A dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, its preparation method and application

Abstract

This invention belongs to the field of adsorption-photocatalytic materials technology, specifically relating to a dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, its preparation method, and its application. An imine-linked COF is synthesized using 4,4',4'',4'''-([9,9'-bicarbazol]-3,3',6,6'-tetramethyl)tetraphenylamine (BCTA) and 2,3-dihydroxynaphthalene-1,4-dicarboxymethyl (DDPD). The obtained dihydroxynaphthalene-type COF (BCTA / DDPD) exhibits good crystallinity and porosity, and can efficiently adsorb and photocatalytically reduce uranium in groundwater and seawater under visible light irradiation, achieving efficient separation and extraction of uranium.

Description

Technical Field

[0001] This invention belongs to the field of adsorption-photocatalytic materials technology, specifically relating to a dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, its preparation method, and its application. Background Technology

[0002] Nuclear energy, as a clean energy source, is an indispensable part of traditional fossil fuels due to its zero-carbon emission nature. Seawater is the largest uranium resource on Earth [1, 2], with sufficient reserves to support the long-term sustainable development of the nuclear energy industry. However, traditional methods for extracting uranium from seawater suffer from poor selectivity, low adsorption capacity, and high energy consumption, limiting their practical application. Photocatalysis technology utilizes photogenerated carriers to achieve chemical reactions, and seawater uranium extraction through photocatalysis can fully utilize the abundant light field resources on the ocean, making it a potentially efficient means of seawater uranium extraction. However, seawater uranium extraction technology faces many challenges such as low concentration, high salinity, and complex composition, and traditional adsorption materials have many shortcomings in terms of efficiency, selectivity, and cost. Therefore, developing efficient and economical photocatalytic technologies and materials for seawater uranium extraction is of significant strategic importance.

[0003] Covalent organic frameworks (COFs) are a class of organic materials linked by reversible covalent bonds, exhibiting highly periodic and modular crystal structures. COFs possess features such as large specific surface area, an impressive π-conjugated framework, high chemical and thermal stability, and tunable pore size.

[0004] However, in the existing technology, covalent organic frameworks cannot perfectly realize the adsorption-photocatalytic high-efficiency uranium extraction. Based on this, the technical problem to be solved in this case is to achieve the adsorption-photocatalytic high-efficiency uranium extraction through functional design. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a method for preparing a dihydroxynaphthalene covalent organic framework catalyst capable of achieving synergistic adsorption-photocatalysis, thus realizing a new strategy, material, and method for the efficient extraction of uranium from groundwater and seawater. The dihydroxynaphthalene covalent organic framework catalyst prepared by this invention has advantages such as high adsorption capacity, high selectivity, high stability, and high catalytic activity, achieving efficient enrichment of uranium in water bodies, and is a highly efficient material for uranium separation and extraction.

[0006] Therefore, a first aspect of the present invention provides a method for preparing a dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, comprising the following steps: (1) 4,4',4'',4'''-([9,9'-bicarbazol]-3,3',6,6'-tetramethyl)tetraphenylamine and 2,3-dihydroxynaphthalene-1,4-dicarboxyl are mixed and dispersed evenly with the first solvent to obtain the first mixture; (2) Mix the first mixture with the second solvent until they are evenly dispersed to obtain the second mixture; (3) Add the third solvent to the second mixture, mix and disperse evenly to obtain the third mixture; (4) The third mixture is rapidly frozen into a solid, and after thawing and cycling, it is vacuum sealed to obtain the fourth mixture; (5) Heat the fourth mixture at 80-120℃ to obtain the product; (6) The product is taken out, washed, and vacuum dried to obtain the dihydroxynaphthalene type adsorption-photocatalytic covalent organic framework material.

[0007] Dihydroxynaphthalene possesses a high π-conjugated electronic structure and electron-donating effect, providing abundant electron donors for the generation of photocatalytically active electrons. Furthermore, the two adjacent hydroxyl groups of dihydroxynaphthalene exhibit high activity, effectively providing loading sites for 4-6 coordinated uranyl groups. Therefore, the preparation of dihydroxynaphthalene COFs has high potential for adsorption-photocatalytic separation of uranium. Utilizing the photon energy of natural light, semiconductor COFs can be catalyzed to generate active electrons, photocatalytically reducing highly mobile hexavalent uranium ions in water to tetravalent uranium with strong complexing ability. This achieves highly selective separation of uranium from different water bodies, providing material and technical references for uranium extraction from seawater.

[0008] As a preferred embodiment, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, the molar ratio of 4,4',4'',4'''-([9,9'-bicarbazolium]-3,3',6,6'-tetramethyl)tetraphenylamine and 2,3-dihydroxynaphthalene-1,4-dicarboxylic acid is 1:1.9~2.1. Controlling the molar ratio of BCTA to DDPD within this range ensures complete imine bond formation and avoids monomer residue. A ratio close to the theoretical value of 2:1 (DDPD contains two acyl groups) allows for sufficient cross-linking of bicarbazolium tetraphenylamine and dihydroxynaphthalene-dicarboxylic acid, forming a regular crystal framework, thereby increasing the specific surface area and porosity of the material.

