A trans-stacked covalent organic framework material, its preparation method and application

Abstract

The present invention discloses a trans-stacked covalent organic framework material, a preparation method thereof, and an application thereof. Mix BTTPA, DBTH, mesitylene, and 1,4-dioxane uniformly, and then add acetic acid to obtain a mixed solution; let the mixed solution crystallize statically in a sealed anaerobic environment, wash and dry the solid product obtained by crystallization to obtain the trans-stacked covalent organic framework material COF-DB; disperse COF-DB in dichloromethane, dropwise add methyl trifluoromethanesulfonate, stir and react, and then filter, wash, and dry to obtain an ion-functionalized trans-stacked covalent organic framework material. By selecting monomers containing pyridine groups, the present invention constructs a trans-stacked covalent organic framework structure with pyridine sites that are more easily exposed, further improving the specific surface area, radiation resistance, and acid-base stability of the COF. This material can not only adsorb iodine vapor, but also adsorb organic iodine and I- in liquids.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption materials, and particularly relates to a trans-stacked covalent organic framework material, a preparation method thereof, and an application thereof. Background Art

[0002] As a low-carbon and efficient clean energy, nuclear energy is playing an increasingly important role in the current energy supply. However, the development of nuclear energy also brings some intractable problems, such as nuclear fission waste liquid generated in the spent fuel reprocessing process and volatile radioactive pollutants brought by nuclear accident leakage. Among them, the radioactive iodine isotopes produced account for about 0.69% of the mass of fission products in the nuclear fuel cycle. Moreover, a large amount of radioactive iodine is released during the reprocessing process. The main chemical substances in the radioactive waste gas are highly volatile diatomic element iodine (I2, 90% - 100%) and a small amount of organic iodides (such as methyl iodide and iodoethyl iodide, 0% - 10%). And the iodide ions oxidized in the waste liquid are easy to combine with iodine molecules to form highly soluble I3 - and I5 - . The main concern among radioactive iodine isotopes is 129 I, with its extremely long half-life (1.6×10 7 years) and high toxicity, and it exists as a highly mobile pollutant in most geological environments. 131 I is also extremely dangerous. Especially during a nuclear accident, due to its much higher specific activity, but with a half-life of only 8.02 days. It is the main cause of short-term radioactive toxicity to the human body in the initial stage of a nuclear accident. In addition, it can affect the human metabolic process by continuous accumulation in the environment or through food chain enrichment, which will pose a greater threat to human health and the environment. Therefore, it is of great significance to develop functional materials for effectively controlling the emission of radioactive iodine.

[0003] Covalent organic framework polymer materials (COFs) are favored because they have advantages over other solid adsorbents due to their low density, high specific surface area, adjustable pore properties, periodic network, and excellent chemical stability. For example, the patent with the application number 202210782820.5 discloses a preparation method of a porous covalent organic framework and its application in uranium extraction from seawater, selecting two ligands, TP and BHTH, to synthesize a porous covalent organic framework with selective uranium adsorption and a novel structure. Currently, studies have confirmed that COFs are excellent iodine adsorption materials. However, carbon and hydrogen in the COF framework show weak affinity for iodine, restricting the application of the materials in the field of iodine adsorption. For example, the patent with the application number 202210549219.1 discloses a porous hydrazone-based covalent organic framework material with a flexible skeleton, its preparation method and application, which uses a flexible monomer as the skeleton and has a large adsorption capacity for gaseous iodine. The generation of radioactive iodine poses a threat to public safety, and iodine-containing wastewater has attracted people's attention to environmental pollution. Preparing COF materials that can be used in the field of iodine adsorption has important value for both theoretical research and practical applications. Summary of the Invention

