Bipyridyl imino covalent organic framework photocatalyst capable of utilizing natural light as well as preparation method and application of bipyridyl imino covalent organic framework photocatalyst

Abstract

The invention discloses a bipyridine imino covalent organic framework photocatalyst capable of utilizing natural light as well as a preparation method and application thereof, and the photocatalyst is prepared by taking benzo [1, 2-b: 3, 4-b ': 5, 6-b'] trithiophene-2, 5, 8-trialdehyde and 2, 2 '-bipyridine-5, 5'-diamine as raw materials and carrying out condensation reaction. The dipyridyl imino covalent organic framework photocatalyst prepared by the invention has the advantages of significant difference in internal charge density, wide light absorption range, high utilization rate of natural light and the like, has very high photocatalytic activity under the condition of natural light, and also has the advantages of high charge separation efficiency, high conductivity, stable physical and chemical properties and the like; as a novel natural light photocatalyst with excellent photocatalytic performance, the photocatalyst can be used for treating antibiotic wastewater under the condition of natural light, can realize efficient degradation of antibiotics, and is high in use value and good in application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and relates to a bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light, and a preparation method and application thereof. Background Art

[0003] Covalent organic frameworks (COFs) are crystalline network materials composed of strong covalent bonds of symmetric organic molecules. Such materials have advantages such as a large specific surface area and excellent photocatalytic performance, and have been used in the field of photocatalytic degradation of antibiotics. However, so far, the method of using COFs materials for photocatalytic degradation of antibiotics is mainly carried out under the condition of xenon lamps in the laboratory, but there are still few reports on the method of photocatalytic treatment under natural light. The reason may be that the existing COFs materials only have the ability to absorb sunlight in certain bands, but do not have the full-spectrum absorption characteristics. As a result, it is difficult for the existing COFs materials to improve their photocatalytic activity under natural light, and thus it is difficult for the existing COFs materials to achieve efficient degradation of antibiotics under natural light conditions. In addition, the internal charge density difference of the existing COFs materials is small, which is not conducive to promoting the improvement of charge separation efficiency and electron transfer efficiency, nor is it conducive to reducing the energy consumption from the excited state to the acceptor. This is another reason why the existing COFs materials cannot exhibit excellent photocatalytic performance under natural light conditions. The existence of the above technical defects greatly limits the application of COFs materials in photocatalytic degradation of antibiotics in water bodies. Therefore, finding a covalent organic framework photocatalyst with a significant difference in internal charge density, a wide light absorption range, and high natural light utilization rate is of great significance for effectively removing antibiotics in water bodies under sunlight and is also an urgent need. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light, with a significant difference in internal charge density, a wide light absorption range, and high natural light utilization rate, and a preparation method and application thereof.

[0005] To solve the above technical problem, the present invention adopts the following technical solutions:

[0006] A bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light, wherein the bipyridyl imine-based covalent organic framework photocatalyst is prepared by a condensation reaction using benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials.

[0007] For the above-mentioned bipyridyl imine-based covalent organic framework photocatalyst, in a further improvement, the mass ratio of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is 33:28.

[0008] For the above-mentioned bipyridyl imine-based covalent organic framework photocatalyst, in a further improvement, the structure of the bipyridyl imine-based covalent organic framework photocatalyst is formed by connecting periodic structural units, and the structure of the periodic structural unit is:

[0009] The wavy line in the formula is the omitted repeating structural unit.

[0010] As a general technical concept, the present invention also provides a preparation method of a bipyridyl imine-based covalent organic framework photocatalyst. The preparation method uses benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials to prepare the bipyridyl imine-based covalent organic framework photocatalyst through a condensation reaction.

[0011] For the above-mentioned preparation method, in a further improvement, it includes the following steps:

[0012] S1. Mix benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine, and sequentially add an organic solvent and an acid catalyst to obtain a mixture.

[0013] S2. Perform a freeze-pump-thaw cycle degassing on the mixture obtained in step S1, and seal it under vacuum.

[0014] S3. Perform a condensation reaction on the mixture obtained after the freeze-pump-thaw cycle degassing treatment in step S2 to obtain the bipyridyl imine-based covalent organic framework photocatalyst.

