Method for degrading ammonia nitrogen in wastewater and application

Abstract

The application relates to a method for degrading ammonia nitrogen in wastewater and application, and belongs to the technical field of electrochemical water treatment. The electrode is prepared through a simple hydrothermal synthesis and calcination process. Co(NO3)3.6H2O and Cu(CH3COO)2 are dissolved in deionized water, mixed with a sodium citrate solution, and then subjected to a hydrothermal reaction. Subsequently, the CuCo2O4 is converted through washing, drying and calcination. By adjusting the amount of Co(NO3)3.6H2O and Cu(CH3COO)2, CuCo2O4 samples with different compositions can be prepared. The CuCo2O4 electrode of the application exhibits excellent ammonia nitrogen oxidation performance in the activation of persulfate (PMS), has a high ammonia nitrogen removal rate and nitrogen selectivity. The preparation method is simple, the cost is low, the raw materials are easy to obtain, and the electrode is suitable for large-scale production and application. In addition, the electrode exhibits good reusability in electrochemical treatment of wastewater containing ammonia nitrogen, and provides a new way for efficient, economical and environmentally-friendly wastewater treatment.

Description

Technical Field

[0001] The invention relates to the field of electrochemical water treatment technology, specifically to a method and application for degrading ammonia nitrogen in wastewater. Background Technology

[0002] The discharge of high-concentration ammonia nitrogen industrial wastewater is one of the main causes of eutrophication in water bodies. This type of wastewater exhibits significant pH variations, but mostly falls within the range of 9-13. Ammonia nitrogen exists in wastewater in the forms of free ammonia (NH3) and ionic ammonium (NH4⁺). When the pH is above 9.25, ammonia nitrogen primarily exists in the form of free ammonia, which is dozens of times more biotoxic than ionic ammonia. Ammonia nitrogen pollution remains a serious global problem. Its negative environmental impacts, large-scale production, and widespread use as fertilizer make the treatment of ammonia-containing wastewater a crucial issue for environmental protection. Excessive ammonia in water bodies severely threatens ecosystem quality, leading to water toxicity and eutrophication. Therefore, the removal of NH4⁺-N from wastewater is of great significance.

[0003] Various existing methods for removing ammonia nitrogen, including microbial processes, physical processes (membrane separation, ion exchange, physical adsorption, air stripping), and chemical processes (breakpoint chlorination, advanced oxidation technologies, etc.), have been applied to ammonia removal. However, each method has its advantages and disadvantages under specific conditions. Biological methods, such as nitrification-denitrification and anaerobic ammonium oxidation, utilize microorganisms to convert ammonia nitrogen into nitrogen gas. Nitrification-denitrification can significantly remove ammonia nitrogen, but the operating conditions are relatively harsh, and a large amount of chemicals are generated during the treatment process. Anaerobic ammonium oxidation can reduce sludge production, but the technology is not yet mature. In addition, traditional biological treatment methods have poor tolerance to high concentrations of ammonia nitrogen in industrial wastewater; high ammonia nitrogen concentrations, high pH, ​​and toxic pollutants can all affect the activity of microorganisms and reduce reaction efficiency. Among physical methods, air stripping removes ammonia nitrogen by converting ammonia in wastewater from the liquid phase to the gas phase, but it is energy-intensive and less efficient at low temperatures. Membrane separation technology is easy to operate and produces no secondary pollution, but it has high investment costs and strict water quality requirements. In chemical methods, breakpoint chlorination oxidizes ammonia nitrogen into nitrogen gas by adding excess chlorine or sodium hypochlorite. This method is highly efficient and unaffected by water temperature, but has high operating costs, and byproducts may cause secondary pollution. Ion exchange methods utilize ion exchange resins to remove ammonia nitrogen, but require large resin volumes, are difficult to regenerate, and have high operating costs. Therefore, there is an urgent need to explore feasible processes for removing ammonia from wastewater, ideally converting NH4⁺-N into harmless N2. Advanced oxidation processes (AOPs) have developed rapidly in recent years and have received widespread attention. Active substances generated in AOPs, such as hydroxyl radicals (•OH), play a dominant role in pollutant degradation. Notably, under strongly alkaline conditions, NH4⁺-N is converted into free ammonia (NH3-N). Converting ammonia nitrogen into gaseous nitrogen (N2) rather than NO3⁻ and NO2⁻ is an ideal water purification objective. However, there is limited research on the high-efficiency ammonia oxidation and high N2 conversion selectivity of the sulfate radical-based AOP / OH process. Therefore, there is an urgent need to explore feasible processes for removing ammonia from wastewater. Summary of the Invention