[0004] Aiming at the above-mentioned prior art, the purpose of the present invention is to provide a trans-stacked covalent organic framework material, its preparation method and application. The present invention constructs a trans-stacked covalent organic framework structure with pyridine sites more easily exposed by selecting monomers containing pyridine groups, further improving the specific surface area, radiation resistance, and acid-base stability of COF. The iodine vapor capture of this material has the outstanding advantages of fast adsorption rate and high adsorption capacity. In addition, by combining COF framework charge regulation and ion functionalization in the pores to adsorb iodide ions in water, it can also adsorb organic iodine (CH3I), significantly improving the iodine adsorption rate and adsorption capacity compared with traditional adsorbents, providing a technical reference for the removal of iodine in the environment.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect of the present invention, a preparation method of a trans-stacked covalent organic framework material is provided, including the following steps:

[0007] (1) Mix 1,3,5-tris(2-formylpyridin-5-yl)benzene, 2,5-dibutoxyterephthalohydrazide, mesitylene, and 1,4-dioxane evenly, and then add acetic acid to obtain a mixed solution;

[0008] (2) Let the mixed solution crystallize in a sealed anaerobic environment, wash and dry the solid product obtained by crystallization to obtain a porous covalent organic framework material COF-DB;

[0009] (3) Disperse COF-DB in dichloromethane, dropwise add methyl trifluoromethanesulfonate and stir and react, then filter, wash and dry to obtain an ion-functionalized trans-stacked covalent organic framework material (COF-DB-Me-TFO).

[0010] Preferably, in step (1), the addition amounts of 1,3,5-tris(2-formylpyridin-5-yl)benzene, 2,5-dibutoxyterephthalohydrazide, mesitylene, 1,4-dioxane and acetic acid are in a ratio of 39.3 mg: 33.8 mg: 1.0 mL: 1.0 mL: 0.20 mL.

[0011] Preferably, in step (1), the mixing is ultrasonic mixing, and the ultrasonic mixing time is 15 min; the concentration of the acetic acid is 6 mol / L.

[0012] Preferably, in step (2), the airtight anaerobic environment is obtained by cooling in liquid nitrogen, removing the oxygen in the container by freeze-thaw cycling and degassing three times, and then flame-sealing.

[0013] Preferably, in step (2), the static crystallization temperature is 120 °C and the time is 72 h; the washing is carried out by washing three times with acetone and ethanol; the drying is vacuum drying at 60 °C.

[0014] Preferably, in step (3), the addition amount ratio of COF-DB to methyl trifluoromethanesulfonate is 100 mg: 0.2 mL; the volume ratio of dichloromethane to methyl trifluoromethanesulfonate is 100:1.

[0015] Preferably, in step (3), the reaction temperature is room temperature and the time is 12 h; the washing is carried out by washing successively with absolute ethanol and chloroform; the drying is vacuum drying at 60 °C.

[0016] In the second aspect of the present invention, there is provided a trans-stacked covalent organic framework material obtained by the above preparation method.

[0017] Preferably, the trans-stacked covalent organic framework material has a trans-stacked two-dimensional structure: between adjacent single-layer crystal structures, the stacking directions are opposite.

[0018] In the third aspect of the present invention, there is provided the application of the trans-stacked covalent organic framework material in any one of the following 1) to 3):

[0019] 1) Adsorbing iodine vapor;

[0020] 2) Adsorbing organic iodine;

[0021] 3) Adsorbing I in liquid - .

[0022] The beneficial effects of the present invention:

[0023] (1) The trans-stacked covalent organic framework iodine adsorbent of the present invention is synthesized in one step under relatively mild conditions, with simple operation, short process, low cost and high yield. The yield can reach more than 90% under simple synthesis conditions.

[0024] (2) The multifunctional trans-stacked covalent organic framework iodine adsorbent of the present invention has high thermal stability and chemical stability. By regulating the charge distribution and ions in the pores of the trans-stacked covalent organic framework through methylation reaction, it shows ultra-high adsorption capacity for I3 - , I5 - anions in water and iodine or organic iodine in vapor, and has excellent adsorption ability, overcoming the practical application problems that existing COF materials can only partially capture iodine from gas and are difficult to capture I3 - , I5 - anions and organic iodine in water.

