Preparation method of porous few-layer carbon nitride / aminooxime-based seawater uranium extraction composite material with multi-level structure and material

Abstract

This application discloses a method for preparing a porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure, relating to the field of seawater uranium extraction materials. The composite material is prepared by repeatedly calcining melamine at high temperatures to obtain a porous few-layer carbon nitride material with high photocatalytic performance. Polyacrylonitrile is functionalized with mescapto-oxime to obtain a polymescapto-oxime solution. The porous few-layer carbon nitride is then uniformly dispersed in the polymescapto-oxime solution, and a sacrificial pore-forming agent, polyvinylpyrrolidone, is added to obtain a spinning solution. Finally, a one-step electrospinning technique is used to prepare a porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with high adsorption performance. The resulting composite material exhibits excellent uranium adsorption performance and adsorption rate, is recyclable, and the preparation method is simple and environmentally friendly. The prepared composite material has excellent uranium adsorption performance and adsorption rate, is recyclable, and has broad application prospects in the field of seawater uranium extraction.

Description

Technical Field

[0001] This invention relates to the field of seawater uranium extraction materials, and in particular to a method and material for preparing a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure. Background Technology

[0002] Nuclear energy, as a relatively green energy source, offers an effective way to address global energy shortages and increasingly serious environmental problems through vigorous development of the nuclear power industry. While terrestrial uranium resources, currently the primary fuel for nuclear energy, are not abundant, the ocean contains vast amounts of uranium, approximately 1000 times the amount found on land. Extracting uranium from seawater and developing seawater uranium extraction materials are crucial for securing uranium resources for future nuclear energy development. To achieve high efficiency and economy in seawater uranium extraction, these materials must possess characteristics such as good adsorption capacity and rate, and recyclability.

[0003] Metallo-oxime-based fiber adsorbents have become the most important materials for uranium extraction from seawater due to their excellent affinity for uranium ions and their recyclability. While the adsorption of uranium-containing wastewater using metallo-oxime-based fibers has been reported, the uranium concentration in wastewater is high (typically at the ppm level), while the uranium concentration in seawater is extremely low (~3.3 ppb). Furthermore, uranium-containing wastewater contains toxic pollutants, and uranium exists in various forms (uranates, uranium fluorides, uranium oxides, etc.), while uranium in seawater mainly exists in the form of uranates. Therefore, the materials currently reported for treating uranium-containing wastewater are not suitable for direct application in seawater uranium extraction. In general, metallo-oxime-based materials prepared by existing methods generally suffer from limited adsorption sites and are prone to saturation, thus affecting the adsorption capacity and uranium extraction efficiency. Therefore, there is an urgent need to develop a new, high-performance, and sustainably usable material for seawater uranium extraction.

[0004] The utilization of external resources (such as sunlight) during seawater uranium extraction can make the reaction more economical and sustainable. Chinese patent CN115228500A discloses a highly dispersed C3N4-based seawater uranium extraction composite material and its preparation method, which achieves a uranium removal rate of 89.47% using a 5% Cring-WSGCN photocatalyst. CN118341398B discloses a method for preparing a multifunctional uranium extraction material, in which the prepared carbon nitride-based material reaches reaction equilibrium in approximately 40 minutes, achieving an adsorption capacity of 52.1 mg / g. However, the carbon nitride material exists in powder form, making it difficult to handle and recycle, thus limiting its practical application. Combining powdered adsorbent materials with a polymer matrix overcomes the difficulty of recycling single powdered materials; however, the particle size and content of nanoparticles can cause agglomeration in the polymer. This uneven loading reduces the effective specific surface area of ​​the material's outer surface, thereby affecting the diffusion kinetics of uranyl ions on the adsorbent, resulting in low adsorption capacity and slow adsorption rate. Therefore, improving the adsorption performance of seawater uranium extraction materials has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for preparing a porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure. Utilizing a combination of adsorption and photocatalysis, mescapto-oxime-based fibers are combined with carbon nitride photocatalysts. Electrospinning technology is used to effectively composite the photocatalyst and polymer-based material, overcoming the difficulty of achieving uniform loading of nanomaterials on a polymer substrate in existing technologies. The introduction of porous few-layer carbon nitride enhances the photocatalytic performance of the composite material under visible light. Simultaneously, by constructing multi-level continuous adsorption channels, mass transfer resistance is reduced, and the contact between the adsorbed liquid and the material is enhanced, thereby improving the uranium adsorption performance and adsorption rate of the seawater uranium extraction composite material.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] First, this application provides a method for preparing a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure, the specific steps of which are as follows:

