Thorium adsorption COF material with ultrahigh thorium-uranium separation selectivity and preparation method

Abstract

The invention provides a thorium adsorption COFs material with ultrahigh thorium-uranium separation selectivity and a preparation method, and relates to the technical field of material chemistry. The method comprises the following steps: mixing adamantane with a tetrahedral structure and a pyrene monomer in a sample bottle, then adding a catalyst, sealing by using filter paper with air holes, and crystallizing in a supercritical carbon dioxide reactor to finally obtain the solid thorium adsorption COFs material. The COFs material prepared by the invention has a double-layer interpenetrating pt structure, a large specific surface area, an ion diffusion channel with a specific size, and adsorption sites with high affinity to thorium. The material can quickly adsorb and separate thorium from an aqueous solution, and the thorium / uranium separation factor exceeds 200.

Description

Technical Field

[0001] The present invention relates to the technical field of material chemistry, and particularly relates to a thorium-adsorbing COF material with ultra-high thorium / uranium separation selectivity and a preparation method thereof. Background Art

[0002] As a safe, economic, and efficient clean energy source, nuclear energy is an important choice for humans to address energy security and an important option for achieving carbon neutrality. In the booming development of the nuclear industry, the demand for nuclear fuel by humans has been increasing continuously. Due to the rich thorium mineral resources, the development of a new thorium-based molten salt reactor using thorium as nuclear fuel has become increasingly prominent. In the processes of thorium resource extraction, utilization, treatment, and recycling, thorium-containing wastewater will inevitably be generated. As a radioactive heavy metal element, the direct discharge of thorium not only poses a serious threat to the ecological environment but also causes serious waste of nuclear fuel resources. In addition, 228 Th and its daughter products 212 Bi and 208 Tl will release strong γ radiation during the β decay process. Therefore, researching and developing efficient capture technologies for radioactive thorium is of great practical significance, which will directly affect the health of the ecological environment and the development of human society.

[0003] Due to its simple operation, low cost, and high efficiency, the adsorption method shows great application prospects in the large-scale treatment of thorium-containing wastewater. Currently, there are many research reports on the adsorption and recovery of thorium from aqueous solutions using metal-organic framework materials (MOFs). However, the stability of MOFs materials is poor, and their framework adsorption sites usually bind competitive ions such as uranyl, so the adsorption selectivity for thorium is poor.

[0004] Covalent Organic Frameworks (COFs) are a class of novel crystalline porous polymers formed by covalently linking organic precursors. They not only have the advantages of MOFs materials, such as regular structure, large specific surface area, and easy functionalization modification of the framework, but also have more potential bonding modes, excellent thermal stability, and chemical stability. Therefore, COFs materials are expected to show greater application potential in thorium adsorption and separation.

[0005] COF materials can be divided into two-dimensional (2D) COFs and three-dimensional (3D) COFs according to their dimensions. Different from the layered stacking structure of 2D COFs, 3D COFs are constructed with three-dimensional structural units and can form a zeolite-like interpenetrating topological structure with a higher specific surface area, which not only significantly increases the adsorption area and accessibility of adsorption sites of the material, but also forms a more abundant pore structure and diffusion channels of specific sizes due to its three-dimensional configuration, enabling effective selective adsorption of specific metal ions. Therefore, the research and development of a new type of 3D COF material with high thorium / uranium separation selectivity for the adsorption and recovery of thorium is of great scientific research significance for the sustainable development of nuclear energy. Summary of the Invention

[0006] In view of this, the present invention provides a thorium-adsorbing COF material with ultra-high thorium / uranium separation selectivity and a preparation method thereof.

[0007] The present invention uses an amine unit containing adamantane and a pyrene aldehyde unit as structural units to prepare a 3D COF material with thorium adsorption. This COF material exhibits excellent adsorption performance in capturing and separating radioactive thorium from aqueous solutions.

