An Fe single-atom catalyst material with electrocatalytic nitrate reduction performance and its preparation method

Abstract

The present invention discloses an Fe single-atom catalyst material with electrocatalytic nitrate reduction performance and a preparation method thereof, an electrocatalyst of Te-doped Fe-N4 material loaded on graphene and a preparation method thereof. Te and Fe are gradually doped onto ZIF-8 formed by zinc nitrate and 2-methylimidazole. After high-temperature pyrolysis, a catalyst with a catalytic site structure of Fe-N3Te is formed. After calcination, its microscopic shape is an irregular hexagon. The present invention performs Te doping modification on the traditional Fe-N4 site, changes the original geometric symmetry, thereby strengthening the adsorption of polar intermediates by the catalytic site, reducing the energy barrier of the rate-determining step, and improving the activity and selectivity of the catalyst. The catalyst can have good stability through sixteen cyclic tests and the preparation method is simple. It can effectively convert nitrate pollutants in sewage and has a large-scale application prospect.

Description

Technical Field

[0001] The present invention relates to the field of single-atom catalyst materials for electrocatalytic nitrate reduction to ammonia. Specifically, it relates to an electrocatalytic material modified with Fe-N4 sites and a preparation method thereof, that is, an Fe single-atom catalyst material with electrocatalytic nitrate reduction performance and a preparation method thereof. Background Art

[0002] Ammonia (NH3) is an important raw material for the production of amino fertilizers. Currently, the annual global demand for ammonia is 150 million tons, and by 2023, the demand in China will reach more than 60 million tons, with a huge market demand. Currently, industrial ammonia synthesis mainly uses the Haber-Bosch process, but this process consumes a large amount of energy and requires high temperature (400 - 500 °C) and high pressure (150 - 250 atm). According to statistics, the Haber-Bosch process accounts for 1% - 2% of the total global energy consumption and emits approximately 4 billion tons of carbon dioxide per year. Its heavy carbon footprint brings corresponding pressure to energy and environmental protection. Therefore, it is very important to find a new green and mild ammonia synthesis method to replace the existing technology.

[0003] Electrocatalytic ammonia synthesis is divided into electrocatalytic nitrogen reduction to ammonia (NRR) and electrocatalytic nitrate reduction to ammonia (NO3RR). However, the nitrogen-nitrogen triple bond energy (941 kJ mol −1 ) of nitrogen molecules is relatively high and difficult to break; at the same time, the solubility of nitrogen in aqueous solution is low, resulting in a low ammonia production rate for this reaction. In contrast, the lower dissociation energy of N=O (204 kJ mol -1 ) and the higher solubility of nitrate make NO3RR easier to drive than NRR. In addition, NO3RR can simultaneously achieve the treatment of nitrate, which is a water pollutant. In recent years, the improper treatment of industrial sewage and the overuse of chemical fertilizers have led to too high nitrate concentrations in wastewater, which may disrupt the balance of the water ecosystem and cause human diseases such as methemoglobinemia, blue baby syndrome, and even cancer. Currently, the main methods for treating water-soluble nitrate pollutants include ion exchange method, biological denitrification method, electrodialysis method, reverse osmosis method, etc. However, these methods have problems such as low efficiency, serious secondary pollution, and high energy consumption, and are difficult to be further promoted. Therefore, electrocatalytic nitrate reduction to ammonia is a promising ammonia synthesis method, taking into account two important aspects of environmental protection and energy conservation. Therefore, it is of great significance to develop efficient NO3RR catalysts.

[0004] In recent years, single-atom catalysts with a structure of metal-N4 sites dispersed on nitrogen-doped carbon have the highest atomic utilization rate and structural stability, such as Fe-N4 sites and Cu-N4 sites, and these sites exhibit good electrocatalytic activity for NO3RR. NO3RR is a complex electrocatalytic reduction process involving 8 electrons and 9 protons. Designing efficient catalytic sites, enhancing their adsorption of nitrate intermediates (*HNO2), promoting the deep reduction rather than desorption of the intermediates (*HNO2), reducing the generation of toxic by-product nitrite, and improving the selectivity and catalytic activity of ammonia as the main product are all key scientific problems that need to be urgently solved. However, the metal-N4 sites are geometrically symmetric and have weak adsorption of polar intermediates during the electrocatalytic process, and their catalytic activity and selectivity need to be improved. Therefore, how to effectively enhance the polarity of the metal-N4 sites to strengthen their adsorption of *HNO2 intermediates is an effective method to improve the catalytic activity and selectivity of the catalytic sites for NO3RR, but it is challenging.

