Preparation method and application of catalyst for electro-reduction of nitro-nitrogen to ammonia in high-salinity wastewater

Abstract

The application relates to the technical field of electrochemical reduction, and discloses a preparation method and application of a catalyst for electro-reduction of nitro nitrogen into ammonia in high-salt wastewater, which comprises the following steps: (1) stirring and dissolving metal salts, a carbon source and a nitrogen source in an alcohol-water mixed solvent to obtain a precursor solution; wherein the metal salts are cobalt salts and copper salts, the Co:Cu molar ratio is 1-5:1, and the nitrogen source is a cyanamide-containing compound; (2) evaporating and crystallizing the precursor solution to obtain an organic metal salt; and (3) adding the organic metal salt into a dimethylimidazole-ethanol solution, performing ball milling treatment, and pyrolyzing in an inert atmosphere to obtain a nitrogen-doped carbon-based cobalt-copper bimetallic catalyst. The organic nitrogen and metal coordination are doped twice and anchored on the carbon matrix, the catalyst active sites and stability are effectively improved, the corrosion failure of the catalyst under the condition of high-salt wastewater is avoided, and efficient and stable reduction conversion of nitrate in high-salt wastewater is realized.

Description

Technical Field

[0001] This invention relates to the field of electrochemical reduction technology, and in particular to a method for preparing and applying catalysts for the electroreduction of nitrate nitrogen in high-salt wastewater to produce ammonia. Background Technology

[0002] Electrochemical reduction, as a green and efficient water treatment technology, can directly reduce nitrates in industrial wastewater to ammonia. This not only removes nitrogenous pollutants from wastewater but also simultaneously recovers ammonia resources, resulting in significant environmental and economic benefits. However, in actual industrial wastewater treatment processes, the wastewater composition is complex, especially high-salinity industrial wastewater. Besides high concentrations of nitrates, it often contains various anions and cations, such as chlorides, ammonium salts, and sulfates. After pretreatment processes such as membrane concentration and evaporation concentration, these salts further accumulate in the concentrate, forming a high-salinity wastewater system.

[0003] High-salt environments pose a significant challenge to the electrocatalytic reduction of nitrate. On one hand, high concentrations of salt ions (especially chloride ions) compete with active sites on the electrode surface for adsorption, inhibiting the reduction reaction of nitrate ions. On the other hand, concentrated wastewater contains high concentrations of chlorine and ammonia nitrogen. Due to the strong corrosiveness of high-chlorine, high-ammonia-nitrogen wastewater, traditional metal-based / metal oxide / metal hydroxide catalysts are easily corroded and dissolved, resulting in a decrease in electrochemical reaction efficiency. Corrosion leads to the loss of active catalyst components and structural damage, thereby reducing the electrochemical active area and significantly decreasing catalytic efficiency. Simultaneously, corrosion products may detach and enter the solution, causing secondary pollution and shortening the electrode's lifespan.

[0004] Patent CN121775844A discloses a method for preparing and applying a controllable Co-Cu bimetallic oxide nanocatalyst. This method constructs an atomically dispersed Co-Cu dual-active-site catalyst on a nickel foam substrate, which can remove low-concentration nitrate pollutants. However, this catalyst struggles to balance high activity, stability, and long-term corrosion resistance. The chloride ion concentration in the applied water is 0.01~0.05 mol / L, which is insufficient for the electrocatalytic reduction of nitrates in high-salinity wastewater with chloride ion concentrations ≥0.6 mol / L. Therefore, there is an urgent need to develop a catalyst that can operate stably for a long time under high-salinity wastewater conditions and maintain highly efficient electrocatalytic nitrate reduction performance. Summary of the Invention

