Polyamidoxime-covalent organic framework composite material as well as preparation method and application thereof

Abstract

The invention provides a polyamidoxime-covalent organic framework composite material as well as a preparation method and application thereof. The composite material comprises polyamidoxime and covalent organic framework nanosheets, the covalent organic framework nanosheets contain active groups, and the polyamidoxime is connected with the covalent organic framework nanosheets through covalent bonds. Effective dispersion of the polyamidoxime is achieved through the covalent organic framework nanosheet, fiber diameter reduction caused by agglomeration of the polyamidoxime is avoided, the uranium adsorption capacity of the polyamidoxime is improved, meanwhile, the polyamidoxime and the covalent organic framework nanosheet are connected through covalent bonds, connection of the polyamidoxime is firmer and more stable, and the uranium adsorption capacity of the polyamidoxime is improved. Therefore, the mechanical stability of the polyamidoxime is improved, and the uranium adsorption performance of the polyamidoxime is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of uranium adsorption materials, and in particular to a polyamidoxime-covalent organic framework composite material, a preparation method thereof, and an application thereof. Background Art

[0002] The stable development of nuclear energy is inseparable from the continuous supply of nuclear fuel, and the uranium resources in the ocean are 1000 times the total amount of terrestrial uranium resources. Uranium exists in the form of uranyl carbonate in the ocean, and its concentration is only about 3.3 ppb. At the same time, other metal ions in the ocean will also hinder the uranium extraction process. Therefore, screening out suitable functional groups and reducing the preparation cost of materials are the keys to realizing industrial seawater uranium extraction.

[0003] Since the last century, polyamidoxime-based materials have been proven to have the potential for seawater uranium extraction. However, the previous polyamidoxime-based materials generally have a large fiber diameter, which results in a significant reduction in the effective active sites of the materials. Although effective dispersion of the polyamidoxime material can change the aggregation between molecular chains and reduce the final fiber diameter, the materials can only be combined through hydrogen bond interactions inside, resulting in poor mechanical stability and easy phase dispersion in water. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the prior art to some extent. To this end, an object of the present invention is to provide a polyamidoxime-covalent organic framework composite material, a preparation method thereof, and an application thereof.

[0005] In a first aspect of the present invention, a polyamidoxime-covalent organic framework composite material is provided. The composite material includes polyamidoxime and covalent organic framework nanosheets. The covalent organic framework nanosheets contain active groups, and the polyamidoxime is connected to the covalent organic framework nanosheets through covalent bonds.

[0006] According to the above polyamidoxime-covalent organic framework composite material provided by the present invention, which includes polyamidoxime and covalent organic framework nanosheets, since the covalent organic framework nanosheets contain active groups, the polyamidoxime can be connected to the covalent organic framework nanosheets through covalent bonds. The effective dispersion of polyamidoxime is achieved through the covalent organic framework nanosheets, avoiding the reduction of fiber diameter caused by the aggregation of polyamidoxime and improving the uranium adsorption ability of polyamidoxime; at the same time, because the polyamidoxime is connected to the covalent organic framework nanosheets through covalent bonds, the polyamidoxime is connected more firmly and stably, so it is not easy to aggregate, improving the mechanical stability of polyamidoxime and further enhancing the uranium adsorption performance of polyamidoxime.

[0007] According to the polyamidoxime-covalent organic framework composite material provided by the present invention, the active groups include at least one of hydroxyl group, amino group, carboxyl group, and amidoxime group, and preferably the amidoxime group. The presence of the above active groups enables the stable connection between the covalent organic framework nanosheets and polyamidoxime, improving the dispersibility and stability of polyamidoxime.

[0008] It should be noted that in the case where some covalent organic frameworks do not have the above active groups, the covalent organic frameworks can be treated to make them have active groups. For example, for the COF-316 covalent organic framework, which has no active groups, it can be subjected to amidoximation treatment.

[0009] As an example, the amidoximation conditions for COF-316 are as follows: the solvent is tetrahydrofuran, the reagent is 50% aqueous hydroxylamine solution, the reaction temperature is 70 °C, and the reaction time is 3 days.