[0025] (3) The trans-stacked covalent organic framework of the present invention can be prepared on a large scale, thereby improving the synthesis efficiency, and is expected to be applied in industrial production. It shows great potential application value in deiodination in nuclear power plants and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Synthesis and functionalization roadmap of trans-stacked covalent organic framework;

[0027] Figure 2 : (A) X-ray diffraction pattern of trans-stacked covalent organic framework, (B) simulated front and side structure diagrams of trans-stacked;

[0028] Figure 3 : (A) N2 adsorption-desorption diagram of COF-DB and (inset) BJH pore size distribution diagram, (B) scanning electron micrograph of COF-DB;

[0029] Figure 4 : (A) Infrared spectra of COF-DB, COF-DB-Me-TFO and monomer, (B) 13 13 C solid nuclear magnetic spectra of COF-DB and COF-DB-Me-TFO;

[0030] Figure 5 : (A) Thermogravimetric analysis diagram of COF-DB, (B) PXRD patterns of COF-DB after treatment with HNO3 (12M), NaOH (12M) and γ-ray irradiation (200 kGy, 400 kGy);

[0031] Figure 6 : (A) Adsorption curve of COF-DB in gaseous iodine at 75 °C, (B) Adsorption curve of COF-DB in gaseous iodomethane at 75 °C;

[0032] Figure 7 : (A) UV spectrum of the liquid after the functionalized trans-stacked covalent organic framework COF-DB-Me-TFO adsorbs iodine in groundwater, (B) Adsorption rate graph of COF-DB-Me-TFO for I3 - . Detailed implementation manners

[0033] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0034] As introduced in the background art section, COFs are excellent iodine adsorption materials. However, carbon and hydrogen in the COF skeleton show weak affinity for iodine, which limits the application of the materials in the field of iodine adsorption. Although there have been reports on using BTTPA or DBTH to prepare covalent organic framework materials, the prepared ones are all forward-stacked organic framework materials, that is, the stacking directions between the crystal layers are the same.

[0035] Based on this, the purpose of the present invention is to provide a trans-stacked covalent organic framework material, its preparation method and application. The present invention discovers through research that using BTTPA, DBTH and mesitylene as raw materials, the prepared covalent organic framework crystal has a trans-stacked two-dimensional structure: between adjacent single-layer crystal structures, the stacking directions are opposite, and they are reversely parallel stacked by inducing adjacent layers through the C(δ+)O(δ) and O(δ)-R(δ+) dipole moments. This trans-stacked structure can fully expose the adsorption sites and adjust the charge distribution between layers. When adsorbing iodomethane or undergoing methylation reaction, the framework can carry more positive charges, thereby constructing a cation channel to achieve the effect of adsorbing more iodine. Therefore, the covalent organic framework material prepared by the present invention can not only adsorb a large amount of iodine vapor, but also adsorb organic iodine and I in liquid - . Introducing electron-rich atoms into the framework is beneficial to adsorb electron-deficient iodine, thereby enhancing the interaction between the porous material and iodine and being beneficial to enhancing the iodine adsorption capacity of the material.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in combination with specific embodiments.

[0037] The test materials used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels.

[0038] Embodiment:

[0039] 39.3 mg of 1,3,5-tris(2-formylpyridin-5-yl)benzene (BTTPA), 33.8 mg of 2,5-bis(3-hydroxypropoxy)terephthalohydrazide (DBTH), 1.0 mL of mesitylene, and 1.0 mL of 1,4-dioxane were added to an ampoule tube. The reaction mixture was ultrasonically treated for 15 min to obtain a homogeneous solution. Then, 0.20 mL of 6 mol / L acetic acid was added as a catalyst, and the mixture was ultrasonically homogenized again. The ampoule tube was frozen in a liquid nitrogen bath, and the oxygen in it was removed by three freeze-thaw cycles of degassing. The ampoule tube was sealed with a flame. Then, the reaction mixture was placed in an oven at 120 °C and allowed to stand for 3 days. After cooling to room temperature, the solid product was collected. The obtained solid product was washed three times with acetone and ethanol successively, and then purified by vacuum drying at 60 °C for 24 h to obtain light yellow trans-stacked covalent organic framework COF-DB. 100 mg of COF-DB was uniformly dispersed in 20 mL of dichloromethane, ultrasonically dispersed evenly, 0.2 mL of methyl trifluoromethanesulfonate was added dropwise thereto, and the mixture was stirred for 12 h. The product was filtered, washed with absolute ethanol and chloroform, and dried in vacuo to obtain bright yellow ion-functionalized trans-stacked covalent organic framework material COF-DB-Me-TFO. Figure 1 Schematic diagram of the synthesis route of trans-stacked covalent organic framework material COF-DB-Me-TFO.