[0015] For the above-mentioned preparation method, in a further improvement, in step S1, the mass ratio of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is 33:28; the ratio of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde to the organic solvent and the acid catalyst is 33 mg:1 mL:0.1 mL; the organic solvent is a mixed solvent of ortho-dichlorobenzene and N,N-dimethylacetamide, and the volume ratio of ortho-dichlorobenzene to N,N-dimethylacetamide in the mixed solvent of ortho-dichlorobenzene and N,N-dimethylacetamide is 1:1, and the acid catalyst is acetic acid.

[0016] In the above preparation method, for further improvement, in step S2, the temperature of the condensation reaction is 120 °C, and the time of the condensation reaction is 48 h to 72 h; after the condensation reaction, the following treatments are further included: washing, filtering, and drying the reaction product; the washing is carried out by washing with tetrahydrofuran and acetone three times respectively, the filtering is carried out with a 0.22 μm organic filter membrane, the drying is carried out under vacuum conditions, the temperature of the drying is 80 °C, and the time of the drying is 24 h.

[0017] In the above preparation method, for further improvement, the structure of the bipyridyl imine-based covalent organic framework photocatalyst is formed by connecting periodic structural units, and the structure of the periodic structural unit is as follows:

[0018] The wavy line in the formula represents an omitted repeating structural unit.

[0019] As a general technical concept, the present invention also provides an application of the above bipyridyl imine-based covalent organic framework photocatalyst or the bipyridyl imine-based covalent organic framework photocatalyst prepared by the above preparation method in degrading antibiotics.

[0020] In the above application, for further improvement, the degradation treatment of antibiotics in water by using the bipyridyl imine-based covalent organic framework photocatalyst includes the following steps: mixing the bipyridyl imine-based covalent organic framework photocatalyst with antibiotic wastewater, stirring, and carrying out a photocatalytic reaction under light conditions to complete the degradation treatment of antibiotics in water; the addition amount of the bipyridyl imine-based covalent organic framework photocatalyst is 0.08 g to 0.1 g of the bipyridyl imine-based covalent organic framework photocatalyst added per liter of the antibiotic wastewater.

[0021] In the above application, for further improvement, the initial concentration of the antibiotic wastewater is 5 mg / L to 10 mg / L; the antibiotics in the antibiotic wastewater are quinolone antibiotics and / or tetracycline antibiotics; the quinolone antibiotics are at least one of ofloxacin and norfloxacin; the tetracycline antibiotic is tetracycline; the stirring is carried out under dark conditions, the rotation speed of the stirring is 300 r / min to 400 r / min, the time of the stirring is 0.5 h to 1 h; the light source used in the process of the photocatalytic reaction is a xenon lamp and / or natural light; the time of the photocatalytic reaction is 30 min to 50 min

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] (1) Aiming at the deficiencies in existing COFs materials, such as small internal charge density difference and poor absorption ability of natural light, and the resulting defects that existing COFs materials are difficult to exhibit excellent photocatalytic activity under natural light conditions, the present invention creatively proposes a bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light, which is prepared by a condensation reaction using benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials. Compared with the conventional organic framework (Bpy-COF), the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in the present invention has the following advantages by introducing bipyridyl sites: (a) By introducing bipyridyl sites, the structure of the imine-based covalent organic framework can be optimized, enabling it to have excellent absorption ability for the full-spectrum sunlight, which is beneficial to improving the utilization rate of natural light, and further enabling the bipyridyl imine-based covalent organic framework photocatalyst to exhibit very excellent photocatalytic activity under natural light; (b) By introducing bipyridyl sites, the optical band gap of the imine-based covalent organic framework can be improved, making it have a suitable optical band gap, being more easily excited to form electrons and holes, and generating more active species, thus being beneficial to improving the photocatalytic activity of the bipyridyl imine-based covalent organic framework photocatalyst under natural sunlight irradiation; (c) Through bipyridyl regulation, a significant difference in the internal charge density of the covalent organic framework is achieved, enabling the bipyridyl imine-based covalent organic framework photocatalyst to establish a suitable electron donor-acceptor interaction, which can not only promote the separation of photogenerated carriers, being beneficial to improving the charge separation efficiency, but also promote the aggregation of electrons in the bipyridyl unit, being beneficial to improving the electron transfer efficiency. At the same time, it can also reduce the energy consumption from the excited state to the acceptor during the water pollution process, which is also beneficial to improving the photocatalytic activity of the bipyridyl imine-based covalent organic framework photocatalyst under natural sunlight irradiation. The bipyridyl imine-based covalent organic framework photocatalyst of the present invention has the advantages of significant difference in internal charge density, wide light absorption range and high natural light utilization rate, etc. It has very high photocatalytic activity under natural light conditions, and also has the advantages of high charge separation efficiency, high conductivity, stable physical and chemical properties, etc. As a new type of natural light photocatalyst with excellent photocatalytic performance, it can treat antibiotic wastewater under natural light conditions and can achieve efficient degradation of antibiotics, with high use value and good application prospects.