[0005] In the present invention, Te element is used to dope and modify the Fe-N4 sites to form Fe-Te bonds, thereby breaking the geometric symmetry of the Fe-N4 sites, enhancing the polarity of the catalytic sites, improving their adsorption of the reaction intermediate *HNO2, enabling further deep reduction instead of desorption, and improving the activity and selectivity of the catalyst. Summary of the Invention

[0006] The purpose of the present invention is to provide an Fe single-atom catalyst material with electrocatalytic nitrate reduction performance and its preparation method, which can solve the problems that the single-atom catalyst of Fe-N4 sites has weak adsorption of polar intermediates, low reaction activity and selectivity during the electrocatalytic reduction of nitrate to ammonia, effectively improve the polarity of the catalytic sites, enhance the adsorption of the catalytic sites to polar intermediates, and improve the catalytic activity and selectivity of electrocatalytic nitrate reduction to ammonia; the present invention has the advantages of simple preparation process, low cost, etc., and has a breakthrough improvement in electrocatalytic nitrate reduction performance, and is expected to further carry out industrial research in the fields of nitrate sewage treatment and synthetic fertilizers.

[0007] To solve the above technical problems, the present invention is realized through the following technical solutions:

[0008] An Fe single-atom catalyst material with electrocatalytic nitrate reduction performance, namely Fe-N3Te / CN material, includes Fe-N3Te as the catalytic site and a graphene carrier with carbon and nitrogen as the main body (carbon:nitrogen mass ratio is 1:7~1:10), presenting a hexagonal structure.

[0009] The diameter of the Fe single atom in the Fe-N3Te / CN material is 0.1-0.3 nm;

[0010] The diameter of Te single atoms in the Fe-N3Te / CN material is 0.1 - 0.3 nm.

[0011] The diameter of the Fe-N3Te / CN material is 200 - 500 nm.

[0012] In the Fe-N3Te / CN, Te single atoms are introduced beside Fe single atoms to form Fe-Te chemical bonds.

[0013] A preparation method of an Fe single-atom catalyst material with electrocatalytic nitrate reduction performance includes preparing a Te / ZIF-8 material, preparing an Fe-Te / ZIF-8 material, and preparing an Fe-N3Te / CN material, specifically as follows:

[0014] (1) Add Zn(NO3)2·6H2O and Te powder to methanol and dissolve them, denoted as solution A; prepare a 2-methylimidazole methanol solution, denoted as solution B; quickly pour solution B into solution A, stir at room temperature for 6 - 48 hours, centrifuge, wash three times with ethanol, and dry overnight at 45 - 65 °C to obtain Te / ZIF-8.

[0015] (2) Add DMF to the Te / ZIF-8 prepared in step (1) and dissolve it, denoted as solution C; add iron acetylacetonate to DMF and dissolve it, denoted as solution D; add solution D to solution C, stir, centrifuge, wash, and dry to obtain Fe-Te / ZIF-8 powder.

[0016] (3) Heat the Fe-Te / ZIF-8 prepared in step (2) and perform high-temperature pyrolysis to obtain black powder Fe-N3Te / CN.

[0017] In step (1), the molar ratio of Zn(NO3)2·6H2O to Te powder is 5:16 - 10:1.

[0018] In step (1), add 2.97 - 11.90 g of Zn(NO3)2·6H2O and 0.5 - 4 g of Te powder to 75 - 300 mL of methanol.

[0019] The molecular weight of Te / ZIF-8 in step (1) is 357.2.

[0020] The size of the Te / ZIF-8 material in step (1) is 200 - 500 nm.

[0021] The atomic radius of Te in solution A in step (1) is 0.97 Å.

[0022] After adding Zn(NO3)2·6H2O and Te powder to methanol in step (1), ultrasonicate for half an hour to dissolve them.

[0023] In step (1), the molar concentration of the 2-methylimidazole methanol solution is 0.0375 - 0.150 mol / L.

[0024] In step (1), 75 - 300 mL of methanol is added to 3.08 - 12.32 g of 2-methylimidazole to prepare a 2-methylimidazole methanol solution.

