Composite electrode material for removing uranium through photoelectrocatalysis as well as preparation method and application of composite electrode material

Abstract

The invention discloses a composite electrode material for removing uranium through photoelectrocatalysis and a preparation method and application of the composite electrode material, and belongs to the technical field of catalytic materials and wastewater treatment.The preparation method of the composite electrode material comprises the following steps that a ZIF-8 material, copper salt and ferric salt are mixed, and a first metal composite material is prepared; reacting the first metal composite material with a KOH solution to prepare a second metal composite material; carrying out carbonization treatment on the second metal composite material, and then carrying out acid treatment by using acid to obtain a bimetallic atom catalytic material; the preparation method comprises the following steps: dispersing a bimetallic atom catalytic material and a g-C3N4 material in a mixed solution containing phytic acid and a Nafion solution to obtain catalyst ink; and coating the catalyst ink on a substrate, and carrying out illumination drying to obtain the composite electrode material. According to the composite electrode material, under the synergistic effect of the bimetallic single atomic cluster catalyst and g-C3N4, respective advantages are fully exerted, and efficient deposition removal of uranium is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalytic materials and wastewater treatment technology, and particularly relates to a composite electrode material for photoelectrocatalytic removal of uranium as well as a preparation method and application thereof. BACKGROUND

[0002] As a core resource of nuclear energy development, uranium is widely used in nuclear fuel cycle, medical diagnosis, military industry and other fields. However, the uranium-containing wastewater generated in the process of uranium mining and processing will pose a serious threat to the ecological environment and human health. Uranium in wastewater mainly exists in the form of uranyl ion (UO2 2+ ), which is radioactive, chemically toxic and biologically cumulative, can enter the human body through the food chain, and cause kidney damage, genetic mutation and even cancer. At present, the amount of uranium-containing wastewater generated by nuclear industrial activities is high worldwide every year, and the uranium concentration exceeds the standard. At the same time, the global uranium resources are becoming increasingly scarce, so the recovery of uranium resources from wastewater can not only solve the pollution problem, but also alleviate the pressure of uranium resource shortage.

[0003] At present, the more universal uranium removal methods include chemical precipitation, ion exchange, adsorption, electrochemical method, etc. The electrochemical reduction method drives the reduction reaction of uranium U(VI) on the electrode surface by applying voltage, converts it into insoluble U(IV) (such as UO2), so as to realize uranium removal, and has broad application prospects in the field of nuclear industrial wastewater treatment and uranium resource recovery. However, due to the adsorption of uranium on the electrode surface to occupy the adsorption sites, the uranium adsorption capacity is limited. The metal single-atom catalyst disperses the metal atoms (such as Fe, Co, Ni) on the surface of the carrier (such as graphene, MOFs) to form high active sites and maximize the atom utilization rate (close to 100%). And the metal single-atom catalyst removes uranium by deposition, without occupying active sites. However, there is still a large space for improvement in the uranium extraction rate of the metal single-atom catalyst.

[0004] As a metal-free semiconductor material, g-C3N4 (graphitic carbon nitride) exhibits significant potential for the removal of radioactive uranium due to its unique layered structure, tunable photoelectric properties, and chemical stability. Its two-dimensional layered structure and composites with other materials increase the density of active sites, promoting both physical adsorption and chemical binding of uranium, resulting in rapid uranium removal. However, inherent shortcomings of g-C3N4, such as a high recombination rate of photogenerated electron-hole pairs, low quantum efficiency, a wide bandgap, and easy aggregation in water, significantly impair its photocatalytic performance, limiting its practical application in water treatment. A prominent issue is that uranium dioxide (UO2) produced by photocatalytic reduction can adsorb and accumulate on the electrode surface due to these defects, occupying valuable active sites and severely limiting the uranium removal capacity of the electrode material. To overcome these limitations, modification through composites with metal materials can effectively enhance the photocatalytic efficiency. Whether combining metal atom catalysts with g-C3N4 can fully leverage the advantages of both, inhibit photogenerated electron-hole recombination, improve light energy utilization efficiency, and achieve rapid deposition and removal of uranyl ions remains to be investigated. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a composite electrode material for photoelectrocatalytic uranium removal, so as to solve the problems raised in the above background technology.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] A method for preparing a composite electrode material for photoelectrocatalytic uranium removal comprises the following steps:

[0008] The ZIF-8 material is added to a solvent, and copper salt and iron salt are added and mixed, and then the mixture is centrifuged to collect the obtained first metal composite material;

[0009] The first metal composite material is dispersed in a solvent, and a KOH solution is added dropwise to react, and then centrifuged to collect the obtained second metal composite material;

[0010] carbonizing the second metal composite material, then treating it with an acid, and washing and drying it to obtain a bimetallic atom catalytic material;

[0011] Dispersing the bimetallic atom catalytic material and the g-C3N4 material in a mixed solution containing phytic acid and Nafion solution to obtain a catalyst ink;

[0012] The catalyst ink is applied on a substrate and dried under light to obtain a composite electrode material.

[0013] Preferably, the preparation method of the ZIF-8 material comprises the following steps: adding a zinc nitrate solution with a concentration of 80-120 mmol / L into a 2-methylimidazole solution with a concentration of 300-500 mmol / L to react, so as to obtain the ZIF-8 material.

[0014] Preferably, the solvent is methanol.

[0015] Preferably, the copper salt is CuCl2·2H2O; the iron salt is FeCl3·6H2O; and the mass ratio of the ZIF-8 material to the copper salt and the iron salt is 200:(7-10):(10-15).

[0016] Preferably, the temperature of the carbonization treatment is 850-950℃.

[0017] Preferably, the acid is a 0.4-0.6 mol / L nitric acid solution; and the temperature of the acid treatment is 75-85℃.

[0018] Preferably, the mass ratio of the bimetallic atomic catalytic material to the g-C3N4 material is 1:(0.8-1.2).

[0019] Another object of the present application is to provide a composite electrode material for photoelectrocatalytic uranium removal, which is prepared by the above preparation method.

[0020] Another object of the present application is to provide an application of the above composite electrode material in photoelectrocatalytic uranium removal.

[0021] Another object of the present application is to provide an application of the above composite electrode material in treating uranium-containing wastewater.

[0022] Preferably, the method for treating uranium-containing wastewater and / or extracting uranium from seawater comprises the following steps:

[0023] Adjusting the pH value of the uranium-containing wastewater and / or seawater, and adding an electrolyte and / or performing microalgae pretreatment to obtain a to-be-treated liquid;

[0024] Taking the composite electrode material as a cathode and a graphite plate as an anode, the to-be-treated liquid is subjected to photoelectrocatalysis.

