A photoelectrocatalytic system for denitrification of nitrogen-containing groundwater by cathode reduction coupled with anodic oxidation to produce hydrogen peroxide.

Abstract

This invention provides a photoelectrocatalytic system for denitrifying nitrogen-containing groundwater via cathodic reduction coupled with anodic oxidation to produce hydrogen peroxide. This system can be used for the reduction and denitrification of nitrogen-containing groundwater and the oxidation of water to produce hydrogen peroxide. The electrolyte solution in the cathode chamber is nitrogen-containing groundwater from agricultural areas in Northeast China, and the electrolyte in the anode chamber is a sodium sulfate solution. After 3 hours of photoelectrocatalytic treatment, the nitrate content in the groundwater is lower than the national drinking water standard, and the hydrogen peroxide concentration in the anode chamber solution meets the disinfection requirements for medical or household environments. This device features a small footprint, modular assembly, and easy automation control. Furthermore, the process offers advantages such as low cost, no pollution, and significant treatment effect, combining water pollution control with resource utilization. It is a novel treatment method suitable for household applications.

Description

Technical Field

[0001] This invention belongs to the field of water pollution synergistic control and resource regeneration technology. Specifically, it involves the preparation of Co-Cu2O / CFC electrodes and CuW-C3N4 / CFC electrodes, and a water treatment and resource utilization system for the simultaneous electrocatalytic cathodic reduction of nitrate nitrogen in groundwater and anodic oxidation of water to produce hydrogen peroxide. This system can efficiently remove nitrates from groundwater and produce hydrogen peroxide, providing important reference value for the integrated technology of photoelectrocatalytic treatment of nitrogen-containing groundwater and in-situ supply of functional chemicals. Background Technology

[0002] The accumulation of nitrate nitrogen in aquatic environments can seriously endanger human health. Long-term consumption of water containing NO3- nitrates can lead to serious health risks. - Polluted groundwater poses an extremely high risk of causing methemoglobinemia in humans, and also leads to the accumulation of NO3 in the body. - Under certain conditions, nitrates can transform into highly carcinogenic, teratogenic, and mutagenic nitrosamines, inducing serious diseases such as esophageal cancer, stomach cancer, intestinal cancer, and thyroid tumors. Industrially, physicochemical and biological methods are commonly used to remove nitrates from water. However, adsorption, ion exchange, membrane separation, and electrodialysis methods have a drawback: they cannot remove NO3-. - Completely eliminate, but rather reduce NO3 - The NO3 is transferred to another medium requiring secondary treatment, such as concentrate or regenerated solution. Biological methods, based on biological denitrification, are difficult to apply to groundwater with low C / N ratios for NO3-reducing without the addition of a carbon source. - The removal of NO3 from groundwater. Therefore, solving the problem of NO3 in groundwater... - Pollution has become an important task in environmental governance.

[0003] Hydrogen peroxide, due to its suitable oxidizing and bleaching properties and the absence of secondary pollution during use, is widely used in chemical synthesis, wastewater treatment, medical applications, metallurgy, and food processing. Currently, the main industrial production process for large-scale hydrogen peroxide production is the anthraquinone process. This process includes steps such as hydrogenation, oxidation, extraction, regeneration, purification, and concentration to obtain an aqueous hydrogen peroxide solution. This method is highly suitable for the large-scale production of high-concentration hydrogen peroxide. Although continuous optimization and improvement of the process have led to its increasing maturity, several serious sustainability challenges remain. These include the need for large-scale plants, high energy consumption, organic waste pollution, and the urgent need to address the safe storage and transportation of high-concentration hydrogen peroxide. Considering these issues, a greener, more economical, and environmentally friendly solution is needed for the flexible, small-scale on-site production of hydrogen peroxide.

