A hollow flower ball-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst and a preparation method and application thereof

Abstract

The application discloses a hollow flower-like Bi2O3 / g-C3N4 heterojunction photocatalyst and a preparation method and application thereof, and belongs to the technical field of photocatalytic materials. The hollow flower-like Bi2O3 / g-C3N4 heterojunction photocatalyst is successfully synthesized by taking melamine and cyanuric acid as raw materials, synthesizing hollow nanospheres g-C3N4 by using a supramolecular self-assembly method, and loading Bi2O3 nanosheets on the g-C3N4 by using a solvothermal synthesis method with the hollow nanospheres g-C3N4 as a substrate. Meanwhile, the photocatalyst has a unique hollow flower-like microstructure, a high specific surface area (39.34-78.12 m 2 / g), and a large number of active sites, can improve light utilization, and thus improves the redox performance of the photocatalysis. When the photocatalyst is applied to photo-assisted extraction of uranium, the removal rate of U(VI) can reach 98.45%, the photocatalyst has excellent anti-interference and stability, and has good repeatable recycling, and the removal rate of U(VI) is still as high as 90.77% after 5 times of recycling, and the photocatalyst has good practical application value for efficiently enriching uranium in uranium-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] The limited reserves of uranium (U) ore and the application of nuclear energy have led to environmental pollution problems, hindering the sustainable development of nuclear energy. Throughout the entire application process of the nuclear industry (including mining, processing, and reprocessing), uranium-containing wastewater is generated. This wastewater is chemically toxic and radioactive, and improper handling and accidental leaks during mining and use pose a significant threat to humans and other life on Earth. Seawater is a vast liquid uranium deposit; it is estimated to contain approximately 4.5 billion tons of uranium, thousands of times the proven uranium reserves on land. Therefore, how to efficiently extract uranium resources from uranium wastewater and seawater is an urgent problem to be solved. Currently, uranium extraction methods mainly rely on enrichment through porous adsorption materials; therefore, improving the efficient and selective extraction of uranium is a key focus in the design of adsorption materials. U(VI) exhibits strong migration capabilities and is widely present in uranium-containing wastewater or seawater, primarily in the form of uranyl ions or their complexes. The discharge of untreated radioactive uranium-containing wastewater poses a serious threat to the ecological environment. Therefore, the reduction of highly toxic and soluble U(VI) to the relatively less toxic and insoluble U(IV) is attracting increasing research attention and is considered a reasonable solution for the efficient extraction of uranyl. Solar energy is an inexhaustible resource; photocatalytic reduction methods can reduce highly migratory hexavalent uranium to tetravalent uranium with high complexing ability, thereby improving the efficiency of uranium extraction.

[0003] Graphite-phase carbon nitride (g-C3N4) nonmetallic photocatalysts possess advantages such as visible light response, two-dimensional conjugated structure, non-toxicity, and ease of preparation. However, pure g-C3N4 photocatalysts still suffer from low photogenerated carrier separation efficiency, resulting in unsatisfactory photocatalytic activity. Current methods to improve the photocatalytic efficiency of g-C3N4 mainly include morphology control, elemental doping, nanocluster encapsulation, noble metal deposition, and heterojunction construction. Bismuth trioxide (Bi2O3) is a wide-bandgap semiconductor with good electron mobility and chemical inertness. However, unmodified Bi2O3 has a relatively wide bandgap (~2.8 eV), exhibiting insufficient absorption capacity in the visible spectrum. Coupled with hollow nanospheres (g-C3N4) to form a heterojunction semiconductor, the bandgap of Bi2O3 can be controlled, and the photogenerated carrier separation efficiency of g-C3N4 can be improved, thereby enhancing the redox performance of the material.

[0004] Methods for preparing g-C3N4 include thermal polycondensation, template method, and solvothermal method. Thermal polycondensation yields g-C3N4 with a single morphology. The template method can synthesize g-C3N4 with specific morphologies, but this method requires further etching with HF or NH4HF2, resulting in high preparation costs and potential environmental pollution. The solvothermal method has a simpler reaction process, but the reaction conditions significantly affect the synthesized product. Supramolecular self-assembly, a process in which molecules spontaneously assemble into stable aggregates under equilibrium conditions using weak forces such as hydrogen bonds, van der Waals forces, and electrostatic interactions, has been widely applied in crystal engineering, molecular recognition, and catalysis. Because supramolecular self-assembly can form supramolecular aggregates with controllable morphologies between melamine and triazine derivatives, it has been widely used to synthesize g-C3N4 with different morphologies to further enhance its photocatalytic activity. Generally, triazine derivatives (such as melamine and cyanuric acid) are selected as raw materials, and g-C3N4 with different morphologies is synthesized through molecular self-assembly and subsequent high-temperature calcination. Bi₂O₃ samples prepared by the solvothermal method have advantages such as good dispersibility, high purity, and easy control of particle size and morphology, making them widely used in the preparation of nanomaterials. Therefore, this invention uses a supramolecular self-assembly method combined with solvothermal synthesis to synthesize hollow flower-shaped spherical Bi₂O₃ / g-C₃N₄ heterojunction photocatalysts with high specific surface area and numerous active sites. Summary of the Invention