[0009] As a preferred embodiment, the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material has a volume ratio of 3~5:3~5:1 for the first solvent, the second solvent, and the third solvent, and satisfies at least one of the following characteristics: the first solvent is 1,4-dioxane; the second solvent is mesitylene; and the third solvent is acetic acid with a concentration of 3M~9M. 1,4-dioxane as the first solvent effectively dissolves the two organic monomers, promoting initial mixing homogeneity; mesitylene as the second solvent maintains the stability of the reaction system during heating due to its high boiling point, avoiding local overheating; 3~9M acetic acid as the third solvent provides an acidic environment to catalyze the imine condensation reaction, while the concentration range ensures controllable reaction rates, preventing over-polymerization. Overall advantages: the optimized volume ratio of the three solvents balances dissolution, dispersion, and reaction kinetics, providing an ideal environment for crystal growth and significantly improving the crystallinity of the material.

[0010] As a preferred option, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, in step (2), ultrasonic dispersion is used for 3 to 5 minutes to shorten the particle aggregation time, so that the monomer is uniformly dispersed in the solvent, laying the foundation for subsequent orderly assembly and avoiding the formation of amorphous regions.

[0011] As a preferred embodiment, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, step (4) is performed within 20 seconds after step (3) is completed. The microstructure of the mixture is fixed by rapid freezing with liquid nitrogen, and the internal stress is eliminated by thawing cycle, thereby improving the crystal defect repair ability and enhancing the mechanical stability of the material.

[0012] As a preferred embodiment, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, the heating time in step (5) is 2 to 4 days. Sufficient reaction time ensures complete formation of imine bonds, while avoiding excessive reaction that could lead to framework collapse and maintaining the porous structure.

[0013] As a preferred embodiment, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, step (7) involves washing with ethanol and / or acetone. Ethanol / acetone washing: efficiently removes unreacted monomers and solvent residues, ensuring material purity.

[0014] As a preferred embodiment, in the preparation method of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, in step (7), the vacuum drying temperature is 25-50℃ and the time is 10-30h. This avoids high temperature damage to imine bonds and pore structure, and maintains specific surface area and hydrophilicity.

[0015] A second aspect of the present invention provides a dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, prepared by the above-described preparation method. The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material has micropores and mesopores. The cell parameters of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material are a=28.002 Å, b=27.156 Å, c=3.636 Å, α=β=γ=90°, R p =3.46%, R wp =4.41%, interlayer distance is 3.54 Å. Infrared spectrum of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material at 1624 cm⁻¹. -1 An imine bond vibration peak appears at this location.

[0016] A third aspect of the present invention provides the application of the above-mentioned dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material in uranium extraction from water, wherein the water includes groundwater and / or seawater; the application includes mixing the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material with the water. Under laboratory conditions, the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material can be mixed with uranium-containing water, and uranium extraction can be performed under 420-780 nm xenon lamp irradiation and constant temperature conditions of 22-28 °C.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The COF catalyst prepared by the method of this invention has high purity. The dihydroxynaphthalene-type COFs (BCTA / DDPD) prepared by this method not only have uranium adsorption properties, but can also further enhance the enrichment capacity of uranium in water through an adsorption-photocatalysis process under photocatalysis. BCTA / DDPD is effective for uranium-containing groundwater (CO(UO2)2) 2+ The photocatalytic extraction yield of uranium in a solution with a concentration of 20 ppm and a m / v ratio of 1 / 60 was 1.33 g / g, and the photocatalytic extraction yield of uranium in actual uranium-containing seawater was 864 mg / g.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments. The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels. Specifically, both ligand raw materials were purchased from [Company Name].

[0020] The following detailed description is illustrative and intended to provide further explanation of this application, but does not limit the invention to the scope of the described embodiments. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] Example 1: A method for preparing a dihydroxynaphthalene adsorption-photocatalytic covalent organic framework material The covalent organic framework material was prepared as follows: 4,4',4'',4'''-([9,9'-bicarbazol]-3,3',6,6'-tetramethyl)tetraphenylamine (BCTA, 0.03 mmol, 20.90 mg) and 2,3-dihydroxynaphthalene-1,4-dicarboxyyl (DDPD, 0.06 mmol, 12.97 mg) were added to a heat- and pressure-resistant glass tube, followed by 1,4-dioxane (0.4 mL). The mixture was ultrasonically mixed and dispersed thoroughly to obtain the first mixture. Trimethylbenzene (0.4 mL) was then added and dispersed for 5 min to obtain the second mixture. A 6 M glacial acetic acid aqueous solution (AcOH, 0.1 mL) was rapidly added, and the mixture was ultrasonicated for 2 min to obtain a uniformly dispersed solution. Within 5–20 seconds after ultrasonication, the mixture was rapidly placed in a container filled with liquid nitrogen for freezing. After three pump-thaw cycles, the mixture was vacuum-sealed. The glass tube, after returning to room temperature, was then heated at 120°C for 3 days. The product was washed several times with ethanol (EtOH), collected by vacuum filtration, and then vacuum dried overnight at 45°C to obtain COF material.

