Preparation method of carboxyl functionalized covalent organic framework material for extracting uranium from seawater

Abstract

The invention relates to the technical field of uranium extraction from seawater, and provides a preparation method of a carboxyl functionalized covalent organic framework material for uranium extraction from seawater, and the carboxyl functionalized covalent organic framework material is prepared by taking a covalent organic framework material as a raw material, and performing hydrophilic group post-modification by adopting a thiol-olefin click reaction, the hydrophilic group is selected from carboxyl. The carboxyl functionalized covalent organic framework material has good crystallinity, excellent stability and rich active adsorption sites, and can be selectively coordinated with uranyl ions when being used as an adsorbent.

Description

Technical Field

[0001] This invention relates to the field of uranium extraction technology from seawater, and more particularly to a method for preparing a carboxyl-functionalized covalent organic framework material for uranium extraction from seawater. Specifically, it relates to an adsorbent for uranium extraction from seawater, its preparation method, and its application. Background Technology

[0002] One of the major challenges facing human society in the 21st century is the transition to clean energy that promotes deep decarbonization and sustainable development. Nuclear energy, with its advantages of high energy density, stable and continuous power supply, and low carbon emissions, is widely recognized as a mature and safe technology. Uranium is the prerequisite and guarantee for the sustainable development of the nuclear industry. The reserves of natural uranium ore on land are limited and difficult to mine. In contrast, the total uranium reserves in seawater are approximately 4.5 billion tons, about 1,000 times the proven uranium ore reserves on land, and the uranium reserves in seawater are sufficient to ensure the long-term stable operation of nuclear power plants. Therefore, there is an urgent need to develop new materials and technologies for extracting uranium from seawater to meet the ever-growing demand for uranium resources.

[0003] Using solid porous adsorbent materials for uranium extraction from seawater is a feasible approach. In recent years, emerging nanoframework materials, such as porous carbon materials, hydrogels, porous organic polymers, porous aromatic frameworks, hydrogen-bonded organic frameworks, and metal-organic frameworks, have been applied to uranium extraction from seawater. However, their overall performance is unsatisfactory, specifically exhibiting poor adsorption capacity, poor stability, slow kinetics, poor resistance to biofouling, and poor mass transfer due to disordered structures. These limitations significantly restrict their application in uranium extraction from seawater.

[0004] Covalently bonded carbon (COF) materials possess advantages such as programmable chemical structures, excellent crystallinity, outstanding stability, large specific surface area, and ease of post-modification. The amylopyram group is the most commonly used functionalization for uranium binding, and amylopyram-modified COF-based adsorbents have already been applied in seawater uranium extraction. However, vanadium is the main competing ion in seawater uranium extraction, and the selectivity of amylopyram groups for uranium / vanadium in seawater is limited. Therefore, it is essential to develop new materials for seawater uranium extraction with novel specific adsorption sites. Summary of the Invention

[0005] This invention provides a method for preparing a carboxyl-functionalized covalent organic framework material for uranium extraction from seawater. This carboxyl-functionalized covalent organic framework material is synthesized using a solvothermal method with specific key monomers and exhibits excellent crystallinity. Furthermore, a post-modification strategy using a "thiol-ene" click reaction is employed to introduce hydrophilic functional groups onto the covalent organic framework material, resulting in an adsorbent. This adsorbent possesses excellent stability and abundant active adsorption sites, enabling selective coordination with uranyl ions.

[0006] Specifically, in the first aspect, a method for preparing an adsorbent includes: using a covalent organic framework material as a raw material, modifying it with a hydrophilic group via a thiol-olefin click reaction; wherein the hydrophilic group is selected from carboxyl groups; The covalent organic framework material includes compounds with the following structural formulas: The acylhydrazine-carbonyl site embedded in the COF backbone of this invention can act as a "nanotrap" for binding uranium, and the extraction of uranium is further enhanced by the synergistic effect of hydrophilic functional groups on the side chains.

[0007] This invention introduces hydrophilic functional groups through a "thiol-ene" click reaction, attaches flexible carboxylic acid groups to the pore surface, and generates a synergistic adsorption effect with the acylhydrazine-carbonyl "uranium nanotrap" embedded in a covalent organic framework, significantly enhancing the adsorption capacity for uranium; at the same time, the acylhydrazine-carbonyl "uranium nanotrap" and the antiparallel AA stacked structure can selectively coordinate with uranyl ions.

