rGO supported copper monatomic catalyst / g-c3n4 composite electrode material and preparation method and application thereof

Abstract

The application relates to a rGO loaded copper monatomic catalyst / g-C3N4 composite electrode material, a preparation method thereof and application, and relates to the technical field of uranium resource recovery and water treatment. The foregoing preparation method comprises the following steps: dissolving melamine in deionized water, stirring and dissolving, and then performing heating treatment; the obtained product is subjected to solid-liquid separation, washing and drying, and then is subjected to heat treatment in an inert atmosphere to obtain g-C3N4; graphene, copper oxalate and chitosan are added into an acidic aqueous solution, stirred, dried, and then subjected to heat treatment in an inert atmosphere to obtain a rGO loaded copper monatomic catalyst; the rGO loaded copper monatomic catalyst and the g-C3N4 are dispersed in an organic-water mixed solvent containing Nafion, and then phytic acid is added; the catalyst ink is obtained through ultrasonic treatment; the catalyst ink is coated on the surface of a substrate, and then dried to obtain the composite electrode material. The composite electrode material prepared by the application can realize efficient and high-selectivity photoelectrocatalytic reduction of uranium in water bodies such as uranium-containing wastewater, seawater, concentrated salt water of seawater desalination, concentrated seawater of a seawater salt factory, salt lake water and the like.

Description

Technical Field

[0001] This invention relates to the field of uranium resource recovery and water treatment technology, and in particular to an rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material, its preparation method, and its application. Background Technology

[0002] In current seawater uranium extraction technologies, adsorption methods have become a research hotspot due to their advantages such as simple operation and low cost. Commonly used adsorbent materials include porous organic polymers, metal-organic frameworks (MOFs), and metallo-aminooxime functionalized materials. These materials work by binding uranyl ions (UO2) with functional groups such as amino and metallo-aminooxime groups. 2+ Uranium can be coordinating and adsorbed. However, the actual concentration of uranium in seawater is only about 3.3 µg / L, and it contains high concentrations of magnesium ions, calcium ions, and various interfering ions (such as iron, zinc, nickel, vanadium, etc.). Competitive adsorption severely inhibits the enrichment kinetics of uranium, causing traditional materials to typically require tens of days to achieve an adsorption capacity of a few mg / g, which is difficult to meet the requirements of industrial applications.

[0003] Compared to physicochemical adsorption methods, electrochemical methods are widely used due to their significant advantages in adsorption rate and capacity. Electrochemical uranium extraction directly reduces U(VI) in solution to insoluble U(IV) (such as UO2) by applying a specific potential to the electrode, which then deposits it on the electrode surface. For example, a study reported a structurally engineered molybdenum nitride-carbon cloth (E-MON / CC) electrode that achieved a 99% uranium removal rate within 1 h in simulated seawater (10 ppm). Although the electrochemical uranium extraction rate and adsorption capacity are significantly superior to physicochemical adsorption, the reduced U(IV) deposited on the electrode surface easily covers the active sites, leading to a sharp drop in subsequent adsorption rate and capacity.

[0004] Photocatalytic reduction utilizes semiconductor materials (such as TiO2 and g-C3N4) to generate photoelectrons under illumination, reducing U(VI) to lower valence uranium on the material surface. Carbon nitride, in particular, exhibits excellent chemical stability, making it suitable for long-term aquatic applications and a hot research topic in photocatalysis. For example, a novel oxygen-deficient Co3O4 catalyst has been reported. 4-x / g-C3N4p-n heterojunction for efficient light-assisted uranium extraction from seawater, under simulated sunlight irradiation without sacrificial agents, Co3O 4-x / g-C3N4 achieved a uranium removal rate of 99.6% within 90 minutes and extracted 1.08 mg·g⁻¹ from 25 L of natural seawater in 7 days. -1Uranium enrichment is achieved through photocatalysis. Photocatalysis utilizes electron-hole pairs generated during photoexcitation to reduce mobile U(VI) to insoluble U(IV), thus separating and enriching uranium from seawater. While both photocatalysis and electrocatalysis can achieve rapid uranium enrichment, their reduction products (reduced uranium) tend to occupy active sites, affecting subsequent uranium enrichment efficiency. Currently, research on the application of these technologies in seawater desalination systems is still relatively lacking.

[0005] Therefore, there is an urgent need to develop a new type of electrode material that is suitable for seawater desalination and has both high efficiency and high selectivity, so as to achieve sustainable uranium extraction. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing an rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material, the resulting electrode material being able to achieve efficient and highly selective photoelectrocatalytic reduction of uranium in concentrated brine of seawater desalination.

