Confined bimetallic catalysts for electrocatalytic reduction reactions, their preparation methods and applications

Abstract

This invention discloses a confined bimetallic catalyst for electrocatalytic reduction reactions, its preparation method, and its application. Belonging to the field of electrocatalysis technology, the preparation method includes the following steps: mixing tetrapropylammonium hydroxide with ultrapure water, adding tetraethyl orthosilicate, and stirring to obtain mixture one; mixing nickel chloride hexahydrate, ethylenediamine, and ultrapure water to obtain mixture two; mixing copper nitrate trihydrate, ethylenediamine, and ultrapure water to obtain mixture three; adding mixture two and mixture three dropwise to mixture one, and performing hydrothermal synthesis to obtain the reaction product; centrifuging and collecting the obtained reaction product to obtain the catalyst precursor; calcining the catalyst precursor in air, and then heat-treating it in a flowing hydrogen-argon mixed atmosphere to obtain the confined bimetallic catalyst. The confined bimetallic catalyst prepared by this invention can improve the efficiency of nitrate removal in the electrocatalytic treatment of groundwater.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a confined bimetallic catalyst for electrocatalytic reduction reactions, its preparation method, and its application. Background Technology

[0002] Groundwater is a vital water resource for humanity, serving as a primary source of water for production, daily life, and industrial and agricultural use in many countries and regions. Nitrate is a major form of nitrogen pollution in groundwater and one of the most difficult-to-control stable pollutants. Data from a nationwide survey of nitrate levels in deep and shallow groundwater systems across 52 basins show that in 25 out of 36 major basins with shallow aquifers, 90% of the surveyed points exceeded my country's drinking water quality standards; and in 10 out of 37 major basins with deep or karst aquifers, the levels exceeded standards. Excessive nitrate release from groundwater not only affects the quality of environmental components but also endangers human health through the food chain. Nitrates can be converted into nitrites in the human mouth and gastrointestinal tract. Excessive nitrites can lead to methemoglobinemia, which can cause suffocation and even death in severe cases. Infants and young children are more susceptible to methemoglobinemia after ingesting nitrates, commonly known as "blue baby syndrome." Therefore, the sustainable and effective method of decomposing or removing nitrates from groundwater has become an urgent task.

[0003] Conventional nitrate removal technologies mainly include physical, biological, and chemical methods. However, their high cost and low efficiency limit their further development and application. Electrochemical treatment technology removes nitrates by using a metallic or non-metallic material as the cathode. An applied current is applied, and the nitrate is reduced to nitrogen, ammonia, and other products through electrolysis on the electrode surface during the reaction. Compared with traditional nitrate removal methods, electrochemical methods offer advantages such as environmental friendliness, ease of remote automation control, and the ability to utilize renewable energy sources (such as solar, wind, and electrical energy), making them a highly efficient and promising method for nitrate removal.

[0004] Noble metals are widely used in nitrate reduction. However, due to their high cost, susceptibility to poisoning, and limited lifespan, the large-scale application of noble metals such as Pt, Pb, and Au in nitrate reduction reactions is significantly hindered. Transition metal catalysts all possess a certain degree of nitrate catalytic activity. Among them, Cu, given its unique catalytic properties towards nitrates, has become an important research target for nitrate reduction catalysts. Compared to other transition metal catalysts, copper-based catalysts have advantages such as a stronger binding capacity for nitrates, a lower driving potential for nitrate catalytic reduction, and relatively lower hydrogen evolution activity. Therefore, Cu-based catalysts are the most widely used metal catalysts in nitrate reduction.

[0005] Although copper-based catalysts have achieved good results in nitrate reduction, the kinetics of nitrate reduction by single-metal catalysts are slow and the efficiency is poor. Bimetallic catalysts, due to the synergistic effect of bimetallic active sites, exhibit high denitrification activity and rapid reduction kinetics. Noble metals have excellent hydrogen adsorption properties, and copper has good catalytic performance for nitrogen and intermediates. Combining the two can effectively improve the catalytic activity of the catalyst for nitrate. Researchers have improved the nitrate reduction ability of catalysts by introducing noble metal doping. For example, Chen et al. synthesized a ruthenium-dispersed copper nanowire catalyst (Ru-Cu NW) via cation exchange. This catalyst fully utilizes the unique catalytic properties of both Ru and Cu. The highly dispersed Ru atoms can provide highly active nitrate reduction sites, while the surrounding Cu sites can inhibit the competitive hydrogen evolution reaction, giving the catalyst excellent electrocatalytic nitrate reduction performance. However, the price and abundance of noble metals limit their large-scale application. By combining Cu with non-noble metals, not only can the cost of the electrode be reduced, but the catalytic activity and stability of the electrode can also be enhanced. Considering that Ni atoms serve as H* binding sites and exhibit strong adsorption for key intermediates such as NO2* and NH2*, the addition of Ni atoms to Cu-based catalysts can significantly enhance the hydrogenation capacity of these intermediates. Furthermore, Cu-Ni bimetallic catalysts can effectively regulate the adsorption strength between the two active sites and the intermediates through interatomic synergistic enhancement effects, overcoming the limitations of single active sites and further maximizing catalytic activity. Therefore, a stable Cu-Ni bimetallic catalyst design strategy is crucial for achieving efficient nitrate removal.

[0006] Bimetallic catalysts have been extensively studied in the electrocatalytic reduction of nitrates. However, current research indicates that due to increased surface free energy, metal sites tend to aggregate, resulting in fewer and less dispersed active sites, leading to poor catalyst stability and a shorter lifetime, thus significantly reducing nitrate reduction performance. Confining sub-nanometer metals in a zeolite matrix is ​​a promising special type of catalyst, offering significant advantages in size control, position tuning, and nanostructure design. Yu et al. demonstrated well-dispersed and small-volume Pd nanoparticles in nanoscale silica (Pd / S-1-in). In the complete decomposition of formic acid to H2, the Pd / S-1-in-K catalyst exhibited the highest conversion rate, approximately 1.1 times that of Pd / S-1-in-Na, 1.4 times that of Pd / S-1-in, 5 times that of Pd / S-1-im, and 19 times that of Pd / C catalysts. The beauty of zeolite-confined metals lies in their unique confinement effect at the molecular scale, enabling space-confined catalysis similar to enzyme catalysis. Confined catalysts can optimize the electronic structure of the catalyst, improve the synergistic effect between the support and metal nanoparticles, promote rapid charge transfer, and enhance the catalytic activity, selectivity and stability of the catalyst. Moreover, confined engineering has not been reported in the electrocatalytic nitrate reduction reaction, so this study uses confined engineering to improve the performance of the catalyst.

