Benzocarbazole covalent organic framework as well as preparation method and application thereof

Abstract

The invention provides a benzocarbazole covalent organic framework as well as a preparation method and application thereof. The preparation method of the benzocarbazole covalent organic framework comprises the following steps: dissolving reaction raw materials of 4, 4 ', 4' ', 4 '''-([9, 9 '-dicarbazole]-3, 3', 6, 6 '-tetrayl) tetrabenzaldehyde and tetra-(4-aminobenzene) ethylene in a mixed solvent at 10-25 DEG C, and uniformly mixing to obtain a mixed solution; a catalyst acetic acid is added into the mixed solution, then freezing-unfreezing circulation degassing and sealing are carried out, a reaction is carried out for 72-120 h at the temperature of 120-150 DEG C, a reaction solution is obtained, the reaction solution is subjected to aftertreatment, and the benzocarbazole covalent organic framework is obtained. The carbazole covalent organic framework provided by the invention is applied to uranium-containing wastewater as a photocatalyst, and has the advantages of multiple catalytic sites, good stability and cyclic utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalysts, and in particular relates to a benzocarbazole covalent organic framework and a preparation method and application thereof. Background Art

[0002] As an efficient, clean, and low-carbon energy source, nuclear energy has become one of the important options for energy transformation in countries around the world. Uranium is the main fuel for nuclear energy. It is a radioactive and chemically toxic nuclide. It is mostly in the form of uranyl ions (UO 2 2+ ) form, once it enters the environment, it will enter the human body through the food chain and cause long-term harm to humans. At present, uranium pollution mainly comes from uranium mining and nuclear power plant operation, especially the nuclear fuel cycle process and nuclear accident leakage will produce a large amount of uranium-containing wastewater. Prevention and control of uranium pollution is the premise of developing the nuclear industry.

[0003] At present, people have been studying the uranium (UO 2 2+ ) Wastewater treatment technologies mainly include: chemical precipitation, adsorption, ion exchange, membrane separation, microbial method, evaporation concentration, storage decay, and inert solidification. In recent years, the strategy of photocatalytic separation and extraction of uranyl has attracted much attention due to its green, low energy consumption, environmental protection, high efficiency, simple operation, and large removal capacity. The characteristic of this technology is to convert the water-soluble UO 2 2+ By adding photocatalyst and combining with light, the U species (UO 2 and UO 2 (O 2 )·2H 2 O, etc.) to achieve the purpose of heterogeneous separation. Theoretically, under illumination conditions, the excited state electron energy level generated can meet the reduction potential requirements of uranyl under aqueous solution conditions, but in actual scenarios, it is necessary to consider the influence of multiple factors on photocatalytic uranium reduction. The main influencing factors are: catalyst selection, different illumination conditions, electron donors, solution pH, uranium chemical species, photoelectron migration efficiency, etc. At present, the photocatalysts reported for photocatalytic extraction and separation of uranium in water systems mainly include: metal inorganic compounds, single-atom metal catalysts, metal-organic compounds, covalent organic polymers, carbon-based nanomaterials, etc.

[0004] Covalent organic frameworks (COFs) are a class of crystalline organic polymers that are all composed of non-metallic elements arranged periodically in the form of covalent bonds. COFs have the characteristics of stable properties, structural designability, high specific surface area, and high crystallinity. Among them, the unique interlayer π-electron conjugation system of two-dimensional COFs provides them with unique advantages in the field of optoelectronics, giving COFs materials excellent physical and chemical properties. Recently, a variety of two-dimensional COFs materials have been developed for the photocatalytic removal of uranyl in water environments. Their performance is mainly affected by the ligand units of COFs, the exciton separation efficiency of COFs after photoexcitation, and the distribution of catalytic sites of COFs. Based on the above factors, through structural design, the electron donor (Donor) group that is easy to generate photogenerated electrons is connected to the electron acceptor (Acceptor) group that is easy to generate photogenerated holes through covalent bonds to prepare a donor-acceptor-covalent organic framework (DA-COFs), which is an effective method to increase the exciton separation efficiency and thus improve the photocatalytic efficiency. However, in the literature reported on COFs-based photocatalytic uranium removal, the poor photostability of COFs, the utilization of catalytic sites, the poor selectivity of the material for uranyl ions and the low recycling rate of the material have always been the main factors limiting the application of COFs in practical scenarios. Summary of the invention

[0005] The purpose of the present invention is to provide a new covalent organic framework material as a photocatalyst for treating uranium-containing wastewater. The covalent organic framework material is an imine-bridged benzocarbazole covalent organic framework, which has the advantages of multiple catalytic sites, good stability and recyclability.

