Device for photocatalytically degrading organic pollutants by using natural light

Abstract

The invention discloses a device for photocatalytic degradation of organic pollutants by using natural light, the device comprises a transparent water tank, a plurality of light-transmitting plates are arranged in the transparent water tank, the surface of each light-transmitting plate is coated with a photocatalytic material film containing a bipyridine imino covalent organic framework photocatalyst, and the photocatalyst is prepared from benzo [1, 2-b: 3, 4-b ': 5, 6-b'] trithiophene-2, 5, 6-triazine-2, 4, 6-triazine-2, 4, 6-triazine-2, 4-triazine-2, 4-triazine-2, 4-triazine-2, 4-triazine-2, 4-triazine-2, 4-triazine-2, the compound is prepared by taking 2, 4, 6, 7, 8-trialdehyde and 2, 2 '-bipyridine-5, 5'-diamine as raw materials through condensation reaction. According to the invention, the dipyridyl imino covalent organic framework photocatalyst with excellent performance is used as a natural light photocatalyst to coat the surface of the light-transmitting plate, so that the device can utilize natural light and can realize efficient degradation of organic pollutants under the irradiation of the natural light; and the device also has the advantages of convenience in cleaning and maintenance, high catalytic efficiency, large effective reaction area, simple structure, convenience in operation and the like, and is convenient for realizing effective treatment on organic pollutant wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic degradation of pollutants, and relates to a device for photocatalytically degrading organic pollutants by using natural light. Background Art

[0002] The photocatalytic degradation technology has the advantages of easy operation, low cost, high efficiency, no secondary pollution, etc., and has great potential in degrading organic pollution. However, the existing photocatalytic degradation technology still has the following defects: (1.1) The existing photocatalytic materials can efficiently remove pollutants under the condition of xenon lamp, but the removal efficiency of organic pollutants under actual natural light irradiation is relatively low; (1.2) The existing photocatalytic materials are powder materials, which are usually not easy to recover from water. Especially in the treated water, the catalyst is easy to float and difficult to separate, which not only causes waste of the catalyst, but also may pollute the water body and hinder the practical application of the photocatalyst. Further, to solve the problem of material recovery, the photocatalytic materials are gradually made into membrane devices. However, these photocatalytic membrane devices still have the following defects: (2.1) The surface of the photocatalytic membrane device usually accumulates pollutants or is blocked with the increase of the use time, which may lead to a decrease in the permeability of the membrane, thereby reducing the treatment effect; (2.2) The photocatalytic membrane is usually a single and continuous thin film surface, which may limit the effective area of the catalytic reaction. Especially when the fluid passes through the membrane, there may be local areas with relatively low flow velocity on the surface, affecting the uniformity and efficiency of the catalytic reaction; (2.3) The cleaning and maintenance of the integral membrane material are relatively complex, and the manufacturing and replacement costs of the membrane material are relatively high. Especially when large-scale treatment is required, the replacement frequency of the membrane may affect the overall operation cost. Therefore, constructing a reaction device that can not only make full use of natural light, but also achieve the degradation of organic pollutants only under natural sunlight, and is also easy to clean and maintain, is of great significance for the wide application of photocatalytic technology in the field of organic pollutant wastewater treatment and reducing the treatment cost. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a device for photocatalytically degrading organic pollutants by using natural light, which has a simple structure, is easy to operate, is easy to clean and maintain, has a large effective reaction area, has a high catalytic efficiency and good removal effect under natural light conditions.

[0004] To solve the above technical problem, the present invention adopts the following technical solutions:

[0005] An apparatus for photocatalytic degradation of organic pollutants using natural light, comprising a transparent water tank, wherein a plurality of light-transmitting plates are arranged in the transparent water tank, and a photocatalytic material film is coated on the surface of the light-transmitting plates; the photocatalytic material film contains a bipyridyl imine-based covalent organic framework photocatalyst, and 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.

[0006] In the above-mentioned apparatus, further improved, 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.

[0007] In the above-mentioned apparatus, further improved, 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:

[0008] The wavy line in the formula is an omitted repeating structural unit.

[0009] In the above-mentioned apparatus, further improved, the preparation method of the bipyridyl imine-based covalent organic framework photocatalyst comprises the following steps:

[0010] 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;

[0011] S2. Perform freeze-pump-thaw cycling degassing on the mixture obtained in step S1, and seal it under vacuum;

[0012] S3. Perform a condensation reaction on the mixture obtained after the freeze-pump-thaw cycling degassing treatment in step S2 to obtain a bipyridyl imine-based covalent organic framework photocatalyst.

