption-photocatalytic degradation residual rate of tetracycline by the circulating BiOI / 10% QDS-RTCOF was calculated. The results are shown in Fig.15 shown.

[0106] Fig.15 This is a diagram showing the cyclic degradation effect of bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst (BiOI / 10% QDS-RTCOF) on tetracycline wastewater in Example 6 of the present invention. Fig.15 It can be seen that after the BiOI / 10% QDS-RTCOF of the present invention is recycled for 5 times by adsorption-photocatalysis, the catalytic degradation efficiency of tetracycline is still more than 73%, which indicates that the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst of the present invention has good stability.

[0107] Example 7

[0108] The photocatalytic performance of bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalysts prepared under different solvent conditions was investigated, including the following steps:

[0109] (1) Weighing 200 mg of the bismuth iodide prepared in Example 1, mixing with 50 mL of different solvents (ethanol, methanol, ethylene glycol, acetic acid), and ultrasonically treating for 30 min to form BiOI solutions or BiOI suspensions prepared under different solvent conditions; weighing 20 mg of the quantum dot self-modified imine-based covalent organic framework prepared in Example 1, adding it to different BiOI solutions, stirring continuously for 8 h, and finally repeatedly filtering and washing with ultrapure water, and drying the material in a vacuum drying oven to obtain a yellow-brown solid powder, that is, obtaining bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalysts prepared under different solvent conditions.

[0110] (2) Weigh 20 mg of the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst prepared in step (1), add them into 100 mL of a 10 mg / L tetracycline aqueous solution, stir magnetically for 1 h in the dark to reach adsorption equilibrium, place under a xenon lamp, and irradiate with visible light of a wavelength >420 nm for 60 min to complete the adsorption-photocatalytic treatment of the tetracycline aqueous solution.

[0111] The reaction solution obtained after each photocatalytic degradation was filtered through a 0.22 μm filter membrane, and the tetracycline content in the filtrate was determined by ultraviolet spectrophotometry at a wavelength of 358.3 nm. The residual rate of photocatalytic degradation of tetracycline by the bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst prepared under different solvent conditions was calculated. The results are shown in FIG. Fig.16 shown.

[0112] Fig.16 The degradation effect of bismuth iodide / quantum dot self-modified imine-based covalent organic framework heterojunction photocatalyst on tetracycline wastewater prepared under different solvent conditions in Example 7 of the present invention is shown in FIG. Fig.16 It can be seen that when methanol, ethylene glycol and acetic acid are used as solvents to prepare bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalysts, the degradation effect of tetracycline is not as good as that of the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst prepared using ethanol as a solvent. The reason may be that bismuth iodide is difficult to completely dissolve in methanol, ethylene glycol and acetic acid, making it difficult to evenly and firmly disperse bismuth iodide in the cavity and surface of the quantum dot self-modified imine covalent organic framework, and thus it is difficult to obtain a heterojunction photocatalyst with excellent photocatalytic performance.

[0113] From the above results, it can be seen that the bismuth iodide / quantum dot self-modified imine covalent organic framework heterojunction photocatalyst of the present invention has higher photocatalytic activity under the synergistic effect of the quantum dot self-modified imine covalent organic framework and the bismuth iodide nanosheets, and has the advantages of good photocatalytic activity, high visible light absorption intensity, wide absorption range, high photogenerated charge transfer and separation efficiency, strong adaptability and stability to high-concentration wastewater, etc. When used for treating medical wastewater, it has the advantages of good degradation effect, no secondary pollution, low cost, simple and convenient operation, etc., and can be widely used in the harmless treatment and toxicity elimination of antibiotics in wastewater, which is of great significance for the development of quantum dot self-modified imine covalent organic framework-based materials and their application in the field of environmental protection.

[0114] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst, characterized in that: The invention comprises a quantum dot self-modified imine-based covalent organic framework, wherein bismuth iodide oxide nanosheets are loaded on the cavity and the surface of the quantum dot self-modified imine-based covalent organic framework.

2. The bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst according to claim 1, characterized in that: The mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth iodide oxide nanosheets is 1 to 4:

20.