[0008] The technical solution of the present invention is realized as follows:

[0009] A thorium-adsorbing COF material, the structural formula of the COF material is shown in formula (1):

[0010]

[0011] The COFs material prepared by the present invention has a double-layer interpenetrating pts structure, a large specific surface area, ion diffusion channels of specific sizes, and adsorption sites with high affinity for thorium.

[0012] The present invention provides a preparation method of a thorium-adsorbing COF material, comprising the following steps: adding an adamantane monomer, a pyrene monomer and a catalyst into a sample bottle, then ultrasonicating for 2 - 3 min to form a uniform suspension, sealing the sample bottle mouth with a filter paper with air holes, and then putting it into a supercritical carbon dioxide reactor for heating and crystallization. After the reaction is completed, the sample bottle is taken out, washed with a solvent and subjected to Soxhlet extraction, and dried in vacuum to obtain the thorium-adsorbing COF material.

[0013] Further, the adamantane monomer is 1,3,5,7-tetra(4-benzylamino)adamantane; the pyrene monomer is 1,3,6,8-tetra(p-formylphenyl)pyrene; the molar ratio of 1,3,5,7-tetra(4-benzylamino)adamantane to 1,3,6,8-tetra(p-formylphenyl)pyrene monomer is 1:0.5 - 16.

[0014] Further, the ratio of the total mass of the adamantane monomer and the pyrene monomer to the catalyst volume is 20 - 100 mg: 1 - 6 mL; the catalyst is a 3 - 9 M acetic acid solution. Further still, the catalyst is preferably a 3 - 6 M acetic acid solution.

[0015] Further, the ultrasonic time is 2 - 3 min.

[0016] Further, the reaction temperature for the heating crystallization is 45 - 100 °C, the pressure is 5 - 11 Mpa, and the reaction time is 1 - 24 h; preferably, the reaction temperature is 60 - 70 °C, and the reaction time is 1.5 - 2.5 h; more preferably, the reaction temperature is 65 °C, and the reaction time is 2 h.

[0017] Further, the temperature for the vacuum drying is 60 - 120 °C, and the drying time is 3 - 20 h.

[0018] Further, the solvent is at least one of tetrahydrofuran, acetone, N,N-dimethylformamide, and 1,4-dioxane; the solvent for Soxhlet extraction is tetrahydrofuran, and the Soxhlet extraction time is 6 - 24 h, preferably 10 - 14 h, and more preferably 12 h.

[0019] Application of a thorium-adsorbing COF material or a COF material prepared by the preparation method described in any one of the above as a solid adsorbent in thorium adsorption.

[0020] Further, the ratio of the mass of the COF material to the volume of the thorium ion solution is 1:2 - 6 mg / mL.

[0021] Further, the pH value of the adsorbed thorium solution is 3.0 - 5.0.

[0022] Further, the adsorption temperature is 20 - 35 °C, the stirring speed is 150 - 550 rpm, the adsorption time is 0 - 60 min, and the initial concentration of thorium ions is 25 - 350 ppm.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) Most COFs are prepared by the solvothermal method, which requires a long reaction time, especially for 3D COFs, hindering their practical applications. The present invention for the first time uses the supercritical method to synthesize a 3D thorium-adsorbing COF material from 1,3,5,7-tetra(4-benzylamino)-adamantane monomer and 1,3,6,8-tetra-(p-formylphenyl)-pyrene monomer. This method greatly shortens the reaction time and provides a new idea for the rapid synthesis of 3D COF materials.

[0025] (2) The thorium-adsorbing COF material prepared by the present invention has an ultra-fast adsorption rate, and the adsorption equilibrium can be reached within 20 min.

[0026] (3) The thorium-adsorbing COF material prepared by the present invention has a specific pore size formed by its double-layer interpenetrating pts structure, has a high shape-selective effect on thorium, and the abundant N sites in the framework have a unique affinity for thorium, making its thorium / uranium separation factor exceed 200. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a synthetic route diagram of the thorium-adsorbing COFs material in the embodiment of the present invention.