[0024] (2) In the present invention, the mass ratio of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is optimized to be 33∶28. By optimizing the dosages of each raw material and the condensation reaction conditions, the nucleation and growth rates during the reaction can be precisely controlled, so as to obtain high-quality covalent organic framework crystals. In particular, even a slight change in the above conditions may lead to the inability to obtain the corresponding covalent organic framework structure with bipyridine imine groups.

[0025] (3) In the present invention, the bipyridine imine-based covalent organic framework photocatalyst can directly utilize natural sunlight to effectively purify antibiotics in water. Taking ofloxacin as an example, 100% of ofloxacin can be removed within 40 minutes, and the utilization efficiency of natural light is remarkable. In addition, under the conditions of xenon lamp, natural water, and aquaculture wastewater, complete removal of pollutants can be achieved within 30 - 50 minutes, with high application value and good application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] Figure 1 It is a synthesis route diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) in Embodiment 1 of the present invention and the covalent organic framework (Bpy-COF) in Comparative Example 1.

[0028] Figure 2 It is an XRD diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Embodiment 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1.

[0029] Figure 3 It is an ultraviolet-visible diffuse reflection diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Embodiment 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1.

[0030] Figure 4 It is an electrochemical impedance spectrum and fluorescence photoluminescence spectrum diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Embodiment 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1.

[0031] Figure 5 It is a degradation effect diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) and the covalent organic framework (Bpy-COF) on ofloxacin in Embodiment 2 of the present invention.

[0032] Figure 6 This is the degradation effect of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 3 of the present invention on ofloxacin under actual sunlight irradiation for different time periods.

[0033] Figure 7 This is the degradation effect diagram of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 4 of the present invention on ofloxacin in actual water under natural light irradiation.

[0034] Figure 8 This is the degradation effect diagram of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 5 of the present invention on ofloxacin under different pH conditions. Detailed implementation manners

[0035] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0036] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the obtained data are the averages of more than three repeated experiments.

[0037] Example 1

[0038] A bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light is prepared by a condensation reaction using benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials, wherein the mass ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is 33:28.

[0039] In this example, the structure of the bipyridyl imine-based covalent organic framework photocatalyst is composed of periodic structural units connected together, and the structure of the periodic structural unit is:

[0040] The wavy line in the formula represents the omitted repeating structural unit.

[0041] A preparation method of the bipyridyl imine-based covalent organic framework photocatalyst in the above example, the synthesis route is as Figure 1 shown, and it includes the following steps:

[0042] (1) Weigh 33 mg of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde and 28 mg of 2,2'-bipyridine-5,5'-diamine and mix them in a vacuum tube. Then add 0.5 mL of o-dichlorobenzene and 0.5 mL of N,N-dimethylacetamide respectively, sonicate for 15 min to mix evenly, add 0.1 mL of acetic acid, sonicate for 3 min to mix evenly, and obtain a mixture.

[0043] (2) Conduct three freeze-pump-thaw cycles of degassing on the mixture in step (1), that is, freeze it with liquid nitrogen, then suck out the gas in the frozen mixture through an oil pump, and then thaw it. This process is cycled 3 times, vacuum seal it, heat it at 120 °C for 72 h for condensation reaction, and take it out and cool it after completion.

[0044] (3) Wash the reaction product in step (2) three times with tetrahydrofuran and acetone respectively (10 mL each time), filter it with a 0.22 μm organic filter membrane, and then dry it under vacuum at 80 °C for 24 h to obtain a bipyridyl imine-based covalent organic framework photocatalyst that can utilize natural light, denoted as Bby-COF.

[0045] Comparative Example 1

[0046] A covalent organic framework (Bpy-COF), whose synthesis route is as Figure 1 shown, and the specific preparation method is as follows:

[0047] (1) Weigh 33 mg of benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde and 27 mg of 6-(4-aminophenyl)pyridin-3-amine and mix them in a vacuum tube. Then add 0.5 mL of o-dichlorobenzene and 0.5 mL of N,N-dimethylacetamide respectively, sonicate for 15 min to mix evenly, then add 0.1 mL of acetic acid, sonicate for 3 min to mix evenly, and obtain a mixture.