[0005] To address the issues of traditional catalysts' easy deactivation and poor stability in high-salt corrosive environments, this invention provides a method for preparing and applying a catalyst for the electroreduction of nitrate nitrogen to ammonia in high-salt wastewater. By doping organic nitrogen and coordinating and anchoring it on a carbon matrix, the active sites and stability of the catalyst are effectively improved, thus avoiding its corrosion failure under high-salt wastewater (high chlorine and high ammonia nitrogen) conditions, achieving efficient and stable reduction and conversion of nitrate in high-salt wastewater.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater, comprising the following steps: (1) Dissolve the metal salt, carbon source and nitrogen source in a mixed solvent of alcohol and water by stirring to obtain a precursor solution; wherein the metal salt is a cobalt salt and a copper salt, and the molar ratio of Co:Cu is 1~5:1; the nitrogen source is a compound containing a cyanamide group; (2) After evaporating and crystallizing the precursor solution, an organometallic salt is obtained; (3) Add the organometallic salt to a dimethylimidazolium-ethanol solution, ball mill it, and then pyrolyze it in an inert atmosphere to obtain a nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0007] This invention employs a one-step evaporation process to efficiently and rapidly convert metal salts, carbon sources, and nitrogen sources in a precursor solution into organometallic salt crystalline solids, allowing for initial bonding between the metal sites and nitrogen-doped organic carbon. A compound containing a cyanamide group is selected as the nitrogen source, which can uniformly anchor Co and Cu within the organic salt molecular framework, improving the dispersibility of the metal precursor molecules. Furthermore, the pyrolysis process itself releases nitrogen, introducing nitrogen doping in situ into the carbon matrix bulk phase, serving as the nitrogen source for the carbon framework. Simultaneously, cyanamide itself contains carbon, which can supplement the carbon source and participate in carbon framework construction. While nitrogen-doped carbon has a stable structure, its electrochemical activity is insufficient. By introducing anchoring metal sites, the energy gap is adjusted and the electron transfer process is accelerated.

[0008] Subsequently, the organometallic salt and dimethylimidazole undergo a mechanochemical reaction via ball milling, and the cobalt-copper bimetallic compound is re-anchored to the organic carbon matrix using a nitrogen source, enhancing stability. Furthermore, the two additions of the nitrogen source generate various types of nitrogen (pyrrole nitrogen, pyridine nitrogen, graphitic nitrogen, etc.), and a unique interaction exists between the nitrogen-doped carbon structure and the Co and Cu metal centers. This not only increases carbon defects but also allows for fine-tuning of the catalyst's physical and chemical properties, thereby improving electrocatalytic activity. A nitrogen-doped carbon-based cobalt-copper bimetallic catalyst is then obtained through high-temperature pyrolysis, which electrocatalyzes the electroreduction of nitrate to ammonia under the synergistic effect of the cobalt-copper bimetallic compound. Simultaneously, this method produces catalysts with high yields, high bimetallic loadings, and easily controllable elemental ratios among the bimetallic compound, nitrogen, and carbon, which is beneficial for optimizing active sites in the catalyst.

[0009] Preferably, the molar ratio of the metal salt, carbon source, and nitrogen source is 1 to 3:1:5.

[0010] Preferably, the mass ratio of the nitrogen source to the alcohol-water mixed solvent is 1:60~80, and more preferably, the mass ratio of the nitrogen source to the alcohol-water mixed solvent is 1:60~70.

[0011] Preferably, the alcohol-water mixed solvent is a mixture of methanol and water in a volume ratio of 0.6 to 1.5:1. More preferably, the alcohol-water mixed solvent is a mixture of methanol and water in a volume ratio of 1.0 to 1.5:1.

[0012] Preferably, the carbon source is one or more of glucose and soluble starch.

[0013] Preferably, the nitrogen source is one or more of cyanamide, dicyanamide, and melamine.

[0014] Preferably, the temperature for stirring and dissolving is 50-70°C.

[0015] Preferably, the evaporation crystallization temperature is 150-160℃ and the time is 6-10 h.

[0016] Preferably, the concentration of dimethylimidazole in the dimethylimidazole-ethanol solution is 0.15~0.3M, and more preferably, the concentration of dimethylimidazole in the dimethylimidazole-ethanol solution is 0.15~0.25M.

[0017] Preferably, the mass ratio of the organometallic salt to the dimethylimidazole-ethanol solution is 1:0.5~1; more preferably, the mass ratio of the organometallic salt to the dimethylimidazole-ethanol solution is 1:0.6~1.

[0018] Preferably, the ball milling process is performed at a rotation speed of 400-600 rpm for 1-2 hours.

[0019] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the pyrolysis is to raise the temperature to 500-700°C at a rate of 1-5°C / min and hold it at that temperature for 2-4 hours.

