Preparation method of a crown ether-containing covalent organic framework material and its application in strontium and cesium adsorption and separation

Abstract

The present application provides a preparation method of a crown ether-containing covalent organic framework material and its application in the adsorption and separation of strontium and cesium. In the present invention, the 18-crown-6 ether group is introduced into the structure of the covalent organic framework material for the work of strontium and cesium separation. Since the covalent organic framework material can achieve channels conducive to proton transport through ordered stacking, and at the same time, the 18-crown-6 ether can selectively complex strontium ions, the purpose of strontium and cesium separation can be achieved. The covalent organic material prepared in the present application has high-efficiency removal kinetics for low-concentration strontium ions, and the removal rate can reach more than 99% within 5 s. At the same time, under the condition of coexistence of low-concentration strontium and cesium ions with the same molar concentration, it has excellent selective complexation ability for strontium ions, and the separation factor of strontium and cesium is as high as 1868.

Description

Technical Field

[0001] The present application relates to the field of material preparation, and particularly relates to a preparation method of a crown ether-containing covalent organic framework material and its application in the adsorption and separation of strontium and cesium. Background Art

[0002] Strontium and cesium are high heat-releasing elements generated during the nuclear fission of uranium and plutonium, with half-lives of 29 and 30 years respectively, and have persistent radioactivity and biological toxicity. The intake of radioactive strontium can cause cancer and genetic diseases, and the intake of radioactive cesium can cause damage to the human hematopoietic system and nervous system. On the other hand, the separated Sr and Cs can be used for food sterilization, industrial measuring instruments, etc., and can also be used as calibration sources for diagnosis and treatment in hospitals and sterilization of medical devices. Therefore, it is very necessary to efficiently separate strontium and cesium.

[0003] The mainstream methods for removing strontium and cesium include chemical precipitation, solvent extraction, and adsorption. Chemical precipitation (Volkovich, V.A., et al., Treatment of molten salt wastes by phosphate precipitation: removal of fission product elements after pyrochemical reprocessing of spent nuclear fuels in chloride melts. Journal of Nuclear Materials 2003, 323(1), 49-56.) is based on the principle of solubility product, making radioactive elements form insoluble salts to achieve separation and removal. Precipitants usually include heteropolyacids, complex salts, polyhalides, etc. This method is applicable to systems with relatively high ion concentrations, but there are problems such as a relatively complex precipitation process and low product purity. Solvent extraction mainly uses phenolic alcohols, crown ethers (Sharma, J.N., et al, Separation of strontium-90 from a highly saline high level liquid waste solution using 4,4′(5′)-[di-tert-butyldicyclohexano]-18-crown-6 + isodecyl alcohol / n-dodecane solvent. Separation and Purification Technology 2019, 229, 115502.), dinitrodiphenylamine and its derivatives, etc. to separate ions. In this method, the reagents are relatively expensive, and multiple extractions and back-extractions are required to achieve the purpose of enrichment. Moreover, most solvents are biotoxic, which limits their application in actual industries.

[0004] In contrast, the adsorption method has the characteristics of a wide range of adsorbent sources, simple processes, and strong selectivity, and is thus widely used. Therefore, the development and preparation of new materials for strontium and cesium separation have become the key to research. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a crown ether-containing covalent organic framework material and its application in strontium and cesium adsorption and separation. The prepared material has a high level of strontium removal ability (removal rate of 99%) and strontium and cesium separation ability (separation factor of 1868).

[0006] To achieve the above purpose, the preparation method of the present invention includes the following steps:

[0007] 1) Prepare a crown ether aldehyde monomer from a crown ether-containing precursor through an organic synthesis reaction;

[0008] 2) Synthesize a crown ether-containing covalent organic framework material by solvothermal method: Add 20 - 30 mg of the crown ether aldehyde monomer and 10 - 15 mg of 4,4”,4””,4”″”-(pyrene-1,3,6,8-tetrayl)tetraaniline into a 10 ml long-neck glass tube, then add 1 - 2 ml of solvent and ultrasonically mix evenly, then add 100 - 200 μl of an acetic acid catalyst with a concentration of 6 - 9 M, freeze-pump three times to reduce the vacuum to below 100 Pa, seal the tube with a blowtorch flame, react at 90 - 120 °C for 48 - 72 h, after the reaction, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 24 - 48 h, and dry in vacuum at 70 - 80 °C to obtain a highly crystalline crown ether-containing covalent organic framework material.