[0048] (2) Conduct three freeze-pump-thaw cycles of degassing on the mixture in step (1), that is, freeze it with liquid nitrogen, then suck out the gas in the frozen mixture through an oil pump, and then thaw it. This process is cycled 3 times. Then vacuum seal it and heat it at 120 °C for 72 h, and take it out and cool it after completion.

[0049] (3) Wash the reaction product in step (2) three times with tetrahydrofuran and acetone respectively (10 mL each time), filter it with a 0.22 μm organic filter membrane, and then dry it under vacuum at 80 °C for 24 h to obtain a covalent organic framework, denoted as Bpy-COF, and the structure of its periodic structural unit is:

[0050] The wavy lines in the formula are omitted repeating structural units.

[0051] Performance detection

[0052] (1) XRD detection

[0053] Powder XRD detection was carried out on the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 above and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1. The results are as Figure 2 shown.

[0054] Figure 2 This is the XRD pattern of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1. As Figure 2 shown, these two covalent organic framework materials have similar characteristic peaks. The strong diffraction peak at 2θ = 2.8° of the material corresponds to the (100) crystal plane, which is consistent with the crystal structure of COFs materials, indicating that the main body of these two materials is a covalent organic framework. In addition, as Figure 2 shown, the XRD results of Bby-COF are closer to the theoretical structure simulation, indicating that Bby-COF has a more perfect AA stacking and a better pore stacking mode. The simulation results show through the residual coefficient that the figure variance factor (Rp) and the weighted figure variance factor (Rwp) of Bby-COF are 5.45% and 7.81% respectively, while those of Bpy-COF are 9.53% and 6.55%.

[0055] (2) UV-Vis diffuse reflectance detection

[0056] UV-Vis diffuse reflectance detection was carried out on the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 above and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1. The results are as Figure 3 shown.

[0057] Figure 3 This is the UV-Vis diffuse reflectance diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1. As Figure 3 shown, the light absorption ranges of these two covalent organic framework materials are around 400 - 600 nm, and they have excellent light absorption performance in visible light (λ > 420 nm), with the potential to actually utilize solar energy.

[0058] (3) Electrochemical impedance and fluorescence photoluminescence spectroscopy detection

[0059] The electrochemical impedance and fluorescence photoluminescence spectra of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 above and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1 were detected, and the results are as Figure 4 shown.

[0060] Figure 4 are the electrochemical impedance spectra and fluorescence photoluminescence spectra of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 of the present invention and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1. Figure 4 In, a is the electrochemical impedance spectrum and b is the fluorescence photoluminescence spectrum. As Figure 4 shown in a, compared with Bpy-COF in Comparative Example 1, Bby-COF prepared in Example 1 exhibits the smallest arc radius, indicating a lower charge transfer resistance, which is beneficial to the migration and diffusion of carriers at the interface. As Figure 4 shown in b, there is an obvious emission peak in Bpy-COF in Comparative Example 1, while Bby-COF in Example 1 exhibits a relatively low emission peak, confirming that the recombination rate of photo-generated carriers in Bby-COF in Example 1 is low and it performs best in the separation and transmission of photo-generated electron-hole pairs.

[0061] In addition, the temperature-variable emission spectra of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 and the covalent organic framework (Bpy-COF) prepared in Comparative Example 1 were detected. The results show that the exciton activation energy of Bby-COF is 33.8 meV, which is lower than 37.5 meV of Bpy-COF. This indicates that under the same sunlight irradiation, Bby-COF has the potential to generate more electron-hole pairs, which is beneficial to the degradation of pollutants.

[0062] Example 2

[0063] Application of a bipyridyl imine-based covalent organic framework photocatalyst in the degradation of antibiotics, specifically: using the bipyridyl imine-based covalent organic framework photocatalyst to degrade ofloxacin in water, including the following steps:

[0064] Weigh 5 mg of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1, add it to 60 mL of ofloxacin solution with a concentration of 5 mg / L, stir magnetically at a speed of 400 r / min for 1 h under dark conditions to reach adsorption equilibrium, then turn on the light source and irradiate under simulated sunlight (visible light with λ≥420 nm) for 50 min for photocatalytic reaction to complete the degradation of ofloxacin in water.

