A method for preparing and applying an iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater.

Abstract

A method for preparing and applying an iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater is disclosed. This method aims to address the technical problem of low adsorption capacity in existing metal-organic framework uranium adsorbents. The method involves: 1. Preparing ZIF-8 nanocrystals; 2. Adjusting the pH of a tannic acid solution to 8 with potassium hydroxide, then adding it to the ZIF-8 nanocrystal solution to form a stable ZIF-8@K-TA complex; 3. Soaking ZIF-8@K-TA in ferric nitrate nonhydrate to obtain ZIF-8@Fe-TA; 4. Calcination under a dry argon flow to obtain the iron single-atom porous framework adsorbent. This adsorbent achieves an adsorption capacity of 491.46 mg / g for uranium in uranium-containing wastewater at pH 6, with a removal rate of 98.29%. It can be used in the field of deep purification treatment of uranium-containing wastewater.

Description

Technical Field

[0001] This invention relates to the preparation method and application of adsorbents for deep purification of uranium-containing wastewater. Background Technology

[0002] With the development and widespread application of nuclear energy, the treatment and purification of uranium-containing wastewater has become an important environmental protection task. Uranium, as a radioactive element, poses a serious threat to the ecological environment and human health if present in water bodies. Therefore, developing efficient adsorbents for uranium-containing wastewater purification is particularly important. Existing adsorbent materials still have many shortcomings in terms of adsorption capacity, selectivity, and regeneration performance, making it difficult to meet the needs of practical applications. In recent years, metal-organic frameworks (MOFs) have become a highly promising adsorbent material due to their advantages such as high specific surface area, porous structure, and tunable chemical properties. Chinese Patent Application No. CN202410469977.1 discloses a uranium adsorbent, its preparation method, and its application. The uranium adsorbent disclosed is a metal-organic framework with a nanocage structure, in-situ encapsulating a keggin-type heteropolyacid within the nanocage; the metal-organic framework is MIL-101(Cr). However, the uranium adsorbent of this adsorbent has a low uranium adsorption capacity of only 280.60 mg / g. Summary of the Invention

[0003] This invention aims to address the technical problem of low adsorption capacity in existing metal-organic framework uranium adsorbents by providing a method for preparing and applying an iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater. This adsorbent is a highly efficient iron single-atom porous framework adsorbent used for the deep purification of uranium-containing wastewater.

[0004] The preparation method of the iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater of the present invention is carried out according to the following steps:

[0005] I. Preparation of ZIF-8 nanocrystals;

[0006] II. ZIF-8@K-TA Synthesis:

[0007] ZIF-8 nanocrystals were dispersed in deionized water at a concentration of 20–25 g / L and stirred for 1–2 h to obtain a ZIF-8 dispersion.

[0008] An aqueous solution of tannic acid (TA) with a concentration of 6–24 mmol / L was adjusted to pH 8 with KOH solution to obtain an alkaline tannic acid solution.

[0009] Then, according to the volume ratio of alkaline tannic acid solution to ZIF-8 dispersion of 3:10, the alkaline tannic acid solution was added to the ZIF-8 dispersion, stirred for 7-10 minutes, and then centrifuged. The solid product was washed three times with deionized water and methanol respectively, and dried to obtain ZIF-8@K-TA.

[0010] III. Synthesis of ZIF-8@Fe-TA: ZIF-8@K-TA was soaked in a methanol solution of ferric nitrate and stirred for 2-3 hours. After centrifugation, the solid product was washed three times with methanol and dried under vacuum to obtain ZIF-8@Fe-TA.

[0011] IV. Synthesis of Fe-NC: ZIF-8@Fe-TA was transferred to a ceramic crucible and placed in a furnace under a dry argon flow. It was heated from room temperature to 900-950℃ at a heating rate of 5℃ / min and held for 2-3 hours for annealing. Then it was cooled to room temperature to obtain an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater, denoted as Fe-NC.