[0025] In step (1), after adding methanol to 2-methylimidazole, it is ultrasonicated for half an hour to dissolve it.

[0026] In step (1), liquid B is quickly poured into liquid A according to a volume ratio of 1:1.

[0027] In step (1), liquid B is quickly poured into liquid A, stirred at room temperature for 6 - 48 hours, centrifuged, washed three times with ethanol, and dried at 45 - 65 °C overnight to obtain Te / ZIF-8.

[0028] In step (2), 25 - 100 mL of DMF is added to 0.25 - 1 g of Te / ZIF-8 prepared in step (1).

[0029] In step (2), after adding DMF to Te / ZIF-8, it is ultrasonicated for 0.5 - 1 hour to dissolve it.

[0030] In step (2), 25 - 100 mL of DMF is added to 0.25 - 1 g of iron acetylacetonate.

[0031] In step (2), after adding DMF to iron acetylacetonate, it is ultrasonicated for 0.5 - 1 hour to dissolve it.

[0032] In step (2), liquid D is added to liquid C, stirred at room temperature for 6 - 48 hours, centrifuged, washed three times with ethanol, and dried to obtain Fe-Te / ZIF-8 powder.

[0033] In step (2), the size of the Fe single atoms in the Fe-Te / ZIF-8 material is 0.1 - 0.3 nm.

[0034] In step (3), Fe-Te / ZIF-8 is placed in a porcelain boat and heated in a tube furnace.

[0035] In step (3), the high-temperature pyrolysis temperature is 800 - 1200 °C.

[0036] In step (3), the heating rate of the high-temperature pyrolysis is 2 °C·min -1 。

[0037] In step (3), the heat preservation time of the high-temperature pyrolysis is 1 - 5 h.

[0038] In step (3), the high-temperature pyrolysis is carried out in an inert atmosphere.

[0039] In step (3), the high-temperature pyrolysis is carried out in an argon atmosphere.

[0040] An Fe single-atom catalytic material with electrocatalytic nitrate reduction performance is used for electrocatalytic reduction of nitrate to ammonia.

[0041] An Fe single-atom catalytic material with electrocatalytic nitrate reduction performance is used for nitrate sewage treatment and synthetic fertilizer production.

[0042] An application method of an Fe single-atom catalytic material with electrocatalytic nitrate reduction performance:

[0043] Add Fe-N3Te / CN powder to ethanol and water to make a homogeneous ink-like black solution; coat this solution evenly on carbon paper and dry it to obtain a working electrode for electrocatalysis.

[0044] The beneficial effects of the present invention are as follows:

[0045] 1. The Fe single-atom catalyst material of the present invention has a nitrogen-doped carbon graphene material with an irregular hexagon as the main body, breaking the original geometric symmetry structure of Fe-N4. Compared with the traditional Fe-N4 sites, the catalytic sites of this catalyst material have increased polarity, greatly increasing the adsorption of polar intermediates by the catalytic sites, which can optimize the activity and selectivity of the catalyst and significantly improve the performance of the catalyst.

[0046] 2. The Fe single-atom catalyst material of the present invention simultaneously supports Te single atoms to form Fe-Te bonds, which are loaded on the graphene material doped with nitrogen on carbon. The nitrate reduction reaction is carried out at the Fe-Te single-atom sites, effectively improving the adsorption of polar intermediates by this catalytic site, enabling the nitrite intermediate to undergo further deep reduction rather than desorption.

[0047] 3. The preparation method of the Fe single-atom catalyst material of the present invention has a simple operation process, does not require large-scale instrument equipment, is economical and feasible; at the same time, its preparation process has strong controllability and excellent electrocatalytic nitrate reduction to ammonia performance.

[0048] 4. The Fe single-atom catalyst material of the present invention can be used as an efficient electrocatalytic material. Specifically, it can be used for electrocatalytic reduction of nitrate to ammonia, efficiently converting nitrate in industrial sewage into more valuable ammonia, and effectively solving the current problems of nitrate sewage treatment and high energy consumption in ammonia production. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is the XRD pattern of Fe-N3Te / CN in Example 1.

[0050] Figure 2 It is the TEM image of Fe-N3Te / CN in Example 1, and the scale bar is 2 - 200 nm.