[0025] The application introduces the copper-iron double atom sites by adopting the bimetallic atomic catalytic material and the g-C3N4 material to prepare a composite electrode material, and under the synergistic effect of the bimetallic single atom cluster catalyst and the g-C3N4, the respective advantages are fully exerted to realize the efficient deposition and removal of uranium; the composite electrode material maintains a high uranium removal rate in a wide pH range, and meanwhile, the composite electrode material exhibits a high uranium removal capacity in the initial uranium concentration range of 10-150 mg / L. In the photoelectrocatalysis process, the chlorella source can be introduced to participate in the uranium removal of the actual wastewater, and the control measures such as regulating the electrolyte quality in the real seawater to improve the removal rate can be taken to effectively make up for the gap from the laboratory simulation to the real environment application of the photoelectrocatalysis system, and lay a foundation for the efficient removal and recovery of uranium in the low-concentration uranium-containing wastewater and the application of seawater uranium extraction in the real environment. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figures are part of the characterization results of the material prepared in example 1 of the application; wherein a and b are TEM and HAADF-STEM images of Cu / Fe-N-C respectively; c, d, e, f are EDS maps, which respectively show the uniform distribution of C (red), N (blue), Fe (green) and Cu (yellow) on the carbon matrix; g is the aberration-corrected HAADF-STEM image of Cu / Fe-N-C, which shows the atomic dispersion of iron and copper; h and i are SEM images of Cu / Fe-N-C and g-C3N4 respectively.

[0027] Figure 2 The figures are other characterization results of the material prepared in example 1 of the application; wherein a and b are the photocurrent maps of g-C3N4 and Cu / Fe-N-C respectively; c and d are the PL spectrum maps of g-C3N4 and Cu / Fe-N-C respectively; e is the BET map of g-C3N4; f is the BET map of Cu / Fe-N-C; g, h, i, j are the ultraviolet-visible diffuse reflectance spectra of g-C3N4 and Cu / Fe-N-C;

[0028] Figure 3 The figures are the electrocatalytic uranium removal experimental results of the material prepared in example 1 of the application; wherein a is the influence of different precursor preparation methods on the electrocatalytic uranium removal of Cu / Fe-N-C-P; b is the electrocatalytic uranium removal efficiency of two single atom cluster catalysts; c is the performance comparison results of g-C3N4 photocatalysis (g-C3N4 Light) uranium removal, g-C3N4 photoelectricity (g-C3N4 Photoelectricity) uranium removal, Cu / Fe-N-C-P / g-C3N4 photoelectricity (Cu / Fe-N-C-P / g-C3N4 Photoelectricity) uranium removal; d is the influence of the initial pH of the solution on the uranium removal rate; e is the influence of the initial uranium concentration on the uranium removal rate;

[0029] Figure 4 Fig. 12 is a mechanism analysis result chart, wherein a, b, c, d, f are XPS spectra of Cu / Fe-N-C-P / g-C3N4 before and after uranium adsorption; e is a precipitate product Na2O(UO3·H2O) x Fig. 13 is a Raman spectrum of the product; g is an FTIR spectrum of g-C3N4, Cu / Fe-N-C and Cu / Fe-N-C-P / g-C3N4; h, i are electrocatalytic reaction products of Cu / Fe-N-C-P; j is a PXRD chart of the precipitate product Na2O(UO3·H2O) x Fig. 14 is a SEM chart of Cu / Fe-N-C-P / g-C3N4 before and after uranium adsorption; k, m are SEM charts of Cu / Fe-N-C-P / g-C3N4 before and after uranium adsorption, respectively;

[0030] Figure 5 Fig. 15 is an application effect and regulation result chart in real seawater and wastewater, wherein a is a SEM and mapping chart of Chlorella vulgaris; b is a SEM and mapping chart of the precipitate product after Chlorella vulgaris cooperates with photoelectric treatment of uranium; c is a removal efficiency of simulated fluoride ion wastewater; d is a removal efficiency of actual wastewater and microalgae pretreated wastewater; e is a removal efficiency comparison chart before and after seawater regulation; f is a removal rate of other metals in wastewater after Chlorella vulgaris pretreatment and Chlorella vulgaris cooperates with photoelectric catalysis of Cu / Fe-N-C-P / g-C3N4; g is a U4f spectrum of the precipitate product after Chlorella vulgaris cooperates with photoelectric treatment of uranium; h is an FTIR spectrum of the precipitate product after Chlorella vulgaris, Chlorella vulgaris pretreatment and Chlorella vulgaris cooperates with photoelectric treatment of uranium. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0032] As an important nuclear fuel, uranium is produced and utilized in large quantities, which results in a large amount of uranium-containing wastewater, posing a serious threat to the environment and human health. It is urgent to remove and recover low-concentration uranium in wastewater. Embodiments of the present application synthesize a new type of bimetallic monatomic cluster catalyst (Cu / Fe-N-C) using ZIF-8 as a precursor, and composite the catalyst with carbon nitride (g-C3N4) at a certain mass ratio and phosphorize to prepare a composite electrode material (Cu / Fe-N-C-P / g-C3N4). In addition, embodiments of the present application systematically study the photoelectric synergistic removal performance of the Cu / Fe-N-C-P / g-C3N4 composite electrode material on uranium, and explore the effects of factors such as the initial pH value of the solution, the initial uranium concentration, and the adsorption time on the uranium removal performance and the mechanism. Through multi-dimensional characterization (SEM, XPS, PL, XRD, FT-IR, HAADF-STEM, etc.) and mechanism analysis, the dynamic process of "adsorption-photo / electricity synergistic reduction oxidation-deposition" is revealed, which provides a theoretical basis for efficient removal of uranium in complex systems.

[0033] Specifically, in an embodiment of the present application, a preparation method of a composite electrode material for photoelectrocatalytic uranium removal is provided, which comprises the following steps:

[0034] S1, adding ZIF-8 material into a solvent, and adding copper salt and iron salt for mixing, then centrifuging to collect the obtained first metal composite material;

[0035] S2, dispersing the first metal composite material in a solvent, and adding dropwise a solution containing KOH for reaction, then centrifuging to collect the obtained second metal composite material;

[0036] S3, carbonizing the second metal composite material, then acidizing with acid, and washing and drying to obtain a bimetallic atomic catalyst material;

[0037] S4, dispersing the bimetallic atomic catalyst material and g-C3N4 material in a mixed solution containing phytic acid and Nafion solution to obtain catalyst ink;

[0038] S5, smearing the catalyst ink on a substrate and performing light drying to obtain a composite electrode material.

[0039] In a preferred embodiment of the present application, the preparation method of ZIF-8 material comprises the following steps: adding a zinc nitrate solution with a concentration of 80-120 mmol / L into a 2-methylimidazole solution with a concentration of 300-500 mmol / L for reaction to obtain ZIF-8 material.

[0040] In a preferred embodiment of the present application, the solvent is preferably methanol, and other organic solvents or inorganic solvents capable of dissolving or dispersing the raw materials can also be used.

[0041] In a preferred embodiment of the present application, the copper salt can be copper chloride, copper nitrate, copper sulfate and the like, and the iron salt can be iron chloride, iron nitrate, iron sulfate and the like, but is not limited thereto; preferably, the copper salt is copper chloride dihydrate (CuCl2·2H2O), and the iron salt is iron chloride hexahydrate (FeCl3·6H2O); the mass ratio of the ZIF-8 material to the copper salt and the iron salt is 200:(7-10):(10-15).