[0004] To address the aforementioned issues, this study developed a CuCo2O4 / PMS / OH system for degrading ammonia nitrogen in water. This method utilizes a low-cost CuCo2O4 electrode as the cathode and employs electrocatalysis to effectively oxidize and decompose over 90% of ammonia nitrogen in water. The specific mechanism is as follows: Cu⁺ and Co²⁺ on the CuCo2O4 surface activate persulfate (PMS) through electron transfer, generating hydroxyl radicals (•OH) and sulfate radicals (SO₄²⁻). •⁻ Simultaneously, it self-oxidizes to Cu²⁺ and Co³⁺; the higher oxidation states of Cu²⁺ / Co³⁺ further activate PMS to generate persulfate radicals (SO₅). •⁻The PMS is then reduced back to Cu⁺ / Co²⁺, forming a dynamic redox cycle. Based on the potential difference between Co³⁺ / Co²⁺ and Cu²⁺ / Cu⁺, Co²⁺ can drive Cu²⁺ reduction through electron transfer, promoting the regeneration of active sites until the PMS is completely consumed. The generated free radicals (SO₄²⁻) •⁻ The ammonia nitrogen is gradually oxidized and removed using the hydroxyl group (OH) radical, ultimately converting the vast majority into nitrogen gas. This method is low-cost, easy to recover, and highly efficient, providing a promising technology for the treatment and selective oxidation of ammonia in alkaline ammonia-containing wastewater.

[0005] The technical solution adopted in this invention is as follows:

[0006] Using a CuCo₂O₄ electrode as the cathode and a platinum electrode as the anode, ammonia nitrogen in water was degraded via electrocatalysis. The electrode spacing between the CuCo₂O₄ cathode and the platinum anode was 4 cm, the operating voltage for the electrocatalytic reaction was 2.8 V, and the pH of the electrolyte was 12.

[0007] The preparation method of CuCo2O4 electrode specifically includes the following steps:

[0008] S1: Weigh 3.27 g Co(NO3)3·6H2O and 1.459 g Cu(CH3COO)2, dissolve them in 50 mL of deionized water to form solution A;

[0009] S2: Weigh 2.31 g of sodium citrate and dissolve it in 30 mL of deionized water. Adjust the pH to 10 with 1 M NaOH solution to form solution B.

[0010] S3: Under constant temperature stirring at 40℃, solution A is slowly added to solution B to form a homogeneous mixed solution;

[0011] S4: Transfer the mixed solution to a polytetrafluoroethylene-lined reactor and hydrothermally treat it at 100°C for 24 hours.

[0012] S5: The precipitate obtained was purified by centrifugation, washed alternately with alcohol and water, and then dried at 70°C for 12 hours.

[0013] S6: The dried product was calcined in air at 350°C for 2 hours at a rate of 5 °C / min to obtain a CuCo2O4 electrode.

[0014] Furthermore, in step S2, pH adjustment is performed by adding NaOH solution dropwise to maintain the homogeneity of the solution system.

[0015] Furthermore, in step S5, the washing process adopts centrifugal separation, with a centrifugal speed of 8000 rpm and each washing lasts for 5 minutes.

[0016] Furthermore, the preparation methods for different samples in step S6 include: when 1.64 g Co(NO3)3·6H2O and 1.463 g Cu(CH3COO)2 are weighed, they are labeled as CuCo2O4-2; when 3.27 g Co(NO3)3·6H2O and 0.729 g Cu(CH3COO)2 are weighed, they are labeled as CuCo2O4-3.

[0017] Furthermore, the calcination process in step S6 is carried out in a tube furnace with an air flow rate controlled at 50 mL / min.

[0018] Furthermore, in step S6, the calcination temperature is 350°C and the time is 2 hours.

[0019] Furthermore, in step S6, the calcination process is carried out in a tube furnace, and the air flow rate is controlled at 50 mL / min.

[0020] The present invention also provides a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, prepared by the above method.

