Carbon-coated nickel-cobalt spinel electrooxidation ammonia-nitrogen wastewater catalyst
A carbon-coated nickel-cobalt spinel catalyst was prepared by combining urea slow-release precipitation with hydrothermal-pyrolysis, which solved the problem of structural instability of traditional catalytic materials in high-salt environments and achieved efficient and environmentally friendly treatment of high-salt ammonia nitrogen wastewater.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGXI UNIV
- Filing Date
- 2026-03-06
- Publication Date
- 2026-04-28
AI Technical Summary
Traditional spinel-type catalytic materials are prone to structural collapse, metal ion loss, and decreased conductivity in high-salt environments, resulting in reduced catalytic activity and shortened service life, making it difficult to effectively treat high-salt ammonia nitrogen wastewater.
A carbon-coated nickel-cobalt spinel catalyst was prepared by combining urea slow-release precipitation with hydrothermal-pyrolysis to form a uniform and dense carbon layer, thereby improving the catalyst's conductivity, corrosion resistance, and stability.
It significantly improves the structural stability and salt corrosion resistance of the catalyst, enhances the efficiency and stability of electrochemical oxidation treatment of high-salt ammonia nitrogen wastewater, and is simple and environmentally friendly.
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Figure CN121927604A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of novel materials for wastewater treatment, specifically to a carbon-coated nickel-cobalt spinel electro-oxidation catalyst for ammonia nitrogen wastewater. Background Technology
[0002] With the acceleration of industrialization, industries such as chemical, pharmaceutical, printing and dyeing, and electroplating generate large amounts of high-salt ammonia nitrogen wastewater. This type of wastewater is characterized by complex organic pollutants, high ionic strength, and difficulty in effective degradation by traditional biological methods. If discharged directly without effective treatment, it will lead to eutrophication of water bodies and imbalance of ecosystems.
[0003] Currently, high-salinity ammonia nitrogen wastewater is mainly treated using methods such as evaporation crystallization, reverse osmosis membrane separation, chemical oxidation, and electrochemical oxidation. Among these, electrochemical oxidation has become an important means of advanced treatment of high-salinity ammonia nitrogen wastewater due to its advantages of mild reaction conditions, strong controllability, and no secondary pollution. However, in the electrochemical oxidation process, the conductivity, stability, and salt resistance of the electrocatalytic material significantly affect the treatment efficiency. Although traditional spinel-type catalytic materials (such as NiCo2O4 and Co3O4) have good redox activity, they are prone to structural collapse, metal ion loss, and decreased conductivity in high-salt environments, leading to decreased catalytic activity and shortened service life.
[0004] To address these issues, researchers have attempted to enhance the stability and electrochemical performance of nickel-cobalt spinel catalysts using composite carbon materials. However, conventional composite carbon materials still suffer from drawbacks such as insufficient exposure of active sites and poor interfacial contact due to uneven coating or loose carbon layer structures. Therefore, developing a method for preparing nickel-cobalt spinel catalysts with stable carbon coating structures, excellent electrical conductivity, good corrosion resistance and cycle stability in high-salt environments is of great significance for improving the efficiency and stability of electrochemical oxidation treatment of high-salt ammonia nitrogen wastewater. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a carbon-coated nickel-cobalt spinel electro-oxidation catalyst for ammonia nitrogen wastewater and its preparation method. By synergistically regulating the metal ion precipitation process and the carbon coating structure, the invention aims to improve the catalyst's conductivity, corrosion resistance, and operational stability, thereby achieving efficient treatment of high-salt ammonia nitrogen wastewater.
[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:
[0007] A carbon-coated nickel-cobalt spinel catalyst utilizes a precipitant that undergoes slow-release decomposition during a hydrothermal reaction, resulting in uniform precipitation of metal ions and preventing agglomeration caused by localized supersaturation. This yields a primary product with fine particle size and good dispersion. High-temperature calcination then yields a nickel-cobalt spinel precursor with good crystallinity. Furthermore, the specific adsorption of metals by biomass carbon is utilized to coat the surface of the precursor. After pyrolysis, a uniform and dense carbon layer forms on the surface of the nickel-cobalt spinel, resulting in a structurally stable and highly conductive carbon-coated nickel-cobalt spinel composite catalyst.