[0051] Figure 3 It is the Mapping image corresponding to the aberration-corrected electron microscopy of Fe-N3Te / CN in Example 1.

[0052] Figure 4 It is the LSV image of the electrocatalytic nitrate-to-ammonia production of Fe-N3Te / CN in Example 1.

[0053] Figure 5 It is the Faraday efficiency and ammonia production rate image of the 16-cycle test of Fe-N3Te / CN in Example 1.

[0054] Figure 6 It is the selectivity image of the 16-cycle test of Fe-N3Te / CN in Example 1.

[0055] Figure 7 It is the LSV image of the catalysts prepared in Examples 1 - 7. Detailed implementation manners

[0056] The present invention will be further described in detail through specific examples below. The following examples can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0057] Example 1:

[0058] (1) Preparation of Te / ZIF-8

[0059] Prepare a methanol solution containing 0.133 M Zn(NO3)2·6H2O and 0.104 M Te powder, that is, add Zn(NO3)2·6H2O (5.58 g, 0.02 mol) and 2 g Te powder to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution A; prepare a 0.5 M 2-methylimidazole methanol solution, that is, add 2-methylimidazole (6.16 g, 0.075 mol) to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution B; quickly pour solution B into solution A at a volume ratio of 1:1, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry overnight at 50 °C to obtain Te / ZIF-8.

[0060] (2) Preparation of Fe-Te / ZIF-8

[0061] Add 0.5 g of Te / ZIF-8 prepared in step (1) to 50 mL of DMF and sonicate for 1 hour to dissolve it, denoted as solution C; add 0.5 g of iron acetylacetonate to 50 mL of DMF and sonicate for 1 hour to dissolve it, denoted as solution D. Quickly add solution D to solution C, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe-Te / ZIF-8 powder.

[0062] Preparation of Fe-N3Te / CN

[0063] Place the Fe-Te / ZIF-8 prepared in step (2) in a porcelain boat and heat it in a tube furnace at 920 °C, 2 °C·min -1 , for 3 h, maintaining an argon atmosphere to obtain black powder Fe-N3Te / CN, which is an Fe single-atom catalytic material with electrocatalytic nitrate reduction performance, and the single-atom diameter is 0.15 nm.

[0064] In the above step (1), the molecular weight of Te / ZIF-8 is 357.2.

[0065] In the above step (1), the diameter of the Te / ZIF-8 material is 200 - 500 nm.

[0066] In the above step (1), the atomic radius of Te in solution A is 0.97 Å.

[0067] Figure 1 This is the XRD pattern of the Fe single-atom catalyst prepared in Example 1. As shown in the XRD pattern, there are only two broad peaks assigned to the diffraction peaks of carbon (002)(100) / (101), which are 25° and 44° respectively, and no peaks related to iron-based substances are formed.

[0068] Figure 2 This is the TEM image of the Fe single-atom catalyst in Example 1. As shown in the figure, no obvious nanoparticles are formed, and the diameter of Fe-N3Te / CN is 200 - 500 nm.

[0069] Figure 3 This is the aberration-corrected electron microscope of Fe-N3Te / CN in Example 1 and the corresponding. As shown in the figure, the bright spots represent Fe single atoms or Te single atoms, and the results of the Mapping diagram show that the distributions of C, N, Fe, and Te are relatively uniform.

[0070] Table 1

[0071]

[0072] Table 1 shows the inductively coupled plasma optical emission spectrometer data of Fe-N3Te / CN in Example 1. It proves that the material has indeed loaded trace amounts of Fe and Te elements.

[0073] (4)Fe-N3Te / CN for electrocatalytic nitrate reduction to ammonia

[0074] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, and ultrasonicate for half an hour to make it a homogeneous ink-like black solution. Coat this solution evenly on a 2×2 cm 2 carbon paper, dry it, and use it as the working electrode for electrocatalysis. The three-electrode system is adopted in the electrochemistry test part of the present invention. The platinum sheet electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode. Use Chenhua CHI-760E to test its electrochemical performance. Use a UV-visible spectrometer to quantitatively test the ammonia concentration by colorimetry, and then calculate the Faraday efficiency, ammonia production rate, and the selectivity of the catalyst.