[0042] In a preferred embodiment of the present application, the carbonization treatment temperature is 850-950°C, preferably 900°C; the carbonization treatment can be carried out in a protective atmosphere such as nitrogen.

[0043] In a preferred embodiment of the present application, the acid is a 0.4-0.6 mol / L nitric acid solution, but is not limited thereto, and other organic acids or inorganic acids can also be used; the acid treatment temperature is 75-85°C.

[0044] In a preferred embodiment of the present application, the mass ratio of the bimetallic atomic catalytic material to the g-C3N4 material is 1:(0.8-1.2), preferably 1:1.

[0045] In a preferred embodiment of the present application, the preparation method of the g-C3N4 material comprises the following steps: melamine is added to deionized water, fully stirred at 85-95°C until it is completely dissolved, then transferred to a high-pressure reaction kettle, heated at 1701-190°C; after cooling to room temperature, washed with deionized water and anhydrous ethanol three times, vacuum dried at 55-65°C, and the dried sample is placed in a tube furnace, heated to 500-600°C at a heating rate of 4-6°C / min under a protective atmosphere such as nitrogen to obtain the product g-C3N4 material.

[0046] In a preferred embodiment of the present application, the mixed solution containing phytic acid and Nafion solution comprises ethanol, phytic acid, Nafion solution and deionized water; the volume ratio of ethanol, phytic acid, Nafion solution and deionized water is (8-9):(1.5-2):(0.1-1):(0.1-1); the concentration of the Nafion solution is 4-6 wt%.

[0047] In a preferred embodiment of the present application, the substrate is carbon felt, but is not limited thereto; the light irradiation is carried out using infrared rays.

[0048] In another embodiment of the present application, the use of the above-mentioned composite electrode material in photoelectrocatalytic uranium removal is also provided, specifically in the treatment of uranium-containing wastewater and / or seawater uranium extraction.

[0049] In a preferred embodiment of the present application, the method for treating uranium-containing wastewater and / or seawater uranium extraction comprises the following steps:

[0050] S1, adjusting pH value of the uranium-containing wastewater and / or seawater, and adding electrolyte and / or performing microalgae pretreatment to obtain a to-be-treated liquid;

[0051] S2, performing photoelectrocatalysis on the to-be-treated liquid by using the composite electrode material as a cathode and a graphite plate as an anode.

[0052] In actual application, the pH value can be adjusted by 0.5-1.5 mol / L sodium carbonate solution or 0.005-0.015 mol / L nitric acid solution; the electrolyte is sodium chloride; and the method for microalgae pretreatment is introducing chlorella sources.

[0053] In the following specific examples, some of the chemical reagents involved and their sources are as follows: zinc nitrate hexahydrate (content ≥ 99%, PubChem CID 329752354), 2-methylimidazole (content ≥ 98%, PubChem 24896976), copper chloride dihydrate (PubChem CID 329753575), iron chloride hexahydrate (PubChem 329799693), phytic acid, Nafion (perfluorinated resin) solution, copper acetylacetonate, ferric ammonium citrate (PubChem 24894895) purchased from Macklin Reagent Co., Ltd.; sodium chloride, ethanol, acetone, and methanol purchased from Shanghai Huishi Co., Ltd.; all reagents are analytical pure.

[0054] Example 1: The example provides a preparation method of a composite electrode material for photoelectrocatalytic uranium removal, which comprises the following steps:

[0055] S1, 50 mL of zinc nitrate hexahydrate solution with a concentration of 100 mmol / L is added to 50 mL of 2-methylimidazole solution with a concentration of 400 mmol / L, and the reaction is carried out at room temperature for 5 h. After the reaction is completed, the obtained ZIF-8 material is washed with water.

[0056] S2, 200 mg of the ZIF-8 material prepared above is added to 40 mL of methanol and ultrasonically dispersed for 0.5 h, then 8.5 mg of CuCl2·2H2O and 13.5 mg of FeCl3·6H2O are dissolved in 10 mL of methanol and then added dropwise to the above solution, and the stirring is continued at room temperature for 12 h, and then the first metal composite material CuCl2-FeCl3@ZIF-8 powder is collected by centrifugation and vacuum dried overnight.

[0057] S3, the first metal composite material CuCl2-FeCl3@ZIF-8 obtained above was dispersed in 40 mL of methanol, and a methanol solution (10 mL) containing 12 mg of KOH was added dropwise for reaction. After stirring at room temperature for 12 h, the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8 was collected by centrifugation, washed with methanol, and dried at 60°C under vacuum overnight.

[0058] S4, the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8 obtained above was placed in a tube furnace under a nitrogen atmosphere, and was heated at a rate of 5°C / min to 900°C for carbonization treatment for 2 h, then was reduced to room temperature at a rate of 5°C / min, and then was subjected to acid treatment with a 0.5 mol / L nitric acid solution at 80°C for 24 h, and was washed with deionized water until neutral, and then was dried at 60°C overnight to obtain the bimetallic atomic catalytic material Cu / Fe-N-C.

[0059] S5, 1 g of melamine was added to 60 mL of deionized water, and was completely dissolved by stirring at 90°C, and then was transferred to a 100 mL high-pressure reaction kettle, and was heated at 180°C for 24 h. After cooling to room temperature, the product was washed with deionized water and anhydrous ethanol three times, and then was dried under vacuum at 60°C. The dried sample was placed in a tube furnace, and was calcined at a heating rate of 5°C / min to 550°C under nitrogen protection for 4 h to obtain the product g-C3N4 material.

[0060] S6, 5 mg of the bimetallic atomic catalytic material Cu / Fe-N-C and 5 mg of the g-C3N4 material prepared above were dispersed in a mixed solution containing 8.8 mL of ethanol, 1.92 mL of phytic acid, 0.4 mL of a 5 wt% Nafion solution, and 0.4 mL of deionized water, and were ultrasonically dissolved to obtain a catalyst ink.

[0061] S7, the catalyst ink above was applied to a 5 cm x 5 cm carbon felt, and was irradiated under an infrared lamp for 3 h until completely dry to obtain the composite electrode material Cu / Fe-N-C-P / g-C3N4.

[0062] Example 2: The example provides a preparation method of a composite electrode material for photoelectrocatalytic removal of uranium, which comprises the following steps:

[0063] S1, 50 mL of a 80 mmol / L zinc nitrate hexahydrate solution was added to 50 mL of a 300 mmol / L 2-methylimidazole solution, and was reacted at room temperature for 5 h. After the reaction was completed, the ZIF-8 material was obtained by washing with water.

[0064] S2, 200 mg of the ZIF-8 material prepared above was added to 40 mL of methanol and ultrasonically dispersed for 0.5 h, then 7 mg of CuCl2.2H2O and 10 mg of FeCl3.6H2O were dissolved in 10 mL of methanol and added dropwise to the above solution, which was continuously stirred at room temperature for 12 h, then centrifuged to collect the first metal composite material CuCl2-FeCl3@ZIF-8 powder, which was vacuum dried overnight.

