An amidoximated g-C3N4 / ZrO2 adsorbent, its preparation method and application, and uranium extraction method

Abstract

The present disclosure provides an amidoximated g-C3N4 / ZrO2 adsorbent, a preparation method and application thereof, and a uranium extraction method. The amidoximated g-C3N4 / ZrO2 adsorbent has good adsorption performance, and its preparation method has low cost and can be applied to large-scale synthesis, making the uranium extraction method using the same more economical. The preparation method includes: synthesizing g-C3N4 / ZrO2 by a one-pot calcination method; synthesizing a polyacrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a blending method; and introducing an amidoxime group into the polyacrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a hydroxylamine method to obtain a polyacrylonitrile composite material loaded with amidoximated g-C3N4 / ZrO2.

Description

Technical Field

[0001] The present disclosure relates to the technical field of material preparation, and in particular to an amidoximated g-C3N4 / ZrO2 adsorbent, a preparation method and application thereof, and a uranium extraction method. Background Art

[0002] The rich uranium resources in seawater are the key to the further development of nuclear energy. However, the complex seawater environment leads to the diversity of uranium forms, which limits the extraction of uranium. Due to the dissolution of atmospheric CO2, carbonate (CO3 2- ) and bicarbonate (HCO3 - ) anions become the main coexisting ions in seawater and combine with uranyl ions in seawater to form U(VI)-CO3 complexes, such as UO2(CO3)2 2- and UO2(CO3)3 4- These U(VI)-CO3 complex anions are also the main forms of uranium in seawater. The presence of these complex species will lead to changes in uranium adsorption behavior, which is different from the traditional adsorption of uranyl ions (UO22+) under acidic conditions.

[0003] At present, the main methods for extracting uranium from seawater are roughly divided into: membrane filtration, solvent extraction, ion exchange, adsorption, etc. Among them, the adsorption method is recognized as the most promising uranium extraction method due to its advantages of high efficiency, simple preparation, and low cost. Among the many adsorption materials, amidoxime-based materials have the greatest development potential due to their high affinity and ion selectivity for uranyl ions, acid and alkali resistance, and long service life. Summary of the invention

[0004] In view of the current status of the above-mentioned prior art, the embodiments of the present disclosure provide an amidoximated g-C3N4 / ZrO2 adsorbent and its preparation method and application, and a uranium extraction method. The amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure has good adhesion performance, its preparation method is low in cost and can be applied to large-scale synthesis, making the uranium extraction method using it more economical.

[0005] To achieve the above objectives, the embodiments of the present disclosure adopt the following technical solutions:

[0006] In a first aspect, the present disclosure provides a method for preparing an amidoximated g-C3N4 / ZrO2 adsorbent, the preparation method comprising:

[0007] Step 1: Synthesize g-C3N4 / ZrO2 by one-pot calcination method;

[0008] Step 2: synthesize g-C3N4 / ZrO2-loaded polyacrylonitrile-based or acrylonitrile-based composite materials by blending method;

[0009] Step 3: Introduce amidoxime groups into the composite material obtained in Step 2 to obtain the amidoximated polyacrylonitrile or acrylonitrile composite material loaded with g-C3N4 / ZrO2.

[0010] Optionally, Step 1: Synthesize g-C3N4 / ZrO2 by a one-pot calcination method, including:

[0011] Mix melamine and Zr(NO3)4·5H2O in a mortar and grind them, then put them into a crucible. Heat the crucible in a muffle furnace at a heating rate of 5 °C min-1 to 550 °C, and then calcine at this temperature for 4 hours to obtain g-C3N4 / ZrO2.

[0012] Optionally, Step 2: Synthesize the polyacrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a blending method, including:

[0013] Add polyacrylonitrile fibers to N,N-dimethylformamide, and stir them in an oil bath at 95 °C until the fibers are completely dissolved; subsequently, disperse the g-C3N4 / ZrO2 obtained in Step 1 into this solution, and reflux for 12 h at 95 °C; after the reaction, add the mixed solution dropwise to cold deionized water under magnetic stirring while it is still hot, then filter and separate by suction, and dry to obtain the polyacrylonitrile composite material PAN-g-C3N4 / ZrO2.

