Method for electrochemical reduction of nitrate using transition metal nitrides and applications thereof

Abstract

The application provides a method and application of electrochemical reduction of nitrate by using a transition metal nitride, and belongs to the field of environmental catalysis, wherein the method of electrochemical reduction of nitrate by using a transition metal nitride comprises the following steps: constructing an electrochemical catalytic system by taking a transition metal nitride catalytic electrode as a working electrode; and under the condition of power supply, the mutual transformation between metal ions on the surface of the transition metal nitride and zero-valent transition metals generated by electrochemical reduction promotes the reduction of nitrate in an electrolyte, wherein the transition metal is a transition metal of the iron group.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis, specifically relating to a method and application of electrochemical reduction of nitrate using transition metal nitrides, and more specifically to a method and application of electrochemical reduction of nitrate using iron-based transition metal nitrides. Background Technology

[0002] Nitrate (NO3) - As the highest oxidized form of nitrogen in the Earth's nitrogen cycle, nitrates accumulate in industrial and agricultural wastewater as well as domestic sewage. Their main anthropogenic sources include fertilizer use and fossil fuel combustion. Excessive nitrates not only severely impact aquatic ecosystems, leading to problems such as eutrophication, toxic algal blooms, and water hypoxia, but also threaten human health by affecting drinking water.

[0003] Existing NO3 - The transformation mainly proceeds in two directions: (1) it is reduced to nitrogen (N2) through the denitrification process in the sewage treatment plant for harmless treatment; (2) it is reduced to ammonium (NH4) through the dissimilatory nitrate process by nitrate / nitrite reductase secreted by microorganisms. + The process involves resource recovery and combines it with techniques such as air extraction, ion exchange, and struvite precipitation to recover ammonium nitrogen.

[0004] Commonly used for NO3 - The reducing metal catalysts include supported Cu-based catalysts, doped metal alloy catalysts, and noble metal catalysts. However, because the metals used are noble metals, the preparation cost is high, and they cannot meet the requirements for NO3 reduction. - With the increasing production of NO3, there is a need to develop NO3 based on inexpensive metals. - Reduction catalysts have practical significance.

[0005] Although transition metals in NO3 - There are also some applications in the design of reduction catalysts, but they mostly exhibit better performance as a second metallic element doped in alloys and their oxides. They are not the main elements providing active sites, but rather play a role in adjusting the binding energy of the metal and the D-band center, thereby improving the material's resistance to NO3. - And the adsorption and dissociation of reaction intermediates. Furthermore, catalysts with transition metals as the main component reduce NO3. - Relatively slowly, ordered mesoporous carbon-supported nano-zero-valent iron exhibited a slow electrocatalytic reaction in 24 hours with 50 mg / L NO3 in the electrolyte. - Only 65% ​​conversion rate. Nitrogen-doped graphite carbon-encapsulated iron nanoparticles showed a 24-hour conversion rate of 50 mg / L NO3 in the electrolyte. - Only 83% conversion rate. The effect of polymer bead-loaded nZVI on 50 mg / L NO3 in the electrolyte over 24 hours. -The conversion rate was 80%. The nanozyme catalyst FeNPs@MXene achieved 97.8% NO3 conversion. - Conversion rate, but its target product NH4 + The selectivity remains low, at only 76.8%. Furthermore, many reported transition metal catalysts also suffer from poor stability and corrosion resistance. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method and application for the electrochemical reduction of nitrate using transition metal nitrides, aiming to at least partially solve the above-mentioned technical problems. The specific technical solution provided by this invention is as follows.

[0007] As a first aspect of the present invention, the present invention provides a method for electrochemically reducing nitrate ions using transition metal nitrides, comprising:

[0008] An electrochemical catalytic system was constructed using a transition metal nitride catalytic electrode as the working electrode. Under the condition of energization, the interconversion between metal ions on the surface of the transition metal nitride and the zero-valent transition metal generated by electroreduction promotes the reduction of nitrate in the electrolyte. The transition metal is an iron group transition metal.

[0009] As a second aspect of the present invention, the present invention provides an application of the above-described method in wastewater treatment.