[0008] (1) Melamine was placed in a sealed crucible and calcined in a muffle furnace at 550°C for 2 hours. After cooling, it was ground to obtain a blocky carbon nitride yellow powder. A certain amount of blocky carbon nitride was placed in a boat and sintered in a muffle furnace at 550°C under air atmosphere to obtain white, fluffy, porous, few-layer carbon nitride.

[0009] (2) Hydroxylamine hydrochloride and N,N-dimethylformamide are mixed in a three-necked flask. After the hydroxylamine hydrochloride is completely dissolved in the N,N-dimethylformamide by mechanical stirring (e.g., at a speed of 400 rpm), sodium hydroxide is added and the mixture is stirred vigorously (e.g., at a speed of 600 rpm) for 30 to 60 minutes. Then, polyacrylonitrile powder is added and stirred until the polyacrylonitrile is completely swollen (about 40 minutes). The mixture is then placed in an oil bath preheated at 80 to 90°C and stirred at a speed of 400 rpm for 12 to 18 hours. After the reaction is completed, the supernatant is obtained by centrifugation, which is the polyamine oxime solution.

[0010] (3) Mix polyamine oxime solution, porous few-layer carbon nitride, and polyvinylpyrrolidone, and then disperse and stir by ultrasonication to obtain porous few-layer carbon nitride / amine oxime-based spinning solution;

[0011] (4) The prepared porous few-layer carbon nitride / mercaptooxime-based spinning solution was stretched and stacked using an electrospinning machine under the action of an electric field to prepare nanofibers. The nanofiber composite material was immersed in an ethanol aqueous solution, soaked for a period of time, and then soaked in methanol. It was then dried in a vacuum drying oven to constant weight to remove polyvinylpyrrolidone, thus obtaining a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure. The electrospinning technology used in this step is a conventional technology in this field, as disclosed in the literature "Mishra KR, Mishra P, Verma K, et al. Electrospinning production of nanofibrous membranes[J].Environmental Chemistry Letters,2019,17(2):767-800."

[0012] Preferably, in the preparation method of the above-mentioned porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with multi-level structure, the calcination heating rate of the bulk carbon nitride in step (1) is controlled at 5-10℃ / min, the calcination heating rate of the porous few-layer carbon nitride is controlled at 5-10℃ / min, and the sintering time is 1-5h. The heating rate affects the degree of exfoliation of carbon nitride nanosheets, and ultimately affects the photocatalytic reduction performance of the final product photocatalyst.

[0013] Preferably, in the preparation method of the above-mentioned porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure, the preferred mass-to-volume ratio of hydroxylamine hydrochloride, sodium hydroxide, and N,N-dimethylformamide in step (2) is (2-4 g):(3-6 g):(40-50 mL). The mass-to-volume ratio of polyacrylonitrile to N,N-dimethylformamide is (3-4 g):(40-50 mL).

[0014] Preferably, in the preparation method of the above-mentioned porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with multi-level structure, the mass-volume ratio of polymercaptooxime solution, porous few-layer carbon nitride and polyvinylpyrrolidone in step (3) is preferably 5 mL:(0.5~2g):(0.05~0.25g); the ultrasonic time in step (3) is 15~30 min; and the stirring time is 12~16 h.

