Synthesis method and application of Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalyst for enhancing reduction of nitrate into ammonia

Abstract

The invention discloses a synthesis method and application of a Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalyst for enhancing reduction of nitrate into ammonia, and relates to MOF catalyst preparation, and the synthesis method is characterized by comprising the following steps: S1, dissolving cupric acetate monohydrate and nickel acetate tetrahydrate or zinc acetate dihydrate in ultrapure water to prepare a solution A; s2, dissolving 2, 3, 6, 7, 10, 11-hexahydroxy tribenzene and ammonia water into N, N-dimethylformamide (DMF), so as to obtain a solution B; s3, mixing the solution A and the solution B, and performing ultrasonic treatment for 10-30 minutes to prepare a solution C; and S4, heating the solution C in an isothermal oven at 85 DEG C for 1-3 hours, naturally cooling to room temperature, respectively washing with deionized water and acetone for 6 times, and finally drying in a vacuum oven at 60 DEG C to obtain a dark blue crystal. The Cu / Zn and Cu / Ni bimetallic conductive MOF prepared by the method has high specific surface area, and the prepared electrode has high responsivity to nitrate ions, has a remarkable nitrate removal effect, has high removal efficiency and has high ammonia selectivity.

Description

Technical Field

[0001] The present invention relates to the preparation of MOF catalysts, and more particularly to a synthesis method and application of Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalysts for enhancing the reduction of nitrates to ammonia. Background Art

[0002] With the abuse of industrial production and nitrogen-containing fertilizers, nitrate pollution in water bodies has become increasingly serious. The enrichment of nitrates can easily cause water quality to deteriorate and destroy the balance of the ecological environment. Nitrates in drinking water enter the human body, destroy the oxygen transport mechanism of red blood cells, cause methemoglobinemia, and endanger human health. Ammonia (NH3), as a high-value-added chemical, plays an indispensable role in maintaining the continuous development of the social economy and population growth. If the nitrate pollutants in the water can be converted into high-value-added ammonia in an efficient and clean way, the recycling of waste can be achieved, which will not only greatly alleviate the pressure of nitrate pollution, but also meet the high demand for ammonia.

[0003] Traditional technology:

[0004] The methods for removing nitrate from water are mainly divided into physical and chemical technology, biological denitrification technology, and chemical reduction technology.

[0005] (1) Physical and chemical technologies mainly include: adsorption, membrane separation technology and ion exchange technology. 1. The adsorption process refers to the process in which soluble compounds in a solution gather on an appropriate barrier to separate the solute from the solution. The adsorption method for removing nitrates is a method of using porous materials with high specific surface areas such as zeolite, activated carbon, and molecular sieves to adsorb nitrates in water onto corresponding materials. 2. Membrane separation technology refers to the technology of achieving selective separation of a mixture of molecules of different particle sizes at the molecular level when passing through a semipermeable membrane. 3. The main principle of ion exchange technology is that when nitrate wastewater passes through an ion exchange resin, the nitrate ions in the wastewater are exchanged with the bicarbonate ions or chloride ions in the exchange resin, and the nitrate ions are transferred from the wastewater to the resin and thus removed.

[0006] (2) Biological denitrification technology refers to the process in which organic nitrogen and inorganic nitrogen in sewage are converted into nitrogen gas through ammoniation, nitrification and denitrification under the action of microorganisms. Denitrification is the most important process in treating nitrate sewage. In an anaerobic or anoxic environment, denitrifying bacteria use NO 3- or NO 2- It acts as the final electron acceptor to complete respiration, reducing nitrate to nitrogen gas.

[0007] (3) Chemical reduction technology refers to the process of reducing nitrate nitrogen in water to nitrite nitrogen by adding a reducing agent to the water body, and then further reducing it to nitrogen gas or ammonia nitrogen. Due to the different types of reducing agents, it can be divided into active metal reduction method and catalytic reduction method.

[0008] Electrocatalytic nitrate reduction technology:

[0009] Electrochemical catalysis is a catalytic process that accelerates the reaction by moving charges at the interface of electrodes and electrolytes. Electrocatalytic nitrate reduction (NO3-RR) is a complex multi-electron transfer process with multiple possible reaction pathways. In the process of nitrate reduction to ammonia, nitrogen changes from a high valence state of +5 (NO3 - ) to the low-valent state (NH3) of -3. In addition to ammonia, the reaction pathway can also produce NO2 - , NO, N2O, N2, NH2OH and a series of nitrogen-containing intermediates. Among them, N2 and NH3 have the highest stability, and electrocatalytic nitrate reduction also mostly uses N2 and NH3 as the final products.

