Pyridine-rich imine type covalent organic framework as well as preparation method and application thereof

Abstract

The invention relates to the technical field of covalent organic framework functional materials, in particular to a pyridine-rich imine type covalent organic framework as well as a preparation method and application thereof. The pyridine-rich imine type covalent organic framework disclosed by the invention has a structure as shown in the following formula (I): # imgabs0 # formula (I). The pyridine-enriched imine type covalent organic framework disclosed by the invention contains rich pyridine-N active sites, can efficiently adsorb iodine through Lewis acid-base action, and can effectively fix iodomethane through methylation reaction, so that two iodine pollutants can be efficiently captured at the same time. The pyridine-rich imine type covalent organic framework disclosed by the invention also has good crystallinity, larger specific surface area and excellent thermal stability and acid-base stability, and can realize efficient adsorption of iodine and iodomethane.

Description

Technical Field

[0001] The present invention relates to the technical field of covalent organic framework functional materials, and in particular to a pyridine imine-rich covalent organic framework, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the problems of environmental pollution and energy shortage are becoming increasingly prominent. As one of the clean energies, nuclear energy has received extensive attention from countries around the world due to its characteristics such as low carbon and high energy density. However, the rapid development of the nuclear industry has also brought problems such as spent fuel reprocessing and radioactive pollution caused by nuclear accidents. Iodine is a volatile by-product generated by nuclear fission reactions. During the spent fuel reprocessing process, the treatment conditions of strong acids and high temperatures will cause a large amount of volatile and radioactive gases to be released from nuclear waste, and among them, the more harmful ones include iodine vapor and organic iodine (iodomethane, iodoethane, etc.). The radioactive isotopes of iodine include I-129 with a relatively long half-life (1.57×10⁷ years) and I-131 with a relatively short half-life (8.02 days). Radioactive iodine has biological toxicity and can induce thyroid diseases and endanger the human reproductive and metabolic systems. In addition, man-made nuclear accidents will also cause volatile iodine and methyl iodide to randomly enter the atmosphere and water bodies, posing a huge threat to the environment and human health. Therefore, the capture and storage of radioactive iodine are of great significance for environmental protection and human health. However, due to the high volatility and high fluidity of iodine and organic iodine, the capture of radioactive iodine has become a challenging problem.

[0003] The methods for removing iodine pollutants in industry are generally divided into two categories: wet method and dry method. The wet method usually uses a solvent to wash iodine from the gas phase; the dry method is to directly capture radioactive iodine using a solid adsorbent. The wet method has always been the commonly used method for treating radioactive iodine at present, but the actual application effect is not very ideal. The waste liquid after washing will not only cause secondary pollution but also corrode the equipment, resulting in an increase in treatment costs. Compared with the wet method, the dry method has obvious advantages. The dry method refers to using a solid porous material to adsorb and store radioactive iodine, with simple operation, low cost, good reusability, and excellent effect. However, the existing porous adsorption materials used in the dry method have poor thermal stability and acid-base stability, and the adsorption effects on iodine and iodomethane are not ideal. Summary of the Invention

[0004] The present invention provides a pyridine imine-rich covalent organic framework, a preparation method thereof, and an application thereof, so as to solve the problems that the existing porous adsorption materials used in the dry method have poor thermal stability and acid-base stability, and the adsorption effects on iodine and iodomethane are not ideal.

[0005] According to the first aspect of the present invention, the present invention provides a pyridine imine-rich covalent organic framework, and the pyridine imine-rich covalent organic framework has a structure shown in the following formula (I): Formula (I).

[0006] Covalent organic framework (COF) is a new type of porous material. In this invention, pyridine-rich monomers are designed independently for COF synthesis, and finally a pyridine-imine-rich covalent organic framework is obtained. The pyridine-imine covalent organic framework of this invention is connected by covalent bonds and has a regular specific pore structure, which makes this porous material have good thermal stability and chemical stability. Through experimental thermogravimetric analysis, it is found that this pyridine-imine-rich covalent organic framework can remain stable at 350 °C, and after being soaked in 3M and 6M nitric acid and sodium hydroxide solutions for 24 hours respectively, the material can still maintain very good crystallinity. The pyridine-imine covalent organic framework of this invention is rich in highly efficient active adsorption sites of pyridine-N. Pyridine-N can not only form a charge transfer complex with iodine molecules through Lewis acid-base interaction to achieve efficient adsorption of iodine, but also fix iodomethane through methylation reaction, which enables the porous material of this invention to achieve efficient capture of iodine vapor and organic iodine and has good application prospects. Through experiments, it is obtained that the pyridine-imine-rich covalent organic framework of this invention shows excellent adsorption performance in both static adsorption and dynamic breakthrough experiments, and has outstanding comprehensive performance among a group of solid adsorbents for iodine / iodomethane.