[0009] The step 1) includes:

[0010] 1.1) Take 0.5 g - 1 g of benzo-18-crown-6 and 0.2 - 0.4 ml of liquid bromine, add them successively to 20 - 30 ml of acetic acid, stir slowly overnight at room temperature. After the reaction is completed, wash the obtained solid-liquid mixture with an alkaline aqueous solution to quench the unreacted bromine, stir until the color of the solid-liquid mixture just changes from reddish-brown to colorless, filter by suction and then extract, and obtain a white solid after rotary evaporation;

[0011] 1.2) Take 1 - 2 g of the white solid, 2 - 3 g of 4-formylphenylboronic acid pinacol ester, 300 - 350 mg of tetrakis(triphenylphosphine)palladium, add them to a 250 ml flask. At the same time, prepare 30 - 40 ml of a 2 M carbonate solution and add it to the flask. Finally, add a mixed solution of 160 ml of tetrahydrofuran and toluene as the solvent, reflux and react at 80 °C in a nitrogen atmosphere for 72 h to obtain a crude yellow-brown liquid product. After cooling to room temperature, filter the crude product using diatomaceous earth, separate and purify the crude product by silica gel column chromatography, with the eluent being a mixture of petroleum ether and ethyl acetate, collect the liquid, and the white solid product obtained after rotary evaporation is the crown ether-containing aldehyde monomer.

[0012] The acetic acid in the step 1.1) is glacial acetic acid with a concentration of 17.5 M.

[0013] The alkaline aqueous solution in the step 1.1) uses an aqueous solution of sodium carbonate, potassium carbonate, sodium thiosulfate or sodium hydroxide with a concentration of 2 M.

[0014] The extraction solvent in the step 1.1) is dichloromethane.

[0015] The carbonate in the step 1.2) is one of sodium carbonate, potassium carbonate or cesium carbonate.

[0016] In step 1.2), the volume ratio of the mixed solvent of tetrahydrofuran and toluene is 1:1 to 2:1.

[0017] In step 1.2), the volume ratio of the developing agent petroleum ether:ethyl acetate is 10:1 to 1:1.

[0018] The solvent in step 2) is o-dichlorobenzene or a mixed solvent of o-dichlorobenzene and n-butanol with a volume ratio of 9:1 to 7:3.

[0019] Application of the crown ether-containing covalent organic framework material prepared by the above preparation method in the adsorption and separation of strontium and cesium ions.

[0020] In the present invention, the 18-crown-6 functional group is introduced into the structure of the covalent organic framework material for the separation of strontium and cesium ions. Since the covalent organic framework material is composed of light elements such as C, H, O, and N, it can form a highly ordered framework structure through the polymerization of two monomers, which is conducive to the transfer of protons in the pores. At the same time, the crown ether group can selectively adsorb strontium ions, providing a platform for the separation of strontium and cesium. The prepared material has good strontium removal ability (removal rate 99%) and strontium-cesium separation ability (separation factor 1868). Description of the Drawings

[0021] Figure 1 It is the infrared spectrum of the crown ether-containing covalent organic framework material 18C6-COF of Example 1 of the present invention.

[0022] Figure 2 It is the powder X-ray diffraction pattern of the crown ether-containing covalent organic framework material 18C6-COF of Example 1 of the present invention.

[0023] Figure 3 It is the scanning electron microscope images of the crown ether-containing covalent organic framework material 18C6-COF of Example 1 of the present invention magnified 11,000 times and 22,000 times, and the scales are 5 microns and 2 microns respectively.