[0040] The crystal structure of trans-stacked COF-DB was analyzed by X-ray powder diffraction pattern (PXRD) and Materials Studio theoretical simulation. The experimental PXRD pattern of COF-DB is as shown in Figure 2 (A). Peaks appeared at 2.5°, 4.8°, and 6.2°, corresponding to the (100), (200), and (210) crystal planes respectively. Using Materials Studio software, according to the experimental results, Pawley refinement was performed on the structural model based on the conformation of COF-DB. The results showed that COF-R crystallized in the hexagonal P-6cc space group, and the unit cell parameters α = β = 90°, γ = 120°, R p = 3.89%, R wp = 5.71%. The experimental PXRD diffraction peak profile was more consistent with the trans-stacked simulation results compared to the AA stacking and AB stacking. Figure 2 (B) shows the trans-stacked two-dimensional structure of COF-DB-Me, and its theoretical dynamic pore size is The interlayer distance is about The results show that a highly crystalline trans-stacked covalent organic framework material was successfully synthesized by the method of the present invention.

[0041] The specific surface area and porosity of COF-DB were measured by N2 adsorption-desorption isotherms. Figure 3(A) The COF-DB sample exhibits a typical type-IV adsorption isotherm, with a BET specific surface area of 1698.6 m 2 / g. The pore volume is 1.04 cm 3 / g. Compared with the COF material stacked with AA, the trans-stacked COF material has a larger effective surface area and exposes more adsorption sites to promote the iodine adsorption efficiency. It can be seen from the pore size distribution diagram that the pore size is mainly distributed at 3.1 nm, which is close to the theoretical simulation value. At the same time, the relatively large pore size is also conducive to the diffusion of iodine molecules in the pores. To better observe the morphology of the material, COF-DB was characterized by scanning electron microscopy (SEM). As Figure 3 (B) shows, COF-DB all presents a uniform spherical flower-like morphology with an average diameter of about 800 nm.

[0042] Fourier transform infrared spectroscopy (FTIR) was used to study the chemical bond changes before and after the reaction. As Figure 4 (A) shows, the amino stretching vibration peaks in DBTH are at 3298 cm -1 and 3204 cm -1 , and the aldehyde group in BTTPA disappears after polycondensation at 1701 cm -1 , indicating that the raw materials are almost completely consumed in the chemical reaction. The peak at 1672 cm -1 of the COF-DB material belongs to the stretching vibration of the imine bond (C=N), indicating the connection of the two precursors. Similarly, in the infrared spectrum of COF-DB-Me-TFO, stretching vibration peaks of C=N (1672 cm -1 ) and N-H (3257 cm -1 ) can be found. In addition, the in-plane bending vibration peak of pyridine nitrogen (1540 cm -1 ) in COF-DB undergoes a red shift in COF-DB-Me-TFO, and a stretching vibration peak of C-N appears at 1411 cm -1 , and stretching vibration peaks of S=O (1031 cm -1 ), S-C (644 cm -1 ) bonds and C-F (1161 cm -1 ) bonds exist, indicating that the pyridine nitrogen site of COF-DB is methylated and trifluoromethanesulfonate ions exist in the pores. Immediately afterwards, the structures of COF-DB before and after functionalization were further characterized by solid-state 13 13C nuclear magnetic resonance spectroscopy. As Figure 4 (B) shows, the solid-state 13The signal peak of the C atom on the C=O bond of the amide appears at 162 ppm in the 13C NMR spectrum. The C=N carbon characteristic resonance signal at 151 ppm proves the imine bond, and the appearance of this characteristic peak also proves the progress of the reaction between the aldehyde group and the amine group. The signal peaks appearing at 70, 31, 18, and 12 ppm are the characteristic peaks of the butoxy group in COF-DB. The solid state of COF-DB-Me-TFO 13 The signal peaks near 58 and 46 ppm in the 13C nuclear magnetic resonance spectrum are the characteristic peaks of pyridine nitrogen methylation. In summary, through 13 the characterization of the trans-stacked covalent organic framework and its functionalized materials by the 13C-NMR diagram, it proves the successful synthesis of the functionalized trans-stacked covalent organic framework iodine adsorbent, that is, the trans-stacked covalent organic framework iodine adsorbent can be effectively prepared by the preparation method provided by the present invention.