[0015] Preferably, in the preparation method of the above-mentioned porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with multi-level structure, the electrospinning process parameters in step (4) are as follows: at a temperature of 30℃ and a humidity of 40%, the voltage is 10-25kV, the needle distance from the receiving plate is 10-20cm, the injection pump speed is 0.2-0.5mL / h, and the obtained fiber diameter range is 200-900nm. The large specific surface area of ​​nanofibers is beneficial for providing more adsorption sites.

[0016] Furthermore, in step (4) above, the ethanol-water solution refers to an ethanol solution with a volume concentration of 30%–50%, the soaking temperature is 45–55°C, and the soaking time is 12–24 hours. The methanol soaking time is 3–7 days at room temperature. The drying conditions are 90–100°C for 12–16 hours. Methanol soaking removes the pore-forming agent polyvinylpyrrolidone, thereby obtaining a porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material.

[0017] This application not only utilizes the amylopectin group to adsorb uranyl ions, but also breaks through the chemisorption equilibrium through photocatalytic reduction. Simultaneously, a multi-level structure is designed to reduce mass transfer resistance during the mass transfer process, allowing for better contact between uranium and the adsorption sites. This promotes the binding of the chelating amylopectin group to uranyl ions, further enhancing adsorption performance. Furthermore, while using the amylopectin functional group for adsorption, carbon nitride, a photocatalyst, is introduced to convert soluble U(VI) adsorbed at the amylopectin group adsorption sites into insoluble U(IV). This U(IV) can be detached after stirring, releasing the adsorption sites and providing a location for subsequent adsorption, thus improving adsorption performance and rate. Compared with existing seawater uranium extraction materials, it has the following beneficial effects:

[0018] 1) The preparation process of this application is simple and easy to industrialize.

[0019] 2) The present application proposes to introduce polyvinylpyrrolidone (PVP) as a sacrificial pore-forming agent into the composite polymer spinning solution, and then remove the PPVP by simple soaking after the formation of composite nanofibers. On the one hand, this gives the prepared uranium extraction seawater-derived amine oxime-based composite fibers a porous structure and a large specific surface area; on the other hand, it acts as a dispersant, effectively achieving particle dispersion and stabilization.

[0020] 3) This application employs a simple high-temperature calcination method to exfoliate bulk carbon nitride into porous, few-layer carbon nitride nanosheets. The porous structure improves the material's adsorption performance, while the few-layer structure shortens the photogenerated electron-hole recombination path, enhancing the photocatalytic performance of carbon nitride for uranium, and thus improving its adsorption performance for uranium.

[0021] 4) This invention employs a one-step method to prepare a composite material for seawater uranium extraction with a multi-level structure. By loading porous few-layer carbon nitride nanomaterials into porous ammonia oxime-based fibers, and further introducing the microporous / mesoporous structure of nanoscale adsorbents on the basis of the macropores formed by fiber interweaving, the seawater penetration is accelerated, the adsorption of uranyl ions is accelerated, the adsorption rate is improved, and the problems of nanomaterials being difficult to recycle and easy to agglomerate are solved at the same time.

[0022] 5) This invention utilizes electrospinning technology to stably load porous few-layer carbon nitride with photocatalytic properties into a amine oxime-based nanofiber, thereby obtaining a hierarchical seawater uranium extraction composite material. On one hand, by constructing multi-level continuous channels, the specific surface area of ​​the nanofiber material is further increased, and the adsorption effect is also further enhanced. On the other hand, it solves the shortcomings of photocatalyst powder being prone to agglomeration and difficult to recover, while further improving the uranium extraction capacity and selectivity of the nanofiber, thus obtaining a hierarchical nanofiber composite material with efficient uranium adsorption through a dual adsorption-photocatalytic effect. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation of the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material of the present invention.

[0024] Figure 2 This is a synthetic route diagram for the oxime-based ammonium hydroxide solution.