[0010] In embodiments of this invention, an electrochemical catalytic system is constructed using the prepared transition metal nitride catalytic electrode as the working electrode. Under energized conditions, the working electrode undergoes transition metal reduction, nitrate reduction, and hydrogen evolution reactions. The interconversion between metal ions on the surface of the transition metal nitride and the zero-valent transition metal generated through electroreduction promotes the reduction of nitrate in the electrolyte, with nitrate reduction being the primary reaction. This improves the nitrate conversion rate, conversion speed, and product selectivity. Furthermore, transition metal nitrides are relatively stable and not easily corroded, enabling long-term stable operation. This invention utilizes transition metal nitrides for electrochemical reduction of nitrate, and the operation method is relatively convenient. Additionally, the method of electrochemical reduction of nitrate using transition metal nitrides in this invention can be combined with new energy power utilization and ammonium nitrogen utilization and collection technologies in wastewater, making it suitable for achieving energy storage while purifying water, such as treating agricultural wastewater, domestic sewage, and some industrial water. Attached Figure Description

[0011] Figure 1 The X-ray diffraction (XRD) pattern of the iron nitride prepared in Example 1;

[0012] Figure 2 The image shows a transmission electron microscope (TEM) image of the iron nitride prepared in Example 1.

[0013] Figure 3 The image shows the deconvolution of the X-ray photoelectron spectroscopy (XPS) of the iron nitride prepared in Example 1. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0015] To solve the current problem of transition metals in NO3 - The present invention addresses the problems of low conversion rate, slow conversion speed, low product selectivity, and poor stability and corrosion resistance of the working electrode encountered in the reduction catalyst. It utilizes the prepared transition metal nitride catalytic electrode to construct an electrochemical catalytic system for the removal of nitrate ions in water. It can reduce nitrate ions relatively quickly and stably, and the catalytic electrode still maintains good catalytic performance after multiple uses.

[0016] Specifically, as a first aspect of the present invention, the present invention provides a method for electrochemically reducing nitrate ions using transition metal nitrides, comprising:

[0017] An electrochemical catalytic system was constructed using a transition metal nitride catalytic electrode as the working electrode. Under the condition of energization, the interconversion between metal ions on the surface of the transition metal nitride and the zero-valent transition metal generated by electroreduction promotes the reduction of nitrate in the electrolyte. The transition metal is an iron group transition metal.

[0018] In embodiments of the present invention, an electrochemical catalytic system is constructed using the prepared transition metal nitride catalytic electrode as the working electrode. Under energized conditions, the working electrode undergoes transition metal reduction, nitrate reduction, and hydrogen evolution reactions. The interconversion between metal ions on the surface of the transition metal nitride and the zero-valent transition metal generated by electroreduction promotes the reduction of nitrate in the electrolyte, with nitrate reduction being the dominant reaction. This improves the nitrate conversion rate, conversion speed, and product selectivity. Furthermore, the transition metal nitride is relatively stable and resistant to corrosion, enabling stable operation over extended periods.

[0019] According to an embodiment of the present invention, the transition metal nitride catalytic electrode includes a support and a transition metal nitride attached to the support. The transition metal is an iron group transition metal, wherein the iron group transition metal is iron. The transition metal nitride catalytic electrode is an iron nitride catalytic electrode. The iron nitride on the iron nitride catalytic electrode has a (111) crystal structure, and the atomic ratio of iron to nitrogen in the crystal structure is 2:1.

[0020] In the embodiments of the present invention, iron nitride has a (111) crystal structure. Under energized conditions, the surface divalent iron and the zero-valent iron generated under electroreduction conditions synergistically enhance the reduction performance of nitrate. At the same time, N doping also plays a certain promoting role in the adsorption of nitrate, thereby improving the reaction rate and product selectivity of the electrochemical reduction of nitrate by the iron nitride catalytic electrode. In addition, the Earth's crust contains abundant iron, which is low in cost and widely available, and can be applied on a large scale.

[0021] According to an embodiment of the present invention, a transition metal nitride catalytic electrode is obtained through the following steps:

[0022] A transition metal salt and a surfactant were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath and a cold reducing agent was added to carry out a reduction reaction. After aging and separation, a transition metal precursor was obtained.

[0023] A dispersion containing a transition metal precursor is coated onto a support and sintered under an ammonia atmosphere to obtain a transition metal nitride catalytic electrode with transition metal nitrides distributed on the support; or

[0024] Transition metal precursors are sintered in an ammonia atmosphere to obtain transition metal nitrides. A dispersion containing transition metal nitrides is then coated onto a support to obtain a transition metal nitride catalytic electrode.