[0008] The method for preparing the adsorbent for uranium extraction from seawater as described above according to the present invention comprises: reacting a covalent organic framework material, 2,2-azobisisobutyronitrile, and 3-mercaptopropionic acid as main raw materials under heating conditions.

[0009] According to the preparation method of the adsorbent for uranium extraction from seawater provided by the present invention, the mass ratio of covalent organic framework material and 2,2-azobisisobutyronitrile is (10~11):(1~1.5). And / or, the mass-to-volume ratio of covalent organic framework material to 3-mercaptopropionic acid is (100~110):(4~5).

[0010] More preferably, the preparation method of the adsorbent for uranium extraction from seawater can be as follows: a covalent organic framework material is mixed with 3-mercaptopropionic acid and 2,2-azobisisobutyronitrile, and the mixture is placed at 80°C for two days to obtain a product mixture. The solid is then separated and washed, and vacuum dried to obtain the adsorbent, denoted as COF-IHEP5-COOH. Preferably, the solvent used for washing is water and acetone.

[0011] According to the preparation method of the adsorbent as described above provided by the present invention, the specific surface area of ​​the covalent organic framework material is 800 m². 2 / g or more, pore volume is 0.45cm³ 3 / g or more, with pore sizes below 3nm accounting for more than 95%; Preferably, the compound forms an antiparallel AA stacked structure. The antiparallel AA stacked structure in this invention facilitates metal transport and chelation within the material channels.

[0012] This invention synthesizes an olefin-functionalized covalent organic framework material via a hydrothermal method. This framework possesses hydrazide-carbonyl coordination sites and an antiparallel AA stacked structure. The covalent organic framework material exhibits excellent crystallinity and a large specific surface area. The good crystallinity indicates that the material has regular internal channels, and the specific surface area is as high as 800 m². 2 / g, these two advantages play an important role in promoting the ion transport effect.

[0013] According to the preparation method of the adsorbent as described above provided by the present invention, the preparation method of the covalent organic framework material includes: using trialdehyde phloroglucinol and 2,5-bis(allyloxy)terephthalohydrazide as raw materials, and synthesizing them by a solvothermal method.

[0014] According to the method for preparing the adsorbent as described above provided by the present invention, the covalent organic framework material is obtained by catalytic reaction in a solvent composed of mesitylene and 1,4-dioxane; Preferably, the catalyst is selected from acetic acid.

[0015] The specific steps of the preparation method of the covalent organic framework material can be as follows: (1) Using trialdehyde phloroglucinol and 2,5-bis(allyloxy) terephthalohydrazide as reaction raw materials, mesitylene and 1,4-dioxane as solvents, and acetic acid as catalyst, the mixed solvent was ultrasonically treated for 20 minutes to obtain the first mixture. (2) The first mixture is subjected to three cycles of freezing-pumping-thawing and degassing to remove air and dissolved gases from the solvent, and then the mixture is sealed with a flame to obtain the second mixture; (3) After cooling the second mixture to room temperature, it is placed at 120°C for three days to obtain a third mixture. The solids are separated and washed, and then vacuum dried to obtain a covalent organic framework material, denoted as COF-IHEP5. Preferably, the solvents used for washing are ethanol and tetrahydrofuran.

[0016] According to the preparation method of the adsorbent as described above provided by the present invention, the mass ratio of the trialdehyde phloroglucinol and 2,5-bis(allyloxy)terephthalohydrazide is 1:(1.4~1.5). And / or, the volume ratio of the trimethylbenzene and 1,4-dioxane is 1:0.5~1.5; And / or, the catalyst is an aqueous solution of acetic acid with a concentration of 5 M or higher, and the volume ratio of mesitylene to the aqueous solution of acetic acid is 1:0.1~0.3; And / or, the mass-to-volume ratio of the trialdehyde phloroglucinol and the mesitylene is 15-25 mg: 1 mL.

[0017] This invention overcomes the technical challenge of crystallization by optimizing various parameters in the above preparation process, with the solvent playing a key role.

