Preparation method of metal covalent organic framework material and application thereof

Abstract

The application discloses a preparation method and application of a metal covalent organic framework material. The metal covalent organic framework material prepared by the method can be used for adsorption and separation of elemental iodine pollutants, and has excellent iodine adsorption capacity and rate. The preparation method is to prepare a copper ion cyclotri-nuclear metal complex with an aldehyde group by a solvothermal reaction of 1H-pyrazole-4-formaldehyde and copper nitrate trihydrate, and then to prepare the metal covalent organic framework material containing copper ions by a Schiff base reaction of the copper ion cyclotri-nuclear metal complex and 1,3,5-tris(4-aminophenyl)benzene. The metal covalent organic framework material of the application not only keeps a developed microporous structure, but also retains the active adsorption sites of copper ions in the chemical structure, significantly strengthens the interaction intensity of the pores to iodine, and thus significantly improves the iodine adsorption rate and capacity. The preparation method is simple, universal and controllable, and can realize the large-scale production and manufacturing of the metal covalent organic framework adsorption material.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material preparation technology, and particularly relates to a method for preparing a metal covalent organic framework material and its application. Background Technology

[0002] Promoting the development of clean energy has become an important means to drive the energy structure towards a low-carbon transformation. Nuclear energy, as a safe, efficient, and high-quality clean energy source, has advantages such as no greenhouse gas emissions and stable and reliable operation. Promoting nuclear power as a fundamental pillar energy source for the power system is a major strategic direction for optimizing the energy structure and ensuring energy supply security. However, the operation of nuclear reactors inevitably produces volatile radioactive iodine (such as...). 129 I, 131 I), its long half-life ( 129 I has a half-life of 1.57 × 10⁻⁶. 7 The high mobility of radioactive gaseous iodine poses a long-term threat to the ecological environment and human health. Therefore, the efficient capture and fixation of radioactive gaseous iodine is one of the core challenges for the safe disposal of nuclear waste and the high-quality development of nuclear energy.

[0003] Iodine adsorbers are crucial equipment used in nuclear power plant reprocessing plants to remove radioactive iodine pollutants from process exhaust gases. In China, the adsorption materials used in iodine adsorbers are primarily coal-based or coconut shell activated carbon impregnated with triethylenediamine (TEDA) and potassium iodide (KI). Activated carbon serves as a porous substrate, and radioactive iodine pollutants are adsorbed and immobilized within the pores of the impregnated activated carbon through a specific chemical reaction between the impregnating agent TEDA and iodine compounds. However, limited by a low TEDA loading (<5%), the adsorption capacity of the impregnated activated carbon is low. To meet requirements, the activated carbon loading in the iodine adsorber needs to be increased, significantly increasing the operating costs and solid waste volume of nuclear facilities. Covalent organic frameworks (COFs) are a class of novel crystalline porous materials with a highly ordered structure, composed of organic building blocks linked by strong covalent bonds. They possess high specific surface area, a regularly distributed pore structure, tunable structural chemistry, and excellent chemical and thermal stability, demonstrating excellent application potential in radioactive iodine capture. To further improve the adsorption strength and effect of adsorbent materials for radioactive iodine pollutants, it is urgent to propose a novel method for preparing covalent organic frameworks to replace the iodine adsorbers used in existing technologies, which are costly and generate large amounts of solid waste. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for preparing metal covalent organic framework materials and their applications. This method uses metal complexes as monomers for synthesizing covalent organic framework materials. Copper ions are immobilized within the covalent organic framework material structure through in-situ synthesis, thereby preparing a metal covalent organic framework. The high density of copper ions within the structure can significantly enhance the material's adsorption strength for iodine through charge transfer interactions with elemental iodine. The metal covalent organic framework material obtained by this invention has extremely broad application prospects in iodine adsorption.

