A 2D cofs material based on flexible building blocks and preparation method and application thereof

Abstract

The application provides a 2D COFs material based on a flexible building block and a preparation method and application thereof. A novel 2D COFs material is prepared by using a flexible monomer and p-phenylenediamine or a p-phenylenediamine derivative, wherein the flexible monomer is 4,4',4''-((1,3,5-triazine-2,4,6-triyl)tris(oxy))tritolylbenzaldehyde. The 2D COFs material prepared by the application has a large specific surface area, excellent thermal stability and chemical stability; meanwhile, the 2D COFs material has very excellent adsorption capacity, adsorption rate and adsorption selectivity to thorium, and high-efficiency adsorption to thorium under a strong acid condition is also achieved. Therefore, the 2D COFs based on the flexible building block prepared by the application can be used as an excellent solid adsorption material and applied to selective adsorption and separation of thorium.

Description

Technical Field

[0001] This invention relates to the field of materials, and in particular to a 2D COFs material based on flexible building blocks, its preparation method, and its application. Background Technology

[0002] Nuclear energy is a low-carbon, stable, efficient, and clean energy source with advantages such as controllable reaction, stable energy output, and high energy payback rate, and it is not limited by geographical or natural environment. However, with the large-scale development and utilization of nuclear power, the shortage of traditional uranium resources has prompted humanity to accelerate the search for sustainable and reliable alternative energy technologies. Thorium, as a potential nuclear energy resource, has a natural abundance 3 to 4 times that of uranium and is expected to replace the increasingly scarce uranium resources as the main fuel for future nuclear reactors. Therefore, thorium reactors are also known as the ultimate energy solution before nuclear fusion. Currently, the world's first fourth-generation nuclear energy technology, the thorium-based lava reactor, has been successfully tested in Wuwei, Gansu, my country, representing a groundbreaking technological innovation in the field of nuclear power.

[0003] Thorium can be isolated from minerals such as monazite and thorium ore, but thorium ore typically coexists with rare earth elements and uranium. Furthermore, nuclear fuel is not completely consumed during the "burning" process in a reactor; it still contains a large amount of unfissified uranium and generated nuclear materials such as plutonium and thorium that can be used for fission, as well as highly radioactive fission products. For safety, environmental protection, and energy reuse purposes, spent fuel must be reprocessed. However, due to their extremely similar chemical properties, separating thorium from rare earth elements and uranium is quite challenging.

[0004] Adsorption is considered an effective separation method, offering advantages such as simple operation, minimal secondary waste, and selective adsorption of target nuclides, and has attracted increasing attention in the separation of radionuclides. However, the weak stability, low adsorption capacity, and low selectivity of current adsorbent materials remain major bottlenecks restricting the development of this technology. Therefore, there is an urgent need to develop novel solid-state adsorbents with high adsorption capacity and high adsorption selectivity for thorium.

[0005] Covalent organic frameworks (COFs) are a class of regularly ordered crystalline porous polymer materials composed of organic monomer molecules linked by covalent bonds, possessing advantages such as porosity and structural designability. Due to their diverse topologies, regular channels, and large specific surface area, COFs show great potential in the adsorption and separation of metal ions. Currently, COFs are mainly used for the adsorption and separation of organic dyes, heavy metals, or gases.

[0006] In the field of thorium adsorption, currently used COFs materials are all linked by imine bonds, which have a certain affinity for thorium. However, imine-linked COFs materials are only suitable for weakly acidic or neutral conditions, and their adsorption capacity is limited, falling far short of the saturation adsorption capacity of the COF adsorption sites themselves. Furthermore, the adsorption selectivity needs to be significantly improved. Therefore, there is an urgent need to develop a new 2D COF material to solve these problems. Summary of the Invention

[0007] In view of this, the present invention proposes a 2D COFs material based on flexible building blocks, its preparation method and application.

[0008] Flexible building blocks possess high rotational freedom and scalability. Compared to traditional COFs, COFs based on flexible building blocks often exhibit superior crystal quality and larger lattice sizes. Therefore, expanding their types and properties is of significant research importance.