[0021] The present invention also provides an application of the above-mentioned CuCo2O4 electrode in the electrocatalytic oxidation of ammonia nitrogen.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] CuCo2O4 electrodes offer significant advantages in the cathodic electrocatalytic oxidation of ammonia nitrogen in wastewater. The high binding energy of copper and cobalt metal surfaces to PMS allows for rapid PMS reduction, generating a large number of sulfate radicals (SO4⁻·), which in turn produce hydroxyl radicals (·OH). These radicals possess extremely strong oxidizing power, rapidly oxidizing ammonia nitrogen to nitrogen gas. Furthermore, the unique nanosheet structure of CuCo2O4 electrodes significantly increases the electrode's specific surface area, providing more active sites for ammonia nitrogen adsorption and promoting rapid nitrogen release. This avoids the accumulation of products on the electrode surface, which could negatively impact the reaction. The CuCo2O4 electrode exhibits high nitrogen selectivity during ammonia nitrogen oxidation, meaning that ammonia nitrogen can be converted into nitrogen gas more efficiently than other byproducts, thus improving ammonia nitrogen removal efficiency. Compared with traditional noble metal oxide electrodes, the main components of the CuCo2O4 electrode, copper and cobalt, are abundant and inexpensive. This low cost and easy recycling make it a promising candidate for large-scale wastewater treatment. The CuCo2O4 electrode incorporates abundant oxygen vacancies during its preparation, which significantly improves the electrode's electrochemical performance, resulting in higher specific capacitance and better charge transfer capability. Attached Figure Description

[0024] Figure 1The image shows the XRD characterization of the CuCo2O4 material of this invention.

[0025] Figure 2 This is a SEM image of the CuCo2O4-1 material of the present invention.

[0026] Figure 3 This is a TEM image of the CuCo2O4-1 material of the present invention.

[0027] Figure 4 The effect of different materials on NH4 over time is the subject of this invention. + The effect of -N removal rate;

[0028] Figure 5 The effect of different pH values ​​on NH4 over time is the subject of this invention. + The effect of -N removal rate;

[0029] Figure 6 The effect of different PMS contents over time on NH4 in this invention + The effect of -N removal rate.

[0030] Figure 7 The effect of different voltages over time on NH4 according to the present invention + The effect of -N removal rate.

[0031] Figure 8 The effect of different initial ammonia nitrogen concentrations on NH4 over time is described in this invention. + The effect of -N removal rate. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0033] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under standard conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications in the art, unless otherwise stated. Example

[0034] This embodiment provides a method for preparing a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps:

[0035] First, accurately weigh 3.27 g of Co(NO3)3·6H2O and 1.459 g of Cu(CH3COO)2, and dissolve them in 50 mL of deionized water to form solution A. Weigh 2.31 g of sodium citrate, dissolve it in 30 mL of deionized water, and adjust the pH to 10 with 1 M NaOH solution to form solution B. Under constant temperature and stirring conditions at 40℃, slowly add solution A to solution B to form a homogeneous mixture. Transfer this mixture to a polytetrafluoroethylene-lined reactor and place it in a 100℃ oven for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, and dry it at 70℃ for 12 h. Place the dried product in a tube furnace and calcine it in air at 350℃ for 2 hours (heating rate of 5℃ / min) to convert it into CuCo2O4, labeled as: CuCo2O4-1. Example

[0036] This embodiment provides a method for preparing a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps:

[0037] Weigh 1.64 g Co(NO3)3·6H2O and 1.463 g Cu(CH3COO)2, dissolve them in 50 mL of deionized water to form solution A. Weigh 2.31 g sodium citrate, dissolve it in 30 mL of deionized water, and adjust the pH to 10 with 1 M NaOH solution to form solution B. Under constant temperature and stirring conditions at 40℃, slowly add solution A to solution B to form a homogeneous mixture. Transfer the mixture to a polytetrafluoroethylene-lined reactor and place it in a 100℃ oven for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, dry it at 70℃ for 12 h, and place the dried product in a tube furnace and calcine it in air at 350℃ for 2 hours (heating rate of 5℃ / min) to convert it into CuCo2O4, labeled as: CuCo2O4-2. Example

[0038] This embodiment provides a method for preparing a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps:

[0039] Weigh 3.27 g Co(NO3)3·6H2O and 0.729 g Cu(CH3COO)2, dissolve them in 50 mL of deionized water to form solution A. Weigh 2.31 g sodium citrate, dissolve it in 30 mL of deionized water, and adjust the pH to 10 with 1 M NaOH solution to form solution B. Under constant temperature and stirring conditions at 40℃, slowly add solution A to solution B to form a homogeneous mixture. Transfer the mixture to a polytetrafluoroethylene-lined reactor and place it in a 100℃ oven for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, dry it at 70℃ for 12 h, and place the dried product in a tube furnace and calcine it in air at 350℃ for 2 hours (heating rate of 5℃ / min) to convert it into CuCo2O4, labeled as: CuCo2O4-3.