[0008] The method for preparing the carbon-coated nickel-cobalt spinel catalyst as described above includes the following steps:
[0009] (1) Using nickel salt and cobalt salt as metal sources, dissolve them in deionized water at a certain molar ratio, add precipitant, stir to obtain a mixed solution, put the mixed solution into a reaction vessel, carry out the first hydrothermal reaction, cool to room temperature after the reaction is completed, filter, wash and dry, and then calcine the obtained material at high temperature to form a nickel cobalt spinel precursor with good crystallinity.
[0010] (2) The nickel-cobalt spinel precursor obtained in step (1) is mixed with biomass carbon at a certain mass ratio and subjected to a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed and dried. The mixture obtained after the second hydrothermal treatment is placed in a protective atmosphere for pyrolysis, so that biomass carbon is decomposed to generate a carbon layer, thereby forming a uniform, dense and continuous carbon coating layer on the surface of nickel-cobalt spinel particles, and obtaining a carbon-coated nickel-cobalt spinel composite catalyst.
[0011] Preferably, the molar ratio of nickel salt, cobalt salt and precipitant in step (1) is 1:(1~5):(2~10); the first hydrothermal reaction in step (1) is maintained at 120~160 degrees Celsius for 10~14 hours.
[0012] Preferably, the nickel salt in step (1) is one of nickel nitrate, nickel chloride, nickel acetate or nickel citrate; the cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate; and the precipitant is one of urea, sodium hydroxide or ethylenediamine.
[0013] Preferably, the nickel salt in step (1) is nickel nitrate, the cobalt salt is cobalt nitrate, and the precipitant is urea; the first hydrothermal reaction in step (1) is maintained at 120 degrees Celsius for 12 hours.
[0014] Preferably, the high-temperature calcination in step (1) is at a temperature of 350-550 degrees Celsius, and the holding time at this temperature is 1-3 hours, with a heating rate of 1-5 degrees Celsius / minute; the calcination can be carried out in a tube furnace, high-throughput furnace, high-pressure furnace, box furnace or muffle furnace.
[0015] Preferably, the filtration, washing and drying in steps (1) and (2) are all performed by vacuum filtration, followed by washing with deionized water and anhydrous ethanol in sequence, and drying at 40-80 degrees Celsius for 10-16 hours.
[0016] Preferably, in step (2), the mass ratio of nickel-cobalt spinel precursor to biomass carbon is 1:1 to 9; the biomass carbon in step (2) is at least one of glucose, sucrose, fructose, chitosan, cellulose or lignin; the protective atmosphere is nitrogen; and the second hydrothermal reaction in step (2) is carried out at 140 to 180 degrees Celsius for 14 to 24 hours.
[0017] Preferably, the pyrolysis temperature in step (2) is 350~450 degrees Celsius, the holding time at this temperature is 0.5~1 hour, the heating rate is 1~5 degrees Celsius / minute, and the calcination is carried out in a tube furnace.
[0018] The application of carbon-coated nickel-cobalt spinel catalysts in the degradation of high-salt ammonia nitrogen wastewater, as described above.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0020] This invention employs a carbon coating strategy combining urea slow-release precipitation and hydrothermal-pyrolysis. During the reaction, urea slowly decomposes, releasing alkaline components, causing the pH of the system to rise and achieving uniform precipitation of metal ions, resulting in a fine-particle-size, well-dispersed nickel-cobalt spinel precursor. By combining hydrothermal pre-carbonization with high-temperature pyrolysis, a firmly bonded, dense carbon layer is formed on the surface of the nickel-cobalt spinel, effectively inhibiting metal ion loss and crystal phase collapse, significantly improving the catalyst's structural stability and salt corrosion resistance. The catalyst prepared by this method exhibits high conductivity and excellent cycle performance, significantly improving the removal efficiency of ammonia nitrogen and organic pollutants from high-salt ammonia nitrogen wastewater by electrochemical oxidation. Furthermore, this invention is simple, environmentally friendly, and requires no additional chemical reagents, demonstrating promising prospects for industrial application. Attached Figure Description
[0021] Figure 1 This is a flowchart illustrating the preparation process of the catalyst of this invention.
[0022] Figure 2 This is the X-ray diffraction (XRD) pattern of the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 4 of this invention.
[0023] Figure 3 (a) is the Raman spectrum of the nickel-cobalt spinel catalyst prepared in Comparative Example 2 of this invention; Figure 3 (b) is the Raman spectrum of the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 4 of the present invention.
[0024] Figure 4 (a) is a high-resolution transmission electron microscope (HRTEM) image of the nickel-cobalt spinel catalyst prepared in Comparative Example 2 of the present invention; Figure 4 (b) is an HRTEM image of the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 4 of the present invention.