[0012] Furthermore, the preparation method of ZIF-8 nanocrystals is carried out according to the following steps:

[0013] (1) Weigh out 2-methylimidazole (MeIM) and zinc nitrate hexahydrate according to the molar ratio of 2-methylimidazole (MeIM) to zinc nitrate hexahydrate of 4.71:1;

[0014] (2) Prepare a mixture of N,N-dimethylformamide (DMF), methanol (MeOH) and ethanol (EtOH) in a volume ratio of 3:1:1; then dissolve the 2-methylimidazole weighed in step (1) in the mixture to obtain solution A; wherein the concentration of 2-methylimidazole in solution A is 1.5 to 1.6 mol / L;

[0015] (3) N,N-dimethylformamide (DMF) and methanol (MeOH) are mixed in a volume ratio of 3:2 to prepare a mixed solvent; then the zinc nitrate hexahydrate (Zn(NO3)2·6H2O) weighed in step (1) is dissolved in the mixed solvent to obtain solution B; the concentration of zinc nitrate hexahydrate in solution B is 0.20~0.25mol / L;

[0016] (4) Add the solution A prepared in step (2) to the solution B prepared in step (3), stir at room temperature for 20 to 24 hours, centrifuge, wash the solid with methanol three times, and vacuum dry to obtain ZIF-8 nanocrystals;

[0017] Furthermore, the concentration of the KOH solution mentioned in step two is 6 mol / L.

[0018] Furthermore, the drying process described in step two involves drying in an oven at a temperature of 35–40°C for 8–10 hours.

[0019] Furthermore, the vacuum drying described in step three involves drying in a vacuum drying oven at a temperature of 45–50°C for 10–12 hours.

[0020] The application of the single-atom porous framework adsorbent for the deep purification of iron in uranium-containing wastewater prepared by the above method involves treating uranium-containing wastewater using the single-atom porous framework adsorbent. The specific method is as follows: the single-atom porous framework adsorbent is added to the uranium-containing wastewater, and the pH value is adjusted to 6-9; after adsorption at a temperature of 15-55℃ for 10-20 hours, the single-atom porous framework adsorbent is separated to complete the treatment of uranium-containing wastewater.

[0021] The method of this invention first prepares ZIF-8@K-TA powder using ZIF-8 powder. ZIF-8, as a typical metal-organic framework material, has a high specific surface area and excellent chemical stability. By combining it with tannic acid (TA), its adsorption performance can be further enhanced. Subsequently, ZIF-8@Fe-TA powder is prepared by soaking the ZIF-8@K-TA powder in a methanol solution containing ferric nitrate. Ferric nitrate provides iron ions in this process, and TA coordinates with the iron ions through its abundant phenolic hydroxyl groups, forming a stable iron single-atom dispersion system. Finally, ZIF-8@Fe-TA is converted into Fe-NC adsorbent through high-temperature heat treatment. This adsorbent not only retains the porous structure of ZIF-8, but also significantly improves its selectivity and adsorption capacity for uranium ions by introducing iron single atoms.

[0022] The iron single-atom porous framework adsorbent of this invention exhibits excellent performance in adsorbing uranium ions, especially at pH=6, where the adsorption capacity reaches 491.46 mg / g and the removal rate is 98.29%. The adsorbent prepared by the method of this invention effectively solves the problems of low adsorption capacity, poor selectivity, and inadequate regeneration performance in existing technologies, and can be used in the field of deep purification treatment of uranium-containing wastewater. Attached Figure Description

[0023] Figure 1 This is a microscopic morphology image of ZIF-8 in Example 1;

[0024] Figure 2 The image shows the microstructure of ZIF-8@K-TA in Example 1.

[0025] Figure 3 The image shows the microstructure of ZIF-8@Fe-TA in Example 1.

[0026] Figure 4The image shows the microstructure of Fe-NC-6 in Example 1.