[0004] Photoelectrochemical electrocatalysis (PEC) can convert solar energy into chemical energy that can be stably accumulated over a long period, and is considered one of the promising options for solving global energy and environmental problems. PEC combines the advantages of photocatalysis and electrocatalysis, achieving higher solar energy conversion efficiency than photocatalysis while significantly reducing electricity consumption compared to electrocatalysis, making it more sustainable in terms of energy consumption. The production of H2O2 via PEC mainly involves three processes: light absorption, charge separation, and surface reaction. When the semiconductor photoanode absorbs appropriate light energy, electrons are excited from the valence band to the conduction band, leaving holes in the valence band. These photogenerated electrons are transferred to the counter electrode, reducing water to hydrogen. Then, under conditions where the valence band redox potential is greater than that of H2O / H2O2, the photogenerated holes are transferred by an electric field to the semiconductor / electrolyte interface, undergoing a 2e-WOR reaction to generate hydrogen peroxide. Therefore, by simultaneously producing H2 and high-value-added hydrogen peroxide chemicals, the conversion and accumulation efficiency of solar energy can be improved, enhancing related economic benefits. Photoelectrocatalytic reduction of nitrates requires no chemical reagents, directly utilizing electrons generated by the electric field on the electrode surface as electron donors for nitrate reduction. This avoids secondary pollution and reprocessing costs. The electrochemical reduction reaction of nitrates exhibits high efficiency, rapid reaction rate, and controllable products. By optimizing electrode materials, reactors, and operating parameters, nitrogen generation and other recoverable products can be effectively controlled. The process is electrically driven, and this energy can be provided by renewable energy sources such as solar and wind power. The electrochemical reactor has a small footprint, can be modularly assembled, and is easily automated, already achieving large-scale application in advanced wastewater treatment. Therefore, photoelectrocatalytic removal of nitrates from water and the production of hydrogen peroxide from water resources is a feasible and promising technology. Summary of the Invention

[0005] The purpose of this invention is to combine anodizing and cathodic reduction in a photoelectrocatalytic water treatment system, successfully constructing a modular cathode for high-efficiency treatment of nitrogen-containing groundwater for denitrification, while simultaneously producing hydrogen peroxide through anodizing. A sequencing batch reactor (SBR) is used to supply the anode and cathode solutions; the anode is a sodium sulfate solution, and the cathode is actual nitrate-containing groundwater. By utilizing solar and electrical energy, coupled with the photoelectric response and catalytic capabilities of the anode and cathode catalysts, highly efficient treatment of nitrogen-containing groundwater is achieved.

[0006] The technical solution of this invention:

[0007] A photoelectrocatalytic system for denitrification of nitrogen-containing groundwater via cathodic reduction coupled with anodic oxidation to produce hydrogen peroxide is disclosed. The photoelectrocatalytic system includes an electrode chamber, electrodes, a membrane, an electrolyte solution, an external circuit, a visible light source, and auxiliary components. The electrode chamber includes an anode chamber 9 and a cathode chamber 4, which are separated by a membrane. The electrolyte solution in the anode chamber 9 and cathode chamber 4 is introduced and discharged in a top-in, bottom-out sequential batch processing mode. The external circuit includes wires and a DC power supply 1. The wires are used to connect the anode electrode 10 and the cathode electrode 5. The DC power supply 1 is located between the anode electrode 10 and the cathode electrode 5. A visible light source 7 is added above the electrodes, thus constituting the photoelectrocatalytic system.

[0008] The anode catalyst is a CuW-C3N4 composite catalyst, and the cathode catalyst is a Co-Cu2O composite catalyst.

[0009] Furthermore, in a photoelectrocatalytic system for denitrification of nitrogen-containing groundwater by cathodic reduction coupled with anodic oxidation of water to produce hydrogen peroxide, the inlet water to the anode chamber 9 and the cathode chamber 4 is added to the electrolyte solution through a sampling port sealed with a rubber stopper above the electrode chamber, and the outlet water to the anode chamber 9 and the cathode chamber 4 is discharged to the electrolyte solution through an outlet connected to a rubber tube below the electrode chamber.