[0006] In order to achieve the above object, the present invention provides a benzocarbazole covalent organic framework, the chemical structure of the benzocarbazole covalent organic framework is:

[0007]

[0008] The present invention also provides a method for preparing a benzocarbazole covalent organic framework, the preparation method comprising the following steps:

[0009] The invention relates to a step (1) dissolving the reaction raw materials 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde and tetrakis-(4-aminophenyl)ethylene in a mixed solvent at 10 to 25° C. and mixing them evenly to obtain a mixed solution; and a step (2) adding a catalyst, acetic acid, to the mixed solution, degassing the solution through a freeze-thaw cycle, sealing the solution, and reacting the solution at 120 to 150° C. for 72 to 120 hours to obtain a reaction solution, and the reaction solution is subjected to post-treatment to obtain the benzocarbazole covalent organic framework.

[0010] In a specific embodiment, the molar ratio of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde to tetrakis-(4-aminophenyl)ethylene in the reaction raw materials is 1:(1-1.5).

[0011] In a specific embodiment, the mixed solvent includes 1,2-dichlorobenzene and n-butanol, and the volume ratio of 1,2-dichlorobenzene to n-butanol is 1:(1-1.5).

[0012] In a specific embodiment, the molar concentration of the reaction raw material 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde in the mixed solution is 0.01-0.03 mmol / mL, and the molar concentration of the reaction raw material tetrakis-(4-aminophenyl)ethylene is 0.01-0.03 mmol / mL.

[0013] In a specific embodiment, the concentration of the acetic acid is 4-6 mol / L, and the volume ratio of the acetic acid to the mixed solvent is 1:(10-20).

[0014] The present invention also provides a use of the benzocarbazole covalent organic framework as described above or the benzocarbazole covalent organic framework prepared by the preparation method described above in a photocatalytic material.

[0015] The present invention also provides a use of the benzocarbazole covalent organic framework as described above or the benzocarbazole covalent organic framework prepared by the preparation method as described above as a photocatalyst in treating uranium-containing wastewater.

[0016] In a specific embodiment, the method for treating uranium-containing wastewater includes: adding a photocatalyst benzocarbazole covalent organic framework and a hole characteristic agent methanol to the uranium-containing wastewater under visible light conditions and stirring to reduce the uranyl in the uranium-containing wastewater, and controlling the reduction treatment temperature to 10°C to 25°C.

[0017] In a specific embodiment, the pH value of the uranium-containing wastewater is 3-6.

[0018] The beneficial effects of the present invention include at least:

[0019] 1. In view of the defects of existing covalent organic framework materials, such as poor photostability, low utilization rate of catalytic sites, poor selectivity of materials for uranyl ions, and low recycling rate of materials, the present invention prepares benzocarbazole covalent organic frameworks through acid-catalyzed Schiff base condensation reaction of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetraalkyl)tetrabenzaldehyde (which can be used as an electron donor unit) and tetrakis-(4-aminophenyl)ethylene (which can be used as an electron acceptor unit) through structural design, and applies it to uranium-containing wastewater. The frameworks have good stability, recyclability and ion selectivity, indicating that the carbazole COFs have great potential for uranyl removal in complex water environments.

[0020] 2. The preparation method provided by the present invention is used to prepare a benzocarbazole covalent organic framework, which has the advantages of high yield and good product crystallinity. The prepared benzocarbazole bridged covalent organic framework has good porosity and pore volume, which facilitates uranyl ions to enter the pores and contact more catalytic sites.

[0021] 3. The method of reducing and separating uranyl ions in wastewater by photocatalysis using the benzocarbazole covalent organic framework prepared by the present invention is environmentally friendly and efficient. The process has low energy consumption and the amount of uranium removed exceeds that of most of the reported nanomaterials. Specifically, within 24 hours, the concentration of uranyl in uranium waste liquid decreased by more than 90%. In uranium waste liquid with an initial uranium concentration of 600 mg / L, COF BCTB-TBE Under simulated sunlight conditions, it demonstrated a uranium removal capacity of 5768 mg / g.