[0027] Figure 5 This is a microscopic morphology diagram of Fe-NC-12 in Example 2;

[0028] Figure 6 This is a microscopic morphology diagram of Fe-NC-24 in Example 3;

[0029] Figure 7 This is a high-resolution transmission electron microscope image of Fe-NC-6 in Example 1;

[0030] Figure 8 This is an elemental distribution diagram of Fe-NC-6 in Example 1;

[0031] Figure 9 This is a specific surface area diagram of Fe-NC-6 in Example 1;

[0032] Figure 10 This is a specific surface area diagram of Fe-NC-12 in Example 2;

[0033] Figure 11 This is a specific surface area diagram of Fe-NC-24 in Example 3;

[0034] Figure 12 This is a graph showing the effect of pH on the adsorption capacity of Fe-NC-6 in Application Example 1;

[0035] Figure 13 This is a graph showing the effect of pH on the removal rate of Fe-NC-6 in Application Example 1.

[0036] Figure 14 This is a graph showing the effect of temperature on the adsorption capacity of Fe-NC-6 in Application Example 2;

[0037] Figure 15 This is a graph showing the effect of time on the removal rate of Fe-NC-6 in Example 3.

[0038] Figure 16 The graph shows the effect of initial concentration on the adsorption capacity of Fe-NC-6 in Application Example 4;

[0039] Figure 17 The graph shows the effect of competing ions on the adsorption capacity of Fe-NC-6 in Application Example 5;

[0040] Figure 18 The image shows the microstructure and energy dispersive spectroscopy (EDS) of the Fe-NC-6 adsorbent after purifying uranium-containing wastewater in Application Example 1. Detailed Implementation

[0041] The beneficial effects of the present invention are verified using the following examples:

[0042] Example 1: The preparation method of the iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater in Example 1 is carried out according to the following steps:

[0043] I. Preparation of ZIF-8 nanocrystals:

[0044] (1) Weigh 2.626g of 2-methylimidazole (MeIM) and 2.238g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O);

[0045] (2) Mix 12 mL of N,N-dimethylformamide (DMF), 4 mL of methanol (MeOH) and 4 mL of ethanol (EtOH) evenly to prepare a mixture; then dissolve the 2-methylimidazole weighed in step (1) in the mixture to obtain solution A;

[0046] (3) Mix 18 mL of N,N-dimethylformamide (DMF) and 12 mL of methanol (MeOH) evenly to prepare a mixed solvent; then dissolve the zinc nitrate hexahydrate (Zn(NO3)2·6H2O) weighed in step (1) in the mixed solvent to obtain solution B;

[0047] (4) Add the solution A prepared in step (2) to the solution B prepared in step (3), stir at room temperature for 24 hours, centrifuge, wash the solid with methanol 3 times, and dry in a vacuum oven at 40°C for 8 hours to obtain ZIF-8 nanocrystals.

[0048] II. ZIF-8@K-TA Synthesis:

[0049] 200 mg of ZIF-8 nanocrystals were dispersed in 10 mL of deionized water and stirred for 2 h to obtain a ZIF-8 dispersion.

[0050] An alkaline tannic acid solution was obtained by adjusting the pH of a 6 mmol / L tannic acid (TA) aqueous solution to 8 with a 6 mol / L KOH solution.

[0051] Add 3 ml of alkaline tannic acid solution to 10 ml of ZIF-8 dispersion, stir for 7 minutes, then centrifuge to separate the solid product. Wash the solid product three times with deionized water and methanol respectively, and dry it in an oven at 40°C for 8 hours to obtain ZIF-8@K-TA.

[0052] III. Synthesis of ZIF-8@Fe-TA:

[0053] 300 mg of ZIF-8@K-TA was soaked in 120 mL of a methanol solution of 0.5 g / L ferric(III) nonahydrate (Fe(NO3)3·9H2O). After stirring for 2 hours, the product was centrifuged, washed three times with methanol, and dried in a vacuum drying oven at 50 °C for 12 hours to obtain ZIF-8@Fe-TA.