[0007] Furthermore, the pyridine-imine-rich covalent organic framework is prepared from raw materials including 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine.

[0008] Preferably, the molar ratio of 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde to 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine is (0.5 - 2):1, preferably 1:1. Under the above molar ratio conditions, the target product can be obtained more effectively.

[0009] Furthermore, the specific surface area of the pyridine-imine-rich covalent organic framework is 1000 - 1500 m 2 / g, and the pore diameter is 18 - 25 Å. The pyridine-imine-rich covalent organic framework with such specifications can achieve efficient adsorption of iodine / iodomethane.

[0010] According to the second aspect of this invention, this invention also provides a preparation method of the above pyridine-imine-rich covalent organic framework, including the following steps: Two pyridine-rich monomers, namely 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine, were prepared through Suzuki coupling reaction. Using 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine as raw monomers, a pyridine-rich imine-based covalent organic framework was synthesized by solvothermal method.

[0011] The preparation method of the pyridine-rich imine-based covalent organic framework of the present invention is simple to operate and suitable for wide applications. After the reaction, the product can be directly used for the synthesis of COF without further purification by column chromatography.

[0012] Furthermore, the method for preparing 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction includes the following steps: Dissolve halogenated pyridine-2-carbaldehyde, 1,3,5-benzenetriboronic acid tris(pinacol) ester, and the first basic compound in the first solvent and react under the action of the first catalyst.

[0013] Preferably, the reaction temperature for preparing 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction is 100 - 120 °C, and the reaction time is 12 - 24 h. The Suzuki coupling reaction involved in the present invention is simple to operate.

[0014] Furthermore, the method for preparing 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction further includes the following steps: After the reaction, let the solution stand, wait for the product to precipitate, pour off the supernatant, centrifuge and filter, wash with methanol, ethanol, and deionized water multiple times, and finally dry under vacuum at 50 - 70 °C overnight.

[0015] During the experimental process of the present invention, it was found that in the process of preparing 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction, the types of raw materials and the dosage ratio between various raw materials play an important role in the reaction efficiency. In order to improve the reaction efficiency and achieve high yield, the present invention further optimizes the types of raw materials and the dosage ratio between various raw materials as follows.

[0016] Furthermore, the halogenated pyridine-2-carbaldehyde is selected from one or more of 5-bromo-pyridine-2-carbaldehyde, 5-iodo-pyridine-2-carbaldehyde, or 5-chloro-pyridine-2-carbaldehyde.

[0017] Further, the molar ratio of the halopyridine-2-carboxaldehyde to the 1,3,5-benzenetriboronic acid tris(pinacol) ester is 1:(3 - 5), preferably 1:4.

[0018] Further, the first basic compound is selected from one or more of sodium carbonate, potassium carbonate, or cesium carbonate.

[0019] Further, the molar amount of the first basic compound is 2 - 5 times the sum of the molar amounts of the halopyridine-2-carboxaldehyde and the 1,3,5-benzenetriboronic acid tris(pinacol) ester.

[0020] Further, the first solvent is selected from one or more of 1,4-dioxane, ethanol, toluene, and water. In some specific embodiments, the first solvent is a mixture of 1,4-dioxane and water, and the volume ratio of 1,4-dioxane to water is 3:1 - 5:1.

[0021] Further, the first catalyst is selected from one of tetrakis(triphenylphosphine)palladium, palladium dichloride, palladium acetate, and bis(triphenylphosphine)palladium dichloride.

[0022] Further, the molar amount of the first catalyst is 1% - 5% of the molar amount of the halopyridine-2-carboxaldehyde.

[0023] Further, the method for preparing 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine by Suzuki coupling reaction comprises the following steps: Dissolve the trihalopyridine, 2-aminopyridine-5-boronic acid pinacol ester, and the second basic compound in the second solvent, and react under the action of the second catalyst.