[0005] To address the above problems, this invention provides a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst, its preparation method, and its application. Hollow nanospheres g-C3N4 are synthesized using a supramolecular self-assembly method, and then Bi2O3 nanosheets are loaded onto g-C3N4 via a solvothermal synthesis method, successfully synthesizing the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst. This photocatalyst is then applied to photo-assisted uranium extraction for efficient enrichment of uranium in uranium wastewater.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst includes the following steps:

[0008] (1) Preparation of g-C3N4 precursor: Melamine was dissolved in dimethyl sulfoxide to form solution A, cyanuric acid was dissolved in dimethyl sulfoxide to form solution B, and then solution B was added to solution A. The resulting mixed solution was stirred and then added to water for standing. The resulting precipitate was centrifuged, washed, dried, ground, and calcined under inert gas protection to obtain hollow nanosphere g-C3N4 precursor;

[0009] (2) Preparation of Bi2O3 / g-C3N4 heterojunction photocatalyst: Bi(NO3)3·5H2O was dissolved in ethylene glycol to form a clear solution. Ethanol was added and stirred. Then g-C3N4 precursor was added. The resulting solution was stirred and transferred to a reaction vessel for solvothermal reaction. After the reaction was completed, the product was centrifuged, washed and dried. The resulting solid product was dispersed in water and NaOH solution was added. After stirring, the product was collected by centrifugation, washed and dried to obtain hollow flower spherical Bi2O3 / g-C3N4 heterojunction photocatalyst.

[0010] Further, in step (1), the mass ratio of melamine to dimethyl sulfoxide in solution A is 15-20 mg:1 mL; the mass ratio of cyanuric acid to dimethyl sulfoxide in solution B is 35-50 mg:1 mL; the mass ratio of melamine to cyanuric acid is 1:1.5-2; and the ratio of water to melamine is 0.2-0.3 mL:1 mg.

[0011] Further, in step (1), the calcination is carried out under nitrogen or argon protection, heating to 450-500°C at a rate of 2-3°C / min for 4-5 hours.

[0012] Further, in step (1), the stirring is carried out at a speed of 600-700 r / min for 1.5-2 hours; the settling time is 13-15 hours.

[0013] Further, in step (2), the ratio of Bi(NO3)3·5H2O, ethylene glycol and ethanol is 0.5-2 mmol:17 mL:32-38 mL; the ratio of Bi(NO3)3·5H2O to g-C3N4 precursor is 0.5-2 mmol:100 mg.

[0014] Further, in step (2), the ratio of NaOH solution, water and Bi(NO3)3·5H2O is 1mL:45~60mL:0.5~2mmol; the concentration of NaOH solution is 4~6mol / L.

[0015] Furthermore, in step (2), the solvothermal reaction is carried out at a temperature of 150–180°C for 4–5 hours.

[0016] A hollow flower spherical Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the method described above.

[0017] Furthermore, the hollow flower-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst has a hollow flower-shaped microstructure and a specific surface area of ​​39.34–78.12 m². 2 / g.

[0018] Application of a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst as described above in the extraction of uranium from radioactive wastewater.

[0019] The preparation principle of the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst of the present invention:

[0020] Supramolecular self-assembly is a process in which molecules form stable aggregates through non-covalent bonds. This invention uses supramolecular self-assembly to create tunable morphologies of supramolecular aggregates between melamine derivatives such as melamine and cyanuric acid. These aggregates are then stirred to form polymer microspheres, which are stabilized through static precipitation aging. Hollow nanospheres g-C3N4 are formed through high-temperature calcination and thermal condensation. Using the hollow nanospheres g-C3N4 as a substrate, Bi2O3 nanosheets are uniformly grown on the hollow nanospheres g-C3N4 using a solvothermal method, thereby forming a hollow flower-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0022] 1. This invention uses melamine and cyanuric acid as raw materials to synthesize hollow nanospheres g-C3N4 via supramolecular self-assembly. Then, using the hollow nanospheres g-C3N4 as a substrate, Bi2O3 nanosheets are loaded onto g-C3N4 via a solvothermal synthesis method, thus successfully synthesizing a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst. Simultaneously, this photocatalyst possesses a unique hollow flower-shaped spherical microstructure and a high specific surface area (39.34–78.12 m²). 2 With its numerous active sites ( / g) and high light utilization rate, it can enhance the redox performance of photocatalysis. Applying it to light-assisted uranium extraction can efficiently enrich uranium in uranium wastewater.