[0065] Control group 1: The covalent organic framework (Bpy-COF) prepared in Comparative Example 1 was used instead of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1, and other conditions were the same.

[0066] Figure 5 This is the degradation effect diagram of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) and the covalent organic framework (Bpy-COF) on ofloxacin in Example 2 of the present invention. From Figure 5 It can be seen that after 1 h of dark reaction adsorption and 50 min of light irradiation, the removal rates of ofloxacin by Bby-COF and Bpy-COF are 100% and 90% respectively. In addition, the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) can achieve a 100% removal efficiency in 30 min, and the rate constant is 0.2814 min -1 , which is much larger than 0.0445 min of Comparative Example 1 -1 , and is superior to the photocatalytic degradation efficiency of most reported catalysts for quinolone antibiotics. This is because the presence of bipyridine expands the absorption range of the material in visible light, promotes the transport of carriers at the surface and interface, enables it to better migrate to the active sites that can be contacted by pollutants, and realizes the effective attack on pollutants. Thus, it can be seen that the bipyridine imine-based covalent organic framework photocatalyst of the present invention has a narrow optical band gap, weak fluorescence intensity, high charge separation efficiency, and the best photocatalytic degradation effect.

[0067] Example 3

[0068] Application of a bipyridine imine-based covalent organic framework photocatalyst in degrading antibiotics, specifically: using the bipyridine imine-based covalent organic framework photocatalyst to degrade ofloxacin in water under natural light conditions, including the following steps:

[0069] Weigh 5 mg of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1, add it to 60 mL of ofloxacin solution with a concentration of 5 mg / L, magnetically stir at a speed of 400 r / min for 1 h under dark conditions to reach adsorption equilibrium, and then carry out photocatalytic reaction for 50 min under the irradiation of actual sunlight at different time periods, where the light irradiation time periods are 10:44 - 11:34 in the morning, 12:10 - 13:00 at noon, and 13:40 - 14:30 in the afternoon, to complete the degradation of ofloxacin in water.

[0070] Control group: Use a xenon lamp with a light intensity of 0.4 W to irradiate the ofloxacin solution instead of actual sunlight, and other conditions are the same.

[0071] During the magnetic stirring and photocatalysis processes, 1 mL of the sample was taken every 10 min, and the sample was filtered using a 0.22-μm filter head. The filtrate was taken and determined by a liquid chromatograph to determine the antibiotic concentration after adsorption and after light irradiation, so as to obtain the adsorption effect of Bby-COF on ofloxacin and the photocatalytic degradation effect.

[0072] Figure 6 This is the degradation effect of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 3 of the present invention on ofloxacin under actual sunlight irradiation at different time periods. Figure 6 In it, a is the sunlight intensity and actual temperature at each time period, and b is the corresponding degradation effect at each time period. From Figure 6 It can be seen from b that the bipyridyl imine-based covalent organic framework (Bby-COF) of the present invention can achieve 100% removal effect on ofloxacin within 30 - 50 min under the actual sunlight corresponding to different time periods, which indicates that the bipyridyl imine-based covalent organic framework of the present invention has an excellent visible light absorption range and can achieve the absorption of sunlight in the full wavelength band.

[0073] Example 4

[0074] An application of a bipyridyl imine-based covalent organic framework photocatalyst in degrading antibiotics, specifically: using the bipyridyl imine-based covalent organic framework photocatalyst to degrade ofloxacin in different water bodies, including the following steps:

[0075] Weigh 5 portions of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1, 5 mg for each portion, and add them to 5 portions of ofloxacin solutions (60 mL, 5 mg / L) prepared from pure water, tap water, lake water, river water and aquaculture wastewater respectively. Under dark conditions, magnetic stirring was carried out at a speed of 400 r / min for 1 h to reach the adsorption equilibrium, and then photocatalytic reaction was carried out under the irradiation of actual sunlight for 50 min to complete the degradation of ofloxacin in different water bodies.

[0076] During the magnetic stirring and photocatalysis processes, 1 mL of the sample was taken every 10 min, and the sample was filtered using a 0.22-μm filter head. The filtrate was taken and determined by a liquid chromatograph to determine the antibiotic concentration after adsorption and after light irradiation, so as to obtain the adsorption effect of Bby-COF on ofloxacin and the photocatalytic degradation effect.