[0025] Figure 3 Fourier transform infrared spectra of PAN (polyacrylonitrile) and PAO (polyamine oxime);

[0026] Figure 4 Microscopic morphology of the porous few-layer carbon nitride / mercapto-oxime seawater uranium extraction composite material of Example 1:

[0027] Among them, a is a low-magnification (5000x) SEM image of the composite material, b is a high-magnification (100000x) SEM image of the composite material, and c is a SEM image of the porous few-layer carbon nitride filler.

[0028] Figure 5 The diagram shows the uranium adsorption kinetics of Example 1 and Comparative Example 2. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. The raw materials, reagents, instruments, equipment and other items involved in the embodiments are all commercially available products and can be purchased through commercial channels.

[0030] Example 1

[0031] The preparation process of the porous few-layer carbon nitride / mercapto-oxime seawater uranium extraction composite material in this embodiment is as follows: Figure 1 As shown, the specific steps are as follows:

[0032] (1) Place 5g of melamine in a sealed crucible and heat it to 550℃ at a heating rate of 5℃ / min for 2h. After cooling, grind it to obtain a yellow powder, which is block carbon nitride. Then take 0.5g of powder and place it in a boat (60mm×30mm×15mm) and heat it to 550℃ at a rate of 5℃ / min in air atmosphere for 5h. After the end, porous few-layer carbon nitride is obtained.

[0033] (2) Mix 2g of hydroxylamine hydrochloride and 40mL of N,N-dimethylformamide (DMF) in a three-necked flask and stir mechanically at 400r / min. After the hydroxylamine hydrochloride is completely dissolved, add 3g of sodium hydroxide and stir rapidly at 600r / min for 30min. Then add 3g of polyacrylonitrile powder and stir at 400r / min for 40min until the polyacrylonitrile is completely swollen. Continue stirring at 400r / min for 12h at 80℃. After the reaction is complete, centrifuge three times at 8000r / min for 10min each time, and take the supernatant, which is the poly(dimethylamine) oxime solution. The synthetic route of this step is as follows: Figure 2 As shown.

[0034] (3) Mix the poly(ammoxime) solution prepared in step (2), the porous few-layer carbon nitride prepared in step (1), and polyvinylpyrrolidone, then disperse by ultrasonication (450W) for 15 min, and then stir and react for 12 h to obtain a porous few-layer carbon nitride / ammoxime-based spinning solution; the mass-volume ratio of the added poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone is 5 mL: 1 g: 0.1 g.

[0035] (4) The prepared porous few-layer carbon nitride / mercaptooxime-based spinning solution was stretched and stacked into nanofibers by an electrospinning machine (Huizhi Electrospinning Electrospinning Machine HZ-01) under the action of an electric field. The composite nanofiber material was immersed in an ethanol aqueous solution preheated to 45°C (30% by volume) and kept at 45°C for 12 hours. Then it was taken out and immersed in methanol (purchased from Sinopharm Chemical Reagent Co., Ltd., AR grade, ≥99.5%) for 3 days at room temperature. Finally, it was placed in a vacuum drying oven at 100°C for 12 hours to remove polyvinylpyrrolidone, and a multi-level porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material was obtained.

[0036] In this step, the electrospinning process parameters are: temperature 30℃, humidity 40%, voltage 12kV, needle distance from receiving plate 10cm, and injection pump speed 0.2mL / h.

[0037] Figure 3 The infrared spectra of poly(amine oxime) (PAO) prepared in step (2) of this embodiment and the raw material polyacrylonitrile (PAN) are shown. In the spectrum of PAN, 2248 cm⁻¹ -1 The stretching vibration peak of -C≡N in PAN exists at 2248 cm⁻¹, which is a characteristic peak of PAN; in the spectrum of PAO, the peak is at 2248 cm⁻¹. -1 The characteristic peak of -C≡N disappears at 1653 cm⁻¹, while the peak at 1653 cm⁻¹... -1 and 931cm -1 The appearance of new peaks (originating from the stretching vibrations of -C=N and -NO in the amylopyrime group, respectively) indicates the success of the amylopyrime reaction.