[0025] In embodiments of the present invention, transition metal salts are reduced to elemental transition metals by adding a reducing agent. Since the reduction reaction is quite vigorous, it must be carried out in an ice-water bath. During aging, the elemental transition metals are oxidized to transition metal oxides. The presence of surfactants gives the transition metal precursors nanoscale dimensions. Subsequently, the transition metal precursors can be coated onto a support and directly sintered to form a transition metal catalytic electrode, resulting in a more robust catalytic electrode during electrochemical reactions. Alternatively, sintering can be performed first, followed by coating, allowing for the selection of different supports for electrochemical reactions. Furthermore, the method for preparing the transition metal nitride catalytic electrode of the present invention is simple and easily scalable.

[0026] In one embodiment of the present invention, iron nitride catalytic electrode is prepared using transition metal iron, and the specific preparation method is as follows:

[0027] (1) Mix the iron salt solution with the surfactant in ultrapure water, stir to obtain a mixed solution, and then place the mixed solution in an ice-water bath;

[0028] (2) Add a reducing agent (such as potassium borohydride) to the mixed solution in the ice-water bath to carry out a reduction reaction, and then age it.

[0029] (3) Collect the aged products and wash them to obtain the iron-based precursor;

[0030] (5) The dispersion containing the iron-based precursor is coated onto a support and sintered under an ammonia atmosphere to obtain an iron nitride catalytic electrode; or

[0031] Iron-based precursors were sintered in an ammonia atmosphere to obtain iron nitride. The dispersion of iron nitride was coated onto a support and dried to obtain an iron nitride catalytic electrode.

[0032] According to an embodiment of the present invention, the size of the transition metal precursor is 50-250 nm, and the size of the transition metal nitride is 100-300 nm. Since the transition metal precursor is nanoscale, the resulting transition metal nitride also has a nanoscale size. Utilizing the high specific surface area of ​​the transition metal nitride, it can adsorb nitrate ions in water and provide more reaction sites for subsequent catalytic reduction reactions.

[0033] According to an embodiment of the present invention, during the sintering process under an ammonia atmosphere, the NH3 flow rate is 50-100 mL / min, the sintering temperature is 400-600 °C, the sintering heating rate is 5-10 °C / min, and the sintering time is 100-150 min. Different sintering temperatures, heating rates, and times will affect the final structure of the nitride formed. Excessive or insufficient sintering time, or excessively high or low sintering temperatures, may lead to incomplete nitriding or changes in the crystal structure of the product.

[0034] According to embodiments of the present invention, the transition metal salt is selected from any one of chloride transition metal salts, sulfate transition metal salts, and nitrate transition metal salts; the surfactant is selected from any one of polyoxyethylene ethers, polyoxyethylene esters, and polyoxyethylene amines; the molar ratio of the transition metal salt to the surfactant and water is 6-10:1-4:2.2*10 5 Surfactants can induce transition metal precursors to have nanoscale dimensions during the aging stage through their amphiphilicity, encapsulation ability, and adjustment of reaction conditions.

[0035] According to embodiments of the present invention, the reducing agent is selected from potassium borohydride or sodium borohydride, and the molar ratio of the reducing agent to the transition metal salt is 4-10:1. The transition metal salt is reduced to the elemental transition metal by adding the reducing agent.

[0036] According to an embodiment of the present invention, the aging temperature is 2-6°C and the aging time is 4-6 hours. The transition metal element undergoes oxidation during the aging process; the degree of oxidation is controlled by adjusting the aging temperature and aging time.

[0037] According to an embodiment of the present invention, the dispersion is a mixed solution of an alcohol solvent and a film-forming agent. The alcohol solvent is selected from any one of ethanol, methanol, propanol, butanol, ethylene glycol, and propylene glycol. The film-forming agent is a Nafion-type film-forming agent, and the volume ratio of the alcohol solvent to the film-forming agent is 8-10:1. The transition metal nitride is immobilized on the carrier by the film-forming agent.

[0038] According to embodiments of the present invention, the carrier is any one of carbon paper, carbon cloth, carbon rod, carbon felt, foamed titanium board, and conductive glass, and the loading amount of transition metal nitrides on the carrier is 0.5-1.5 mg / cm³ based on the transition metal content. 2 .

[0039] As a second aspect of the present invention, the present invention provides an application of the above-described method in wastewater treatment.

