A zif-8 composite iron monatomic doped porous carbon nitride material, a preparation method thereof and seawater uranium extraction application

Abstract

This invention relates to the fields of new materials and seawater uranium extraction technology, specifically to a ZIF-8 composite iron single-atom doped porous carbon nitride material, its preparation method, and its application in seawater uranium extraction. The method involves nucleating and growing ZIF-8 on a Fe@PCN substrate, resulting in ZIF-8 crystals tightly adhering to the Fe@PCN surface. The resulting Fe@ZPCN composite material can efficiently adsorb and catalytically reduce [UO2(CO3)3] in seawater under visible light irradiation. 4‑ It has high uranium extraction efficiency, strong resistance to ion and microbial interference, and excellent cycle stability, which can meet the actual needs of seawater uranium extraction.

Description

Technical Field

[0001] This invention relates to the fields of new materials and seawater uranium extraction technology, specifically to a ZIF-8 composite iron single-atom doped porous carbon nitride material, its preparation method, and its application in seawater uranium extraction. Background Technology

[0002] Nuclear energy, as a clean energy source, relies heavily on a stable supply of nuclear fuel—uranium. However, terrestrial uranium resources are limited and increasingly depleted, making it difficult to meet future demand. The ocean holds vast uranium resources, nearly a thousand times the amount on land, and seawater uranium extraction has a relatively small environmental impact. Current seawater uranium extraction technology faces two core challenges: firstly, extremely low uranium concentration and stable form of uranium: the concentration of uranium in seawater is extremely low (approximately 3.3 ppb), and it mainly exists as the extremely stable uranyl carbonate anion [UO2(CO3)3]. 4- First, the uranium ions in the seawater are difficult to capture and fix directly. Second, there are complex environmental disturbances: a large number of coexisting ions exist in the seawater, which compete with the target uranium ions for adsorption, seriously affecting the selectivity of uranium extraction materials. At the same time, marine microorganisms easily proliferate on the material surface, forming biofilms (biofouling), which block the active sites of the material and cause its performance to decline rapidly.

[0003] To address these issues, researchers have developed various uranium extraction materials, such as metal-organic frameworks (MOFs). Among them, zeolite imidazole ester framework-8 (ZIF-8) has attracted considerable attention due to its high porosity, large specific surface area, and the presence of Zn-N active sites capable of coordinating with uranyl ions. However, using ZIF-8 alone has significant drawbacks: First, it exhibits poor stability: its structure is unstable in aqueous environments (especially during recycling), and the Zn-N bonds are easily hydrolyzed, leading to performance degradation and a short cycle life. Second, it has weak photocatalytic activity: its response to visible light is weak, and electron-hole recombination is rapid, making it unable to effectively utilize light energy to reduce the captured soluble U(VI) to the insoluble U(IV) for secure uranium locking.

[0004] Porous carbon nitride (PCN) is an excellent photocatalyst, especially Fe@PCN modified with single-atom doping of metals such as iron (Fe), which exhibits superior photocatalytic activity and antibacterial properties. However, Fe@PCN also has its limitations: insufficient specific surface area and active sites. Compared to MOF materials such as ZIF-8, Fe@PCN has a lower specific surface area and lacks specific high-density binding sites for uranyl ions, resulting in limited adsorption capacity for uranium.

[0005] Therefore, there is an urgent need to develop a new type of uranium extraction material that can simultaneously possess the high adsorption capacity of ZIF-8 and the high photocatalytic activity, high stability, and antibacterial properties of Fe@PCN. Through synergistic effects, the defects of using either material alone can be overcome, achieving efficient, selective, stable, and biofouling-resistant extraction of uranium from seawater. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing seawater uranium extraction materials, such as low adsorption capacity, poor photocatalytic efficiency, weak anti-interference ability, and insufficient cycle stability. This invention provides a ZIF-8 composite iron single-atom doped porous carbon nitride seawater uranium extraction material, along with its preparation method and application, to achieve efficient extraction of seawater uranium resources.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of this invention provides a method for preparing ZIF-8 composite iron single-atom doped porous carbon nitride material, comprising the following steps:

[0009] (1) Preparation of Fe-doped porous carbon nitride: 1-vinyl-3-butylimidazolium bromide, FeCl3·6H2O and cyanuric acid were dissolved in deionized water, stirred, melamine was added, stirring was continued, centrifuged and dried, the dried material was heated in a tube furnace, kept warm, and cooled to room temperature to obtain brown and fluffy Fe-doped porous carbon nitride, namely Fe@PCN;

[0010] (2) Preparation of ZIF-8 composite Fe-doped porous carbon nitride: At room temperature, a methanol solution of Zn(NO)3·6H2O was poured into a methanol solution of 2-methylimidazole, and Fe@PCN was added at the same time. The mixture was stirred, and then washed with methanol solution by centrifugation and drying to obtain ZIF-8 composite Fe-doped porous carbon nitride, i.e. Fe@ZPCN.

[0011] As a further improvement of the present invention, the molar ratio of FeCl3·6H2O, cyanuric acid and melamine in step (1) is 1.3-1.5:13-15:13.5-15.5, preferably 1.3:13:13.5;

[0012] As a further improvement of the present invention, in step (2), the molar ratio of Zn(NO)3·6H2O and 2-imidazole is 1:3-5, and the mass ratio of Zn(NO)3·6H2O and Fe@PCN is 149:150.

[0013] As a further improvement of the present invention, in step (1), the mixture is stirred for 20-40 minutes before adding melamine and stirred for 2-4 minutes after adding melamine, with a rotation speed of 7000-8000 r / min.

[0014] As a further improvement of the present invention, in step (1), the tubular furnace operates at 1-5°C·min. -1 Rapidly heat to 500-600℃ and hold for 2-4 hours.

[0015] As a further improvement of the present invention, the stirring time in step (2) is 10-14h and the rotation speed is 7000-8000r / min.

[0016] As a further improvement of the present invention, the mass-to-volume ratio of Fe@PCN to methanol solution in the reaction system in step (2) is 1.5-2g:100mL.

[0017] The second aspect of the present invention provides a ZIF-8 composite iron single-atom doped porous carbon nitride material obtained by the above preparation method.

[0018] The third aspect of this invention provides the application of the ZIF-8 composite iron single-atom doped porous carbon nitride material obtained by the above preparation method in seawater uranium extraction.

[0019] As a further improvement of the present invention, the application is as follows: take a uranium-containing solution, add the ZIF-8 composite iron single-atom doped porous carbon nitride material as an adsorbent, and perform adsorption separation.

[0020] As a further improvement of the present invention, the application is as follows: the Fe@ZPCN material is put into uranium-containing water at pH=8.3, and adsorption and catalytic reduction of [UO2(CO3)3]4- in the water are achieved under visible light irradiation.

[0021] The beneficial effects of adopting the above technical solution are as follows:

[0022] This invention rapidly mixes a metal salt solution and an organic ligand solution, while simultaneously adding pre-prepared Fe@PCN powder. This allows ZIF-8 to nucleate and grow on the Fe@PCN growth substrate, resulting in ZIF-8 crystals tightly adhering to the Fe@PCN surface. This strengthens interfacial bonding and synergistic activity of active sites, combining the advantages of ZIF-8's high specific surface area and abundant active sites with the characteristics of Fe@PCN's high photocatalytic activity and antibacterial properties.

[0023] The Fe@ZPCN composite material provided by this invention can efficiently adsorb and catalytically reduce [UO2(CO3)3] in seawater under visible light irradiation. 4- It has high uranium extraction efficiency, strong resistance to ion and microbial interference, and excellent cycle stability, which can meet the actual needs of seawater uranium extraction. Attached Figure Description

[0024] Figure 1These are scanning electron microscope images of Fe@ZPCN prepared in Example 2 of this invention and a comparative material;

[0025] Figure 2 X-ray diffraction patterns of Fe@ZPCN prepared in the embodiments of the present invention and the comparative materials;

[0026] Figure 3 The nitrogen adsorption-desorption isotherms of Fe@ZPCN prepared in the embodiments of the present invention and the comparative material are shown below.