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

[0008] The preparation method of rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material includes the following steps:

[0009] Melamine was dissolved in deionized water, and after stirring and dissolving, it was heated. The resulting product was then subjected to solid-liquid separation (e.g., centrifugation), washing and drying, and then heat-treated in an inert atmosphere (e.g., N2, flow rate 50 mL / min) to obtain g-C3N4.

[0010] Graphene (reduced graphene oxide, i.e. rGO), copper oxalate and chitosan were added to an acidic aqueous solution, stirred and treated, dried and then heat-treated in an inert atmosphere (e.g., N2, flow rate 50 mL / min) to obtain an rGO-supported copper single-atom catalyst (Cu-SA).

[0011] The rGO-supported copper single-atom catalyst and g-C3N4 were dispersed in an organic-water mixed solvent containing Nafion, followed by the addition of phytic acid (PA), and the mixture was ultrasonically treated to obtain catalyst ink. The catalyst ink was coated on the surface of a substrate (such as a carbon felt electrode) and dried to obtain a composite electrode material.

[0012] Furthermore, in the step of preparing g-C3N4, each 1g of melamine corresponds to 60 mL of deionized water.

[0013] Furthermore, in the step of preparing g-C3N4, the heat treatment is performed by heating at 180°C for 24 h.

[0014] Furthermore, in the step of preparing g-C3N4, the heat treatment is to heat to 550°C at a rate of 5°C / min and hold at that temperature for 4 h.

[0015] Furthermore, in the step of preparing the rGO-supported copper single-atom catalyst, the mass ratio of graphene to copper oxalate is 3:2.

[0016] Furthermore, in the step of preparing the rGO-supported copper single-atom catalyst, each 1.5 g of graphene and 1.0 g of copper oxalate corresponds to 4 mL of chitosan. For example, the following amounts are used: 1.5 g graphene, 1.0 g copper oxalate, and 4 mL chitosan.

[0017] Furthermore, in the step of preparing the rGO-supported copper single-atom catalyst, the acidic aqueous solution is an acetic acid solution.

[0018] Furthermore, in the step of preparing the rGO-supported copper single-atom catalyst, the stirring is performed using magnetic stirring and is carried out in a closed container.

[0019] Furthermore, in the step of preparing the rGO supported copper single-atom catalyst, the heat treatment is to heat to 900°C at a heating rate of 15°C / min and calcine for 3 h.

[0020] Furthermore, in the step of preparing the composite electrode material, the mass ratio of the rGO-supported copper single-atom catalyst to g-C3N4 is 2:3.

[0021] Furthermore, in the step of preparing the composite electrode material, each 5.2 mg rGO-supported copper single-atom catalyst and 7.8 mg g-C3N4 corresponds to 400 μL Nafion (solution) and 1.92 mL phytic acid. For example, the following amounts are used: 5.2 mg rGO-supported copper single-atom catalyst, 7.8 mg g-C3N4, 400 μL Nafion, and 1.92 mL phytic acid.

[0022] Furthermore, in the step of preparing the composite electrode material, the organic-water mixed solvent is a mixture of anhydrous ethanol and deionized water. The volume ratio of anhydrous ethanol to deionized water is 11:1 (e.g., 8.8 mL: 0.8 mL).

[0023] Another object of the present invention is to provide an rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material, which is prepared by the preparation method described above.

[0024] The rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material can be used in photoelectrocatalytic uranium removal.

[0025] Furthermore, the photocatalysis is carried out under the drive of a square wave potential.

[0026] The rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material can also be used to recover uranium from uranium-containing wastewater, seawater, concentrated brine from seawater desalination plants, concentrated seawater from sea salt plants, or salt lake water.

[0027] Furthermore, the present invention also provides a method for recovering uranium from uranium-containing wastewater, seawater, concentrated brine from seawater desalination, concentrated seawater from a sea salt plant, or salt lake water, which includes the following steps:

[0028] The pH of the water body is adjusted and electrolytes are added. Optional microalgae pretreatment is performed (either with or without this treatment) to obtain the solution to be treated.

[0029] Using the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material as the cathode and a graphite sheet as the anode, the liquid to be treated is subjected to photoelectrocatalytic treatment under square wave potential drive.

[0030] Furthermore, the microalgae pretreatment is performed using Chlorella.

[0031] The rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material prepared in this invention can efficiently and selectively extract uranium from concentrated seawater desalination brine. By introducing a square-wave voltage drive, the reduction of uranyl ions can be effectively promoted, achieving rapid uranium deposition and separation, with a uranium removal rate significantly higher than that of the traditional constant-voltage mode. In high-salinity complex water bodies (such as concentrated seawater desalination brine), this composite electrode exhibits high selectivity for uranium. Even in the presence of a large number of coexisting competing ions (such as magnesium, calcium, and vanadium ions), it can still effectively enrich uranium. Further combining it with a microalgae pretreatment strategy can improve the reaction microenvironment, thereby increasing the uranium extraction efficiency of the electrode. In addition, this electrode exhibits good cyclic stability under continuous operation conditions, maintaining high uranium removal efficiency even after multiple uses, demonstrating practical application feasibility.