[0022] 4. The benzocarbazole covalent organic framework prepared by the present invention has high acid-base and heat-resistant stability and is suitable for the treatment of uranium-containing wastewater in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The synthetic route for preparing the benzocarbazole covalent organic framework of the present invention is as follows;

[0024] Figure 2 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE XRD pattern of

[0025] Figure 3 The reaction raw materials BCTB-CHO and TBE-NH in Example 1 of the present invention are 2 The reaction product COF BCTB-TBE FT-IR graph of

[0026] Figure 4 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE SEM image (resolution 500nm);

[0027] Figure 5 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE SEM image (resolution 20um);

[0028] Figure 6 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE UV-VIS diagram;

[0029] Figure 7 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE BET isotherm of nitrogen in a 77K liquid nitrogen bath;

[0030] Figure 8 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE Photocatalytic removal rate of uranyl in treating uranium-containing wastewater with different pH values ​​as a photocatalyst (treatment time 24 h);

[0031] Fig. 9 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE As a photocatalyst for the treatment of uranyl, the initial concentration C 0 =600ppm, solution pH = 4, the change of uranyl concentration over time;

[0032] Fig.10 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE When used as a photocatalyst to treat uranium-containing wastewater, the removal rate changes after three cycles;

[0033] Fig.11 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE X-ray powder diffraction data of solid products from photocatalytic removal of uranium-containing wastewater in air;

[0034] Fig.12 The benzocarbazole covalent organic framework COF prepared in Example 1 of the present invention BCTB-TBE X-ray powder diffraction data of the solid product from the photocatalytic removal of uranium-containing wastewater in argon. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] The present invention aims at the defects of poor photostability, low utilization rate of catalytic sites, poor selectivity of materials for uranyl ions, and low recycling rate of materials in existing covalent organic framework materials. Through structural design, 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetraalkyl)tetrabenzaldehyde (which can be used as an electron donor unit) and tetra-(4-aminophenyl)ethylene (which can be used as an electron acceptor unit) are prepared into benzocarbazole imine donor-acceptor-COFs with a topological structure of [4+4] type through an acid-catalyzed Schiff base condensation reaction. The material shows good removal ability of uranyl in a weak acid (pH=4-6) environment of a water system under visible light irradiation conditions, and the removal amount under pH=4 exceeds that of most reported nanomaterials. In addition, the material also has good stability, recyclability and ion selectivity, indicating the great potential of the carbazole COFs in the removal of uranyl in complex water environments.

[0037] The present invention provides a benzocarbazole covalent organic framework, wherein the chemical structural formula of the benzocarbazole covalent organic framework is:

[0038]

[0039] In the present invention, the benzocarbazole covalent organic framework is an imine-bridged benzocarbazole covalent organic framework.

[0040] The present invention also provides the use of the benzocarbazole covalent organic framework as described in the above structural formula in photocatalytic materials.

[0041] The present invention also provides the use of the benzocarbazole covalent organic framework as described in the above structural formula as a photocatalyst in treating uranium-containing wastewater.

[0042] The method for treating uranium-containing wastewater is specifically as follows: under visible light conditions and stirring, a photocatalyst benzocarbazole covalent organic framework and a hole characteristic agent methanol are added to the uranium-containing wastewater to reduce the uranyl in the uranium-containing wastewater, and the reduction treatment temperature is controlled to be 10°C to 25°C.

[0043] Preferably, the ratio of the added mass of the photocatalyst to the volume of the uranium-containing wastewater is (0.02-1) g / L, and the ratio of the added volume of the vacancy characteristic agent methanol to the volume of the uranium-containing wastewater is 1:(20-100).

[0044] More preferably, the visible light condition can use a 300W Xe lamp with an ultraviolet cutoff filter (λ≥420nm) as a simulated sunlight light source.

[0045] More preferably, the initial concentration of uranium in the uranium-containing wastewater is 50 mg / L to 600 mg / L.

[0046] More preferably, the pH value of the uranium-containing wastewater is 3-6.