[0024] Figure 4 It is the adsorption kinetics diagram of the crown ether-containing covalent organic framework material 18C6-COF of Example 1 of the present invention for strontium ions.

[0025] Figure 5 It is the diagram of the change of the removal rate of the crown ether-containing covalent organic framework material 18C6-COF of Example 1 of the present invention for strontium and cesium with the same molar ratio over time. Detailed Description of the Invention

[0026] The following further elaborates the present application with reference to the examples.

[0027] Example 1:

[0028] 1) Preparation of the aldehyde-functionalized monomer containing crown ether

[0029] 1.1) Take 0.5 g of benzo - 18 - crown - 6 and 0.4 ml of liquid bromine, and add them successively to 20 ml of 17.5 M glacial acetic acid. Stir slowly overnight at room temperature. After the reaction is completed, stir and wash the obtained solid - liquid mixture with 2 M aqueous sodium carbonate solution to quench the unreacted bromine until the color of the solid - liquid mixture just changes from reddish - brown to colorless. After suction filtration, extract with dichloromethane, and obtain a white solid after rotary evaporation;

[0030] 1.2) Take 1.2 g of the said white solid, 2.8 g of 4 - formylphenylboronic acid pinacol ester, and 350 mg of tetrakis(triphenylphosphine)palladium, add them to a 250 - ml flask. At the same time, prepare 40 ml of 2 M sodium carbonate solution and add it to the flask. Finally, add 160 ml of a mixed solution of tetrahydrofuran and toluene with a volume ratio of 2:1 as the solvent. React under reflux at 80 °C for 72 h in a nitrogen atmosphere to obtain a crude product of a yellow - brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and separate and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 1:1. Collect the liquid, and the white solid product obtained after rotary evaporation is the aldehyde - group monomer containing crown ether;

[0031] 2) Synthesize the covalent organic framework material containing crown ether by solvothermal method: Add 25 mg of the crown - ether aldehyde monomer and 13.65 mg of 4,4”,4””,4”″”-(pyrene - 1,3,6,8 - tetrayl)tetraaniline to a 10 - ml long - neck glass tube. Then add 1 ml of o - dichlorobenzene, ultrasonically mix evenly, and then add 100 μl of 6 M acetic acid catalyst. Use a double - row tube to freeze - pump the glass tube three times to reduce the vacuum degree to 500 Pa, and seal the tube with a blowtorch flame. React at 120 °C for 72 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 48 h, and dry in vacuo at 80 °C to obtain a highly crystalline covalent organic framework material containing crown ether.

[0032] Characterize the material using a Fourier transform infrared spectrometer, a powder X - ray diffractometer, and a scanning electron microscope. Figure 1 This is the infrared spectrum of the covalent organic framework material prepared in this example. It can be seen from the figure that a stretching vibration peak of C=N appears at 1620 cm -1 −1, indicating that the amine monomer and the aldehyde - group monomer have successfully undergone a polymerization reaction. Figure 2 This is the PXRD pattern of the material prepared in this example. It can be seen that two sharp diffraction peaks appear at 3.8° and 4.9°, corresponding to the (101) and (200) crystal planes of the material respectively, and two weaker diffraction peaks appear at 7.2° and 21.72°, corresponding to the (102) and (110) crystal planes of the material respectively, indicating that the prepared framework material has good crystallinity. Figure 3SEM image of the material prepared in this example. It can be seen from the figure that the material presents a regular strip-like structure in the microscopic morphology. The length of the strip is about 1 - 2 microns, and the width is about 200 nanometers.