[0025] Figure 5 The graph shows the electrocatalytic oxidation polarization curves (LSV) of ammonia nitrogen wastewater prepared by the catalysts in all examples and comparative examples.
[0026] Figure 6 This is a graph showing the degradation performance of high-salt ammonia nitrogen wastewater by the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 4 of this invention.
[0027] Figure 7 This is a graph showing the degradation performance of high-salt ammonia nitrogen wastewater by the nickel-cobalt spinel catalyst prepared in Comparative Example 2 of this invention. Detailed Implementation
[0028] The following detailed description, in conjunction with the accompanying drawings, outlines specific embodiments. However, it should be understood that the scope of protection of this invention is not limited to these specific embodiments. Unless otherwise specified, all raw materials and reagents used in the examples are commercially available.
[0029] Example 1
[0030] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0031] (1) Dissolve 1.0 mmol nickel chloride, 1.0 mmol cobalt nitrate and 2.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 150 degrees Celsius for the first hydrothermal reaction for 10 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours. Transfer the dried solid powder to an alumina crucible and place it in a tube furnace. Keep the heating rate at 5 degrees Celsius / minute and calcine at 400 degrees Celsius for 2 hours to form a nickel cobalt spinel precursor with good crystallinity.
[0032] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1), add it to 35mL of deionized water along with 2.0g of glucose and 2.0g of fructose, and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor, and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 140 degrees Celsius and maintain it for 18 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature and take... The obtained substance was subjected to vacuum filtration and washed successively with deionized water and anhydrous ethanol until the filtrate was neutral. The washed substance was dried at 60 degrees Celsius for 12 hours. Subsequently, the dried solid powder was transferred to an alumina crucible and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was raised at a rate of 5 degrees Celsius / minute and pyrolyzed at 400 degrees Celsius for 0.5 hours to decompose biomass carbon and generate a carbon layer. This resulted in a uniform, dense, and continuous carbon coating layer on the surface of the nickel-cobalt spinel particles, thus obtaining a carbon-coated nickel-cobalt spinel composite catalyst.
[0033] Example 2
[0034] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0035] (1) Dissolve 1.0 mmol nickel nitrate, 1.0 mmol cobalt acetate and 4.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 140 degrees Celsius for the first hydrothermal reaction for 12 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours. Transfer the dried solid powder to an alumina crucible and place it in a muffle furnace. Keep the heating rate at 5 degrees Celsius / minute and calcine at 450 degrees Celsius for 2 hours to form a nickel cobalt spinel precursor with good crystallinity.
[0036] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1) and 2.0g of glucose, add them to 35mL of deionized water, and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor, and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 150 degrees Celsius and maintain it for 20 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature and take out the product. The material was subjected to vacuum filtration and washed sequentially with deionized water and anhydrous ethanol until the filtrate was neutral. The washed material was then dried at 60°C for 12 hours. Subsequently, the dried solid powder was transferred to an alumina crucible and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was maintained at a rate of 5°C / min and pyrolyzed at 450°C for 0.75 hours to decompose the biomass carbon and generate a carbon layer. This resulted in a uniform, dense, and continuous carbon coating layer on the surface of the nickel-cobalt spinel particles, thus obtaining a carbon-coated nickel-cobalt spinel composite catalyst.
[0037] Example 3
[0038] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0039] (1) Dissolve 1.0 mmol nickel acetate, 3.0 mmol cobalt sulfate and 6.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution in a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 130 degrees Celsius for the first hydrothermal reaction for 13 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours. Transfer the dried solid powder to an alumina crucible and place it in a box furnace. Keep the heating rate at 5 degrees Celsius / minute and calcine at 450 degrees Celsius for 3 hours to form a nickel cobalt spinel precursor with good crystallinity.
[0040] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1), and add it to 35mL of deionized water along with 2.0g of fructose and 2.0g of lignin. Stir magnetically to obtain a mixed solution. Place the mixed solution into a stainless steel reactor lined with polytetrafluoroethylene. Then place the reactor in a forced-air drying oven and raise the temperature in the oven to 160 degrees Celsius and maintain it for 20 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature. The obtained substance was removed and filtered under reduced pressure. It was washed sequentially with deionized water and anhydrous ethanol until the filtrate was neutral. The washed substance was dried at 60 degrees Celsius for 12 hours. Subsequently, the dried solid powder was transferred to an alumina crucible and placed in a tube furnace. The furnace was pyrolyzed at 450 degrees Celsius for 1 hour under a nitrogen atmosphere at a heating rate of 5 degrees Celsius / minute. This process decomposed biomass carbon to generate a carbon layer, thereby forming a uniform, dense, and continuous carbon coating layer on the surface of the nickel-cobalt spinel particles, thus obtaining a carbon-coated nickel-cobalt spinel composite catalyst.