[0032] This invention provides a highly efficient, stable, and highly selective photoelectrocatalytic uranium extraction method suitable for concentrated brine systems in seawater desalination, offering a new approach for the recovery of low-concentration uranium resources. The method can be extended to other uranium-containing, high-salinity, complex water bodies, such as concentrated seawater from sea salt plants and salt lake water. Attached Figure Description

[0033] Figure 1 middle:

[0034] (a) is a schematic diagram of the uranium removal efficiency of the g-C3N4 electrode under PC, EC and EPC conditions;

[0035] (b) is a schematic diagram of the uranium removal efficiency of the Cu-SA electrode under PC, EC and EPC conditions;

[0036] (c) is a schematic diagram of the uranium removal efficiency of g-C3N4, Cu-SA and Cu-SA / g-C3N4 electrodes under EPC;

[0037] (d) is a schematic diagram of the uranium removal efficiency of Cu-SA and Cu-SA / g-C3N4 electrodes under constant pressure conditions;

[0038] (e) is a schematic diagram showing the effect of different Cu-SA and g-C3N4 mass ratios on the uranium removal efficiency of the Cu-SA / g-C3N4 electrode;

[0039] (f) is a schematic diagram showing the effect of different total masses of Cu-SA and g-C3N4 on the uranium removal efficiency of Cu-SA / g-C3N4 electrode;

[0040] (g) is a schematic diagram of the uranium removal efficiency of Cu-SA / g-C3N4 electrode on 10 mg / L uranium solution under different pH conditions;

[0041] (h) is a schematic diagram of the uranium removal efficiency of Cu-SA / g-C3N4 electrode for uranium solutions with different initial concentrations;

[0042] Figure 2 middle:

[0043] (a) is a schematic diagram of the uranium removal efficiency of Cu-SA / g-C3N4 electrode on actual wastewater;

[0044] (b) is a schematic diagram of the selective adsorption of uranium in concentrated brine by the Cu-SA / g-C3N4 electrode.

[0045] (c) is a schematic diagram of the uranium removal efficiency of Cu-SA / g-C3N4 electrode for untreated concentrated brine and concentrated brine pretreated with Chlorella.

[0046] (d) is a schematic diagram of the uranium removal efficiency of the Cu-SA / g-C3N4 electrode in a dynamic cyclic experiment;

[0047] (e) is a schematic diagram of the uranium removal efficiency of the Cu-SA / g-C3N4 electrode in simulated concentrated seawater;

[0048] (f) is a schematic diagram comparing the performance of different adsorbents in uranium extraction from seawater. Detailed Implementation

[0049] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention. It should be noted in advance that the following embodiments were completed in a laboratory. Those skilled in the art should understand that the amounts of each component given in the embodiments only represent the ratio between the components, and are not specific limitations.

[0050] Seawater uranium extraction is considered the most promising method for obtaining uranium resources, but its extremely low uranium concentration (approximately 3.3 µg / L) poses a significant challenge to efficient extraction. To overcome the bottlenecks of low efficiency and poor selectivity in current seawater uranium extraction technologies within high-salt and complex systems, this embodiment focuses on the concentrated brine produced during seawater desalination. Uranium is enriched in this concentrated brine, but Mg... 2+ Ca 2+ V 5 + Coexisting ions are also enriched simultaneously, further intensifying competitive adsorption and placing higher demands on the uranium extraction efficiency and selectivity of the material.

[0051] Square Wave Exchange (SWE) effectively avoids side reactions in water electrolysis by periodically removing competing ions from the system, and significantly promotes the production of uranyl ions (UO2). 2+ The directional migration of uranium exhibits unique technical advantages such as high adsorption capacity, high selectivity and rapid kinetics, providing important support for efficient uranium extraction.

[0052] To address the issues of traditional adsorption methods being susceptible to interference from competing ions and the tendency of electrochemical reduction products to passivate electrode active sites, this embodiment proposes a novel uranium extraction pathway that does not rely on long-term occupancy of active sites: combining photoelectrocatalysis and square wave voltage driving to construct a phosphorylated (phosphate group modified) rGO-supported copper single-atom catalyst (Cu-SA) / g-C3N4 composite electrode. The phosphate group enhances the resistance to uranyl ions (UO2). 2+ The specific recognition of uranium is achieved by square wave voltage, which helps to suppress side reactions and promote rapid reduction and deposition separation of uranium.