[0027] Figure 4 The uranium extraction kinetics curves of Fe@ZPCN and the comparative material in Example 4 of this invention are shown.

[0028] Figure 5 The results of the experiment on the influence of coexisting ions on the Fe@ZPCN material in Example 5 of this invention;

[0029] Figure 6 The results of the recycling performance test of the Fe@ZPCN material in Example 6 of this invention;

[0030] Figure 7 The results of the antibacterial performance test of Fe@ZPCN and the comparative material in Example 7 of this invention;

[0031] Figure 8 The results are actual seawater uranium extraction tests of the Fe@ZPCN material in Example 8 of this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the invention will be described clearly and completely below in conjunction with specific embodiments and accompanying drawings.

[0033] Example 1: Preparation of Fe-doped porous carbon nitride (Fe@PCN)

[0034] 0.4 g of 1-vinyl-3-butylimidazolium bromide, 0.541 g of FeCl3·6H2O and 2.522 g of cyanuric acid were dissolved in 100 mL of deionized water. After stirring for 30 min, 2.581 g of melamine was added and stirring was continued for 12 h. The mixture was then centrifuged and dried overnight in a vacuum drying oven.

[0035] The dried material was heated in a tube furnace at 3°C / min. -1 The temperature was rapidly increased to 550℃ and held for 3 h. After cooling to room temperature, brown, fluffy Fe-doped porous carbon nitride (Fe@PCN) was obtained.

[0036] Example 2 Preparation of Fe@ZPCN composite material

[0037] 1.49 g of Zn(NO3)2·6H2O and 1.64 g of 2-MeIM were dissolved in 50 mL of methanol solution respectively. After complete dissolution, the methanol solution of Zn(NO3)2 was quickly poured into the methanol solution of 2-methylimidazole under stirring at room temperature. At the same time, 1.5 g of Fe@PCN prepared in Example 1 was added. After 3 h, the mixed solution was collected, 30 mL of methanol was added and centrifuged. The solution was washed with methanol to remove the mother liquor, and the product was collected. The product was dried in a vacuum oven at 60 °C for 12 h to obtain Fe@ZPCN.

[0038] Comparative Example 1: Preparation of ZIF-8

[0039] 1.49 g of Zn(NO3)2·6H2O and 1.64 g of 2-MeIM were dissolved in 50 mL of methanol solution respectively. After complete dissolution, the Zn(NO3)2 methanol solution was quickly poured into the 2-methylimidazole methanol solution. After stirring at room temperature for 3 h, the milky white mixed solution was collected, and 30 mL of methanol was added for centrifugation and washing. This process was repeated 3 times to remove the mother liquor and collect the white product, thus obtaining ZIF-8 nanomaterials.

[0040] Example 4: Material particle size, XRD and adsorption-desorption experiments

[0041] Electron microscopy was performed on Fe@PCN obtained in Example 1, Fe@ZPCN obtained in Example 2, and ZIF-8 obtained in Comparative Example 1. The results are as follows: Figure 1 As shown, the original ZIF-8 particle size is approximately 300–400 nm. Rough-surfaced microspheres were formed on the Fe@ZPCN material, and the particle size was reduced to 50–100 nm.

[0042] X-ray diffraction was performed on Fe@PCN obtained in Example 1, Fe@ZPCN obtained in Example 2, and ZIF-8 obtained in Comparative Example 1. The spectra are shown below. Figure 2 As shown, the composite Fe@ZPCN exhibits the characteristic diffraction peaks of both materials, indicating that the two materials were successfully composited and their crystal structures were fully preserved.

[0043] Elution and adsorption experiments were performed on Fe@PCN obtained in Example 1, Fe@ZPCN obtained in Example 2, and ZIF-8 obtained in Comparative Example 1. The results are as follows: Figure 3 As shown, the surface area of ​​Fe@ZPCN is about 40 times larger than that of CN and about 4 times larger than that of Fe@PCN.