[0028] Figure 2 It is the PXRD spectrum of the thorium-adsorbing COFs material; in the figure, Experimental: experimental data; Refinement: refined curve (XRD spectrum line fitted by structure refinement); Difference: difference curve (the difference between experimental data and refined results); Calculation: theoretical calculation curve (XRD peak positions simulated based on the crystal structure model).

[0029] Figure 3 It is a schematic diagram of the interpenetrating structure model of the thorium-adsorbing COFs material;

[0030] Figure 4 It is the FT-IR spectrum of the thorium-adsorbing COFs material; in the figure, Wavenumber: wave number; Transmittance: transmittance.

[0031] Figure 5 It is the nitrogen adsorption-desorption curve and pore size distribution diagram of the thorium-adsorbing COFs material; in the figure, Adsorption: adsorption curve; Desorption: desorption curve; Relative Pressure: relative pressure (the ratio of the actual pressure to the saturated vapor pressure); N 2 uptake: nitrogen adsorption amount; Pore width: pore width.

[0032] Figure 6 It is the SEM image of the thorium-adsorbing COFs material.

[0033] Figure 7 It is the adsorption amount diagram of the thorium-adsorbing COFs material at different pH values.

[0034] Figure 8 It is the adsorption kinetics diagram of the thorium-adsorbing COFs material.

[0035] Figure 9 It is the adsorption isotherm diagram of the thorium-adsorbing COFs material.

[0036] Figure 10 It is the competitive ion selectivity diagram of the thorium-adsorbing COFs material. Detailed implementation manners

[0037] To better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0038] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0039] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can all be obtained from commercial channels.

[0040] The adamantane monomer used in Embodiments 1-3 of the present invention is 1,3,5,7-tetra(4-benzylamino)-adamantane, which is a commercially available raw material; the pyrene aldehyde monomer is 1,3,6,8-tetra(p-formylphenyl)-pyrene, which is a commercially available raw material.

[0041] 1,3,5,7-tetra(4-benzylamino)-adamantane is abbreviated as TAM);

[0042] 1,3,6,8-tetra(p-formylphenyl)-pyrene is abbreviated as TFP.

[0043] The calculation is based on the following formula:

[0044] Adsorption capacity calculation formula:

[0045] Removal rate calculation formula:

[0046] In the formula: q e is the adsorption capacity of thorium at adsorption equilibrium, mg / g

[0047] C 0 is the mass concentration of thorium in the initial solution, mg / L

[0048] C e is the mass concentration of thorium in the solution at equilibrium, mg / L

[0049] V is the volume of the solution, L

[0050] m is the mass of the adsorbent, g

[0051] η is the removal rate, 100%

[0052] A preparation method of a thorium-adsorbing COFs material of the present invention includes the following steps: Add adamantane monomer, pyrene monomer and a catalyst (i.e., 3-9M acetic acid solution) into a 5 mL sample bottle. Then, ultrasonicate the sample bottle for 2-3 min to form a uniform suspension. Seal the bottle mouth with a filter paper with air holes, and then place it in a supercritical carbon dioxide reactor at 45-100 °C and a pressure of 5-11 Mpa for crystallization for 1-24 h. After the reaction is completed, take out the sample bottle, wash it with a solvent and purify it by Soxhlet extraction for 6-24 h, and heat it to 60-120 °C for vacuum drying for 3-20 h to obtain a 3D COF material.

[0053] The above-mentioned adamantane monomer is 1,3,5,7-tetra(4-benzylamino)-adamantane (TAM), and the pyrene monomer is 1,3,6,8-tetra(p-formylphenyl)-pyrene (TFP); the molar ratio of 1,3,5,7-tetra(4-benzylamino)-adamantane to 1,3,6,8-tetra(p-formylphenyl)-pyrene is 1:0.5-16.