[0038] The microstructure of the porous few-layer carbon nitride / mercapto-oxime seawater uranium extraction composite material prepared in this embodiment is as follows: Figure 4 As shown, a is a low-magnification (5000x) SEM image of the composite material, b is a high-magnification (100000x) SEM image of the composite material, and c is a SEM image of the porous few-layer carbon nitride filler prepared in step (1). The nanofibers in the composite material are uniformly distributed with a relatively uniform diameter distribution and good fiber morphology, without any agglomeration or droplet phenomena, indicating that high-quality nanofibers were successfully prepared by electrospinning. Among them, the photocatalyst nanomaterial (porous few-layer carbon nitride) is well dispersed and uniformly distributed in the fibers, and the prepared porous few-layer carbon nitride / mercaptooxime-based composite material has a hierarchical porous structure.

[0039] Example 2

[0040] 1) Place 5g of melamine in a sealed crucible and calcine it at 550℃ for 2h in air at a heating rate of 5℃ / min. After cooling, grind it to obtain a yellow powder sample of blocky carbon nitride. Take 0.5g of powder and place it in a boat (60mm×30mm×15mm) and calcine it at 550℃ for 3h in air at a heating rate of 5℃ / min. After the calcination, porous few-layer carbon nitride is obtained.

[0041] 2) Mix 3g of hydroxylamine hydrochloride and 45mL of N,N-dimethylformamide (DMF) in a three-necked flask. Stir mechanically at 400r / min until the hydroxylamine hydrochloride is completely dissolved. Add 5g of sodium hydroxide and stir at 600r / min for 30min. Then add 3.5g of polyacrylonitrile powder and continue stirring at 400r / min for 40min until the polyacrylonitrile is completely swollen. Continue stirring at 400r / min at 80℃ for 15h. After the reaction is complete, centrifuge at 8000r / min three times for 10min each time. Take the supernatant, which is the polyamine oxime solution.

[0042] 3) Mix poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone, and ultrasonically disperse at 450W for 15 min, then stir and react for 12 h to obtain porous few-layer carbon nitride / ammoxime-based spinning solution; the mass-volume ratio of poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone in this step is 5 mL: 0.5 g: 0.05 g.

[0043] 4) The prepared porous few-layer carbon nitride / mercaptooxime-based spinning solution was stretched and stacked into nanofibers by electrospinning under the action of electric field. The composite nanofiber material was immersed in a 40% volume concentration ethanol aqueous solution preheated to 50°C and kept at 50°C for 18 hours. Then it was taken out and soaked in methanol at room temperature for 5 days. Finally, it was placed in a vacuum drying oven at 100°C for 14 hours to remove polyvinylpyrrolidone, thus obtaining a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure.

[0044] The electrospinning process parameters for this example are as follows: at a temperature of 30℃ and a humidity of 40%, the voltage is 15kV, the distance between the needle tip and the receiving plate is 15cm, and the injection pump speed is 0.3mL / h.

[0045] Example 3

[0046] 1) Place 5g of melamine in a sealed crucible and calcine it at 550℃ for 2 hours in air at a heating rate of 5℃ / min. After cooling, grind it to obtain a yellow powder, which is block carbon nitride. Take 0.5g of block carbon nitride powder and place it in a boat (60mm×30mm×15mm). Calcine it at 520℃ for 3 hours in air at a heating rate of 5℃ / min. After the calcination, porous few-layer carbon nitride is obtained.

[0047] 2) Mix 4g of hydroxylamine hydrochloride and 50mL of N,N-dimethylformamide (DMF) in a three-necked flask. Stir the hydroxylamine hydrochloride at 400r / min until completely dissolved. Then add 6g of sodium hydroxide and stir at 600r / min for 30min. Next, add 4g of polyacrylonitrile powder and stir at 400r / min for 40min until the polyacrylonitrile is completely swollen. Continue stirring at 400r / min at 90℃ for 18h. After the reaction is complete, centrifuge three times at 8000r / min for 10min each time. Take the supernatant, which is the poly(dimethylamine) oxime solution.

