Method for degrading ammonia nitrogen in wastewater and application

Abstract

The invention 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, firstly, Co (NO). 6HO and Cu (CH3COO) 2 are dissolved in deionized water and mixed with a sodium citrate solution to be subjected to a hydrothermal reaction, and then CuCoO is obtained through washing, drying and calcination. CuCoO samples with different compositions can be prepared by adjusting the dosage of Co (NO). 6HO and Cu (CH3COO) 2. The CuCoO electrode provided by the invention shows excellent ammonia nitrogen oxidation performance in the process of activating persulfate (PMS), and has high ammonia nitrogen removal rate and nitrogen selectivity. The preparation method is simple, low in cost, easily available in raw materials and suitable for large-scale production and application. In addition, the electrode shows good reusability when being used for electrochemically treating ammonia-nitrogen-containing wastewater, and a new way is provided for efficient, economical and environment-friendly wastewater treatment.

Description

Technical Field

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

[0002] The discharge of high-concentration ammonia nitrogen industrial wastewater is one of the main causes of water eutrophication. The pH of this type of wastewater varies greatly, but mostly ranges from 9 to 13. Ammonia nitrogen exists in wastewater in the forms of free ammonia (NH3) and ionic ammonium (NH4⁺). When the pH is higher than 9.25, ammonia nitrogen mainly exists in the form of free ammonia, and its biological toxicity is dozens of times higher than that of ionic ammonia. Ammonia nitrogen pollution remains a serious global problem. Its negative impact on the environment, large-scale production, and extensive use as fertilizers make the treatment of ammonia-containing wastewater an important topic in environmental protection. Excessive ammonia in water bodies will seriously threaten the quality of the ecosystem, leading to water toxicity and eutrophication. Therefore, the removal of NH4⁺-N in wastewater is of great significance.

[0003] Existing various 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 technology, etc.), have been applied to ammonia removal. However, under specific conditions, each method has its advantages and disadvantages. Biological methods, such as nitrification-denitrification and anaerobic ammonium oxidation, utilize microorganisms to convert ammonia nitrogen into nitrogen gas. The nitrification-denitrification method can significantly remove ammonia nitrogen, but the operating conditions are relatively harsh, and a large amount of chemical substances are generated during the treatment process. The anaerobic ammonium oxidation process can reduce the sludge production, but the current technology is not yet mature. In addition, the traditional biological treatment method has poor tolerance to industrial wastewater with high ammonia nitrogen concentration. High ammonia nitrogen concentration, high pH, and toxic pollutants may all affect the activity of microorganisms and reduce the reaction efficiency. Among the physical methods, air stripping removes ammonia nitrogen by converting ammonia in the wastewater from the liquid phase to the gas phase, but it has high energy consumption and low efficiency at low temperatures. The membrane separation technology is convenient to operate and has no secondary pollution, but the investment cost is high, and it has strict requirements on water quality. Among the chemical methods, breakpoint chlorination oxidizes ammonia nitrogen into nitrogen gas by adding excessive chlorine or sodium hypochlorite. The treatment efficiency is high and it is not affected by water temperature, but the operating cost is high, and the by-products may cause secondary pollution. The ion exchange method uses ion exchange resin to remove ammonia nitrogen, but the resin consumption is large, regeneration is difficult, and the operating cost is high. Therefore, it is urgent to explore a feasible process for removing ammonia in wastewater, preferably converting NH4⁺-N into harmless N2. Advanced oxidation processes (AOPs) have developed rapidly in recent years and have received extensive attention. The active substances generated in AOPs, such as hydroxyl radicals (•OH), play a leading role in the degradation of pollutants. It should be noted that under strong alkaline conditions, NH4⁺-N is converted into free ammonia (NH3-N). Converting ammonia nitrogen into gaseous nitrogen (N2) rather than NO3⁻ and NO2⁻ is the ideal water purification goal. However, there is little research on the efficient ammonia oxidation and high conversion selectivity to N2 of the sulfate radical-based AOP / OH process. Therefore, it is urgent to explore a feasible process for removing ammonia in wastewater. Summary of the Invention