[0024] Preferably, the reaction temperature for preparing 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine by Suzuki coupling reaction is 100 - 120 °C, and the reaction time is 12 - 24 h. The Suzuki coupling reaction involved in the present invention is simple to operate.

[0025] Further, the method for preparing 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine by Suzuki coupling reaction further comprises the following steps: After the reaction is completed, let the solution stand, wait for the product to precipitate, pour off the supernatant, centrifuge and filter, wash with methanol, ethanol, and deionized water multiple times, and finally dry under vacuum at 50 - 70 °C overnight.

[0026] In the process of the experiment of the present invention, it is found that in the process of preparing the 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine by Suzuki coupling reaction, the types of raw materials and the dosage ratio between various raw materials play a very important role in the reaction efficiency. In order to improve the reaction efficiency and achieve high yield, the present invention further optimizes the types of raw materials and the dosage ratio between various raw materials as follows.

[0027] Further, the trihalopyridine is selected from one or two of 2,4,6-tribromopyridine or 2,4,6-trichloropyridine.

[0028] Further, the molar ratio of the trihalopyridine to the 2-aminopyridine-5-boronic acid pinacol ester is 1:(3-5), preferably 1:4.

[0029] Further, the second basic compound is selected from one or more of sodium carbonate, potassium carbonate or cesium carbonate.

[0030] Further, the molar dosage of the second basic compound is 1.5 to 5 times the sum of the molar dosages of the trihalopyridine and the 2-aminopyridine-5-boronic acid pinacol ester.

[0031] Further, the second solvent is selected from one or more of 1,4-dioxane, ethanol, toluene and water. In some specific embodiments, the second solvent is a mixture of 1,4-dioxane and water, and the volume ratio of 1,4-dioxane to water is 3:1 to 5:1.

[0032] Further, the second catalyst is selected from one of tetrakis(triphenylphosphine)palladium, palladium dichloride, palladium acetate, bis(triphenylphosphine)palladium dichloride.

[0033] Further, the molar dosage of the second catalyst is 0.5% to 5% of the molar dosage of the 2-aminopyridine-5-boronic acid pinacol ester.

[0034] Further, the reaction temperature for synthesizing the pyridine imine-rich covalent organic framework by the solvothermal method is 100-150 °C, and the reaction time is 60-84 h. By limiting the reaction temperature and reaction time in the solvothermal synthesis process within appropriate range values, it is beneficial to improve the synthesis efficiency of the target product.

[0035] Preferably, the method for synthesizing the pyridine imine-rich covalent organic framework by the solvothermal method is as follows: (1) Add 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine to a solvent. After ultrasonic treatment for 10 - 15 minutes, a uniform dispersion is formed. Add a catalyst to the mixture and continue ultrasonic treatment for 3 - 8 minutes to mix evenly. (2) Quickly freeze the mixture at 70 - 80 K and degas it through three freeze-pump-thaw cycles. Then seal the glass tube and heat it at 100 - 150 °C for 2 - 4 days. After the reaction is completed, the product is purified by filtration and Soxhlet extraction in tetrahydrofuran for 36 - 60 hours, and then vacuum dried at 100 - 150 °C overnight.

[0036] Preferably, the solvents used in the solvothermal synthesis of pyridine imine-rich covalent organic frameworks include 1,4-dioxane, and the catalyst is acetic acid (concentration greater than 12 mol / L). In some specific embodiments, the solvents used in the solvothermal synthesis of pyridine imine-rich covalent organic frameworks are 1,4-dioxane and mesitylene, and the volume ratio of 1,4-dioxane to mesitylene is (1 - 2):1.

[0037] Further, the molar amount of the catalyst used in the solvothermal synthesis of pyridine imine-rich covalent organic frameworks is 10 - 15 times the sum of the molar amounts of 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine.

[0038] According to the third aspect of the present invention, the present invention provides the application of the above pyridine imine-rich covalent organic framework or the pyridine imine-rich covalent organic framework prepared by the above preparation method in the adsorption of iodine and iodomethane.

[0039] The pyridine imine-rich covalent organic framework of the present invention can achieve static and dynamic adsorption of iodine and iodomethane. Specifically, a static closed device is used to test the static adsorption capacity of the pyridine imine-rich covalent organic framework for iodine and iodomethane at 70 - 80 °C; a fixed-bed breakthrough device is used to test the dynamic adsorption performance of the pyridine imine-rich covalent organic framework for iodine at room temperature.