[0075] Figure 4 It is the LSV diagram of Fe-N3Te / CN electrocatalytic nitrate reduction to ammonia in Example 1. It can be observed that after adding potassium nitrate, the absolute value of the current density increases significantly, indicating that the catalyst can catalyze nitrate reduction.

[0076] Figure 5 It is the diagram of the Faraday efficiency and ammonia production rate of the 16-cycle test of Fe-N3Te / CN in Example 1. It can be seen from the figure that the catalyst has a relatively stable Faraday efficiency (average value 94.6%) and ammonia production rate (average value 1.95 mg h -1 cm -2 ) after multiple cycles.

[0077] Figure 6 It is the selectivity diagram of the 16-cycle test of Fe-N3Te / CN in Example 1. It can be seen from the figure that the catalyst has a relatively high selectivity for the deep reduction of nitrate to ammonia, with an average of 83.9%.

[0078] Figure 7 It is the electrocatalytic LSV test results of the catalysts prepared in Examples 1-7. It can be seen that the catalyst in Example 1 has the best performance. Figure 7

[0079] Example 2:

[0080] (1)Preparation of Te / ZIF-8

[0081] ​Prepare a methanol solution containing 0.133 M Zn(NO3)2·6H2O and 0.0261 M Te powder. That is, add Zn(NO3)2·6H2O (5.58 g, 0.02 mol) and 0.5 g Te powder to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution A; prepare a methanol solution containing 0.5 M 2-methylimidazole. That is, add 2-methylimidazole (6.16 g, 0.075 mol) to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution B; quickly pour solution B into solution A at a volume ratio of 1:1, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry overnight at 50 °C to obtain Te / ZIF-8.

[0082] (2)Preparation of Fe-Te / ZIF-8 (0.5 g)

[0083] Add 0.5 g of Te / ZIF-8 prepared in step (1) to 50 mL of DMF, ultrasonically dissolve it for 1 hour, denoted as solution C; add 0.5 g of iron acetylacetonate to 50 mL of DMF, ultrasonically dissolve it for 1 hour, denoted as solution D. Quickly add solution D to solution C, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe-Te / ZIF-8 powder.

[0084] (3)Preparation of Fe-N3Te / CN

[0085] Put the Fe-Te / ZIF-8 prepared in step (2) into a porcelain boat and heat it in a tube furnace at 920 °C, 2 °C·min -1 , for 3 h, maintaining an argon atmosphere to obtain black powder Fe-N3Te / CN, with a single-atom diameter of 0.14 nm.

[0086] (4)Use of Fe-N3Te / CN for electrocatalytic reduction of nitrate to ammonia

[0087] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, ultrasonically dissolve it for half an hour to form a homogeneous ink-like black solution. Coat this solution evenly on a 2×2 cm 2 carbon paper, dry it, and use it as a working electrode for electrocatalysis. The electrochemistry test part of this invention uses a three-electrode system. Among them, the counter electrode uses a platinum sheet electrode, and the reference electrode uses an Ag / AgCl electrode. Use Chenhua CHI-760E to test its electrochemical performance. Use a UV-visible spectrometer to quantitatively test the ammonia concentration by colorimetry, and then calculate the Faraday efficiency, ammonia production rate, and catalyst selectivity.

[0088] The LSV of the catalyst prepared in Example 2 is as Figure 7As shown, its Faraday efficiency is 70.0% and the ammonia production rate is 1.01 mg h -1 cm -2 .

[0089] Example 3:

[0090] (1) Preparation of Te / ZIF-8

[0091] Prepare a methanol solution containing 0.133 M Zn(NO3)2·6H2O and 0.0522 M Te powder, that is, add Zn(NO3)2·6H2O (5.58 g, 0.02 mol) and 1 g Te powder to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution A; prepare a methanol solution containing 0.5 M 2-methylimidazole, that is, add 2-methylimidazole (6.16 g, 0.075 mol) to 150 mL of methanol, and ultrasonically dissolve it for half an hour, denoted as solution B; quickly pour solution B into solution A at a volume ratio of 1:1, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry at 50 °C overnight to obtain Te / ZIF-8.

[0092] (2) Preparation of Fe-Te / ZIF-8

[0093] Add 0.5 g of Te / ZIF-8 prepared in step (1) to 50 mL of DMF, ultrasonically dissolve it for 1 hour, denoted as solution C; add 0.5 g of iron acetylacetonate to 50 mL of DMF, ultrasonically dissolve it for 1 hour, denoted as solution D. Quickly add solution D to solution C, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe-Te / ZIF-8 powder.