[0004] To address the above problems, this study developed a CuCo2O4 / PMS / OH system to degrade ammonia nitrogen in water. It is a method that effectively oxidizes and decomposes more than 90% of ammonia nitrogen in water by electrocatalysis using a CuCo2O4 electrode with very low preparation cost as the cathode. The specific mechanism is as follows: Cu⁺ and Co²⁺ on the surface of CuCo2O4 activate persulfate (PMS) through electron transfer, generating hydroxyl radicals (•OH) and sulfate radicals (SO4• ⁻ ), while being oxidized to Cu²⁺ and Co³⁺ themselves; the high-valent Cu²⁺ / Co³⁺ further activates PMS to generate peroxymonosulfate radicals (SO5• ⁻)(and is restored to Cu⁺ / Co²⁺ again, forming a dynamic redox cycle. Based on the potential difference between Co³⁺ / Co²⁺ and Cu²⁺ / Cu⁺, Co²⁺ can drive the reduction of Cu²⁺ through electron transfer, promoting the regeneration of active sites until PMS is completely consumed. The generated free radicals (SO4• ⁻ / •OH) gradually oxidize and remove ammonia nitrogen, and ultimately most of it is converted into nitrogen. This method has low cost, is easy to recycle, and has high decomposition efficiency, providing a promising technology for the treatment and selective oxidation of ammonia in alkaline ammonia-containing wastewater.

[0005] The technical solution adopted in the present invention is as follows: Using the CuCo2O4 electrode as the cathode and the platinum electrode as the anode, ammonia nitrogen in water is degraded by electrocatalysis. Among them, the electrode spacing between the CuCo2O4 cathode and the platinum electrode anode is 4 cm, the working voltage of the electrocatalytic reaction is 2.8 V, and the pH of the electrolyte is 12. The preparation method of the CuCo2O4 electrode specifically includes the following steps: S1: 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; S2: Weigh 2.31 g of sodium citrate and dissolve it in 30 mL of deionized water, and adjust the pH = 10 with 1 M NaOH solution to form solution B; S3: Under the condition of constant temperature stirring at 40 °C, slowly add solution A to solution B to form a uniformly mixed solution; S4: Transfer the mixed solution to a reaction kettle with a polytetrafluoroethylene liner and perform hydrothermal treatment at 100 °C for 24 hours; S5: After the obtained precipitate is centrifugally purified and washed alternately with alcohol and water, it is dried at 70 °C for 12 hours; S6: Heat the dried product to 350 °C at a heating rate of 5 °C / min in an air atmosphere and calcine it for 2 hours to obtain the CuCo2O4 electrode.

[0006] Furthermore, in step S2, the pH adjustment is carried out by dropping NaOH solution drop by drop to maintain the uniformity of the solution system.

[0007] Furthermore, in step S5, the washing process adopts the centrifugal separation method, the centrifugal speed is 8000 rpm, and each washing lasts for 5 minutes.

[0008] Further, the preparation methods for different samples in step S6 include: when weighing 1.64 g of Co(NO3)3·6H2O and 1.463 g of Cu(CH3COO)2, it is labeled as CuCo2O4-2; when weighing 3.27 g of Co(NO3)3·6H2O and 0.729 g of Cu(CH3COO)2, it is labeled as CuCo2O4-3.

[0009] Further, in step S6, the calcination process is carried out in a tube furnace, and the air flow rate is controlled at 50 mL / min.

[0010] Further, in step S6, the calcination temperature is 350 °C and the time is 2 hours.

[0011] Further, in step S6, the calcination process is carried out in a tube furnace, and the air flow rate is controlled at 50 mL / min.

[0012] The present invention also provides a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater prepared by the above method.

[0013] The present invention also provides an application of the above CuCo2O4 electrode in the electrocatalytic oxidation of ammonia nitrogen.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The CuCo2O4 electrode has significant advantages in the electrocatalytic oxidation of ammonia nitrogen in wastewater at the cathode. The binding energy of copper and cobalt metals on the surface to PMS is relatively high, which can quickly reduce PMS to generate a large amount of sulfate radicals (SO4⁻·), and then generate hydroxyl radicals (·OH). These radicals have extremely strong oxidation ability and can quickly oxidize ammonia nitrogen into nitrogen gas. In addition, the CuCo2O4 electrode has a unique nano-sheet structure, which can significantly increase the specific surface area of the electrode, provide more active sites for adsorbing ammonia nitrogen, and promote the rapid release of nitrogen gas, avoiding the inhibitory effect of product accumulation on the electrode surface on the reaction. The CuCo2O4 electrode also shows a high nitrogen selectivity during the oxidation of ammonia nitrogen, which means that ammonia nitrogen can be more efficiently converted into nitrogen gas rather than other by-products, improving the ammonia nitrogen removal efficiency. Compared with traditional noble metal oxide electrodes, the main components of the CuCo2O4 electrode, copper and cobalt, are rich in resources and low in price. This low-cost and easy-to-recycle feature makes it have broad application prospects in large-scale wastewater treatment. Abundant oxygen vacancies are introduced during the preparation of the CuCo2O4 electrode, and these oxygen vacancies can significantly improve the electrochemical performance of the electrode, with higher specific capacitance and better charge transfer ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an XRD characterization diagram of the CuCo2O4 material of the present invention.