[0077] Figure 7 This is the degradation effect diagram of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 4 of the present invention on ofloxacin in actual water bodies under natural light irradiation. From Figure 7It can be seen that compared with the conditions of laboratory pure water, actual water bodies including tap water, lake water, river water, and aquaculture wastewater can all accelerate the removal efficiency of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) for ofloxacin, and a 100% removal effect can be achieved within 30 minutes. This is because actual water bodies contain natural organic matter, and these organic matters have various functional groups, which can serve as a bridge between ofloxacin and Bby-COF. One side of the hydrophobic part can bind to Bby-COF through π-π interactions to form a Bby-COF / organic matter aggregate. Then, the aggregated hydrophilic part fixes the pollutant molecules through hydrophilic interactions, thereby promoting the removal and degradation of ofloxacin. The above results prove that the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) of the present invention is feasible in actual sewage treatment and has high application prospects.

[0078] Example 5

[0079] Application of a bipyridyl imine-based covalent organic framework photocatalyst in degrading antibiotics, specifically: using the bipyridyl imine-based covalent organic framework photocatalyst to degrade ofloxacin in different water bodies, including the following steps:

[0080] Weigh 5 portions of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1, 5 mg for each portion, and add them to ofloxacin solutions with pH values of 3, 5, 7, 9, and 11 (the volume of the solution is 60 mL and the concentration is 5 mg / L) respectively. Stir magnetically at a speed of 400 r / min for 1 h under dark conditions to reach adsorption equilibrium, and then carry out photocatalytic reaction for 50 min under the irradiation of actual sunlight to complete the degradation of ofloxacin in different water bodies.

[0081] During magnetic stirring and photocatalysis, take 1 mL of sample every 10 minutes, filter the sample with a 0.22 μm filter head, and take the filtrate to be determined by a liquid chromatograph to determine the antibiotic concentration after adsorption and after light irradiation, so as to obtain the adsorption effect and photocatalytic degradation effect of Bby-COF on ofloxacin.

[0082] Figure 8 It is the degradation effect diagram of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) in Example 5 of the present invention on ofloxacin under different pH conditions. From Figure 8It can be seen that the removal rates of ofloxacin by the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) of the present invention are 100%, 100.0%, 100%, 100%, and 100% at pH values of 3, 5, 7, 9, and 11, respectively. It can be seen that the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) prepared in the present invention has excellent degradation performance at pH 3-11, which indicates that the bipyridyl imine-based covalent organic framework (Bby-COF) of the present invention has strong stability and excellent adaptability.

[0083] From the above results, it can be seen that compared with the conventional organic framework (Bpy-COF), by introducing bipyridyl sites in the present invention, the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) has the following advantages: (a) By introducing bipyridyl sites, the structure of the imine-based covalent organic framework can be optimized, so that it has excellent absorption capacity for full-spectrum sunlight, which is beneficial to improving the utilization rate of natural light, and further enables the bipyridyl imine-based covalent organic framework photocatalyst to exhibit very excellent photocatalytic activity under natural light; (b) By introducing bipyridyl sites, the optical band gap of the imine-based covalent organic framework can be improved, so that it has a suitable optical band gap, is more easily excited to form electrons and holes, and generates more active species, thus being beneficial to improving the photocatalytic activity of the bipyridyl imine-based covalent organic framework photocatalyst under natural sunlight irradiation; (c) Through bipyridine regulation, there is a significant difference in the internal charge density of the covalent organic framework, so that the bipyridyl imine-based covalent organic framework photocatalyst can establish a suitable electron donor-acceptor interaction, which can not only promote the separation of photogenerated carriers, is beneficial to improving the charge separation efficiency, but also can promote the aggregation of electrons in the bipyridine unit, is beneficial to improving the electron transfer efficiency, and at the same time can reduce the energy consumption from the excited state to the acceptor in the water pollution process, which is also beneficial to improving the photocatalytic activity of the bipyridyl imine-based covalent organic framework photocatalyst under natural sunlight irradiation. The bipyridyl imine-based covalent organic framework photocatalyst of the present invention has the advantages of significant difference in internal charge density, wide light absorption range and high natural light utilization rate, etc., has very high photocatalytic activity under natural light conditions, and also has the advantages of high charge separation efficiency, high conductivity, stable physical and chemical properties, etc. As a new type of natural light photocatalyst with excellent photocatalytic performance, it can treat antibiotic wastewater under natural light conditions and can achieve efficient degradation of antibiotics, with high use value and good application prospects.