[0040] XRD analysis was used to analyze the phase composition and crystal structure of CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 materials, such as... Figure 1 As shown. The diffraction peaks at 31.1°, 36.6°, 44.5°, 59.0°, and 64.8° of the three samples correspond to the (220), (311), (400), (333), and (440) crystal planes of spinel-type CuCo2O4 (JCPDS: 37-0878), respectively, indicating that the three samples have the same phase. The main diffraction peak of the (311) crystal plane of CuCo2O4-1 is wider, indicating that its primary grain size is smaller, which helps to provide more surface sites and higher catalytic performance. SEM and TEM images of CuCo2O4-1 material are shown below. Figure 2 and 3 As shown in the image, the CuCo2O4-1 material consists of a porous, sheet-like structure. These nanosheets significantly increase the specific surface area of ​​the electrode, providing better connectivity and active sites. They offer more channels and shorten the distance for ion and electron transport, thus accelerating the electrocatalytic reaction process. The adsorption of ammonia nitrogen at these active sites facilitates the rapid release of nitrogen gas.

[0041] In this embodiment, the preparation of solutions A and B requires precise control of reagent dosage and dissolution conditions to ensure the homogeneity and completeness of the reaction. The hydrothermal reaction is a crucial step in the formation of the CuCo₂O₄ precursor; precise control of temperature and time has a decisive impact on the crystallinity and morphology of the product. The washing process helps remove impurities that may be generated during the reaction, thereby improving the purity of the final product. The drying and calcination steps are important for converting the precursor into the final target product CuCo₂O₄; the selection of calcination temperature and time directly affects the phase structure and properties of the product.

[0042] The metal electrodes prepared in the above embodiments were tested as follows:

[0043] 1. The effect of different materials on NH4 over time + The effect of -N removal rate: 480 μL of ethanol and 20 μL of 5 wt% Nafion membrane solution were mixed evenly. Then, 20 mg of CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 catalyst materials (powdered) prepared using Examples 1, 2, and 3 were dispersed in the above mixture and sonicated to obtain a suspension. 200 μL of the suspension was taken and evenly dropped onto a 1 cm² nickel foam, and then placed in an 80°C oven for heating. The dried CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 materials were used as cathodes, and a 1.5 cm × 2 cm Pt electrode was used as an anode for ammonia nitrogen electrochemical oxidation testing. The electrolyte solution was 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS. Add 40 mL of the prepared electrolyte mixture to each side of the H-type electrolytic cell, and adjust the pH of both cells to 12 using freshly prepared 1M sodium hydroxide solution. After treating the three materials under a constant current mode of 2.8 V for 30 min, the experimental results are as follows. Figure 4 As shown.

[0044] Figure 4 The removal efficiency of three materials, CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3, for NH4⁺-N under the same conditions was demonstrated. The figure shows that CuCo2O4-1 exhibited the highest removal rate, followed by CuCo2O4-2, and then CuCo2O4-3. This indicates that CuCo2O4-1 possesses the best catalytic activity, likely due to its superior crystal structure and higher specific surface area resulting from the high copper content, which provides more active sites and thus enhances catalytic efficiency. CuCo2O4, as a p-type semiconductor material, possesses a unique electronic structure and catalytic properties. In water treatment, its surface can serve as active sites, promoting the activation of persulfate and generating highly oxidizing sulfate radicals (SO4⁻·) and hydroxyl radicals (·OH).

[0045] 2. Effects of different pH values ​​on NH4+ over time + The effect of -N removal rate

[0046] 480 μL of ethanol and 20 μL of 5 wt% Nafion membrane solution were mixed thoroughly. Then, 20 mg of CuCo₂O₄⁻¹ catalyst material (powder) prepared in Example 1 was dispersed in the mixture, and the mixture was sonicated to obtain a suspension. 200 μL of the suspension was evenly dropped onto a 1 cm² nickel foam and then heated in an 80°C oven for later use. The dried CuCo₂O₄⁻¹ material was used as the cathode, and a 1.5 cm × 2 cm Pt electrode as the anode for ammonia nitrogen electrochemical oxidation testing. The electrolyte solution consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS. 40 mL of the prepared electrolyte mixture was added to each side of an H-type electrolytic cell. For the first group, the pH of both electrolytic cells was adjusted to 8 using freshly prepared 1M sodium hydroxide solution. For the second group, the pH of both electrolytic cells was adjusted to 10 using freshly prepared 1M sodium hydroxide solution. The third group used freshly prepared 1M sodium hydroxide solution to adjust the pH of both electrolytic cells to 12. The fourth group used freshly prepared 1M sodium hydroxide solution to adjust the pH of both electrolytic cells to 14. After treatment in a constant current mode of 2.8 V for 30 min, the experimental results are as follows: Figure 5 As shown.