3. The bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst according to claim 2, characterized in that: The mass ratio of the quantum dot self-modified imine-based covalent organic framework to the bismuth oxyiodide nanosheet is 1.6 to 3:20; the bismuth oxyiodide nanosheet is BiOI; the quantum dot self-modified imine-based covalent organic framework is QDS-RTCOF; the quantum dot self-modified imine-based covalent organic framework is a dispersed particle block structure; the bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is a porous microsphere; the particle size of the bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is 2 μm to 5 μm.

4. A method for preparing a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: The bismuth iodide, quantum dot self-modified imine-based covalent organic framework and ethanol are mixed for electrostatic self-assembly, filtered, washed and dried to obtain a bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst.

5. The preparation method according to claim 4, characterized in that: The electrostatic self-assembly comprises: mixing bismuth iodide and ethanol, ultrasonically treating for 30 to 60 minutes, adding quantum dot self-modified imine covalent organic framework, stirring for 8 to 10 hours, and obtaining bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst.

6. The preparation method according to claim 5, characterized in that: The mass volume ratio of the bismuth iodide oxide to the ethanol is 4 mg: 1 mL to 4 mL; the mass volume ratio of the bismuth iodide oxide to the quantum dot self-modified imine-based covalent organic framework is 20: 1 to 4.

7. The preparation method according to any one of claims 4 to 6, characterized in that The preparation method of the bismuth iodide oxide comprises the following steps: (1.1) Mixing a bismuth salt with ethylene glycol and stirring for 1 h to 2 h to obtain a bismuth salt solution; mixing an iodine salt with ethylene glycol and stirring for 1 h to 2 h to obtain an iodine salt solution; the mass ratio of the bismuth salt to the iodine salt is 1.5 to 3:1; the mass volume ratio of the bismuth salt to the ethylene glycol in the bismuth salt solution is 2.43 g: 40 mL to 60 mL; the mass volume ratio of the iodine salt to the ethylene glycol in the iodine salt solution is 0.83 g: 40 mL to 60 mL; the bismuth salt is bismuth nitrate pentahydrate; and the iodine salt is potassium iodide; (1.2) mixing the bismuth salt solution and the iodine salt solution obtained in step (1.1) for hydrothermal reaction to obtain bismuth iodide oxide; the temperature of the hydrothermal reaction is 160° C. to 180° C.; the time of the hydrothermal reaction is 12 h to 6 h; The method for preparing the quantum dot self-modified imine-based covalent organic framework comprises the following steps: (2.1) Dissolving 1,3,5-tris(4-aminophenyl)benzene in an acetic acid solution to obtain a solution A; dissolving 1,3,5-benzenetricarboxaldehyde in an acetic acid solution to obtain a solution B; the mass ratio of the 1,3,5-tris(4-aminophenyl)benzene to 1,3,5-benzenetricarboxaldehyde is 50-80:23-46; the ratio of 1,3,5-tris(4-aminophenyl)benzene to the acetic acid solution in the solution A is 50 mg:7.0 mL-12.4 mL; the ratio of 1,3,5-benzenetricarboxaldehyde to the acetic acid solution in the solution B is 23 mg:7.0 mL-12.4 mL; the concentration of the acetic acid solution is 3 mol / L; (2.2) Solution A and solution B obtained in step (2.1) are mixed to carry out quantum dot self-modification reaction, washed, and dried to obtain a quantum dot self-modified imine-based covalent organic framework; the time for the quantum dot self-modification reaction is 72h to 96h, and the drying time is 48h to 72h.

8. Use of the bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst as described in any one of claims 1 to 3 or the bismuth oxyiodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst prepared by the preparation method as described in any one of claims 4 to 7 in treating medical wastewater.

9. The use according to claim 8, characterized in that: When using bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst to treat medical wastewater, the method comprises the following steps: mixing the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst with the medical wastewater, stirring, and performing a photocatalytic degradation reaction under light conditions to complete the treatment of the medical wastewater; the addition amount of the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst is 150 mg to 350 mg of the bismuth iodide / quantum dot self-modified covalent organic framework heterojunction photocatalyst per liter of the medical wastewater.

10. The use according to claim 9, characterized in that: The antibiotic in the pharmaceutical wastewater is tetracycline; the concentration of the antibiotic in the pharmaceutical wastewater is 10 mg / L to 50 mg / L; the stirring time is 20 min to 80 min; the photocatalytic degradation reaction is carried out under visible light with a wavelength greater than 420 nm; and the photocatalytic degradation reaction time is 10 min to 60 min.

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