[0010] Furthermore, the electrolyte solution in the anode chamber 9 is a sodium sulfate solution.

[0011] Furthermore, the diaphragm is a cation exchange membrane 11; the auxiliary components include silicone gaskets and stud nuts for sealing.

[0012] Furthermore, the electrolyte solution in the cathode chamber 4 is an aqueous solution containing nitrate ions from underground water.

[0013] Furthermore, the CuW-C3N4 / CFC electrode is prepared by a method of first high-temperature calcination followed by sol-gel coating; the Co-Cu2O / CFC electrode is prepared by a method of first impregnation growth followed by high-temperature calcination.

[0014] Furthermore, the preparation method of the CuW-C3N4 / CFC electrode is as follows:

[0015] Step (1) W-C3N4 synthesis: Dissolve urea and tungstic acid in deionized water and mix well, then dry in an oven; then transfer to a muffle furnace for calcination to obtain W-C3N4 catalyst;

[0016] Step (2) CuW-C3N4 / CFC electrode preparation: Basic copper carbonate and W-C3N4 catalyst are mixed and added to silica sol solution to obtain coating solution. The coating solution is then brushed onto both sides of carbon fiber cloth to obtain CuW-C3N4 / CFC electrode.

[0017] Furthermore, in step (1), the molar ratio of urea to tungstic acid is 1:0.01 to 0.1; the drying temperature is 50 to 80°C, and the drying time is 4 to 8 hours; the calcination heating rate is 1 to 10°C / min; the calcination temperature is 500 to 600°C; and the calcination time is 2 to 4 hours. In step (2), the mass ratio of basic copper carbonate to W-C3N4 catalyst is 1:0.5 to 2; the mass content of silica sol solution is 10 to 30%; and the mass content of basic copper carbonate in silica sol solution is 25% to 75%.

[0018] Furthermore, the preparation method of the Co-Cu2O / CFC electrode is as follows:

[0019] Copper sulfate pentahydrate was dissolved in deionized water to form solution A; sodium hydroxide was dissolved in deionized water to form solution B; solution B was then slowly poured into solution A while stirring to obtain a catalyst precursor mixture solution, which was then sonicated; the support was immersed in the precursor mixture solution, removed and dried in an oven, then a cobalt salt solution was added dropwise, and then dried in an oven again; the dried electrode was placed in a tube furnace and calcined under an inert atmosphere, and then cooled naturally to obtain a Co-Cu2O / CFC electrode.

[0020] Furthermore, the concentration of solution A is 1–2 mol / L; the concentration of solution B is 2–5 mol / L; the molar ratio of copper sulfate pentahydrate to sodium hydroxide is 1:2–3; the carrier is carbon fiber cloth, activated carbon, or carbon felt; the impregnation time is 10–30 min; the oven drying temperature is 50–80 °C; the drying time is 4–8 h; the cobalt salt is cobalt chloride, cobalt bromide, cobalt iodide, cobalt carbonate, or cobalt sulfate; the concentration is 0.1–0.5 mol / L; the mass ratio of the carrier to the cobalt salt-containing solution is 1:2–8; the calcination heating rate is 1–10 °C / min; the calcination temperature is 400–600 °C; and the calcination time is 2–4 h.

[0021] The beneficial effects of this invention: This invention provides a modular cathode for high-efficiency treatment of nitrogen-containing groundwater for denitrification, while simultaneously producing hydrogen peroxide through anodic oxidation. It innovatively couples anodic oxidation, cathode reduction, and photoelectrocatalysis, achieving a nitrate removal rate of 90.5%, a nitrogen selectivity of 81.5%, a Faraday efficiency of 91.9%, and a hydrogen peroxide yield of 0.32 mol / (L·h) per gram of catalyst. After 3 hours of photoelectrocatalytic treatment, the nitrate content in the groundwater meets the national drinking water standard (NO3). -The hydrogen peroxide solution has a concentration of -N≤10mg / L, reaching the concentration of disinfectant in medical or household environments (≥0.89mol / L). Furthermore, the device has a small footprint, can be modularly assembled, and is easy to automate. Therefore, this treatment system has broad and feasible application prospects in the removal of nitrates from groundwater and the production of hydrogen peroxide from water resources. Attached image description:

[0022] Figure 1 This is a schematic diagram of a modular cathode reduction anodic oxidation photoelectrocatalytic device according to the present invention.