[0020] Secondly, the present invention also provides an application of the catalyst in the electrocatalytic reduction of nitrate to ammonia in high-salt wastewater, wherein the high-salt wastewater has a conductivity ≥80 mS / cm, a chloride ion concentration of 0.6~2.4 mol / L, an ammonia nitrogen concentration of 0.1~0.4 mol / L, and a nitrate ion concentration ≥40 mmol / L; ammonia is synthesized in the high-salt wastewater by using the catalyst as the cathode via an electrochemical reduction method.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The nitrogen-doped carbon-based cobalt-copper bimetallic catalyst is anchored on the carbon matrix by double doping of organic nitrogen and metal coordination. The cobalt and copper metal loading is large and the ratio is controllable, which effectively improves the active sites and stability of the catalyst, so as to avoid its corrosion failure under high-salt wastewater (high chlorine and high ammonia nitrogen) conditions, and realizes the efficient conversion of nitrates into ammonia. (2) The catalyst has the characteristics of high current efficiency, high nitrate conversion rate, high ammonia selectivity, and high stability under high salinity wastewater conditions; (3) The solution evaporation-ball milling-high temperature pyrolysis process is adopted. The preparation method is simple, the raw material utilization rate is high, the production cost is low, the evaporated solvent can be condensed and recycled for reuse, there is no secondary pollution of wastewater, and it is easy to achieve large-scale production and use. Attached Figure Description

[0022] Figure 1 The linear voltammetric scan curve (scan rate 25 mV / s) of the catalyst in Example 1 is shown.

[0023] Figure 2 This is a scanning electron microscope image of the catalyst in Example 1.

[0024] Figure 3 Raman spectra of the catalysts in Example 1 and Comparative Example 4 (NC-CoCu: nitrogen-doped carbon-based cobalt-copper bimetallic catalyst; NC: nitrogen-doped organic carbon catalyst).

[0025] Figure 4 The image shows the XPS analysis spectrum of the catalyst in Example 1. Detailed Implementation

[0026] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] Example 1

[0028] The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0029] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0030] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst (NC-CoCu).

[0031] Example 2

[0032] The catalyst preparation method includes the following steps: (1) Weigh out 1g of copper acetate monohydrate, 6.25g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 5:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0033] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0034] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0035] Example 3

[0036] The catalyst preparation method includes the following steps: (1) Weigh out 4.5g of copper acetate monohydrate, 5.6g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.045mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 3:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0037] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0038] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0039] Example 4

[0040] The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1.5:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0041] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0042] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0043] Example 5

[0044] The catalyst preparation method includes the following steps: (1) Weigh out 1.5g of copper acetate monohydrate, 1.85g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.015mol), 2.7g of glucose and 3.15g of cyanamide, with a metal salt:carbon source:nitrogen source molar ratio of 1:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0045] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0046] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0047] Example 6

[0048] The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0049] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0050] (3) Weigh 5g of organometallic salt, add 3g of 0.15M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 700℃ for 3h to obtain nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

[0051] Comparative Example 1 The catalyst preparation method includes the following steps: (1) Weigh out 4g of copper acetate monohydrate, 2.5g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:2, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0052] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0053] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain the catalyst.

[0054] Comparative Example 2 The catalyst preparation method includes the following steps: (1) Weigh out 0.6g of copper acetate monohydrate, 6.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 9:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0055] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0056] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain the catalyst.

[0057] Comparative Example 3 The catalyst preparation method includes the following steps: (1) Weigh out 6g of copper acetate monohydrate, 2.7g of glucose and 9.46g of melamine respectively. The molar ratio of metal salt: carbon source: nitrogen source is 2:1:5. Add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio is 1:1). Stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0058] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0059] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain the catalyst.

[0060] Comparative Example 4 The catalyst preparation method includes the following steps: (1) Weigh 2.7g of glucose and 9.46g of melamine respectively. The molar ratio of carbon source to nitrogen source is 1:5. Add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio is 1:1). Stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0061] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain a solid.

[0062] (3) Weigh 5g of solid and add it to 3g of 0.25M dimethylimidazolium-ethanol solution and mix. Then, ball mill the mixture at 400rpm for 1h. Pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep it at 600℃ for 3h to obtain nitrogen-doped organic carbon catalyst (NC).

[0063] Comparative Example 5 The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 0.25:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0064] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0065] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain the catalyst.

[0066] Comparative Example 6 The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 5.4g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:2:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0067] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0068] (3) Weigh 5g of organometallic salt, add 3g of 0.25M dimethylimidazolium-ethanol solution and mix, then ball mill at 400rpm for 1h; pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep at 600℃ for 3h to obtain the catalyst.