[0048] 3) Mix poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone, and ultrasonically disperse at 450W for 15 min, then stir and react for 12 h to obtain porous few-layer carbon nitride / ammoxime-based spinning solution; the preferred mass-volume ratio of poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone in this step is 5 mL: 2 g: 0.25 g.

[0049] 4) The prepared porous few-layer carbon nitride / mercaptooxime-based spinning solution was stretched and stacked into nanofibers by an electrospinning machine under the action of an electric field. The composite nanofiber material was immersed in a 50% (v / v) ethanol aqueous solution preheated to 55°C and maintained at 55°C for 24 hours. Then it was taken out and soaked in methanol at room temperature for 7 days. Finally, it was placed in a vacuum drying oven at 100°C for 16 hours to remove polyvinylpyrrolidone, thus obtaining a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure.

[0050] The electrospinning process parameters for this example are as follows: the temperature is 30℃, the humidity is 40%, the voltage is 25kV, the distance between the needle tip and the receiving plate is 20cm, and the injection pump speed is 0.5mL / h.

[0051] Comparative Example 1

[0052] 5g of melamine was placed in a sealed crucible and calcined at 550℃ for 2 hours in air at a heating rate of 5℃ / min. After cooling, it was ground to obtain a yellow powder sample, which is blocky carbon nitride.

[0053] Comparative Example 2

[0054] 1) Mix 2g of hydroxylamine hydrochloride and 40mL of N,N-dimethylformamide (DMF) in a three-necked flask. Stir mechanically at 400r / min until the hydroxylamine hydrochloride is completely dissolved. Then add 3g of sodium hydroxide and stir vigorously at 600r / min for 30min. Then add 3g of polyacrylonitrile powder and stir for 40min until the polyacrylonitrile is completely swollen. Continue stirring at 400r / min at 80℃ for 12h. After the reaction is complete, centrifuge three times at 8000r / min for 10min each time. Take the supernatant, which is the polyamine oxime solution.

[0055] 2) The poly(ammoxime) solution prepared in step 1) is stretched and stacked into nanofibers by using an electrospinning machine under the action of an electric field. The nanofibers are then placed in a vacuum drying oven at 50°C for 24 hours to obtain ammoxime-based nanofibers.

[0056] In this comparative example, the electrospinning process parameters are as follows: the temperature is 30℃, the humidity is 40%, the voltage is 12kV, the distance between the needle tip and the receiving plate is 10cm, and the injection pump speed is 0.2mL / h.

[0057] Comparative Example 3

[0058] 1) In an air atmosphere, 5g of melamine was placed in a muffle furnace and heated to 550℃ at a rate of 5℃ / min. After sintering for 2 hours, the product was cooled to room temperature and ground to obtain a yellow powder, which is blocky carbon nitride.

[0059] 2) Mix 3g of hydroxylamine hydrochloride and 40mL of N,N-dimethylformamide (DMF) in a three-necked flask. Stir the mixture mechanically at 400r / min until the hydroxylamine hydrochloride is completely dissolved. Then add 3g of sodium hydroxide and stir at 600r / min for 30min. Next, add 3g of polyacrylonitrile powder and stir at 400r / min for 40min until the polyacrylonitrile is completely swollen. Continue stirring at 80℃ for 12h. After the reaction is complete, centrifuge the mixture three times at 8000r / min for 10min each time. The supernatant obtained is the polyamine oxime solution.

[0060] 3) Mix the poly(ammoxime) solution prepared in step (2), the bulk carbon nitride prepared in step (1), and polyvinylpyrrolidone, disperse by ultrasonication at 450W for 15 min, and then stir and react for 12 h to obtain bulk carbon nitride / ammoxime-based spinning solution; the mass-volume ratio of poly(ammoxime) solution, bulk carbon nitride, and polyvinylpyrrolidone in this step is 5 mL: 1 g: 0.1 g.