[0013] In the above-mentioned apparatus, further improved, in step S1, 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 33mg∶1mL∶0.1mL; the organic solvent is a mixed solvent of o-dichlorobenzene and N,N-dimethylacetamide, 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.

[0014] For the above-mentioned device, in a 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 three 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 temperature of the drying is 80°C, and the time of the drying is 24 h.

[0015] For the above-mentioned device, in a further improvement, the method for preparing the photocatalytic material thin film includes the following steps:

[0016] (1) Mix the bipyridine imine-based covalent organic framework photocatalyst, binder, and solvent, and stir for 20 min to 40 min under the conditions of a temperature of 20°C to 30°C and a rotation speed of 300 r / min to 500 r / min to obtain a coating;

[0017] (2) Coat the coating obtained in step (1) on the surface of the light-transmitting plate, and dry it at a temperature of 50°C to 70°C to obtain a light-transmitting plate coated with a photocatalytic material thin film.

[0018] For the above-mentioned device, in a further improvement, the mass ratio of the bipyridine imine-based covalent organic framework photocatalyst to the binder is 3:1 to 1:1; the binder is at least one of polyvinyl fluoride and polyvinylidene fluoride; the mass-volume ratio of the bipyridine imine-based covalent organic framework photocatalyst to the solvent is 30 mg:0.8 mL to 1.5 mL; the solvent is at least one of N-dimethylacetamide and N-methylpyrrolidone.

[0019] For the above-mentioned device, in a further improvement, the light-transmitting plate is detachably installed at the bottom of the transparent water tank in an array form; the light-transmitting plate is perpendicular to the bottom of the transparent water tank; the height of the light-transmitting plate is lower than the depth of the transparent water tank; the light-transmitting plate includes a first light-transmitting plate and a second light-transmitting plate, the height of the first light-transmitting plate is less than that of the second light-transmitting plate, and the first light-transmitting plate and the second light-transmitting plate are arranged alternately; the thickness of the light-transmitting plate is 10 mm; the materials of the light-transmitting plate and the transparent water tank are acrylic materials.

[0020] For the above-mentioned device, in a further improvement, an aeration device is further provided in the transparent water tank; the aeration device is an aeration stone.

[0021] For the above-mentioned device, in a further improvement, a water outlet is further provided at the bottom of the transparent water tank, and a water inlet is further provided at the upper part of the transparent water tank.

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

[0023] (1) In view of the deficiencies existing in existing COFs materials, such as being difficult to recycle, having a small internal charge density difference, poor light absorption ability for natural light, and the resulting defects that existing COFs materials are difficult to exhibit excellent photocatalytic activity under natural light conditions, and also in view of the deficiencies in photocatalytic membranes in photocatalytic devices, such as being easily contaminated, having poor permeability, being easily damaged, difficult to clean and maintain, high cost, and small effective reaction area, the present invention creatively proposes a device for photocatalytic degradation of organic pollutants using natural light, which includes a transparent water tank and a plurality of light-transmitting plates disposed in the transparent water tank. A photocatalytic material thin film is coated on the surface of the light-transmitting plates, wherein the photocatalytic material thin film contains a bipyridine imine-based covalent organic framework photocatalyst, and the bipyridine 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. In the present invention, the adopted bipyridine imine-based covalent organic framework photocatalyst has the advantages of a significant difference in internal charge density, a wide light absorption range, high natural light utilization rate, etc., and has very high photocatalytic activity under natural light conditions. At the same time, it also has the advantages of high charge separation efficiency, high conductivity, stable physical and chemical properties, etc. Therefore, when it is used as a natural light photocatalyst and coated on the surface of the light-transmitting plate, the device can utilize natural light and can achieve efficient degradation of antibiotics under the irradiation of natural light. In addition, in the device of the present invention, the light-transmitting plates coated with the photocatalytic material thin film are installed in the transparent water tank to form a staggered array structure, which has the following advantages: (a) It is convenient for cleaning and maintenance. Once the repair is completed, the entire array plate can be taken out without damaging the aquatic environment or releasing pollutants; (b) High catalytic efficiency. Both the transparent water tank and the transparent plate are made of acrylic materials, which have good light transmittance. When the photocatalytic material is loaded on the surface of the acrylic plate, the light intensity and uniformity in the reaction area are guaranteed, thereby improving the photocatalytic efficiency; (c) Large effective reaction area. Both sides of the transparent plate are coated with the photocatalytic material, providing more catalytic surfaces, and the addition of aeration stones improves the contact efficiency between the fluid and the catalytic material, avoiding the dead zone phenomenon; (d) Simple structure, convenient operation, low cost, green and environmentally friendly, suitable for industrial application, and convenient for effectively treating organic pollutant wastewater. Taking ofloxacin as an example, the device of the present invention can directly utilize natural sunlight, and the removal rate of 4.2 L of ofloxacin wastewater reaches about 96% within 4 h, and the photocatalytic degradation effect is remarkable. At the same time, after 14 cycles, the average treatment efficiency is maintained at about 91%, which can provide a new idea for the actual treatment of organic pollutant wastewater.