[0007] In summary, electrocatalytic reduction of nitrates has advantages such as being environmentally friendly, easy to remotely and automatically control, and utilizing renewable energy sources (such as solar, wind, and electricity), making it a highly efficient and promising method for nitrate removal. However, conventional catalyst materials face challenges such as slow catalytic kinetics of single metals, limited catalytic active sites, poor catalyst stability, and side reactions affecting catalytic efficiency. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a confined bimetallic catalyst for electrocatalytic reduction reactions, so as to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0010] A method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, comprising the following steps:

[0011] Tetrapropylammonium hydroxide was mixed with ultrapure water, and tetraethyl orthosilicate was added and stirred to obtain mixture one;

[0012] Nickel chloride hexahydrate, ethylenediamine, and ultrapure water were mixed and stirred to obtain mixture two;

[0013] Copper nitrate trihydrate, ethylenediamine, and ultrapure water were mixed and stirred to obtain mixture three;

[0014] Mixtures 2 and 3 were added dropwise to mixture 1, and the mixture was stirred under no precipitation conditions. Then, it was placed in an autoclave and subjected to hydrothermal synthesis at 165-175 °C to obtain the reaction product.

[0015] The obtained reaction products were centrifuged and collected, and then washed and dried to obtain the catalyst precursor.

[0016] The catalyst precursor was first calcined in air, and then heat-treated in a flowing hydrogen-argon mixed atmosphere to obtain the confined bimetallic catalyst.

[0017] Preferably, the molar ratio of nickel chloride hexahydrate to copper nitrate trihydrate is 1:(0.8-1.2).

[0018] Preferably, the drying temperature is 75-85 ℃.

[0019] Preferably, the calcination temperature is 500-600 ℃.

[0020] Preferably, the heat treatment temperature is 350-450 ℃.

[0021] Preferably, the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:93.

[0022] Another objective of this invention is to provide a confined bimetallic catalyst prepared by the above-described method.

[0023] Another objective of this invention is to provide an application of the above-mentioned confined bimetallic catalyst in the electrocatalytic reduction of nitrate.

[0024] Another objective of this invention is to provide an application of the above-mentioned confined bimetallic catalyst in the removal of nitrates from water.

[0025] Another objective of this invention is to provide an electrocatalytic reduction device, comprising a cathode and an anode, wherein the cathode is made using the aforementioned confined bimetallic catalyst.

[0026] This invention prepares a sub-nanometer hybrid bimetallic cluster catalyst in pure silica S-1 zeolite nanocrystals. Using this catalyst for electrocatalytic treatment of nitrates in groundwater can improve the efficiency of nitrate removal by electrocatalysis, providing a more economical and effective method for achieving high-efficiency removal of nitrate pollution from groundwater. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the technical principle of the confined bimetallic catalyst for electrocatalytic removal of nitrates in water, as provided in an embodiment of the present invention.

[0028] Figure 2Synthesis pathway diagrams for different materials;

[0029] Figure 3 This is a schematic diagram of an electrocatalytic reduction device provided in an embodiment of the present invention; in the figure, 1-external power supply; 2-single-chamber electrolytic cell; 3-electrolyte; 4-anode; 5-cathode;

[0030] Figure 4 SEM images of S-1(a) and Cu-Ni / S-1(b);

[0031] Figure 5 (a) is the SEM image of Cu-Ni@S-1, and (b) is the elemental distribution map of Cu-Ni@S-1.

[0032] Figure 6 XPS spectra of Cu-Ni@S-1;

[0033] Figure 7 XRD pattern of Cu-Ni@S-1;

[0034] Figure 8 The BET results are shown for S-1 (a) and Cu-Ni@S-1 (b).

[0035] Figure 9 Electrochemical impedance spectroscopy (EIS) spectra of Cu-Ni@S-1, Cu-Ni / S-1, and S-1;

[0036] Figure 10 Linear scanning voltammetry curves for different materials;

[0037] Figure 11 A comparison chart of Tafel slopes (vs. RHE) for different materials;

[0038] Figure 12 A comparison of (a) nitrate removal efficiency, (b) nitrite generation efficiency, and (c) ammonia nitrogen generation efficiency for different catalyst materials;

[0039] Figure 13 The graph shows the cycle performance test results of the Cu-Ni@S-1 catalyst.

[0040] Figure 14 A comparison chart of metal leaching amounts from different materials;

[0041] Figure 15 The graph shows the effect of different current densities on the electrocatalytic reduction of nitrate.

[0042] Figure 16 The graph shows the effect of different pH values ​​on the electrocatalytic reduction of nitrate.

[0043] Figure 17The graph shows the effect of different initial nitrate concentrations on the electrocatalytic reduction of nitrate.

[0044] Figure 18 The graph shows the effect of different chloride ion concentrations on the electrocatalytic reduction of nitrate.

[0045] Figure 19 The graph shows the effect of different TBA concentrations on the electrocatalytic reduction of nitrate.

[0046] Figure 20 The reaction pathway diagram for the electrocatalytic reduction of nitrates using Cu-Ni@S-1 is shown.

[0047] Figure 21 The diagram shows the reaction process and the change in Gibbs free energy.

[0048] Figure 22 A comparison of the overall differential charge and adsorption energy of nitrate adsorption in Cu-Ni / S-1 and Cu-Ni@S-1.

[0049] Figure 23 The partial density of states diagrams are shown for (a) Cu 3d orbitals and (b) Ni 3d orbitals of Cu-Ni@S-1 and Cu-Ni / S-1. Detailed Implementation

[0050] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] Conventional nitrate treatment technologies mainly include physical, biological, and chemical methods. Physical treatment technologies are costly, and since nitrates are only transferred or concentrated without complete removal, they can potentially cause secondary pollution. Biological treatment technologies have limitations in practical applications due to the large size of the reactors, slow processing cycles, and susceptibility to environmental influences. Chemical methods have the disadvantage of not being able to completely convert nitrates into non-toxic nitrogen gas, and can also produce pollutants such as metal ions, causing secondary pollution.

[0052] Renewable energy-driven electrocatalytic nitrate reduction is a promising method for removing nitrates (NOx) from groundwater. 3-This technology is favored by many due to its environmental friendliness, ease of remote automation control, and utilization of renewable energy sources (such as solar, wind, and electricity). The cathode catalyst is one of the main influencing factors in the electrochemical reduction of nitrates. However, single metal catalysts suffer from slow kinetics, few catalytic active sites, poor catalyst stability, and side reactions affecting catalytic efficiency.

[0053] To improve the reaction rate of electrocatalytic nitrate removal technology, the nitrate reduction mechanism at the cathode was investigated. Specifically, the nitrate reduction mechanism can be explained by two types of reactions: (I) involving electrons; and (II) involving hydrogen atoms.

[0054] Type (I) reactions for the electrocatalytic removal of nitrates at different potentials:

[0055] NO3 - +H₂O + 2e - →NO2 - +2OH - E 0 =0.01V (1)

[0056] NO3 - +3H₂O + 5e - →0.5N2+6OH - E 0 =0.26V (2)

[0057] NO3 - +6H2O+8e - →NH3+9OH - E 0 =-0.12V (3)

[0058] NO3 - +2H₂O + 3e - →0.5N2+4OH - E 0 =-0.406V (4)

[0059] NO3 - +5H₂O + 6e - →NH3+7OH - E 0 =-0.165V (5)

[0060] NO3 - +4H₂O + 4e - →NH2OH + 5OH - E 0 =-0.45V (6)

[0061] According to type (I) reactions, nitrates react on the cathode surface under electronic catalysis, which may involve nitrites, nitrogen and other redox products.