[0023] 2. This invention not only effectively overcomes the shortcomings of insufficient visible light response and small specific surface area of ​​g-C3N4, but also solves the problem of its fast carrier recombination rate. This invention uses a supramolecular self-assembly method to synthesize hollow nanospheres of g-C3N4, and then loads Bi2O3 nanosheets onto g-C3N4 via a solvothermal synthesis method. This not only completely preserves the existing shape of the hollow nanospheres of g-C3N4, but also ensures that the Bi2O3 nanosheets grow uniformly on the g-C3N4 substrate, thereby increasing its specific surface area and enriching its surface active sites, thus enhancing the photocatalytic activity. Furthermore, the strong heterogeneous coupling between Bi2O3 and g-C3N4 at the interface effectively promotes the separation of photogenerated carriers and improves the photosensitivity, thereby enhancing the redox performance of the photocatalyst.

[0024] 3. The preparation method of this invention is simple to operate, uses readily available raw materials, operates under simple and mild conditions, and has low production costs. When the photocatalysis of this invention is applied to uranium extraction, it exhibits excellent uranium extraction performance under visible light irradiation, achieving a U(VI) removal rate of up to 98.45%. It maintains good photocatalytic oxidation-reduction performance under different cation interference and acid / alkali conditions, demonstrating excellent anti-interference and stability. Furthermore, this photocatalyst has excellent recyclability; after five cycles, the U(VI) removal rate remains as high as 90.77%, making it highly valuable for the efficient enrichment of uranium from uranium wastewater. Attached Figure Description

[0025] Figure 1 This is a SEM image of Bi2O3 / g-C3N4 HFs-2 prepared in Example 2.

[0026] Figure 2 This is a TEM image of Bi2O3 / g-C3N4 HFs-2 prepared in Example 2.

[0027] Figure 3 The XRD patterns are of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0028] Figure 4 The images show the FT-IR spectra of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0029] Figure 5 The BET diagrams are for Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0030] Figure 6 The PL plots are for Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0031] Figure 7EIS diagrams of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0032] Figure 8 Transient photocurrent diagrams of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 in Application Examples 1-3 and Comparative Examples 1-2 are shown.

[0033] Figure 9 The graphs show the effects of photocatalytic removal of U(VI) in Application Examples 1-3, Comparative Examples 1-2, and under the conditions of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, Bi2O3, and without a catalyst.

[0034] Figure 10 The graph shows the effect of Bi2O3 / g-C3N4 HFs-2 in removing U(VI) in the presence of different interfering cations in Application Example 2.

[0035] Figure 11 The graph shows the effect of Bi2O3 / g-C3N4 HFs-2 on U(VI) removal under different pH conditions in Application Example 2.

[0036] Figure 12 The image shows the effect of removing U(VI) by 5 cycles of photocatalytic reaction of Bi2O3 / g-C3N4 HFs-2 in Example 2.

[0037] Figure 13 XPS image of Bi2O3 / g-C3N4 HFs-2 after U(VI) removal in Application Example 2. Detailed Implementation

[0038] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0039] Example 1

[0040] Preparation of hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst:

[0041] (1) Preparation of g-C3N4 precursor: 450 mg of melamine was dissolved in 30 mL of dimethyl sulfoxide and stirred to form solution A. 700 mg of cyanuric acid was dissolved in 20 mL of dimethyl sulfoxide and stirred to form solution B. Solution B was added dropwise to solution A under stirring at 600 r / min. The resulting mixed solution was stirred at 600 r / min for 2 h. After stirring, 90 mL of deionized water was added and the mixture was allowed to stand for 13 h. The resulting precipitate was centrifuged, washed, dried, and ground. Then it was placed in a tube furnace and calcined at 450 °C for 5 h at a rate of 2 °C / min under pure argon protection to obtain hollow nanosphere g-C3N4 precursor.

[0042] (2) Preparation of Bi2O3 / g-C3N4 heterojunction photocatalyst: 0.5 mmol of Bi(NO3)3·5H2O was dissolved in 17 mL of ethylene glycol to form a clear solution. Then, 32 mL of ethanol was added and stirred for 10 min. 100 mg of g-C3N4 precursor was added and the resulting solution was stirred for 1 h. The solution was then transferred to a polytetrafluoroethylene reactor and reacted at 150 °C for 5 h. After the reaction was completed, the reaction product was centrifuged, washed, and dried. The obtained solid product was dispersed in 45 mL of deionized water and 1 mL of 4 mol / L NaOH solution was added. After stirring for 1 h, the product was collected by centrifugation, washed, and dried to obtain hollow flower-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst (denoted as Bi2O3 / g-C3N4 HFs-1).