[0040] In the embodiments of the present invention, nitrate ions are reduced electrochemically using transition metal nitrides, a relatively convenient operation method. Furthermore, the method of reducing nitrate ions electrochemically using transition metal nitrides in this invention can be combined with new energy power utilization and ammonium nitrogen utilization and collection technologies in wastewater, making it suitable for achieving energy storage while purifying water, such as treating agricultural wastewater, domestic sewage, and some industrial water.

[0041] The present invention will be further illustrated below through embodiments and related test experiments. In the following detailed description, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present invention. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict. All instruments, consumables, and reagents used in the following embodiments are commercially available unless otherwise specified.

[0042] Example 1

[0043] The transition metal nitride catalytic electrode prepared in Example 1 is an iron nitride catalytic electrode, and its preparation process is as follows:

[0044] (1) Mix 1 mL of the prepared 400 mmol / L ferric chloride solution with 1 g of an aqueous dispersion containing 10 wt% polyoxyethylene octyl ether (TX-114) as a surfactant in 193 mL of ultrapure water and stir magnetically for 15 min to obtain a well-dispersed mixed solution. Then, place the mixed solution in an ice-water bath for 15 min to keep the mixed solution at a low temperature.

[0045] (2) Add 5 mL of 4.8 mmol / L KBH4 solution, which has been prepared and kept warm with ice water, as a reducing agent to the mixed solution in the ice water bath obtained in step (1). After stirring rapidly for 1 min, remove the rotor immediately and let the mixed solution age at 4°C for 5 h.

[0046] (3) The blackish-brown solid (mainly iron oxide and elemental iron) formed after aging was collected by natural sedimentation and magnetic adsorption. The iron-based precursor was removed and washed twice with ethanol to remove surfactants and other unreacted reactants. Finally, the obtained iron-based precursor was dispersed in 10 mL of dispersion, which consisted of 9 mL of ethanol and 1 mL of 5% Nafion 117 solution.

[0047] (4) A 1cm*2.5cm carbon paper electrode, model TGP-H-060, was used as a carrier. The carbon paper electrode was first purified. The purification process was as follows: the carbon paper electrode was immersed in concentrated nitric acid and heated to 130℃. After cooling, it was taken out and washed three times with deionized water. The dispersion containing the iron-based precursor was drop-coated onto the purified carbon paper electrode and placed in a ceramic boat. The ceramic boat was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under an atmosphere of NH3 flow rate of 75mL / min. The temperature was held for 120min and cooled to room temperature to obtain a carbon paper electrode with a surface covered with black powder (i.e., iron nitride), which is the catalytic electrode supported on iron nitride.

[0048] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the iron nitride prepared in Example 1.

[0049] like Figure 1 As shown, iron nitride is a typical Fe2N phase.

[0050] Figure 2 This is a transmission electron microscope (TEM) image of the iron nitride prepared in Example 1.

[0051] like Figure 2 As shown, the morphology of iron nitride is mainly granular, with the particles either stacked or dispersed on the carbon fibers constituting the carbon paper electrode, and the size of a single particle is 50-300 nm.

[0052] Figure 3 The image shows the deconvolution of the X-ray photoelectron spectroscopy (XPS) of the iron nitride prepared in Example 1.

[0053] like Figure 3 As shown, the Fe elements on the surface of iron nitride are mainly divalent and trivalent Fe sites coordinated with N atoms, verifying the successful nitridation of the iron-based precursor.

[0054] Application Example 1

[0055] Application Example 1 utilizes the iron nitride catalytic electrode prepared in Example 1 as the working electrode for electrochemical experiments. The electrochemical experiments were conducted using a three-electrode system on an electrochemical workstation in an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane, with magnetic stirring at 600 rpm. A platinum plate and an Ag / AgCl electrode were used as the counter electrode and reference electrode, respectively, with a solution containing 50 mg / L NO3. - An aqueous solution of -N and 50 mmol / L sodium sulfate was used as the electrolyte (50 mL); before the experiment, the electrolyte was bubbled with pure nitrogen to remove oxygen. The applied voltage was -1.3 V for 3 hours. All voltages were recorded with an Ag / AgCl electrode as the reference electrode. The results of the electrocatalytic conversion of nitrate by the iron nitride catalytic electrode are shown in Table 1.

[0056] Table 1. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 1.

[0057]

[0058] Application Example 2

[0059] The electrochemical experimental conditions in Application Example 2 are the same as those in Application Example 1. The main difference is that the applied voltage is -1.1V. The evaluation results of the electrocatalytic conversion of nitrate by the iron nitride catalytic electrode are shown in Table 2.

[0060] Table 2. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 2.