[0062] According to type (II) reactions, the reaction begins with the adsorption of H₂O (Equation 7) and nitrate (Equation 9) onto the catalyst electrode (*), and rapidly reaches dynamic equilibrium. When a constant current is applied to the electrode surface, the adsorbed H₂O can be reduced to adsorbed hydrogen atoms (*H). This then completes a series of subsequent hydrogenation reactions. Therefore, *H plays a major role in the entire electrocatalytic reduction of nitrate.

[0063] *H participates in reaction (II) for the electrocatalytic removal of nitrates:

[0064] 2H2O+2e - →H2+2OH - (7)

[0065] H2+2*→2*H (8)

[0066] NO3 - +H→NO2+OH - (9)

[0067] *NO2 - +*H→*NO+OH - (10)

[0068] *NO+*→*N+*O (11)

[0069] *N+*N→2*+N2(12)

[0070] *NH+*H→*NH2+* (13)

[0071] *NH2+*H→*NH3+* (14)

[0072] *NH3→NH3+* (15)

[0073] The electrocatalytic reduction mechanisms of nitrate differ across electrodes, leading to varying effects. For instance, when Pt, Fe, and Ni are used as cathodes, type (II) reactions are more likely to occur. These metals possess empty d-orbital outer electron structures, which can be attributed to the adsorption of hydrogen atoms, resulting in the formation of *H. Admittedly, the intermediate steps of type (II) reactions are not entirely consistent under different materials and reaction conditions, requiring specific analysis on a case-by-case basis. The nitrate reduction reaction on the Cu electrode mainly follows type (I) reactions due to the strong adsorption capacity of Cu electrodes for nitrates. Therefore, designing efficient and highly selective electrode materials is crucial for the electrocatalytic reduction of nitrates.

[0074] To address the aforementioned technical problems, this invention provides a novel Cu-Ni@S-1 catalytic material for the electrocatalytic treatment of nitrates (such as...) in groundwater. Figure 1 This effectively solved the following problems:

[0075] (1) Conventional single-metal catalysts face the problem of slow kinetics during electrocatalytic reduction. However, in this study, a sub-nanometer hybrid bimetallic cluster catalyst Cu-Ni@S-1 was prepared in pure silica S-1 zeolite nanocrystals via hydrothermal synthesis using a Cu-Ni metal ethylenediamine complex mixture as a precursor. Due to the synergistic effect of the bimetals, electron transport in the catalytic reaction was accelerated, the problem of slow kinetics in nitrate reduction was solved, and the performance of the catalyst was enhanced.

[0076] (2) Conventional metal catalysts have high surface free energy, and active sites are prone to agglomeration, which leads to a reduction in active sites and thus reduces catalytic activity. Confinement engineering can effectively disperse Cu-Ni bimetallic active sites, increase the number of active sites, and generate smaller sub-nano particles. Sub-nano-sized metal clusters have better catalytic activity or selectivity than nano-sized metal clusters, thus solving the problem of low catalyst activity.

[0077] (3) Harsh external environments may lead to corrosion, deactivation, or structural changes in the catalyst. Based on the confinement effect, Cu and Ni active sites can be encapsulated in the nanopores of zeolite molecular sieves to avoid direct contact with harsh external environments (such as strong acids and strong bases), thereby delaying and preventing the deactivation of active sites, extending the service life of the catalyst, and solving the problem of poor catalyst stability.

[0078] (4) In transition metal-based catalysts, the interaction between the adsorbed state and the surface d electrons usually generates bonding orbitals and antibonding orbitals. The higher the d-band center, the higher the antibonding state and the stronger the adsorption force. The confinement effect causes the d-band center of Cu and Ni to shift upward, thereby promoting the adsorption of nitrates in water by Cu-Ni@S-1, significantly reducing the reaction energy barrier for the electrocatalytic reduction of nitrates, inhibiting the occurrence of side reactions, and solving the problem of side reactions affecting catalytic efficiency.

[0079] (5) The rate-limiting step in the electrocatalytic removal of nitrate is NH3 synthesis. The Cu-Ni bimetallic structure reduces the gap between the center of the d-band of the Ni 3d orbital and the N 2p orbital, which enhances the interaction between the metal atom and the key NOH* intermediate, lowers the limiting potential for selective NH3 synthesis, accelerates the reaction rate, and solves the problem that the rate-limiting step affects the efficiency of electrocatalytic removal of nitrate.

[0080] Specifically, in one embodiment of the present invention, a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction is provided, comprising the following steps:

[0081] S1. Mix tetrapropylammonium hydroxide with ultrapure water, add tetraethyl orthosilicate and stir to obtain mixture one;

[0082] S2. Mix and stir nickel chloride hexahydrate, ethylenediamine and ultrapure water to obtain mixture two;

[0083] S3. Mix and stir copper nitrate trihydrate, ethylenediamine and ultrapure water to obtain mixture trihydrate; wherein the molar ratio of nickel chloride hexahydrate and copper nitrate trihydrate is 1:(0.8-1.2), preferably 1:1;

[0084] S4. Add mixture 2 and mixture 3 dropwise to mixture 1, stir under no precipitation conditions, then put it into an autoclave and carry out hydrothermal synthesis at 165-175 ℃ to obtain the reaction product;

[0085] S5. The obtained reaction products are centrifuged and collected, then washed and dried to obtain the catalyst precursor; wherein the drying temperature is 75-85 ℃.

[0086] S6. The catalyst precursor is first calcined in air at 500-600 °C, cooled, and then linearly heated to 350-450 °C in a flowing hydrogen-argon mixed atmosphere to obtain a confined bimetallic catalyst; wherein the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:93, preferably 5:95.

[0087] Example 1: As Figure 2 As shown, this embodiment provides a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, which includes the following steps:

[0088] S1. Mix 13 g of tetrapropylammonium hydroxide with 15.45 g of ultrapure water, stir continuously on a magnetic stirrer for 10 min, then add 8.32 g of tetraethyl orthosilicate and stir for 6 h to obtain a clear mixture.

[0089] S2. Mix 1.19 g of nickel chloride hexahydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water and stir for 10 min to obtain mixture two;

[0090] S3. Mix 1.21 g of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water and stir for 10 min to obtain mixture three;

[0091] S4. Take 1 mL of each of the above mixtures 2 and 3 and add them dropwise to the above mixture 1. Stir for 30 min under no precipitation conditions, then put it into an autoclave and carry out hydrothermal synthesis at 170 °C for 4 days to obtain the reaction product.

[0092] S5. The obtained reaction product was centrifuged and collected, then washed three times with ethanol and three times with ultrapure water, and then dried overnight at 80 °C to obtain the catalyst precursor A-Cu-Ni@S-1.