[0010] Those skilled in the art can understand that for covalent organic frameworks without active groups, those skilled in the art can use existing conventional methods to activate the covalent organic frameworks, and the present invention does not make special limitations on the specific treatment methods.

[0011] According to the polyamidoxime-covalent organic framework composite material provided by the present invention, the mass ratio of polyamidoxime to the covalent organic framework nanosheets is (70-99):(30-1). By controlling the mass ratio of polyamidoxime to the covalent organic framework nanosheets within the above range, the dispersing effect of the covalent organic framework nanosheets can be fully exerted, and the uranium adsorption performance of the composite material can be improved.

[0012] In the second aspect of the present invention, the present invention provides a method for preparing the above polyamidoxime-covalent organic framework composite material, which includes: (1) Dissolving polyamidoxime in an alkaline solution to obtain a polyamidoxime alkaline solution; (2) Mixing and stirring the polyamidoxime alkaline solution with an aqueous solution of covalent organic framework nanosheets to obtain a mixed solution; (3) Freeze-drying the mixed solution and then performing high-temperature treatment.

[0013] According to the preparation method of the above-mentioned polyamidoxime-covalent organic framework composite material provided by the present invention, first, polyamidoxime is dissolved in an alkaline solution to obtain a polyamidoxime alkaline solution, and then the polyamidoxime alkaline solution is mixed and stirred with an aqueous solution of covalent organic framework nanosheets to obtain a mixed solution. Polyamidoxime and covalent organic framework nanosheets are connected together by hydrogen bond self-assembly. Finally, the mixed solution is freeze-dried and then heat-treated at a high temperature. Through high-temperature curing treatment, polyamidoxime and covalent organic framework nanosheets are connected by covalent bonds, thus significantly improving the dispersibility and stability of polyamidoxime, and further improving the uranium adsorption performance of polyamidoxime. And this method provides a new idea for the development and application of polyamidoxime-based uranium extraction materials from seawater.

[0014] According to the preparation method of the above-mentioned polyamidoxime-covalent organic framework composite material provided by the present invention, the concentration of the alkaline solution is 0.1 mol / L - 0.3 mol / L.

[0015] In some embodiments of the present invention, the alkaline solution includes but is not limited to at least one of sodium hydroxide and potassium hydroxide.

[0016] According to the preparation method of the above-mentioned polyamidoxime-covalent organic framework composite material provided by the present invention, the temperature of the mixing and stirring is 20 - 35 °C. It should be noted that the mixing and stirring method is not particularly limited, as long as polyamidoxime and covalent organic framework nanosheets are fully mixed and uniform.

[0017] According to the preparation method of the above-mentioned polyamidoxime-covalent organic framework composite material provided by the present invention, in step (3), the temperature of the high-temperature treatment is 90 °C - 180 °C.

[0018] According to the preparation method of the above-mentioned polyamidoxime-covalent organic framework composite material provided by the present invention, in step (3), the time of the high-temperature treatment is 5 h - 7 h.

[0019] In some embodiments of the present invention, the material after freeze-drying treatment is placed in a tube furnace for high-temperature treatment.

[0020] In some embodiments of the present invention, the time of the freeze-drying treatment is 20 - 30 h.

[0021] In the third aspect of the present invention, the present invention proposes the application of the above-mentioned polyamidoxime-covalent organic framework composite material in uranium adsorption.

[0022] The present invention at least includes the following technical effects: The polyamidoxime-covalent organic framework composite material provided by the present invention comprises polyamidoxime and covalent organic framework nanosheets. Since the covalent organic framework nanosheets contain active groups, polyamidoxime and the covalent organic framework nanosheets can be connected by covalent bonds. The effective dispersion of polyamidoxime is achieved through the covalent organic framework nanosheets, avoiding the reduction of fiber diameter caused by the aggregation of polyamidoxime, and enhancing the uranium adsorption capacity of polyamidoxime. At the same time, because polyamidoxime and the covalent organic framework nanosheets are connected by covalent bonds, polyamidoxime is more firmly and stably connected, thus not easily aggregating, improving the mechanical stability of polyamidoxime, and further enhancing the uranium adsorption performance of polyamidoxime.