[0053] Specifically, this embodiment optimizes the electrode's microstructure and photoelectric response performance by adjusting the mass ratio and total mass of the rGO-supported copper single-atom catalyst (Cu-SA) to carbon nitride (g-C3N4). The effects of pH, initial uranium concentration, and other factors on removal efficiency are systematically investigated. Furthermore, its uranium extraction performance is evaluated in actual wastewater, simulated seawater, and concentrated brine systems. In addition, Chlorella is introduced to pretreat the concentrated brine, and dynamic circulation experiments are conducted to verify the feasibility and stability of the electrode in practical applications.

[0054] Experimental results show that by applying a square wave voltage, under seawater pH (pH=8) conditions, the uranium removal rate of a 10 mg / L uranium solution can reach 98% within 5 minutes, and the uranium is deposited as sediment at the bottom of the electrolytic cell. However, under the same conditions, applying a constant voltage results in a uranium removal rate of only 70.8% within 5 minutes, and no yellow precipitate (containing uranium radioactive compounds) is observed. Therefore, square wave voltage is key to achieving rapid uranium removal through deposition. In the concentrated brine selectivity experiment, the uranium selectivity was significantly higher than that of coexisting ions, even for magnesium ions, which have the greatest influence. d The ratio reached 72.6 times, indicating that the Cu-SA / g-C3N4 composite electrode has excellent selectivity for uranium; after seawater desalination concentrated brine was inoculated with microalgae and cultured for 12 hours, the maximum uranium extraction yield reached 3.336 mg·g⁻¹ in the photoelectrocatalytic experiment. -1 ·h -1 The uranium extraction rate was increased by 4 times compared to that of uninoculated microalgae. Furthermore, the electrode exhibited excellent stability in dynamic adsorption experiments, maintaining a 100% uranium removal rate even after 24 consecutive cycles.

[0055] In summary, this embodiment provides a novel, highly efficient, selective, and stable photoelectrocatalytic uranium extraction pathway suitable for concentrated brine from seawater desalination by combining material design, driving strategy optimization, and biological pretreatment.

[0056] The following specific examples will provide a detailed explanation.

[0057] The raw materials and reagents used are as follows: Reduced graphene oxide was purchased from Suzhou Tanfeng Graphene Technology Co., Ltd., China; copper oxalate, melamine, phytic acid, anhydrous ethanol, sodium carbonate, and nitric acid were purchased from Shanghai Chemical Reagent Co., Ltd., China; chitosan (degree of deacetylation ≥95%, viscosity 100-200 mPa·s) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., China; Nafion perfluorinated resin solution (polymer content 5.0-5.4%) was purchased from Aladdin Co., Ltd., China; sodium chloride and acetic acid were commercially available analytical grade reagents. Carbon felt was used as the electrode substrate, cut into 4cm × 4cm squares for later use.

[0058] (1) Preparation of carbon nitride (g-C3N4)

[0059] 1 g of melamine was dissolved in 60 mL of deionized water and stirred thoroughly at 90 °C until completely dissolved. The solution was transferred to a 100 mL autoclave and heated at 180 °C for 24 h. After cooling to room temperature, the solid sample obtained by centrifugation was washed three times with deionized water and anhydrous ethanol. The sample was then dried in a vacuum drying oven at 60 °C. Finally, the dried sample was placed in a tube furnace and heated to 550 °C at a rate of 5 °C / min under N2 (50 mL / min) protection and held for 4 h to obtain g-C3N4 (carbon nitride).

[0060] (2) Preparation of rGO supported copper single-atom catalyst (Cu-SA)

[0061] Graphene (reduced graphene oxide) and copper oxalate were mixed evenly in a beaker at a mass ratio of 3:2 (1.5 g graphene and 1.0 g copper oxalate were used in this example). Then, 2.5 g of the mixture and 4 mL of chitosan (7.5 wt%) were added to 22 mL of acetic acid (2 wt%) solution. A rotor (magnetic stirrer) was placed in the beaker, the mouth of the beaker was sealed with plastic wrap, and the beaker was placed in an oil bath at 80 °C (driven by a magnetic stirrer) and stirred vigorously for 5 h. The plastic wrap was then removed, and the sample was dried in an oven at 60 °C for 10 h. The dried sample was placed in a tube furnace and heated to 900 °C at a heating rate of 15 °C / min under N2 (50 mL / min) protection, and calcined for 3 h to obtain the catalyst (Cu-SA).

[0062] Under the premise of keeping other preparation conditions constant, the effects of reducing graphene oxide, copper oxalate and chitosan on the catalytic performance of Cu-SA were systematically investigated by adjusting their mass ratio, and the optimal ratio was determined.