[0041] Example 4
[0042] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0043] (1) Dissolve 1.0 mmol nickel nitrate, 2.0 mmol cobalt nitrate and 5.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 120 degrees Celsius for the first hydrothermal reaction for 12 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours. Transfer the dried solid powder to an alumina crucible and place it in a tube furnace. Keep the heating rate at 5 degrees Celsius / minute and calcine at 400 degrees Celsius for 2 hours to form a nickel cobalt spinel precursor with good crystallinity.
[0044] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1) and 4.0g of lignin, add them to 35mL of deionized water, and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor, and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 170 degrees Celsius and maintain it for 22 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature and take out the obtained material for further processing. The sample was filtered under reduced pressure and washed sequentially with deionized water and anhydrous ethanol until the filtrate was neutral. The washed material was then dried at 60°C for 12 hours. The dried solid powder was then transferred to an alumina crucible and placed in a tube furnace. Pyrolysis was performed at 350°C for 2 hours under a nitrogen atmosphere, maintaining a heating rate of 5°C / min. This process decomposed biomass carbon to generate a carbon layer, forming a uniform, dense, and continuous carbon coating on the surface of the nickel-cobalt spinel particles, thus obtaining a carbon-coated nickel-cobalt spinel composite catalyst (X-ray diffraction pattern as shown). Figure 2 As shown, due to the low crystallinity of the carbon layer, its diffraction peaks are broad peaks at around 20 degrees. Figure 3 The presence of a carbon layer was detected by Raman spectroscopy. The samples before and after coating were characterized by transmission electron microscopy, such as... Figure 4 As shown, an amorphous carbon layer of about 2 nm appears on the surface of the carbon-coated nickel-cobalt spinel catalyst.
[0045] Example 5
[0046] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0047] (1) Dissolve 1.0 mmol nickel citrate, 1.0 mmol cobalt carbonate and 2.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 160 degrees Celsius for the first hydrothermal reaction for 10 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours. Transfer the dried solid powder to an alumina crucible and place it in a tube furnace. Keep the heating rate at 5 degrees Celsius / minute and calcine at 500 degrees Celsius for 2 hours to form a nickel cobalt spinel precursor with good crystallinity.
[0048] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1) and 4.0g of chitosan, add them to 35mL of deionized water, and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor, and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 180 degrees Celsius and maintain it for 24 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature and take out the obtained solution. The material was subjected to vacuum filtration and washed sequentially with deionized water and anhydrous ethanol until the filtrate was neutral. The washed material was then dried at 60°C for 12 hours. Subsequently, the dried solid powder was transferred to an alumina crucible and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was maintained at a rate of 5°C / min and pyrolyzed at 400°C for 1 hour to decompose the biomass carbon and generate a carbon layer. This resulted in a uniform, dense, and continuous carbon coating layer on the surface of the nickel-cobalt spinel particles, thus obtaining a carbon-coated nickel-cobalt spinel composite catalyst.
[0049] Comparative Example 1
[0050] A method for preparing a carbon-coated nickel-cobalt spinel catalyst, comprising the following steps:
[0051] (1) Dissolve 1.0 mmol nickel chloride, 1.0 mmol cobalt nitrate and 2.0 mmol urea in 35 ml deionized water and stir magnetically to obtain a mixed solution. Place the mixed solution into a polytetrafluoroethylene-lined stainless steel reactor and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 150 degrees Celsius for the first hydrothermal reaction for 10 hours. After the reaction is completed, cool to room temperature, take out the substance obtained after the reaction and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in turn until the filtrate is neutral. Dry the substance obtained after washing at 60 degrees Celsius for 12 hours.
[0052] Step (2) is the same as in Example 1.