[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 dosage of each raw material and the conditions of the condensation reaction, 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, by optimizing the ratio of the bipyridine imine group covalent organic framework photocatalyst, binder and solvent, a photocatalytic coating with a more uniform texture can be better formed, and natural sunlight can be better utilized to achieve efficient removal of pollutants. In addition, when their ratio is too high or too low, the photocatalytic material cannot be evenly dispersed, affecting the treatment effect of the device. 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 the front view of the device for photocatalytic degradation of organic pollutants using natural light in Embodiment 1 of the present invention.

[0028] Figure 2 It is the top view of the device for photocatalytic degradation of organic pollutants using natural light in Embodiment 1 of the present invention.

[0029] Figure 3 It is the physical diagram of the device for photocatalytic degradation of organic pollutants using natural light in Embodiment 1 of the present invention.

[0030] Figure 4 It is the degradation effect diagram of ofloxacin by the device for photocatalytic degradation of organic pollutants using natural light in Embodiment 2 of the present invention.

[0031] Figure 5 It is the degradation effect of ofloxacin by the bipyridine imine group covalent organic framework photocatalyst (Bby-COF) under actual sunlight irradiation at different time periods in Embodiment 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] 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.

[0033] 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.

[0034] Example 1

[0035] As Figure 1 shown, a device for photocatalytic degradation of organic pollutants using natural light includes a transparent water tank. A number of light-transmitting plates are provided in the transparent water tank, and a photocatalytic material thin film is coated on the surface of the light-transmitting plates. The photocatalytic material thin film contains a bipyridyl imine-based covalent organic framework photocatalyst, and 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']terthiophene-2,5,8-tricarbaldehyde and 2,2'-bipyridine-5,5'-diamine as raw materials.

[0036] In this example, 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.

[0037] In this example, 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:

[0038] The wavy line in the formula is the omitted repeating structural unit.

[0039] In this example, the preparation method of the used bipyridyl imine-based covalent organic framework photocatalyst includes the following steps:

[0040] (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. Add 0.5 mL of o-dichlorobenzene and 0.5 mL of N,N-dimethylacetamide respectively, ultrasonicate for 15 min, mix evenly, add 0.1 mL of acetic acid, ultrasonicate for 3 min, and mix evenly to obtain a mixture.

[0041] (2) Perform 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-sealed, heated to 120 °C for a condensation reaction for 72 h, and then taken out and cooled after the reaction.

[0042] (3) Wash the reaction product in step (2) three times with tetrahydrofuran and acetone (10 mL each time), filter it using a 0.22 μm organic filter membrane, and then dry it under vacuum conditions 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.

[0043] In this embodiment, the preparation method of the photocatalytic material thin film comprises the following steps:

[0044] (1) Mix 30 mg of bipyridine imine-based covalent organic framework photocatalyst, 12 mg of polyvinylidene fluoride, and 1 mL of N-methylpyrrolidone, and stir for 30 min under the conditions of a temperature of 25 °C and a rotation speed of 400 r / min to obtain a coating.

[0045] (2) Coat the coating obtained in step (1) on the surface of a light-transmitting plate (acrylic plate), dry it at a temperature of 60 °C, and repeat the above operation to coat a photocatalytic material thin film on the surface of the light-transmitting plate (acrylic plate) to obtain a light-transmitting plate coated with a photocatalytic material thin film.