[0005] In a first aspect, the present invention discloses a method for preparing a metal covalent organic framework material, comprising the following steps: S1. Preparation of metal complexes 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate (Cu(NO3)2·3H2O) were selected as reactants and dissolved in a mixed solvent of N,N-dimethylformamide (DMF), ethanol and deionized water to prepare copper ion ring trinuclear metal complexes with aldehyde groups by solvothermal reaction. S2. Preparation of metal covalent organic framework materials A copper-ion-containing metal covalent organic framework material Cu-TAPB-COF was prepared by using a copper ion cyclic trinuclear metal complex as the aldehyde monomer and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as the amine monomer, dissolved in a mixed solvent of 1,4-dioxane and mesitylene, and using glacial acetic acid as the reaction catalyst via a solvothermal reaction.

[0006] Furthermore, in step S1, the molar ratio of 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate is 1~2:1~5.

[0007] Furthermore, in the mixed solvent of step S1, the volume ratio of DMF, ethanol and deionized water is 2~4:2.5~5:1~2.

[0008] Furthermore, in step S1, the solvothermal reaction conditions are: standing reaction at 80~120℃ for 6~24h.

[0009] Furthermore, in step S1, after the solvothermal reaction is completed, the solid product is separated from the solution by vacuum filtration. After the solid product is thoroughly washed with ethanol, it is dried in a vacuum oven at 30~100℃ for 6~24h to obtain a copper ion ring trinuclear metal complex with an aldehyde group.

[0010] Furthermore, in step S2, the molar ratio of the copper ion cyclic trinuclear metal complex, TAPB, and glacial acetic acid is 1~2:1~5:0.01~0.1.

[0011] Furthermore, in the mixed solvent of step S2, the volume ratio of 1,4-dioxane and mesitylene is 1~2:1~10.

[0012] Furthermore, in step S2, the solvothermal reaction conditions are as follows: the reaction is carried out in a vacuum at a temperature of 120~150℃ for 3~5 days.

[0013] Furthermore, in step S2, after the solvothermal reaction is completed, the solid product separated from the solution by filtration is washed three to five times with tetrahydrofuran (THF) and DMF in sequence. Then, the washed solid product is solvent-displaced with THF for 2 to 3 days, and then the solid product is dried in a vacuum oven at 120 to 150°C for 12 to 24 hours to obtain Cu-TAPB-COF.

[0014] Secondly, the present invention also discloses the application of a metal covalent organic framework material in iodine adsorption. The metal covalent organic framework material is prepared by the preparation method of the metal covalent organic framework material of the first aspect of the present invention and is used to adsorb radioactive elemental iodine pollutants.

[0015] Traditional iodine adsorbers use activated carbon impregnated with TEDA. Radioactive iodine is adsorbed, captured, and immobilized within the pores of the TEDA-impregnated activated carbon through a specific chemical reaction between the impregnating agent TEDA and iodine compounds. However, excessively high impregnating agent loading significantly lowers the ignition point of the activated carbon, thus increasing its fire safety in practical applications. Therefore, the impregnating agent loading in the impregnated activated carbon is typically controlled below 5%, making it difficult to achieve high adsorption rates and large adsorption capacities. Compared to existing technologies, this application has at least the following advantages: (1) The metal covalent organic framework material obtained by the preparation method of this application can be used for the adsorption and separation of iodine, and exhibits excellent iodine adsorption capacity. The metal covalent organic framework material of this application retains the active adsorption sites of copper ions in the chemical structure while maintaining the well-developed microporous structure, which significantly enhances the interaction strength between the pores and iodine, thereby achieving a significant improvement in iodine adsorption rate and adsorption capacity.