[0040] The beneficial effects of the technical solution provided by the present invention are as follows: A pyridine imine-rich covalent organic framework of the present invention contains abundant pyridine-N active sites, which can not only efficiently adsorb iodine through Lewis acid-base interaction, but also effectively fix iodomethane through methylation reaction, thus achieving efficient capture of two iodine pollutants simultaneously.

[0041] The covalent organic framework rich in pyridine imine of the present invention has good crystallinity and a large specific surface area, and also has excellent thermal stability and acid-base stability, and can achieve efficient adsorption of iodine and iodomethane.

[0042] The preparation method of the covalent organic framework rich in pyridine imine of the present invention is simple and suitable for wide application. Brief Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 1H NMR spectrum of 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde (BTPA) obtained in Example 1 of the present invention.

[0045] Figure 2 1H NMR spectrum of 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine (TAPyrPyr) obtained in Example 1 of the present invention.

[0046] Figure 3 SEM and HRTEM images of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention. Among them, Figure 3 (a) SEM image of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention; Figure 3 (b) HRTEM image of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0047] Figure 4 XRD image obtained through experiment, simulated XRD spectrum, and Pawley refined XRD diagram of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0048] Figure 5 XPS spectrum of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0049] Figure 6 FT-IR spectrum of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0050] Figure 713C-NMR spectrum of the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0051] Figure 8 Nitrogen adsorption-desorption isotherm and pore size distribution diagram of the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0052] Figure 9 Thermogravimetric curve of the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0053] Figure 10 XRD spectrum of the pyridine-imine-rich covalent organic framework PyN-COF after acid-base treatment obtained in Example 1 of the present invention.

[0054] Figure 11 Static adsorption curve of iodine and iodomethane by the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention, wherein Figure 11 (a) Static adsorption curve of iodine by the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention; Figure 11 (b) Static adsorption curve of iodomethane by the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention.

[0055] Figure 12 Dynamic breakthrough curve of iodine by the pyridine-imine-rich covalent organic framework PyN-COF obtained in Example 1 of the present invention. Detailed implementation manners

[0056] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments in the present invention fall within the protection scope of the present invention.

[0057] Example 1 This example provides a pyridine-imine-rich covalent organic framework having the structure shown in the following formula (I): Formula (I).

[0058] This example also provides a preparation method of the pyridine-imine-rich covalent organic framework, which includes the following steps: Step S1: Prepare two pyridine-rich monomers, namely 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine, through Suzuki coupling reaction.

[0059] Specifically, the reaction equation for preparing 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde (BTPA) through Suzuki coupling reaction is shown as Equation (1) below. Equation (1).

[0060] Its preparation method includes the following steps: (1) Dissolve 1,3,5-benzenetriboronic acid tris(pinacol) ester (3.0 mmol, 1.37 g), 5-bromo-pyridine-2-carbaldehyde (10.0 mmol, 1.86 g), and potassium carbonate (27 mmol, 3.73 g) in a mixed solution of 1,4-dioxane (24 ml) and water (6 ml). Stir for 0.5 hour under an argon (or nitrogen) atmosphere, and then add the catalyst tetrakis(triphenylphosphine)palladium (150 mg) to this solution. Stir at 110 °C for 24 hours.

[0061] After the reaction is completed, let the solution stand still until the product precipitates. Pour off the supernatant, centrifuge and filter, wash with methanol, ethanol, and deionized water multiple times, and finally dry under vacuum at 60 °C overnight to obtain white powder BTPA (879.1 mg, yield: 74.5%). The purity of the product is detected by 1H NMR as Figure 1 shown.

[0062] The reaction equation for preparing 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine (TAPyrPyr) through Suzuki coupling reaction is shown as Equation (2) below. Equation (2).

[0063] Its preparation method includes the following steps: (1) Dissolve 2,4,6-tribromopyridine (3.0 mmol, 947.37 mg), 2-aminopyridine-5-boronic acid pinacol ester (11.7 mmol, 2.57 g), and potassium carbonate (24 mmol, 3.32 g) in a mixed solution of 1,4-dioxane (15 ml) and water (5 ml). Stir for 0.5 hour under an argon atmosphere, and then add the catalyst tetrakis(triphenylphosphine)palladium (80 mg) to this solution. Stir at 110 °C for 24 hours.