[0046] As Figure 2 shown, in this embodiment, the light-transmitting plate is detachably installed at the bottom of the transparent water tank in the form of an array. The light-transmitting plate is perpendicular to the bottom of the transparent water tank, and the height of the light-transmitting plate is lower than the depth of the transparent water tank. The light-transmitting plate comprises a first light-transmitting plate and a second light-transmitting plate. The height of the first light-transmitting plate is less than that of the second light-transmitting plate, and the first light-transmitting plate and the second light-transmitting plate are arranged alternately.

[0047] In this embodiment, the materials of the light-transmitting plate and the transparent water tank are acrylic materials, that is, both the light-transmitting plate and the transparent water tank are prepared from acrylic materials.

[0048] In this embodiment, the size (width × height × thickness) of the first light-transmitting plate is 40 × 60 × 10 mm, and the size (width × height × thickness) of the second light-transmitting plate is 40 × 60 × 10 mm, that is, the thickness of the light-transmitting plate is 10 mm.

[0049] In this embodiment, the number of light-transmitting plates is 9, among which the number of the first light-transmitting plates is 3, and the number of the second light-transmitting plates is 6, forming a 3×3 rectangular array in the transparent water tank.

[0050] In this embodiment, the size (width × height × thickness) of the transparent water tank is 250 mm × 200 mm × 180 mm.

[0051] In this embodiment, an aeration device is further provided in the transparent water tank. The aeration device is an aeration stone, and the number is 2, with a diameter of 2 cm.

[0052] In this embodiment, a water outlet is further provided at the bottom of the transparent water tank, and a water inlet is provided at the upper part of the transparent water tank.

[0053] In this embodiment, insert the first light-transmitting plate and the second light-transmitting plate into the bottom of the transparent water tank to form the device for photocatalytic degradation of organic pollutants using natural light of the present invention, as Figure 3 shown.

[0054] Example 2

[0055] To investigate the degradation effect of the device of the present invention on organic pollutants, specifically: the device of the present invention is used to degrade ofloxacin, including the following treatments:

[0056] (1) Transfer 4.2 L of ofloxacin simulated wastewater with a concentration of 5 mg / L to the device as Figure 3 shown, and carry out photocatalytic reaction for 4 h under actual natural sunlight irradiation.

[0057] (2) After the photocatalytic reaction in step (1) is completed, continue to transfer 4.2 L of ofloxacin simulated wastewater with a concentration of 5 mg / L to the device as Figure 3 shown, and a total of 58.8 L of wastewater is treated.

[0058] During the photocatalytic reaction process, samples are taken every 20 min. After filtering through a 0.22 μm organic filter membrane, the absorbance is measured with a high-performance liquid chromatograph to determine the concentration of each pollutant after degradation in each time period, and analyze its degradation situation.

[0059] Figure 4 This is the degradation effect diagram of ofloxacin by the device for photocatalytic degradation of organic pollutants using natural light in Example 2 of the present invention. As Figure 4 can be seen, the device of the present invention can directly utilize natural sunlight, and the removal rate of 4.2 L of ofloxacin wastewater reaches about 96% within 4 h, and the photocatalytic degradation effect is remarkable. At the same time, after 14 cycles, the average treatment efficiency is maintained at about 91%, which can provide new ideas for the actual treatment of organic pollutant wastewater.

[0060] Example 3

[0061] To investigate the photocatalytic performance of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF), specifically as follows:

[0062] 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, and 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 to complete the degradation of ofloxacin in the water body.

[0063] Control group 1: Replace the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) prepared in Example 1 with a covalent organic framework (Bpy-COF), and other conditions are the same.

[0064] The specific preparation method of the covalent organic framework (Bpy-COF) used in this example is as follows:

[0065] (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, mix them in a vacuum tube, 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.

[0066] (2) Perform 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 seal it under vacuum and heat it at 120 °C for 72 h, and take it out and cool it after completion.

[0067] (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. The structure of its periodic structural unit is:

[0068] The wavy line in the formula represents the omitted repeating structural unit.

[0069] Performance detection

[0070] (1) XRD detection

[0071] Perform powder XRD detection on the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) and covalent organic framework (Bpy-COF) prepared in Example 1 above. The results show that 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 in line with the crystal structure of COFs materials, indicating that the main body of these two materials is covalent organic framework. In addition, it can be seen from the XRD detection results that the XRD result of Bby-COF is closer to the theoretical structure simulation, which indicates 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 profile variance factor (Rp) and weighted profile variance factor (Rwp) of Bby-COF are 5.45% and 7.81% respectively, while those of Bpy-COF are 9.53% and 6.55%.