[0047] It is understood that if the pH value of the uranium-containing wastewater is not within the range of 3 to 6, the pH of the uranium-containing wastewater can be changed by adding acid or alkali to improve the removal rate of uranyl.

[0048] The present invention also provides a method for preparing a benzocarbazole covalent organic framework. The synthetic process diagram of the preparation method is shown in Figure 1 The raw material 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde is referred to as BCTB-CHO, and the raw material tetrakis-(4-aminophenyl)ethylene is referred to as TBE-NH 2 The reaction product, benzocarbazole covalent organic framework, is named COF BCTB-TBE .

[0049] In the present invention, the benzocarbazole covalent organic framework is an imine-bridged benzocarbazole covalent organic framework.

[0050] The preparation method comprises the following steps:

[0051] Step (1), at 10-25° C., dissolving the reaction raw materials 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde and tetrakis-(4-aminophenyl)ethylene in a mixed solvent and mixing them evenly to obtain a mixed solution.

[0052] Preferably, the molar ratio of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde to tetrakis-(4-aminophenyl)ethylene in the reaction raw materials is 1:(1-1.5).

[0053] Preferably, the mixed solvent comprises 1,2-dichlorobenzene and n-butanol, and the volume ratio of 1,2-dichlorobenzene to n-butanol is 1:(1-1.5).

[0054] More preferably, the molar concentration of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde in the mixed solution is 0.01-0.03 mmol / mL, and the molar concentration of tetrakis-(4-aminophenyl)ethylene in the mixed solution is 0.01-0.03 mmol / mL.

[0055] In step (1) of the present invention, the reaction raw materials and the mixed solvent are subjected to ultrasonic treatment for 10 minutes to 15 minutes to achieve uniform mixing.

[0056] Step (2), adding catalyst acetic acid to the mixed solution, then degassing and sealing through a freeze-thaw cycle, and then reacting at 120° C. to 150° C. for 72 h to 120 h to obtain a reaction solution, and the reaction solution is post-treated to obtain the benzocarbazole covalent organic framework.

[0057] In the present invention, the freeze-thaw cycle degassing refers to freezing in liquid nitrogen and vacuum degassing, and the vacuum operation after the next freeze-drying is performed after the solvent of the previous freeze-drying is melted.

[0058] In the present invention, the sealing is flame sealing.

[0059] In the present invention, the concentration of the acetic acid is 4-6 mol / L, and the volume ratio of the acetic acid to the mixed solvent is 1:(10-20).

[0060] Preferably, the post-treatment includes solid-liquid separation, washing, and vacuum drying, and the benzocarbazole covalent organic framework is a light yellow-green powder.

[0061] More preferably, the washing is washing with tetrahydrofuran, methanol and acetone in sequence for 2 to 5 times, the centrifugal speed is 8000 to 9900 r / min, and the centrifugal time is 5 to 10 min.

[0062] More preferably, the vacuum drying conditions include: drying temperature of 80° C. to 100° C., and drying time of 10 to 16 hours.

[0063] The present invention also provides the use of the benzocarbazole covalent organic framework prepared by the preparation method described above in a photocatalytic material.

[0064] The present invention also provides the use of the benzocarbazole covalent organic framework prepared by the preparation method described above as a photocatalyst in treating uranium-containing wastewater.

[0065] Preferably, the method for treating uranium-containing wastewater is specifically: under visible light conditions and stirring, adding a photocatalyst benzocarbazole covalent organic framework and a hole characteristic agent methanol to the uranium-containing wastewater to reduce the uranyl in the uranium-containing wastewater, and controlling the reduction treatment temperature to 10°C to 25°C.

[0066] Preferably, the added mass ratio of the photocatalyst to the volume of the uranium-containing wastewater is (0.02-1) g / L, and the added volume ratio of the vacancy characteristic agent methanol to the volume of the uranium-containing wastewater is 1:(20-100).

[0067] Preferably, the visible light condition can use a 300W Xe lamp with an ultraviolet cutoff filter (λ≥420nm) as a simulated sunlight light source.

[0068] Preferably, the initial concentration of uranium in the uranium-containing wastewater is 50 mg / L to 600 mg / L.

[0069] Preferably, the pH value of the uranium-containing wastewater is 3-6.