[0064] (2)After the reaction was completed, the solution was allowed to stand until the product precipitated. The supernatant was decanted, and the product was centrifuged and filtered. It was washed multiple times with methanol, ethanol, and deionized water, and finally dried under vacuum at 60 °C overnight to obtain a pale yellow powder TAPyrPyr (773.6 mg, yield: 72.4%). The purity of the product was detected by 1H NMR as Figure 2 shown.

[0065] Step S2: Using 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine as raw material monomers, a pyridine-rich imine-based covalent organic framework was synthesized by the solvothermal method. The reaction equation is shown in Equation (3) below, Equation (3).

[0066] Specifically, the synthesis of the pyridine-rich imine-based covalent organic framework by the solvothermal method includes the following steps: (1) Add BTPA (0.2 mmol, 78.68 mg) and TAPyrPyr (0.2 mmol, 71.03 mg) to a mixed solvent of 1,4-dioxane (1.0 mL) and mesitylene (1.0 mL). After ultrasonic treatment for 10 - 15 minutes, a homogeneous dispersion was formed. Add glacial acetic acid (0.2 ml) as a catalyst to the mixture. Continue ultrasonic treatment for 5 minutes and mix evenly; (2) The mixture was quickly frozen at 77 K and degassed by three freeze-pump-thaw cycles. Then the glass tube was sealed and heated at 120 °C for 3 days. After the reaction was completed, the product was purified by filtration and Soxhlet extraction in tetrahydrofuran for 48 hours, and then dried under vacuum at 120 °C overnight to obtain the pyridine-rich imine-based covalent organic framework PyN-COF.

[0067] Perform performance characterization on the obtained pyridine-rich imine-based covalent organic framework PyN-COF.

[0068] Figure 3 are the SEM and HRTEM images of the obtained pyridine-rich imine-based covalent organic framework PyN-COF, where Figure 3 (a) is the SEM image of the obtained pyridine-rich imine-based covalent organic framework PyN-COF; Figure 3 (b) is the HRTEM image of the obtained pyridine-rich imine-based covalent organic framework PyN-COF.

[0069] Figure 4The experimental XRD image, simulated XRD spectrum, and Pawley refined XRD pattern of the obtained pyridine-rich imine-based covalent organic framework PyN-COF are shown. It can be seen that the experimental and refined PXRD spectra are in good agreement, indicating that the experimentally obtained structure is consistent with the preset structure. In addition, the main peaks of the PXRD are obvious, indicating that the obtained pyridine-rich imine-based covalent organic framework PyN-COF has very good crystallinity.

[0070] Figure 5 The XPS spectrum of the obtained pyridine-rich imine-based covalent organic framework PyN-COF is shown. It can be seen that there are two nitrogen species in PyN-COF, namely the nitrogen in the imine bond and pyridine, which is in line with expectations.

[0071] Figure 6 The FT-IR spectrum of the obtained pyridine-rich imine-based covalent organic framework PyN-COF is shown. It can be seen that the peaks attributed to -NH2 and -CHO are significantly weakened or even disappear, while a new peak appears at ~1627 cm -1 which is attributed to the imine bond, indicating that the Schiff base reaction proceeds smoothly and PyN-COF is successfully prepared.

[0072] Figure 7 The 13C-NMR spectrum of the obtained pyridine-rich imine-based covalent organic framework PyN-COF is shown. It can be seen that characteristic chemical shift peaks belonging to the imine bond appear at ~151 ppm and ~157 ppm, further confirming the progress of the Schiff base reaction and the successful preparation of PyN-COF.

[0073] Figure 8 The nitrogen adsorption-desorption isotherm and pore size distribution diagram of the obtained pyridine-rich imine-based covalent organic framework PyN-COF are shown. It can be seen that the specific surface area of the pyridine-rich imine-based covalent organic framework is 1002 m 2 / g, and the pore size distribution is mainly concentrated between 8 - 25 Å.

[0074] Figure 9 The thermogravimetric curve of the obtained pyridine-rich imine-based covalent organic framework PyN-COF is shown. It can be seen that this COF has good thermal stability and can remain stable within 300 °C.

[0075] Figure 10 The XRD spectrum of the obtained pyridine-rich imine-based covalent organic framework PyN-COF after acid-base treatment is shown.