[0033] Using the crown ether-containing covalent organic material prepared in this example as an adsorbent, the performance of adsorbing and separating strontium and cesium ions was tested. The removal ability of the adsorbent for strontium ions over time (kinetics) and the separation ability for strontium and cesium at the same strontium-to-cesium molar ratio were tested. For the kinetic experiment of strontium, the specific experimental steps were as follows: Add 20 mg of the prepared adsorbent material into a 100 ml glass bottle containing 50 ml of 1 mg / L -1 Sr(NO₃)₂ aqueous solution, and continuously stir on a magnetic stirrer. At a given time, a certain amount (about 0.5 ml) of the mixture was removed with a disposable syringe and filtered through a 0.2-micron aqueous phase needle filter. Subsequently, the above filtrate was diluted 20 times, and the concentration of strontium in the solution was measured by inductively coupled plasma mass spectrometry. The removal rate of strontium (%) was calculated by C t / C₀×100%, where C t and C₀ are the concentrations of strontium in the solution at the initial and reaction time t (min), respectively. For the separation experiment of strontium and cesium, the specific steps were as follows: Add 20 mg of the prepared adsorbent material into a 100 ml glass bottle containing 50 ml of a mixed aqueous solution of 0.0114 mol / L Sr(NO₃)₂ and Cs(NO₃)₂, and continuously stir on a magnetic stirrer. At a given time, a certain amount (about 0.5 ml) of the mixture was removed with a disposable syringe and filtered through a 0.2-micron aqueous phase needle filter. Subsequently, the above filtrate was diluted 20 times, and the concentrations of strontium and cesium in the solution were measured by inductively coupled plasma mass spectrometry. The removal rates of strontium and cesium ions (%) were calculated by C t / C₀×100%. And the concentrations of strontium and cesium ions at the equilibrium point were taken, and the distribution coefficients of strontium and cesium were calculated using (unit cm 3 / g). and The separation factor of strontium and cesium was calculated by . The experimental results are shown in Figure 5 . It can be seen that the crown ether-containing covalent organic framework material of this application has good removal ability for strontium, and the removal rate can reach more than 99% within 5 s. It also has good separation ability for strontium and cesium, and the separation factor reaches 1868.

[0034] Example 2:

[0035] 1) Preparation of aldehyde-functionalized monomers containing crown ethers

[0036] 1.1) Take 0.8 g of benzo-18-crown-6 and 0.2 ml of liquid bromine, and add them successively to 25 ml of 17.5 M glacial acetic acid. Stir slowly at room temperature overnight. After the reaction is completed, wash the obtained solid-liquid mixture with 2 M aqueous sodium carbonate solution to quench the unreacted bromine. Stir until the color of the solid-liquid mixture just changes from reddish-brown to colorless. After suction filtration, extract with dichloromethane, and obtain a white solid after rotary evaporation;

[0037] 1.2) Take 1 g of the white solid, 2.5 g of 4-formylphenylboronic acid pinacol ester, and 300 mg of tetrakis(triphenylphosphine)palladium, and add them to a 250 ml flask. At the same time, prepare 30 ml of 2 M sodium carbonate solution and add it to the flask. Finally, add 160 ml of a mixed solution of tetrahydrofuran and toluene with a volume ratio of 1:1 as the solvent. React under reflux at 80 °C in a nitrogen atmosphere for 72 h to obtain a crude product of a yellowish-brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 5:1. Collect the liquid and obtain a white solid product after rotary evaporation, which is the aldehyde group monomer containing crown ether;

[0038] 2) Synthesize the crown ether-containing covalent organic framework material by solvothermal method: Add 20 mg of the crown ether aldehyde group monomer and 10 mg of 4,4”,4””,4”″”-(pyrene-1,3,6,8-tetrayl)tetraaniline to a 10 ml long-neck glass tube. Then add 1.5 ml of o-dichlorobenzene and ultrasonically mix evenly, and then add 200 μl of 8 M acetic acid catalyst. Use a double-row tube to freeze-pump the glass tube three times to reduce the vacuum to 90 Pa, and seal the tube with a blowtorch flame. React at 100 °C for 36 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 48 h, and dry in vacuum at 70 °C to obtain a highly crystalline crown ether-containing covalent organic framework material.

[0039] Characterized by Fourier transform infrared spectrometer, powder X-ray diffractometer, and scanning electron microscope, it has good crystallinity, forms a C=N bond, the microscopic size length is about 1-2 microns, and the width is about 230 nanometers.