[0061] 4) The prepared bulk carbon nitride / mercaptooxime-based spinning solution was stretched and stacked into nanofibers by an electrospinning machine under the action of an electric field. The nanofiber material was then immersed in an aqueous ethanol solution preheated to 45°C (30% by volume) and kept at 45°C for 12 hours. After that, it was taken out and immersed in methanol at room temperature for 3 days. Finally, it was placed in a vacuum drying oven at 100°C for 12 hours to remove polyvinylpyrrolidone, thus obtaining a multi-level structured bulk carbon nitride / mercaptooxime-based seawater uranium extraction composite material.

[0062] In this comparative example, the electrospinning process parameters are as follows: the temperature is 30℃, the humidity is 40%, the voltage is 12kV, the distance between the needle tip and the receiving plate is 10cm, and the injection pump speed is 0.2mL / h.

[0063] The uranium adsorption performance of the adsorbent materials prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The test method was based on the reference "Yan BJ, Ma CX, Gao JX, et al. An Ion-Crosslinked Supramolecular Hydrogel for Ultrahigh and Fast Uranium Recovery from Seawater.[J].Advanced Materials,2020,32(10):e1906615.", specifically as follows: 3 mg of the test material was added to a conical flask containing 100 mL of a 32 mg / L uranium solution. The pH of the solution was adjusted to seawater pH (8.2±0.1) using 0.1 mol / L HCl and NaOH solutions. The flask was then placed on a magnetic stirrer at a constant temperature of 25°C for adsorption, with a stirring speed of 150 r / min. After the adsorption reaction was completed, arsene III was used as the uranium colorimetric reagent, and the uranium concentration before and after adsorption was measured using a UV-Vis spectrophotometer. The adsorption capacity was determined using the formula Q. e =(C0-C t The saturated adsorption capacity can be obtained by calculating V / m, where Q e C0: Adsorption capacity at equilibrium (mg / g); C0: Initial uranium concentration (mg / L); C e : Uranium concentration at equilibrium (mg / L), V: volume of uranium solution (L), m: mass of adsorbent (g). The detection results are shown in Table 1 below:

[0064] Table 1

[0065] sample Uranium adsorbent Saturated adsorption capacity (mg / g) Example 1 Porous few-layer carbon nitride / mercapto-oxime composite fibers 482.4 Example 2 Porous few-layer carbon nitride / mercapto-oxime composite fibers 450.1 Example 3 Porous few-layer carbon nitride / mercapto-oxime composite fibers 436.6 Comparative Example 1 Bulk carbon nitride 10.8 Comparative Example 2 Harmonic oxime nanofibers 306.6 Comparative Example 3 Bulk carbon nitride / mercapto-oxime composite fibers 405.2

[0066] Table 1 shows that the saturated adsorption capacity of uranium by the porous few-layer carbon nitride / mercapto-oxime-based composite materials in Examples 1-3 differs, and the adsorption performance of the composite materials is highly correlated with the modification steps. Meanwhile, the saturated adsorption capacity of the hierarchical porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite materials prepared in Examples 1-3 is significantly better than that of the bulk carbon nitride, mescapto-oxime-based nanofibers, and bulk carbon nitride / mercapto-oxime-based composite fiber adsorbents in Comparative Examples 1-3.

[0067] Table 2 shows the adsorption kinetics test results of the materials prepared in Example 1 and Comparative Example 2. Figure 5The uranium adsorption kinetics diagrams for both are shown. The adsorption kinetics test method is referenced in "Yan BJ, Ma CX, Gao JX, et al. An Ion-Crosslinked Supramolecular Hydrogel for Ultrahigh and Fast Uranium Recovery from Seawater.[J].Advanced Materials,2020,32(10):e1906615."