[0010] The traditional Haber-Bosch ammonia synthesis method mainly uses high-purity N2 and H2 as raw materials, and is completed under the catalysis of iron-based catalysts in a high temperature (400-550°C) and high pressure (15-30MPa) environment.

[0011] However, traditional nitrate removal methods have the following main disadvantages:

[0012] (1) Physical and chemical technologies mainly include: adsorption, membrane separation and ion exchange. 1. The definition of adsorption is: it does not really remove nitrates, but only transfers pollutants from the water body to the adsorbent. It has poor selectivity for pollutants, and the adsorbent material needs to be frequently replaced during the working process to ensure the smooth progress of the adsorption process. 2. Disadvantages of membrane separation technology: Membrane separation technology has no selectivity for nitrates. Its principle is to remove all inorganic ions in the water, but the high-concentration inorganic salt wastewater produced is easy to cause secondary pollution. The treatment of these wastewaters will increase the treatment cost. Therefore, from the perspective of operability and treatment cost, membrane separation technology is less practical for removing nitrates from water. 3. Disadvantages of ion exchange technology: When there are high concentrations of other polluting competing ions in the solution, its efficiency in removing nitrates will be greatly reduced. At the same time, ion exchange resin regeneration is troublesome and requires a large amount of eluent, so ion exchange is not the most ideal method for removing nitrates from sewage.

[0013] (2) Biological denitrification technology is currently widely used in nitrate removal. However, the biological denitrification process has high requirements for external conditions such as dissolved oxygen concentration, external carbon source, carbon-nitrogen ratio, pH value, temperature, etc. The treatment time is long and the area occupied is large. A large amount of sludge will be generated during the treatment process and needs to be further treated. In addition, microbial leakage is likely to occur during the treatment process, causing secondary pollution of the water body.

[0014] (3) Chemical reduction technology is divided into active metal reduction and catalytic reduction. 1. Active metal reduction: Although it has high activity and surface area, it is an extremely unstable form and easily reacts with oxygen in air and water. Its reduction efficiency is also affected by other ions in water (Cl - , Ca 2+ 2. Catalytic reduction: Since H2, as a reducing agent, has strong reducing properties and can react under mild conditions, and the reduction product will not cause secondary water pollution, catalytic hydrogenation technology is considered to be the most promising water denitrification process. However, the passivation and deactivation of the catalyst and the control of the selectivity of the reduction product are still the limitations of the development of this technology.

[0015] Among the existing electrocatalytic nitrate reduction catalysts, the specific surface area of ​​the catalyst is small and the stability is poor, which makes it difficult to adapt to the complex environment of nitrate removal in water. Although the stability and specific surface area have been improved after the introduction of metal organic framework (MOF), the conductivity of the traditional MOF is poor, which affects the efficiency of electrocatalytic nitrate removal. For example, Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalysts are also commonly used for electrocatalytic nitrate reduction to ammonia. The synthesis method of the traditional Cu / Ni bimetallic conductive MOF is as follows:

[0016] 7.2mmolCu(NO3)23H2O and Ni(NO3)26H2O in different molar ratios were dissolved in 10mL DMF (solution A), 4.8mmolH3BTC and 0.43gPVP were dissolved in another 10mL DMF (solution B), then solution B was added to solution A and magnetically stirred for 30min, then the mixture was transferred to a 50mL stainless steel autoclave and stored at 150℃ for 1.5h, the blue-green precipitate was collected by centrifugation, washed with anhydrous ethanol 3 times, and dried at 60℃ for 12h. For CuBTC, the synthesis conditions were the same, except that the solvothermal temperature was reduced to 120℃ to avoid the generation of Cu2O impurities, and CuNi / NC catalysts with different Cu-Ni molar ratios were obtained by pyrolysis of CuNiBTC precursor in a nitrogen atmosphere. Typically, 300mgCuNiBTCMOF was placed in a porcelain boat and annealed at 800℃ for 1h with a heating rate of 5℃ / min. After cooling to room temperature, a black CuNi / NC catalyst was obtained.