[0053] Comparative Example 2
[0054] (1) Step (1) is the same as in Example 4;
[0055] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1) and add it to 35mL of deionized water. Stir magnetically to obtain a mixed solution. Place the mixed solution into a stainless steel reactor lined with polytetrafluoroethylene. Then place the reactor in a forced-air drying oven and raise the temperature in the forced-air drying oven to 160 degrees Celsius and maintain it for 18 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment, so that biomass carbon is initially deposited on the catalyst surface to form a carbon precursor layer. After the reaction is completed, cool to room temperature, take out the obtained material and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in sequence until the filtrate is neutral. Place the washed material at 60 degrees Celsius and dry for 12 hours. Then, transfer the dried solid powder to an alumina crucible and place it in a tube furnace. In a nitrogen atmosphere, maintain the heating rate at 5 degrees Celsius / minute and pyrolyze at 350 degrees Celsius for 2 hours to obtain nickel-cobalt spinel.
[0056] Comparative Example 3
[0057] (1) Step (1) in this comparative example is the same as in Example 4.
[0058] (2) Weigh 1.0g of the nickel-cobalt spinel precursor obtained in step (1) and 4.0g of lignin (biomass carbon source), add 35mL of deionized water, and stir magnetically to obtain a mixed solution. Place the mixed solution in a polytetrafluoroethylene-lined stainless steel reactor, and then place the reactor in a forced-air drying oven. Raise the temperature in the forced-air drying oven to 170 degrees Celsius and maintain it for 22 hours to carry out a second hydrothermal reaction to achieve pre-carbonization treatment. After the reaction is completed, cool to room temperature, take out the obtained material and filter under reduced pressure. Wash with deionized water and anhydrous ethanol in sequence until the filtrate is neutral. Place the washed material at 60 degrees Celsius and dry for 12 hours to obtain carbon-coated nickel-cobalt spinel catalyst.
[0059] Comparative Example 4
[0060] In this comparative example, the urea precipitant in step (1) is replaced with sodium hydroxide, and the rest of the operation is the same as in Example 4.
[0061] Comparative Example 5
[0062] In this comparative example, the urea precipitant in step (1) was replaced with ethylenediamine, and the rest of the operation was the same as in Example 4.
[0063] The nickel-cobalt spinel catalysts and carbon-coated nickel-cobalt spinel catalysts prepared in Examples 1-5 and Comparative Examples 1-5 of this invention were applied to the electrochemical oxidation treatment of high-salt ammonia nitrogen wastewater under uniform testing conditions. The specific testing methods are as follows:
[0064] (1) The prepared catalyst and Ketjen black were mixed and dispersed in 10 ml of N-methylpyrrolidone solution at a mass ratio of 4:6 (total mass of 100 mg) and ground to prepare a slurry. The slurry was then uniformly sprayed onto a square titanium plate with a diameter of 2 cm.
[0065] (2) The test conditions are as follows: The catalysts prepared in each example and the comparative example are used as anodes, and pure titanium plates are used as cathodes. The anodes and cathodes are installed in an electrocatalytic oxidation device and applied to the electrochemical oxidation treatment of landfill leachate wastewater. The distance between the plates is 5 mm, and the temperature and pressure are normal. The catalysts prepared in Example 4 and Comparative Example 2 are used to test the degradation efficiency of high-salt ammonia nitrogen wastewater (high-salt ammonia nitrogen wastewater is prepared by dissolving ammonium chloride in deionized water, with a composition of 17.5 g / L NaCl and 4.6 g / L NH3-N, of which ammonia nitrogen is provided by ammonium chloride). The time-current program is used and the degradation is carried out at a voltage of 3.0 V for 6 hours. The ammonia nitrogen value in the water sample is analyzed every 1 hour.
[0066] Figure 5 The graphs show the electrocatalytic oxidation polarization (LSV) curves of ammonia nitrogen wastewater prepared by the catalysts in all examples and comparative examples. As can be seen from the graphs, the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 4 exhibits superior oxidation performance compared to the other catalysts. Specifically, at 3.0 V, the catalyst in Example 4 achieved 161 mA / cm². 2 The current density of the nickel-cobalt spinel prepared in Comparative Example 2 was only 62 mA / cm². 2 The results showed significant differences. Comparative Examples 4 and 5, prepared using sodium hydroxide and ethylenediamine as precipitants respectively, exhibited lower catalytic performance than Example 4, which used urea as a precipitant. This indicates that the slow-release decomposition of urea helps achieve uniform precipitation of metal ions, resulting in a precursor with fine particle size and good dispersion, providing a good foundation for the uniform formation of the carbon coating layer. Therefore, the carbon-coated nickel-cobalt spinel electro-oxidation catalyst for ammonia nitrogen wastewater effectively improves the efficiency of electrocatalytic oxidation of ammonia nitrogen wastewater. However, when the carbon content in the carbon coating is too high (as in the carbon-coated nickel-cobalt spinel composite catalyst prepared in Example 5), the current density decreases, dropping to 133 mA / cm². 2 Therefore, it can be concluded that the carbon layer thickness within an appropriate range can improve catalytic performance.