[0044] Example 5: Uranium Extraction Performance Test of Fe@ZPCN Material

[0045] The uranium extraction efficiency of materials under illumination was investigated using a photocatalytic reaction chamber. 6 mg of Fe@PCN, Fe@ZPCN, and ZIF-8 prepared in Examples 1-2 and Comparative Example 1, respectively, were added, along with 5 mL of methanol and 3 mL of methanol at an initial concentration of 200 mg·L⁻¹. -1 A uranyl carbonate solution, 52 mL of deionized water, pH adjusted to 8.3, was used with a light power density of 200 W·m⁻¹. -2 The suspension was irradiated with a xenon lamp with a wavelength of 420-780 nm, and the temperature of the suspension was kept constant at room temperature using circulating condensate. The supernatant was collected by filtration through a 0.22 μm filter at different time points, and the absorbance was measured using the arsene III method. The extraction rate of uranyl carbonate by the material was calculated based on the initial concentration and the measured residual concentration.

[0046] The results are as follows Figure 4 As shown in the uranium extraction kinetics curve, Fe@ZPCN exhibits extremely high extraction capability under illumination, reaching an extraction efficiency of 96.6% at 210 min. Its photocatalytic extraction effect is significantly higher than that of Fe@PCN and ZIF-8.

[0047] Example 6: Test of the influence of coexisting ions on Fe@ZPCN materials

[0048] (1) Fe@ZPCN prepared in Example 2 was added to a 10 mg∙L solution at a concentration of 0.1 g / L. -1 In a uranyl carbonate solution with pH = 8.3, 0.01 M background ion solution (i.e., Na+) was added sequentially. + K + Mn 2+ Cu 2+ Al 3+ NO3 - V 5+ CO3 - SO4 2- Place it in a shaker and shake it overnight.

[0049] (2) After the reaction is complete, centrifuge the supernatant, measure its absorbance, and calculate its remaining uranium concentration using a standard curve.

[0050] (3) Calculate the equilibrium concentration and the amount of uranyl carbonate adsorbed by the material based on the initial concentration and the measured residual concentration.

[0051] (4) Compare the adsorption amounts without adding background ions and with adding different background ions, and summarize the effects of different ions on the adsorption capacity of the material.

[0052] The results are as follows Figure 5 As shown, in the metal cation (Mn 2+ Cu 2+ Al3+ Under the influence of ), the performance of Fe@ZPCN decreases less.

[0053] Example 7: Cyclic Performance Testing of Fe@ZPCN Materials

[0054] 1 M Na₂CO₃ was used as the desorbent in desorption experiments after the Fe@ZPCN material prepared in Example 2 had reached saturation. The concentration of uranium in the desorption solution was measured to ensure complete desorption. The desorption solution was then reused for uranium extraction experiments, with six cycles.

[0055] The results are as follows Figure 6 The results show that Fe@ZPCN retains more than 85% of its initial uranium extraction activity after 6 cycles, demonstrating excellent cycle stability.

[0056] Example 7: Antibacterial performance test of Fe@ZPCN material

[0057] The antibacterial performance was tested using the dilution plating method, with the number and size of colonies directly reflecting the material's antibacterial effect. Common marine Gram-negative bacterium *Escherichia coli* was selected, and the specific steps are as follows:

[0058] (1) Prepare a nutrient solution using 0.3 g beef extract, 1 g peptone, 0.5 g NaCl and 100 mL deionized water. Both the glassware and the solution were autoclaved at 121°C for 30 min.

[0059] (2) Add 3 mL of deionized water and 15 mL of nutrient solution to the conical flask, adjust the pH to 6.5-7.5, take a loop of bacteria and transfer Escherichia coli into the culture medium, incubate at 24℃ and 130 rpm∙min -1 Activation was achieved by constant temperature shaking incubation for 24 h.

[0060] (3) Take 0.15 mL of bacterial culture, 20 mg of materials from Examples 1-2 and Comparative Example 1, and 15 mL of new nutrient broth, and culture them in the dark and under light (temperature controlled by circulating cooling water) for 2 h with shaking. No materials were added to the blank group.