[0076] Example 2 This example provides the application of the pyridine-rich imine-based covalent organic framework PyN-COF obtained in Example 1 in iodine or iodomethane adsorption, and the specific application is as follows: Static iodine or iodomethane (q t , g·g-1 The adsorption amount of ) is calculated as follows: q t (g·g -1 ) represents the amount of iodine or methyl iodide captured at a specific time t; m t (g) represents the weight of the vial containing PyN-COF at time t; m1 (g) represents the weight of the vial before adsorption; m0 (g) represents the weight of the empty PyN-COF bottle; M t (g) represents the weight of the blank vial at time t; M0 (g) represents the weight of the blank vial before adsorption.

[0077] (1) Non-radioactive iodine was used to simulate radioactive iodine in nuclear waste. Static iodine and methyl iodide adsorption experiments were performed using sealed glassware. Three 5 ml glass bottles were placed in a 100 ml wide-mouth bottle. The first glass bottle contained 10.0 mg of activated PyN-COF sample. The second glass bottle contained iodine or methyl iodide, and the third glass bottle served as a blank control.

[0078] (2) Tighten the jar and place it in an oven set at 75°C. After a period of time, remove the jar from the oven and cool it to room temperature. Weigh the small glass bottle containing the PyN-COF sample. Put it back into the jar and continue to adsorb iodine or iodomethane at 75°C until the weight of the bottle remains unchanged. Determine its static equilibrium adsorption capacity by measuring the increase in the weight of the PyN-COF sample.

[0079] like Figure 11 As shown in (a), PyN-COF has a fast adsorption rate for iodine in the first 40 hours, and after 50 hours, the material gradually reaches a saturated adsorption state. Figure 11 As shown in (b), for methyl iodide, PyN-COF exhibits more excellent adsorption kinetics, reaching saturated adsorption of methyl iodide in less than 20 hours, and the saturated adsorption capacity is as high as 1.5g / g, with excellent performance. After 20 hours, the material reaches saturated adsorption.

[0080] Example 3 This example provides the application of the pyridine imine-rich covalent organic framework PyN-COF obtained in Example 1 in the adsorption of iodine or methyl iodide, and the specific application is as follows: (1) Vacuum dry 15 mg of PyN-COF at 100 °C overnight. Subsequently, place the PyN-COF into a glass tube (inner diameter 5 mm, outer diameter 7 mm, length 100 mm), and fix the PyN-COF in the middle of the glass tube with absorbent cotton.

[0081] (2) Purge the adsorbent with N2 (5 ml / min) at room temperature. Subsequently, the dry N2 passes through a glass bottle filled with iodine, and the generated N2 / I2 mixed gas passes through the adsorption column. Finally, the gas flowing out of the adsorption column is absorbed by the cyclohexane solution, and the iodine content in the cyclohexane solution is detected by ultraviolet-visible spectroscopy at 523 nm.

[0082] (3) Finally, use a glass column filled only with absorbent cotton to conduct a blank experiment. The measured flow rate of iodine in the mixed gas stream is 1.38 mg / h. Finally, accurately weigh the dynamic iodine adsorption capacity of the material by the gravimetric method.

[0083] As Figure 12 shown, within the first 20 hours, almost all of the iodine in the mixed gas is adsorbed by the COF. After 20 hours, an iodine signal begins to be detected in the mixed gas after passing through the material, indicating that the iodine in the mixed gas begins to penetrate the material and enter the cyclohexane solution. As time goes by, the COF material gradually reaches saturation adsorption, so that the iodine in the mixed gas stream can completely pass through the COF material and directly enter the cyclohexane solution. Generally speaking, there is a 20-hour plateau stage in the early stage, indicating that this COF has excellent dynamic adsorption performance for iodine and is a very promising solid adsorbent for iodine adsorption.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pyridine-rich imine-based covalent organic framework, characterized in that, The pyridine-rich imine-based covalent organic framework has the structure shown in the following formula (I): Formula (I).

2. The pyridine-rich imine-based covalent organic framework according to claim 1, characterized in that, The pyridine-rich imine-based covalent organic framework is prepared from raw materials including 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine; Preferably, the molar ratio of 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde to 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine is (0.5 - 2):

1.