[0067] Figure 6 and Figure 7The results of ammonia nitrogen electrochemical oxidation degradation performance and cycle stability tests are shown for the carbon-coated nickel-cobalt spinel composite catalyst and the nickel-cobalt spinel catalyst prepared in Example 4 and Comparative Example 2, respectively. The data show that the carbon-coated catalyst of Example 4 maintains good catalytic activity after multiple cycles, while Comparative Example 2 shows a significant decrease in catalytic efficiency. This indicates that the carbon layer coating on the surface of nickel-cobalt spinel can improve the operational stability of the catalyst.
[0068] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.
Claims
1. A carbon-coated nickel-cobalt spinel catalyst, characterized in that: A precipitant is used to decompose the metal ions during the hydrothermal reaction, and the precursor is obtained by high-temperature calcination. Then, biomass carbon is used to coat the metal surface, and after pyrolysis, a carbon layer is formed on the surface of the nickel-cobalt spinel to obtain a carbon-coated nickel-cobalt spinel composite catalyst.
2. The method for preparing the carbon-coated nickel-cobalt spinel catalyst as described in claim 1, characterized in that, The operation includes the following steps: (1) Using nickel salt and cobalt salt as metal sources, dissolve them in water at a certain molar ratio, add precipitant, stir to obtain a mixed solution, put the mixed solution into a reaction vessel, carry out the first hydrothermal reaction, filter, wash and dry after the reaction is completed, and then calcine the obtained material at high temperature to form nickel cobalt spinel precursor; (2) The nickel-cobalt spinel precursor obtained in step (1) is mixed with biomass carbon at a certain mass ratio and subjected to a second hydrothermal reaction. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed and dried. The mixture obtained after the second hydrothermal treatment is placed in a protective atmosphere for pyrolysis to obtain carbon-coated nickel-cobalt spinel composite catalyst.
3. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: In step (1), the molar ratio of nickel salt, cobalt salt, and precipitant is 1:(1~5):(2~10); the first hydrothermal reaction in step (1) is carried out at 120~160 degrees Celsius for 10~14 hours.
4. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: The nickel salt mentioned in step (1) is one of nickel nitrate, nickel chloride, nickel acetate or nickel citrate; the cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate; the precipitant is one of urea, sodium hydroxide or ethylenediamine.
5. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: The nickel salt mentioned in step (1) is nickel nitrate, the cobalt salt is cobalt nitrate, and the precipitant is urea; the first hydrothermal reaction mentioned in step (1) is maintained at 120 degrees Celsius for 12 hours.
6. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: The high-temperature calcination in step (1) is at a temperature of 350~550 degrees Celsius, and is held at this temperature for 1~3 hours with a heating rate of 1~5 degrees Celsius / minute. The calcination can be carried out in a tube furnace, high-throughput furnace, high-pressure furnace, box furnace or muffle furnace.
7. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: The filtration, washing and drying described in steps (1) and (2) are all performed by vacuum filtration, followed by washing with deionized water and anhydrous ethanol in sequence, and drying at 40-80 degrees Celsius for 10-16 hours.
8. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: In step (2), the mass ratio of nickel-cobalt spinel precursor to biomass carbon is 1:1 to 9; the biomass carbon mentioned in step (2) is at least one of glucose, sucrose, fructose, chitosan, cellulose or lignin; the protective atmosphere is nitrogen; the second hydrothermal reaction mentioned in step (2) is carried out at 140 to 180 degrees Celsius for 14 to 24 hours.
9. The method for preparing the carbon-coated nickel-cobalt spinel catalyst according to claim 2, characterized in that: The pyrolysis temperature in step (2) is 350~450 degrees Celsius, the holding time at this temperature is 0.5~1 hour, the heating rate is 1~5 degrees Celsius / minute, and the calcination is carried out in a tube furnace.
10. The application of the carbon-coated nickel-cobalt spinel catalyst as described in claim 1 or the carbon-coated nickel-cobalt spinel catalyst prepared by any of the methods in claims 2-9 in the degradation of high-salt ammonia nitrogen wastewater.