[0043] Example 2

[0044] Preparation of hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst:

[0045] (1) Preparation of g-C3N4 precursor: 500 mg of melamine was dissolved in 30 mL of dimethyl sulfoxide and stirred to form solution A. 800 mg of cyanuric acid was dissolved in 20 mL of dimethyl sulfoxide and stirred to form solution B. Solution B was added dropwise to solution A under stirring at 600 r / min. The resulting mixed solution was stirred at 600 r / min for 2 h. After stirring, 100 mL of deionized water was added and the mixture was allowed to stand for 15 h. The resulting precipitate was centrifuged, washed, dried, and ground. Then it was placed in a tube furnace and calcined at 500 °C for 4 h at a rate of 2 °C / min under pure argon protection to obtain hollow nanosphere g-C3N4 precursor.

[0046] (2) Preparation of Bi2O3 / g-C3N4 heterojunction photocatalyst: 1 mmol of Bi(NO3)3·5H2O was dissolved in 17 mL of ethylene glycol to form a clear solution. Then, 34 mL of ethanol was added and stirred for 10 min. 100 mg of g-C3N4 precursor was added and stirred for 1 h. The resulting solution was then transferred to a polytetrafluoroethylene reactor and reacted at 160 °C for 5 h. After the reaction was completed, the reaction product was centrifuged, washed, and dried. The obtained solid product was dispersed in 50 mL of deionized water and 1 mL of 5 mol / L NaOH solution was added. After stirring for 1 h, the product was collected by centrifugation, washed, and dried to obtain hollow flower-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst (denoted as Bi2O3 / g-C3N4 HFs-2).

[0047] Example 3

[0048] Preparation of hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst:

[0049] (1) Preparation of g-C3N4 precursor: 600 mg of melamine was dissolved in 30 mL of dimethyl sulfoxide and stirred to form solution A. 900 mg of cyanuric acid was dissolved in 20 mL of dimethyl sulfoxide and stirred to form solution B. Solution B was added dropwise to solution A under stirring at 700 r / min. The resulting mixed solution was stirred at 700 r / min for 1.5 h. After stirring, 100 mL of deionized water was added and the mixture was allowed to stand for 15 h. The resulting precipitate was centrifuged, washed, dried, and ground. Then it was placed in a tube furnace and calcined at 500 °C for 5 h at a rate of 3 °C / min under pure argon protection to obtain hollow nanosphere g-C3N4 precursor.

[0050] (2) Preparation of Bi2O3 / g-C3N4 heterojunction photocatalyst: 2 mmol of Bi(NO3)·5H2O was dissolved in 17 mL of ethylene glycol to form a clear solution. Then, 36 mL of ethanol was added and stirred for 10 min. 100 mg of g-C3N4 precursor was added and the resulting solution was stirred for 1 h. The solution was then transferred to a polytetrafluoroethylene reactor and reacted at 180 °C for 5 h. After the reaction was completed, the reaction product was centrifuged, washed, and dried. The resulting solid product was dispersed in 60 mL of deionized water and 1 mL of 5 mol / L NaOH solution was added. After stirring for 1 h, the product was collected by centrifugation, washed, and dried to obtain hollow flower-shaped Bi2O3 / g-C3N4 heterojunction photocatalyst (denoted as Bi2O3 / g-C3N4 HFs-3).

[0051] Comparative Example 1

[0052] Preparation of g-C3N4: 500 mg of melamine was dissolved in 30 mL of dimethyl sulfoxide and stirred to form solution A. 800 mg of cyanuric acid was dissolved in 20 mL of dimethyl sulfoxide and stirred to form solution B. Solution B was added dropwise to solution A while stirring at 600 r / min. The resulting mixed solution was stirred at 600 r / min for 2 h. After stirring, 100 mL of deionized water was added and the mixture was allowed to stand for 15 h. The resulting precipitate was centrifuged, washed, dried, and ground. Then, it was placed in a tube furnace and calcined at 500 °C for 4 h at a rate of 2 °C / min under pure argon protection to obtain hollow nanospheres g-C3N4.