[0018] Secondly, the present invention also provides an adsorbent prepared by the method described above, wherein the specific surface area of ​​the adsorbent is 40 m². 2 / g or more, pore volume is 0.05cm³ 3 / g or more, with pore sizes below 1.5nm accounting for more than 95%; Preferably, the adsorbent is in the form of porous nanofibers.

[0019] According to the adsorbent provided by the present invention as described above, the adsorbent contains a compound with the following structural formula: .

[0020] This invention relates to a β-ketoenamine COF linked by an hydrazone bond, which exhibits superior thermal and acid-base stability compared to other imine COFs.

[0021] Thirdly, the present invention also provides an adsorbent prepared by the preparation method described above, and the application of the adsorbent described above in uranium extraction from seawater, wherein the adsorbent achieves adsorption of uranyl ions in seawater through chemical adsorption. Preferably, the adsorbent has an adsorption capacity of uranyl ions of 500 mg / g or higher; Preferably, the mass-to-volume ratio of the adsorbent to the seawater is 0.2 g: 1 L or more; Preferably, the uranium content in the seawater is 2 ppm or higher.

[0022] The adsorbent of this invention exhibits excellent adsorption performance in both batch adsorption experiments and in natural seawater environments, demonstrating outstanding overall performance.

[0023] This invention provides a method for preparing carboxyl-functionalized covalent organic framework materials for uranium extraction from seawater. First, an olefin-functionalized covalent organic framework material is synthesized. Then, a post-modification strategy using a "thiol-ene" click reaction is employed to introduce hydrophilic functional groups onto the covalent organic framework material. By attaching flexible carboxylic acid groups to the pore surface of the covalent organic framework material and synergizing with "uranium nanotraps" embedded within the framework, the adsorption capacity of uranium active sites can be further enhanced, achieving highly efficient adsorption of uranyl acyl groups. This material exhibits good crystallinity, excellent stability, and abundant hydrazide-carbonyl uranium active adsorption sites, making it a highly promising and efficient solid adsorbent for uranium extraction from seawater. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 The image shows the powder X-ray diffraction pattern of the covalent organic framework material prepared in Example 1A.

[0026] Figure 2 The image shows the powder X-ray diffraction pattern of the adsorbent prepared in Example 1A.

[0027] Figure 3 The infrared spectrum of the covalent organic framework material prepared in Example 1A is shown.

[0028] Figure 4 The infrared spectrum of the adsorbent prepared in Example 1A is shown.

[0029] Figure 5 The solid-state NMR 13C spectra of the covalent organic framework material and adsorbent prepared in Example 1A are shown.

[0030] Figure 6 The attached diagram shows the nitrogen adsorption / desorption process and pore size distribution of the covalent organic framework material prepared in Example 1A.

[0031] Figure 7 The attached diagram shows the nitrogen adsorption / desorption process and pore size distribution of the adsorbent prepared in Example 1A.

[0032] Figure 8 Thermogravimetric analysis (TGA) diagram of the covalent organic framework material prepared in Example 1A.

[0033] Figure 9 The thermogravimetric analysis diagram is shown for the adsorbent prepared in Example 1A.

[0034] Figure 10 This is a scanning electron microscope image of the adsorbent prepared in Example 1A.

[0035] Figure 11 This is a transmission electron microscope image of the adsorbent prepared in Example 1A.

[0036] Figure 12 This is a saturated adsorption capacity diagram of the covalent organic framework material and adsorbent prepared in Example 1B.

[0037] Figure 13 The selective adsorption performance of the adsorbent prepared in Example 2B is shown.

[0038] Figure 14 The adsorbent prepared in Example 3B exhibits adsorption performance in real seawater. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] The following is combined Figures 1-14 This invention describes a method for preparing a carboxyl-functionalized covalent organic framework material for uranium extraction from seawater.

[0041] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0042] Example 1A This embodiment also provides an adsorbent containing a compound with the following structure: This embodiment also provides a method for preparing the above-mentioned adsorbent, the steps of which are as follows: (1) Trialdehyde pyrogallol and 2,5-bis(allyloxy) terephthalohydrazide were added to a glass reactor as reaction raw materials, and mesitylene, 1,4-dioxane and 6M acetic acid (aqueous solution) were added to it to obtain mixture A.

[0043] The mass ratio of trialdehyde phloroglucinol to 2,5-bis(allyloxy)terephthalohydrazide is 21:46.