[0065] S3, the first metal composite material CuCl2-FeCl3@ZIF-8 obtained above was continuously dispersed in 40 mL of methanol, and a methanol solution (10 mL) containing 10 mg of KOH was added dropwise for reaction, which was stirred at room temperature for 12 h, then centrifuged to collect the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8, which was washed with methanol and vacuum dried at 60°C overnight.

[0066] S4, the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8 obtained above was placed in a tube furnace under a nitrogen atmosphere, heated to 850°C at a rate of 5°C / min for carbonization treatment for 2 h, then reduced to room temperature at a rate of 5°C / min, then treated with a 0.4 mol / L nitric acid solution at 75°C for 24 h, washed with deionized water until neutral, and then dried at 55°C overnight to obtain a bimetallic atomic catalytic material Cu / Fe-N-C.

[0067] S5, 1 g of melamine was added to 60 mL of deionized water, fully stirred at 85°C until completely dissolved, then transferred to a 100 mL high-pressure reaction kettle, heated at 180°C for 24 h; after cooling to room temperature, washed with deionized water and anhydrous ethanol three times, then vacuum dried at 60°C, and the dried sample was placed in a tube furnace, heated to 500°C at a rate of 5°C / min under nitrogen protection for calcination for 4 h to obtain a product g-C3N4 material.

[0068] S6, 5 mg of the bimetallic atomic catalytic material Cu / Fe-N-C prepared above and 4 mg of the g-C3N4 material were dispersed in a mixed solution containing 8 mL of ethanol, 1.5 mL of phytic acid, 0.1 mL of a 4 wt% Nafion solution, and 0.1 mL of deionized water, and ultrasonically dissolved to obtain a catalyst ink.

[0069] S7, the catalyst ink above was applied to a 5 cm x 5 cm carbon felt, which was irradiated under an infrared lamp for 3 h until completely dry to obtain a composite electrode material Cu / Fe-N-C-P / g-C3N4.

[0070] Embodiment 3: The embodiment provides a preparation method of a composite electrode material for photoelectrocatalytic removal of uranium, which comprises the following steps:

[0071] S1, 50 mL of a zinc nitrate hexahydrate solution with a concentration of 120 mmol / L is added to 50 mL of a 2-methylimidazole solution with a concentration of 500 mmol / L, and the reaction is carried out at room temperature for 5 h. After the reaction is completed, the obtained ZIF-8 material is washed with water.

[0072] S2, 200 mg of the ZIF-8 material prepared in the above step is added to 40 mL of methanol and ultrasonically dispersed for 0.5 h, then 10 mg of CuCl2·2H2O and 15 mg of FeCl3·6H2O are dissolved in 10 mL of methanol and then added dropwise to the above solution, and the stirring is continued at room temperature for 12 h, and then the first metal composite material CuCl2-FeCl3@ZIF-8 powder is collected by centrifugation and vacuum dried overnight.

[0073] S3, the first metal composite material CuCl2-FeCl3@ZIF-8 obtained in the above step is continuously dispersed in 40 mL of methanol, and a methanol solution (10 mL) containing 15 mg of KOH is added dropwise for reaction, and the stirring is continued at room temperature for 12 h, and then the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8 is collected by centrifugation, washed with methanol, and vacuum dried at 60°C overnight.

[0074] S4, under the protection of a nitrogen atmosphere, the second metal composite material Cu(OH)2-Fe(OH)3@ZIF-8 obtained in the above step is placed in a tube furnace, heated to 950°C at a rate of 5°C / min for carbonization treatment for 2 h, then reduced to room temperature at a rate of 5°C / min, and then subjected to acid treatment with a 0.4-0.6 mol / L nitric acid solution at 85°C for 24 h, washed with deionized water until neutral, and then dried at 65°C overnight to obtain a bimetallic atomic catalytic material Cu / Fe-N-C.

[0075] S5, 1 g of melamine is added to 60 mL of deionized water, fully stirred at 95°C until it is completely dissolved, and then transferred to a 100 mL high-pressure reaction kettle, heated at 180°C for 24 h; after cooling to room temperature, the sample is washed with deionized water and anhydrous ethanol three times, and then vacuum dried at 60°C, and the dried sample is placed in a tube furnace, heated to 600°C at a rate of 5°C / min under nitrogen protection for calcination for 4 h to obtain a product g-C3N4 material.

[0076] S6, 5 mg of the above prepared bimetallic atomic catalyst Cu / Fe-N-C and 5 mg of g-C3N4 material were dispersed in a mixed solution containing 9 mL of ethanol, 2 mL of phytic acid, 1 mL of 6 wt% Nafion solution and 1 mL of deionized water, and ultrasonically dissolved to obtain a catalyst ink.

[0077] S7, the above catalyst ink was applied on a 5 cm x 5 cm carbon felt, and irradiated under an infrared lamp for 3 h to completely dry to obtain a composite electrode material Cu / Fe-N-C-P / g-C3N4.

[0078] Comparative Example 1: This comparative example provides another preparation method other than the bimetallic atomic catalyst used in the implementation of the present application, which comprises the following steps:

[0079] 86.39 mg of copper acetylacetonate, 890 mg of zinc nitrate hexahydrate and 28.82 mg of ferric ammonium citrate were added to a 70 mL methanol solution and ultrasonically dispersed. 1.036 g of 2-methylimidazole powder was dissolved in 30 mL of anhydrous methanol and quickly poured into the above solution, and after stirring for 12 h, it was washed with anhydrous methanol three times and then placed in an oven at 80°C for drying for 12 h to obtain a FeCu-ZIF precursor. The FeCu-ZIF precursor was pyrolyzed at 950°C under N2 environment conditions at a heating rate of 5°C / min for 3 h, and cooled to room temperature to obtain the target product, a ZIF-8 derived copper-iron bimetallic site catalyst FeCu-ZIF-8.

[0080] Experimental Application Example: This experiment verifies the adsorption effect by adsorbing 200 mL of uranium solution. By adding 1 mol / L sodium carbonate or 0.01 mol / L nitric acid solution to control the pH value, the composite electrode material Cu / Fe-N-C-P / g-C3N4 prepared in the above Example 1 was used as the cathode, and a 5 x 5 cm graphite plate was used as the anode, and placed in 200 mL of uranium solution containing 7 g of sodium chloride, and photoelectrocatalyzed for 30 min, and sampled three times at 5 min, 10 min and 20 min, and the uranium concentration in the solution after adsorption was determined by a spectrophotometer.