[0061]

[0062] Application Example 3

[0063] The electrochemical experimental conditions in Application Example 3 are the same as those in Application Example 1. The main difference is that the applied voltage is -1.2V. The evaluation results of the electrocatalytic conversion of nitrate by the iron nitride catalytic electrode are shown in Table 3.

[0064] Table 3. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 3.

[0065]

[0066] Application Example 4

[0067] Application Example 4 is based on the same electrochemical experimental conditions as Application Example 1. The main difference is that the applied voltage is -1.4V. The evaluation results of the electrocatalytic conversion of nitrate by the iron nitride catalytic electrode are shown in Table 4.

[0068] Table 4. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 4.

[0069]

[0070] Application Example 5

[0071] Application Example 5 is based on the same electrochemical experimental conditions as Application Example 1. The main difference is that the applied voltage is -1.5V. The evaluation results of the electrocatalytic conversion of nitrate by the iron nitride catalytic electrode are shown in Table 5.

[0072] Table 5. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 5.

[0073]

[0074]

[0075] Application Example 6

[0076] The electrochemical experimental conditions in Application Example 6 are the same as those in Application Example 1. The main difference is that the nitrate concentration in the electrolyte is 20 mg / L NO3. - The evaluation results of the electrocatalytic conversion of nitrate by the -N, iron nitride catalytic electrode are shown in Table 6.

[0077] Table 6. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 6.

[0078]

[0079] Application Example 7

[0080] The electrochemical experimental conditions in Application Example 7 are the same as those in Application Example 1. The main difference is that the nitrate concentration in the electrolyte is 100 mg / L NO3. - The evaluation results of the electrocatalytic conversion of nitrate by the -N, iron nitride catalytic electrode are shown in Table 7.

[0081] Table 7. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 7.

[0082]

[0083] Application Example 8

[0084] Application Example 8 uses the same electrochemical experimental conditions as Application Example 1, the main difference being that the nitrate concentration in the electrolyte is 200 mg / L NO3. - The evaluation results of the electrocatalytic conversion of nitrate by the -N, iron nitride catalytic electrode are shown in Table 8.

[0085] Table 8. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 8.

[0086]

[0087]

[0088] Application Example 9

[0089] The electrochemical experimental conditions in Application Example 9 are the same as those in Application Example 1. The main difference is that the nitrate concentration in the electrolyte is 400 mg / L NO3. - The evaluation results of the electrocatalytic conversion of nitrate by the -N, iron nitride catalytic electrode are shown in Table 9.

[0090] Table 9. Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 9.

[0091]

[0092] Application Example 10

[0093] Application Example 10 uses the same electrochemical experimental conditions as Application Example 1. The main difference is that the electrolyte is replaced with 50 mg / L NO3 after 3 hours of reaction. - The electrolyte was prepared with -N and 50 mmol / L sodium sulfate. This process was repeated 5 times to allow the catalytic electrode to undergo 6 complete electrochemical processes. The evaluation results of the electrocatalytic conversion activity of the iron nitride catalytic electrode for nitrate are shown in Table 10.

[0094] Table 10 Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 10

[0095]

[0096] To illustrate the necessity of the nitriding treatment (i.e., sintering under an ammonia atmosphere) of the present invention for regulating the electronic structure of transition metal elements, the following experiments were conducted.

[0097] Comparative Example 1

[0098] The difference between Comparative Example 1 and Application Example 1 is that the iron-based precursor prepared in Example 1 was dispersed in a dispersion solution and then directly drop-coated onto carbon paper. After drying, an iron-based precursor catalytic electrode was obtained. The obtained iron-based precursor catalytic electrode was directly used for electrocatalytic nitrate reduction. The electrochemical experimental conditions were the same as in Application Example 1. The evaluation results of the electrocatalytic conversion activity of this iron-based precursor catalytic electrode for nitrate are shown in Table 11.

[0099] Table 11 Catalytic activity of the catalytic electrode under electrochemical conditions in Comparative Example 1

[0100]

[0101] The electrochemical experiments in Application Examples 1-10 and Comparative Example 1 show that, compared to the iron-based precursor catalytic electrode obtained by nitriding the iron-based precursor, the iron nitride catalytic electrode can effectively increase the reduction of NO3- through electrochemical reactions by catalyzing nitrate ions. -The removal rate and product selectivity were improved. Furthermore, the iron nitride catalytic electrode exhibited good NO3 stability over a wide voltage and substrate concentration range. - The conversion activity is high; under optimal voltage and nitrate concentration, it can rapidly, stably, and selectively convert nitrate to ammonium nitrogen, with lower nitrite selectivity. The nitrate removal rate exceeds 90%, and the selectivity for nitrate to ammonium nitrogen conversion exceeds 90%. Furthermore, the iron nitride catalytic electrode maintains good catalytic performance even after multiple uses.