[0069] Comparative Example 7 The catalyst preparation method includes the following steps: (1) Weigh out 3g of copper acetate monohydrate, 3.7g of cobalt acetate tetrahydrate (Co:Cu molar ratio of 1:1, total molar amount of metal salt 0.03mol), 2.7g of glucose and 9.46g of melamine, with a metal salt:carbon source:nitrogen source molar ratio of 2:1:5, add them to 500mL of alcohol-water mixed solvent (methanol and water volume ratio of 1:1), stir at 60℃ for 30min to obtain a homogeneous precursor solution.

[0070] (2) The precursor solution was heated and evaporated in an oven at 150°C for 8 hours to obtain the crystalline solid of the organometallic salt.

[0071] (3) Weigh 5g of organometallic salt, add it to 3g of ethanol solution and mix. Then, ball mill the mixture at 400rpm for 1h. Pyrolyze the ball-milled product in N2 atmosphere at a heating rate of 5℃ / min and keep it at 600℃ for 3h to obtain the catalyst.

[0072] Table 1 shows the raw material ratios in the catalyst preparation process of Examples 1-6 and Comparative Examples 1-7. The catalysts prepared above were tested for electrochemical reduction of nitrate under high chlorine and high ammonia nitrogen conditions.

[0073] The catalyst, ethanol, and 5% Nafion solution were mixed at a mass ratio of 1:100:10, ultrasonically dispersed for 30 min, and then sprayed onto pretreated nickel foam. After natural drying, the catalyst-loaded nickel foam was obtained and used as a cathode for the electrochemical reduction of nitrates (4 cm). 2 A Pt sheet electrode was used as the anode, and an Ag / AgCl electrode was used as the reference electrode. The electrocatalytic reduction effect on nitrate was tested using an electrochemical workstation. The test was conducted in an H-type electrolytic cell, with the cathode and anode chambers separated by a cation exchange membrane. Constant current electrolysis (200 mA·cm⁻¹) was performed in 400 mL of simulated high-salt wastewater containing 1.7 M sodium chloride + 0.3 M ammonium chloride + 0.1 M sodium nitrate. -2 Table 3 shows a comparison of the effects after 20 hours of electrolysis.

[0074] To test the stability of the catalyst in Example 1 for the electrochemical reduction of nitrate to ammonia in high-salt wastewater, a continuous long-term test of approximately 1100 hours was conducted, with 36 cycles of electrocatalytic reduction of nitrate to ammonia as described above. The results are shown in Table 2. The nitrate removal rate remained stable at 98% or higher, and the ammonia Faraday efficiency remained stable at 96% or higher, demonstrating excellent stability.

[0075] Table 1. Raw material ratios in Examples 1-6 and Comparative Examples 1-6

[0076] Table 2 Catalytic performance of the catalyst in Example 1 after 36 consecutive cycles

[0077] Table 3 Comparison of electrolysis effects between Examples 1-6 and Comparative Examples 1-7

[0078] like Figure 1 The image shows nickel foam with a catalyst supported in Example 1, prepared in 1.7M sodium chloride + 0.3M ammonium chloride (NO3-free) solutions. - ) and 1.7M sodium chloride + 0.3M ammonium chloride + 0.1M sodium nitrate (containing NO3) - Linear voltammetric scans for the two electrolytes are shown. The graphs reveal a significant increase in current density in the electrolyte containing nitrate, indicating that the catalyst exhibits catalytic reduction of nitrate.

[0079] like Figure 2 The image shown is a scanning electron microscope image of the catalyst in Example 1, combined with... Figure 4 As shown in the XPS analysis spectrum, the present invention has successfully prepared a cobalt-copper bimetallic catalyst supported on a nitrogen-doped carbon substrate, with high contents of pyrrole nitrogen and pyridine nitrogen in the nitrogen element, and Co and Cu anchored on pyridine N / pyrrole N doped carbon.

[0080] like Figure 3 The image shows the Raman spectrum of the nitrogen-doped carbon-based cobalt-copper bimetallic catalyst in Example 1. In the figure, the ratio of the D peak to the G peak (ID / IG) of nitrogen-doped carbon (NC) without metal introduction is 1.07, while the ID / IG ratio of (NC-CoCu) after metal introduction is 1.17. This indicates that the introduction of CoCu metal increases carbon defects, which are beneficial for anchoring metal single atoms and promoting the smooth progress of the electrochemical reduction reaction.