[0063] (3) Preparation of Cu-SA / g-C3N4 composite electrode

[0064] 5.2 mg Cu-SA and 7.8 mg carbon nitride (g-C3N4) were dispersed in a mixture of 8.8 mL anhydrous ethanol and 800 μL deionized water (containing 400 μL of 5.0–5.4 wt% Nafion solution). Then, 1.92 mL of phytic acid was added under ultrasonic stirring to prepare the catalyst ink. The ink was uniformly dropped onto the surface of a pre-cleaned carbon felt electrode and dried under infrared light to obtain the composite electrode material.

[0065] While keeping the other preparation conditions unchanged, the effects of adjusting the mass ratio of Cu-SA to g-C3N4 and the total mass of the two on the photoelectrocatalytic performance of the composite electrode were systematically investigated, and the optimal ratio and total amount were determined.

[0066] To conduct a control experiment, this embodiment also prepared single-component electrodes containing only Cu-SA or only g-C3N4.

[0067] (4) Photoelectrocatalytic uranium removal performance test

[0068] Uranyl carbonate stock solution with a concentration of 12.0804 g / L was diluted to obtain uranyl solutions of different concentrations. The pH of the uranyl solutions was adjusted to 6.0 ± 0.02 using sodium carbonate and nitric acid solutions. The experiment was conducted in an electrolytic cell containing 200 mL of uranyl solution, with 7 g of NaCl added as a supporting electrolyte and completely dissolved by ultrasonic treatment. Electrocatalysis experiments were performed using a graphite sheet as the anode and a Cu-SA electrode as the cathode, with an AC voltage (frequency 400 Hz) applied using an arbitrary waveform generator from -5 V to 0 V. Photoelectrochemical synergistic catalysis experiments were conducted under the same conditions, using a composite electrode as the cathode under incandescent lamp illumination.

[0069] In this embodiment, "electro-photocatalysis" refers to photoelectrocatalysis.

[0070] To verify the photoelectric synergistic effect, this embodiment compares and analyzes the uranium removal performance of Cu-SA, g-C3N4 single-component, and composite electrodes under different catalytic modes. In the following text, "Cu-SA" and "g-C3N4" refer to single-component electrodes, respectively; "Cu-SA / g-C3N4" refers to composite electrodes.

[0071] The uranium removal performance of three catalytic systems—photocatalysis (PC), electrocatalysis (EC), and electrophoto-catalysis (EPC)—was compared. Figure 1 (a) and (b)). For example Figure 1 As shown in Figure (a), the uranium removal rate of g-C3N4 under three catalytic systems was investigated using 10 mg / L uranyl carbonate solution at pH 6.0. The uranium removal rates of g-C3N4 under photocatalysis were 39.7%, 37.6%, and 36.7% at 5 min, 10 min, and 20 min, respectively; under electrocatalysis, the uranium removal rates were 80.2%, 81.3%, and 78.7% at 5 min, 10 min, and 20 min, respectively; and under electro-photocatalysis, the uranium removal rates were 85.7%, 89.3%, and 91.8% at 5 min, 10 min, and 20 min, respectively. Under the same conditions, the uranium removal effect of Cu-SA under the three catalytic systems was also investigated. Figure 1 As shown in Figure (b), the uranium removal rates of Cu-SA under photocatalysis were 42.4%, 41.7%, and 39.2% for 5 min, 10 min, and 20 min, respectively; under electrocatalysis, the uranium removal rates were 67.2%, 82.9%, and 85.3% for 5 min, 10 min, and 20 min, respectively; and under electro-photocatalysis, the uranium removal rates were 89.1%, 94.2%, and 95.9% for 5 min, 10 min, and 20 min, respectively. These results confirm the superiority of electro-photocatalytic synergy.

[0072] This embodiment also compares the electro-photocatalytic synergistic catalytic experiments of three electrode materials: g-C3N4, Cu-SA, and Cu-SA / g-C3N4. For example... Figure 1 As shown in (c), under the same conditions (pH 6.0, 10 mg / L uranyl carbonate solution), the Cu-SA / g-C3N4 composite electrode achieved a uranium removal rate of 94.5% after 5 min, and 98.3% and 98.5% after 10 min and 20 min, respectively. The uranium removal performance of the Cu-SA / g-C3N4 composite electrode is significantly better than that of g-C3N4 and Cu-SA alone. Therefore, under the conditions of this embodiment, the Cu-SA / g-C3N4 composite electrode exhibits the best uranium removal performance.

[0073] Figure 1 Figure (d) illustrates the effect of constant voltage driving on the electro-photocatalytic uranium removal performance of Cu-SA and Cu-SA / g-C3N4 electrodes. The results show that the uranium removal rate of Cu-SA / g-C3N4 is only 70.8% at 5 min, and even after 120 min, the removal rate only increases to 79.5%; the uranium removal rate of Cu-SA at 120 min is only about 61.3%, and no yellow uranium precipitate was observed. Figure 1 In the middle (c), the result of square wave voltage driving is shown by comparison. Figure 1 In (c) and (d), it is evident that the uranium removal efficiency driven by square wave voltage is significantly higher than that driven by constant voltage. This result indicates that the periodic potential change of square wave voltage is more conducive to the electro-optic synergistic effect of Cu-SA / g-C3N4 composite electrode, which is key to achieving rapid deposition uranium removal.