[0043] Test Example 1: Thermal stability test

[0044] Thermogravimetric analysis (TGA) was performed on the COF-DB prepared in the example to evaluate its thermal stability. Under a N2 atmosphere, it was heated to 800 °C at a rate of 10 °C / min. From Figure 5 A, it can be observed that around 150 °C, COF-DB has a small mass loss, which is mainly due to a small amount of water and solvent remaining on the surface and in the pores of the material. When the temperature is between 150 °C and 400 °C, the weight of COF-DB is stable. Even when the temperature rises above 400 °C, there is a 28% mass loss, and about 50% of the material COF-DB before thermogravimetric analysis remains. The above results indicate that COF-DB has good thermal stability. The COF-DB prepared in the example was immersed in strong acid and strong base solutions of HNO3 (12M) and NaOH (12M) and irradiated with γ-rays (200 kGy, 400 kGy) for 24 hours to explore the solvent stability and irradiation stability of the COF material. As Figure 5 (B) shows, the crystal structure of COF-DB remains basically unchanged, which indicates the excellent acid and alkali resistance and irradiation stability of COF-DB.

[0045] Test Example 2: Iodine adsorption test

[0046] 1. The I2 or CH3I adsorption experiment was carried out according to the gravimetric method, and the steps are as follows:

[0047] Put 10 mg of the COF-DB prepared in the example into an open glass bottle (2 mL), put 500 mg of I2 or CH3I into a glass bottle (25 mL) and another glass bottle (2 mL) as a reference, and adsorb in an environment of 75 °C. After contacting for a period of time, cool the adsorbed material to room temperature and weigh it. Then, put it back and continue to adsorb I2 or CH3I until its weight reaches a stable value. The I2 or CH3I capture ability is measured by the weight increment of the COF-DB prepared in the example. The static I2 or CH3I capture amount (q t , g / g) is calculated by the following formula:

[0048]

[0049] where q t (g / g) is the static iodine vapor capture ability at time t, mt (g) is the weight of the vial containing COF at time t, m1 (g) is the weight of the vial containing COFs before adsorption, m0 (g) is the weight of the empty vial containing COF before adsorption, m t (g) is the weight of the reference vial at time t, and m0 (g) is the weight of the reference vial before adsorption.

[0050] According to Figure 6 (A), the graph shows that the trans-stacked covalent organic framework prepared in the present invention can capture 432 wt% of iodine in a short time, and the adsorption amount reaches 473 wt% after 46 hours when the adsorption equilibrium is reached. It can be seen that the trans-stacked covalent organic framework iodine adsorbent prepared in the present invention can be effectively applied to the capture of radioactive iodine. On the other hand, the absorption efficiency of COF-DB for CH3I vapor is as Figure 6 (B) shows that the saturated adsorption capacity reaches 1.62 g / g at 348 k in 24 hours, and COF-DB can capture 0.675 g / g of CH3I vapor in 10 hours, indicating that the high nitrogen content and trans-stacking in the COF-DB framework expose more adsorption sites, enabling CH3I passing through the pores to be adsorbed quickly.