[0081] I. The materials such as Cu / Fe-N-C and g-C3N4 prepared in the above Example 1 were characterized, and the results are shown in Figure 1 and Figure 2 The morphology of the materials was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM (a) and HAADF-STEM (b) of the Cu / Fe-N-C material are shown in Figure 1 Figure 1 ​There are no obvious metal particles in b), which indicates that Fe and Cu elements are highly dispersed in the carbon matrix in the form of sub-nanometer atomic clusters or single atoms. Compared with large nanoparticles, sub-nanometer clusters have a surface atomic ratio close to 100%, exposing more unsaturated coordination sites, which enhances the affinity of UO2 2+ Combined with EDS ( Figure 1 c, d) C, N cover the entire field of view, ( Figure 1 e, f) show that Fe and Cu are evenly distributed in the carbon matrix, and the dispersed Fe and Cu expose active sites, which improves the uranium adsorption capacity. Aberration-corrected HAADF-STEM ( Figure 1 The bright spots in g) further confirm that Fe and Cu are in the form of small atomic clusters, and may form diatomic active sites (such as Fe-Cu pairs). EDS surface scans show that Cu, Fe, N, and C elements are evenly distributed in the carbon matrix, without obvious element segregation, indicating that the bimetallic active centers form a tight composite structure with the carbon matrix, which is conducive to synergistic catalysis. The continuous structure of the carbon matrix provides a stable anchoring point for metal single atoms. The Fe-Cu diatoms appear as adjacent bright spots in HAADF-STEM. Combined with the co-localization distribution of EDS, it shows that the two form active centers, which may enhance the uranium adsorption and reduction performance through electronic coupling effects. Through the above analysis, the successful construction of bimetallic single atom catalysts in Cu / Fe-NC materials can be clarified, providing a structural basis for its efficient uranium removal performance. Cu / Fe-NC presents irregular granular agglomerates ( Figure 1 The surface roughness of g-C3N4 is probably caused by the composite of metal and carbon matrix. The SEM of g-C3N4 shows a typical two-dimensional layered stacking structure ( Figure 1 h), the surface is smooth and has a small amount of holes, which is convenient for combining with Cu / Fe-NC.

[0082] According to the BET test results, the specific surface area of ​​g-C3N4 is 24.25m 2 / g, the value is small, indicating that the effective area of ​​its surface available for adsorption or reaction is limited. The pore size is 18.09nm. Combined with the N2 adsorption-desorption isotherm and the embedded pore size distribution curve ( Figure 2 The e of Cu / Fe-NC shows that it has a certain mesoporous structure, but the contribution of micropores is relatively weak. The specific surface area of ​​Cu / Fe-NC is 492.03m 2 / g, the large specific surface area means that there are a large number of active sites on the surface of the material that can participate in adsorption, catalysis and other effects. The pore size is 2.11nm, combined with the N2 adsorption-desorption isotherm and the embedded pore size distribution curve ( Figure 2The f-value indicates a well-developed mesoporous structure. The introduction of Cu and Fe, along with optimized carbon supports (e.g., nitrogen doping), enhances porosity, resulting in abundant and relatively regular pores. This pore structure facilitates the transport and diffusion of substances within the pores, providing ample contact area and suitable reaction space for reactants in catalytic reactions.

[0083] The absorption edge of g-C3N4 is located at about 460nm, corresponding to a band gap of 2.76eV ( Figure 2 j), which is consistent with its semiconductor characteristics of visible light response. The absorption peak is in the range of 300-450nm, which originates from the π-π electronic transition of the triazine ring. The absorption range is limited to the visible light region (<460nm), and the utilization rate of long-wavelength photons is low, which limits the photocatalytic efficiency. Cu / Fe-NC shows continuous broadband absorption in the range of 200-800 nm, and the absorption intensity is significantly higher than that of g-C3N4, especially in the near-infrared region (>600nm). There is an obvious tailing, and the pyridinic nitrogen and graphitic nitrogen defect states in the carbon matrix form intermediate energy levels, which promote multi-photon transitions. The indirect band gap of Cu / Fe-NC is 1.63eV ( Figure 2 h), indicating that it has a narrower band gap, which is beneficial to the visible-near-infrared light response.

[0084] g-C3N4( Figure 2 b) The photocurrent density is 0.95 μA / cm². The lower photoresponse is due to the fast carrier recombination (high PL intensity). Cu / Fe-NC ( Figure 2 a) Photocurrent density is 1.15μA / cm², and the metal-carbon interface partially promotes electron transport. Under light, the electrons in the g-C3N4 conduction band jump to the Cu / Fe-NC conduction band, and the holes remain in the g-C3N4 valence band. The built-in electric field drives the electrons to migrate to the electrode surface to participate in the UO2 2+ Reduction (Cu / Fe-NC→UO2 2+ ), the holes are replaced by H2O / OH in the electrolyte - Consumption and inhibition of recombination. Photocurrent kinetic analysis supplements the action path of photogenerated electrons to the "adsorption-reduction-oxidation-deposition" mechanism. Figure 2 In the c-steady-state photoluminescence spectrum, g-C3N4 has a strong emission peak at 500nm, the photogenerated electron-hole pairs are easy to recombine, and the carrier recombination rate is high, which will reduce the effective utilization of carriers in processes such as photocatalysis; the PL intensity of Cu / Fe-NC is extremely low, with almost no obvious emission peak, the photogenerated carrier recombination is significantly suppressed, the carrier separation efficiency is high, and it is more conducive to the participation of electrons and holes in the photocatalytic reaction. Figure 2The fluorescence decay of g-C3N4 is slow in the d time-resolved photoluminescence spectrum, and the slow decay is dominated by the recombination, and the carriers are difficult to effectively migrate and participate in the reaction; the fluorescence decay of Cu / Fe-N-C is faster, the carriers are quickly separated and migrated, the carrier lifetime is short but the effective utilization is high, which meets the demand of catalytic materials.

[0085] II. Electro-catalytic uranium removal experiment of metal monatomic cluster catalyst: the copper-iron bimetallic cluster catalyst FeCu-ZIF and Cu / Fe-N-C (Example 1) prepared by using two different precursors were subjected to electro-catalytic uranium removal, and in the 180 min electro-catalytic process, as shown in a of Figure 3 The uranium removal efficiency of Cu / Fe-N-C reached 96% in 60 min, and the uranium removal efficiency of FeCu-ZIF was only 71% in 180 min. It is shown that the copper-iron bimetallic cluster catalyst Cu / Fe-N-C prepared in the present application has better uranium removal effect.

[0086] In addition, Cu and Fe monatomic cluster catalysts (Fe-N-C and Cu-N-C) were prepared according to the method provided in Example 1, and subjected to electro-catalytic uranium removal for 180 min, and the experimental results are shown in b of Figure 3 The uranium removal rate reached the highest value in 180 min, the uranium removal rate of the Fe-N-C monatomic cluster catalyst was 59%, the uranium removal rate of the Cu-N-C monatomic cluster catalyst was 51%, and the uranium removal rate of the Cu / Fe-N-C bimetallic cluster catalyst reached 96% in 60 min. It is shown that the bimetallic catalyst can increase the number of active sites, adjust the electronic structure, and thus enhance the uranium removal performance.