[0014] Optionally, in Step 3, introducing amidoxime groups by the hydroxylamine method includes:

[0015] Mix the PAN-g-C3N4 / ZrO2 composite material obtained in Step 2, hydroxylamine hydrochloride and sodium carbonate in pure water, and then react at 65 °C for 5 h; after the reaction, filter and wash the precipitate, and dry it under vacuum to obtain the final amidoximated polyacrylonitrile fiber composite material g-C3N4 / ZrO2-AO.

[0016] Optionally, in Step 1, the masses of melamine and Zr(NO3)4·5H2O are 10 g and 3.3 g respectively; in Step 2, the masses of polyacrylonitrile fibers, N,N-dimethylformamide and g-C3N4 / ZrO2 obtained in Step 1 are 1.25 g, 25 g and 0.25 g respectively; in Step 3, the masses of the PAN-g-C3N4 / ZrO2 composite material obtained in Step 2, hydroxylamine hydrochloride and sodium carbonate are 0.5 g, 8 g and 5.8 g respectively.

[0017] Optionally, the method for introducing amidoxime groups in Step 3 can adopt the hydroxylamine method.

[0018] Second aspect, embodiments of the present disclosure provide an amidoximated g-C3N4 / ZrO2 adsorbent, and the amidoximated g-C3N4 / ZrO2 adsorbent is obtained by the preparation method described in the first aspect.

[0019] Third aspect, embodiments of the present disclosure provide an application of the amidoximated g-C3N4 / ZrO2 adsorbent described in the second aspect, and the amidoximated g-C3N4 / ZrO2 adsorbent is applied in radioactive element separation, environmental treatment, etc.

[0020] Third aspect, embodiments of the present disclosure provide a uranium extraction method, and the uranium extraction method uses the amidoximated g-C3N4 / ZrO2 described in the second aspect as an adsorbent.

[0021] Optionally, in the uranium extraction method, the application environment of the amidoximated g-C3N4 / ZrO2 as an adsorbent is mainly the weak alkaline condition of seawater: pH initial = 7.9 - 8.4 and [NaHCO3] = 2.3 - 5 mmol·L -1 .

[0022] The amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure has good adsorption performance, and its preparation method has low cost and can be applied to large-scale synthesis, making the uranium extraction method using it more economical. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a flow chart of the preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent of the embodiments of the present disclosure.

[0025] Figure 2.1 It is a comparison of the adsorption amounts of modified materials.

[0026] Figure 2.2 It is the influence of time (a); the first-order and second-order models in the first 2h (b); the first-order and second-order models after 2h (c).

[0027] Figure 2.3 It is the influence of the initial uranium concentration (a); the Langmuir model fitting (b); the Freundlich model fitting (c).

[0028] Figure 2.4 It is the influence of pH (a); CO32- Effect (b).

[0029] Figure 2.5 It is the temperature effect. Specific implementation mode

[0030] As described in the background art, among many adsorption materials, amidoxime-based materials have the greatest development potential. As one of the most effective functional groups for uranium adsorption, the amidoxime group is currently widely used in the work of extracting uranium from seawater. Since the first proposal of uranium extraction from seawater in the 1980s, the amidoxime group has been applied to the actual uranium extraction work from seawater. For example, the amidoxime-based fiber non-woven fabric adsorbent prepared in Japan around 2000 was exposed to seawater in the form of an adsorption bed to adsorb uranium, and the uranium adsorption capacity reached 0.5 mg / g after 30 days. On this basis, the adsorption capacity of the SB12-8 adsorbent jointly developed by the Oak Ridge National Laboratory (ORNL) of the United States and the University of Tennessee in 2016 has been increased to 6.56 mg / g. Around 2022, the biaxially stretched polyethylene membrane containing amidoxime functional groups (PAO-BSPE) developed by the Shanghai Institute of Applied Physics, Chinese Academy of Sciences, reached 11.17 mg / g and 12.67 mg / g respectively after 56 days and 64 days of uranium adsorption in natural seawater. This series of research results show that amidoxime-based adsorbents are more suitable for practical applications, especially amidoximated fiber-based adsorbents.