[0023] The preparation method of the polyamidoxime-covalent organic framework composite material provided by the present invention connects polyamidoxime and covalent organic framework nanosheets in a covalent bond manner through high-temperature curing treatment, thereby significantly enhancing the dispersion and stability of polyamidoxime, and this method provides a new idea for the development and application of polyamidoxime-based materials for extracting uranium from seawater. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a schematic diagram of the synthesis of COF-316 in Example 1 of the present invention; Figure 2 It is a schematic diagram of the synthesis of COF-316AO in Example 1 of the present invention; Figure 3 It is an SEM image of COF-316AO in Example 1 of the present invention; Figure 4 It is a physical diagram of the polyamidoxime-covalent organic framework composite material in Example 1 of the present invention; Figure 5 It is an SEM image of the polyamidoxime-covalent organic framework composite material prepared in Example 1 of the present invention; Figure 6 It is a representative uranium adsorption kinetics test result diagram of the polyamidoxime-covalent organic framework composite material prepared in Example 1 of the present invention; Figure 7 It is a uranium competitive ion adsorption test result diagram of the polyamidoxime-covalent organic framework composite material prepared in Example 1 of the present invention in real seawater with a 100-fold concentration magnification of the representative element; Figure 8It is the uranium adsorption performance result diagram of the composite materials in Examples 1-3 of the present invention under different heat treatment temperature conditions; Figure 9 It is the uranium adsorption performance result diagram of the composite materials of Examples 1, 4-6 and Comparative Example 1 of the present invention. Specific embodiments

[0026] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The following describes the present invention with reference to specific embodiments. It should be noted that these embodiments are only descriptive and do not limit the present invention in any way.

[0027] Example 1 (1)Preparation of COF-316 covalent organic framework nanosheets Refer to Figure 1 , the carboxyl-modified polyacrylonitrile membrane was first cut into samples with a diameter of 3.5 cm and placed in a self-made diffusion cell with an inner diameter of 3 cm. 2,3,6,7,10,11-Hexahydroxytriphenylene benzene (HHTP, 0.046 mmol) and triethylamine catalyst (3.0 equivalents) were dissolved in the aqueous phase, while tetrafluorophthalonitrile (TFPN, 0.069 mmol) was dissolved in the organic phase. Subsequently, the temperature of the diffusion cell was fixed at 80 °C. After the reaction proceeded for 3 days, COF-316 nanosheets were synthesized in the aqueous phase, and these nanosheets could be easily collected by a dropper. The obtained nanosheet colloidal dispersion was dialyzed in deionized water for 5 days, and then the solution was freeze-dried to obtain a solid. The product was detected by infrared spectroscopy.

[0028] (2)Oximation treatment of COF-316 Reference can be made to Figure 2 , in a 10 mL pressure-resistant tube, pre-prepared COF-316 nanosheets (30.0 mg), anhydrous tetrahydrofuran (THF) (3.0 mL), and hydroxylamine (NH2OH) solution (50 wt% in water) (2.0 mL) were added. The mixture was stirred and heated to 70 °C for 1 day. Subsequently, THF (0.5 mL) and NH2OH solution (0.5 mL) were continuously added, and it was maintained for 1 day under heating and stirring. Finally, NH2OH solution (0.5 mL) was added again, and heating and stirring were continued for 1 day. The mixture was then cooled to room temperature and dialyzed in deionized water for 3 days. Finally, the solution was freeze-dried to obtain the solid product COF-316AO. The product was detected by infrared spectroscopy. The SEM image of COF-316AO can be seen Figure 3 .