[0054] IV. Synthesis of Fe-NC: ZIF-8@Fe-TA was transferred to a ceramic crucible and placed in a furnace under a dry argon flow. It was annealed by heating from room temperature to 900℃ at a heating rate of 5℃ / min and holding for 2 hours. Then it was cooled to room temperature to obtain an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater, denoted as Fe-NC-6.

[0055] Example 2: This example differs from Example 1 in that the concentration of the tannic acid aqueous solution in step two is 12 mmol / L. The other steps and parameters are the same as in Example 1, resulting in an iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater, denoted as Fe-NC-12.

[0056] Example 3: This example differs from Example 1 in that the concentration of the tannic acid aqueous solution in step two is 24 mmol / L. The other steps and parameters are the same as in Example 1, resulting in an iron single-atom porous framework adsorbent for the deep purification of uranium-containing wastewater, denoted as Fe-NC-24.

[0057] The scanning electron microscope image of ZIF-8 prepared in step one in Example 1 is shown below. Figure 1 As shown, from Figure 1 It can be seen that ZIF-8 is a framework cubic nanoparticle.

[0058] The scanning electron microscope image of ZIF-8@K-TA prepared in step two of Example 1 is shown below. Figure 2 As shown, from Figure 2 It can be seen that TA is a pore-forming agent, and the amount of Fe dispersed in ZIF-8 can be controlled by adjusting the amount of TA.

[0059] The scanning electron microscope image of ZIF-8@Fe-TA prepared in step three of Example 1 is shown below. Figure 3 As shown, from Figure 3 It can be seen that after coordination with iron ions, the nanoparticles still maintain their framework cubic structure.

[0060] Scanning electron microscope (SEM) image of Fe-NC-6 prepared in step four of Example 1 is shown below. Figure 4 As shown, from Figure 4It can be seen that after high-temperature pyrolysis, the dodecahedral shape is maintained, with the whole body concave towards the center and the edges protruding, indicating that a hollow structure is formed. The hollow structure will facilitate the transport of Fe charges, thereby increasing the amount of uranium adsorbed.

[0061] Example 2: Scanning electron microscope image of Fe-NC-12 prepared in step four is shown below. Figure 5 As shown, from Figure 5 It can be seen that after high-temperature pyrolysis, a hollow structure is formed, but the tannic acid aggregates to form nano-wires.

[0062] Example 3: Scanning electron microscope image of Fe-NC-24 prepared in step four is shown below. Figure 6 As shown, from Figure 6 It can be seen that after high-temperature pyrolysis, a hollow structure is formed, but a large number of nanowires are aggregated.

[0063] The Fe-NC-6 prepared in step four of Example 1 was subjected to high-resolution transmission electron microscopy (TEM) scanning, and the resulting crystal structure microstructure is shown in the figure. Figure 7 As shown, the element distribution is as follows Figure 8 As shown, from Figure 7 The microscopic scanning electron microscope image shows that Fe-NC-6 is a framework cubic nanoparticle with Fe element uniformly distributed within the porous framework.

[0064] Specific surface area was measured using a surface area and porosity analyzer (BET). The specific surface area diagram of Fe-NC-6 prepared in step four of Example 1 is shown below. Figure 9 As shown, from Figure 9 It can be seen that the specific surface area of ​​Fe-NC-6 is 512.606 m². 2 g -1 Example 2: Specific surface area diagram of Fe-NC-12 prepared in step four is shown below. Figure 10 As shown, from Figure 10 It can be seen that the specific surface area of ​​Fe-NC-12 is 512.672 m². 2 g -1 Example 3: The specific surface area diagram of Fe-NC-24 prepared in step four is shown below. Figure 11 As shown, from Figure 11 It can be seen that the specific surface area of ​​Fe-NC-24 is 435.808 m². 2 g -1 .