[0031] Based on the research status of the above related technologies, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0032] In the first aspect, as Figure 1 shown, the embodiments of the present disclosure provide a preparation method of an amidoximated g-C3N4 / ZrO2 adsorbent, and the preparation method includes:

[0033] Step1: Synthesize g-C3N4 / ZrO2 by a one-pot calcination method;

[0034] Specifically, mix melamine and Zr(NO3)4·5H2O in a mortar and grind them, then put them into a crucible, heat them to 550°C at a heating rate of 5°C min-1 in a muffle furnace, and then calcine them at this temperature for 4 hours to obtain g-C3N4 / ZrO2.

[0035] Step2: Synthesize a polyacrylonitrile-based or acrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a blending method;

[0036] Specifically, polyacrylonitrile fibers were added to N,N-dimethylformamide and stirred in an oil bath at 95 °C until the fibers were completely dissolved. Subsequently, the g-C3N4 / ZrO2 obtained in Step1 was dispersed into this solution and refluxed for 12 h at 95 °C. After the reaction, the mixture was added dropwise to cold deionized water under magnetic stirring while it was still hot, and then separated by suction filtration. After drying, the polyacrylonitrile composite material PAN-g-C3N4 / ZrO2 was obtained.

[0037] Step3: Introduce amidoxime groups into the composite material obtained in Step2 to obtain amidoximated polyacrylonitrile or acrylonitrile composite material loaded with g-C3N4 / ZrO2.

[0038] Specifically, the PAN-g-C3N4 / ZrO2 composite material obtained in step2, hydroxylamine hydrochloride and sodium carbonate were mixed in pure water, and then reacted at 65 °C for 5 h. After the reaction, the precipitate was filtered and rinsed, and the final amidoximated polyacrylonitrile fiber composite material g-C3N4 / ZrO2-AO was obtained after vacuum drying.

[0039] Optionally, in Step1, the mass ratio of melamine to Zr(NO3)4·5H2O is 100:33; in Step2, the mass ratio of polyacrylonitrile fibers, N,N-dimethylformamide to the g-C3N4 / ZrO2 obtained in Step1 is 5:100:1; in step3, the mass ratio of the PAN-g-C3N4 / ZrO2 composite material, hydroxylamine hydrochloride and sodium carbonate obtained in step2 is 5:80:58.

[0040] To more clearly illustrate and describe the preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure, a specific implementation manner is provided below:

[0041] First, g-C3N4 / ZrO2 was synthesized by a one-pot calcination method: 10 g of melamine and 3.3 g of Zr(NO3)4·5H2O were mixed and ground in a mortar and then placed in a crucible. The temperature was raised to 550 °C at a heating rate of 5 °C min-1 in a muffle furnace, and then calcined at this temperature for 4 hours to obtain g-C3N4 / ZrO2.

[0042] The polyacrylonitrile-based composite material was synthesized by a blending method. 1.25 g of waste commercially available polyacrylonitrile fibers were added to 25 g of N,N-dimethylformamide and stirred in an oil bath at 95 °C until the fibers were completely dissolved. Subsequently, 0.25 g of g-C3N4 / ZrO2 was dispersed into the above solution and refluxed for 12 h at 95 °C. After the reaction, the mixture was added dropwise to cold deionized water under magnetic stirring while it was still hot, and then separated by suction filtration. After drying, the polyacrylonitrile composite material (PAN-g-C3N4 / ZrO2) was obtained.

[0043] Finally, the final amidoximated polyacrylonitrile composite material was obtained by the hydroxylamine method. 0.5 g of PAN-g-C3N4 / ZrO2 composite material, 8.0 g of hydroxylamine hydrochloride and 5.8 g of sodium carbonate were mixed in 100 ml of pure water, and then reacted at 65 °C for 5 h. After the reaction, the precipitate was filtered and rinsed, and the final amidoximated polyacrylonitrile fiber composite material (g-C3N4 / ZrO2-AO) was obtained after vacuum drying.