[0016] (2) The preparation method of this application uses 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate to prepare a copper ion cyclic trinuclear metal complex with an aldehyde group through a solvothermal reaction, and further reacts it with 1,3,5-tris(4-aminophenyl)benzene through a Schiff base reaction to prepare a metal covalent organic framework containing copper ions. This preparation method is simple, universal, and highly controllable, and can realize the large-scale production of metal covalent organic framework adsorbent materials. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a SEM image of the copper ion cyclic trinuclear metal complex in Example 1 of the present invention; Figure 2 The XRD pattern of Cu-TAPB-COF in Example 1 of this invention; Figure 3 This is a SEM image of Cu-TAPB-COF in Embodiment 1 of the present invention. Detailed Implementation

[0019] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Unless otherwise specified, all temperatures mentioned herein are in degrees Celsius, and the preferred embodiments can be freely combined as needed. Those skilled in the art will understand that the data and parameters described in the examples are merely exemplary and do not constitute a limitation of the invention. All components used in the following examples and comparative examples are compounds known in the art, and all equipment used is equipment publicly known in the art. All components and equipment used in this invention can be obtained commercially or prepared using known techniques.

[0021] This invention provides a method for preparing a metal covalent organic framework material, comprising the following steps: S1. Preparation of metal complexes 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate (Cu(NO3)2·3H2O) were selected as reactants and dissolved in a mixed solvent of N,N-dimethylformamide (DMF), ethanol and deionized water to prepare copper ion ring trinuclear metal complexes with aldehyde groups by solvothermal reaction. S2. Preparation of metal covalent organic framework materials The metal covalent organic framework material Cu-TAPB-COF was prepared by using a copper ion cyclic trinuclear metal complex as the aldehyde monomer and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as the amine monomer, dissolved in a mixed solvent of 1,4-dioxane and mesitylene, and using glacial acetic acid as the reaction catalyst via a solvothermal reaction.

[0022] In step S1, the molar ratio of 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate is preferably 1~2:1~5.

[0023] In step S1, a mixed solvent is composed of DMF, ethanol and deionized water in order to improve the solubility of 1H-pyrazole-4-carboxaldehyde in the solvent. The volume ratio of DMF, ethanol and deionized water in the mixed solvent is preferably 2~4:2.5~5:1~2.

[0024] In step S1, the reactants 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate are dissolved in a mixed solvent to form a solution. To ensure sufficient dispersion of the reactant solids in the solution, the reactants are dissolved in the mixed solvent, stirred thoroughly, and then ultrasonically dispersed for 10-30 minutes. Since the synthesis reaction in step S1 is a solid-phase reaction, sufficient dispersion of the solids is more conducive to improving the reaction yield and the crystallinity of the product.

[0025] In step S1, the above solution can be transferred to a high-pressure reactor for a solvothermal reaction, and allowed to stand at 80-120°C for 6-24 hours. After the solvothermal reaction is complete, the reactor is allowed to cool to room temperature, and the solid product is separated from the solution by vacuum filtration. To remove residual solvent from the reaction product and prevent it from affecting the subsequent chemical reactions, the solid product is thoroughly washed with ethanol and then dried in a vacuum oven at 30-100°C for 6-24 hours. The resulting pale yellow needle-like crystals are the copper ion ring trinuclear metal complex with aldehyde groups.

[0026] In step S2, the preferred molar ratio of the copper ion cyclic trinuclear metal complex, TAPB, and glacial acetic acid is 1~2:1~5:0.01~0.1.

[0027] In the mixed solvent of step S2, the volume ratio of 1,4-dioxane and mesitylene is preferably 1~2:1~10.

[0028] In step S2, the copper ion cyclic trinuclear metal complex, TAPB, and glacial acetic acid are dissolved in a mixed solvent to form a solution. To ensure thorough and uniform mixing of the solids in the solution, the reactants and catalyst are dissolved in the mixed solvent and then sonicated for 10–30 min. Then, the solution is mechanically stirred at 500–800 rpm for 1–3 hours at 30–50 °C. Since the synthesis reaction in step S2 is a solid-phase reaction, uniform solid mixing is beneficial for improving the crystallinity of the synthesized product.