[0017] The synthesis method of Cu / Zn bimetallic conductive MOF refers to a Chinese patent with publication number CN118325110A, which discloses a Zn-Cu bimetallic MOF material, a Cu-based carbon material, and a preparation method and application thereof, which comprises ultrasonically treating a solution containing a copper source, a zinc source and an imidazole ligand, and heat-treating the solution after ultrasonic treatment.

[0018] However, the Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalysts prepared by traditional synthesis methods have poor conductivity, which affects the efficiency of electrocatalytic nitrate removal.

[0019] The traditional ammonia synthesis method, the Haber-Bosch method, requires external conditions such as high temperature and high pressure. It has a huge demand for energy such as coal and natural gas, and is accompanied by the emission of greenhouse gases such as CO2. It also puts great pressure on the environment, creating tremendous pressure on achieving the goals of carbon peak and carbon neutrality.

[0020] Therefore, the prior art has the following deficiencies:

[0021] Traditional nitrate removal technology has the disadvantages of poor removal efficiency, poor selectivity for nitrate, insufficient cleanliness, and unstable removal process; the catalyst in the electrocatalytic nitrate removal technology has poor stability, small specific surface area, and poor conductivity of MOF-based catalysts; the traditional ammonia synthesis method Haber-Bosch method has high requirements for high temperature and pressure, high energy consumption, produces a large amount of greenhouse gases, puts great pressure on the environment, and is inefficient.

[0022] Therefore, a new solution needs to be proposed to solve this problem. Summary of the invention

[0023] In view of the shortcomings of the prior art, the object of the present invention is to provide a synthesis method and application of Cu / Ni and Cu / Zn bimetallic conductive MOF-based catalysts for enhancing the reduction of nitrate to ammonia.

[0024] The above technical objectives of the present invention are achieved through the following technical solutions: A method for synthesizing a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia, comprising the following steps:

[0025] S1: dissolving cupric acetate monohydrate and nickel acetate tetrahydrate or zinc acetate dihydrate in ultrapure water to prepare solution A;

[0026] S2: dissolving 2,3,6,7,10,11-hexahydroxytriphenyl and ammonia water in N,N-dimethylformamide (DMF) to prepare solution B;

[0027] S3: Solution A and solution B are mixed and ultrasonicated for 10 to 30 minutes to obtain solution C;

[0028] S4: Solution C was heated in an isothermal oven at 85°C for 1-3 h, and then naturally cooled to room temperature, washed with deionized water and acetone for 6 times, and finally dried in a vacuum oven at 60°C to obtain dark blue crystals;

[0029] When nickel acetate tetrahydrate is used in step S1, the dark blue crystals prepared and synthesized are Cu / Ni bimetallic conductive MOF-based catalysts; when zinc acetate dihydrate is used in step S1, the dark blue crystals prepared and synthesized are Cu / Zn bimetallic conductive MOF-based catalysts.

[0030] An application of a Cu / Ni or Cu / Zn bimetallic conductive MOF-based catalyst for enhancing the reduction of nitrate to ammonia, wherein the Cu / Ni or Cu / Zn bimetallic conductive MOF prepared by the synthesis method according to claim 1 is used as a catalyst.

[0031] The present invention is further configured to use Cu / Ni or Cu / Zn bimetallic conductive MOF for electrocatalytic reduction of nitrate to ammonia.

[0032] The present invention is further configured as follows: the specific steps of electrocatalytic reduction of nitrate to ammonia by Cu / Ni or Cu / Zn bimetallic conductive MOF are as follows:

[0033] A1: preparing a catalyst to form a catalyst ink;

[0034] A2: Apply the catalyst ink dropwise onto carbon paper, dry it at room temperature, and then drop Nafion reagent onto the carbon paper;

[0035] A3: Carbon paper is made into a carbon paper electrode (CC), and the carbon paper electrode (CC), saturated calomel electrode (SCE) and graphite rod are used as the working electrode, reference electrode and counter electrode respectively, and electrocatalysis is carried out in a three-electrode electrochemical reaction cell to reduce nitrate to ammonia.

[0036] The present invention is further configured as follows: the specific step of A1 is: mixing the catalyst, superconductive carbon black (SCCB), N,N-dimethylformamide (DMF) and ultrapure water, and obtaining the catalyst ink after ultrasonic treatment for 10 to 40 minutes.