[0044] The volume ratio of mesitylene to 1,4-dioxane is 1:1.

[0045] The mass-to-volume ratio of trialdehyde phloroglucinol and mesitylene is 21 mg: 1 mL.

[0046] The volume ratio of mesitylene to 6M acetic acid (aqueous solution) is 1:0.2.

[0047] (2) The mixture A was ultrasonically treated for 20 minutes, and the uniformly dispersed mixture A was frozen in liquid nitrogen. The mixture was subjected to three cycles of freezing-pumping-thawing and degassing and sealed with a flame. The reactor was then placed in a 120°C oven and left to stand for three days. After cooling to room temperature, the solids were collected.

[0048] (3) The solid obtained in step (2) was washed with ethanol and tetrahydrofuran, and then dried under vacuum at 100°C to constant weight to obtain a yellow powdery covalent organic framework material, denoted as COF-IHEP5, with the following structure: .

[0049] (4) The COF-IHEP5, 2,2-azobisisobutyronitrile and 3-mercaptopropionic acid obtained in step (3) above are added to a glass reactor to obtain mixture B.

[0050] The mass ratio of COF-IHEP5 to 2,2-azobisisobutyronitrile is 10:1.

[0051] The mass-to-volume ratio of COF-IHEP5 and 3-mercaptopropionic acid is 100 mg: 4 mL.

[0052] (5) Sonicate the mixture B for 20 minutes, freeze the uniformly dispersed mixture B in liquid nitrogen, and seal it after three cycles of freezing-pumping-thawing and degassing. Then place the reactor in an 80°C oil bath and stir for two days. After cooling to room temperature, collect the solids.

[0053] (6) The solid obtained in step (5) was washed with deionized water and acetone and dried under vacuum at 100°C to constant weight to obtain a yellow-green powder adsorbent, denoted as COF-IHEP5-COOH.

[0054] Test case The COF-IHEP5 and COF-IHEP5-COOH prepared in Example 1A were tested as follows: (1) The crystal structure of COF-IHEP5 was determined using X-ray powder diffraction (PXRD) and Materials Studio simulation. For example... Figure 1 As shown, diffraction peaks appear at 3.61°, 6.21°, and 7.12°, corresponding to the (100), (110), and (200) crystal planes, respectively. Possible stacking modes were simulated in Materials Studio software. Based on the experimental data, the structural model was refined using Pawley. The results show that COF-IHEP5 has a hexagonal unit cell in space group P6-CC, with cell parameters a=b=29.9461Å, c=7.0826Å, α=β=90°, and γ=120.0° (Rp=1.36%, Rwp=2.06%). The experimental data match well with the antiparallel AA stacking model. The results indicate that COF-IHEP5 has a two-dimensional hexagonal honeycomb structure with a pore size of approximately 2.1 nm and an interlayer spacing of approximately 3.54 Å. The PXRD pattern of COF-IHEP5-COOH shows a diffraction pattern comparable to that of COF-IHEP5 (e.g., ...). Figure 2 This indicates that the excellent crystallinity of the modified COF material was preserved.

[0055] (2) Fourier transform infrared spectroscopy (FT-IR) was used to verify the chemical structure and composition. For example... Figures 3-5 As shown, at ~1631cm -1 A characteristic signal exists at this location, corresponding to the lower energy characteristic of the carbonyl stretching vibration in the β-ketoenamine bond, while the monomer's NH (3290cm) -1 ) and CH (2893cm) -1 The signal almost disappeared, indicating that COF-IHEP5 was highly polymerized. The Fourier transform infrared spectrum of COF-IHEP5-COOH showed that at 1724 cm⁻¹... -1 The presence of a C=O stretching band (carboxylic acid) at this point confirms the success of the post-synthetic modification. Furthermore, the characteristic peak of the β-keto-enamine bond is observed at 1631 cm⁻¹. -1 The fact that the chemical structure of COF-IHEP5 modified by the "thioene" click reaction was preserved demonstrates that the chemical structure of COF-IHEP5 was preserved, and also proves the excellent stability of COF-IHEP5.