[0016] Figure 2 This is the SEM image of the CuCo2O4-1 material of the present invention.

[0017] Figure 3 This is the TEM image of the CuCo2O4-1 material of the present invention.

[0018] Figure 4 It is the influence diagram of different materials of the present invention on the NH4 + -N removal rate over time; Figure 5 It is the influence diagram of different pH values of the present invention on the NH4 + -N removal rate over time; Figure 6 It is the influence diagram of different PMS contents of the present invention on the NH4 + -N removal rate over time.

[0019] Figure 7 It is the influence diagram of different voltages of the present invention on the NH4 + -N removal rate over time.

[0020] Figure 8 It is the influence diagram of different initial ammonia nitrogen concentrations of the present invention on the NH4 + -N removal rate over time. Detailed implementation manners

[0021] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0022] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are usually in accordance with conventional conditions or the conditions recommended by the manufacturers. Various raw materials used in the following embodiments are all commercially available products according to conventional specifications in the art unless otherwise specified. Embodiment

[0023] This embodiment provides a preparation method of a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps: First, accurately weigh 3.27 g of Co(NO3)3·6H2O and 1.459 g of Cu(CH3COO)2, 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 the condition of constant temperature stirring at 40 °C, slowly add solution A to solution B to form a homogeneous mixed solution. Transfer this mixed solution to a reaction kettle lined with polytetrafluoroethylene, and place it in an oven at 100 °C for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, dry it at 70 °C for 12 h. Place the dried product in a tube furnace and calcine it in an air atmosphere at 350 °C for 2 hours (heating rate of 5 °C / min) to convert it into CuCo2O4, labeled as: CuCo2O4-1. Example

[0024] This example provides a preparation method of a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps: Weigh 1.64 g of Co(NO3)3·6H2O and 1.463 g of Cu(CH3COO)2, 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 the condition of constant temperature stirring at 40 °C, slowly add solution A to solution B to form a homogeneous mixed solution. Transfer this mixed solution to a reaction kettle lined with polytetrafluoroethylene, and place it in an oven at 100 °C for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, dry it at 70 °C for 12 h. Place the dried product in a tube furnace and calcine it in an air atmosphere at 350 °C for 2 hours (heating rate of 5 °C / min) to convert it into CuCo2O4, labeled as: CuCo2O4-2. Example

[0025] This example provides a preparation method of a CuCo2O4 electrode for oxidizing ammonia nitrogen in wastewater, specifically including the following steps: Weigh 3.27 g of Co(NO3)3·6H2O and 0.729 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 the condition of constant temperature stirring at 40 °C, slowly add solution A to solution B to form a homogeneous mixed solution. Transfer this mixed solution to a reaction kettle lined with polytetrafluoroethylene, and place it in an oven at 100 °C for hydrothermal treatment for 24 hours. After cooling, wash the precipitate with water and ethanol respectively, dry it at 70 °C for 12 h, and place the dried product in a tubular furnace. Calcinate it in an air atmosphere at 350 °C for 2 hours (heating rate: 5 °C / min) to convert it into CuCo2O4, labeled as: CuCo2O4-3.

[0026] Analyze the phase composition and crystal structure information of CuCo2O4-1, CuCo2O4-2 and CuCo2O4-3 materials by XRD, as Figure 1 shown. The diffraction peaks of the three samples at 31.1°, 36.6°, 44.5°, 59.0° and 64.8° respectively correspond to the (220), (311), (400), (333) and (440) crystal planes of spinel-type CuCo2O4 (JCPDS: 37-0878), indicating that the three have the same phase; the diffraction main peak of the (311) crystal plane of CuCo2O4-1 is wider, indicating that its primary grain size is smaller, which helps to provide more abundant surface sites and higher catalytic performance. The SEM and TEM of CuCo2O4-1 material are as Figure 2 and 3 shown. The images show that the CuCo2O4-1 material is composed of a porous flake structure. These nanostructures can significantly increase the specific surface area of the electrode, provide good connectivity and active sites, have more channels and shorten the distance for ion and electron transport, and accelerate the electrocatalytic reaction process. After these active sites adsorb ammonia nitrogen, it is beneficial to the rapid release of nitrogen.