[0087] III. Photo-electro-catalytic uranium removal experiment of g-C3N4 electrode and Cu / Fe-N-C-P / g-C3N4 composite electrode material: the carbon nitride material g-C3N4 is rich in active sites and has excellent electron transport capacity, and shows potential in the field of photocatalysis. The traditional electro-catalytic experiment needs to be carried out for 180 min, and the uranium removal rate is low. Therefore, the Cu / Fe-N-C bimetallic atomic catalyst material and the g-C3N4 material are combined to form a Cu / Fe-N-C-P / g-C3N4 composite electrode material in Example 1 of the present application, and under the synergistic catalysis of photo-electro, the uranium removal rate is significantly improved, and the uranium removal rate can reach 95.5% in 5 min and more than 98% in 10 min. However, as shown in Figure 3As shown in Figure c, a cathode made of g-C3N4 material alone can remove only about 30% of uranium after 20 minutes of photocatalysis. When photocatalysis is combined with photocatalysis, the efficiency is improved, but the uranium removal efficiency is still less than 50%. This shows that the use of Cu / Fe-NCP / g-C3N4 composite electrode material can fully utilize the advantages of g-C3N4 and Cu / Fe-NCP materials to achieve efficient and rapid uranium removal.

[0088] IV. Effect of initial solution pH and initial uranium concentration: Solution pH is an important factor affecting uranium removal. The existence form of uranium and the binding strength between the material and uranium are affected by pH. The optimal pH value for uranium removal determines the application field of the material. The present invention studies the uranium removal performance of the Cu / Fe-NCP / g-C3N4 composite electrode material prepared in Example 1 in the pH range of 4.0-9.0±0.02 for 10 mg / L uranium solution. The results are as follows: Figure 3 As shown in d. As can be seen from the figure, the initial pH value of the solution has a significant effect on the uranium removal performance of the Cu / Fe-NCP / g-C3N4 composite electrode material. The uranium removal rate can reach more than 90% in the pH range of 5-8. The optimal pH value is 6.0, and the uranium removal rate reaches 99% in 20 minutes. When the initial pH value is low, the uranium in the solution is mainly in the form of UO2 2+ It exists in the form of UO2(OH) as the pH value increases. + 、UO2 2+ 、(UO2)2(OH)2 2 + and (UO2)3(OH) 5+ As the pH increases further, the main form of uranium is UO2(OH) 3- , (UO2)3(OH) 7- , UO2(OH)2, resulting in a decrease in uranium removal rate. In addition, Figure 3 As shown in the figure, when the pH value is 5-7, the Cu / Fe-NCP / g-C3N4 composite electrode material has the best ability to remove uranium. Under the conditions of superacidity and superalkalinity, the ability to remove uranium gradually decreases, which indicates that under the conditions of superacidity and superalkalinity, the H + and OH - The effect of uranium concentration on the removal of uranium by Cu / Fe-NCP / g-C3N4 composite electrode materials is shown in Figure 2. Figure 3 The uranium removal capacity of the Cu / Fe-NCP / g-C3N4 composite electrode material reached over 99% at 10 mg / L and slowly decreased with increasing concentration. However, within the uranium concentration range of 10-150 mg / L, the uranium removal rate reached over 95% within 5 minutes.

[0089] 5. Mechanism analysis experiment, the experimental results are as follows Figure 4 As shown: the Cu / Fe-NC particles prepared in Example 1 are uniformly loaded on the surface of the g-C3N4 layer ( Figure 4 k), forming a multi-level pore structure, avoiding the agglomeration problem of a single component. SEM after electrocatalysis ( Figure 4 m) shows that the material morphology remains intact and there is no obvious structural collapse, proving that the material has excellent stability. Figure 4 a, b, c, d, and f are the XPS spectra of Cu / Fe-NCP / g-C3N4 before and after uranium adsorption. Figure 4 As shown in d, the peak representing U4f appears on Cu / Fe-NCP / g-C3N4-U. In the N1s spectrum ( Figure 4 a) The peak near 399.49eV is pyridinic nitrogen, and the peak near 398.29eV is graphitic carbon, indicating the bonding mode of C and N atoms in the material. O1s spectrum ( Figure 4 b) The peak near 531.68eV represents the PO peak shifting toward higher binding energy after uranyl ions are adsorbed by PO, indicating that the material is successfully phosphated and the phosphorus-containing groups participate in the adsorption of uranium. 530.73eV is typical lattice oxygen, which can be attributed to Cu / Fe-O (metal-oxygen bond) in a single-atom system. C1s spectrum ( Figure 4 c) The peak around 284.8 eV is due to the C=C or C—C bonds that may exist in the form of sp2 or sp3 hybridization in the Cu / Fe-NCP / g-C3N4 structure.

[0090] FTIR spectra of g-C3N4, Cu / Fe-NC and Cu / Fe-NCP / g-C3N4 are shown in Figure 4. Figure 4 As shown in Figure 5, the peaks mainly appear at 810, 1154, 1230-1600, 1018, 1380, 1560 and 1623 cm -1 , it can be seen that the 810 cm -1 The peak of the triazine ring breathing vibration is 1230-1600cm -1 is the stretching vibration of CN heterocyclic ring; 1560cm of Cu / Fe-NC -1 and 1380cm -1 The C=N and CO vibration peaks appear at 1018 cm -1 The peak at 1623 cm is the asymmetric stretching vibration of COC. -1 、1154cm -1The addition of a new P=O peak indicates successful phosphate grafting. Taken together, these results suggest that the material successfully binds to phosphate ions, and that phosphorus-containing groups participate in uranium adsorption. The irregular pores on the Cu / Fe-NCP / g-C3N4 surface also enhance uranium adsorption.

[0091] Cu / Fe-NCP is used as cathode material. During the electrocatalytic reaction, yellow solids are precipitated into the electrolytic cell. As the reaction proceeds, more and more yellow solids are produced. The product is insoluble in water. After the reaction is completed, the large amount of yellow precipitates produced are filtered, washed, dried, and collected. Figure 4 As shown in h and i. After powder XRD analysis, it was found that the precipitate product corresponds to PDF#12-0112 card, indicating that the precipitate is Na2O(UO3·H2O) x ( Figure 4 When the Cu / Fe-NCP / g-C3N4 composite electrode was used for photoelectrocatalytic experiments, yellow precipitates were also produced. The precipitates were collected and characterized. Figure 4 As shown in d, from the XPS spectrum of the uranium element of the photoelectrocatalytic precipitation product, it can be seen that the main peaks at 381.12eV and 391.80eV correspond to U(VI)4f 5 / 2 and U(VI)4f 7 / 2 , indicating that most of the U in the product has a valence of +6, which is Na2O(UO3·H2O) x , and other valence states of U are generated. To more clearly characterize the specific valence state of non-hexavalent uranium in the precipitate, 0.1 mol / L HCl and 0.05 mol / L ascorbic acid were used to stir and dissolve the precipitate for 30 min, dissolve the hexavalent uranium, filter and dry, and store the product in a N2 atmosphere to perform XPS analysis of its uranium element. 380.77 eV and 391.64 eV correspond to U4f 7 / 2 and U4f 5 / 2 The 383.86 eV peak is a satellite peak, proving that the uranium valence state at this time is +4, indicating that the uranyl ions reaching the electrode surface are partially photocatalytically reduced to U(IV) and co-precipitated with Na2O(UO3·H2O)x produced by the bimetallic single atom cluster catalyst to the bottom of the electrolytic cell, forming a mixture of hexavalent uranium and tetravalent uranium. Figure 4 Raman spectrum of the precipitated product shown in e at 220 cm -1 、278cm -1 The peak at UO2 2+ The bending vibration of 811cm -1 、903cm -1 The peak at is attributed to UO2 2+Raman spectra of the precipitate after removal of U(Ⅵ). The intensity ratio of D-band to G-band (Ip / Ic) in the Raman spectrum of the precipitate after removal of U(Ⅵ). The D-band (diamond) represents sp hybridized carbon and defect structure in the graphite sheet, while the G-band (graphite) represents sp2 hybridized carbon and graphite order.1565cm -1 The G-band at 1349cm -1 is from sp3 hybridized structure. The ID / IG ratio is in the range of 1.01 to 1.04, indicating that the degree of graphitization of the precipitate after removal of U(Ⅵ) is not greatly affected.