[0029] In step S2, the solvothermal reaction process must ensure that the reaction tube is always under vacuum. Since oxygen can participate in the synthesis reaction of this invention, its presence during the reaction will lead to oxidation of the reaction products, thereby altering their chemical properties. Therefore, the synthesis reaction involved in this invention must be carried out under vacuum conditions. To ensure the solvothermal reaction is carried out under vacuum, the solution is subjected to a cycle of liquid nitrogen freezing-vacuuming-thawing before this step. The thoroughly stirred solution is transferred to a pressure-resistant vacuum reaction tube, and after three to five cycles of liquid nitrogen freezing-vacuuming-thawing, the reaction tube is placed in an oven at 120-150°C for static reaction for 3-5 days. During the reaction, the reaction tube must always be under vacuum.

[0030] The liquid nitrogen freezing process involves immersing the vacuum reaction tube in liquid nitrogen for 10-15 minutes until the solution inside the tube changes from liquid to solid. The vacuuming process involves connecting the frozen vacuum reaction tube to a vacuum pump, turning on the pump for 1-3 minutes to create a high vacuum inside the reaction tube, then closing the valve connecting the reaction tube to the vacuum pump and turning off the pump. The thawing process involves placing the vacuumed reaction tube in room temperature deionized water for 5-10 minutes until the solution inside the tube changes from solid to liquid. This cyclical operation of liquid nitrogen freezing, vacuuming, and thawing ensures a high vacuum environment inside the reaction tube.

[0031] After the solvothermal reaction in step S2 is completed, the solution is filtered to separate the solid product. The product is then washed three to five times sequentially with 30-50 mL of tetrahydrofuran and 30-50 mL of DMF. The washing procedure is as follows: thoroughly mix the reaction product with 30-50 mL of the washing solution in a centrifuge tube, then centrifuge at 5000-8000 rpm for 5-10 minutes. The supernatant is then separated to complete the washing operation. The purpose of washing is to remove any residual reaction solvent from the reaction product. To ensure thorough cleaning, washing can be performed three to five times.

[0032] To further remove residual reaction solvents from the reaction product, the less volatile reaction solvents dioxane and mesitylene can be replaced with more volatile tetrahydrofuran. Therefore, after washing, the washed solid product is solvent-displaced with tetrahydrofuran for 2-3 days, and then dried in a vacuum oven at 120-150°C for 12-24 hours to obtain the copper-ion-containing metal covalent organic framework material Cu-TAPB-COF, with the following chemical structure: .

[0033] This invention also provides an application of a metal covalent organic framework material in iodine adsorption, wherein the metal covalent organic framework material is prepared by the preparation method described above. The metal covalent organic framework material prepared by this invention can be used for iodine adsorption, and is particularly suitable for adsorbing radioactive elemental iodine pollutants.

[0034] The present invention will now be described in more detail with reference to exemplary embodiments. The following embodiments or experimental data are intended to illustrate the present invention by way of example, and those skilled in the art should understand that the present invention is not limited to these embodiments or experimental data.

[0035] Example 1 The preparation method for copper-ion-containing metal covalent organic framework material Cu-TAPB-COF includes the following steps: S1. Preparation of metal complexes According to the molar ratio of 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate (Cu(NO3)2·3H2O) of 1:2, 0.15 mol of 1H-pyrazole-4-carboxaldehyde and 0.3 mol of Cu(NO3)2·3H2O were weighed and dissolved in a glass containing 20 mL of N,N-dimethylformamide (DMF), 25 mL of ethanol and 15 mL of deionized water. After thorough stirring, the mixture was ultrasonically dispersed for 30 min. The resulting solution was transferred to a high-pressure reactor and placed in an oven at 120 °C for 6 h. After the reactor cooled to room temperature, the solid product was separated from the solution by vacuum filtration. The solid product was thoroughly washed with ethanol and then dried in a vacuum oven at 100 °C for 6 h. The resulting pale yellow crystals were the copper ion ring trinuclear metal complex with an aldehyde group. Its SEM image is shown below. Figure 1 As shown.