3. The pyridine-rich imine-based covalent organic framework according to claim 1 or 2, characterized in that, The specific surface area of the pyridine-rich imine-based covalent organic framework is 1000 - 1500 m 2 / g, and the pore size is 8 - 25 Å.

4. The preparation method of the pyridine-rich imine-based covalent organic framework according to any one of claims 1-3, characterized in that, It includes the following steps: Through Suzuki coupling reaction, two pyridine-rich monomers are prepared, namely 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine; Using 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde and 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine as raw material monomers, the pyridine-rich imine-based covalent organic framework is synthesized by solvothermal method.

5. The preparation method according to claim 4, characterized in that, The method for preparing the 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction includes the following steps: Dissolve halogenated pyridine-2-carbaldehyde, 1,3,5-benzenetriboronic acid tri-pinacol ester, and the first basic compound in the first solvent, and react under the action of the first catalyst; Preferably, the reaction temperature for preparing the 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde through Suzuki coupling reaction is 100 - 120 °C, and the reaction time is 12 - 24 h.

6. The preparation method according to claim 5, characterized in that, The halogenated pyridine-2-carbaldehyde is selected from one or more of 5-bromo-pyridine-2-carbaldehyde, 5-iodo-pyridine-2-carbaldehyde, or 5-chloro-pyridine-2-carbaldehyde; And / or, the molar ratio of the halogenated pyridine-2-carbaldehyde to the 1,3,5-benzenetriboronic acid tri-pinacol ester is (3 - 5):1; And / or, the first basic compound is selected from one or more of sodium carbonate, potassium carbonate, or cesium carbonate; And / or, the molar amount of the first basic compound is 2 - 5 times the sum of the molar amounts of the halogenated pyridine-2-carbaldehyde and the 1,3,5-benzenetriboronic acid tri-pinacol ester; And / or, the first solvent is selected from one or more of 1,4-dioxane, ethanol, toluene, and water; And / or, the first catalyst is selected from one of tetrakis(triphenylphosphine)palladium, palladium dichloride, palladium acetate, and bis(triphenylphosphine)palladium dichloride; And / or, the molar amount of the first catalyst is 1% - 5% of the molar amount of the halogenated pyridine-2-carbaldehyde.

7. The preparation method according to claim 4, characterized in that, The method for preparing the 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine through Suzuki coupling reaction includes the following steps: Dissolve a trihalopyridine, 2-aminopyridine-5-boronic acid pinacol ester, and a second basic compound in a second solvent, and react under the action of a second catalyst; Preferably, the reaction temperature for preparing the 6'-(6-aminopyridin-3-yl)-[3,2',4',3''-terpyridine]-6,6''-diamine by Suzuki coupling reaction is 100-120 °C, and the reaction time is 12-24 h.

8. The preparation method according to claim 7, characterized in that, The trihalopyridine is selected from one or two of 2,4,6-tribromopyridine or 2,4,6-trichloropyridine; And / or, the molar ratio of the trihalopyridine to the 2-aminopyridine-5-boronic acid pinacol ester is 1:(3-5); And / or, the second basic compound is selected from one or more of sodium carbonate, potassium carbonate or cesium carbonate; And / or, the molar amount of the second basic compound is 1.5-5 times the sum of the molar amounts of the trihalopyridine and the 2-aminopyridine-5-boronic acid pinacol ester; And / or, the second solvent is selected from one or more of 1,4-dioxane, ethanol, toluene and water; And / or, the second catalyst is selected from one of tetrakis(triphenylphosphine)palladium, palladium dichloride, palladium acetate, bis(triphenylphosphine)palladium dichloride; And / or, the molar amount of the second catalyst is 0.5%-5% of the molar amount of the 2-aminopyridine-5-boronic acid pinacol ester.

9. The preparation method according to any one of claims 4-8, characterized in that, The reaction temperature for synthesizing the pyridine imine-rich covalent organic framework by the solvothermal method is 100-150 °C, and the reaction time is 60-84 h; preferably, the solvent used for synthesizing the pyridine imine-rich covalent organic framework by the solvothermal method includes 1,4-dioxane, and the catalyst is acetic acid.

10. Use of the pyridine imine-rich covalent organic framework according to any one of claims 1-3 or the pyridine imine-rich covalent organic framework prepared by the preparation method according to any one of claims 4-9 in the adsorption of iodine and iodomethane.

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