[0092] Based on the above analysis, the embodiment of the present application proposes a mechanism for photoelectric synergistic uranium removal, as follows: the Cu / Fe-N-C-P / g-C3N4 modified by phosphoric acid groups not only enhances the uranium affinity but also provides abundant uraniumyl ion chelation sites. The presence of phosphoric acid groups improves the selective adsorption of Cu / Fe-N-C-P / g-C3N4 for uranium. Cu / Fe-N-C-P / g-C3N4 provides many (Fe / Cu-NX) active sites to participate in the deposition and removal of uraniumyl ions. During the reaction process, UO2 2+ is accelerated to move to the Fe / Cu-NX sites on the Cu / Fe-N-C-P / g-C3N4 under the action of photocatalysis, where it obtains electrons and is reduced to UO 2+ (U(V)). The reduced U(Ⅴ) is re-oxidized to U(Ⅵ) in the square wave cycle and combines with Na + to form Na2O(UO3·H2O)x precipitate. The regenerated active sites then combine with more uraniumyl ions. Due to the electron transfer of unstable U(V), Fe 3+ and Cu 2+ are reduced to Fe 2+ and Cu + . The interaction between Na + and the reversible single-electron transfer between Fe x+ , Cu x+ and UO x+ promote the formation of Na2O(UO3·H2O) x in the photoelectric synergistic catalysis process. NaCl plays a crucial role in the photoelectric synergistic catalytic conversion of uranium, and the applied electric field also accelerates the movement of uraniumyl ions to the cathode, thereby accelerating the combination of uraniumyl ions with active sites on the electrode, resulting in an ultrafast adsorption rate of the Fe / Cu-NX electrode. In addition, the photo-generated electrons of Cu / Fe-N-C-P / g-C3N4 promote the partial reduction of U(Ⅵ) to U(Ⅳ), which co-precipitates with Na2O(UO3·H2O) x at the bottom of the electrolytic cell.

[0093] Six, the application effect and regulation experiment in real seawater and wastewater, as follows: in order to verify the application potential of Cu / Fe-N-C-P / g-C3N4 composite electrode material prepared in example 1 in various nuclear wastewater and seawater, experiments were carried out in simulate fluorine uranium wastewater, actual uranium tailings wastewater and actual seawater respectively, and the results are shown in Figure 5 . Specifically, as shown in Figure 5 , in the simulate fluorine uranium wastewater, the uranium removal efficiency reached from 62% to 93% within 5-20 min, indicating that Cu / Fe-N-C-P / g-C3N4 composite electrode material has good application prospect for fluorine uranium wastewater. In addition, as shown in Figure 5 , in order to further explore the application effect of Cu / Fe-N-C-P / g-C3N4 composite electrode material in real uranium tailings seepage water, photoelectrocatalytic experiment was carried out on real wastewater with pH=6 and uranium concentration of 10 mg / L using Cu / Fe-N-C-P / g-C3N4 composite electrode material. The uranium removal rate was 56.6% at 5 min, and the uranium removal rate reached 58% at 20 min. Due to the high concentration of coexisting metal ions in the wastewater, the direct photoelectrocatalytic effect is not ideal. Under the condition of 30℃ and light, Chlorella was introduced and cultured in real uranium tailings seepage water containing 10 mg / L uranium for 12 h for pretreatment. The chlorophyll content in the pretreated wastewater was 27.89 mg / L, and the uranium removal rate reached 80.2%, indicating that microalgae and part of uranium ions were complexed and removed. Continue to use Cu / Fe-N-C-P / g-C3N4 composite electrode material to carry out photoelectrocatalytic treatment on the wastewater, and the uranium removal rate can reach 100% at 5 min. During the experiment, Chlorella settled down during photoelectrocatalysis and generated yellow-green precipitate. After the experiment, the chlorophyll content in the solution was 3.65 mg / L. There are usually Al, Fe, Mn and other cations in uranium-containing wastewater. The removal rates of Al, Fe and Mn ions in the actual wastewater after Chlorella pretreatment were 97.85%, 82.61% and 80.19% respectively, while the removal rates of Al, Fe and Mn ions after Chlorella / Cu / Fe-N-C-P / g-C3N4 photoelectrocatalytic treatment were 96.87%, 78.26% and 84.17% respectively Figure 5 (f). After the coexistence of microalgae and photoelectric treatment, the removal rate of metal ions decreased slightly, which may be due to the rupture of part of the algae cells after photoelectrocatalysis, which makes a small amount of metal re-release into the water. In addition, 10 mg of Cu / Fe-N-C-P / g-C3N4 composite electrode material was used for photoelectrocatalytic treatment on 200 mL of real seawater with pH=8 and uranium concentration of 10 mg / L, and no NaCl was added during the experiment. Figure 5 As shown in Figure 5, the uranium removal rate was only 66.8% at 20 minutes. Furthermore, 4g of NaCl electrolyte was added and the experiment was repeated. At 5 minutes, the uranium removal rate reached approximately 95%. Extending the experiment to 15 minutes stabilized the uranium removal rate at 95%. By adding 7g of NaCl electrolyte and repeating the experiment, the uranium removal rate reached over 95% at 5 minutes, and reached 100% at 20 minutes. These real-world wastewater and seawater experiments demonstrate that microalgae pretreatment or control measures such as the addition of sodium chloride can effectively bridge the gap between laboratory and practical application. Furthermore, microalgae utilize natural photosynthesis to remove metal ions, reducing the energy consumption and carbon emissions of traditional treatment processes, which is in line with the current international trend toward low-carbon and environmentally friendly practices.