[0037] The present invention is further configured as follows: after the catalyst, superconductive carbon black (SCCB), N,N-dimethylformamide (DMF) and ultrapure water in step A1 are mixed, they are stirred and mixed by a magnetic stirrer.

[0038] In summary, the present invention has the following beneficial effects: the Cu / Zn and Cu / Ni bimetallic conductive MOFs prepared by the present invention have a high specific surface area, and the prepared electrodes have a high response to nitrate ions, a significant nitrate removal effect, a high removal efficiency, and a relatively high selectivity for ammonia. In the process, no waste gas or toxic gas is produced, which complies with clean production, realizes the conversion from nitrate pollutants to high value-added ammonia, removes nitrate pollutants in water bodies, and produces high value-added ammonia chemicals, realizing the recycling of waste resources, which is in line with the concept of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Microscopic diagram of Cu1Zn1 / HHTP Figure 1 ;

[0040] Figure 2 Microscopic diagram of Cu1Zn1 / HHTP Figure 2 ;

[0041] Figure 3 Microscopic diagram of Cu1Zn1 / HHTP Figure 3 ;

[0042] Figure 4 Microscopic diagram of Cu1Zn1 / HHTP Figure 4 ;

[0043] Figure 5 Microscopic diagram of Cu2Ni1 / HHTP Figure 1 ;

[0044] Figure 6 Microscopic diagram of Cu2Ni1 / HHTP Figure 2 ;

[0045] Figure 7 Microscopic diagram of Cu2Ni1 / HHTP Figure 3 ;

[0046] Figure 8 Microscopic diagram of Cu2Ni1 / HHTP Figure 4 ;

[0047] Fig. 9 This is a diagram of the experimental setup;

[0048] Fig.10 is a conversion pathway diagram of nitrate under the action of the designed catalyst;

[0049] Fig.11 This is the LSV curve of Cu1Zn1 / HHTP, which proves that its current is clear in nitrate solution and its catalytic effect is obvious;

[0050] Fig.12This is the LSV curve of Cu2Ni1 / HHTP, which proves that its current is clear in nitrate solution and its catalytic effect is obvious;

[0051] Fig.13 The contents of each component in the electrocatalytic nitrate reduction for 10 h (a) Cu1Zn1 / HHTP, (b) Cu2Ni1 / HHTP prove that in actual nitrate wastewater, this design has a higher nitrate removal efficiency and ammonia yield. DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0053] Embodiment 1:

[0054] A method for synthesizing a Cu / Zn bimetallic conductive MOF for enhancing nitrate reduction to ammonia comprises the following steps:

[0055] S1: copper acetate monohydrate (40 mg, 0.2 mmol) and zinc acetate dihydrate (43.9 mg, 0.2 mmol) were dissolved in 5 mL of ultrapure water, and stirred and mixed by a magnetic stirrer to increase the diffusion rate during the reaction, thereby preparing solution A;

[0056] S2: 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP, 65 mg, 0.2 mmol) and 0.12 mL of aqueous ammonia were dissolved in 5 mL of N,N-dimethylformamide (DMF), and stirred and mixed by a magnetic stirrer to increase the diffusion rate during the reaction, to prepare solution B;

[0057] S3: Solution A and solution B were mixed and ultrasonicated for 20 min to obtain solution C;

[0058] S4: Solution C was heated in an isothermal oven at 85°C for 2 h. After cooling naturally to room temperature, it was washed with deionized water and acetone for 6 times respectively; then dried in a vacuum oven at 60°C for 24 h to obtain a dark blue crystalline Cu1Zn1 / HHTP conductive MOF.

[0059] Similarly, different ratios of Cu / Zn can be used to obtain Cu x Zn y / HHTP conductive MOF, (where x and y are the ratios of different metals, respectively).

[0060] like Figure 1-4As shown in the figure, the surface morphology and microstructure of the catalyst were characterized by SEM and XRD. The Cu and Zn metals were completely and evenly attached to the surface of the carrier to form a spherical structure with a dendritic surface, which greatly increased the metal active sites and the specific surface area of ​​the catalyst, providing sufficient adsorption sites for the electrocatalytic nitrate reduction.