[0074] This embodiment also investigated the influencing factors of photoelectrocatalytic uranium removal performance, including the mass ratio of Cu-SA to g-C3N4 and the total mass, solution pH, and initial uranium concentration.

[0075] The effects of the mass ratio of Cu-SA and g-C3N4 and the total mass on uranium removal performance are as follows.

[0076] To further determine the optimal mass ratio of Cu-SA to g-C3N4 in the composite electrode, this embodiment conducted photoelectrocatalytic experiments with Cu-SA / g-C3N4 composite electrodes at different mass ratios. Figure 1As shown in Figure (e), within 5 min, the uranium removal rate was 98.6% when the mass ratio of Cu-SA to g-C3N4 was 2:3, while the uranium removal rates were 94.2% and 94.3% for the mass ratios of 1:1 and 3:2, respectively. After 20 min of reaction, the uranium removal rate of the electrode with a mass ratio of 2:3 remained stable at 98.7%, indicating that it had reached equilibrium at 5 min and the electrode was operating stably; while the uranium removal rates of the composite electrodes with the other mass ratios were 98.3% and 96.6%, respectively. Therefore, under the conditions of this embodiment, the composite electrode exhibits the best photoelectrochemical uranium removal performance when the mass ratio of Cu-SA to g-C3N4 is 2:3.

[0077] This embodiment also investigated the optimal total amount of Cu-SA and g-C3N4 in the composite electrode when the mass ratio of Cu-SA to g-C3N4 was 2:3. Figure 1 As shown in Figure (f), when the total mass of the composite electrode material is 13 mg, the uranium removal rate reaches 99% after 5 min of reaction and remains stable at 99% after 20 min, indicating a high removal rate. When the total mass of the composite electrode is 10 mg, the uranium removal rates at 5 min, 10 min, and 20 min are 98.6%, 97.1%, and 98.7%, respectively. When the total mass of the composite electrode is 16 mg, the uranium removal rate decreases significantly, reaching 52.5%, 70.4%, and 54.2% at 5 min, 10 min, and 20 min, respectively. These results indicate that under the conditions of this embodiment, the composite electrode exhibits optimal performance when the total mass is 13 mg. With increasing dosage, the number of active sites in the system increases, and the uranium removal rate increases accordingly. However, when the dosage is too high (e.g., 16 mg), the material dispersibility decreases, and particles are prone to agglomeration, resulting in insufficient exposure of active sites and a decrease in the removal rate instead of an increase.

[0078] The effect of solution pH on uranium removal performance is as follows.

[0079] pH is a key factor affecting uranium removal because different pH values ​​influence the speciation of uranium, ultimately affecting removal performance. In this embodiment, a Cu-SA / g-C3N4 composite electrode with a Cu-SA to g-C3N4 mass ratio of 2:3 and a total mass of 13 mg was used to conduct electro-photocatalytic experiments at different pH values ​​(3-8) in a 10 mg / L uranium solution. Figure 1As shown in (g), within the initial pH range of 4-6, the uranium removal rate exceeded 95%, with the best results observed at 10 min, reaching 99.8%, 98.0%, and 99.9%, respectively. When pH=3, the uranium removal rate gradually increased with time, reaching 64.3%, 75.1%, and 89.3% at 5 min, 10 min, and 20 min, respectively. However, at pH 7-8, the uranium removal rate decreased with time, but the removal rates at 5 min reached 95.7% and 97.9%, respectively. This indicates that the composite electrode has good uranium removal performance across a wide pH range of 3-8 and has broad application potential.

[0080] The effect of initial uranium concentration on uranium removal performance is as follows.

[0081] Electrophotocatalytic experiments were conducted at pH 6.0 with different uranium concentrations (including 5 mg / L, 10 mg / L, 30 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, and 300 mg / L). Figure 1 As shown in Figure (h), when the uranium concentration is in the range of 5-100 mg / L, the uranium removal rate of the composite electrode first increases and then decreases with time, reaching its highest level of over 98% at 10 min. Under high uranium concentrations (200 mg / L and 300 mg / L), when the uranium concentration is 200 mg / L, the uranium removal rate of the Cu-SA / g-C3N4 composite electrode first increases and then decreases with time, achieving the best uranium removal effect at 10 min with a removal rate of 97.6%; when the uranium concentration is 300 mg / L, the uranium removal rate of the Cu-SA / g-C3N4 composite electrode first decreases and then increases with time, achieving the best uranium removal effect at 20 min with a removal rate of 85.89%.