[0072] (2) UV-Vis diffuse reflectance detection

[0073] The UV-Vis diffuse reflectance of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) and covalent organic framework (Bpy-COF) prepared in Example 1 above was detected. The results showed that the light absorption ranges of these two covalent organic framework materials were both around 400 - 600 nm, and they had excellent light absorption performance in visible light (λ > 420 nm), with the potential for practical utilization of solar energy.

[0074] (3) Electrochemical impedance and fluorescence photoluminescence spectroscopy detection

[0075] The electrochemical impedance and fluorescence photoluminescence spectroscopy of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) and covalent organic framework (Bpy-COF) prepared in Example 1 above were detected. The results showed that compared with Bpy-COF, Bby-COF prepared in Example 1 exhibited the smallest arc radius, indicating a lower charge transfer resistance, which was beneficial to the migration and diffusion of carriers at the interface. At the same time, there was an obvious emission peak in Bpy-COF, while Bby-COF in Example 1 showed a relatively low emission peak, confirming that the recombination rate of photogenerated carriers in Bby-COF in Example 1 was low, and it performed best in the separation and transport of photogenerated electron-hole pairs.

[0076] In addition, the variable-temperature photoluminescence spectra of the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) and covalent organic framework (Bpy-COF) prepared in Example 1 were detected. The results showed that the exciton activation energy of Bby-COF was 33.8 meV, lower than 37.5 meV of Bpy-COF, which indicated that under the same sunlight irradiation, Bby-COF had the potential to generate more electron-hole pairs, thus being beneficial to the degradation of pollutants.

[0077] During magnetic stirring and photocatalysis, 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 and photocatalytic degradation effect of Bby-COF on ofloxacin. The results showed 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 were 100% and 90% respectively. In addition, the bipyridyl imine-based covalent organic framework photocatalyst (Bby-COF) could achieve a 100% removal efficiency in 30 min, and the rate constant was 0.2814 min -1 , which was much greater than 0.0445 min of Bpy-COF -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 visible light absorption range of the material, promotes the transport of carriers at the surface and interface, enables them to better migrate to the active sites accessible to pollutants, and realizes an 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, efficient charge separation, and the best photocatalytic degradation effect.

[0078] Example 4

[0079] Investigate the degradation effect of the bipyridine imine-based covalent organic framework photocatalyst on ofloxacin in water under natural light conditions, including the following steps:

[0080] 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, and magnetically stir it at a speed of 400 r / min for 1 h in the dark to reach adsorption equilibrium. Then, carry out a photocatalytic reaction for 50 min under the irradiation of actual sunlight at different time periods. 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.

[0081] Control group: Use a xenon lamp with a light intensity of 0.4 W to replace the actual sunlight and irradiate the ofloxacin solution, with other conditions being the same.

[0082] During magnetic stirring and photocatalysis, take 1 mL of the sample every 10 min, filter the sample using 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.

[0083] Figure 5 This is the degradation effect of the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) in Example 4 of the present invention on ofloxacin under the irradiation of actual sunlight at different time periods. Figure 5 Among them, a is the sunlight intensity and actual temperature at each time period, and b is the corresponding degradation effect. From Figure 5 b, it can be seen that the bipyridine imine-based covalent organic framework (Bby-COF) of the present invention can achieve 100% removal of ofloxacin within 30 - 50 min under the actual sunlight corresponding to different time periods, which shows that the bipyridine imine-based covalent organic framework of the present invention has an excellent visible light absorption range and can realize the absorption of sunlight in the full wavelength band.