[0065] Application Example 1: 0.005 g of Fe-NC adsorbent was added to a series of conical flasks, followed by 50 mL of uranium-containing solution; the uranium-containing solution contained UO2. 2+The concentration was 50 ppm, and the pH values ​​of the solution were adjusted to 2, 3, 4, 5, 6, 7, 8, and 9 respectively. The conical flask was placed in a constant temperature shaker, and the shaking speed was set to 180 rpm. The adsorption experiment was carried out at room temperature. After 24 hours of adsorption, the concentration of uranium ions in the supernatant was measured, and the adsorption capacity and removal rate were calculated.

[0066] The adsorption capacities of Fe-NC-6, Fe-NC-12, and Fe-NC-24 as a function of pH are shown below. Figure 12 As shown, Fe-NC-6, Fe-NC-12, and Fe-NC-24 affect the concentration of UO2 in uranium-containing solutions. 2+ The removal rate changes with pH value as follows: Figure 13 As shown, from Figure 12 and Figure 13 It can be seen that under strongly acidic conditions (pH=2), the adsorption capacity and removal rate of Fe-NC are very low. However, the adsorption performance gradually increases with increasing pH, reaching its optimal performance at pH=6, where the Fe-NC-6 adsorption capacity is 491.46 mg g. -1 The removal rate was 98.29%; the adsorption capacity of Fe-NC-12 was 480.16 mg / g. -1 The removal rate was 96.03%; the adsorption capacity of Fe-NC-24 was 462.41 mg g. -1 The removal rate was 92.48%, and then showed a decreasing trend with increasing pH. From Figure 12 and 13 It can be seen that the optimal pH value is 6 to 9.

[0067] Application Example 2: 0.005 g of Fe-NC adsorbent was added to a series of conical flasks, followed by 50 mL of uranium-containing solution. The uranium-containing solution contained UO2. 2+ The concentration was 60 ppm, and the pH of the solution was adjusted to 6. The conical flask was placed in a constant temperature shaker, and the shaking speed was set to 180 rpm. Adsorption experiments were carried out at temperatures of 15℃, 25℃, 35℃, 45℃ and 55℃ respectively. After 24 h of adsorption, the concentration of uranium ions in the supernatant was measured, and the adsorption capacity and removal rate were calculated.

[0068] The adsorption capacities of Fe-NC-6, Fe-NC-12, and Fe-NC-24 change with temperature as follows: Figure 14 As shown, from Figure 14 It can be seen that within the temperature range of 15–55℃, Fe-NC-6, Fe-NC-12, and Fe-NC-24 adsorb UO2. 2+ The adsorption capacity of Fe-NC-6 gradually increased with increasing temperature, from 483.55 mg / g.-1 It increased to 592.68 mg g -1 Fe-NC-12 consists of 449.55 mg g -1 It increased to 590.28 mg g -1 Fe-NC-24 consists of 420.15 mg g -1 It increased to 583.88 mg g -1 This demonstrates that increasing the temperature is beneficial for the adsorption of uranyl ions.

[0069] Application Example 3: 0.005 g of Fe-NC adsorbent was added to a series of conical flasks, followed by 50 mL of uranium-containing solution; the uranium-containing solution contained UO2. 2+ The concentration was 50 ppm, and the pH of the solution was adjusted to 6. The conical flask was placed in a constant temperature shaker, and the shaking speed was set to 180 rpm. Adsorption experiments were carried out at a temperature of 25℃ for 0 to 22 hours. Every hour, a sample was taken to measure the concentration of uranium ions in the supernatant, and the adsorption capacity and removal rate were calculated.