[0056] (3) The inherent porosity of COF-IHEP5 was studied by N2 adsorption-desorption isotherm curves at 77 K, such as... Figures 6-7 As shown, the Brunauer-Emmett-Teller surface areas of COF-IHEP5 and COF-IHEP5-COOH are 828 m² and 828 m², respectively. 2 / g and 47m 2 The pore volumes were 0.49 cm / g and 0.08 cm / g, respectively. Pore size distribution analysis based on the nonlocal density functional theory (NLDFT) model showed that the pore sizes of COF-IHEP5 and COF-IHEP5-COOH were concentrated at 2.0 and 1.3 nm, respectively. This is a good match for the antiparallel AA stacked structures (21.2 and 13.8 Å). The reduction in pore size also verifies the success of the post-modification.

[0057] (4) Thermal stability: Thermogravimetric analysis of COF-IHEP5 and COF-IHEP5-COOH is as follows: Figures 8-9 As shown, thermogravimetric analysis indicates that the above-mentioned adsorbent can remain stable at 250℃.

[0058] (5) such as Figures 10-11 As shown, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the morphology of the uniform porous nanofibers of COF-IHEP5-COOH.

[0059] (6) Acid and base stability: COF-IHEP5-COOH can still maintain very good crystallinity after being soaked in 3M and 6M nitric acid and sodium hydroxide solutions for 24 hours respectively.

[0060] Example 1B This embodiment provides an application of carboxyl-functionalized covalent organic frameworks in seawater uranium extraction, the steps of which include: (1) Prepare uranium solutions with concentrations of 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm and 300 ppm using ultrapure water, such as Figure 12 As shown. The pH of the solution was then adjusted to approximately 5.0.

[0061] (2) Take uranium solutions with different initial uranium concentrations into centrifuge tubes, and then add COF-IHEP5-COOH prepared in Example 1A. Perform an adsorption test on a constant temperature shaker at 25°C. The mass-volume ratio of COF-IHEP5-COOH to uranium solution is 5mg:25mL. After adsorption, filter out the insoluble matter to obtain the filtrate.

[0062] Saturated adsorption capacity test: The concentration of uranyl ions in the filtrate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the adsorption capacity was calculated. Figure 14 As shown, COF-IHEP5-COOH exhibits a maximum adsorption capacity of 543 mg / g for uranyl ions.

[0063] Fitting the Langmuir adsorption isotherm and Freundlich adsorption isotherm models revealed that the active adsorption sites are uniformly distributed on the material surface, and the adsorption of uranyl ions by COF-IHEP5-COOH is a uniform monolayer adsorption.

[0064] Example 2B This embodiment provides an application of carboxyl-functionalized covalent organic frameworks in seawater uranium extraction, the steps of which include: (1) Adding ions: UO2 to natural seawater (originating from the South China Sea (Haikou, Hainan)) 2+ VO4 3- Fe 3+ Co 2+ Ni 2+ Zn 2+ Pb 2+ Ba 2+ and Sr 2+ Simulated seawater containing all of the aforementioned ions was obtained. The amount of each ion added was 0.05 mmol / L.

[0065] (2) The COF-IHEP5-COOH prepared in Example 1A was placed in simulated seawater, wherein the mass-to-volume ratio of COF-IHEP5-COOH to simulated seawater was 20 mg: 100 mL; ion adsorption was carried out in a constant temperature shaker at 25 °C. After reaching adsorption equilibrium, samples were taken with a syringe and filtered through a 0.22 μm aqueous filter. The adsorption capacity of different ions was detected by ICP-OES. The test results are as follows: Figure 13 As shown in Table 1 below (the horizontal axis is labeled with the corresponding elements), the specific data is as follows.

[0066] Table 1

[0067] The results of ion selectivity experiments were conducted in simulated seawater to detect different interfering ions. Table 1 above shows the results for VO4+ ion selectivity. 3- Fe 3+ Co 2+ Ni 2+ Zn 2+ Pb 2+ Ba 2+ and Sr 2+ Under the interference of [unclear], the COF-IHEP5-COOH of the present invention exhibits excellent ion selectivity for uranyl ions.

[0068] Example 3B This embodiment provides an application of carboxyl-functionalized covalent organic frameworks in seawater uranium extraction, the steps of which include: (1) Uranium ions were added to natural seawater (originating from the South China Sea (Haikou, Hainan)) that had been filtered through a 0.22um aqueous filter membrane to remove insoluble substances (such as particulate matter) to obtain seawater 1 and seawater 2; the concentration of uranium in seawater 1 was 2 ppm and the concentration of uranium in seawater 2 was 10 ppm.