[0054] The ratio of the total mass of the above reaction monomers to the volume of the catalyst is 20-100 mg: 1-6 mL.

[0055] The above solvent is at least one of tetrahydrofuran, acetone, N,N-dimethylformamide, and 1,4-dioxane.

[0056] The above Soxhlet extraction solvent is tetrahydrofuran.

[0057] The synthesis route of a thorium-adsorbing COF material in an embodiment of the present invention is as Figure 1 shown.

[0058] Example 1 A preparation method of a novel thorium-adsorbing COFs material

[0059] Add 25.0 mg (0.05 mmol) of 1,3,5,7-tetra(4-benzylamino)-adamantane monomer, 30.9 mg (0.05 mmol) of 1,3,6,8-tetra(p-formylphenyl)-pyrene monomer and 1.0 mL of 6M acetic acid solution as the catalyst into a 5 mL sample bottle. Then, ultrasonicate the sample bottle for 2 min to form a uniform suspension. Seal the bottle mouth with a filter paper with air holes, and place it in a supercritical carbon dioxide reactor. The reaction temperature is 65 °C, the pressure is 8.5 Mpa, and the reaction time is 2 h. After the reaction is completed, take out the sample bottle, wash it repeatedly with tetrahydrofuran solvent and purify it by Soxhlet extraction with tetrahydrofuran for 12 h, and then vacuum dry it at 100 °C for 12 h. Finally, obtain 3D TAM-TFP COF, which is a yellow powder product.

[0060] Figure 1 For the synthesis route of TAM-TFP COF, the synthesis steps have been specifically described above; Figure 2Powder X-ray diffraction (PXRD) pattern of the synthesized TAM-TFPCOF. It can be seen that the highly crystalline pure-phase COF material was successfully prepared by the method of the present invention. Figure 3 Schematic diagram of the interpenetrating structure model of TAM-TFPCOF drawn by structural analysis. Its simulated XRD curve is consistent with the experimental test curve, confirming that TAM-TFPCOF has a bilayer interpenetrating pts structure.

[0061] Figure 4 Fourier transform infrared spectroscopy (FT-IR) of TAM-TFPCOF. It can be seen from the figure that obvious stretching vibration peaks of C=N bonds appear in this material, and the infrared absorption peaks corresponding to aldehyde groups and amino groups in the raw materials disappear, indicating that the Schiff base polycondensation reaction between the two monomers successfully occurs to form imine covalent bonds.

[0062] Figure 5 Nitrogen adsorption-desorption isotherm curve and pore size distribution of TAM-TFPCOF. It can be known from the figure that this material has a large specific surface area and small pore size, which is a typical type I isotherm and conforms to the microporous characteristics.

[0063] Figure 6 SEM image of TAM-TFPCOF. It can be seen from the figure that this material has a regular hollow rod-like morphology.

[0064] Adsorption performance experiment of TAM-TFPCOF prepared in Example 2 as an adsorbent for capturing thorium

[0065] Adsorption experiments were carried out on the TAM-TFPCOF prepared in Example 1 in thorium solutions with different pH values. The pH range was 3.0 - 5.0, the initial concentration of the thorium solution was 100 mg / L, the solid-liquid ratio was 1:5 mg / mL, and the adsorption time was 24 h. The experimental results are as Figure 7 shown. The material in Example 1 has excellent adsorption ability for thorium ions when pH ≥ 4.0.

[0066] Adsorption kinetics experiment was carried out on the TAM-TFPCOF prepared in Example 1. The initial concentration of the thorium solution was 100 mg / L, the solid-liquid ratio was 1:5, the pH value was 4.0, and the adsorption time was 0 - 60 min. The experimental results are as Figure 8 shown. This material has an ultra-fast adsorption rate and can reach the adsorption equilibrium in 20 min.