[0053] Comparative Example 2

[0054] Preparation of Bi2O3: 2 mmol of Bi(NO3)3·5H2O was dissolved in 17 mL of ethylene glycol to form a clear solution. Then, 34 mL of ethanol was added and the mixture was stirred for 70 min. The resulting solution was then added to a polytetrafluoroethylene reactor and reacted at 160 °C for 5 h. After the reaction was completed, the reaction product was centrifuged, washed, and dried. The obtained solid product was dispersed in 50 mL of deionized water and 1 mL of 5 mol / L NaOH solution was added. After stirring for 1 h, the product was collected by centrifugation, washed, and dried to obtain Bi2O3.

[0055] Material characterization analysis

[0056] (I) SEM Analysis

[0057] The Bi2O3 / g-C3N4 HFs-2 prepared in Example 2 was characterized and analyzed using scanning electron microscopy (SEM). The characterization results are as follows: Figure 1 As shown. By Figure 1 As can be seen, the Bi2O3 / g-C3N4 HFs-2 prepared in Example 2 presents a hollow flower sphere shape. It can be clearly observed that its surface is loaded with ultrathin Bi2O3 nanosheets coupled with hollow nanospheres g-C3N4 to form a hollow flower sphere microstructure. This unique open structure not only has a high surface area but also has abundant active sites.

[0058] (II) TEM Analysis

[0059] The Bi2O3 / g-C3N4 HFs-2 prepared in Example 2 was characterized and analyzed by transmission electron microscopy (TEM). The characterization results are as follows: Figure 2 As shown. Figure 2 It was further demonstrated that Bi2O3 / g-C3N4 HFs-2 exhibits a hollow flower-like microstructure, with its surface consisting of a heterogeneous structure formed by the coupling of ultrathin Bi2O3 nanosheets and g-C3N4 interfaces. The Bi2O3 nanosheets grow uniformly on the surface of the hollow nanosphere g-C3N4 sphere.

[0060] (III) XRD Analysis

[0061] X-ray diffraction (XRD) was used to characterize and analyze the Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively. The characterization results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the new characteristic diffraction peaks of g-C3N4 in Comparative Example 1 at 2θ = 13.0° and 27.3° correspond to the in-plane repeating unit (100) crystal plane and the graphite-like layered structure (002) crystal plane, respectively. This is a significant X-ray diffraction pattern feature of g-C3N4. The main peaks of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3 prepared in Examples 1-3 and Bi2O3 prepared in Comparative Example 2 at 2θ = 25.754°, 26.904°, 27.392°, 28.009°, 33.030°, 33.256° and 46.334° are attributed to the (002), (111), (120), (012), (121), (200) and (221) crystal planes, respectively. These characteristic peaks are consistent with all characteristic peaks of monoclinic α-Bi2O3 of standard card number PDF#71-2274.

[0062] (iv) FT-IR Analysis

[0063] Fourier transform infrared spectroscopy (FT-IR) was used to characterize and analyze Bi2O3 / g-C3N4HFs-1, Bi2O3 / g-C3N4HFs-2, Bi2O3 / g-C3N4HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively. The characterization results are as follows: Figure 4 As shown. By Figure 4 It can be seen that in the FT-IR spectrum, 810 cm⁻¹ -1 The strong peaks centered on the triazine unit are attributed to the tensile vibrations of the triazine units, at 1200 and 1600 cm⁻¹. -1 The multiple peaks between these peaks originate from the vibrational band at the NC=N heterocycle in the heptaazine skeleton. Furthermore, at 3200 cm⁻¹... -1 The location is attributed to the -NH2 stretching mode at 3300cm. -1 The position is attributed to the OH stretching mode. It is noteworthy that the FT-IR spectra of Bi2O3 / g-C3N4HFs-1, Bi2O3 / g-C3N4HFs-2, Bi2O3 / g-C3N4HFs-3, and Bi2O3 at 537 cm⁻¹ are... -1The characteristic absorption peak at the point is attributed to the stretching vibration of Bi-O, further indicating the successful composite of Bi2O3 / g-C3N4 heterojunction.

[0064] (V) Specific Surface Area Analysis

[0065] The Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively, were characterized and analyzed by N2 adsorption-desorption isotherms. The characterization results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the specific surface area of ​​Bi2O3 / g-C3N4 HFs-2 is 78.12 m². 2 / g, which is much higher than that of Examples 1, 3 and Comparative Examples 1-2. The catalyst has a high specific surface area, which not only improves light utilization but also provides more active adsorption sites for U(VI), facilitating further improvement of the photocatalytic reduction efficiency of U(VI).