[0029] (3)Preparation of polyamidoxime Dissolve hydroxylamine hydrochloride (NH2OH·HCl, 5.5 g) in 60 mL of N,N-dimethylformamide (DMF) solvent in a round-bottom flask and heat it to 45 °C in a water bath under magnetic stirring until completely dissolved. Subsequently, add sodium carbonate (Na2CO3, 3.8 g) and sodium hydroxide (NaOH, 1.0 g) to the mixed solution and continuously stir for at least 180 minutes. Then, add polyacrylonitrile (PAN, 4.2 g) until it is completely dissolved. Next, heat the mixed solution to 65 °C and keep it for 24 hours. After that, add sodium bicarbonate (NaHCO3, 1.9 g) and sodium hydroxide (NaOH, 0.5 g) to the above solution and continuously react at 65 °C for 12 hours. After cooling to room temperature, the mixture is centrifuged (10,000 rpm, 20 minutes). The collected PAO supernatant is then dispersed in deionized water to precipitate white flocculates, which are then dried in a vacuum drying oven at 60 °C for 12 hours. Finally, the prepared PAO powder is collected after grinding.

[0030] (4) Preparation of polyamidoxime-covalent organic framework composite PAO powder (2.5 g) is completely dissolved in an aqueous sodium hydroxide solution (50 mL, 0.15 M). Subsequently, a certain amount of COF-316-AO aqueous solution (1 mg / mL) is uniformly mixed with the PAO mixed solution (50 mg / mL) by magnetic stirring, and the mass ratio of PAO powder to COF-316-AO is 90:10.

[0031] Transfer the above mixed solution (0.6 mL) to a polytetrafluoroethylene (PTFE) mold about 1 mm deep. Then, place the mold on the surface of liquid nitrogen and perform bottom-up directional freeze casting for 5 minutes. Finally, a polyamidoxime-based covalent organic framework composite is obtained through freeze-drying for 48 hours.

[0032] The obtained polyamidoxime-based covalent organic framework composite is heat-treated at 150 °C for 6 hours in a tubular furnace under an argon atmosphere.

[0033] The physical picture of the polyamidoxime-covalent organic framework composite prepared in Example 1 can be seen Figure 4 .

[0034] The SEM picture of the polyamidoxime-covalent organic framework composite prepared in Example 1 can be seen Figure 5 , from Figure 5 it can be known that filamentous polyamidoxime is dispersed on the surface of covalent organic framework nanosheets.

[0035] Example 2 The difference between Example 2 and Example 1 is: (4) Preparation of polyamidoxime-covalent organic framework composite The obtained polyamidoxime-based covalent organic framework composite material was heat-treated at 90 °C for 6 hours in a tubular furnace under an argon atmosphere.

[0036] Example 3 The difference between Example 3 and Example 1 is as follows: (4) Preparation of polyamidoxime-covalent organic framework composite material The obtained polyamidoxime-based covalent organic framework composite material was heat-treated at 120 °C for 6 hours in a tubular furnace under an argon atmosphere.

[0037] Example 4 The difference between Example 4 and Example 1 is as follows: (4) Preparation of polyamidoxime-covalent organic framework composite material The mass ratio of PAO powder to COF-316-AO was 80:20.

[0038] Example 5 The difference between Example 5 and Example 1 is as follows: (4) Preparation of polyamidoxime-covalent organic framework composite material The mass ratio of PAO powder to COF-316-AO was 85:15.

[0039] Example 6 The difference between Example 6 and Example 1 is as follows: (4) Preparation of polyamidoxime-covalent organic framework composite material The mass ratio of PAO powder to COF-316-AO was 95:5.

[0040] Comparative Example 1 The polyamidoxime prepared in Example 1 was used as the adsorption material.

[0041] The properties of the materials in the examples and comparative examples were determined as follows: (1) Uranium adsorption kinetic performance test Accurately weigh 5 mg of the polyamidoxime-based covalent organic framework composite material and add it to 500 mL of pre-prepared 8 ppm simulated seawater. The stirring speed during the adsorption process is 200 rpm, the temperature is 25 °C, and samples are taken at specific intervals to test the change in uranium concentration in the solution.