[0040] The crown ether-containing covalent organic framework material prepared in this example has good removal ability for strontium, and the removal rate can reach more than 96% within 5 s. It also has good separation ability for strontium and cesium, and the separation factor reaches 1800.

[0041] Example 3:

[0042] 1) Prepare the aldehyde group monomer containing crown ether

[0043] 1.1) Take 0.6 g of benzo - 18 - crown - 6 and 0.3 ml of liquid bromine, and add them successively to 22 ml of 17.5 M glacial acetic acid. Stir slowly overnight at room temperature. After the reaction is completed, wash the obtained solid - liquid mixture with 2 M aqueous potassium carbonate solution to quench the unreacted bromine. Stir until the color of the solid - liquid mixture just changes from reddish - brown to colorless. After suction filtration, extract with dichloromethane, and obtain a white solid after rotary evaporation;

[0044] 1.2) Take 1.8 g of the above - mentioned white solid, 2 g of 4 - formylphenylboronic acid pinacol ester, and 340 mg of tetrakis(triphenylphosphine)palladium, add them to a 250 - ml flask. At the same time, prepare 35 ml of 2 M potassium carbonate solution and add it to the flask. Finally, add 160 ml of a mixed solution of tetrahydrofuran and toluene with a volume ratio of 1.5:1 as the solvent. React under reflux at 80 °C for 72 h in a nitrogen atmosphere to obtain a crude product of a yellow - brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 3:1. Collect the liquid and obtain a white solid product after rotary evaporation, which is the aldehyde - group monomer containing crown ether;

[0045] 2) Synthesize the crown - ether - containing covalent organic framework material by solvothermal method: Add 28 mg of the above - mentioned crown - ether aldehyde monomer and 12 mg of 4,4”,4””,4”″”-(pyrene - 1,3,6,8 - tetrayl)tetraaniline to a 10 - ml long - neck glass tube. Then add 2 ml of a mixed solvent of o - dichlorobenzene and n - butanol with a volume ratio of 9:1, ultrasonically mix evenly, and then add 130 μl of 7 M acetic acid catalyst. Use a double - row tube to freeze - pump the glass tube three times to reduce the vacuum degree to 70 Pa, and seal the tube with a blowtorch flame. React at 90 °C for 72 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 24 h, and dry under vacuum at 75 °C to obtain a highly crystalline crown - ether - containing covalent organic framework material.

[0046] Characterized by Fourier transform infrared spectrometer, powder X - ray diffractometer, and scanning electron microscope, it has good crystallinity, forms C = N bonds, and the microscopic size has a length of about 1 - 2 μm and a width of about 250 nm.

[0047] The crown - ether - containing covalent organic framework material prepared in this example has good removal ability for strontium, and the removal rate can reach more than 96% within 5 s. It also has good separation ability for strontium and cesium, and the separation factor reaches 1780.

[0048] Example 4:

[0049] 1) Prepare the aldehyde - group - containing monomer containing crown ether

[0050] 1.1) Take 1 g of benzo - 18 - crown - 6 and 0.25 ml of liquid bromine, and add them successively to 30 ml of 17.5 M glacial acetic acid. Stir slowly overnight at room temperature. After the reaction is completed, stir - wash the obtained solid - liquid mixture with 2 M aqueous sodium thiosulfate solution to quench the unreacted bromine until the color of the solid - liquid mixture just changes from reddish - brown to colorless. After suction filtration, extract with dichloromethane, and obtain a white solid after rotary evaporation;

[0051] 1.2) Take 2 g of the said white solid, 2.2 g of 4 - formylphenylboronic acid pinacol ester, and 320 mg of tetrakis(triphenylphosphine)palladium, add them to a 250 - ml flask. At the same time, prepare 38 ml of 2 M cesium carbonate solution and add it to the flask. Finally, add 160 ml of a mixed solution of tetrahydrofuran and toluene with a volume ratio of 1.3:1 as the solvent. React under reflux at 80 °C for 72 h in a nitrogen atmosphere to obtain a crude product of a yellow - brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 10:1. Collect the liquid, and the white solid product obtained after rotary evaporation is the aldehyde - group monomer containing crown ether;