[0066] (VI) PL Analysis

[0067] The Bi₂O₃ / g-C₃N₄ HFs-1, Bi₂O₃ / g-C₃N₄ HFs-2, Bi₂O₃ / g-C₃N₄ HFs-3, g-C₃N₄, and Bi₂O₃ prepared in Examples 1-3 and Comparative Examples 1-2, respectively, were characterized and analyzed using photoluminescence (PL) spectrometry. The characterization results are as follows: Figure 6 As shown. By Figure 6 It can be seen that Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 all exhibit relatively strong emission peaks at a wavelength of approximately 467 nm, which is due to electron-hole recombination. The emission peak of Bi2O3 / g-C3N4 HFs-2 at 467 nm decreases because the heterojunction formed by the effective and uniform growth of Bi2O3 nanosheets in g-C3N4 inhibits electron-hole recombination, thus quenching the originally strong electron plural (PL). This indicates that Bi2O3 / g-C3N4 HFs-2 effectively promotes the separation and migration of free charges.

[0068] (vii) EIS Analysis

[0069] Electrochemical impedance spectroscopy (EIS) was used to characterize and analyze the Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively. The characterization results are as follows: Figure 7 As shown. By Figure 7It can be seen that the order of the arc radius in the EIS impedance spectrum is Bi2O3>g-C3N4>Bi2O3 / g-C3N4 HFs-1>Bi2O3 / g-C3N4 HFs-3>Bi2O3 / g-C3N4 HFs-2. This indicates that the interfacial carrier transfer efficiency is enhanced after the effective coupling between Bi2O3 nanosheets and g-C3N4.

[0070] (viii) Photocurrent Analysis

[0071] The transient photocurrent response of Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 prepared in Examples 1-3 and Comparative Examples 1-2, respectively, was characterized and analyzed. The characterization results are as follows: Figure 8 As shown. By Figure 8 It can be seen that the photocurrent density of the catalysts in Examples 1-3 is much higher than that in Comparative Examples 1-2. This indicates that the Bi2O3 / g-C3N4 heterojunction has rapid photoresponse characteristics and rapid transfer and separation of photogenerated carriers. Furthermore, the HFs-2 content in Bi2O3 / g-C3N4 is significantly higher than that of other components, indicating that it possesses superior photoresponse characteristics and efficient rapid transfer and separation of photogenerated carriers.

[0072] Application Example 1

[0073] 20 mg of the Bi₂O₃ / g-C₃N₄ HFs-1 catalyst prepared in Example 1 was placed in a 50 mL quartz tube for parallel photochemical experiments. 50 mL of 50 ppm UO₂(NO₃)₂·6H₂O solution was added, and the pH of the solution was adjusted to 5 using 0.1 mol / L NaOH and HCl solutions. Before the photochemical reaction, the solution was stirred for 30 min at 25 °C in the dark (hereinafter referred to as the dark reaction). 2 mL of the reaction solution was taken periodically and filtered through a 0.45 μm filter to remove residual particles. Then, a 300 W xenon lamp with an AM 1.5G filter was used as the light source, and the photochemical reaction was carried out under stirring conditions (hereinafter referred to as the light reaction). At different times during the light reaction, the U(VI) concentration was measured at 652 nm using a UV spectrophotometer. The calculated removal rate of U(VI) after 120 min of photochemical reaction was 74.34%.

[0074] Application Example 2

[0075] The difference between Application Example 2 and Application Example 1 is that the catalyst used in Application Example 2 is the Bi2O3 / g-C3N4 HFs-2 catalyst prepared in Example 2, while all other reaction conditions are the same as in Application Example 1. Calculations showed that the removal rate of U(VI) after 120 min of photochemical reaction was 98.45%.

[0076] Application Example 3

[0077] The difference between Application Example 3 and Application Example 1 is that the catalyst used in Application Example 3 is the Bi2O3 / g-C3N4 HFs-3 catalyst prepared in Example 3, while all other reaction conditions are the same as in Application Example 1. Calculations showed that the removal rate of U(VI) after 120 min of photochemical reaction was 89.55%.

[0078] Application Comparative Example 1

[0079] The difference between Comparative Example 1 and Application Example 1 is that the catalyst used in Comparative Example 1 is the g-C3N4 catalyst prepared in Comparative Example 1, while all other reaction conditions are the same as in Application Example 1. Calculations showed that the removal rate of U(VI) after 120 min of photochemical reaction was 47.55%.

[0080] Application Comparative Example 2

[0081] The difference between Comparative Example 2 and Example 1 is that the catalyst used in Comparative Example 2 is the Bi2O3 catalyst prepared in Comparative Example 2, while all other reaction conditions are the same as in Example 1. Calculations showed that the removal rate of U(VI) after 120 min of photochemical reaction was 56.31%.