[0070] Fe-NC-6, Fe-NC-12 and Fe-NC-24 affect UO2 2+ For uranium-containing solutions UO2 2+ The change in removal rate over time is as follows: Figure 15 As shown, from Figure 15 It can be seen that Fe-NC adsorbent can remove 60% of UO2 within the first 6 hours. 2+ With increasing adsorption time, the removal performance gradually improved and reached adsorption equilibrium after 20 hours. The removal rate of Fe-NC-6 was 98.29%; the removal rate of Fe-NC-12 was 96.03%; and the removal rate of Fe-NC-24 was 92.48%.

[0071] Application Example 4: 0.005 g of Fe-NC adsorbent was added to each of a series of conical flasks, followed by 50 mL of uranium-containing solution; the uranium-containing solution contained UO2. 2+ The initial concentration was 30–90 ppm, and the pH of the solution was adjusted to 6. The conical flask was placed in a constant temperature shaker, and the shaking speed was set to 180 rpm. Adsorption experiments were carried out at a temperature of 25 °C. After 24 h of adsorption, the concentration of uranium ions in the supernatant was measured, and the adsorption capacity and removal rate were calculated.

[0072] The effect of initial concentration on the adsorption capacity of Fe-NC-6, Fe-NC-12 and Fe-NC-24 is shown in the figure below. Figure 16 As shown; from Figure 16It can be seen that at initial concentrations of 30 ppm, 40 ppm, and 50 ppm, Fe-NC-6, Fe-NC-12, and Fe-NC-24 can remove most of UO2. 2+ Concentration. The adsorption capacity increases with increasing initial concentration, reaching its maximum at 90 ppm, with Fe-NC-6 adsorption capacity of 590.42 mg g. -1 The adsorption capacity of Fe-NC-12 is 549.02 mg g. -1 The adsorption capacity of Fe-NC-24 is 516.92 mg g. -1 .

[0073] Application Example 5: 0.005 g of Fe-NC-6 adsorbent was added to a series of conical flasks, followed by 50 mL of uranium-containing solution; the uranium-containing solution contained UO2. 2+ The concentration was set at 50 ppm, and the pH of the solution was adjusted to 6. Then, 0.1 mol / L of a competing ion was added; the competing ion was Mg. 2+ K + Na + Ca 2+ Cl - NO3 - SO4 2- CO3 2- The conical flask was placed in a constant-temperature shaker with a shaking speed of 180 rpm. Adsorption experiments were conducted at room temperature. After 24 hours of adsorption, a sample was taken to measure the uranium ion concentration in the supernatant, and the adsorption capacity and removal rate were calculated. The effect of competing ions on the adsorption capacity of Fe-NC-6 is shown in the figure below. Figure 17 As shown, from Figure 17 It can be seen that in uranium-containing wastewater with competing ions, Fe-NC-6 has a greater influence on UO2. 2+ It still possesses high removal capability and strong anti-interference ability.

[0074] The Fe-NC-6 prepared in Example 1 was used to purify uranium-containing wastewater in Example 1, and then subjected to scanning electron microscopy (SEM). The morphology of the adsorbed Fe-NC-6, the uranyl morphology, and the corresponding energy dispersive spectroscopy (EDS) spectra are shown below. Figure 18 As shown, from Figure 18 Microscopic scanning electron microscopy (SEM) images show that the Fe-NC-6 framework cubic nanoparticles remained intact after uranium-containing wastewater purification, indicating that their original structure was not damaged during adsorption. Furthermore, new plate-like crystal morphologies grew vertically on the Fe-NC-6 surface, and elemental analysis revealed that these plates were formed by the aggregation of O and U elements, representing uranyl hydrates. The elemental contents analyzed by energy dispersive spectroscopy (EDS) are shown in Table 1.

[0075] Table 1. Elemental content of Fe-NC-6 after adsorption

[0076]

[0077] The Fe-NC adsorbents prepared in Examples 1, 2, and 3 have high specific surface area and porous structure, which significantly improves the adsorption capacity for uranium ions and the adsorption rate is fast. The uniform distribution of iron single atoms within the framework enhances the selectivity and stability of the adsorbent, and significantly improves the efficiency and service life of uranium-containing wastewater purification.