[0052] 2) Synthesize the crown - ether - containing covalent organic framework material by solvothermal method: Add 30 mg of the crown - ether aldehyde - group monomer and 15 mg of 4,4”,4””,4”″”-(pyrene - 1,3,6,8 - tetrayl)tetraaniline to a 10 - ml long - neck glass tube. Then add 1.8 ml of a mixed solvent of ortho - dichlorobenzene and n - butanol with a volume ratio of 8:2, ultrasonically mix evenly, and then add 180 μl of 9 M acetic acid catalyst. Use a double - row tube to freeze - pump the glass tube three times to reduce the vacuum degree to 80 Pa, and seal the tube with a blowtorch flame. React at 110 °C for 64 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 36 h, and dry in vacuo at 78 °C to obtain a highly crystalline crown - ether - containing covalent organic framework material.

[0053] Characterized by Fourier transform infrared spectrometer, powder X - ray diffractometer, and scanning electron microscope, it has good crystallinity, forms C=N bonds, with a microscopic size of about 2 - 3 microns in length and about 240 nanometers in width.

[0054] The crown - ether - containing covalent organic framework material prepared in this example has good removal ability for strontium, and the removal rate can reach more than 95% within 5 s. It also has good separation ability for strontium and cesium, and the separation factor reaches 1825.

[0055] Example 5:

[0056] 1) Prepare the aldehyde - group - modified monomer containing crown ether

[0057] 1.1) Take 0.7 g of benzo-18-crown-6 and 0.35 ml of liquid bromine, and add them successively to 28 ml of 17.5 M glacial acetic acid. Stir slowly overnight at room temperature. After the reaction is completed, wash the obtained solid-liquid mixture with 2 M aqueous sodium hydroxide solution to quench the unreacted bromine. Stir until the color of the solid-liquid mixture just changes from reddish-brown to colorless. After suction filtration, extract with dichloromethane, and obtain a white solid after rotary evaporation;

[0058] 1.2) Take 1.5 g of the said white solid, 3 g of 4-formylphenylboronic acid pinacol ester, and 330 mg of tetrakis(triphenylphosphine)palladium, and add them to a 250 ml flask. At the same time, prepare 33 ml of 2 M cesium carbonate solution and add it to the flask. Finally, add 160 ml of a mixed solution of tetrahydrofuran and toluene with a volume ratio of 1.8:1 as the solvent. React under reflux at 80 °C for 72 h in a nitrogen atmosphere to obtain a crude product of a yellowish-brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 8:1. Collect the liquid, and the white solid product obtained after rotary evaporation is the aldehyde group monomer containing crown ether;

[0059] 2) Synthesize the crown ether-containing covalent organic framework material by solvothermal method: Add 23 mg of the crown ether aldehyde group monomer and 14 mg of 4,4”,4””,4”″”-(pyrene-1,3,6,8-tetrayl)tetraaniline to a 10 ml long-neck glass tube. Then add 1.3 ml of a mixed solvent of ortho-dichlorobenzene and n-butanol with a volume ratio of 7:3, ultrasonically mix evenly, and then add 150 μl of an 8 M acetic acid catalyst. Use a double-row tube to freeze-pump the glass tube three times to reduce the vacuum degree to 60 Pa, and seal the tube with a blowtorch flame. React at 120 °C for 48 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 40 h, and dry under vacuum at 72 °C to obtain a highly crystalline crown ether-containing covalent organic framework material.

[0060] Characterized by Fourier transform infrared spectrometer, powder X-ray diffractometer, and scanning electron microscope, it has good crystallinity, forms C=N bonds, and the microscopic size is about 1-2 microns in length and about 220 nanometers in width.