[0070] It is understood that if the pH value of the uranium-containing wastewater is not within the range of 3 to 6, the pH of the uranium-containing wastewater can be changed by adding acid or alkali to improve the removal rate of uranyl.

[0071] Example 1

[0072] Preparation of benzocarbazole-based covalent organic frameworks

[0073] Step (1), 29.96 mg (0.04 mmol) of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetraalkyl)tetrabenzaldehyde (BCTB-CHO), 15.7 mg (0.04 mmol) of tetrakis-(4-aminophenyl)ethylene (TBE-NH 2 ), 1 mL of 1,2-dichlorobenzene and 1 mL of n-butanol, and then ultrasonically mixed for 10 minutes to obtain a mixed solution.

[0074] Step (2), adding a catalyst 0.2 mL of acetic acid (6 mol / L) to the mixed solution, and then placing the Pyrex glass tube in liquid nitrogen for three freeze-drying cycles to degas and seal.

[0075] It should be noted that each freeze-drying cycle requires the vacuum operation to be performed after the solvent of the previous freeze-drying has melted.

[0076] Step (3), transfer the sealed Pyrex glass tube of step (2) to a constant temperature oven, and heat at 120°C for three days (72 hours) to obtain a reaction solution.

[0077] Step (4), the reaction solution of step (3) was filtered and collected, washed several times with tetrahydrofuran, methanol and acetone respectively, and finally dried in vacuum at 80°C for 12 hours to obtain a pale yellow-green imine-bridged benzocarbazole covalent organic framework (named COF BCTB-TBE ) powder with a yield of 92%.

[0078] The prepared benzocarbazole covalent organic framework was subjected to structural characterization test. The structural characterization test results are detailed in Figures 2 to 7 .

[0079] Figure 2 is the XRD pattern of the benzocarbazole covalent organic framework prepared in Example 1, Figure 2The main diffraction peaks are 5.50°, 7.78°, 11.06°, and 20.02°, which correspond to crystalline COF BCTB-TBE The crystal plane diffraction of d(110), d(210), d(310), and d(001) of the present invention is shown in Figure 2. Combined with the structural simulation results, it is proved that the COF obtained by the method of the present invention BCTB-TBE High degree of crystallinity.

[0080] Figure 3 The raw materials are BCTB-CHO and TBE-NH 2 The reaction product COF BCTB-TBE FT-IR graph of Figure 3 It can be seen that at 1621cm -1 A new absorption peak representing the imine bond (C=N) appeared at BCTB-TBE The successful construction of

[0081] Figure 4 and Figure 5 COF prepared in Example 1 BCTB-TBE SEM images of powder at different resolutions, from Figure 4 It can be seen that COF BCTB-TBE It is a spherical structure with a particle size of about 200 nanometers, which shows that COF BCTB-TBE A certain amount of agglomeration occurred during the preparation process.

[0082] Figure 6 COF prepared in Example 1 BCTB-TBE UV-VIS image of powder. Figure 6 It can be seen that COF BCTB-TBE The absorption in the visible light region (200-800nm) can be BCTB-TBE The material provides a certain basis for the catalytic reduction and separation of uranyl under visible light.

[0083] Figure 7 COF prepared in Example 1 BCTB-TBE BET isotherm of powder in nitrogen at 77K liquid nitrogen bath. Figure 7 It can be seen that COF BCTB-TBE The specific surface area is 1299m 2 / g, and the pore size distribution is between 0.8 and 1.2 nm based on non-density functional theory (NLDFT) analysis, which reflects the COF BCTB-TBE The characteristics of high specific surface area and high porosity.

[0084] Example 2

[0085] Under visible light conditions, using photocatalyst COF BCTB-TBE Treatment of uranium-containing wastewater with different pH values

[0086] The specific steps are as follows: 100 mL of uranium solution with an initial concentration of 50 mg / L was respectively transferred into a 150 mL conical flask, and the pH of the solution was adjusted to 1, 2, 3, 4, 5, and 6 in sequence using a sodium hydroxide solution (1 mol / L) and a dilute nitric acid solution (1 mol / L), and 0.01 g of the photocatalyst COF prepared in Example 1 was respectively added. BCTB-TBE , and 2 mL of methanol was added as a hole sacrificial agent respectively. The reaction was carried out for 24 hours under a controlled temperature of 25 °C, a rotor speed of 300 rpm, and a 300 W Xe lamp with a UV cutoff filter (λ ≥ 420 nm) as simulated sunlight. The filtrate was filtered through a 0.22 μm nylon membrane filter and the change in uranium concentration of the uranium solution before and after illumination was tested by ICP-OES.