[0061] Embodiment 2:

[0062] A method for synthesizing a Cu / Ni bimetallic conductive MOF for enhancing nitrate reduction to ammonia comprises the following steps:

[0063] S1: copper acetate monohydrate (40 mg, 0.2 mmol) and nickel acetate tetrahydrate (50 mg, 0.2 mmol) were dissolved in 5 mL of ultrapure water, and stirred and mixed by a magnetic stirrer to increase the diffusion rate during the reaction, thereby preparing solution A;

[0064] S2: 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP, 65 mg, 0.2 mmol) and 0.12 mL of aqueous ammonia were dissolved in 5 mL of N,N-dimethylformamide (DMF), and stirred and mixed by a magnetic stirrer to increase the diffusion rate during the reaction, to prepare solution B;

[0065] S3: Solution A and solution B were mixed and ultrasonicated for 20 min to obtain solution C;

[0066] S4: Solution C was heated in an isothermal oven at 85°C for 2 h. After cooling naturally to room temperature, it was washed with deionized water and acetone for 6 times respectively; then dried in a vacuum oven at 60°C for 24 h to obtain a crystalline Cu1Ni1 / HHTP conductive MOF.

[0067] Similarly, by using different ratios of Cu / Ni, different ratios of Cu can be obtained. x Ni y / HHTP conductive MOF, (where x and y are the ratios of different metals, respectively).

[0068] like Figure 5-8 As shown in the figure, after SEM and XRD morphology and structural analysis, it has a good adhesion effect on cMOF, which increases the exposed metal active sites.

[0069] Embodiment three:

[0070] An application of a Cu / Zn bimetallic conductive MOF for enhancing the reduction of nitrate to ammonia, using the Cu / Zn bimetallic conductive MOF prepared by the synthesis method of Example 1 as a catalyst for electrocatalytic reduction of nitrate to ammonia, and the specific steps are as follows:

[0071] A1: 2 mg of catalyst, 0.4 g of superconductive carbon black (SCCB), 250 uL of DMF and 250 uL of ultrapure water were mixed, stirred and mixed by a magnetic stirrer to increase the diffusion rate during the reaction, and the catalyst ink was obtained after ultrasonic treatment for 30 min;

[0072] A2: Then, 30uL of the catalyst ink was dripped onto a 0.5cm×0.5cm carbon paper twice, dried at room temperature, and 15uL of Nafion reagent was dripped onto the carbon paper;

[0073] A3: Carbon paper is made into a carbon paper electrode (CC), and the carbon paper electrode (CC), saturated calomel electrode (SCE) and graphite rod are used as the working electrode, reference electrode and counter electrode respectively. Fig. 9 As shown, electrocatalysis was carried out in a three-electrode electrochemical reaction cell with a capacity of 150 mL and monitored under an electrochemical workstation system to reduce nitrate to ammonia. The conversion pathway of nitrate under the action of the designed catalyst is shown in Fig.10 shown.

[0074] like Fig.11 As shown in the figure, after LSV and other electrochemical characterizations, Cu1Zn1 / HHTP was pre-screened as the best metal ratio. After comparing the catalytic performance of various catalysts under different cathode potential conditions, it was confirmed that Cu1Zn1 / HHTP was the ratio with the best catalytic performance. After adjusting the reaction conditions, the highest ammonia yield of the catalyst was 227.8umolh-1 at the cathode potential of -1.2Vvs.RHE, the initial solution concentration of 0.1M, and the pH of 7. -1 cm -2 , the Faradaic efficiency of ammonia is 89.3%.

[0075] like Fig.13 As shown in the figure, in order to test the stability and practicability of the catalyst, an electrocatalytic reduction experiment was carried out on nitrate wastewater sampled from an actual steel plant. After pretreatment with adjusted pH, the removal rate of nitrate in pickling wastewater by Cu1Zn1 / HHTP was 85.6%, proving that the catalyst can also exhibit good catalytic activity in actual sewage with complex water conditions.

[0076] Embodiment 4:

[0077] An application of a Cu / Ni bimetallic conductive MOF for enhancing the reduction of nitrate to ammonia, which is different from Example 3 in that the Cu / Ni bimetallic conductive MOF prepared by the synthesis method of Example 2 is used as a catalyst for the electrocatalytic reduction of nitrate to ammonia.