[0023] Figure 1 In the middle: 1 DC power supply; 2 external circuit; 3 cathode chamber rubber stopper; 4 cathode chamber; 5 cathode electrode; 6 cathode chamber valve; 7 visible light source; 8 anode chamber rubber stopper; 9 anode chamber; 10 anode electrode; 11 cation exchange membrane; 12 anode chamber valve.

[0024] Figure 2 The figures shown are experimental results of different cathode and anode electrodes in Example 4. (a) is a graph showing the change in nitrate concentration of different cathode electrodes, (b) is a graph showing the change in nitrogen production of different cathode electrodes, with the cathodes being Co-Cu2O / CFC electrodes with different cobalt contents; and (c) is a graph showing the change in hydrogen peroxide production of different anodes, with the anodes being CuW-C3N4 / CFC electrodes with different tungsten contents.

[0025] Figure 3 The following are experimental results from Example 5: (a) shows the change in cathode nitrate concentration, (b) shows the change in cathode nitrogen production, and (c) shows the cathode nitrate removal rate, nitrogen selectivity, and Faraday efficiency. The cathode is a Co-Cu2O / CFC electrode with a cobalt content of 0.25 mmol.

[0026] Figure 4 The following is an experimental result diagram of Example 6, in which (a) is the yield of hydrogen peroxide produced by anodic water oxidation, and (b) is the anodic hydrogen peroxide yield. The anode is a CuW-C3N4 / CFC electrode with a tungsten content of 0.02 mol. Detailed Implementation

[0027] The following description, in conjunction with the technical solutions and accompanying drawings, further illustrates specific embodiments of the present invention, but is not intended to limit the scope of protection of the present invention.

[0028] like Figure 1 As shown, this invention provides a modular cathode for efficient denitrification of nitrogen-containing groundwater, while simultaneously producing hydrogen peroxide through anodic oxidation. This coupled system has the following modular features, and its treatment design comprises:

[0029] The DC power supply 1 is connected to the catalytic electrode through the external circuit 2, providing variable external voltage and current for the photoelectrocatalytic system; the visible light source 7 provides the light energy required for photocatalysis to the electrode.

[0030] Both the cathode chamber rubber stopper 3 and the anode chamber rubber stopper 8 are used to isolate air. The cathode chamber rubber stopper 3 prevents oxygen in the air from affecting the reduction of nitrate ions, while the anode chamber rubber stopper 8 prevents the hydrogen peroxide generated at the anode from volatilizing and decomposing.

[0031] The cathode chamber 4 is used to hold the cathode electrolyte and the cathode electrode 5, and the anode chamber 9 is used to hold the anode electrolyte and the anode electrode 10, which are separated by a cation exchange membrane 11.

[0032] The cathode electrolyte is nitrogen-containing groundwater, which flows into the cathode chamber 4 through the opening under the rubber stopper 3; the anode electrolyte is a 0.5 mol / L sodium sulfate solution, which flows into the anode chamber 9 through the opening under the rubber stopper 8.

[0033] Below the cathode chamber 4 and the anode chamber 9 are two drainage valves, cathode chamber valve 6 and anode chamber valve 12, which are used to collect the treated groundwater solution and hydrogen peroxide solution, respectively.