[0036] S2. Preparation of metal covalent organic framework materials According to the molar ratio of copper ion cyclic trinuclear metal complex, 1,3,5-tris(4-aminophenyl)benzene (TAPB), and glacial acetic acid of 1:1.5:0.05, 0.1 mol of copper ion cyclic trinuclear metal complex, 0.15 mol of TAPB, and 0.005 mol of glacial acetic acid were weighed and dissolved in a glass beaker containing 5 mL of 1,4-dioxane and mesitylene, wherein the volume ratio of 1,4-dioxane to mesitylene was 1:1. The solution was sonicated for 30 min and then mechanically stirred at 500 rpm for 3 hours at 50 °C to ensure thorough mixing.

[0037] The thoroughly stirred solution was transferred to a pressure-resistant vacuum reaction tube. After three cycles of liquid nitrogen freezing, vacuuming, and thawing to ensure a vacuum environment within the reaction tube, it was then placed in a 120°C oven for 5 days. Specifically, the liquid nitrogen freezing process involved immersing the vacuum reaction tube in liquid nitrogen for 15 minutes, until the solution changed from liquid to solid. The vacuuming process involved connecting the liquid nitrogen-frozen reaction tube to a vacuum pump and running the pump for 3 minutes to create a high vacuum within the reaction tube. The valve connecting the reaction tube to the vacuum pump was then closed, and the vacuum pump was turned off. Finally, the thawing process involved placing the vacuum-treated reaction tube in room temperature deionized water for 10 minutes, until the solution changed from solid to liquid.

[0038] After the reaction was complete, the solid product separated by filtration was washed three times sequentially with 30 mL THF and 30 mL DMF. The washing procedure was as follows: the solid product was thoroughly mixed with 30 mL THF in a centrifuge tube and centrifuged at 8000 rpm for 5 min. Then, the solid product obtained after separating the supernatant was thoroughly mixed with 30 mL DMF in a centrifuge tube and centrifuged at 8000 rpm for 5 min. The supernatant was then separated again to obtain the solid product. This washing process was repeated three times until the reaction was complete.

[0039] After washing, the solid product was dissolved in THF and allowed to stand for 3 days. THF was used to replace the residual non-volatile reaction solvents dioxane and mesitylene in the solid product. After standing for 3 days, the filtered solid product was dried in a vacuum oven at 150℃ for 12 hours to obtain the copper-ion-containing metal covalent organic framework material Cu-TAPB-COF. The XRD pattern of Cu-TAPB-COF powder is shown below. Figure 2 As shown, the XRD pattern contains at least three peaks: 2θ = 4.29° ± 0.1°, 2θ = 7.40° ± 0.2°, and 2θ = 11.48° ± 0.3°. These three peaks correspond to the (100), (110), and (120) crystal planes, respectively. The microstructure of Cu-TAPB-COF is shown below. Figure 3 The SEM image is shown in the image.

[0040] Examples 2-4 The reactants, solvents, and preparation processes used in Examples 2-4 are exactly the same as those in Example 1. The only differences are the amounts of reactants and solvents used and the specific parameters of the preparation process, as detailed in Tables 1 and 2.

[0041] Table 1. Raw material ratios for preparing Cu-TAPB-COF

[0042] Table 2. Process parameters for preparing Cu-TAPB-COF

[0043] Comparative Example The comparative example uses 1,4-diazabicyclo[2.2.2]octane (TEDA), which is currently industrially applied. The specific preparation method of TEDA-impregnated activated carbon is as follows: 16-mesh coconut shell activated carbon was washed with sufficient deionized water to remove surface impurities; an appropriate amount of TEDA was weighed and dissolved in ethanol to prepare a 20% TEDA solution; the washed coconut shell activated carbon was immersed in the TEDA solution and then ultrasonically treated for 8 hours; the impregnated activated carbon was placed in an oven and dried at 100℃ for 6 hours to obtain TEDA impregnated activated carbon.