[0082] This embodiment further evaluates the selective removal performance of the composite electrode for uranium in actual wastewater, simulated seawater, and seawater desalination brine systems.

[0083] Electro-photocatalytic experiments were conducted by adding 5 mg / L of uranium solution to the seepage water from a uranium tailings dam to demonstrate the application effect of the Cu-SA / g-C3N4 composite electrode in actual wastewater treatment. Figure 2 As can be clearly seen in (a), the electrode can achieve a uranium removal rate of 99.8% in 5 minutes, and the uranium concentration in the effluent drops to 10 µg / L, indicating that it still has excellent deep uranium removal capability in actual complex wastewater.

[0084] Given the excellent performance of the Cu-SA / g-C3N4 composite electrode in electro-photocatalysis, this embodiment further tests its uranium removal performance in simulated concentrated seawater samples with the addition of 5 mg / L uranyl. Figure 2(e); details of the concentrations of various ions in seawater are shown in Table 1). The experiment was conducted with the concentration of a single ion controlled at 8 times the corresponding concentration in real seawater, and the concentrations of other ions controlled at 4 times the corresponding concentrations in real seawater, to investigate the effects of different ions on uranium removal performance. The electrode achieved a uranium removal rate of over 85% after 5 minutes; particularly, when the concentrations of zinc, nickel, and carbonate ions were 8 times higher, the uranium removal rates reached 99.8%, 96.4%, and 98.7% respectively after only 5 minutes, demonstrating good ion tolerance and high selectivity. However, under the interference of high-concentration magnesium ions (3.2 g / L, 8 times the concentration in real seawater), the uranium removal rate was significantly inhibited, with removal rates of 70.7%, 75.9%, and 79.2% after 5, 10, and 20 minutes, respectively, far lower than the removal efficiency under other ion conditions, indicating that magnesium ions were the main interfering ion. These results demonstrate that the Cu-SA / g-C3N4 composite electrode can maintain a high uranium removal rate under various high-concentration ion backgrounds.

[0085] In addition, in this embodiment, 1 mg / L of uranium was added to the concentrated brine of a seawater desalination center, and an electro-photocatalytic experiment was conducted to investigate the adsorption selectivity of the Cu-SA / g-C3N4 composite electrode for uranium (details of the concentration of each ion in the concentrated brine of the seawater desalination are shown in Table 2). Figure 2 Image (b) shows the competitive adsorption of uranium with other metal ions on the Cu-SA / g-C3N4 composite electrode material. It is clear that the K+ of uranium... d The value is 1.55 × 10 4 mL / g; K of magnesium d The value is 2.14 × 10 3 mL / g; K of calcium d The value is 2.06 × 10 3 mL / g; K of vanadium d The value is 4.81 × 10 2 mL / g; K of uranium d The Kc value is significantly higher than that of other metal ions. Especially in seawater, uranium and vanadium have similar concentrations and properties, making them the main competing ions for uranium extraction via physicochemical adsorption. The Cu-SA / g-C3N composite electrode material exhibits a significantly higher Kc value for uranium. d The value is 323.2 times that of vanadium. This indicates that the electrode material exhibits excellent selectivity for uranium in complex, concentrated seawater. Furthermore, the competitive adsorption results also show that magnesium ions are the key competing ion for uranium extraction, consistent with the experimental results in simulated seawater. However, the uranium-magnesium partition coefficient ratio reaches 72.6, indicating that the uranium extraction method using this composite electrode has good adsorption selectivity and can achieve efficient uranium capture from concentrated brine.

[0086]

[0087]

[0088] This embodiment also conducted Chlorella pretreatment and dynamic cyclic adsorption experiments to evaluate the synergistic uranium extraction performance and stability of the composite electrode in practical application scenarios.

[0089] Seawater desalination brine with a uranium concentration of 1 mg / L was cultured with Chlorella vulgaris at 30°C for 12 hours and then subjected to electro-photocatalytic experiments. Figure 2 (c) Experimental results show that the Cu-SA / g-C3N4 electrode achieved uranium removal rates of 65.5%, 80.9%, and 100% in uncultured uranium solution at 5 min, 10 min, and 20 min, respectively. In contrast, for concentrated brine pretreated with Chlorella, the electrode achieved 100% uranium removal within 5 minutes, effectively shortening the reaction time and increasing uranium extraction efficiency by 4 times. Notably, this embodiment uses Chlorella to pre-culture concentrated brine, improving the photoelectrochemical uranium extraction efficiency. Unlike the traditional uranium extraction material design concept that emphasizes resistance to algal contamination, this microalgae pretreatment strategy provides a new approach for the development of uranium extraction materials.