[0042] For uranium (qt, mg g -1 ) adsorbed in 8 ppm simulated seawater, the adsorption amount calculation formula is as follows: q t (mg·g -1 ) represents the amount of uranium adsorbed at a specific time t; c t (ppm) represents the uranium concentration in the solution at time t; c0 (ppm) represents the initial uranium concentration; m (g) represents the mass of the adsorbent added.

[0043] (2) Testing on the uranium competitive ion adsorption performance Accurately weigh 5 mg of the polyamidoxime-based covalent organic framework composite material and add it to 500 mL of real seawater with the concentrations of six representative elements amplified by 100 times and pre-prepared. The stirring speed during the adsorption process is 200 rpm, and the temperature is 25 °C.

[0044] The test results of the uranium adsorption kinetics performance of the composite material in Example 1 are shown in Figure 6 , from Figure 6 it can be seen that in simulated seawater (pH = 8) with 8 ppm uranium added at room temperature (25 °C), the adsorption capacity of this adsorbent material can reach 275 mg / g within 48 h.

[0045] The test results of the uranium competitive ion adsorption performance of the composite material in Example 1 are shown in Figure 7 , from Figure 7 it can be seen that after the concentrations of six representative elements in real seawater are amplified by 100 times, the polyamidoxime-based covalent organic framework composite material has a higher adsorption capacity for uranium, indicating that the composite material of the present invention has excellent uranium selective adsorption ability.

[0046] The uranium adsorption performance of the composite materials in Examples 1-3 under different heat treatment temperature conditions is shown in Figure 8 , from Figure 8 it can be seen that different heat treatment temperatures of the polyamidoxime-based covalent organic framework composite material will have a certain impact on the final uranium adsorption performance of the composite material. When the heat treatment temperature of Example 1 is 150 °C, the adsorption performance is the best.

[0047] The uranium adsorption performance of the composite materials in Examples 1, 4-6 and Comparative Example 1 is shown in Figure 9 , from Figure 9 it can be seen that compared with using polyamidoxime in Comparative Example 1 as the adsorbent material, the composite material of the present invention can significantly improve the uranium adsorption ability.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A polyamidoxime-covalent organic framework composite material, characterized in that: The invention comprises polyamidoximes and covalent organic framework nanosheets. The covalent organic framework nanosheets contain active groups, and the polyamidoximes are connected with the covalent organic framework nanosheets through covalent bonds.

2. The composite material according to claim 1, characterized in that: The active group includes at least one of a hydroxyl group, an amino group, a carboxyl group, and an amidoxime group.

3. The composite material according to claim 2, characterized in that: The active group is an amidoxime group.

4. The composite material according to claim 3, characterized in that: The covalent organic framework nanosheets include oximated COF-316.

5. The composite material according to any one of claims 1 to 4, characterized in that: The mass ratio of the polyamidooxime to the covalent organic framework nanosheet is (70-99): (30-1).

6. A method for preparing the polyamidoxime-covalent organic framework composite material according to any one of claims 1 to 5, characterized in that: include: (1) dissolving polyamidoximate in an alkaline solution to obtain a polyamidoximate alkaline solution; (2) mixing and stirring the polyamidooxime alkaline solution and the covalent organic framework nanosheet aqueous solution to obtain a mixed solution; (3) freeze-drying the mixed solution and then subjecting it to high temperature treatment.

7. The method according to claim 6, characterized in that: In step (1), the concentration of the alkaline solution is 0.1 mol / L-0.3 mol / L; And / or, the alkaline solution includes at least one of sodium hydroxide and potassium hydroxide.

8. The method according to claim 6, characterized in that: In step (2), the mixing and stirring temperature is 20-35°C.

9. The method according to claim 6, characterized in that: In step (3), the temperature of the high temperature treatment is 90°C-180°C; And / or, the high temperature treatment time is 5h-7h.

10. Use of the polyamidoxime-covalent organic framework composite material according to any one of claims 1 to 5 in uranium adsorption.

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