[0069] (2) Take seawater 1 and seawater 2 into centrifuge tubes respectively, and add COF-IHEP5-COOH prepared in Example 1A to them. The mass-to-volume ratio of COF-IHEP5-COOH to seawater is 0.2g:1L. Shake in a constant temperature shaker at 25℃ for 4 days until adsorption equilibrium is reached. Take samples with a syringe at regular intervals, filter with a 0.22μm water filter, analyze the residual uranium concentration using ICP-OES, calculate the adsorption capacity, and the fitting results of the adsorption kinetics and the corresponding pseudo-second-order kinetic model are as follows: Figure 14 As shown, its adsorption data conforms to the pseudo-second-order kinetic equation, with a correlation coefficient R. 2 With a value as high as 0.99, surface chemisorption dominates the entire adsorption process.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions 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 method for preparing an adsorbent, characterized in that, include: The product was prepared by modifying a hydrophilic group using a thiol-olefin click reaction with a covalent organic framework material as a raw material; the hydrophilic group was selected from carboxyl groups. The covalent organic framework material includes compounds with the following structural formulas: 。 2. The method for preparing the adsorbent according to any one of claims 1, characterized in that, include: It is obtained by reacting covalent organic framework materials, 2,2-azobisisobutyronitrile and 3-mercaptopropionic acid as the main raw materials under heating conditions.

3. The method for preparing the adsorbent according to any one of claims 2, characterized in that, The mass ratio of covalent organic framework material to 2,2-azobisisobutyronitrile is (10~11):(1~1.5). And / or, the mass-to-volume ratio of covalent organic framework material to 3-mercaptopropionic acid is (100~110):(4~5).

4. The method for preparing the adsorbent according to any one of claims 1 to 3, characterized in that, The specific surface area of ​​the covalent organic framework material is 800 m². 2 / g or more, pore volume is 0.45cm³ 3 / g or more, with pore sizes below 3nm accounting for more than 95%; Preferably, the compound forms an antiparallel AA stacked structure.

5. The method for preparing the adsorbent according to claim 4, characterized in that, The preparation method of the covalent organic framework material includes: using trialdehyde phloroglucinol and 2,5-bis(allyloxy)terephthalohydrazide as raw materials, and synthesizing them by a solvothermal method.

6. The method for preparing the adsorbent according to claim 5, characterized in that, The covalent organic framework material was obtained by catalytic reaction in a solvent composed of mesitylene and 1,4-dioxane. Preferably, the catalyst is selected from acetic acid.

7. The method for preparing the adsorbent according to claim 5, characterized in that, The mass ratio of the trialdehyde phloroglucinol and 2,5-bis(allyloxy)terephthalohydrazide is 1:(1.4~1.5). And / or, the volume ratio of the trimethylbenzene and 1,4-dioxane is 1:0.5~1.5; And / or, the catalyst is an aqueous solution of acetic acid with a concentration of 5 M or higher, and the volume ratio of mesitylene to the aqueous solution of acetic acid is 1:0.1~0.3; And / or, the mass-to-volume ratio of the trialdehyde phloroglucinol and the mesitylene is 15-25 mg: 1 mL.

8. The adsorbent prepared by the method of any one of claims 1 to 7, characterized in that, The specific surface area of ​​the adsorbent is 40 m². 2 / g or more, pore volume is 0.05cm³ 3 / g or more, with pore sizes below 1.5nm accounting for more than 95%; Preferably, the adsorbent is in the form of porous nanofibers.

9. The adsorbent according to claim 8, characterized in that, The adsorbent contains a compound with the structural formula shown below: 。 10. The application of the adsorbent prepared by the method according to any one of claims 1 to 7, or the adsorbent according to claim 8 or 9, in uranium extraction from seawater, characterized in that, The adsorbent adsorbs uranyl ions in seawater through chemical adsorption. Preferably, the adsorbent has an adsorption capacity of uranyl ions of 500 mg / g or higher; Preferably, the mass-to-volume ratio of the adsorbent to the seawater is 0.2 g: 1 L or more; Preferably, the uranium content in the seawater is 2 ppm or higher.

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