[0027] In this example, the preparation of solution A and solution B requires precise control of the dosage of reagents and dissolution conditions to ensure the uniformity and completeness of the reaction. The hydrothermal reaction is the key step in forming the CuCo2O4 precursor. The precise control of temperature and time has a decisive influence on the crystallinity and morphology of the product. The washing process helps to remove impurities that may be generated during the reaction, thereby improving the purity of the final product. The drying and calcination steps are important links in converting the precursor into the final target product CuCo2O4. The selection of calcination temperature and time directly affects the phase structure and performance of the product.

[0028] Conduct the following tests on the metal electrodes prepared in the above examples: 1. Influence of different materials on the removal rate of NH4 + -N over time. Mix 480 μL of ethanol and 20 μL of 5 wt% nafion membrane solution evenly, and then disperse 20 mg of the CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 catalyst materials (powdery) prepared in Examples 1, 2, and 3 in the above mixture, and obtain a suspension by ultrasonic treatment. Take 200 μL of the suspension and evenly drop it on 1 square centimeter of nickel foam, and then place it in an 80°C oven for heating and standby. The dried CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 materials are used as the cathode respectively, and a 1.5 cm * 2 cm Pt electrode is used as the anode for ammonia nitrogen electrochemical oxidation test. The electrolyte solution is an ammonia nitrogen solution of 50 mg / L, sodium sulfate of 0.05 mol / L, and 8 g / L of PMS. Add 40 mL of the prepared electrolyte mixture to both sides of the H-type electrolytic cell respectively, and adjust the pH of the two electrolytic cells to 12 with freshly prepared 1M sodium hydroxide solution. After the three materials are treated for 30 minutes in a constant current mode with a voltage of 2.8 V respectively, the experimental results are as Figure 4 shown.

[0029] Figure 4 shows the removal effects of CuCo2O4-1, CuCo2O4-2, and CuCo2O4-3 on NH4⁺-N under the same above conditions. It can be seen from the figure that the removal rate of CuCo2O4-1 is the highest, followed by CuCo2O4-2, and finally CuCo2O4-3. This indicates that CuCo2O4-1 has the best catalytic activity, because the high content of copper endows it with a better crystal structure and a higher specific surface area, providing more active sites, thus improving the catalytic efficiency. CuCo2O4, as a p-type semiconductor material, has a unique electronic structure and catalytic performance. During the water treatment process, its surface can serve as an active site to promote the activation of persulfate, thereby generating strongly oxidizing sulfate radicals (SO4⁻·) and hydroxyl radicals (·OH).

[0030] 2. Influence of different pH values on the removal rate of NH4 + -N over time Mix 480 μL of ethanol and 20 μL of 5 wt% nafion membrane solution evenly. Then disperse 20 mg of the CuCo2O4-1 catalyst material (powder form) prepared in Example 1 in the above mixture and obtain a suspension by ultrasonic treatment. Take 200 μL of the suspension and evenly drop it on a 1 square centimeter nickel foam, and then place it in an 80 °C oven for heating and standby. The dried CuCo2O4-1 material is used as the cathode respectively, and a 1.5 cm * 2 cm Pt electrode is used as the anode for ammonia nitrogen electro-oxidation test. The electrolyte solution is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 8 g / L PMS. Add 40 mL of the prepared electrolyte mixed solution to both sides of the H-type electrolytic cell respectively. For the first group, use freshly prepared 1M sodium hydroxide solution to adjust the pH = 8 in both electrolytic cells. For the second group, use freshly prepared 1M sodium hydroxide solution to adjust the pH = 10 in both electrolytic cells. For the third group, use freshly prepared 1M sodium hydroxide solution to adjust the pH = 12 in both electrolytic cells. For the fourth group, use freshly prepared 1M sodium hydroxide solution to adjust the pH = 14 in both electrolytic cells. After the four groups of experiments are treated for 30 min in the constant current mode at a voltage of 2.8 V, the experimental results are as Figure 5 shown.