[0078] like Fig.12As shown in the figure, the electrochemical characterization screened out the best Cu / Ni ratio of 2:1, because the introduction of a small amount of Ni greatly promoted the reduction of nitrite, and Cu also promoted the process of nitrate conversion to nitrite. The synergistic effect between Cu and Ni metals improved the catalytic activity of the catalyst. However, after a large amount of Ni doping, the active potential of metal Cu would be covered, so that the rate step of nitrate electrocatalytic reduction was limited. The maximum ammonia yield and Faraday efficiency were obtained when the cathode potential was -1.4Vvs.RHE, the initial nitrate concentration was 0.1M, and the pH value was 7. The highest ammonia yield of the catalyst was 259.7umolh -1 cm -2 , the Faradaic efficiency of ammonia is 92.4%.

[0079] like Fig.13 As shown in the figure, in order to test the stability and practicability of the catalyst, an electrocatalytic reduction experiment was carried out on nitrate wastewater sampled from an actual steel plant. After pretreatment with adjusted pH, the removal rate of nitrate in pickling wastewater by Cu2Ni1 / HHTP was 80.1%, proving that the catalyst can also exhibit good catalytic activity in actual sewage with complex water conditions.

[0080] Comparative Example 1:

[0081] MOF-based catalysts were prepared by the traditional synthesis method of Cu / Ni bimetallic conductive MOF. Specifically, 7.2mmolCu(NO3)23H2O and Ni(NO3)26H2O in different molar ratios were dissolved in 10mL DMF (solution A), 4.8mmolH3BTC and 0.43gPVP were dissolved in another 10mL DMF (solution B), and then solution B was added to solution A and magnetically stirred for 30min. The mixture was then transferred to a 50mL stainless steel autoclave and stored at 150℃ for 1.5h. The blue-green precipitate was collected by centrifugation, washed with anhydrous ethanol three times, and dried at 60℃ for 12h. For CuBTC, the synthesis conditions were the same, except that the solvothermal temperature was reduced to 120℃ to avoid the generation of Cu2O impurities. CuNi / NC catalysts with different Cu-Ni molar ratios were obtained by pyrolyzing the CuNiBTC precursor in a nitrogen atmosphere. Typically, 300 mg CuNiBTCMOF was placed in a porcelain boat and annealed at 800 °C for 1 h with a heating rate of 5 °C / min. After cooling to room temperature, a black CuNi / NC catalyst was obtained.

[0082] The Cu / Ni bimetallic conductive MOF-based catalyst prepared by the conventional Cu / Ni bimetallic conductive MOF synthesis method was used to electrocatalyze the reduction of nitrate to ammonia. Under the same experimental conditions as in Example 4, the yield of ammonia was 247.12 umol / h -1 cm -2, and the Faradaic efficiency is 90.18%, proving that its catalytic efficiency is inferior to that of the Cu / Ni bimetallic conductive MOF-based catalyst prepared by the synthesis method of the present invention.

[0083] Comparative Example 2:

[0084] The MOF-based catalyst was prepared by the traditional synthesis method of Cu / Zn bimetallic conductive MOF. Specifically, 1.492g (0.005mol) of zinc nitrate hexahydrate was weighed and dissolved in 100mL of deionized water to form a colorless transparent solution. 1.200g (0.005mol) of copper nitrate trihydrate was weighed and dissolved in 100mL of deionized water to form a light blue solution. 3.347g (0.04mol) of 2-methylimidazole solution was weighed and dissolved in 100mL of deionized water to obtain a colorless 2-methylimidazole aqueous solution. According to the volume ratio of 4:1:3, 60mL of 2-methylimidazole solution, 15mL of zinc nitrate solution and 45mL of copper nitrate solution were taken respectively. The two salt solutions were mixed first, and then poured into a flask containing 2-methylimidazole solution. The bottle mouth was sealed with a vacuum stopper without stirring, and the entire system was placed in an ultrasonic cleaner for 20 minutes at an ultrasonic frequency of 35 kHz (ice was added to the ultrasonic instrument to keep the temperature no higher than 35°C during the ultrasonic treatment process). After the ultrasound was completed, the system was placed in a 30°C constant temperature water bath for 8 hours to obtain a blue-black turbid liquid. A green precipitate was precipitated at the bottom of the flask, and the product was collected by centrifugation at a speed of 8000 rpm, washed three times with anhydrous ethanol, and the product was placed in a vacuum drying oven at 60°C and dried for 6 hours to obtain an emerald green powder solid Cu / Zn bimetallic conductive MOF. The Cu / Zn bimetallic conductive MOF was prepared into a catalyst and used to electrocatalyze the reduction of nitrate to ammonia. Under the same experimental environment as Example 3, the yield of ammonia was 176.25 umol / h -1 cm -2 , and the Faradaic efficiency is 81.73%, proving that its catalytic efficiency is inferior to that of the Cu / Zn bimetallic conductive MOF-based catalyst prepared by the synthesis method of the present invention.