[0009] The applicant team conducted extensive research and designed and prepared a series of novel 2D COFs materials modified with different functional groups for the adsorption of thorium. They achieved efficient and highly selective adsorption and separation under strong acid conditions. The prepared materials also have very fast adsorption rates, ultra-high adsorption capacity, and excellent recyclability.

[0010] The technical solution of this invention is implemented as follows:

[0011] A 2D COFs material based on flexible building blocks, the structure of which is shown in equation (1):

[0012]

[0013] In formula (1), R is at least one of H, OMe, COOH, and SO3H.

[0014] The synthetic route of the 2D COFs material based on flexible building blocks in this invention is as follows:

[0015]

[0016] The present invention utilizes a flexible monomer and p-phenylenediamine or a p-phenylenediamine derivative to prepare the above-mentioned 2D COFs material, wherein the flexible monomer is 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde.

[0017] This invention provides a method for preparing 2D COFs materials, comprising the following steps: adding a flexible monomer and monomer B into a Piezx tube, wherein the flexible monomer is 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde, and monomer B is p-phenylenediamine or a p-phenylenediamine derivative; adding an organic solvent; ultrasonicating to ensure thorough mixing; then adding a catalyst; subsequently freezing in a liquid nitrogen bath; repeatedly evacuating and purging with nitrogen; sealing the tube with a flame gun; heating and crystallizing in an oven; washing with an anhydrous solvent and drying under vacuum; and finally obtaining a 2D COFs material of flexible building blocks.

[0018] Furthermore, the flexible monomer is 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde.

[0019] Furthermore, the p-phenylenediamine derivatives include 2,5-dimethoxy-p-phenylenediamine, 2,5-diamino-1,4-phenylenediic acid, and 2,5-diamino-1,4-phenylenedisulfonic acid.

[0020] Furthermore, the molar ratio of monomer B to flexible monomer is 1 to 3:1.

[0021] Furthermore, the organic solvent is one of the following: a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:0.5 to 10; a mixed solution of N,N-dimethylacetamide and mesitylene in a volume ratio of 0.5 to 10:1; a mixed solution of o-dichlorobenzene and mesitylene in a volume ratio of 0.5 to 10:1; or a mixed solution of o-dichlorobenzene and n-butanol in a volume ratio of 1 to 10:1.

[0022] Furthermore, the ratio of the total mass of the flexible monomer and monomer B to the volume of the organic solvent is 15.4–56.42 mg: 0.6–4.0 mL.

[0023] Furthermore, the catalyst is a 3-6M acetic acid solution, and the molar ratio of the flexible monomer to the volume of the catalyst is 0.04 mmol: 0.01-0.2 mL.

[0024] Furthermore, the reaction temperature for the heating crystallization is 70–150°C, and the reaction time is 1–5 days. Preferably, the reaction temperature is 120°C–150°C, and the reaction time is 3–5 days. More preferably, the reaction temperature is 120°C, and the reaction time is 3 days.

[0025] Furthermore, the vacuum drying temperature is 90–130°C, and the drying time is 6–18 hours, preferably 10–14 hours.

[0026] Furthermore, the anhydrous solvent is at least one of anhydrous tetrahydrofuran, anhydrous acetone, anhydrous N,N-dimethylformamide, and anhydrous 1,4-dioxane.

[0027] A 2D COFs material based on flexible building blocks is prepared by any one of the preparation methods described in this invention.

[0028] This invention relates to the application of 2D COFs materials based on flexible building blocks in thorium adsorption.

[0029] Furthermore, the pH value of the environment for thorium adsorption is 1.0–6.0.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) This invention utilizes flexible building block monomers and p-phenylenediamine or p-phenylenediamine derivative monomers to prepare 2DCOFs materials for the first time. These materials are then used for the selective adsorption and separation of thorium, solving the problems of low adsorption capacity and poor recyclability of current thorium adsorption materials.

[0032] (2) The 2D COFs material prepared by this invention not only enhances the affinity for thorium, but also greatly improves the adsorption capacity for thorium. At the same time, the COFs material prepared by this invention is easy to recycle and can be reused, avoiding secondary pollution, and shows great potential application value in thorium adsorption and separation.