[0031] Figure 5 shows the removal effect of CuCo2O4 on NH4⁺-N at different pH values. It can be seen from the figure that the removal rate reaches the highest at pH values of 10 and 12, while the removal rate decreases significantly at pH values of 8 and 14. Under acidic and neutral conditions, ammonia mainly exists in the form of NH4⁺, while under alkaline conditions, it mainly exists in the form of 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 conducive to the catalytic activation process of CuCo2O4, thus improving the removal efficiency. In addition, the pH value will also affect the charge state on the catalyst surface, and then affect its activation ability for persulfate.

[0032] 3. Influence of different PMS contents on the removal rate of NH4 + -N over time Mix 480 μL of ethanol and 20 μL of 5 wt% nafion membrane solution evenly. Then disperse 20 mg of the CuCo2O4-1 catalyst material (powder form) prepared in Example 1 in the above mixture and obtain a suspension by ultrasonic treatment. Take 200 μL of the suspension and evenly drop it on 1 square centimeter of nickel foam, and then place it in an 80 °C oven for heating and standby. The dried CuCo2O4-1 material is used as the cathode respectively, and a 1.5 cm * 2 cm Pt electrode is used as the anode for ammonia nitrogen electrochemical oxidation test. The first group of electrolyte solutions is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 4 g / L of PMS; the second group of electrolyte solutions is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 6 g / L of PMS; the third group of electrolyte solutions is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 8 g / L of PMS; the fourth group of electrolyte solutions is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 10 g / L of PMS. Add 40 mL of the prepared electrolyte mixed solution to both sides of the H-type electrolytic cell respectively, and adjust the pH of both electrolytic cells to 12 with freshly prepared 1M sodium hydroxide solution. After the four groups of experiments are treated for 30 min in a constant current mode with a voltage of 2.8 V, the experimental results are as Figure 6 shown.

[0033] Figure 6 shows the removal effect of CuCo2O4 on NH4⁺-N at different PMS contents. It can be seen from the figure that as the PMS content increases, the removal rate first increases and then tends to be stable. This indicates that there is an optimal PMS content, and beyond this content, increasing the amount of PMS will not significantly improve the removal rate. PMS, as a strong oxidant, plays a key role in water treatment. An appropriate amount of PMS can provide sufficient oxidation ability to promote the removal of ammonia nitrogen. However, when the PMS content is too high, over-oxidation or the decomposition of PMS itself may occur, reducing its efficiency. Therefore, determining the optimal PMS content is of great significance for improving the ammonia nitrogen removal efficiency and reducing the treatment cost.

[0034] 4. Influence of different voltages changing with time on the removal rate of NH4 + -N Mix 480 μL of ethanol and 20 μL of 5 wt% nafion membrane solution evenly. Then disperse 20 mg of the CuCo2O4-1 catalyst material (powder form) prepared in Example 1 in the above mixture and obtain a suspension by ultrasonic treatment. Take 200 μL of the suspension and evenly drop it on 1 square centimeter of nickel foam, and then place it in an 80°C oven for heating and standby. The dried CuCo2O4-1 material is used as the cathode respectively, and a 1.5 cm * 2 cm Pt electrode is used as the anode for ammonia nitrogen electro-oxidation test.

[0035] The electrolyte solution is an ammonia nitrogen solution of 50 mg / L, sodium sulfate of 0.05 mol / L and 8 g / L of PMS. Add 40 mL of the prepared electrolyte mixed solution to each side of the H-type electrolytic cell respectively, and adjust the pH of the two electrolytic cells to 12 with freshly prepared 1M sodium hydroxide solution. After the four groups of experiments are treated in a constant current mode at a voltage of 2.8 V for 30 min, the experimental results are as Figure 7 shown.

[0036] Figure 7 shows the removal effect of CuCo2O4 on NH4⁺-N at different voltages. It can be seen from the figure that with the increase of voltage, the removal rate gradually increases, but the increasing amplitude gradually decreases. This indicates that the voltage has a positive effect on the removal rate within a certain range, but there is a saturation point. The increase of voltage can increase the driving force of the electrochemical reaction, promote the activation of persulfate and the oxidation and removal of ammonia nitrogen. However, when the voltage increases to a certain extent, further increasing the voltage will not significantly improve the removal rate, because the reaction has reached the kinetic limit, and too high voltage may lead to energy waste and side reactions.