[0102] Furthermore, considering that transition metals have similar atomic structures and exist in similar forms in nature, as well as similar physicochemical conditions for migration and precipitation, the method of electrochemical catalytic reduction of nitrate using the above-mentioned iron nitride catalytic electrode can also be applied to other iron group transition metals, and it also has certain applicability.

[0103] Application Example 11

[0104] Application Example 11 prepared a cobalt nitride catalytic electrode with cobalt as the transition metal nitride. Specifically, the 400 mmol / L ferric chloride solution in Example 1 was replaced with a 400 mmol / L cobalt chloride solution. The prepared cobalt nitride catalytic electrode was subjected to electrochemical experiments under the same conditions as in Application Example 1. The evaluation results of the electrocatalytic conversion activity of the cobalt nitride catalytic electrode for nitrate conversion are shown in Table 12.

[0105] Table 12 Catalytic activity of the catalytic electrode under electrochemical conditions in Application Example 11

[0106]

[0107] Example 11 demonstrates that the method of reducing nitrate ions by electrochemical reaction using iron group transition metal nitrides has certain versatility, and the transition metal raw materials can be selected according to needs.

[0108] As can be seen from the above embodiments, the method of electrochemical reduction of nitrate using transition metal nitrides in this invention has simple operating conditions and can remove nitrate pollution efficiently and stably under relatively mild electrochemical conditions. This invention utilizes inexpensive transition metals to prepare catalysts, catalyzing the reduction of nitrate through electrochemical reactions. This method has certain practical applications in water purification, further reducing the burden of eutrophication and providing the public with an effective water treatment method. Simultaneously, the high selectivity for ammonium nitrogen indicates its potential application in the energy utilization field, in contrast to the large-scale generation of NO3. - By combining wastewater treatment processes, clean ammonia production and energy storage can be achieved through on-site recycling, thereby contributing to the reduction of carbon emissions.

[0109] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the electrochemical reduction of nitrate using transition metal nitrides, comprising: An electrochemical catalytic system was constructed using a transition metal nitride catalytic electrode as the working electrode. Under energized conditions, the interconversion between metal ions on the surface of the transition metal nitride and the zero-valent transition metal generated by electroreduction promoted the reduction of nitrate ions in the electrolyte. The applied voltage was -1.3V, and the duration was 3 hours. The transition metal was an iron group transition metal. Wherein, the iron group transition metal is iron, the transition metal nitride catalytic electrode is iron nitride catalytic electrode, the iron nitride on the iron nitride catalytic electrode has a (111) crystal structure, and the atomic ratio of iron to nitrogen in the crystal structure is 2:1; The transition metal nitride catalytic electrode is obtained through the following steps: A transition metal salt and a surfactant are mixed to obtain a mixed solution. This mixed solution is placed in an ice-water bath and a cold reducing agent is added to carry out a reduction reaction. After aging and separation, a transition metal precursor is obtained. A dispersion containing the transition metal precursor is coated onto a support and sintered under an ammonia atmosphere to obtain a transition metal nitride catalytic electrode with the transition metal nitride distributed on the support. The reducing agent is selected from either potassium borohydride or sodium borohydride, and the molar ratio of the reducing agent to the transition metal salt is 4-10:

1.

2. The method according to claim 1, wherein, The size of the transition metal nitride is 100-300 nm.

3. The method according to claim 1, wherein, The sintering temperature is 400-600℃, the sintering heating rate is 5-10℃ / min, and the sintering time is 100-150min.

4. The method according to claim 1, wherein, The transition metal salt is selected from any one of the following: chloride transition metal salt, sulfate transition metal salt, and nitrate transition metal salt; The surfactant is polyoxyethylene ether; The molar ratio of the transition metal salt to the surfactant and the water is 6-10:1-4:2.

2. 10 5 .

5. The method according to claim 1, wherein, The carrier can be any one of carbon paper, carbon cloth, carbon rod, carbon felt, foamed titanium board, or conductive glass.

6. An application of the method as described in claim 1 in wastewater treatment.

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