[0093] S6. The above catalyst precursor A-Cu-Ni@S-1 was first calcined in air at 550 °C for 8 h. After cooling, it was then linearly heated to 400 °C in a flowing hydrogen-argon mixed atmosphere (volume ratio of hydrogen to argon is 5:95) for 2 h and held for 2 h. After grinding, the confined bimetallic catalyst was obtained and named Cu-Ni@S-1.

[0094] The key aspect of this invention is the confinement of sub-nanometer bimetallic Cu and Ni within a zeolite molecular sieve. This reduces Cu and Ni leaching and blocks direct contact between the active sites and the highly corrosive environment, thereby delaying and preventing catalyst deactivation and improving catalyst stability. Furthermore, the confinement engineering effectively disperses the Cu-Ni bimetallic active sites, increasing their number and shifting the d-band center of the metal upwards, thus enhancing nitrate adsorption performance. The synergistic effect of the Cu-Ni bimetallic compounds accelerates the reaction kinetics, and the bimetallic structure reduces the gap between the Ni 3d orbital d-band center and the N 2p orbital, lowering the limiting potential for selective NH3 synthesis and thereby improving nitrate removal rates.

[0095] Example 2: This example provides a method for preparing a confined bimetallic catalyst for electrocatalytic reduction reactions, which includes the following steps:

[0096] S1. Mix 13 g of tetrapropylammonium hydroxide with 15.45 g of ultrapure water, stir continuously on a magnetic stirrer for 10 min, then add 8.32 g of tetraethyl orthosilicate and stir for 6 h to obtain a clear mixture.

[0097] S2. Mix 5 mmol nickel chloride hexahydrate, 2 mL ethylenediamine and 8 mL ultrapure water and stir for 10 min to obtain mixture two;

[0098] S3. Mix 4 mmol of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water and stir for 10 min to obtain mixture three;

[0099] S4. Take 1 mL of each of the above mixtures 2 and 3 and add them dropwise to the above mixture 1. Stir for 30 min under no precipitation conditions, then place in an autoclave and carry out hydrothermal synthesis at 165 °C for 4 days to obtain the reaction product.

[0100] S5. The obtained reaction product is centrifuged and collected, then washed three times with ethanol and three times with ultrapure water, and then dried overnight at 75 °C to obtain the catalyst precursor.

[0101] S6. The above catalyst precursor was first calcined in air at 500 °C for 8 h. After cooling, it was linearly heated to 350 °C in a flowing hydrogen-argon mixed atmosphere (volume ratio of hydrogen to argon is 3:97) for 2 h and kept for 2 h. Then it was ground to obtain a confined bimetallic catalyst.

[0102] Example 3: This example provides a method for preparing a confined bimetallic catalyst for electrocatalytic reduction reactions, which includes the following steps:

[0103] S1. Mix 13 g of tetrapropylammonium hydroxide with 15.45 g of ultrapure water, stir continuously on a magnetic stirrer for 10 min, then add 8.32 g of tetraethyl orthosilicate and stir for 6 h to obtain a clear mixture.

[0104] S2. Mix 5 mmol nickel chloride hexahydrate, 2 mL ethylenediamine and 8 mL ultrapure water and stir for 10 min to obtain mixture two;

[0105] S3. Mix 6 mmol of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water and stir for 10 min to obtain mixture three;

[0106] S4. Take 1 mL of each of the above mixtures 2 and 3 and add them dropwise to the above mixture 1. Stir for 30 min under no precipitation conditions, then put it into an autoclave and carry out hydrothermal synthesis at 175 °C for 4 days to obtain the reaction product.

[0107] S5. The obtained reaction product is centrifuged and collected, then washed three times with ethanol and three times with ultrapure water, and then dried overnight at 85 °C to obtain the catalyst precursor.

[0108] S6. The above catalyst precursor was first calcined in air at 600 °C for 8 h. After cooling, it was linearly heated to 450 °C in a flowing hydrogen-argon mixed atmosphere (volume ratio of hydrogen to argon is 7:93) for 2 h and kept for 2 h. Then it was ground to obtain a confined bimetallic catalyst.

[0109] Example 4: Figure 3 As shown, this embodiment provides an electrocatalytic reduction device, including an external power supply 1, a cathode 5, and an anode 4; the two ends of the external power supply 1 are connected to the cathode 5 and the anode 4, respectively; the cathode 5 and the anode 4 are disposed in a single-chamber electrolytic cell 2; the single-chamber electrolytic cell 2 is also filled with an electrolyte 3, which can be nitrate wastewater; the anode 4 can be made of platinum sheet, and the cathode 5 is made of the above-mentioned confined bimetallic catalyst; specifically, the preparation method of the cathode 5 is as follows:

[0110] First, the Cu-Ni@S-1 confined bimetallic catalyst, conductive carbon black, and polyvinylidene fluoride prepared in Example 1 were weighed in a mass ratio of 8:1:1 and mixed. Then, the mixture was dissolved in N-methyl-2-pyrrolidone (concentration of 10 g / L) to prepare catalyst ink. Next, the ink was coated on carbon cloth (CC, 1.0×2.0cm) to ensure that both sides were coated evenly. Finally, it was dried at 60°C for 30 minutes to obtain cathode 5.

[0111] In an embodiment of the present invention, the electrocatalytic reduction test of nitrate was conducted in a single-chamber electrolytic cell 2 using a two-electrode system. Electrode plates prepared using Cu-Ni@S-1 and platinum plates were used as the cathode 5 and anode 4, respectively, with the distance between the two plates controlled to be 0.5-2.0 cm. The electrolyte 3 could be a nitrate solution with a concentration of 50 mg / L (calculated as N) prepared using NaNO3. The reason for choosing a concentration of 50 mg / L is that the actual concentration of nitrate in the nitrate-contaminated groundwater collected was 55 mg / L, which is approximately 50 mg / L in the simulation experiment. The nitrate content of the water samples at each time point was measured using ion chromatography, and the nitrate removal rate was calculated.

[0112] The above-mentioned device enhances the electrocatalytic removal of nitrates, significantly improving efficiency. Specifically, the electrocatalytic nitrate removal experiment was conducted in a single-chamber electrolytic cell 2 (50 mL) using a GPS305D DC regulated power supply. 30 mL of electrolyte 3 contained 50 mg / L nitrate (calculated as N). A current of 50 mA was applied to the system, and samples were taken every 30 min. The nitrate content of the water samples at each time point was measured using ion chromatography, and the nitrate removal rate was calculated. Under optimal conditions, 94.99% of nitrates could be degraded within 3 h. Furthermore, the Cu-Ni@S-1 catalyst exhibited good cycling stability, maintaining a degradation rate of 91.92% after 5 cycles of reuse, as shown in Table 1.