[0087] When the pH value of the uranium solution is 1, the photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was 5.2%. When the pH value of the uranium solution was 2, the addition of photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was 2.3%. When the pH value of the uranium solution was 3, the addition of the photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was 88.4%. When the pH value of the uranium solution was 4, the addition of photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was measured to be 98.7%. When the pH value of the uranium solution was 5, the addition of the photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was measured to be 98.2%. When the pH value of the uranium solution was 6, the addition of the photocatalyst COF BCTB-TBE After 12 hours of illumination, the removal rate of uranyl was measured to be 94.5%. The above data were plotted into a curve. Figure 8 .

[0088] The removal rate and Figure 8 It can be seen that COF BCTB-TBE The removal effect of uranium is better at pH = 3-6, and is optimal at pH = 4-5. This pH value is equivalent to the common wastewater pH value, indicating that COF BCTB-TBE The feasibility of the material for uranium removal applications in uranium-containing wastewater.

[0089] Example 3

[0090] Test under visible light conditions, COF BCTB-TBE Kinetic performance of photocatalytic removal of uranyl from uranium-containing wastewater (pH = 4, initial uranium concentration V0 = 603.1 ppm) as a photocatalyst

[0091] The specific steps are as follows: Take 100 mL of the initial concentration V 0 = 600 mg / L uranium solution in a 150 mL conical flask, add 0.01 g COF prepared in Example 1 BCTB-TBE As a photocatalyst, 2 mL of methanol was also added as a hole sacrificial agent. The reaction was carried out for 24 hours under the conditions of controlling the temperature at 25°C and the rotor speed at 300 rpm, using a 300W Xe lamp with an ultraviolet cutoff filter (λ≥420 nm) as simulated sunlight. During the reaction, 0.2 mL was taken at different time points (0, 10, 30, 45, 60, 90, 120, 180, 210, 240, 320, 420, 500, 540, 600, 720, 1560 and 2160 minutes), and the filtrate was taken and diluted with dilute nitric acid (3%), and the uranium concentration change of the uranium solution before and after illumination was tested by inductively coupled plasma atomic emission spectrometer (ICP-OES). As shown in the attached Fig. 9 As shown in Figure 2, within 24 hours, the concentration of uranyl in the uranium waste liquid decreased by more than 90%. In the uranium waste liquid with an initial uranium concentration of 600 mg / L, COF BCTB-TBE Under simulated sunlight conditions, it demonstrated a uranium removal capacity of 5768 mg / g, which exceeds the removal capacity of most uranyl photocatalytic removals reported under the same conditions.

[0092] Example 4

[0093] COF under visible light conditions BCTB-TBE Test of the recycling efficiency of photocatalytic removal of uranyl in uranium-containing wastewater as a photocatalyst

[0094] The specific steps are as follows: Take 100 mL of the initial concentration V 0 = 600 mg / L uranium solution in a 150 mL conical flask, add 0.01 g COF prepared in Example 1 BCTB-TBE As a photocatalyst, 2mL of methanol was added as a hole sacrificial agent. Under the conditions of controlling the temperature at 25°C and the rotor speed at 300rpm, a 300W Xe lamp with a UV cutoff filter (λ≥420nm) was used to simulate sunlight illumination and the reaction was stirred for 24 hours. The final supernatant was filtered using a 0.22μm nylon membrane filter, and the filtrate was taken and the change in uranium concentration of the uranium solution before and after illumination was tested by ICP-OES. After filtering the above uranium waste liquid, the filter residue was taken and desorbed with 1mol / L dilute nitric acid desorbent, washed with methanol and dried at 80°C for 12h. The desorbed material was used to repeat the above photocatalytic uranium removal operation steps. After 3 photocatalytic-desorption cycles, the changes in the removal rate of uranyl of the material in each cycle were summarized. See details for details. Fig.10 .