[0033] (3) The carboxylic acid and sulfonic acid COFs prepared in this invention have for the first time achieved the adsorption of thorium under strong acid conditions (pH=1.0), with an adsorption capacity close to 200 mg / g. Moreover, they have a very fast adsorption rate, reaching adsorption equilibrium in 1 min. At the same time, the 2D COFs based on flexible building blocks prepared in this invention all achieved maximum saturated adsorption capacities close to the theoretical adsorption capacity. In particular, the 2D COF modified with sulfonic acid groups achieved a maximum adsorption capacity of 3138 mg / g for thorium, which is the highest value reported to date.

[0034] (4) The 2D COFs prepared in this invention all have high adsorption selectivity for thorium, especially the 2D COF modified with sulfonic acid groups, which has a separation selectivity for thorium as high as 256, far exceeding the industrial separation requirements. Attached Figure Description

[0035] Figure 1 This is the synthesis route of the flexible building block 2D COFs material according to an embodiment of the present invention;

[0036] Figure 2 PXRD spectra of different functionalized 2D COFs;

[0037] Figure 3FT-IR spectra of different functionalized 2D COFs;

[0038] Figure 4 The adsorption capacity and removal rate of different functionalized 2D COFs at different pH values;

[0039] Figure 5 To assess the recycling performance of thorium adsorption by different functionalized 2D COFs; Detailed Implementation

[0040] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0041] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0042] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0043] The flexible monomer used in Examples 1-4 of this invention is 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde. The flexible monomer 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde (Chem. Mater. 2018, 30, 7, 2299-2308) can be synthesized using methods reported in the literature. p-phenylenediamine, 2,5-diaminoterephthalic acid, 2,5-diaminoterephthalic acid, and 2,5-dimethoxyp-phenylenediamine were purchased.

[0044] The calculation is based on the following formula:

[0045] Adsorption capacity calculation formula:

[0046] Removal rate calculation formula:

[0047] In the formula: q e The adsorption capacity of thorium at adsorption equilibrium is expressed in mg / g.

[0048] C0 is the initial mass concentration of thorium in the solution, in mg / L.

[0049] C e The mass concentration of thorium in the solution at equilibrium, in mg / L.

[0050] V is the volume of the solution, L

[0051] m is the mass of the adsorbent, in grams.

[0052] η represents the removal rate, 100%.

[0053] The present invention discloses a method for preparing 2D COFs materials based on flexible building blocks, comprising the following steps: adding a flexible monomer and monomer B into a Piezx tube, adding an organic solvent, ultrasonically mixing the mixture thoroughly, then adding 0.01-0.2 mL of a 3-6 M acetic acid solution as a catalyst, followed by freezing in a liquid nitrogen bath, repeatedly evacuating and purging with nitrogen, sealing the tube with a flame gun, and then heating and crystallizing in an oven at 70-150°C for 1-5 days. After washing with anhydrous solvent and vacuum drying at 90-130°C for 6-18 hours, the 2D COFs material based on flexible building blocks is finally obtained.

[0054] The aforementioned flexible monomer is 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde, and monomer B is p-phenylenediamine or a p-phenylenediamine derivative, wherein the p-phenylenediamine derivative is 2,5-dimethoxy-p-phenylenediamine, 2,5-diamino-1,4-phthalic acid, or 2,5-diamino-1,4-phenylenedisulfonic acid; the molar ratio of monomer B to the flexible monomer is 1 to 3:1;

[0055] The organic solvent mentioned above is one of the following: a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:0.5 to 10; a mixed solution of N,N-dimethylacetamide and mesitylene in a volume ratio of 0.5 to 10:1; a mixed solution of o-dichlorobenzene and mesitylene in a volume ratio of 0.5 to 10:1; or a mixed solution of o-dichlorobenzene and n-butanol in a volume ratio of 1 to 10:1.

[0056] The ratio of the total mass of the above-mentioned flexible monomer and monomer B to the volume of the organic solvent is 15.4–56.42 mg : 0.6–4.0 mL;

[0057] The anhydrous solvent mentioned above is at least one of anhydrous tetrahydrofuran, anhydrous acetone, anhydrous N,N-dimethylformamide, and anhydrous 1,4-dioxane.

[0058] The synthetic route of 2D COFs materials based on flexible building blocks in this invention is as follows: Figure 1 As shown.