Claims

1. A method for preparing an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater, characterized in that... This method is performed in the following steps: I. Preparation of ZIF-8 nanocrystals; II. Synthesis of ZIF-8@K-TA: ZIF-8 nanocrystals were dispersed in deionized water at a concentration of 20-25 g / L and stirred for 1-2 h to obtain a ZIF-8 dispersion. A tannic acid aqueous solution with a concentration of 6-24 mmol / L was adjusted to pH 8 with KOH solution to obtain an alkaline tannic acid solution. The alkaline tannic acid solution was then added to the ZIF-8 dispersion at a volume ratio of 3:10, and stirred for 7-10 minutes. The mixture was then centrifuged, and the solid product was washed three times with deionized water and methanol, respectively, and dried to obtain ZIF-8@K-TA. III. Synthesis of ZIF-8@Fe-TA: ZIF-8@K-TA was soaked in a methanol solution of ferric nitrate and stirred for 2-3 hours. After centrifugation, the solid product was washed three times with methanol and dried under vacuum to obtain ZIF-8@Fe-TA. IV. Synthesis of Fe-NC: ZIF-8@Fe-TA was transferred to a ceramic crucible and placed in a furnace under a dry argon flow. It was annealed by heating from room temperature to 900~950℃ at a heating rate of 5°C / min and holding for 2~3 hours. Then it was cooled to room temperature to obtain an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater, denoted as Fe-NC.

2. The method for preparing an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater according to claim 1, characterized in that, The preparation method of ZIF-8 nanocrystals in step one is carried out according to the following steps: (1) Weigh out 2-methylimidazole and zinc nitrate hexahydrate according to the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate of 4.71:1; (2) Prepare a mixture of N,N-dimethylformamide, methanol and ethanol in a volume ratio of 3:1:1; then dissolve the 2-methylimidazole weighed in step (1) in the mixture to obtain solution A; wherein the concentration of 2-methylimidazole in solution A is 1.5~1.6 mol / L; (3) N,N-dimethylformamide and methanol are mixed in a volume ratio of 3:2 to form a mixed solvent; then the zinc nitrate hexahydrate weighed in step (1) is dissolved in the mixed solvent to obtain solution B; the concentration of zinc nitrate hexahydrate in solution B is 0.20~0.25mol / L; (4) Add the solution A prepared in step (2) to the solution B prepared in step (3), stir at room temperature for 20-24 hours, centrifuge, wash the solid with methanol 3 times, and vacuum dry to obtain ZIF-8 nanocrystals.

3. A method for preparing an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater according to claim 1 or 2, characterized in that, The concentration of the KOH solution mentioned in step two is 6 mol / L.

4. A method for preparing an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater according to claim 1 or 2, characterized in that, The drying process described in step two involves drying in an oven at a temperature of 35-40℃ for 8-10 hours.

5. A method for preparing an iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater according to claim 1 or 2, characterized in that, The vacuum drying described in step three involves drying in a vacuum drying oven at a temperature of 45-50°C for 10-12 hours.

6. The application of the iron single-atom porous framework adsorbent prepared by the method of claim 1 for the deep purification of uranium-containing wastewater, characterized in that... This application utilizes iron single-atom porous framework adsorbents to treat uranium-containing wastewater.

7. The application of the iron single-atom porous framework adsorbent for deep purification of uranium-containing wastewater according to claim 6, characterized in that... The method for treating uranium-containing wastewater using iron single-atom porous framework adsorbent is as follows: the iron single-atom porous framework adsorbent is added to the uranium-containing wastewater, and the pH value is adjusted to 6-9; after adsorption at a temperature of 15-55℃ for 10-20 hours, the iron single-atom porous framework adsorbent is separated to complete the treatment of uranium-containing wastewater.

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