[0090] This embodiment uses dynamic continuous experiments to investigate the removal performance and electrode stability of Cu-SA / g-C3N4 electrode on 4.8 L of seawater desalination brine inoculated with microalgae. Figure 2 As shown in Figure (d), the Cu-SA / g-C3N4 electrode achieved 100% uranium removal rates at 30 min, 60 min, 90 min, and 120 min. Dynamic continuous experiments demonstrated that the uranium removal performance of this electrode remained stable over 24 cycles, indicating good potential for practical application. Based on uranium concentration measurements using ICP-MS, the uranium extraction capacity was determined to be 3.336 mg / g / h, which is significantly higher than that of materials that capture uranium through physicochemical adsorption, photocatalytic reduction, or electrocatalytic methods. Figure 2 (f); see Table 3 for details).

[0091]

[0092] In summary, to selectively remove uranium from concentrated seawater desalination brine, this embodiment designed and synthesized a Cu-SA / g-C3N4 photoelectrocatalytic composite electrode. By comparing the uranium removal effects of square wave voltage and constant voltage, it was found that the square wave is key to driving the copper single-atom catalyst active site and uranyl ions through reversible single-electron transfer, achieving rapid uranium deposition and removal. Within a pH range of 4-8, the composite electrode maintained a uranium removal rate of over 95%, especially at seawater pH=8, where the removal rate of a 10 mg / L uranium solution reached 98% within 5 minutes. The phosphate groups grafted onto the composite electrode surface significantly enhanced the uranium binding capacity, endowing the electrode with excellent selectivity. In concentrated seawater desalination brine, the uranium partition coefficient (K0) was significantly reduced. d The value reached 1.55 × 10 4 The uranium extraction efficiency (U / g) of the composite electrode was 323.2 times that of the main competing ions vanadium and magnesium, respectively, overcoming the challenge of efficiently capturing uranium from concentrated brine. Furthermore, after 12 hours of pretreatment with Chlorella vulgaris, the composite electrode achieved a uranium extraction capacity of 3.336 mg / g / h under electro-photocatalytic conditions, significantly higher than the untreated system. Moreover, the composite electrode exhibited excellent performance in dynamic adsorption experiments; even after 24 consecutive cycles, the uranium removal rate remained at 100%, demonstrating superior stability.

[0093] This embodiment provides a method for efficiently extracting uranium from concentrated brine. This method is applicable to seawater desalination systems and can also be applied to other complex, high-salinity water bodies containing uranium, such as concentrated seawater from sea salt plants and salt lake water.

[0094] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

Claims

1. A method for preparing rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material, characterized in that, Includes the following steps: Melamine was dissolved in deionized water, and after stirring and dissolving, it was heated. The resulting product was separated into solid and liquid, washed and dried, and then heat-treated in an inert atmosphere to obtain g-C3N4. Graphene, copper oxalate, and chitosan were added to an acidic aqueous solution, stirred, dried, and then heat-treated in an inert atmosphere to obtain an rGO-supported copper single-atom catalyst. The rGO-supported copper single-atom catalyst and g-C3N4 were dispersed in an organic-water mixed solvent containing Nafion, followed by the addition of phytic acid and ultrasonic treatment to obtain catalyst ink; the catalyst ink was coated on the substrate surface and dried to obtain a composite electrode material.

2. The preparation method of the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 1, characterized in that, The mass ratio of graphene to copper oxalate is 3:

2.

3. The preparation method of the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 1, characterized in that, Each 1.5g graphene and 1.0g copper oxalate corresponds to 4mL chitosan.

4. The preparation method of the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 1, characterized in that, The mass ratio of the rGO-supported copper single-atom catalyst to g-C3N4 is 2:

3.

5. The preparation method of the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 1, characterized in that, Each 5.2 mg rGO-supported copper single-atom catalyst and 7.8 mg g-C3N4 corresponds to 400 μL Nafion and 1.92 mL phytic acid.

6. rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The application of the rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 6 in photoelectrocatalytic uranium removal.

8. The application according to claim 7, characterized in that, The photoelectrocatalysis is carried out under the drive of a square wave potential.

9. The rGO-supported copper single-atom catalyst / g-C3N4 composite electrode material according to claim 6 is used to recover uranium from uranium-containing wastewater, seawater, concentrated brine from seawater desalination plants, concentrated seawater from salt plants, or salt lake water.

10. A method for recovering uranium from uranium-containing wastewater, seawater, concentrated brine from seawater desalination, concentrated seawater from a sea salt plant, or salt lake water, characterized in that, Includes the following steps: The pH of the water body is adjusted, and electrolytes are added. Microalgae pretreatment is optionally performed to obtain the solution to be treated. Using the composite electrode material described in claim 6 as the cathode and a graphite sheet as the anode, the liquid to be treated is subjected to photoelectrocatalytic treatment under square wave potential drive.

Images