[0085] The above proves that the Cu / Zn and Cu / Ni bimetallic conductive MOFs prepared by the present invention have a high specific surface area, and the prepared electrodes have a high responsiveness to nitrate ions. From the results, compared with the Cu / Zn and Cu / Ni bimetallic conductive MOF-based catalysts prepared by the prior art, the Cu / Zn and Cu / Ni bimetallic conductive MOF-based catalysts prepared by the synthesis method of the present invention have a significant effect on the removal of nitrates, have a high removal efficiency, and have a relatively high selectivity for ammonia. No waste gas or toxic gas is produced in the process, indicating that the method is in line with clean production. The design realizes the conversion from nitrate pollutants to high value-added ammonia, which not only removes nitrate pollutants in water bodies, but also produces high value-added ammonia chemicals, realizes the recycling of waste resources, and is in line with the concept of sustainable development.

[0086] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for synthesizing Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalysts for enhancing nitrate reduction to ammonia, characterized in that: The following steps are involved: S1: dissolving cupric acetate monohydrate and nickel acetate tetrahydrate or zinc acetate dihydrate in ultrapure water to prepare solution A; S2: dissolving 2,3,6,7,10,11-hexahydroxytriphenyl and ammonia water in N,N-dimethylformamide (DMF) to prepare solution B; S3: Solution A and solution B are mixed and ultrasonicated for 10 to 30 minutes to obtain solution C; S4: Solution C was heated in an isothermal oven at 85°C for 1-3 h, and then naturally cooled to room temperature, washed with deionized water and acetone for 6 times, and finally dried in a vacuum oven at 60°C to obtain dark blue crystals; When nickel acetate tetrahydrate is used in step S1, the dark blue crystals prepared and synthesized are Cu / Ni bimetallic conductive MOF-based catalysts; when zinc acetate dihydrate is used in step S1, the dark blue crystals prepared and synthesized are Cu / Zn bimetallic conductive MOF-based catalysts.

2. An application of a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia, characterized in that: The Cu / Ni or Cu / Zn bimetallic conductive MOF prepared by the synthesis method described in claim 1 is used as a catalyst.

3. The use of a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia according to claim 2, characterized in that: Cu / Ni or Cu / Zn bimetallic conductive MOFs are used for the electrocatalytic reduction of nitrate to ammonia.

4. The use of a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia according to claim 3, characterized in that: The specific steps of Cu / Ni or Cu / Zn bimetallic conductive MOF electrocatalytic reduction of nitrate to ammonia are as follows: A1: preparing a catalyst to form a catalyst ink; A2: Apply the catalyst ink dropwise onto carbon paper, dry it at room temperature, and then drop Nafion reagent onto the carbon paper; A3: Carbon paper is made into a carbon paper electrode (CC), and the carbon paper electrode (CC), saturated calomel electrode (SCE) and graphite rod are used as the working electrode, reference electrode and counter electrode respectively, and electrocatalysis is carried out in a three-electrode electrochemical reaction cell to reduce nitrate to ammonia.

5. The use of a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia according to claim 4, characterized in that: The specific steps of A1 are: mixing the catalyst, superconductive carbon black (SCCB), N,N-dimethylformamide (DMF) and ultrapure water, and ultrasonicating for 10 to 40 minutes to obtain the catalyst ink.

6. The use of a Cu / Ni, Cu / Zn bimetallic conductive MOF-based catalyst for enhancing nitrate reduction to ammonia according to claim 5, characterized in that: The catalyst, superconductive carbon black (SCCB), N,N-dimethylformamide (DMF) and ultrapure water in step A1 are mixed and stirred by a magnetic stirrer.

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