[0034] Preparation of anode: Weigh out a certain mass of basic copper carbonate and W-C3N4 catalyst respectively, add silica sol solution dropwise in a certain proportion, and coat them on both sides of carbon fiber cloth respectively.

[0035] Cathode preparation: A precursor solution of Co-Cu2O catalyst is prepared according to a certain ratio, and carbon fiber cloth is immersed in the solution for a specific time and then dried and calcined.

[0036] Example 1

[0037] Combination Figure 1 First, place the cation exchange membrane 11 between the anode chamber 9 and the cathode chamber 4, then place the anode electrode 5 in the anode chamber 9 and the cathode electrode 10 in the cathode chamber 4, and then test the sealing of the device.

[0038] The anolyte flows into the anode chamber 9 from below the anode rubber plug, and the cathode electrolyte flows into the anode chamber 9 from below the anode rubber plug, and then the rubber plug is tightened.

[0039] Connect the external circuit 3 to the two electrodes with rubber plugs, ensuring that the connection does not come into contact with the electrolyte solution. Then connect the other end of the external circuit 3 to the DC power supply 1. Connect the anode electrode 5 to the positive terminal of the DC power supply 1 and the cathode electrode 10 to the negative terminal of the DC power supply 1.

[0040] Keep the visible light source 7 off, set the DC power supply 1 to 3 volts, take a sample from the rubber stopper every hour to test the electrocatalytic effect, and electrolyze for a total of 3 hours. After electrolysis, open the anode chamber valve 6 to collect the hydrogen peroxide solution and open the cathode chamber valve 12 to collect the groundwater solution.

[0041] Keep the visible light source 7 on, set the DC power supply 1 to 3 volts, take a sample from the rubber stopper every hour to test the electrocatalytic effect, and electrolyze for a total of 3 hours. After electrolysis, open the anode chamber valve 6 to collect the hydrogen peroxide solution and open the cathode chamber valve 12 to collect the groundwater solution.

[0042] Example 2

[0043] CuW-C3N4 / CFC electrodes were prepared as anode electrodes by first calcining at high temperature and then coating with sol.

[0044] Preparation of basic copper carbonate: Prepare 100 mL each of 0.5 mol / L CuSO4 solution and 0.5 mol / L Na2CO3 solution. Under a 65°C water bath heating condition, slowly pour the sodium carbonate solution into the copper sulfate solution while stirring. A blue-green precipitate is observed to form. Continue stirring for 15 minutes to ensure the reaction is complete. Filter using a Buchner funnel and collect the precipitate. Wash the precipitate several times with distilled water, then dry it in a 65°C oven for 6 hours to obtain blue-green basic copper carbonate powder.

[0045] Synthesis of W-C3N4: 0.5 mol of urea and 0.02 mol of tungstic acid were dissolved in a beaker containing 100 ml of deionized water and stirred until homogeneous. The mixture was then dried in an oven at 65 °C for 6 h. The dried mixture was then transferred to a muffle furnace and calcined at 550 °C for 3 h at a heating rate of 5 °C / min to obtain W-C3N4.

[0046] Preparation of CuW-C3N4 / CFC electrode: 0.5 g of basic copper carbonate and W-C3N4 mixed catalyst were weighed in a 1:1 mass ratio. The mixture was then thoroughly mixed with a 15% silica sol solution at a 1:1 mass ratio and coated onto both sides of carbon fiber cloth to obtain the CuW-C3N4 / CFC electrode. The mass content of basic copper carbonate in the silica sol solution was 50%.

[0047] Co-Cu2O / CFC electrodes were prepared as cathode electrodes by first impregnating and growing the material and then calcining it at high temperature.