[0022] Test Example 1: Characterization Method of a Dihydroxynaphthalene Adsorption-Photocatalytic Covalent Organic Framework Material The characterization results of the dihydroxynaphthalene covalent organic framework catalyst (Example 1) are as follows: the cell parameters of the covalent organic framework material are a=28.002 Å, b=27.156 Å, c=3.636 Å, α=β=γ=90°. R p =3.46%, R wp=4.41%, interlayer distance approximately 3.54 Å. Experimental data are consistent with the AA overlap mode. The specific surface area of ​​BCTA / DDPD was measured to be 209.44 m² / g, indicating that the material possesses good crystal structure and porosity. BCTA / DDPD was found to have two main pore sizes: micropores (1.84 nm) and mesopores (2.10 nm). A strong imine bond vibration peak (1624 cm⁻¹) was observed in the infrared spectrum of BCTA / DDPD. -1 This further illustrates the formation of the dihydroxynaphthalene covalent organic framework structure. Thermogravimetric analysis showed that, apart from the loss of pore water and residual organic molecules within the pores at around 150°C, the overall mass of the material maintained thermal stability within the 400°C range. The water contact angle of the material was found to be less than 90°, indicating its hydrophilicity. These analytical results demonstrate the successful synthesis of the dihydroxynaphthalene covalent organic framework structure prepared in Example 1, which possesses a regular crystal structure and a large specific surface area.

[0023] To further verify the performance of the dihydroxynaphthalene covalent organic framework material prepared by this invention, we can conduct auxiliary analysis and verification through the following implementation scheme.

[0024] Test Example 2: Test Method for Photocatalytic Performance of Dihydroxynaphthalene Adsorption-Photocatalytic Covalent Organic Framework Materials in Uranium-Bearing Groundwater The photocatalytic adsorption performance test method for uranium-bearing groundwater was as follows: The uranium extraction efficiency of the material under illumination was investigated using a xenon lamp-catalyzed reaction chamber. Groundwater from a spring in Mentougou District, Beijing, was filtered to remove insoluble substances such as particles, serving as the aqueous solution for the entire uranium extraction process. UO2 was used... 2+ Prepare 100 mL of uranium-containing groundwater with a uranium acyl content of 20 ppm using (NO3)2·6H2O. Weigh 10.0 mg of the material from Example 1 into the uranium-containing groundwater and conduct kinetic analysis under xenon lamp irradiation at 420-780 nm. Maintain the reaction system temperature at 25°C by circulating condensate. Filter the reaction supernatant using a 0.22 μm filter at different time points, measure the absorbance using an azoarsine tricolor spectrophotometer, and calculate the uranium acyl enrichment based on the difference between the initial concentration and the measured residual concentration.

[0025] The kinetic results of BCTA / DDPD photocatalysis of uranium-bearing groundwater showed that BCTA / DDPD reached equilibrium after 520 min under illumination, and the enrichment rate of uranium in the groundwater was 95.6%.

[0026] Test Example 3: Photocatalytic Performance Test of Dihydroxynaphthalene Adsorption-Photocatalytic Covalent Organic Framework Material in Uranium-Bearing Groundwater Test Example 2 demonstrates that BCTA / DDPD exhibits good photocatalytic extraction capability for uranium from groundwater. To explore the potential of this material for photocatalytic uranium enrichment, the solid-liquid ratio was reduced from 1:10 in Test Example 2 to 1:60, while the initial concentration remained constant, and the enrichment kinetics of uranyl by the material were analyzed. The kinetic results of BCTA / DDPD photocatalysis on uranium-containing groundwater show that under xenon lamp irradiation at 420-780 nm, the amount of uranium extracted from groundwater by the material continuously increases with time. At 1020 minutes, the enrichment of uranium by the material reached an astonishing 1.334 g / g, indicating that the material possesses strong uranium enrichment capability.