[0113] Table 1 Comparison of nitrate reduction performance of different electrocatalytic materials

[0114]

[0115] As shown in Table 1, the nitrate reduction performance of different electrocatalytic materials was compared. The nitrate removal rate of the Cu-Ni@S-1 catalytic material prepared in this embodiment reached 94.99%, and the removal time was much shorter than that of other catalytic materials, requiring only 3 hours. The nitrate removal efficiency was significantly higher than that of other iron-based and metal catalysts, and the selectivity for ammonia was also 75.38%. These results demonstrate the excellent performance and remarkable nitrate removal efficiency of Cu-Ni@S-1.

[0116] Comparative Example 1: This comparative example provides a method for preparing zeolite molecular sieve S-1 using a hydrothermal method. The synthesis process is as follows: Figure 2 As shown, the specific steps include:

[0117] 13 g of tetrapropylammonium hydroxide was mixed with 15.45 g of ultrapure water. After stirring continuously on a magnetic stirrer for 10 min, 8.32 g of tetraethyl orthosilicate was added, and the mixture was stirred for 6 h to obtain a clear mixture. The mixture was then placed in an autoclave and subjected to hydrothermal synthesis at 170 °C for 4 days. The obtained product was centrifuged and collected, washed three times with ethanol and three times with ultrapure water, and dried overnight at 80 °C to obtain precursor AS-1. Precursor AS-1 was then calcined at 550 °C for 8 h to obtain a white solid, which was the zeolite molecular sieve, named S-1.

[0118] Comparative Example 2: This comparative example provides a method for preparing a Cu-Ni / S-1 catalyst, the synthesis process of which is as follows: Figure 2 As shown, the specific steps include:

[0119] First, the zeolite molecular sieve S-1 prepared in Comparative Example 1 was impregnated and calcined with 1 mL of 0.8 M nickel chloride solution and 1 mL of 0.8 M copper nitrate solution. Then, the resulting solid was dried overnight in an oven at 80 °C. Next, it was linearly heated to 400 °C within 2 h in a flowing hydrogen-argon mixed atmosphere (volume ratio of hydrogen to argon of 5:95) and held for 2 h. After grinding, the catalyst material was obtained and named Cu-Ni / S-1.

[0120] Performance testing: The Cu-Ni@S-1 catalyst prepared in Example 1 and the S-1 and Cu-Ni / S-1 catalysts prepared in Comparative Examples 1-2 were subjected to relevant performance tests, and the results are as follows:

[0121] I. Scanning electron microscope (SEM) images of the S-1 catalyst and Cu-Ni / S-1 catalyst prepared in Comparative Examples 1-2 are shown below. Figure 4 As shown in (a) and (b). Figure 4 (a) clearly shows the hexagonal structure of the S-1 catalyst. Figure 4(b) shows the SEM image of Cu-Ni / S-1, which clearly shows its sharp edges, regular shape, and very standard hexagonal structure, which is highly similar to the SEM image of S-1 molecular sieve. No effect of the interaction between Cu and Ni and the molecular sieve is shown.

[0122] The SEM image of Cu-Ni@S-1 obtained in Example 1 above is as follows: Figure 5 As shown in (a), the material has a hexahedral shape. The presence of Cu and Ni within the zeolite results in a rough surface. The metal clusters are uniformly distributed within the nanoscale zeolite molecular sieve, indicating successful synthesis. The elemental distribution of the Cu-Ni@S-1 sample was determined by energy dispersive X-ray spectroscopy (EDX), as shown in (a). Figure 5 As shown in (b), O, Si, Cu, and Ni elements are uniformly distributed in almost the same positions, indicating that Cu and Ni are successfully confined within the S-1 molecular sieve. O and Si elements appear more dense, as they are constituent elements of the molecular sieve. Cu and Ni elements are more dispersed compared to the former two, suggesting that Cu and Ni confined within the molecular sieve do not aggregate to form clusters, which is beneficial for increasing the reaction contact area and improving catalyst activity.

[0123] A detailed analysis of the valence states of Cu and Ni was conducted using X-ray photoelectron spectroscopy (XPS), and the results are as follows: Figure 6 As shown. Figure 6 (a) shows the Cu 2p XPS spectrum, with a binding energy of approximately 933.0 eV (Cu 2p 3 / 2 ) and 952.0 eV (Cu 2p 1 / 2 The peak at ) indicates Cu 0 and Cu 2+ The presence of [something] at approximately 932.2 eV (Cu 2p[something]). 3 / 2 ) and 951.4 eV (Cu 2p 1 / 2 The peak at ) corresponds to Cu 0 At approximately 933.4 eV (Cu 2p 3 / 2 ) and 952.7 eV (Cu 2p 1 / 2 The peak at ) corresponds to Cu 2+ . Figure 6 (b) shows the Ni 2p XPS spectrum. Both Cu-Ni / S-1 and Cu-Ni@S-1 show a pair of peaks with binding energies of 853.0 eV and 856.0 eV, which are assigned to Ni. 0 or Ni 2+ state.

[0124] Cu-Ni@S-1 was characterized by X-ray diffraction (XRD), such as Figure 7 As shown, Cu-Ni@S-1 possesses all six main characteristic peaks of S-1 (7.9). ◦ 8.9 ◦ 14.9 ◦ , 23.1 ◦ 24.0 ◦ 30.0 ◦ This demonstrates that Cu-Ni@S-1 with the expected S-1 zeolite structure has been successfully synthesized, and the introduction of metallic substances did not interfere with the crystallization of the zeolite. Comparison of the standard XRD patterns of Cu-Ni@S-1 with those of Cu and Ni confirms the presence of Cu and Ni in the material; the indistinct diffraction peaks of Cu and Ni indicate a uniform distribution of Cu and Ni clusters.

[0125] pass Figure 8 The BET results show that the curves of Cu-Ni@S-1 and S-1 both conform to type I adsorption isotherms, proving that they are both microporous structures. The significant difference between the Cu-Ni@S-1 and S-1 curves is due to the confinement of Cu and Ni within the molecular sieve, which affects the sieve's structure and reduces its pore size, resulting in different adsorption curves for Cu-Ni@S-1. The internal figure shows the pore size distribution curves of the materials; the results show that the pore size of Cu-Ni@S-1 (2.37 nm) is smaller than that of S-1 (4.37 nm), indicating that Cu and Ni are successfully confined within the molecular sieve. Furthermore, the BET specific surface area of ​​Cu-Ni@S-1 is 358.49 m². 2 / g has a BET specific surface area of ​​232.89 m², which is much higher than that of S-1. 2 Cu-Ni@S-1 has a higher specific surface area and more active sites, which is more conducive to improving catalytic activity.

[0126] To obtain the electrochemical performance of the Cu-Ni@S-1 catalyst, Cu-Ni@S-1, Cu-Ni / S-1, and S-1 catalyst materials were coated onto carbon cloth (1.0 × 2.0 cm) to obtain working electrodes (Cu-Ni@S-1 / CC, Cu-Ni / S-1 / CC, and S-1 / CC). The Cu-Ni@S-1 catalyst and other catalysts were electrochemically characterized using an electrochemical workstation. EIS results are shown below. Figure 9 As shown, Cu-Ni@S-1 exhibits a lower charge transfer resistance, further demonstrating the superior performance of the confined material.