[0044] Iodine adsorption performance test Equal weights of Cu-TAPB-COF prepared in Examples 1-4 and TEDA-impregnated activated carbon prepared in the comparative example were placed into five 5mL small glass bottles, with one empty small glass bottle as a blank reference and one small glass bottle containing 1g of elemental iodine. All the small glass bottles were then placed in a 100mL wide-mouth bottle, which was sealed and placed in an oven at 75°C to stand. At regular intervals, the small glass bottles were weighed and returned to the wide-mouth bottle until the weight of the small glass bottles reached a stable value. The iodine adsorption capacity of the adsorbent was measured by the weight change of the adsorbent. The iodine adsorption capacity of the adsorbent was calculated using the following formula:

[0045] Where, q t This represents the iodine adsorption capacity of the adsorbent over time t, expressed in g / g. -1 m t M represents the weight of the small glass bottle containing the adsorbent at time t, in grams; m1 represents the initial weight of the small glass bottle containing the adsorbent, in grams; m0 represents the weight of the small glass bottle without the adsorbent, in grams; M t M0 represents the weight of the reference sample at time t, in grams; M0 represents the initial weight of the reference sample, in grams.

[0046] The iodine adsorption test results for each embodiment and comparative example are shown in Table 3. As can be seen from Table 3, the adsorption rate and adsorption capacity of Cu-TAPB-COF prepared by the method of the present invention are much greater than those of the TEDA-impregnated activated carbon adsorbent in the prior art.

[0047] Table 3 Iodine Adsorption Test Results

[0048] All materials used in this invention are commercially available and can be purchased from retail sources.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a metal covalent organic framework material, characterized in that, Includes the following steps: S1. Preparation of metal complexes 1H-pyrazole-4-carboxaldehyde and copper nitrate trihydrate (Cu(NO3)2·3H2O) were selected as reactants and dissolved in a mixed solvent of N,N-dimethylformamide (DMF), ethanol and deionized water to prepare a copper ion ring trinuclear metal complex with aldehyde group by solvothermal reaction. The molar ratio of 1H-pyrazole-4-carboxaldehyde to copper nitrate trihydrate is 1~2:1~5; the solvothermal reaction conditions are: standing reaction at 80~120℃ for 6~24h. S2. Preparation of metal covalent organic framework materials A copper-ion-containing metal covalent organic framework material Cu-TAPB-COF was prepared by using a copper ion cyclic trinuclear metal complex as an aldehyde monomer and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as an amino monomer, dissolved in a mixed solvent of 1,4-dioxane and mesitylene, and using glacial acetic acid as a reaction catalyst via a solvothermal reaction. The molar ratio of copper ion cyclic trinuclear metal complex, TAPB and glacial acetic acid is 1~2:1~5:0.01~0.1; the solvothermal reaction conditions are: static reaction in vacuum at 120~150℃ for 3~5 days.

2. The preparation method according to claim 1, characterized in that, In the mixed solvent of step S1, the volume ratio of DMF, ethanol and deionized water is 2~4:2.5~5:1~2.

3. The preparation method according to claim 1, characterized in that, In step S1, after the solvothermal reaction is completed, the solid product is separated from the solution by vacuum filtration. After the solid product is thoroughly washed with ethanol, it is dried in a vacuum oven at 30-100°C for 6-24 hours to obtain a copper ion ring trinuclear metal complex with an aldehyde group.

4. The preparation method according to claim 1, characterized in that, In the mixed solvent of step S2, the volume ratio of 1,4-dioxane and mesitylene is 1~2:1~10.

5. The preparation method according to claim 1, characterized in that, In step S2, after the solvothermal reaction is completed, the solid product separated from the solution after filtration is washed three to five times with tetrahydrofuran (THF) and DMF in sequence. Then, the washed solid product is solvent-displaced with THF for 2 to 3 days, and then the solid product is dried in a vacuum oven at 120 to 150°C for 12 to 24 hours to obtain Cu-TAPB-COF.

6. An application of a metal covalent organic framework material in iodine adsorption, characterized in that, The metal covalent organic framework material is prepared by the preparation method of the metal covalent organic framework material according to any one of claims 1-5, and is used to adsorb radioactive elemental iodine pollutants.

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