[0094] Figure 5 a shows that the primitive algae cells are smooth ellipsoids. Figure 5 The precipitation product shown in b has nanoparticles attached to the rough surface of Chlorella cells, with a reduced particle size and improved dispersion, proving that uranium is complexed and adsorbed with the functional groups on the surface of algae cells to form precipitation. The mapping of the precipitation product ( Figure 5 b) Peaks representing phosphorus and uranium were clearly detected. The FTIR spectra of Chlorella (Chlorella), Chlorella-U (Chlorella pretreatment of uranium-containing wastewater), and Chlorella / Cu / Fe-NCP / g-C3N4-U (Chlorella and Cu / Fe-NCP / g-C3N4 synergistic treatment of uranium-containing wastewater) are shown in Figure 2. Figure 5 As shown in h, Chlorella-U in 1250cm -1 、1046cm -1 At 897 cm -1 A very obvious new peak O=U=O appeared, indicating that the phosphorus-containing groups in the algae cells successfully adsorbed U by complexing with uranium. The peak of O=U=O became more obvious after photocatalysis, confirming the effective adsorption of U by the synergistic treatment of Chlorella and Cu / Fe-NCP / g-C3N4. XPS analysis showed that the U4f peaks of the precipitated product were located at 381.85eV and 392.71eV, corresponding to U4f 7 / 2 and U4f 5 / 2 ( Figure 5 The binding energy position of uranium is consistent with that of U(VI), indicating that uranium exists primarily in its hexavalent state. Combining the precipitate color with the XPS data, it is speculated that the yellow-green precipitate is a mixture of two components: U(VI) adsorbed on the surface functional groups (such as phosphate groups) of the microalgae cells; and the photoelectrocatalytic conversion product, U(VI)Na2O (UO3·H2O). xThe formation mechanism involves the following: some algal cells rupture during the catalytic process, releasing intracellular adsorbed U(VI), which forms a precipitate under photoelectrocatalysis, while the U(VI) remaining in the unruptured cells remains in an adsorbed state.

[0095] In summary, the embodiment of the present invention uses a copper-iron bimetallic single-atom cluster catalyst derived from ZIF-8 as a framework and g-C3N4 to synthesize a Cu / Fe-NCP / g-C3N4 composite electrode material, which can be used for photoelectrocatalytic uranium removal. Among them, the Cu / Fe-NCP / g-C3N4 composite electrode material maintains a uranium removal rate of more than 90% in a wide pH range (5-8), and reaches the optimal performance at pH=6. At the same time, the composite electrode material exhibits a high efficiency uranium removal ability within the initial uranium concentration range of 10-150 mg / L. The uranium removal mechanism of the Cu / Fe-NCP / g-C3N4 composite electrode material mainly depends on the sites of the copper-iron diatoms, that is, the deposition and removal of uranium at the Cu-N4 and Fe-N4 sites. During the reaction, the electric field accelerates the migration of uranyl ions, UO2 2+ Migrate to the active site on the Cu / Fe-NCP / g-C3N4 composite electrode material, obtain an electron and be reduced to UO 2+ (U(V)). Unstable U(V) is reoxidized in the square wave cycle. + In the presence of U(VI), it is oxidized to U(VI) and forms Na2O(UO3·H2O)x precipitation. At the same time, the unstable U(V) loses electrons and re-oxidizes Fe 3+ 、Cu 2+ Reduction to Fe 2+ 、Cu + , the regenerated active sites subsequently bind to more uranyl ions. Photocatalysis also accelerates the migration of uranyl ions to the electrode. Some of the uranyl ions that reach the electrode surface are photocatalytically reduced to U(IV), while most are first reduced by the single-atom cluster catalyst and then oxidized to Na2O (UO3·H2O) for deposition and removal. Some of the U(IV) produced by photocatalysis also co-precipitates to the bottom of the electrolytic cell. In addition, the phosphate groups in the electrode enhance the affinity and selectivity of uranium. Due to the complexity of real water conditions, there is a gap between the application effect and the laboratory simulation effect. Using microalgae to pretreat real uranium-containing wastewater and then photoelectric synergistic catalysis can significantly improve the uranium removal rate. In addition, when extracting uranium from real spiked seawater, the uranium removal rate can also be significantly improved by adding an appropriate amount of sodium chloride electrolyte. Therefore, the above-mentioned regulatory measures can bridge the gap from laboratory simulation to real-world application and are the key to achieving engineering application of technology.

[0096] Based on the above-mentioned ideal embodiment of the present invention, and through the above description, relevant personnel can make various changes and modifications without departing from the scope of the technical concept of the present invention. The technical scope of the present invention is not limited to the contents of the specification.

Claims

1. A method for preparing a composite electrode material for photoelectrocatalytic uranium removal, characterized in that: The following steps are involved: The ZIF-8 material is added to a solvent, and copper salt and iron salt are added and mixed, and then the mixture is centrifuged to collect the obtained first metal composite material; The first metal composite material is dispersed in a solvent, and a KOH solution is added dropwise to react, and then centrifuged to collect the obtained second metal composite material; carbonizing the second metal composite material, then treating it with an acid, and washing and drying it to obtain a bimetallic atom catalytic material; Dispersing the bimetallic atom catalytic material and the g-C3N4 material in a mixed solution containing phytic acid and Nafion solution to obtain a catalyst ink; The catalyst ink is applied on a substrate and dried under light to obtain a composite electrode material.

2. The method for preparing a composite electrode material for photoelectrocatalytic uranium removal according to claim 1, characterized in that: The preparation method of the ZIF-8 material comprises the following steps: adding a zinc nitrate solution with a concentration of 80-120 mmol / L to a 2-methylimidazole solution with a concentration of 300-500 mmol / L to carry out a reaction to obtain the ZIF-8 material.

3. The method for preparing a composite electrode material for photoelectrocatalytic uranium removal according to claim 1, characterized in that: The solvent is methanol.

4. The method for preparing a composite electrode material for photoelectrocatalytic uranium removal according to claim 1, characterized in that: The copper salt is CuCl2·2H2O; the iron salt is FeCl3·6H2O; the mass ratio of the ZIF-8 material to the copper salt and the iron salt is 200:(7-10):(10-15).

5. The method for preparing a composite electrode material for photoelectrocatalytic uranium removal according to claim 1, characterized in that: The temperature of the carbonization treatment is 850-950° C.; the acid is 0.4-0.6 mol / L nitric acid solution; and the temperature of the acid treatment is 75-85° C.

6. The method for preparing a composite electrode material for photoelectrocatalytic uranium removal according to claim 1, characterized in that: The mass ratio of the bimetallic atom catalytic material to the g-C3N4 material is 1:(0.8-1.2).

7. A composite electrode material for photoelectrocatalytic uranium removal prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the composite electrode material according to claim 7 in photoelectrocatalytic uranium removal.

9. Use of the composite electrode material according to claim 7 in treating uranium-containing wastewater and / or extracting uranium from seawater.

10. The use according to claim 9, characterized in that The method for treating uranium-containing wastewater and / or extracting uranium from seawater comprises the following steps: Adjusting the pH value of uranium-containing wastewater and / or seawater, and adding electrolytes and / or performing microalgae pretreatment to obtain a liquid to be treated; The composite electrode material is used as a cathode and the graphite plate is used as an anode to perform photoelectrocatalysis on the liquid to be treated.

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