[0059] Example 1 – Preparation method of 2D COFs materials based on flexible building blocks

[0060] 17.66 mg (0.04 mmol) of the flexible monomer and 6.49 mg (0.06 mmol) of p-phenylenediamine were added to a Piezerx tube. 1 mL of a 1:1 mixture of mesitylene and 1,4-dioxane was added, and the mixture was sonicated to ensure thorough mixing. Then, 0.06 mL of a 3M acetic acid solution was added as a catalyst. The tube was then placed in a liquid nitrogen bath for freezing. The tube was repeatedly evacuated and purged with nitrogen three times each, and sealed with a flame gun. It was then heated in a 120 °C oven for crystallization for 3 days. After the reaction was completed, the tube was washed with anhydrous tetrahydrofuran solvent and extracted. The product was then dried under vacuum at 120 °C for 12 h to obtain a yellow powder product, named TPT-PACOF.

[0061] Example 2 – Preparation method of 2D COFs materials based on flexible building blocks

[0062] 17.66 mg (0.04 mmol) of the flexible monomer and 10.09 mg (0.06 mmol) of 2,5-dimethoxy-p-phenylenediamine were added to a Piezerx tube. 2 mL of a mixed organic solvent of N,N-dimethylacetamide and mesitylene in a volume ratio of 8:1 was added, and the mixture was sonicated to ensure thorough mixing. Then, 0.1 mL of a 6M acetic acid solution was added as a catalyst. The tube was then placed in a liquid nitrogen bath for freezing. The tube was repeatedly evacuated and purged with nitrogen three times each, and sealed with a flame gun. The tube was then heated in a 120°C oven for crystallization for 3 days. After the reaction was completed, the tube was washed and soaked in anhydrous tetrahydrofuran and anhydrous acetone, and then dried under vacuum at 120°C for 12 h to obtain a brown powder product, named TPT-PA-OMe COF.

[0063] Example 3 – Preparation method of 2D COFs materials based on flexible building blocks

[0064] 17.66 mg (0.04 mmol) of the flexible monomer and 11.77 mg (0.06 mmol) of 2,5-diaminoterephthalic acid were added to a Piezerx tube. 2 mL of a 3:1 mixture of o-dichlorobenzene and mesitylene was added, and the mixture was sonicated to ensure thorough mixing. Then, 0.1 mL of a 6M acetic acid solution was added as a catalyst. The tube was then placed in a liquid nitrogen bath for freezing. The tube was repeatedly evacuated and purged with nitrogen three times each, and sealed with a flame gun. The tube was then heated in a 120°C oven for crystallization for 3 days. After the reaction was completed, the tube was washed with anhydrous tetrahydrofuran and anhydrous acetone and extracted. The product was then dried under vacuum at 120°C for 12 h to obtain a light green powder product, named TPT-PA-COOH COF.

[0065] Example 4 – Preparation method of 2D COFs materials based on flexible building blocks

[0066] 17.66 mg (0.04 mmol) of the flexible monomer and 16.10 mg (0.06 mmol) of 2,5-diamino-terephthalic acid were added to the corresponding Piercex tubes. 2 mL of a 1:1 mixture of o-dichlorobenzene and n-butanol was added, and the mixture was sonicated to ensure thorough mixing. Then, 0.1 mL of a 6M acetic acid solution was added as a catalyst. The tubes were then placed in a liquid nitrogen bath for freezing. The tubes were repeatedly evacuated and purged with nitrogen three times each, and sealed with a flame gun. The tubes were then heated in a 120°C oven for crystallization for 3 days. After the reaction was completed, the tubes were washed with anhydrous tetrahydrofuran and anhydrous acetone and extracted. The tubes were then dried under vacuum at 120°C for 12 h to obtain a dark brown powder product, named TPT-PA-SO3HCOF.

[0067] like Figure 1 The synthetic route for 2D COFs has been described in detail above; Figure 2 The powder X-ray diffraction pattern of the synthesized 2D COFs confirms that the method of this invention has successfully synthesized novel organic porous materials modified with different functional groups.