[0044] The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure synthesizes g-C3N4 / ZrO2 by a one-pot calcination method, composites g-C3N4 / ZrO2 with polyacrylonitrile by a mechanical blending method, and then obtains an amidoximated polyacrylonitrile-supported g-C3N4 / ZrO2 composite material by the hydroxylamine method. In particular, using waste commercial polyacrylonitrile fibers - an engineering material that can improve the crack resistance of concrete - as the starting material, combined with the mechanical blending method, the preparation cost is greatly reduced. And the preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure can be applied to large-scale synthesis.

[0045] Optionally, in some embodiments, the method for introducing amidoxime groups in step 3 adopts the hydroxylamine method.

[0046] In a second aspect, the embodiments of the present disclosure provide an amidoximated g-C3N4 / ZrO2 adsorbent, which is prepared by the preparation method described in the first aspect.

[0047] As a carbon material, g-C3N4 has unique two-dimensional structure, excellent chemical stability and other characteristics. At present, composites of g-C3N4 have been applied in various fields, such as photocatalysis, capacitors, solar hydrogen production, etc., but there are few studies on its use as an adsorbent in the field of uranium adsorption. As a metal oxide, ZrO2 has good chemical stability and excellent mechanical properties, and the formation of its surface hydroxyl groups also provides adsorption sites. Its properties are similar to those of TiO2, but there are still few studies on its uranium adsorption. Amidoxime group is one of the most effective functional groups for uranium adsorption. The embodiments of the present disclosure use the preparation method described in the first aspect to obtain an amidoximated polyacrylonitrile-supported g-C3N4 / ZrO2 composite material, which can be used as a new type of adsorbent with high adsorption performance.

[0048] In order to more clearly illustrate the excellent performance of the amidoximated polyacrylonitrile-supported g-C3N4 / ZrO2 composite material provided by the embodiments of the present disclosure, the following uses relevant experiments to illustrate this.

[0049] Adsorption experiment

[0050] Weigh 10 mg of g-C3N4 / ZrO2-AO adsorbent into a 50 mL plastic conical flask, add 25 mL of uranium solution with a certain concentration, and under different conditions of initial pH value, contact time, initial concentration, etc., oscillate and react in a 25 °C water bath constant temperature oscillator at a speed of 150 r·min -1 After the reaction, take 4 mL of the uranium solution after adsorption into a 5 mL centrifuge tube, and centrifuge at 10000 r·min -1 for 5 min. After completion, take 1 mL of the supernatant and use the arsenazo(Ⅲ) method. Using a UV-2450 type ultraviolet spectrophotometer, measure the initial and equilibrium uranium concentrations under the condition of a wavelength of 651.8 nm. The adsorption capacity q e and the removal rate S are calculated by equations (1) and (2):

[0051]

[0052]

[0053] In the formula: C0 and C e are the initial and equilibrium concentrations of uranium in the solution (mg / L), V is the volume of the solution (L); m is the mass of the adsorbent (g).

[0054] Experimental results

[0055] 1 Comparison of adsorption amounts of modified materials

[0056] The experimental results before and after material modification are as Figure 2.1 shown. In the uranyl carbonate system, the adsorption amount of ZrO2 is the lowest. The introduction of g-C3N4 increases the adsorption amount of the material. The possible reason is that ZrO2 has the characteristic of easy agglomeration. The introduction of g-C3N4 increases its dispersibility and also provides some adsorption sites. The final amidoximated g-C3N4 / ZrO2 (g-C3N4 / ZrO2-AO) has the highest adsorption amount, because the introduction of the amidoxime group leads to a further increase in the adsorption amount.

[0057] 2 Kinetic influence

[0058] The influence of time is as Figure 2.2 shown in a. The adsorption process reaches equilibrium at about 12 h. Under the conditions of pH initial = 8.0, [U(Ⅵ)] initial = 50 mg·L -1 , T(℃) = 25 °C and [NaHCO3] = 2 mmol·L -1 , the adsorption amount of g-C3N4 / ZrO2-AO for uranium can reach 106.9 mg·g -1Meanwhile, the experimental data were fitted with a kinetic model to further describe the adsorption process, as Figure 2.2 shown in Figures b and c. It can be seen from the figures that the kinetics was very slow within the first 2 h. According to the fitting results, the possible reason is that physical adsorption dominated within the first 2 h. The kinetics accelerated after 2 h because chemical adsorption dominated the adsorption process.