[0061] The crown ether-containing covalent organic framework material prepared in this example has good removal ability for strontium, and the removal rate can reach more than 96% within 5 s. It also has good separation ability for strontium and cesium, and the separation factor reaches 1790.

[0062] The above description is only a preferred embodiment of the present application and an explanation of the technical principles applied. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the aforementioned disclosure concept. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) disclosed in the present application that have similar functions.

Claims

1. A preparation method of a crown ether-containing covalent organic framework material, characterized in that, It includes the following steps: 1) Prepare a crown ether aldehyde monomer from a crown ether-containing precursor through an organic synthesis reaction; 1.1) Take 0.5 g - 1 g of benzo-18-crown-6 and 0.2 - 0.4 ml of liquid bromine, and add them successively to 20 - 30 ml of acetic acid. Stir slowly overnight at room temperature. After the reaction is completed, wash the obtained solid-liquid mixture with an alkaline aqueous solution to quench the unreacted bromine. Stir until the color of the solid-liquid mixture just changes from reddish-brown to colorless. After suction filtration, extract, and rotary evaporate to obtain a white solid; 1.2) Take 1 - 2 g of the white solid, 2 - 3 g of 4-formylphenylboronic acid pinacol ester, and 300 - 350 mg of tetrakis(triphenylphosphine)palladium, and add them to a 250 ml flask. At the same time, prepare 30 - 40 ml of 2M carbonate solution and add it to the flask. Finally, add a mixed solution of 160 ml of tetrahydrofuran and toluene as the solvent. React under reflux at 80 °C for 72 h in a nitrogen atmosphere to obtain a crude product of a yellow-brown liquid. After cooling to room temperature, filter the crude product using diatomaceous earth, and purify the crude product by silica gel column chromatography. The eluent is a mixture of petroleum ether and ethyl acetate. Collect the liquid and rotary evaporate to obtain the white solid product, which is the aldehyde monomer containing crown ether; 2) Synthesize a crown ether-containing covalent organic framework material by solvothermal method: Add 20 - 30 mg of the crown ether aldehyde monomer and 10 - 15 mg of 4,4”,4””,4”””-(pyrene-1,3,6,8-tetrayl)tetraaniline to a 10 ml long-necked glass tube. Then add 1 - 2 ml of the solvent, ultrasonically mix evenly, and then add 100 - 200 μl of an acetic acid catalyst with a concentration of 6 - 9M. Freeze-pump three times to reduce the vacuum to below 100 Pa, and use a torch flame to seal the tube. React at 90 - 120 °C for 48 - 72 h. After the reaction is completed, centrifuge to collect the solid product, perform Soxhlet extraction with tetrahydrofuran for 24 - 48 h, and vacuum dry at 70 - 80 °C to obtain a highly crystalline crown ether-containing covalent organic framework material.

2. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, wherein, The acetic acid in step 1.1) is glacial acetic acid with a concentration of 17.5M.

3. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, characterized in that, The alkaline aqueous solution in step 1.1) uses an aqueous solution of sodium carbonate, potassium carbonate, sodium thiosulfate, or sodium hydroxide with a concentration of 2M.

4. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, characterized in that, The extraction solvent in step 1.1) is dichloromethane.

5. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, characterized in that, The carbonate in step 1.2) is one of sodium carbonate, potassium carbonate, or cesium carbonate.

6. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, wherein, In step 1.2), the volume ratio of the tetrahydrofuran and toluene mixed solvent is 1:1 - 2:

1.

7. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, characterized in that, In step 1.2), the volume ratio of petroleum ether to ethyl acetate in the eluent is 10:1 - 1:

1.

8. The preparation method of the crown ether-containing covalent organic framework material according to claim 1, wherein, The solvent in step 2) is o-dichlorobenzene or a mixed solvent of o-dichlorobenzene and n-butanol with a volume ratio of 9:1 - 7:

3.

9. Application of the crown ether-containing covalent organic framework material prepared by the preparation method according to any one of claims 1 - 8 in the adsorption and separation of strontium and cesium ions.

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