[0082] Analysis of the photocatalytic removal effect of materials on U(VI)

[0083] The photocatalytic removal effects of U(VI) in Application Examples 1-3, Comparative Examples 1-2, and in the absence of a catalyst were analyzed. The results are as follows: Figure 9 As shown. By Figure 9It can be seen that, before conducting photochemical experiments on Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3, a 30-minute dark reaction was performed. The adsorption removal rates of U(VI) were 20.47%, 20.32%, 24.26%, 6.98%, and 14.87%, respectively. After the light was turned on for the photochemical reaction, the removal rates of U(VI) within 10 minutes were 35.47%, 76.21%, 57.77%, 21.62%, and 27.59%, respectively. Among them, Bi2O3 / g-C3N4 HFs-2 showed the most significant removal effect after 10 minutes of light exposure, with a removal rate increase of 275.05%. However, after 60 minutes of illumination, the removal rates of U(VI) by Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, Bi2O3 / g-C3N4 HFs-3, g-C3N4, and Bi2O3 were 63.56%, 94.12%, 82.98%, 35.56%, and 43.9%, respectively. It can be seen that the Bi2O3 / g-C3N4 HFs-2 photocatalyst exhibits excellent performance, but it is also close to its performance limit. To verify the final removal rate, the photocatalytic reaction was continued for 120 min. The removal rates of U(VI) by Bi2O3 / g-C3N4 HFs-1, Bi2O3 / g-C3N4 HFs-2, and Bi2O3 / g-C3N4 HFs-3 were 74.34%, 98.45%, and 89.55%, respectively, while the removal rates of U(VI) by g-C3N4 and Bi2O3 were 47.55% and 56.31%, respectively. The photocatalytic removal efficiency of U(VI) in the absence of a catalyst was approximately 1%, which is mainly due to the influence of error rather than the photoreduction of U(VI) without a catalyst.

[0084] It is evident that the Bi₂O₃ / g-C₃N₄ heterojunction photocatalyst of this invention exhibits a significantly higher U(VI) removal rate than g-C₃N₄ and Bi₂O₃. Compared to g-C₃N₄ and Bi₂O₃, the photocatalyst of this invention demonstrates a substantial improvement in U(VI) removal efficiency. This indicates that the heterojunction of g-C₃N₄ and Bi₂O₃ increases their surface area, thereby enhancing light utilization and the adsorption and extraction of liquid-phase U(VI). Simultaneously, it effectively promotes the separation of photogenerated carriers, thus accelerating the redox rate of the heterogeneous system. Therefore, this invention demonstrates that the photocatalyst possesses excellent photocatalytic redox performance and a superior U(VI) removal effect. Its application in photo-assisted uranium extraction can efficiently enrich uranium in uranium wastewater.

[0085] Material stability and recyclability analysis

[0086] (I) Stability Analysis

[0087] Under the same reaction conditions as in Application Example 2, the Bi2O3 / g-C3N4 HFs-2 in Application Example 2 was tested for different interfering cations (K). + Ca 2+ Mg 2+ 、Sr 2+ Co 2+ The effect of Bi2O3 / g-C3N4 HFs-2 photochemical reaction on the removal of U(VI) in the presence of any of the following is shown in the test results. Figure 10 As shown. By Figure 10 It can be seen that K + It has a positive effect on the photocatalytic reduction of U(VI). Specifically, K + The addition of K can increase the efficiency of photocatalytic reduction of uranium, which is attributed to K + The large ionic radius provides a larger interstitial space for electron transport. Therefore, the presence of potassium ions can enhance the photocatalytic reduction of U(VI). However, other interfering cations (Ca... 2+ Mg 2+ 、Sr 2+ Co 2+ In the presence of any of the ions present, the uranium reduction performance of Bi2O3 / g-C3N4 HFs-2 slightly decreases, which is attributed to the competitive adsorption effect of cations at the active sites. However, Bi2O3 / g-C3N4 HFs-2 still exhibits good overall photocatalytic redox performance. This indicates that Bi2O3 / g-C3N4 HFs-2 has high selectivity for photoelectron reduction. Therefore, the photocatalyst of this invention has good anti-interference and stability. Here, "control" represents the photocatalytic effect of the Bi2O3 / g-C3N4 HFs-2 photocatalyst in the absence of interfering ions, and is only used for comparative analysis.