[0067] Adsorption isotherm test was carried out on the TAM-TFPCOF prepared in Example 1. The initial concentration of the thorium solution was 25 - 350 mg / L, the solid-liquid ratio was 1:5, the pH value was 4.0, and the adsorption time was 1 h. The experimental results are as Figure 9 shown. This material shows a high saturated adsorption capacity, which can reach 541 mg / g.

[0068] A multi-component adsorption selectivity experiment was conducted on the TAM-TFPCOF prepared in Example 1. Different competing ions (such as uranium, samarium, lanthanum, praseodymium, gadolinium, europium, strontium, neodymium, cesium) coexisted with thorium in a mixed solution. The concentrations of the competing ions and thorium were both 50 mg / L, the solid-liquid ratio was 1:5, the pH value was 4.0, and the adsorption time was 1 h. The experimental results Figure 10 showed that the thorium / uranium separation factor (SF Th / U ) of the material in Example 1 was higher than 200, and there was almost no adsorption of samarium, lanthanum, praseodymium, gadolinium, europium, strontium, neodymium, and cesium. Therefore, the novel thorium-adsorbing COFs material prepared in the present invention can exhibit ultra-high adsorption selectivity and affinity for thorium.

[0069] Comparative Example 1

[0070] The difference from Example 1 was that the supercritical method in Example 1 was changed to the solvothermal method to prepare the 3D TAM-TFPCOF material. The synthesis steps were as follows: 25.0 mg (0.05 mmol) of 1,3,5,7-tetra(4-benzylamino)-adamantane and 30.9 mg (0.05 mmol) of 1,3,6,8-tetra-(p-formylphenyl)-pyrene were added to a Pyrex tube, 1.0 mL of o-dichlorobenzene organic solvent was added, and it was ultrasonically mixed thoroughly. Then 0.1 mL of 6M acetic acid solution as a catalyst was added. Subsequently, it was placed in a liquid nitrogen bath for freezing, evacuated and filled with nitrogen three times each, and sealed with a blowtorch. It was placed in an oven at 160 °C for crystallization for 5 days. After the reaction, it was washed repeatedly with tetrahydrofuran and N,N-dimethylformamide solvents and soaked in tetrahydrofuran for 1 d, and then vacuum dried at 120 °C for 3 h. Finally, the pure phase 3D TAM-TFPCOF was obtained.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that the amino monomer and aldehyde monomer in Example 1 are replaced with 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tris(oxy))tribenzaldehyde (TPT) monomer and 2,5-diamino-1,4-dihydroxybenzene (TH) monomer, and an imine bond-linked 2D COF material is prepared by a solvothermal method. The synthesis steps are as follows: 17.66 mg (0.04 mmol) of 4,4',4”-((1,3,5-triazine-2,4,6-triyl)tris(oxy))tribenzaldehyde monomer and 8.41 mg (0.06 mmol) of 2,5-diamino-1,4-dihydroxybenzene are added to a Pyrex tube, 2 mL of a mixed organic solvent of N,N-dimethylacetamide and mesitylene with a volume ratio of 8:1 is added, and it is ultrasonically mixed evenly. After adding 0.1 mL of 6 M acetic acid solution as a catalyst, it is frozen in a liquid nitrogen bath, evacuated and filled with nitrogen three times repeatedly, sealed with a flame gun under a vacuum atmosphere, heated and crystallized in an oven at 120 °C for 3 days. After the reaction is completed, it is washed with anhydrous tetrahydrofuran and anhydrous acetone solvents and Soxhlet extracted overnight, and then vacuum dried at 120 °C for 12 h. Finally, a black powder product is obtained, named 2D TPT-TH COF.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that the amino monomer and aldehyde monomer in Example 1 are replaced with 2,4,6-trimethyl-1,3,5-triazine (TMT) monomer and terephthalaldehyde (DFB) monomer, and a double bond-linked 2D COF material is prepared by a solvothermal method. The synthesis steps are as follows: 2,4,6-trimethyl-1,3,5-triazine (TMT) (6.15 mg), terephthalaldehyde (DFB) (10.05 mg), dimethyltoluene (0.5 mL), methanol (3.5 mL) and sodium hydroxide (8.75 mg) are successively added to a 10 mL Pyrex tube and ultrasonically treated for 20 min. Then the Pyrex tube is immersed in liquid nitrogen until the solvent freezes solid. It is evacuated three times under nitrogen protection, and finally the vacuum is reduced to about 5 Pa. The Pyrex tube is flame sealed, cooled to room temperature, and placed in an oven at 180 °C for 5 days. After the reaction is completed, a yellow solid is obtained by filtration, washed 3 times with water and THF, and then soaked in THF for 2 days. After filtration and drying, a yellow powder is obtained, named 2D TMT-DFB COF.