[0059] 3 Uranium concentration and isothermal model

[0060] The isotherm of the material was investigated to further explore the adsorption process. The influence of the initial uranium concentration on adsorption is shown in Figure 2.3 Figure a. As the initial uranium concentration increased, the adsorption capacity of g-C3N4 / ZrO2-AO for uranium also increased, indicating that the active sites in g-C3N4 / ZrO2-AO were not completely occupied. The experimental results were fitted with the Langmuir and Freundlich models, as Figure 2.3 shown in Figures b and c. The results showed that the Langmuir model had a higher fitting degree (R 2 = 0.998) for the experimental results, and the adsorption process mainly occurred as monolayer homogeneous adsorption.

[0061] 4 Influence of pH and CO3 2-

[0062] pH is a key factor affecting the adsorption of uranium by the adsorbent. Under the alkaline conditions with the presence of CO3 2- , the influence of pH in the range of 7 - 9 on the adsorption of uranium by g-C3N4 / ZrO2-AO was investigated, and the results are shown in Figure 2.4 Figure a. As the pH increased, the adsorption capacity of g-C3N4 / ZrO2-AO for uranium showed a downward trend, which may be due to the fact that as the pH increased, uranium species gradually transformed into UO2(CO3)3 4- . CO3 2- is the main anion in natural uranium-containing water bodies, and its influence on uranium adsorption cannot be ignored. Figure 2.4 The results in Figure b showed that a higher concentration of CO3 2- would inhibit the adsorption of uranium by g-C3N4 / ZrO2-AO. The possible reason is that the increase in the CO3 2- concentration enhanced the complexation between CO3 2- and uranyl ions [7] , thereby weakening the interaction between g-C3N4 / ZrO2-AO and uranyl ions.

[0063] 5 Temperature influence

[0064] The influence of temperature on the adsorption of uranium by g-C3N4 / ZrO2-AO was investigated, as Figure 2.5 ​As shown, from the results, the increase in temperature is beneficial to the adsorption of uranium by g-C3N4 / ZrO2-AO. The possible reason is that the increase in temperature promotes the movement of molecules in the solution and increases the collision probability between uranyl ions and adsorption sites.

[0065] The examples provided in this disclosure utilize waste commercial polyacrylonitrile fibers to synthesize g-C3N4 / ZrO2-AO by mechanical blending method and hydroxylamine method and study its adsorption performance. The results show that at pH initial = 8.0, [U(VI)] initial = 50 mg·L -1 , T(°C) = 25 °C and [NaHCO3] = 2 mmol·L -1 , the adsorption capacity of g-C3N4 / ZrO2-AO for uranium can reach 106.9 mg·g -1 . The fitting results of the isothermal model show that the adsorption process is mainly monolayer homogeneous adsorption. Under the conditions of higher pH and CO3 2- concentration, the adsorption of uranium by g-C3N4 / ZrO2-AO is inhibited. In addition, the increase in temperature is beneficial to improving the adsorption capacity of g-C3N4 / ZrO2-AO for uranium.

[0066] In the third aspect, the embodiments of the present disclosure provide the application of the amidoximated g-C3N4 / ZrO2 adsorbent described in the second aspect. The amidoximated g-C3N4 / ZrO2 adsorbent exhibits excellent performance in uranium adsorption and has great application prospects in the fields of uranium extraction from seawater, separation of radioactive elements, environmental treatment, etc.

[0067] In the fourth aspect, the embodiments of the present disclosure provide a uranium extraction method that uses the amidoximated g-C3N4 / ZrO2 described in the second aspect as an adsorbent.

[0068] Optionally, in the uranium extraction method, the application environment of the amidoximated g-C3N4 / ZrO2 as an adsorbent is mainly the weak alkaline condition of seawater: pH initial = 7.9 - 8.4 and [NaHCO3] = 2.3 - 5 mmol·L -1 . Specifically, in the uranium extraction method, the amidoximated g-C3N4 / ZrO2 is used as an adsorbent for extracting uranium from weak alkaline seawater: pH initial = 8.0, [U(VI)] initial = 50 mg·L -1 , T(°C) = 25 °C and [NaHCO3] = 2 mmol·L -1 .