[0127] The LSV curves of Cu-Ni@S-1, Cu-Ni / S-1, and S-1 were determined using linear sweep voltammetry (LSV). The results are as follows: Figure 10 As shown, the Cu-Ni@S-1 material exhibits a lower overpotential and a higher current density, combined with... Figure 9 Electrochemical impedance spectroscopy revealed that the Cu-Ni@S-1 catalyst had lower impedance and higher current, indicating that the Cu-Ni@S-1 catalyst has excellent conductivity, which is conducive to the transfer of electrons from the cathode to the surface of the Cu-Ni@S-1 catalyst, indicating that the Cu-Ni@S-1 material has good catalytic activity.

[0128] The Tafel slopes of Cu-Ni@S-1, Cu-Ni / S-1, and S-1 were calculated based on the LSV curves, and the results are as follows: Figure 11 As shown. The Tafel slope represents the change in overpotential required when the current changes tenfold. Therefore, the smaller the absolute value of the slope, the better; a smaller slope means a smaller voltage rise and lower energy consumption. From Figure 11 It can be seen that Cu-Ni@S-1 has the lowest Tafel slope (63.87 mV / dec), indicating that Cu-Ni@S-1 has the best reaction kinetics in the nitrate reduction reaction.

[0129] II. Electrocatalytic removal of nitrate was conducted in a single-chamber electrolytic cell (50 mL) using a GPS305D DC regulated power supply. In the two-electrode system, a platinum sheet served as the anode, and different prepared catalytic materials were coated onto a 1.0 × 2.0 cm carbon cloth as the cathode, with the distance between the two electrodes controlled within the range of 0.5–2.0 cm. The 30 mL electrolyte contained 50 mg / L nitrate (calculated as N). A current of 50 mA was applied to the system, and samples were taken every 30 min. The nitrate content of the water samples at each time point was determined using ion chromatography, and the nitrate removal rate was calculated. The ammonia nitrogen concentration during the reaction process was determined by Nessler's reagent spectrophotometry, and the ammonia nitrogen conversion rate was calculated.

[0130] Depend on Figure 12 As shown in (a), after 180 min of reaction, the degradation rate of nitrate by the Cu-Ni@S-1 catalyst reached 94.99%, while the degradation rate of nitrate by the Cu-Ni / S-1 catalyst was only 59.14% after 180 min. As for the S-1 molecular sieve alone and the carbon cloth alone, the degradation rates of nitrate after 180 min were 30.22% and 24.40%, respectively. The S-1 molecular sieve itself does not possess catalytic activity; like the carbon cloth, it can only reduce nitrate in solution through cathode current, hence its poor degradation effect. The Cu-Ni@S-1 catalyst removed as much as 94.99% of nitrate within 180 min, demonstrating an astonishing removal efficiency far exceeding that of other similar catalysts. Therefore, Cu-Ni@S-1 is a high-performance electrocatalytic material for the reduction of nitrate. Figure 12 (b) and Figure 12(c) illustrates the changing trends of the products generated during nitrate removal. With increasing electrolysis time, nitrate is gradually removed, nitrite is generated first and then consumed, while the concentration of ammonia nitrogen continuously increases. Nitrate is mainly reduced to ammonia nitrogen. Since many intermediates generated during nitrate reduction carry a negative charge and are easily repelled by the electric field, they are difficult to accumulate on the cathode, thus inhibiting the nitrogen generation reaction. Furthermore, the generated nitrite is unstable and easily oxidized to nitrate. Therefore, the main product of nitrate reduction is ammonia nitrogen.

[0131] During use, if the Cu-Ni@S-1 catalyst is deactivated due to external environmental influences, the reaction efficiency will decrease significantly, affecting the continued progress of the catalytic reaction. To test the stability of the Cu-Ni@S-1 catalyst, five cyclic experiments were conducted. During each electrocatalytic degradation cycle, the electrode was carefully cleaned and dried, and then repeatedly immersed in the electrocatalytic reduction system to degrade new nitrates. The experimental conditions were 50 mg / L (as N) nitrate and 50 mA / cm². 2 The current density. Experimental results are as follows: Figure 13 As shown. From Figure 13 As can be seen, the nitrate degradation rates of the Cu-Ni@S-1 catalyst within 180 min after five cycles were 97.7%, 95.6%, 94.5%, 92.7%, and 91.9%, respectively. The catalyst maintained a high degradation efficiency even after five cycles, indicating that the Cu-Ni@S-1 catalyst has good cycle stability.

[0132] Atomic absorption spectrometry was performed on the water sample 180 min after the reaction to determine the concentration of heavy metal ions in the water, in order to investigate whether the confinement effect improved the stability of the catalyst and reduced metal leaching. Comparative results are shown below. Figure 14 As shown.

[0133] from Figure 14 As can be seen, after 180°C of reaction, the copper ion concentration in the water containing the Cu-Ni@S-1 catalyst was 0.029 mg / L and the nickel ion concentration was 0.079 mg / L, significantly lower than the 0.153 mg / L copper ion concentration and 0.443 mg / L nickel ion concentration in the water containing the Cu-Ni / S-1 catalyst. This comparison demonstrates that the confinement effect improves the catalyst's stability and reduces the amount of metal leaching. Furthermore, the copper ion concentration met the Class II groundwater quality standard (≤0.05 mg / L), and the nickel ion concentration met the Class IV groundwater quality standard (≤0.1 mg / L), indicating the excellent effect of the confinement effect.

[0134] III. In the electrocatalytic reduction process, current density is undoubtedly a crucial factor affecting the reaction. To verify the effect of current density on the electrocatalytic reduction and degradation of nitrate, the current density was controlled at 1 mA / cm². 2 10 mA / cm 2 25 mA / cm 2 50mA / cm 2 and 100 mA / cm 2 The reaction was carried out for 180 min. Degradation experiments were conducted while maintaining the operating procedures and other degradation conditions, and the nitrate conversion rate and selectivity of various products were obtained as follows: Figure 15 As shown.

[0135] from Figure 15 It can be seen that when the current density is as low as 1 mA / cm 2 At the initial current density, the nitrate removal rate is quite slow. However, as the current density increases, the nitrate removal rate gradually increases. (Current density: 100 mA / cm²) 2 At a reaction time of 180 min, 98.89% of nitrates could be degraded. This is likely because a higher current density can provide more electrons to the electrode surface, promoting the electrocatalytic reaction. However, as the current density increases to a certain level (50 mA / cm²), the removal rate does not increase significantly. 2 At that time, the nitrate conversion rate was only higher than that at a current density of 100 mA / cm². 2 The current density decreased by 1.19%. This is likely due to the mass transfer of nitrate limiting the reaction rate. Therefore, choosing an appropriate current density is crucial to balance nitrate degradation and energy consumption.