[0047] Figure 5 The removal efficiency of CuCo2O4 for NH4⁺-N at different pH values ​​is shown. The figure shows that the removal rate reaches its highest value at pH 10 and 12, while it significantly decreases at pH 8 and 14. Under acidic and neutral conditions, ammonia mainly exists as NH4⁺, while under alkaline conditions, it mainly exists as NH3. Different chemical forms have different effects on the adsorption and reaction activity of the catalyst. Under alkaline pH conditions, the chemical form of ammonia nitrogen is more favorable to the catalytic activation process of CuCo2O4, thus improving the removal efficiency. Furthermore, pH value also affects the charge state of the catalyst surface, thereby affecting its activation ability for persulfate.

[0048] 3. Effects of different PMS contents over time on NH4+ + The effect of -N removal rate

[0049] 480 μL of ethanol and 20 μL of 5 wt% Nafion membrane solution were mixed thoroughly. Then, 20 mg of CuCo2O4-1 catalyst material (powder) prepared in Example 1 was dispersed in the mixture, and the mixture was sonicated to obtain a suspension. 200 μL of the suspension was evenly dropped onto a 1 cm² nickel foam, and then placed in an 80°C oven for heating. The dried CuCo2O4-1 material was used as the cathode, and a 1.5 cm × 2 cm Pt electrode was used as the anode for ammonia nitrogen electrochemical oxidation testing. The first group of electrolyte solutions consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 4 g / L PMS; the second group consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 6 g / L PMS; the third group consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS; and the fourth group consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 10 g / L PMS. 40 mL of the prepared electrolyte mixture was added to each side of the H-type electrolytic cell, and the pH of both sides of the electrolytic cell was adjusted to 12 using freshly prepared 1M sodium hydroxide solution. After treatment in a constant current mode at 2.8 V for 30 min, the experimental results are as follows: Figure 6 As shown.

[0050] Figure 6 The figure shows the removal efficiency of CuCo2O4 for NH4⁺-N under different PMS concentrations. As can be seen from the figure, the removal initially increases with increasing PMS concentration and then stabilizes. This indicates that there is an optimal PMS concentration; exceeding this concentration does not significantly improve the removal rate by increasing the amount of PMS. PMS, as a strong oxidant, plays a crucial role in water treatment. An appropriate amount of PMS can provide sufficient oxidizing power to promote ammonia nitrogen removal. However, when the PMS concentration is too high, over-oxidation or PMS decomposition may occur, reducing its efficiency. Therefore, determining the optimal PMS concentration is of great significance for improving ammonia nitrogen removal efficiency and reducing treatment costs.

[0051] 4. Effects of different voltages on NH4 over time + The effect of -N removal rate

[0052] 480 μL of ethanol and 20 μL of 5 wt% Nafion membrane solution were mixed thoroughly. Then, 20 mg of CuCo2O4-1 catalyst material (powder) prepared in Example 1 was dispersed in the mixture, and the mixture was sonicated to obtain a suspension. 200 μL of the suspension was evenly dropped onto a 1 cm² nickel foam, and then placed in an 80°C oven for heating. The dried CuCo2O4-1 material was used as the cathode, and a 1.5 cm × 2 cm Pt electrode was used as the anode for ammonia nitrogen electrochemical oxidation testing.

[0053] The electrolyte solution consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS. 40 mL of the prepared electrolyte mixture was added to each side of the H-type electrolytic cell. The pH of both electrolytic cells was adjusted to 12 using freshly prepared 1M sodium hydroxide solution. After four sets of experiments were treated under a constant current mode of 2.8 V for 30 min, the experimental results are as follows: Figure 7 As shown.