[0068] like Figure 3 The Fourier transform infrared spectrum of the synthesized 2D COFs shows that the C=N bond stretching vibration peaks were observed in all 2D COFs modified with different functional groups, indicating that the Schiff base condensation reaction between the two monomers successfully formed an imine linker bond.

[0069] Example 5 – Adsorption performance of thorium on the prepared flexible building block 2D COFs material

[0070] Adsorption experiments were conducted on the 2D COFs materials prepared in Examples 1, 2, 3, and 4 at different pH values ​​(pH range 1.0–6.0), with an initial thorium solution concentration of 100 mg / L, a solid-liquid ratio of 1:3, and an adsorption time of 24 h. The experimental results are as follows: Figure 4 As shown. The materials in Examples 1, 2, 3, and 4 all reached a saturated adsorption capacity of 300 mg / g at pH 4.0. Under strongly acidic conditions at pH 1.0, Examples 3 and 4 still exhibited high adsorption capacities for thorium, approaching 200 mg / g.

[0071] Adsorption kinetics experiments were conducted on the 2D COFs materials prepared in Examples 1, 2, 3, and 4. The initial concentration of thorium solution was 100 mg / L, the solid-liquid ratio was 1:3, the pH was 4.0, and the adsorption time was 0–1800 min. The experimental results are shown in Table 1. It can be seen that the adsorption equilibrium time of Examples 3 and 4 was the fastest.

[0072] Table 1 Adsorption kinetics of thorium by different functionalized 2D COFs

[0073]

[0074] Adsorption isotherm tests were conducted on the 2D COFs materials prepared in Examples 1, 2, 3, and 4. The initial concentration of the thorium solution ranged from 25 to 600 mg / L, the solid-liquid ratio was 1:6, the pH was 4.0, and the adsorption time was 24 h. The experimental results are shown in Table 2. The maximum saturated adsorption capacity of the materials in Examples 1, 2, 3, and 4 were very close to the theoretical adsorption capacity. Among them, the material in Example 4 exhibited the best adsorption performance, with an adsorption capacity of 3138 mg / g.

[0075] Table 2 Saturated adsorption capacity of thorium for different functionalized 2D COFs

[0076]

[0077] Multi-component adsorption selectivity experiments were conducted on the 2D COFs materials prepared in Examples 1, 2, 3, and 4. Different competing ions (such as uranium, lanthanum, praseodymium, lutetium, gadolinium, samarium, and rubidium) were coexisted with thorium in a mixed solution. The concentrations of both the competing ions and thorium were 100 mg / L, the solid-liquid ratio was 1:3, the pH was 4.0, and the adsorption time was 24 h. The adsorption capacity for the multi-component elements was measured using ICP-OES (inductively coupled plasma optical emission spectrometry). The experimental results are shown in Table 3. The thorium and uranium separation selectivity (SF6) of the material in Example 1... Th / U The adsorption capacity was 6.9, indicating almost no adsorption of lanthanum, praseodymium, lutetium, gadolinium, samarium, and rubidium. Example 2: SF6 of the material. Th / U The adsorption capacity is 11.5, indicating almost no adsorption of lanthanum, praseodymium, lutetium, gadolinium, samarium, and rubidium. Example 3 material SF Th / U The adsorption rate was 54.9, indicating almost no adsorption of lanthanum, praseodymium, lutetium, gadolinium, samarium, and rubidium. Example 4: SF6 material Th / U The separation selectivity was 256.0, with almost no adsorption of lanthanum, praseodymium, lutetium, gadolinium, samarium, and rubidium. Therefore, the 2D COFs materials based on flexible building blocks prepared in this invention can achieve selective adsorption and separation of thorium, especially the sulfonic acid group-modified 2D COF material (TPT-PA-SO3H COF) prepared in Example 4, which exhibits extremely high adsorption selectivity and affinity for thorium.

[0078] Table 3. Thorium and uranium separation selectivity of materials in Examples 1-4 (SF) Th / U

[0079]

[0080] The 2D COFs materials prepared in Examples 1, 2, 3, and 4 were subjected to recycling performance experiments. The adsorbed flexible building block 2D COFs materials were eluted with 0.1M HNO3. The experimental results are as follows. Figure 5As shown, the adsorption capacity of the COFs material remains almost unchanged after five cycles, indicating that the adsorbent material of the present invention has strong cycle stability and high reusability.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that the flexible monomer 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde (TPT) is replaced with another flexible monomer: 2,4,6-tris(4-vinylbenzoyl)-1,3,5-triazine (TVBT). All other operations are the same as in Example 1.