[0037] 5. Influence of different initial ammonia nitrogen concentrations changing with time on the removal rate of NH4 + -N Mix 480 μL of ethanol and 20 μL of 5 wt% nafion membrane solution evenly. Then disperse 20 mg of the CuCo2O4-1 catalyst material (powder form) prepared in Example 1 in the above mixture and obtain a suspension by ultrasonic treatment. Take 200 μL of the suspension and evenly drop it on 1 square centimeter of nickel foam, and then place it in an 80 °C oven for heating and standby. The dried CuCo2O4-1 material is used as the cathode, and a 1.5 cm * 2 cm Pt electrode is used as the anode for ammonia nitrogen electro-oxidation testing. The first group of electrolyte solutions is 25 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L of PMS; the second group of electrolyte solutions is 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L of PMS; the third group of electrolyte solutions is 100 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L of PMS; the fourth group of electrolyte solutions is 200 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate, and 8 g / L of PMS. Add 40 mL of the prepared electrolyte mixture to both sides of the H-type electrolytic cell respectively, and adjust the pH of both electrolytic cells to 12 with freshly prepared 1M sodium hydroxide solution. After the four groups of experiments are treated for 30 min in a constant current mode with a voltage of 2.8 V, the experimental results are as Figure 8 shown.

[0038] Figure 8 reveals the influence of the initial concentration of ammonia nitrogen on the ability of CuCo2O4 to catalyze and activate persulfate for ammonia nitrogen degradation, showing a trend that as the ammonia nitrogen concentration increases, its degradation efficiency decreases instead. This phenomenon is due to the fact that at high ammonia nitrogen concentrations, the active sites on the catalyst surface reach adsorption saturation, restricting further ammonia nitrogen adsorption and reaction. Excessive ammonia nitrogen concentration leads to limitations in reaction kinetics, causing side reactions or reducing the selectivity of the catalyst, thus affecting the effective degradation of ammonia nitrogen.

Claims

1. A method for degrading ammonia nitrogen in wastewater, characterized in that: A CuCo2O4 electrode is used as a cathode and a platinum electrode is used as an anode to degrade ammonia nitrogen in water by electrocatalysis, wherein the electrode distance between the CuCo2O4 cathode and the platinum electrode anode is 4 cm, the working voltage of the electrocatalytic reaction is 2.8 V, and the pH of the electrolyte is 12, wherein the preparation of the CuCo2O4 electrode includes the following steps: S1: Weigh 3.27 g Co(NO3)3·6H2O and 1.459 g Cu(CH3COO)2 in a Co³⁺:Cu²⁺ molar ratio of 1:1 and dissolve them in 50 mL deionized water to form solution A; S2: Prepare solution B containing 2.31 g of sodium citrate and adjust the pH to 10 with 1 M NaOH; S3: adding solution A dropwise to solution B under constant temperature stirring at 40°C to form a uniform mixed solution; S4: The mixed solution was subjected to hydrothermal reaction at 100 °C for 24 hours; S5: The product was purified by centrifugation, washed alternately with alcohol and water, and dried at 70°C for 12 hours; S6: The dried product was heated to 350° C. at 5° C. / min in air atmosphere and calcined for 2 hours.

2. The method according to claim 1, characterized in that: The electrolyte contains 50 mg / L ammonia nitrogen solution, 0.05 mol / L sodium sulfate and 8 g / L persulfate. The pH value of the electrolyte is adjusted to 12 by 1 M NaOH solution. The ammonia nitrogen solution is prepared with ammonium sulfate as the nitrogen source.

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

4. The method according to claim 2, characterized in that: The persulfate is potassium monopersulfate, and its concentration in the electrolyte is 8 g / L.

5. The method according to claim 1, characterized in that: In step S2, the pH is adjusted by adding NaOH solution dropwise, and the addition rate is controlled to be 1-2 mL / min.

6. The method according to claim 1, characterized in that: The centrifugal purification in step S5 adopts a rotation speed of 8000 rpm, and each washing lasts for 5 minutes.

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

8. The method according to claim 1, characterized in that: Changes in the molar ratio of cobalt salt to copper salt include: when Co³⁺:Cu²⁺=1:1, the product is labeled CuCo2O4-1, when Co³⁺:Cu²⁺=2:1, the product is labeled CuCo2O4-2, and when Co³⁺:Cu²⁺=1:2, the product is labeled CuCo2O4-3.

9. A CuCo2O4 electrode for degrading and oxidizing ammonia nitrogen in wastewater, prepared according to the method of any one of claims 1 to 8.

10. Use of the CuCo2O4 electrode as claimed in claim 9 in electrocatalytic oxidation of ammonia nitrogen.

Images