[0051] 2. Capture of iodide ions in solution, the steps are as follows:

[0052] Add COF-DB-Me-TFO to the groundwater containing I3 - and I5 - (50 mg / L, 5 mL), and shake at room temperature. Collect samples at different time points and filter them. After establishing the corresponding calibration curve, the concentration of iodine in the filtrate is determined by ultraviolet-visible spectroscopy. The iodine removal efficiency E (%) of the studied adsorbent COFs is determined by the following formula:

[0053]

[0054] where C0 (mg / L) and C t (mg / L) are the concentrations of I3 - before and after adsorption, respectively.

[0055] The charge distribution of the framework and the ionic composition of the pores can be adjusted through ionization reactions, enhancing its affinity for I3 - and I5 - ions in water. In the adsorption experiment of groundwater containing 50 ppm iodide ions, the results are as Figure 7 (A) shows that after adding COF-DB-Me-TFO, the I3 - (286 nm) and I5 - (350 nm) in groundwater decreased significantly, and the characteristic peaks of I3 - and I5 - could hardly be seen after 8 hours. As Figure 7 (B) shows, the adsorption rate graph of I3 - indicates that 91% of the iodide ions in groundwater can be adsorbed within 2 h, and the removal rate of iodide ions reaches 99% after 24 h of adsorption equilibrium. The experimental results show that by adjusting the charge characteristics of the covalent organic framework, the interaction of the material with iodide ions can be significantly enhanced. These unique characteristics make the trans-stacked covalent organic framework and its functionalization strategy promising for application in the field of iodine adsorption.

[0056] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a trans-stacked covalent organic framework material, characterized in that, It includes the following steps: (1) Mix 1,3,5-tris(2-formylpyridin-5-yl)benzene, 2,5-dibutoxyterephthalohydrazide, mesitylene and 1,4-dioxane evenly, and then add acetic acid to obtain a mixed solution; (2) Let the mixed solution stand for crystallization in a sealed anaerobic environment, wash and dry the solid product obtained by crystallization to obtain the trans-stacked covalent organic framework material COF-DB; the temperature for standing crystallization is 120 °C and the time is 72 h; (3) Disperse COF-DB in dichloromethane, add methyl trifluoromethanesulfonate dropwise and stir and react, then filter, wash and dry to obtain the ion-functionalized trans-stacked covalent organic framework material COF-DB-Me-TFO.

2. The preparation method according to claim 1, wherein In step (1), the addition ratio of 1,3,5-tris(2-formylpyridin-5-yl)benzene, 2,5-dibutoxyterephthalohydrazide, mesitylene, 1,4-dioxane and acetic acid is 39.3 mg: 33.8 mg: 1.0 mL: 1.0 mL: 0.20 mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the mixing is ultrasonic mixing, and the ultrasonic mixing time is 15 min; the concentration of the acetic acid is 6 mol / L.

4. The preparation method according to claim 1, characterized in that, In step (2), the sealed anaerobic environment is obtained by cooling in liquid nitrogen, removing the oxygen in the container by freeze-thaw cycling degassing three times, and then flame-sealing.

5. The preparation method according to claim 1, characterized in that, In step (2), the washing is washing three times with acetone and ethanol; the drying is vacuum drying at 60 °C.

6. The preparation method according to claim 1, wherein In step (3), the addition ratio of COF-DB to methyl trifluoromethanesulfonate is 100 mg: 0.2 mL; the volume ratio of dichloromethane to methyl trifluoromethanesulfonate is 100:

1.

7. The preparation method according to claim 1, wherein In step (3), the reaction temperature is room temperature and the time is 12 h; the washing is washing successively with absolute ethanol and chloroform; the drying is vacuum drying at 60 °C.

8. The trans-stacked covalent organic framework material obtained by the preparation method according to any one of claims 1 to 7.

9. The trans-stacked covalent organic framework material according to claim 8, wherein The trans-stacked covalent organic framework material has a trans-stacked two-dimensional structure: between adjacent single-layer crystal structures, the stacking directions are opposite.

10. The application of the trans-stacked covalent organic framework material according to claim 8 or 9 in any one of the following 1) to 3): 1) Adsorbing iodine vapor; 2) Adsorbing organic iodine; 3) Adsorb I in the liquid - .

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