[0048] Preparation of Co-Cu2O / CFC electrode: 0.04 mol copper sulfate pentahydrate was dissolved in 25 ml of deionized water to form solution A. 0.1 mol sodium hydroxide was dissolved in 25 ml of deionized water to form solution B. Solution B was then slowly poured into solution A while stirring to obtain a mixed solution of catalyst precursors. The mixed solution was then sonicated for 15 minutes. 0.5 g of carbon fiber cloth was immersed in the mixed solution for 20 minutes, dried in an oven at 65°C for 6 hours, and then 1 ml of 0.25 mol / L cobalt chloride solution was added. The electrode was then dried in an oven at 65°C for 6 hours. The dried electrode was placed in a programmable tube furnace and calcined under a nitrogen atmosphere at a heating rate of 5°C / min. After reaching 500°C, the electrode was calcined for 3 hours and then allowed to cool naturally to obtain the Co-Cu2O / CFC electrode.

[0049] Example 3

[0050] The preparation method is the same as in Example 2, except that the 0.02 mol tungstic acid is replaced with 0 mol, 0.01 mol, 0.03 mol, and 0.04 mol to prepare CuW-C3N4 / CFC electrodes with different tungsten contents; and the 1 ml of 0.25 mol / L cobalt chloride solution is replaced with 0 ml, 2 ml, 3 ml, and 4 ml to prepare Co-Cu2O / CFC electrodes with different cobalt contents. The example with 0 mol tungstic acid and 0 ml cobalt chloride solution serves as a comparative example.

[0051] Example 4

[0052] Combination Figure 1 ,use Figure 1 The photoelectrocatalytic device in this study reduced nitrates in groundwater at the cathode while simultaneously producing hydrogen peroxide at the anode. The cathodes were Co-Cu₂O / CFC electrodes with varying cobalt contents, and the anodes were CuW-C₃N₄ / CFC electrodes with varying tungsten contents. The reaction process lasted 3 hours, with samples taken every hour to measure the nitrate concentration at different cathode electrodes. Figure 2 (a) in the figure; nitrogen production at different cathode electrodes, such as Figure 2 (b) in the figure; hydrogen peroxide production at different anode electrodes, such as Figure 2 (c) in the middle.

[0053] Example 5

[0054] Combination Figure 1 ,use Figure 1 The photoelectrocatalytic device in the study reduced nitrates in groundwater to nitrogen gas. The cathode was a Co-Cu₂O / CFC electrode with a cobalt content of 0.25 mmol. The reaction system was processed for 3 hours, and samples were taken every hour to detect changes in nitrate concentration at the cathode. Figure 3 (a) in the figure; changes in nitrogen production at the cathode, such as Figure 3(b) in the text; nitrate removal rate, nitrogen selectivity, and Faraday efficiency of the cathode, such as Figure 3 (c) in the middle.

[0055] Example 6

[0056] Combination Figure 1 ,use Figure 1 The photoelectrocatalytic device in the experiment oxidizes water to produce hydrogen peroxide. The anode is a CuW-C3N4 / CFC electrode with a tungsten content of 0.02 mol. The reaction time is 3 hours, and samples are taken every hour to detect the hydrogen peroxide yield at the anode. Figure 4 (a) in the figure; hydrogen peroxide yield at the anode, such as Figure 4 (b) in the middle.

Claims

1. A photoelectrocatalytic system for the reduction of nitrogen in groundwater by cathode and the production of hydrogen peroxide by anode oxidation, characterized in that: the photoelectrocatalytic system comprises an electrode chamber, electrodes, a diaphragm, an electrolyte solution, an external circuit, a visible light source and auxiliary components; the electrode chamber comprises an anode chamber (9) and a cathode chamber (4), which are separated by a diaphragm; the electrolyte solution in the anode chamber (9) and the cathode chamber (4) is added from the top and discharged from the bottom in a sequential batch mode; the external circuit comprises wires and a direct current power supply (1); the wires are used to connect the anode electrode (10) and the cathode electrode (5), and the direct current power supply (1) is arranged between the anode electrode (10) and the cathode electrode (5); a visible light source (7) is arranged above the electrodes to form a photoelectrocatalytic system; the anode electrode (10) is a CuW-C3N4 / CFC electrode, wherein the anode catalytic material is a CuW-C3N4 composite catalyst, and the cathode electrode (5) is a Co-Cu2O / CFC electrode, wherein the cathode catalytic material is a Co-Cu2O composite catalyst, and CFC is carbon fiber cloth. The water in the anode chamber (9) and the cathode chamber (4) is added through a sampling port reserved above the electrode chamber and sealed by a rubber plug, and the electrolyte solution is discharged through a water outlet reserved below the electrode chamber and connected by a rubber tube.

2. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 1, characterized in that, The electrolyte solution in the anode chamber (9) is a sodium sulfate solution.

3. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater by cathode reduction coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 1, characterized in that, The diaphragm is a cation exchange membrane (11); the auxiliary components include silica gel gaskets and studs and nuts for sealing.

4. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater by cathode reduction coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 1, characterized in that, The electrolyte solution in the cathode chamber (4) is a groundwater solution containing nitrate ions.

5. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 1, characterized in that, The CuW-C3N4 / CFC electrode is prepared by high-temperature calcination followed by sol coating; and the Co-Cu2O / CFC electrode is prepared by first immersing and growing and then high-temperature calcination.

6. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater by cathode reduction coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 1, characterized in that, The preparation method of the CuW-C3N4 / CFC electrode is as follows:

7. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 6, characterized in that, Step (1) synthesis of W-C3N4: dissolve urea and tungstic acid in deionized water, mix uniformly, and dry in an oven; then transfer to a muffle furnace for calcination to obtain a W-C3N4 catalyst; Step (2) preparation of CuW-C3N4 / CFC electrode: mix basic copper carbonate and W-C3N4 catalyst, and add to a silica sol solution to obtain a coating liquid, and brush the coating liquid on both sides of the carbon fiber cloth to obtain a CuW-C3N4 / CFC electrode. In step (1), the molar ratio of urea to tungstic acid is 1:0.01-0.1; the drying temperature is 50-80℃, and the drying time is 4-8h; the calcination temperature is 500-600℃, and the calcination time is 2-4h; in step (2), the mass ratio of basic copper carbonate to W-C3N4 catalyst is 1:0.5-2; the mass content of the silica sol solution is 10-30%; and the mass content of basic copper carbonate in the silica sol solution is 25%-75%.

8. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 7, characterized in that, The preparation method of the Co-Cu2O / CFC electrode is as follows:

9. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 6, characterized in that, ​ Dissolve copper sulfate pentahydrate in deionized water to form solution A; dissolve sodium hydroxide in deionized water to form solution B; then slowly pour solution B into solution A under stirring to obtain a catalyst precursor mixed solution, and then ultrasonic the catalyst precursor mixed solution; put the carrier into the precursor mixed solution for impregnation, take out and dry in an oven, then drop a solution containing cobalt salt, and then dry in an oven again; place the dried electrode in a tube furnace for calcination under an inert atmosphere, then naturally cool down to obtain a Co-Cu2O / CFC electrode.

10. The photoelectrocatalytic system for denitrification of nitrogen-containing groundwater coupled with anodic oxidation of water to produce hydrogen peroxide according to claim 9, characterized in that, The concentration of solution A is 1-2 mol / L; the concentration of solution B is 2-5 mol / L; the molar ratio of copper sulfate pentahydrate to sodium hydroxide is 1:2-3; the carrier is carbon fiber cloth, activated carbon, or carbon felt; the impregnation time is 10-30 min; the oven drying temperature is 50-80℃; the drying time is 4-8 h; the cobalt salt is cobalt chloride, cobalt bromide, cobalt iodide, cobalt carbonate, or cobalt sulfate; the concentration is 0.1-0.5 mol / L; the mass ratio of the carrier to the solution containing cobalt salt is 1:2-8; the calcination temperature is 400-600℃; and the calcination time is 2-4 h.

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