[0136] IV. As is well known, the initial pH of the reaction system has a significant impact on the reaction process, affecting reduction kinetics and the selectivity of byproducts. To investigate the effect of the initial pH of the reaction system on the electrocatalytic reduction and degradation of nitrates, this embodiment of the invention uses appropriate amounts of H₂SO₄ and NaOH to adjust the pH of the reaction system to avoid side reactions. Degradation experiments were conducted under different pH conditions (3, 5, 7, 9, and 11), keeping the operating steps and other degradation conditions constant, and the nitrate conversion rate and the selectivity of various products were obtained as follows: Figure 16 As shown.

[0137] from Figure 16It can be seen that good performance is achieved under both acidic and neutral conditions, with the best degradation effect at pH=3, where 100% of nitrates are degraded after 180 min. While pH=7 has a slight impact, a 97.70% degradation effect is still achieved after 180 min. However, as the pH increases further to alkaline conditions, the nitrate removal rate decreases. At pH=11, the degradation rate drops to 60.40% after 180 min, indicating that pH has a certain influence on the degradation process. This may be because acidic conditions favor the electrocatalytic generation of *H, thereby increasing the nitrate removal rate. Therefore, the optimal pH for electrocatalytic nitrate removal using the Cu-Ni@S-1 catalyst is 3.

[0138] V. To investigate the effect of initial nitrate concentration on the electrocatalytic reduction and degradation of nitrate, electrocatalytic degradation tests were conducted at nitrate concentrations of 30 mg / L, 50 mg / L, and 100 mg / L (all based on nitrogen). The operating procedures and other degradation conditions were kept constant during the degradation experiments. The nitrate conversion rate and the selectivity of various products were obtained as follows: Figure 17 As shown.

[0139] from Figure 17 The study shows the effect of different initial concentrations on nitrate degradation within a certain range. The nitrate removal rate decreases with increasing nitrate concentration. This may be because excess nitrate in the electrolyte leads to incomplete nitrate reduction, increasing the formation of gaseous N (N2, N2O) through intermediate contact. This results in a decrease in nitrate removal rate and an increase in the selectivity of gaseous nitrogen compounds.

[0140] VI. To investigate the effect of different initial chloride ion concentrations on the electrocatalytic reduction and degradation of nitrate, electrocatalytic degradation tests were conducted at chloride ion concentrations of 0 mg / L, 10 mg / L, 50 mg / L, and 100 mg / L. The operating procedures and other degradation conditions were kept constant during the degradation experiments. The nitrate removal rate and ammonia nitrogen yield were obtained as follows: Figure 18 As shown.

[0141] from Figure 18 It can be seen that different chloride ion concentrations have a certain impact on the degradation efficiency of nitrate. After 180 min of reaction, the nitrate removal rates under chloride ion concentrations of 10 mg / L, 50 mg / L, and 100 mg / L were 90.30%, 78.54%, and 72.87%, respectively. This may be due to the active sites being degraded by Cl. - Occupy, because Cl - The presence of [a substance] can cause side reactions in the reaction system, generating Cl2, thus affecting the removal efficiency of nitrates. Furthermore, with the increase of Cl... -As the concentration increases, the ammonia nitrogen concentration decreases, and more ammonia nitrogen is oxidized into nitrogen gas. This is due to the presence of Cl in the water. - In the case of Cl - During anodic oxidation, Cl2 is generated, which further combines with H2O to form HClO / ClO. - It is a typical strong oxidizing agent that can convert ammonia nitrogen into nitrogen gas.

[0142] VII. Electrocatalytic reduction of nitrate is a complex process involving both electron transfer-mediated direct reduction and atomic H*-mediated indirect reduction. Since tert-butanol (TBA) can act as an H* quencher, to investigate the effect of atomic H*-mediated indirect reduction on the electrocatalytic reduction and degradation of nitrate, electrocatalytic degradation tests were conducted at tert-butanol concentrations of 0 mM / L, 5 mM / L, and 10 mM / L. Degradation experiments were carried out while maintaining the operating procedures and other degradation conditions unchanged. The nitrate removal rate and ammonia nitrogen yield were obtained as follows: Figure 19 As shown.

[0143] from Figure 19 It can be seen that different TPA concentrations have a certain impact on the nitrate degradation effect. After 120 min of reaction, the nitrate removal rate was 61.09% under the condition of 5 mM / L tert-butanol, and only 49.48% under the condition of 10 mM / L tert-butanol, which was 45.58% lower than that under the condition of 0 mM / L tert-butanol. With the increase of tert-butanol concentration, the nitrate removal rate decreased significantly. This indicates that most of the H* was captured by tert-butanol and could not participate in the hydrogenation reaction of the nitrate reduction intermediate, further proving that H* plays a key role in promoting nitrate conversion. As the nitrate degradation effect deteriorated, the production of ammonia nitrogen also decreased. This indicates that H* plays an important role in the electrocatalytic reduction of nitrate by the Cu-Ni@S-1 catalyst.

[0144] 8. To better understand the superior electrocatalytic performance and catalytic reaction mechanism of Cu-Ni@S-1 for nitrate reduction, this invention further incorporates DFT calculations to compare changes in electronic structure and the difference in reaction energy barriers compared to nitrate reduction. The reaction pathway for the electrocatalytic reduction of nitrate using the Cu-Ni@S-1 catalytic material is as follows: Figure 20 , Figure 21 As shown.

[0145] The reduction of nitrate to ammonia involves the transfer of nine protons and eight electrons. Figure 20 The demonstrated reaction pathway is applicable to the electrocatalytic reduction of nitrates to ammonia using a Cu-Ni@S-1 catalyst. The first step is NO3. - The adsorption of NO3 during this process -When adsorbed onto the catalyst Cu-Ni@S-1, no electron transfer is required; the subsequent process involves the stepwise reduction of *NO3, which is successively converted into *NO2, *NO, *NOH, *N, *NH, and *NH2, ultimately desorbing to obtain the catalyst. The specific reaction formula is as follows:

[0146] *+NO3 - +9H + →*NO3+9H + (16)

[0147] *NO3+9H + →*NO2+7H + +H2O (17)

[0148] *NO2+7H + +H2O→*NO+5H + +2H2O (18)

[0149] *NO+5H + +2H₂O→*NOH+4H + +2H2O (19)

[0150] *NOH+4H + +2H₂O→*N+3H + +3H2O (20)

[0151] *N+3H + +3H₂O→*NH₂+2H⁺ + +3H2O (21)

[0152] *NH+2H + +3H₂O→*NH₂+H + +3H2O (22)

[0153] *NH2+H + +3H₂O→*+3H₂O+NH₃(23)

[0154] Figure 21The diagram presents the Gibbs free energy (ΔG) changes of Cu-Ni@S-1 and Cu-Ni / S-1 during nitrate reduction. For Cu-Ni@S-1, the rate-limiting step is from *NH2 to NH3, with a relatively small ΔG upslope of 2.4 eV. For Cu-Ni / S-1, the rate-limiting step is from *NO to *NOH, with a larger ΔG upslope of 2.6 eV. Therefore, the energy barrier of the rate-limiting step in Cu-Ni@S-1 is lower than that in Cu-Ni / S-1, resulting in higher nitrate removal efficiency for Cu-Ni@S-1. DFT calculations show that Cu-Ni@S-1 exhibits good conductivity, strong adsorption capacity for nitrate ions, and no significant reaction barrier for nitrate reduction, thus demonstrating significant electrocatalytic activity.