[0081] As shown in Table 3, the catalyst performance in Comparative Examples 1-4 decreased significantly, indicating that the ratio of added Co and Cu metals has a significant impact on catalytic electrolysis performance. The electrochemical reaction from nitrate to ammonia is a multi-step process involving the transfer of eight electrons, requiring the synergistic effect of Cu and Co. Cu is responsible for adsorbing and activating NO3. - And generate NO2 - Co efficiently generates active hydrogen ( And promote NO2 -Deep hydrogenation to NH3 requires an optimal ratio to achieve the best results. In Comparative Example 5, the methanol content in the alcohol-water mixed solvent was too low, resulting in poor catalyst performance. This highlights the importance of controlling the methanol-water solvent ratio. The reason may be that catalyst synthesis requires a solvent with suitable polarity. Low methanol content leads to strong solvent polarity, high catalyst particle surface energy, easy agglomeration, and larger particle size. Conversely, excessive methanol content results in insufficient polarity and poor catalyst crystallinity, which also affects catalytic electrolysis performance. In Comparative Example 6, the molar ratio of metal salt:carbon source:nitrogen source was not within the specified range. Adding too much carbon source may lead to carbon deposition covering the active sites of the catalyst, causing performance degradation. In Comparative Example 7, the lack of dimethylimidazole during the ball milling process resulted in poor catalyst performance. This is because the present invention not only enhances stability by re-anchoring the cobalt-copper bimetallic matrix to the organic carbon matrix using a nitrogen source, but also because dimethylimidazole has strong coordination ability with metals Co and Cu. After pyrolysis, it can generate more pyrrole nitrogen and pyridine nitrogen, resulting in more edge defects and providing more catalytic active sites. Furthermore, it can complement the N-doped configuration of cyanamide-based nitrogen sources, enriching multiple types of nitrogen active sites. The synergistic coupling of multiple active sites significantly improves catalytic activity and stability.

[0082] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a catalyst for electroreduction of nitro-nitrogen to ammonia in high-salinity wastewater, characterized by, The chloride ion concentration in the high-salinity wastewater is 0.6~2.4 mol / L; the preparation of the catalyst includes the following steps: (1) Dissolve the metal salt, carbon source and nitrogen source in a mixed solvent of alcohol and water by stirring to obtain a precursor solution; wherein the metal salt is a cobalt salt and a copper salt, and the molar ratio of Co:Cu is 1~5:1; the nitrogen source is a compound containing a cyanamide group; (2) After evaporating and crystallizing the precursor solution, an organometallic salt is obtained; (3) Add the organometallic salt to a dimethylimidazolium-ethanol solution, ball mill it, and then pyrolyze it in an inert atmosphere to obtain a nitrogen-doped carbon-based cobalt-copper bimetallic catalyst.

2. The method for preparing the catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, characterized in that, The molar ratio of the metal salt, carbon source, and nitrogen source is 1~3:1:

5.

3. The method for preparing the catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, characterized in that, The mass ratio of the nitrogen source to the alcohol-water mixed solvent is 1:60~80.

4. The process for the preparation of a catalyst for the electroreduction of nitro-nitrogen to ammonia in high-salinity wastewater according to claim 1 or 2 or 3, characterized in that, The carbon source is one or more of glucose and soluble starch; the nitrogen source is one or more of cyanamide, dicyandiamide, and melamine.

5. The method for preparing a catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, 2, or 3, characterized in that, The alcohol-water mixed solvent is a mixture of methanol and water in a volume ratio of 0.6 to 1.5:1; the stirring and dissolving temperature is 50-70℃.

6. The method for preparing a catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, 2, or 3, characterized in that, The evaporation and crystallization process takes place at a temperature of 150-160℃ for 6-10 hours.

7. The method for preparing the catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, characterized in that, The concentration of dimethylimidazole in the dimethylimidazole-ethanol solution is 0.15~0.3 M.

8. The method for preparing the catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, characterized in that, The mass ratio of the organometallic salt to the dimethylimidazole-ethanol solution is 1:0.5~1.

9. The method for preparing a catalyst for the electroreduction of nitrate nitrogen to ammonia from high-salt wastewater according to claim 1, 7, or 8, characterized in that, The pyrolysis is performed by heating to 500-700℃ at a rate of 1-5℃ / min and holding at that temperature for 2-4 hours.

10. The application of a catalyst prepared by the method according to any one of claims 1-9 in the electrocatalytic reduction of nitrate to ammonia in high-salinity wastewater, characterized in that, The high-salt wastewater has a chloride ion concentration of 0.6~2.4 mol / L, an ammonia nitrogen concentration of 0.1~0.4 mol / L, and a nitrate ion concentration of ≥40 mmol / L.

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