[0068] Table 2

[0069] pseudo-second-order dynamics <![CDATA[Theoretical Q e (mg·g -1 )]]> <![CDATA[k(g·mg -1 ·min -1 )]]> Example 1 520.83 <![CDATA[1.9120×10 -6 ]]> Comparative Example 2 442.48 <![CDATA[0.51349×10 -6 ]]>

[0070] Simultaneously combined Figure 5 Table 2 shows that the porous few-layer carbon nitride / mercapto-oxime composite fiber of Example 1 has a higher uranium adsorption capacity and a faster uranium extraction rate compared with the mescapto-oxime nanofiber of Comparative Example 2, especially the adsorption rate k (unit: g·mg) of Example 1. -1 ·min -1 The value is 1.9120 × 10 -6 The adsorption rate was significantly higher than that of Comparative Example 2 (0.51349 × 10⁻⁶). -6 The porous, few-layer carbon nitride nanoscale porous structure effectively improves the photocatalytic reduction efficiency. When combined with amylopectin-based nanofibers that can specifically adsorb uranium, the constructed hierarchical structure is more conducive to the flow of the adsorbed liquid, thus significantly improving the uranium adsorption performance of the composite material.

Claims

1. A method for preparing a porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure, characterized in that, The specific steps are as follows: 1) Place melamine in a sealed container and calcine it at 550°C for 2 hours. After cooling, blocky carbon nitride is obtained. Then, place it in an air atmosphere and sinter it at 550°C for 3-5 hours to obtain porous few-layer carbon nitride for later use. 2) Mix hydroxylamine hydrochloride and N,N-dimethylformamide, add sodium hydroxide and stir for 30-60 min; then add polyacrylonitrile powder and react until the polyacrylonitrile is completely swollen; then stir at 80-90 °C for 12-18 h. After the reaction is complete, centrifuge and take the supernatant, which is the poly(dimethylamine) oxime solution for later use. 3) Mix the poly(ammoxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone evenly to obtain a porous few-layer carbon nitride / ammoxime-based spinning solution; 4) The porous few-layer carbon nitride / mercaptooxime-based spinning solution is electrospun into nanofibers. The nanofibers are then immersed in an ethanol aqueous solution, removed and then immersed in methanol. After drying, the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure is obtained.

2. The method for preparing the porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 1), calcination at 550℃ means heating to 550℃ at a heating rate of 5~10℃ / min; sintering at 550℃ for 3-5 hours means sintering at 550℃ at a heating rate of 5~10℃ / min.

3. The method for preparing the porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 2), the mass-to-volume ratio of hydroxylamine hydrochloride, sodium hydroxide, and N,N-dimethylformamide is (2-4): (3-6): (40-50), with the mass-to-volume ratio in g:g:mL; the mass-to-volume ratio of polyacrylonitrile to N,N-dimethylformamide is (3-4):(40-50), with the mass-to-volume ratio in g:mL.

4. The method for preparing the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 3), the mass-to-volume ratio of poly(ammonia oxime) solution, porous few-layer carbon nitride, and polyvinylpyrrolidone is 5:(0.5~2):(0.05~0.25); the mass-to-volume ratio is in mL:g:g.

5. The method for preparing the porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 3), the mixing refers to sonication for 15-30 minutes, followed by stirring and reaction for 12-16 hours.

6. The method for preparing the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 4), the electrospinning process refers to spinning using an electrospinning machine at a temperature of 30 ℃, a humidity of 40%, a voltage of 10~25 kV, a distance of 10~20 cm between the spinning machine needle and the receiving plate, and a pump speed of 0.2~0.5 mL / h.

7. The method for preparing the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 4), immersing the nanofibers in an ethanol aqueous solution means immersing the nanofibers in an ethanol solution with a volume concentration of 30% to 50% and soaking them at 45 to 55 °C for 12 to 24 hours.

8. The method for preparing the porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 4), soaking in methanol means soaking in methanol for 3 to 7 days.

9. The method for preparing the porous few-layer carbon nitride / mercapto-oxime-based seawater uranium extraction composite material with a multi-level structure according to claim 1, characterized in that, In step 4), the drying refers to vacuum drying at 90~100 ℃ for 12~16 h.

10. A porous few-layer carbon nitride / mercaptooxime-based seawater uranium extraction composite material with a multi-level structure prepared by any one of claims 1-9.

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