[0084] As can be seen from the above results, compared with the conventional organic framework (Bpy-COF), by introducing bipyridine sites in the present invention, the bipyridine imine-based covalent organic framework photocatalyst (Bby-COF) has the following advantages: (a) By introducing bipyridine sites, the structure of the imine-based covalent organic framework can be optimized, enabling it to have excellent absorption capacity for the full-spectrum sunlight, which is beneficial to improving the utilization rate of natural light. Furthermore, the bipyridine imine-based covalent organic framework photocatalyst can exhibit very excellent photocatalytic activity under natural light; (b) By introducing bipyridine sites, the optical bandgap of the imine-based covalent organic framework can be improved, making it have a suitable optical bandgap, being more easily excited to form electrons and holes, and generating more active species, thus being conducive to improving the photocatalytic activity of the bipyridine 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, enabling the bipyridine imine-based covalent organic framework photocatalyst to establish a suitable electron donor-acceptor interaction. This can not only promote the separation of photo-generated carriers, being beneficial to improving the charge separation efficiency, but also promote the aggregation of electrons in the bipyridine 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 conducive to improving the photocatalytic activity of the bipyridine imine-based covalent organic framework photocatalyst under natural sunlight irradiation. In the present invention, the bipyridine imine-based covalent organic framework photocatalyst has the advantages of significant difference in internal charge density, wide light absorption range, 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. Therefore, when it is used as a natural light photocatalyst and coated on the surface of the light-transmitting plate, the device can utilize natural light and achieve efficient degradation of antibiotics under the irradiation of natural light. In addition, in the device of the present invention, the light-transmitting plate coated with the photocatalytic material film is installed in the transparent water tank to form a staggered array structure, which has the following advantages: (a) It is convenient for cleaning and maintenance; (b) High catalytic efficiency; (c) Large effective reaction area; (d) Simple structure, convenient operation, low cost, green and environmentally friendly, suitable for industrial application, and convenient for effectively treating organic pollutant wastewater.

[0085] 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 in this technical field, without departing from the principle of the present invention, improvements and refinements should also be regarded as within the protection scope of the present invention.

Claims

1. An apparatus for photocatalytic degradation of organic pollutants using natural light, comprising a transparent water tank, wherein a plurality of light-transmitting plates are provided in the transparent water tank, characterized in that, The surface of the light-transmitting plate is coated with a photocatalytic material thin film; the photocatalytic material thin film contains a bipyridyl imine-based covalent organic framework photocatalyst, and 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 device according to claim 1, characterized in that The mass ratio of the benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde to the 2,2'-bipyridine-5,5'-diamine is 33:

28.

3. The device according to claim 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. The device according to claim 3, characterized in that, The preparation method of the bipyridyl imine-based covalent organic framework photocatalyst 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 a 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 after the freeze-pump-thaw cycle degassing treatment in step S2 to obtain a bipyridyl imine-based covalent organic framework photocatalyst.

5. The device according to claim 4, characterized in that, In step S1, the ratio of the 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 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. 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 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.

6. The device according to any one of claims 1 to 5, characterized in that, The preparation method of the photocatalytic material thin film includes the following steps: (1) Mix the bipyridyl imine-based covalent organic framework photocatalyst, an adhesive, and a solvent, and stir at a temperature of 20 °C to 30 °C and a rotation speed of 300 r / min to 500 r / min for 20 min to 40 min to obtain a coating. (2) Coat the coating obtained in step (1) on the surface of the light-transmitting plate, and dry it at a temperature of 50 °C to 70 °C to obtain a light-transmitting plate coated with a photocatalytic material thin film.

7. The device according to claim 6, characterized in that The mass ratio of the bipyridyl imine-based covalent organic framework photocatalyst to the binder is 3:1 to 1:1; the binder is at least one of polyvinyl fluoride and polyvinylidene difluoride; the mass-volume ratio of the bipyridyl imine-based covalent organic framework photocatalyst to the solvent is 30 mg: 0.8 mL to 1.5 mL; the solvent is at least one of N-dimethylacetamide and N-methylpyrrolidone.

8. The device according to any one of claims 1 to 5, characterized in that, The light-transmitting plate is detachably installed at the bottom of the transparent water tank in an array form; the light-transmitting plate is perpendicular to the bottom of the transparent water tank; the height of the light-transmitting plate is lower than the depth of the transparent water tank; the light-transmitting plate includes a first light-transmitting plate and a second light-transmitting plate, the height of the first light-transmitting plate is less than that of the second light-transmitting plate, and the first light-transmitting plate and the second light-transmitting plate are arranged alternately; the thickness of the light-transmitting plate is 10 mm; the light-transmitting plate and the transparent water tank are made of acrylic material.

9. The device according to claim 8, characterized in that, An aeration device is further provided in the transparent water tank; the aeration device is an aeration stone.

10. The device according to claim 9, characterized in that, A water outlet is further provided at the bottom of the transparent water tank, and a water inlet is further provided at the upper part of the transparent water tank.

Images