[0094] (3) Preparation of Fe-N3Te / CN

[0095] Put the Fe-Te / ZIF-8 prepared in step (2) into a porcelain boat and heat it in a tube furnace at 920 °C, 2 °C·min -1 , for 3 h, keep an argon atmosphere to obtain black powder Fe-N3Te / CN, and the single-atom diameter is 0.16 nm.

[0096] (4) Use of Fe-N3Te / CN for electrocatalytic reduction of nitrate to ammonia

[0097] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, ultrasonically dissolve it for half an hour to make it a uniform ink-like black solution. Coat this solution evenly on a 2×2 cm 2On the carbon paper, it is dried and used as the working electrode for electrocatalysis. The three-electrode system is adopted in the electrochemistry test part of the present invention. Among them, the platinum sheet electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode. The electrochemical performance is tested by Chenhua CHI-760E. The ultraviolet-visible spectrometer is used to quantitatively test the concentration of ammonia by colorimetry, and then the Faraday efficiency, ammonia production rate and selectivity of the catalyst are calculated.

[0098] The LSV of the catalyst prepared in Example 3 is as Figure 7 shown, and its Faraday efficiency is 73.5%, and the ammonia production rate is 1.41 mg h -1 cm -2 .

[0099] Example 4:

[0100] (1) Preparation of Te / ZIF-8

[0101] The same as in Example 1.

[0102] (2) Preparation of Fe-Te / ZIF-8

[0103] The same as in Example 1.

[0104] (3) Preparation of Fe-N3Te / CN

[0105] Put the Fe-Te / ZIF-8 prepared in step (2) into a porcelain boat and heat it with a tube furnace at 970 °C, 2 °C·min -1 , for 3 h, keep the argon atmosphere, and obtain the black powder Fe-N3Te / CN with a single-atom diameter of 0.15 nm.

[0106] (4) Fe-N3Te / CN is used for electrocatalytic reduction of nitrate to ammonia

[0107] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, and ultrasonicate for half an hour to make it a uniform ink-like black solution. Coat this solution evenly on the 2×2 cm 2 carbon paper, dry it, and use it as the working electrode for electrocatalysis. The three-electrode system is adopted in the electrochemistry test part of the present invention. Among them, the platinum sheet electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode. The electrochemical performance is tested by Chenhua CHI-760E. The ultraviolet-visible spectrometer is used to quantitatively test the concentration of ammonia by colorimetry, and then the Faraday efficiency, ammonia production rate and selectivity of the catalyst are calculated.

[0108] The LSV of the catalyst prepared in Example 4 is as Figure 7As shown, its Faraday efficiency is 74.8%, and the ammonia production rate is 1.56 mg h -1 cm -2 。

[0109] Example 5:

[0110] (1) Preparation of Te / ZIF-8

[0111] Same as Example 2.

[0112] (2) Preparation of Fe-Te / ZIF-8

[0113] Add 0.5 g of Te / ZIF-8 prepared in step (1) to 50 mL of DMF and sonicate for 1 hour to dissolve it, denoted as solution C; add 0.5 g of iron acetylacetonate to 50 mL of DMF and sonicate for 1 hour to dissolve it, denoted as solution D. Add solution D to solution C, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe-Te / ZIF-8 powder.

[0114] (3) Preparation of Fe-N3Te / CN

[0115] Place the Fe-Te / ZIF-8 prepared in step (2) in a porcelain boat and heat it in a tube furnace at 970 °C, 2 °C·min -1 , for 3 h, maintaining an argon atmosphere, to obtain black powder Fe-N3Te / CN with a single atom diameter of 0.14 nm.

[0116] (4) Use of Fe-N3Te / CN for electrocatalytic nitrate reduction to ammonia

[0117] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, and sonicate for half an hour to make it a homogeneous ink-like black solution. Coat this solution evenly on a 2×2 cm 2 carbon paper, dry it, and use it as the working electrode for electrocatalysis. The electrochemical test part of the present invention uses a three-electrode system, in which the counter electrode is a platinum sheet electrode and the reference electrode is an Ag / AgCl electrode. Use Chenhua CHI-760E to test its electrochemical performance. Use a UV-visible spectrometer to quantitatively test the ammonia concentration by colorimetry and then calculate the Faraday efficiency, ammonia production rate, and selectivity of the catalyst.