[0088] Under the same reaction conditions as in Application Example 2, the photochemical removal effect of Bi2O3 / g-C3N4 HFs-2 on U(VI) was tested under different pH conditions. The test results are shown in Figure 11. Figure 11It is evident that Bi₂O₃ / g-C₃N₄ HFs-₂ exhibits excellent removal efficiency for U(VI) at pH 5. Monoclinic α-Bi₂O₃, as a stable semiconductor, is soluble in strong acids but insoluble in strong bases, exhibiting both acid resistance and excellent alkali resistance. g-C₃N₄, on the other hand, is an excellent acid- and alkali-resistant polymer semiconductor. Therefore, the Bi₂O₃ / g-C₃N₄ HFs-₂ photocatalyst demonstrates excellent removal efficiency for U(VI) at pH 4-6. This indicates that the photocatalyst of this invention possesses good anti-interference properties and stability.

[0089] (II) Recyclability Analysis

[0090] Under the same reaction conditions as in Application Example 2, the effect of the Bi2O3 / g-C3N4 HFs-2 photocatalyst in Application Example 2 on the removal of U(VI) through 5 cycles of photocatalytic reaction was tested. The test results are as follows: Figure 12 As shown. Figure 12 It can be seen that after 5 cycles of photocatalytic reaction, the removal rate of U(VI) by Bi2O3 / g-C3N4 HFs-2 is 90.77%, indicating that the photocatalyst of the present invention has good reusability and can be recycled multiple times, and has good practical application value for the efficient removal of U(VI) from wastewater.

[0091] XPS analysis was performed on Bi2O3 / g-C3N4 HFs-2 after U(VI) removal in Application Example 2. The results are as follows: Figure 13 As shown. By Figure 13 It can be seen that U(VI) of U 4f 5 / 2 and U 4f 7 / 2 The characteristic peaks of U4f appear at 392.6 eV and 381.9 eV, respectively. 5 / 2 and U 4f 7 / 2 The peaks clearly appear at 391.8 eV and 381.0 eV, and these two peaks are identified as characteristic peaks of U(IV), indicating that U(VI) is reduced to U(IV). These results demonstrate that the photocatalyst of the present invention possesses the ability to photoreduce U(VI) to U(IV) and has a highly efficient extraction capability for uranium.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst, characterized in that, Includes the following steps: (1) Preparation of g-C3N4 precursor: Melamine was dissolved in dimethyl sulfoxide to form solution A, cyanuric acid was dissolved in dimethyl sulfoxide to form solution B, and then solution B was added to solution A. The resulting mixed solution was stirred and then added to water for standing. The resulting precipitate was centrifuged, washed, dried, ground, and calcined under inert gas protection to obtain hollow nanosphere g-C3N4 precursor; The mass ratio of melamine to dimethyl sulfoxide in solution A is 15–20 mg: 1 mL; the mass ratio of cyanuric acid to dimethyl sulfoxide in solution B is 35–50 mg: 1 mL; the mass ratio of melamine to cyanuric acid is 1:1.5–2; and the ratio of water to melamine is 0.2–0.3 mL: 1 mg. (2) Preparation of Bi2O3 / g-C3N4 heterojunction photocatalyst: Bi(NO3)3·5H2O was dissolved in ethylene glycol to form a clear solution. Ethanol was added and stirred. Then g-C3N4 precursor was added. The resulting solution was stirred and transferred to a reaction vessel for solvothermal reaction. After the reaction was completed, the product was centrifuged, washed and dried. The resulting solid product was dispersed in water and NaOH solution was added. After stirring, the product was collected by centrifugation, washed and dried to obtain hollow flower spherical Bi2O3 / g-C3N4 heterojunction photocatalyst. The ratio of Bi(NO3)3·5H2O, ethylene glycol, and ethanol is 0.5–2 mmol : 17 mL : 32–38 mL; the ratio of Bi(NO3)3·5H2O to g-C3N4 precursor is 0.5–2 mmol : 100 mg.

2. The preparation method of the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, In step (1), the calcination is carried out under nitrogen or argon protection, heating to 450-500℃ at a rate of 2-3℃ / min for 4-5 hours.

3. The preparation method of the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, In step (1), the stirring is carried out at a speed of 600-700 r / min for 1.5-2 h; the settling time is 13-15 h.

4. The method for preparing the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, In step (2), the ratio of NaOH solution, water and Bi(NO3)3·5H2O is 1 mL : 45~60 mL : 0.5~2 mmol; the concentration of NaOH solution is 4~6 mol / L.

5. The method for preparing the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, In step (2), the solvothermal reaction is carried out at a temperature of 150-180°C for 4-5 hours.

6. A hollow flower spherical Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the method described in any one of claims 1-5.

7. The hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 6, characterized in that, The hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst has a hollow flower-shaped microstructure and a specific surface area of ​​39.34–78.12 m². 2 / g.

8. The application of the hollow flower-shaped spherical Bi2O3 / g-C3N4 heterojunction photocatalyst as described in claim 6 in the extraction of uranium from radioactive wastewater.

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