[0155] Figure 22 The adsorption differential charge of nitrates with Cu-Ni / S-1 and Cu-Ni@S-1 was shown. Cu-Ni@S-1 exhibits a significantly higher electron-accepting ability than Cu-Ni / S-1, and the bond length of nitrate adsorbed by Cu-Ni@S-1 is shorter than that of Cu-Ni / S-1. Shorter bond lengths indicate stronger bonds and more stable molecules. Furthermore, the adsorption energies of Cu-Ni@S-1 and Cu-Ni / S-1 were calculated. The adsorption energy of Cu-Ni@S-1 for nitrates is -3.069 eV, which is stronger than that of Cu-Ni / S-1. Therefore, Cu-Ni@S-1 possesses a stronger adsorption capacity for nitrates, making it more readily reacted with and reduced by nitrates.

[0156] The partial wave density of states of Cu and Ni atoms in the d orbitals of Cu-Ni@S-1 and Cu-Ni / S-1 catalysts were calculated respectively. Figure 23In the diagram, (a) represents the partial wave state density of the 3d orbitals of Cu atoms, and (b) represents the partial wave state density of the 3d orbitals of Ni atoms. The dashed lines represent the d-band centers of the two catalysts. In transition metal-based catalysts, the interaction between the adsorbed state and surface d electrons typically forms bonding and antibonding orbitals. The bonding orbitals are below the Fermi level, with lower energy and are fully filled, while the antibonding orbitals are also below the Fermi level, with higher energy but are only partially filled. The higher the d-band center, the higher the antibonding state, and the stronger the adsorption force. The d-band center of Cu atoms in the Cu-Ni@S-1 catalyst is -1.879 eV, which is closer to the Fermi level than that of Cu-Ni / S-1. This indicates that it has a better adsorption capacity for nitrates. The d-band center of Ni atoms in the Cu-Ni@S-1 catalyst is also higher than that in Cu-Ni / S-1, which modulates the gap between the Ni 3d orbital d-band center and the N 2p orbital, increasing the energy of the N 2p antibonding state above the Fermi level. Ultimately, the interaction between the metal atoms and the key *NOH intermediate is enhanced, lowering the limiting potential for selective NH3 synthesis. Therefore, the catalytic activity of Cu-Ni@S-1 is significantly better than that of Cu-Ni / S-1, which is consistent with the experimental results above.

[0157] In summary, this invention prepares a sub-nanometer hybrid bimetallic cluster catalyst in pure silica S-1 zeolite nanocrystals. This catalyst, used for the electrocatalytic treatment of nitrates in groundwater, improves the efficiency of nitrate removal and provides a more economical and effective method for achieving high-efficiency nitrate pollution removal from groundwater. Specifically, this invention has the following technical effects:

[0158] (1) Using a Cu-Ni metal ethylenediamine complex mixture as a catalyst precursor, a sub-nanometer hybrid bimetallic cluster catalyst was prepared in pure silica S-1 zeolite nanocrystals via hydrothermal synthesis. The sub-nanometer hybrid bimetallic cluster catalyst, due to the synergistic effect of the bimetals, solved the problem of slow kinetics in the nitrate reduction reaction, thus enhancing the catalyst's performance.

[0159] (2) Sub-nanometer-sized metal clusters have better catalytic activity or selectivity than nano-sized metal clusters. Confined engineering can effectively disperse Cu-Ni bimetallic active sites, increase the number of active sites, and generate smaller sub-nanometer particles, solving the problem of low catalyst activity and thus improving the nitrate removal rate.

[0160] (3) Based on the confinement effect, Cu and Ni active sites can be encapsulated in the nanopores of zeolite molecular sieves to avoid direct contact with harsh external environments (such as strong acids and strong bases), thereby delaying and preventing the deactivation of active sites, extending the service life of the catalyst, and solving the problem of poor catalyst stability.

[0161] (4) Due to the confinement effect of zeolite, the d-band center of Cu and Ni shifts upward, thereby promoting the adsorption of nitrates in water by Cu-Ni@S-1, significantly reducing the reaction energy barrier of electrocatalytic reduction of nitrates, inhibiting the occurrence of side reactions, solving the problem of side reactions affecting catalytic efficiency, and significantly improving the efficiency of electrocatalytic nitrate reduction reaction.

[0162] (5) The Cu-Ni bimetallic structure reduces the gap between the Ni 3d orbital d-band center and the N 2p orbital, leading to enhanced interaction between the metal atom and the key NOH* intermediate. Meanwhile, since NH3 synthesis is the rate-limiting step in the reaction, it restricts the overall electrocatalytic removal efficiency of nitrates. The bimetallic structure reduces the Gibbs free energy of NH3 synthesis, lowers the limiting potential for selective NH3 synthesis, accelerates the reaction rate, and solves the problem of the rate-limiting step affecting the efficiency of electrocatalytic nitrate removal.

[0163] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, characterized in that, Includes the following steps: Tetrapropylammonium hydroxide was mixed with ultrapure water, and tetraethyl orthosilicate was added and stirred to obtain mixture one; Nickel chloride hexahydrate, ethylenediamine, and ultrapure water were mixed and stirred to obtain mixture two; Copper nitrate trihydrate, ethylenediamine, and ultrapure water were mixed and stirred to obtain a mixture trihydrate; the molar ratio of nickel chloride hexahydrate to copper nitrate trihydrate was 1:(0.8-1.2). Mixtures 2 and 3 were added dropwise to mixture 1, and the mixture was stirred under no precipitation conditions. Then, it was placed in an autoclave and subjected to hydrothermal synthesis at 165-175 °C to obtain the reaction product. The obtained reaction products were centrifuged and collected, and then washed and dried to obtain the catalyst precursor. The catalyst precursor was first calcined in air, and then heat-treated in a flowing hydrogen-argon mixed atmosphere to obtain the confined bimetallic catalyst; the calcination temperature was 500-600 ℃; and the heat treatment temperature was 350-450 ℃.

2. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that, The drying temperature is 75-85 ℃.

3. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that, The volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:

93.

4. A confined bimetallic catalyst prepared by any one of the preparation methods described in claims 1-3.

5. The application of the confined bimetallic catalyst as described in claim 4 in the electrocatalytic reduction of nitrate.

6. The application of the confined bimetallic catalyst as described in claim 4 in the removal of nitrates from water.

7. An electrocatalytic reduction device, comprising a cathode and an anode, characterized in that, The cathode is made using the confined bimetallic catalyst described in claim 4.

Images