[0054] Figure 7 The removal efficiency of CuCo2O4 for NH4⁺-N under different voltages is shown in the figure. As can be seen from the figure, the removal rate gradually increases with increasing voltage, but the rate of increase gradually decreases. This indicates that voltage has a positive impact on the removal rate within a certain range, but there is a saturation point. Increasing the voltage can enhance the driving force of the electrochemical reaction, promoting the activation of persulfate and the oxidative removal of ammonia nitrogen. However, after the voltage increases to a certain level, further increasing the voltage does not significantly improve the removal rate. This is because the reaction has reached its kinetic limit, and excessively high voltage may lead to energy waste and the occurrence of side reactions.

[0055] 5. Effects of different initial ammonia nitrogen concentrations on NH4+ over time + The effect of -N removal rate

[0056] 480 μL of ethanol and 20 μL of 5 wt% Nafion membrane solution were mixed thoroughly. Then, 20 mg of CuCo2O4-1 catalyst material (powder) prepared in Example 1 was dispersed in the mixture, and the mixture was sonicated to obtain a suspension. 200 μL of the suspension was evenly dropped onto a 1 cm² nickel foam, and then placed in an 80°C oven for heating. The dried CuCo2O4-1 material was used as the cathode, and a 1.5 cm × 2 cm Pt electrode was used as the anode for ammonia nitrogen electrochemical oxidation testing. The first group of electrolyte solutions consisted of 25 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS; the second group consisted of 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS; the third group consisted of 100 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS; and the fourth group consisted of 200 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L PMS. 40 mL of the prepared electrolyte mixture was added to each side of the H-type electrolytic cell, and the pH of both electrolytic cells was adjusted to 12 using freshly prepared 1M sodium hydroxide solution. After treatment at a constant current mode of 2.8 V for 30 min, the experimental results are as follows: Figure 8 As shown.

[0057] Figure 8 The study revealed the effect of initial ammonia nitrogen concentration on the ability of CuCo2O4-catalyzed persulfate degradation of ammonia nitrogen, showing a trend of decreasing degradation efficiency with increasing ammonia nitrogen concentration. This phenomenon is attributed to the adsorption saturation of active sites on the catalyst surface at high ammonia nitrogen concentrations, limiting further ammonia nitrogen adsorption and reaction. Excessively high ammonia nitrogen concentrations lead to kinetic limitations, causing side reactions or reducing catalyst selectivity, thus affecting the effective degradation of ammonia nitrogen.

Claims

1. A method for degrading ammonia nitrogen in wastewater, characterized in that: by The electrode is the cathode, and the platinum electrode is the anode. Ammonia nitrogen in water is degraded via electrocatalysis. The electrode spacing between the cathode and the platinum anode is 4 cm. The operating voltage of the electrocatalysis is 2.8 V, and the pH of the electrolyte is 12. Electrode preparation includes the following steps: S1: Weigh 3.27 g and 1.459 g Dissolve in 50 mL of deionized water to form solution A; S2: Prepare solution B containing 2.31 g sodium citrate, and adjust the pH to 10 with 1M NaOH; S3: Add solution A dropwise to solution B under constant temperature stirring at 40℃ to form a homogeneous mixed solution; S4: The mixed solution is subjected to a hydrothermal reaction at 100℃ for 24 hours; S5: The product was purified by centrifugation and then washed alternately with alcohol and water, and dried at 70°C for 12 hours. S6: The dried product is calcined in air at 350°C for 2 hours at a rate of 5°C / min. The electrolyte contains 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 8 g / L persulfate. The pH of the electrolyte is adjusted to 12 using 1 M NaOH solution. The ammonia nitrogen solution is prepared using ammonium sulfate as the nitrogen source.

2. The method according to claim 1, characterized in that: The electrocatalytic reaction was carried out in an H-type electrolytic cell, with 40 mL of electrolyte in both the cathode and anode cells, and the reaction time was 30 minutes.

3. The method according to claim 1, characterized in that: The persulfate is potassium peroxymonosulfate, and its concentration in the electrolyte is 8 g / L.

4. The method according to claim 1, characterized in that: In step S2, pH adjustment is achieved by adding NaOH solution dropwise, with the addition rate controlled at 1-2 mL / min.

5. The method according to claim 1, characterized in that: In step S5, the centrifugation purification is performed at 8000 rpm, and each wash lasts for 5 minutes.

6. The method according to claim 1, characterized in that: In step S6, the calcination process is carried out in a tube furnace, and the air flow rate is controlled at 45-55 mL / min.

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