[0083] The results are shown in Table 4. Compared with the TPT-PA COF material prepared in Example 1, the adsorption capacity of TVBT-PA-COF material prepared in Comparative Example 1 for thorium ions is significantly reduced.

[0084] Table 4

[0085]

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the flexible monomer 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde (TPT) is replaced with another flexible monomer: 4,4',4”,4”-((benzene-1,2,4,5-tetramethyltetra(methylene))tetra(oxy)tetrabenzaldehyde (TFMB). All other operations are the same as in Example 1.

[0088] The results are shown in Table 5. Compared with the TPT-PA COF material prepared in Example 1, the adsorption capacity of TFMB-PA-COF material prepared in Comparative Example 2 for thorium ions decreased significantly.

[0089] Table 5

[0090]

[0091] Comparative Example 3

[0092] The difference from Example 3 is that the 2,5-diaminoterephthalic acid monomer is replaced with 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid. All other operations are the same as in Example 3.

[0093] The results are shown in Table 6. The adsorption performance of the prepared material (TPT-2PA-COOH COF) for thorium ions decreased significantly.

[0094] Table 6

[0095]

[0096] 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. An application of a 2D COFs material based on flexible building blocks in thorium adsorption, wherein the structure of the 2D COFs is as follows (1): （1）， In formula (1), R is at least one of H, OMe, COOH, and SO3H.

2. The application according to claim 1, characterized in that, The preparation method of the 2D COFs material based on flexible building blocks includes the following steps: adding a flexible monomer and monomer B into a Piezx tube, wherein the flexible monomer is 4,4',4''-((1,3,5-triazine-2,4,6-triyl)tri(oxy))tribenzaldehyde, and monomer B is p-phenylenediamine or a p-phenylenediamine derivative; adding an organic solvent; ultrasonicating to mix thoroughly; then adding a catalyst; subsequently freezing in a liquid nitrogen bath; repeatedly evacuating and purging with nitrogen; sealing the tube with a flame gun; heating and crystallizing in an oven; washing with an anhydrous solvent and heating and vacuum drying; and finally obtaining the 2D COFs material based on flexible building blocks.

3. The application according to claim 2, characterized in that, The p-phenylenediamine derivatives include 2,5-dimethoxy-p-phenylenediamine, 2,5-diamino-1,4-phenylenediic acid, and 2,5-diamino-1,4-phenylenedisulfonic acid; the molar ratio of monomer B to the flexible monomer is 1 to 3:

1.

4. The application according to claim 2, characterized in that, The organic solvent is one of the following: a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:0.5 to 10; a mixed solution of N,N-dimethylacetamide and mesitylene in a volume ratio of 0.5 to 10:1; a mixed solution of o-dichlorobenzene and mesitylene in a volume ratio of 0.5 to 10:1; or a mixed solution of o-dichlorobenzene and n-butanol in a volume ratio of 1 to 10:

1.

5. The application according to claim 2 or 4, characterized in that, The ratio of the total mass of the flexible monomer and monomer B to the volume of the organic solvent is 15.4–56.42 mg: 0.6–4.0 mL.

6. The application according to claim 2 or 3, characterized in that, The catalyst is a 3-6 M acetic acid solution, and the molar ratio of the flexible monomer to the volume of the catalyst is 0.04 mmol: 0.01-0.2 mL.

7. The application according to claim 2, characterized in that, The reaction temperature for heating crystallization is 70–150 °C, and the reaction time is 1–5 days; the temperature for vacuum drying is 90–130 °C, and the drying time is 6–18 h.

8. The application according to claim 2, characterized in that, The anhydrous solvent is at least one of anhydrous tetrahydrofuran, anhydrous acetone, anhydrous N,N-dimethylformamide, and anhydrous 1,4-dioxane.

9. The application according to claim 1, characterized in that, The pH range for thorium adsorption is 1.0–6.0.

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