[0095] As attached Fig.10 As shown, COF during 3 cycles BCTB-TBE The photocatalytic removal rates of uranium were 95.6%, 92.3%, and 89.1%, respectively, showing COF BCTB-TBE The material has high stability and practical application potential. Fig.11 As shown, COF BCTB-TBE The photocatalytic product of the material on uranium-containing wastewater under air (oxygen) conditions is UO 2 (O 2 )·2H 2 O.

[0096] Example 5

[0097] COF was tested under the condition of using inert gas to isolate oxygen from the air. BCTB-TBE Photocatalytic products of uranyl in uranium-containing wastewater as photocatalyst

[0098] Take 15mL of the initial concentration V 0 = 600 mg / L uranium solution in a 20 mL capped glass bottle, take 1.5 mg COF BCTB-TBE The powder was added to 15 ml of uranium wastewater, and the argon gas was passed through the lid for 15 minutes. After the gas was passed through, a 300W Xe lamp with an ultraviolet cutoff filter (λ≥420nm) was used as a simulated sunlight light source for 12 hours, and then the product was filtered and the residue was dried and tested for X-ray powder diffraction (XRD). The XRD pattern of the photocatalytic product is shown in Fig.12 As shown, from Fig.12 It can be seen that COF BCTB-TBE The photocatalytic product of the material on uranium-containing wastewater under air (oxygen) conditions is UO 2 The product crystal form is consistent with that reported in the literature (J.Appl.Phys.2019,126,125116).

[0099] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A benzocarbazole covalent organic framework, characterized in that: The chemical structure of the benzocarbazole covalent organic framework is:

2. A method for preparing a benzocarbazole covalent organic framework, characterized in that: The preparation method comprises the following steps: Step (1), dissolving the reaction raw materials 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde and tetrakis-(4-aminophenyl)ethylene in a mixed solvent and mixing them uniformly at 10-25° C. to obtain a mixed solution; Step (2), adding catalyst acetic acid to the mixed solution, then degassing and sealing through a freeze-thaw cycle, and then reacting at 120° C. to 150° C. for 72 h to 120 h to obtain a reaction solution, and the reaction solution is post-treated to obtain the benzocarbazole covalent organic framework.

3. The method for preparing the benzocarbazole covalent organic framework according to claim 2, characterized in that: The molar ratio of 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde to tetrakis-(4-aminophenyl)ethylene in the reaction raw materials is 1:(1-1.5).

4. The method for preparing the benzocarbazole covalent organic framework according to claim 3, characterized in that: The mixed solvent includes 1,2-dichlorobenzene and n-butanol, and the volume ratio of 1,2-dichlorobenzene to n-butanol is 1:(1-1.5).

5. The method for preparing the benzocarbazole covalent organic framework according to claim 4, characterized in that: The molar concentration of the reaction raw material 4,4',4",4"'-([9,9'-bicarbazole]-3,3',6,6'-tetrayl)tetrabenzaldehyde in the mixed solution is 0.01-0.03 mmol / mL, and the molar concentration of the reaction raw material tetrakis-(4-aminophenyl)ethylene is 0.01-0.03 mmol / mL.

6. The method for preparing the benzocarbazole covalent organic framework according to claim 4, characterized in that: The molar concentration of the acetic acid is 4-6 mol / L, and the volume ratio of the acetic acid to the mixed solvent is 1:(10-20).

7. Use of the benzocarbazole covalent organic framework according to claim 1 or the benzocarbazole covalent organic framework prepared by the preparation method according to any one of claims 2 to 6 in photocatalytic materials.

8. Use of the benzocarbazole covalent organic framework according to claim 1 or the benzocarbazole covalent organic framework prepared by the preparation method according to any one of claims 2 to 6 as a photocatalyst in treating uranium-containing wastewater.

9. The use according to claim 8, characterized in that: The method for treating uranium-containing wastewater comprises: adding a photocatalyst benzocarbazole covalent organic framework and a hole characteristic agent methanol to the uranium-containing wastewater under visible light conditions and stirring to reduce uranyl in the uranium-containing wastewater, and controlling the reduction treatment temperature to be 10°C to 25°C.

10. The use according to claim 8 or 9, characterized in that: The pH value of the uranium-containing wastewater is 3-6.

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