[0027] Test Example 4: Photocatalytic Uranium Extraction Experiment from Uranium-Containing Pure Seawater Seawater from the South China Sea near Maoming, Guangdong, was filtered to remove insoluble substances and used as a uranium-containing solution. UO2 was then utilized. 2 + Prepare 100 mL of pure seawater containing uranium with a uranium acyl content of 20 ppm using (NO3)2·6H2O. Weigh 10.0 mg of the material from Example 1 into the pure seawater containing uranium and conduct kinetic experiments under xenon lamp irradiation at 420-780 nm. Maintain the reaction system temperature at 25°C by circulating condensate. Filter the reaction supernatant using a 0.22 μm filter at different time points, measure the absorbance using an azoarsine tricolor spectrophotometer, and calculate the uranium acyl enrichment based on the difference between the initial concentration and the measured residual concentration.

[0028] The kinetic results of BCTA / DDPD photocatalysis of uranium-containing pure seawater showed that after 12 hours of illumination, the enrichment capacity of uranyl reached 77.8%. This result indicates that BCTA / DDPD not only has a high extraction capacity for uranium from groundwater, but also a high extraction efficiency for uranium from pure seawater.

[0029] Test Example 5: Photocatalytic Saturated Extraction Capacity Test of Uranium-Containing Pure Seawater To further analyze the photocatalytic saturation extraction capability of uranium-containing pure seawater, an isotherm experiment was conducted for verification. Specifically, 20 mL of pure seawater containing uranium amide was prepared with initial concentrations of 2 ppm, 5 ppm, 10 ppm, 20 ppm, 40 ppm, and 60 ppm, respectively. 1.0 mg of uranium amide was accurately weighed into each solution and irradiated at 25°C for 24 hours. The enrichment amount of uranium amide was calculated by comparing the initial concentration with the measured residual concentration. The highest adsorption capacity of the material reached 864 mg / g, indicating that the material has high extraction potential and strong selective enrichment capability for uranium in pure seawater. Infrared spectroscopy of the photocatalyzed material revealed that the material exhibited high uranium amide concentration at 903 cm⁻¹. -1 The presence of distinct uranium vibration peaks further indicates that uranyl was effectively enriched in the material.

[0030] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dual-hydroxyl naphthalene type adsorption-photocatalytic covalent organic framework material, characterized in that, Includes the following steps: (1) 4,4',4'',4'''-([9,9'-bicarbazol]-3,3',6,6'-tetramethyl)tetraphenylamine and 2,3-dihydroxynaphthalene-1,4-dicarboxyl are mixed and dispersed evenly with the first solvent to obtain the first mixture; (2) Mix the first mixture with the second solvent until they are evenly dispersed to obtain the second mixture; (3) Add the third solvent to the second mixture, mix and disperse evenly to obtain the third mixture; (4) The third mixture is rapidly frozen into a solid, and after thawing and cycling, it is vacuum sealed to obtain the fourth mixture; (5) Heat the fourth mixture at 80-120℃ to obtain the product; (6) The product is taken out, washed, and vacuum dried to obtain the dihydroxynaphthalene type adsorption-photocatalytic covalent organic framework material.

2. The preparation method of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 1, characterized in that, The molar ratio of 4,4',4'',4'''-([9,9'-bicarbazol]-3,3',6,6'-tetramethyl)tetraphenylamine and 2,3-dihydroxynaphthalene-1,4-dicarboxyl is 1:1.9~2.

1.

3. The preparation method of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 1, characterized in that, The volume ratio of the first solvent, the second solvent, and the third solvent is 3~5:3~5:1, and satisfies at least one of the following characteristics: The first solvent is 1,4-dioxane; The second solvent is mesitylene; The third solvent is acetic acid with a concentration of 3M to 9M.

4. The preparation method of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 1, characterized in that, Satisfy at least one of the following characteristics: In step (2), ultrasonic dispersion is used for 3-5 minutes; Within 20 seconds of completing step (3), proceed to step (4); In step (5), the heating time is 2 to 4 days; In step (7), the washing is performed using ethanol and / or acetone; In step (7), the vacuum drying temperature is 25-50℃ and the time is 10-30h.

5. A dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 5, characterized in that, The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material has micropores and mesopores.

7. The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 5, characterized in that, The unit cell parameters of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material are a=28.002 Å, b=27.156 Å, c=3.636 Å, α=β=γ=90°. R p =3.46%, R wp =4.41%, interlayer distance is 3.54 Å.

8. The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 5, characterized in that, The infrared spectrum of the bishydroxynaphthalene type adsorption-photocatalytic type covalent organic framework material appears an imine bond vibration peak at 1624 cm -1 .

9. The application of dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework materials in uranium extraction from water, characterized by: The dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material is the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to any one of claims 5-8; The water body includes groundwater and / or seawater; The application includes mixing dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework materials with water.

10. The application of the dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material according to claim 9 in uranium extraction from water, characterized in that, The application includes: mixing a dihydroxynaphthalene-type adsorption-photocatalytic covalent organic framework material with uranium-containing water, and extracting uranium under 420-780nm xenon lamp irradiation and constant temperature conditions of 22-28℃.