[0075] The multi-component adsorption selectivity experiment tests were carried out on the materials prepared in Comparative Examples 1-3, and the results are shown in Table 1. Compared with the 3D TAM-TFPCOF material prepared by the supercritical method in Example 1, the thorium / uranium separation factor (SF Th / U ) of the materials prepared in Comparative Examples 1-3 decreased significantly, and the adsorption selectivity and affinity for thorium ions decreased significantly.

[0076] Table 1

[0077]

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A thorium adsorption COF material, characterized in that: The structural formula of COF material is shown in formula (1):

2. The method for preparing a thorium adsorption COF material according to claim 1, characterized in that: The following steps are involved: Adamantane monomer, pyrene monomer and catalyst are added to a sample bottle, followed by ultrasound to form a uniform suspension, the mouth of the sample bottle is sealed with filter paper with air holes, and then placed in a supercritical carbon dioxide reactor for heating and crystallization. After the reaction is completed, the sample bottle is taken out, washed with a solvent, extracted, and vacuum dried to obtain a thorium adsorption COF material.

3. The method for preparing a thorium adsorption COF material according to claim 2, characterized in that: The adamantane monomer is 1,3,5,7-tetrakis(4-benzylamino)-adamantane; the pyrene monomer is 1,3,6,8-tetrakis-(p-formylphenyl)-pyrene; and the molar ratio of the 1,3,5,7-tetrakis(4-benzylamino)-adamantane to the 1,3,6,8-tetrakis-(p-formylphenyl)-pyrene monomer is 1:0.5-16.

4. The method for preparing a thorium adsorption COF material according to claim 2, characterized in that: The total mass ratio of the adamantane monomer and the pyrene monomer to the catalyst volume is 20-100 mg: 1-6 mL; and the catalyst is a 3-9 M acetic acid solution.

5. The method for preparing a thorium adsorption COF material according to claim 2, characterized in that: The ultrasonic time is 2 to 3 minutes; the reaction temperature of the heating crystallization is 45 to 100° C., the pressure is 5 to 11 MPa, and the reaction time is 1 to 24 hours; the vacuum drying temperature is 60 to 120° C., and the drying time is 3 to 20 hours.

6. The method for preparing a thorium adsorption COF material according to claim 2, characterized in that: The solvent is at least one of tetrahydrofuran, acetone, N,N-dimethylformamide and 1,4-dioxane; the solvent for extraction is tetrahydrofuran, and the extraction time is 6 to 24 hours.

7. Use of the thorium adsorption COF material according to claim 1 or the COF material prepared by the preparation method according to any one of claims 2 to 6 as a solid adsorbent in thorium adsorption.

8. The use according to claim 9, characterized in that: The mass ratio of the COF material to the volume of the thorium ion solution is 1:2-6 mg / mL.

9. The use according to claim 9, characterized in that: The pH value of the thorium adsorption solution is 3.0-5.

0.

10. The use according to claim 9, characterized in that: The adsorption temperature is 20-35° C., the stirring speed is 150-550 rpm, the adsorption time is 0-60 min, and the initial concentration of thorium ions is 25-350 ppm.

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