[0118] The LSV of the catalyst prepared in Example 5 is as Figure 7 shown, its Faraday efficiency is 69%, and the ammonia production rate is 1.12 mg h -1 cm -2 。

[0119] Example 6:

[0120] (1) Preparation of Te / ZIF-8

[0121] Same as Example 3.

[0122] (2)Preparation of Fe-Te / ZIF-8

[0123] Same as Example 3.

[0124] (3)Preparation of Fe-N3Te / CN

[0125] Put the Fe-Te / ZIF-8 prepared in step (2) into a porcelain boat and heat it in a tubular furnace at 970 °C, 2 °C·min -1 , 3 h, maintaining an argon atmosphere, to obtain black powder Fe-N3Te / CN, with a single atom diameter of 0.16 nm.

[0126] (4)Use of Fe-N3Te / CN for electrocatalytic reduction of nitrate to ammonia

[0127] Weigh 8 mg of the Fe-N3Te / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, and ultrasonicate for half an hour to make it a homogeneous ink-like black solution. Apply this solution evenly on a 2×2 cm 2 carbon paper, dry it, and use it as the working electrode for electrocatalysis. The electrochemical test part of the present invention uses a three-electrode system, in which the counter electrode uses a platinum sheet electrode and the reference electrode uses an Ag / AgCl electrode. Use Chenhua CHI-760E to test its electrochemical performance. Use a UV-visible spectrometer to quantitatively test the ammonia concentration by colorimetry and then calculate the Faraday efficiency, ammonia production rate, and selectivity of the catalyst.

[0128] The LSV of the catalyst prepared in Example 6 is as Figure 7 shown, with a Faraday efficiency of 75.9% and an ammonia production rate of 1.43 mg h -1 cm -2 .

[0129] Example 7:

[0130] (1)Preparation of ZIF-8

[0131] Prepare a methanol solution containing 0.133 M Zn(NO3)2·6H2O, that is, add 150 mL of methanol to Zn(NO3)2·6H2O (5.58 g, 0.02 mol), and ultrasonically dissolve it for half an hour, denoted as solution A; prepare a methanol solution containing 0.5 M 2-methylimidazole, that is, add 150 mL of methanol to 2-methylimidazole (6.16 g, 0.075 mol), and ultrasonically dissolve it for half an hour, denoted as solution B; quickly pour solution B into solution A, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry at 50 °C overnight to obtain ZIF-8.

[0132] (2)Preparation of Fe / ZIF-8

[0133] Add 50 mL of DMF to 0.5 g of ZIF-8 prepared in step (1), ultrasonically dissolve it for 1 hour, and denote it as solution C; add 50 mL of DMF to 0.5 g of iron acetylacetonate, ultrasonically dissolve it for 1 hour, and denote it as solution D. Quickly add solution D to solution C, stir at room temperature for 24 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe / ZIF-8 powder.

[0134] (3)Preparation of Fe-N4 / CN

[0135] Put the Fe / ZIF-8 prepared in step (2) into a porcelain boat and heat it in a tubular furnace at 920 °C, 2 °C·min -1 , for 3 h, maintaining an argon atmosphere, to obtain black powder Fe-N4 / CN with a single-atom diameter of 0.15 nm.

[0136] (4)Use of Fe-N3 / CN for electrocatalytic reduction of nitrate to ammonia

[0137] Weigh 8 mg of the Fe-N4 / CN powder prepared in step (3), add 470 μL of ethanol and 470 μL of water, and ultrasonically dissolve it for half an hour to form a homogeneous ink-like black solution. Uniformly coat this solution on a 2×2 cm 2 carbon paper, dry it, and use it as a working electrode for electrocatalysis. The electrochemical test part of this invention uses a three-electrode system, where the counter electrode is a platinum sheet electrode and the reference electrode is an Ag / AgCl electrode. Use Chenhua CHI-760E to test its electrochemical performance. Use a UV-visible spectrometer to quantitatively test the ammonia concentration by colorimetry and then calculate the Faraday efficiency, ammonia production rate, and catalyst selectivity.