[0061] (4) After shaking, take 1 mL of the solution and make up to 10 mL, then dilute tenfold to 10 mL. -9 Take 0.5 mL of the diluted solution and spread it onto a new nutrient broth solid medium. Incubate at 37°C for 24 h and then count the surface colonies.

[0062] The results are as follows Figure 7 As shown, under light conditions, ZIF-8, Fe@PCN, and Fe@ZPCN all exhibited some bactericidal activity against Escherichia coli. Among them, Fe@ZPCN had the highest bacterial mortality rate (approximately 92%).

[0063] Example 9: Application of Fe@ZPCN material in real seawater

[0064] (1) The actual seawater sample was taken from the southeast sea area of ​​Xingcheng City, Huludao City, Liaoning Province. The sample was used to dissolve uranyl nitrate ions and prepare a stock solution.

[0065] (2) Take 0.1 g∙L respectively -1 The Fe@PCN and Fe@ZPCN prepared in Examples 1-2 were added to 10 mg·L⁻¹ -1 Place the prepared solution in a shaker and shake for 7 days to react.

[0066] (3) After the reaction is complete, centrifuge and take the supernatant, measure its absorbance, and calculate its remaining uranium concentration through the standard curve.

[0067] (4) Calculate the equilibrium concentration and the amount of adsorption of the material on the spiked seawater based on the initial concentration and the measured residual concentration.

[0068] The results are as follows Figure 8 As shown, the calculated uranium extraction performance of Fe@PCN showed a significant decrease, while the performance of Fe@ZPCN in actual seawater only decreased by 4.6%.

[0069] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a ZIF-8 composite iron single-atom doped porous carbon nitride material in uranium extraction from seawater, characterized in that, The preparation method of the ZIF-8 composite iron single-atom doped porous carbon nitride material includes the following steps: (1) Preparation of Fe-doped porous carbon nitride: 1-vinyl-3-butylimidazolium bromide, FeCl3·6H2O and cyanuric acid were dissolved in deionized water, stirred, melamine was added, stirring was continued, centrifuged and dried, the dried material was heated in a tube furnace, kept warm, and cooled to room temperature to obtain brown and fluffy Fe-doped porous carbon nitride, namely Fe@PCN; (2) Preparation of ZIF-8 composite Fe single-atom doped porous carbon nitride: At room temperature, the methanol solution of Zn(NO3)2·6H2O was poured into the methanol solution of 2-methylimidazolium, and Fe@PCN was added at the same time. After stirring, the methanol solution was added, centrifuged and washed, and dried to obtain ZIF-8 composite Fe single-atom doped porous carbon nitride, i.e. Fe@ZPCN. In step (2), the molar ratio of Zn(NO3)2·6H2O and 2-methylimidazole is 1:3-5, and the mass ratio of Zn(NO3)2·6H2O and Fe@PCN is 149:

150.

2. The application according to claim 1, characterized in that, In step (1), the molar ratio of FeCl3·6H2O, cyanuric acid and melamine is 1.3-1.5:13-15:13.5-15.

5.

3. The application according to claim 1, characterized in that, In step (1), the molar ratio of FeCl3·6H2O, cyanuric acid and melamine is 1.3:13:13.

5.

4. The application according to claim 1, characterized in that, In step (1), stir for 20-40 minutes before adding melamine and stir for 2-4 hours after adding melamine, with a rotation speed of 7000-8000 r / min.

5. The application according to claim 1, characterized in that, In step (1), the tubular furnace operates at 1-5℃∙min -1 Rapidly heat to 500-600℃ and hold for 2-4 hours.

6. The application according to claim 1, characterized in that, The stirring time in step (2) is 10-14 hours and the rotation speed is 7000-8000 r / min.

7. The application according to claim 1, characterized in that, In step (2), the mass-to-volume ratio of Fe@PCN to methanol in the reaction system is 1.5g-2g:100mL.

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