[0084] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, improvements and refinements made without departing from the principle of the present invention shall also be regarded as within the protection scope of the present invention.

Claims

1. A bipyridyl imine-based covalent organic framework photocatalyst capable of utilizing natural light, characterized in that, The bipyridyl imine-based covalent organic framework photocatalyst is prepared by a condensation reaction using benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials.

2. The bipyridyl imine-based covalent organic framework photocatalyst according to claim 1, wherein The mass ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is 33:

28.

3. The bipyridyl imine-based covalent organic framework photocatalyst according to claim 1 or 2, characterized in that, The structure of the bipyridyl imine-based covalent organic framework photocatalyst is formed by connecting periodic structural units, and the structure of the periodic structural unit is: The wavy line in the formula represents the omitted repeating structural unit.

4. A preparation method of a bipyridyl imine-based covalent organic framework photocatalyst, characterized in that, The preparation method is to prepare the bipyridyl imine-based covalent organic framework photocatalyst by a condensation reaction using benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials.

5. The preparation method according to claim 4, characterized in that, It includes the following steps: S1. Mix benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine, and successively add an organic solvent and an acid catalyst to obtain a mixture. S2. Perform freeze-pump-thaw cycle degassing on the mixture obtained in step S1, and seal it under vacuum. S3. Perform a condensation reaction on the mixture obtained by the freeze-pump-thaw cycle degassing treatment in step S2 to obtain the bipyridyl imine-based covalent organic framework photocatalyst.

6. The preparation method according to claim 5, characterized in that, In step S1, the mass ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde to 2,2'-bipyridine-5,5'-diamine is 33:28; the ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde to the organic solvent and the acid catalyst is 33 mg:1 mL:0.1 mL; the organic solvent is a mixed solvent of o-dichlorobenzene and N,N-dimethylacetamide, and the volume ratio of o-dichlorobenzene to N,N-dimethylacetamide in the mixed solvent of o-dichlorobenzene and N,N-dimethylacetamide is 1:1, and the acid catalyst is acetic acid. In step S2, the temperature of the condensation reaction is 120 °C, and the time of the condensation reaction is 48 h to 72 h; after the condensation reaction, the following treatments are also included: washing, filtering, and drying the reaction product; the washing is carried out 3 times with tetrahydrofuran and acetone respectively, the filtering is carried out using a 0.22 μm organic filter membrane, the drying is carried out under vacuum conditions, the drying temperature is 80 °C, and the drying time is 24 h.

7. The preparation method according to any one of claims 4 to 6, characterized in that, The structure of the bipyridyl imine-based covalent organic framework photocatalyst is formed by connecting periodic structural units, and the structure of the periodic structural unit is: The wavy line in the formula represents the omitted repeating structural units.

8. Application of the bipyridyl imine-based covalent organic framework photocatalyst according to any one of claims 1 to 3 or the bipyridyl imine-based covalent organic framework photocatalyst prepared by the preparation method according to any one of claims 4 to 7 in degrading antibiotics.

9. The application according to claim 8, wherein Degrading antibiotics in water by using a bipyridyl imine-based covalent organic framework photocatalyst, comprising the following steps: mixing the bipyridyl imine-based covalent organic framework photocatalyst with antibiotic wastewater, stirring, and performing a photocatalytic reaction under light irradiation conditions to complete the degradation treatment of antibiotics in the water; the addition amount of the bipyridyl imine-based covalent organic framework photocatalyst is 0.08 g to 0.1 g of the bipyridyl imine-based covalent organic framework photocatalyst added per liter of the antibiotic wastewater.

10. The application according to claim 9, wherein The initial concentration of the antibiotic wastewater is 5 mg / L to 10 mg / L; the antibiotics in the antibiotic wastewater are quinolone antibiotics and / or tetracycline antibiotics; the quinolone antibiotics are at least one of ofloxacin and norfloxacin; the tetracycline antibiotic is tetracycline; the stirring is carried out under dark conditions, the rotation speed of the stirring is 300 r / min to 400 r / min, and the stirring time is 0.5 h to 1 h; the light source used in the process of the photocatalytic reaction is a xenon lamp and / or natural light; the photocatalytic reaction time is 30 min to 50 min.

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