[0138] The LSV of the catalyst prepared in Example 7 is as Figure 7 shown, with a Faraday efficiency of 59.2% and an ammonia production rate of 0.76 mg h -1 cm -2 .

[0139] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many specific transformations in various forms without departing from the spirit of the present invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. An Fe single-atom catalyst material with electrocatalytic nitrate reduction performance, namely the Fe-N3Te / CN material, is characterized in that It includes Fe-N3Te as the catalytic site and a graphene support with carbon and nitrogen as the main body, presenting a hexagonal structure; Te single atoms are introduced beside the Fe single atoms to form Fe-Te chemical bonds. The preparation method is as follows: (1) Add Zn(NO3)2·6H2O and Te powder to methanol and dissolve them, denoted as solution A; prepare a 2-methylimidazole methanol solution, denoted as solution B; quickly pour solution B into solution A, stir at room temperature for 6 - 48 hours, centrifuge, wash three times with ethanol, and dry overnight at 45 - 65 °C to obtain Te / ZIF-8. (2) Add DMF to the Te / ZIF-8 prepared in step (1) and dissolve it, denoted as solution C; add iron acetylacetonate to DMF and dissolve it, denoted as solution D. Add solution D to solution C, stir, centrifuge, wash, and dry to obtain Fe-Te / ZIF-8 powder. (3) Heat the Fe-Te / ZIF-8 prepared in step (2) and perform high-temperature pyrolysis to obtain black powder Fe-N3Te / CN.

2. The Fe single-atom catalyst material with electrocatalytic nitrate reduction performance according to claim 1, characterized in that The mass ratio of carbon to nitrogen is 1:7 - 1:

10. The diameter of the Fe-N3Te / CN material is 200 - 500 nm. The diameter of the Fe single atoms in the Fe-N3Te / CN material is 0.1 - 0.3 nm. The diameter of the Te single atoms in the Fe-N3Te / CN material is 0.1 - 0.3 nm.

3. The Fe single-atom catalyst material with electrocatalytic nitrate reduction performance according to claim 1, characterized in that In step (1), the molar ratio of Zn(NO3)2·6H2O to Te powder is 5:16 - 10:

1.

4. The Fe single-atom catalyst material with electrocatalytic nitrate reduction performance according to claim 1, characterized in that In step (1), add 2.97 - 11.90 g of Zn(NO3)2·6H2O and 0.5 - 4.0 g of Te powder to 75 - 300 mL of methanol; add 3.08 - 12.32 g of 2-methylimidazole to 75 - 300 mL of methanol, ultrasonically dissolve it for half an hour to prepare a 2-methylimidazole methanol solution; quickly pour solution B into solution A, stir at room temperature for 6 - 48 hours, centrifuge, wash three times with ethanol, and dry overnight at 45 - 65 °C to obtain Te / ZIF-8.

5. The Fe single-atom catalyst material with electrocatalytic nitrate reduction performance according to claim 1, characterized in that In step (2), add 0.25 - 1 g of the Te / ZIF-8 prepared in step (1) to 25 - 100 mL of DMF, ultrasonically dissolve it for 0.5 - 1 hour; add 0.25 - 1 g of iron acetylacetonate to 25 - 100 mL of DMF, ultrasonically dissolve it for 0.5 - 1 hour; add solution D to solution C, stir at room temperature for 6 - 48 hours, centrifuge, wash three times with ethanol, and dry to obtain Fe-Te / ZIF-8 powder.

6. The Fe single-atom catalyst material with electrocatalytic nitrate reduction performance according to claim 1, characterized in that In the step (3), the Fe-Te / ZIF-8 is placed in a porcelain boat and heated in a tube furnace. The high-temperature pyrolysis temperature is 800-1200 °C, and the heating rate of the high-temperature pyrolysis is 2 °C·min -1 , the heat preservation time of the high-temperature pyrolysis is 1-5 hours, and the high-temperature pyrolysis is carried out in an argon atmosphere.

7. Use of the Fe single-atom catalytic material with electrocatalytic nitrate reduction performance according to any one of claims 1 to 6, characterized in that It is used for electrocatalytic reduction of nitrate to ammonia.

8. Application of the Fe single-atom catalytic material with electrocatalytic nitrate reduction performance according to any one of claims 1 to 6, characterized in that It is used for nitrate sewage treatment and synthesis of chemical fertilizers.

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