[0069] The amidoximated g-C3N4 / ZrO2 adsorbent provided by the embodiments of the present disclosure has good adsorption performance, and its preparation method has low cost and can be applied to large-scale synthesis, making the uranium extraction method using it more economical.

[0070] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In the description of this specification, the description referring to terms such as "optional" and "this embodiment" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0071] The above are only the specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present disclosure should be covered by the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A preparation method of an amidoximated g-C3N4 / ZrO2 adsorbent, characterized in that, The preparation method includes: Step1: Synthesize g-C3N4 / ZrO2 by a one-pot calcination method; Step2: Synthesize a polyacrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a blending method; Step3: Introduce amidoxime groups into the composite material obtained in Step2 to obtain a g-C3N4 / ZrO2-loaded amidoximated polyacrylonitrile composite material.

2. The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 1, wherein, Step1: Synthesizing g-C3N4 / ZrO2 by a one-pot calcination method includes: Mix melamine and Zr(NO3)4·5H2O in a mortar, grind them, then put them into a crucible, and heat them in a muffle furnace at a heating rate of 5 °C min -1 to 550 °C, and then calcine at this temperature for 4 hours to obtain g-C3N4 / ZrO2.

3. The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 2, characterized in that, Step2: Synthesizing a polyacrylonitrile-based composite material loaded with g-C3N4 / ZrO2 by a blending method includes: Add polyacrylonitrile fibers to N,N-dimethylformamide and stir in an oil bath at 95 °C until the fibers are completely dissolved; Subsequently, disperse the g-C3N4 / ZrO2 obtained in Step1 into this solution and reflux for 12 h at 95 °C; After the reaction, add the mixed solution dropwise to cold deionized water under magnetic stirring while it is still hot, then filter and separate by suction filtration, and dry to obtain the polyacrylonitrile composite material PAN-g-C3N4 / ZrO2.

4. The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 3, characterized in that, Introducing amidoxime groups in Step3 includes: Mix the PAN-g-C3N4 / ZrO2 composite material obtained in Step2, hydroxylamine hydrochloride, and sodium carbonate in pure water, and then react at 65 °C for 5 h; After the reaction, filter and wash the precipitate, and vacuum dry to obtain the final amidoximated polyacrylonitrile fiber composite material g-C3N4 / ZrO2-AO.

5. The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 4, characterized in that, In Step1, the masses of melamine and Zr(NO3)4·5H2O are 10 g and 3.3 g; in Step2, the masses of polyacrylonitrile fibers, N,N-dimethylformamide, and g-C3N4 / ZrO2 obtained in Step1 are 1.25 g, 25 g, and 0.25 g respectively; in Step3, the masses of the PAN-g-C3N4 / ZrO2 composite material obtained in Step2, hydroxylamine hydrochloride, and sodium carbonate are 0.5 g, 8 g, and 5.8 g.

6. The preparation method of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 1, characterized in that, The method for introducing amidoxime groups in Step3 adopts the hydroxylamine method.

7. An amidoximated g-C3N4 / ZrO2 adsorbent, characterized in that, The amidoximated g-C3N4 / ZrO2 adsorbent is prepared by any of the preparation methods of claims 1-6.

8. Use of the amidoximated g-C3N4 / ZrO2 adsorbent according to claim 7, characterized in that: The amidoximated g-C3N4 / ZrO2 adsorbent is applied in the separation of radioactive elements and environmental treatment.

9. A uranium extraction method, characterized in that, The uranium extraction method uses the amidoximated g-C3N4 / ZrO2 described in claim 7 as an adsorbent.

10. The uranium extraction method according to claim 9, characterized in that, In the uranium extraction method, the application environment of the amidoximated g-C3N4 / ZrO2 as an adsorbent is mainly the weak alkaline condition of seawater: pH initial = 7.9 - 8.4 and [NaHCO3] = 2.3 - 5 mmol·L -1 .

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