Preparation method and application of nitrogen-doped carbon support-supported iron-manganese bimetallic catalyst

Abstract

This invention relates to a method for preparing and applying a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. Glucose is dissolved in water to form a solution, which is then subjected to high-temperature hydrothermal treatment. The hydrothermally treated substance is washed and dried with water and alcohol to obtain a catalyst precursor. The catalyst precursor, two transition metal salts, and a nitrogen source are dispersed in an aqueous solution, and the mixture is heated and stirred until the solvent is completely evaporated. Then, under an inactive gas atmosphere, the resulting substance is calcined at 700-900℃ to obtain the nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. 2.5 mg of the catalyst is added to 0.15 mL of water, 0.35 mL of anhydrous ethanol, and 0.015 mL of 5 wt% Nafion solution. The solution is mixed and sonicated for 15 min, then uniformly dropped onto a 2×2 cm pretreated carbon cloth and dried for later use. The carbon cloth is prepared by soaking raw carbon cloth in water, anhydrous ethanol, and 1 mol / L nitric acid for 30 min each. This invention possesses a suitable pore structure, high specific surface area, and a large number of active sites for oxygen reduction and degradation, exhibiting good degradation performance for organic pollutants.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a method for preparing and applying a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. Background Technology

[0002] In recent years, with the rapid growth of the population and the rapid development of science and technology, the large-scale discharge of organic micropollutants (such as pharmaceuticals, personal care products, and industrial and agricultural chemicals) has made water pollution a more and more serious problem. Advanced oxidation processes are considered an effective environmental remediation technology that can be used to remove organic pollutants from the aquatic environment. Fenton oxidation is an important component of advanced oxidation processes, utilizing Fenton's reagent (usually Fe...). 2+ The active oxygen generated by H2O2 degrades organic pollutants. It has attracted widespread attention due to its advantages such as high selectivity for organic pollutants, fast reaction rate and high degree of mineralization. However, it also has disadvantages such as poor stability, large amount of iron sludge generated and strict requirements for chemical reagents, which limit its large-scale application.

[0003] The electro-Fenton process is an improved process developed to overcome some limitations of the Fenton process. Based on the sources of Fe and H₂O₂ in the system, the electro-Fenton process can be divided into five types: 1. Fe is generated at the anode, and H₂O₂ is generated at the cathode; 2. Fe is added externally, and H₂O₂ is generated at the cathode; 3. Both Fe and H₂O₂ are added externally; 4. Fe is generated at the anode, and H₂O₂ is added externally; 5. Both Fe and H₂O₂ are generated at the cathode. Type 5 is a more environmentally friendly and efficient system because it avoids both anode consumption and the addition of an external oxidant, thus reducing sludge production and avoiding the risks associated with the transportation and storage of H₂O₂.

[0004] Existing electro-Fenton catalysts suffer from problems such as low activity (Environmental Research 204(2022)112117), severe metal leaching (Journal of Environmental Chemical Engineering 11(2023)109698), and difficulty in coupling the oxygen reduction process with the degradation process (Chemosphere 312(2023)137353), resulting in poor prospects for industrialization. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. In the bimetallic catalyst, iron serves as the main degradation active site, which can decompose H2O2 generated by oxygen reduction into hydroxyl radicals to degrade pollutants. Manganese serves as an auxiliary degradation active site and has a synergistic effect with iron, thereby improving the degradation activity.

[0006] This invention also provides an application of a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst, which utilizes an electro-Fenton reaction to degrade organic pollutants.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] A method for preparing a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst includes the following steps:

[0009] Step 1: Preparation of catalyst precursor:

[0010] Dissolve 3g of glucose in 60mL of deionized water and stir to form a solution. Place the solution in a 100mL hydrothermal reactor for high-temperature hydrothermal treatment at a temperature of 160-180℃ for 8-12 hours. Wash the hydrothermally treated substance three times with a mixture of water and ethanol, and then freeze-dry it at -45-60℃ and 10-50Pa for 10-12 hours to remove moisture and dry it to obtain the catalyst precursor.

[0011] Step 2: The catalyst precursor obtained in Step 1 is heated and evaporated.

[0012] Weigh 0.1 g of the catalyst precursor obtained in step 1 and place it in a 100 mL beaker. Add the metal salt and nitrogen source to the beaker in sequence, and add 50 mL of deionized water. Stir in a heating mantle at 80-90℃ for 10-12 h until the solvent is completely evaporated.

[0013] Step 3: Calcine the substance obtained in Step 2 to obtain the catalyst.

[0014] The material obtained in step 2 was transferred to the ark and carbonized in a tube furnace under nitrogen atmosphere. The temperature was raised from room temperature to 700-900℃ and maintained for 1-3 hours before being naturally cooled to room temperature. The heating rate was 1-3℃ / min. The black sample obtained from the calcination was collected as the catalyst, denoted as FeMn@NHGC.

[0015] Furthermore, in step 2, the nitrogen source is at least one of melamine, urea, or dicyandiamide.

[0016] Furthermore, in step 2, the metal salt is an iron or manganese nitrate, acetate, or chloride salt, the mass ratio between iron and manganese metals is 1:2 to 1:0.5, the mass ratio of the metal salt to the carbon precursor is 1:10 to 1:3, and the mass ratio of the nitrogen source to the carbon precursor is 1:4 to 1:2.

[0017] The application of a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst in the catalytic oxidation of organic pollutants in wastewater includes the following steps:

[0018] Step 1: Prepare 100 mL of carbamazepine solution with 10 ppm and pH=3 in 0.05 mol / L sodium sulfate solution, and sonicate for 30 minutes to simulate organic pollutant wastewater;

[0019] Step 2: Weigh 2.5 mg of catalyst and disperse it in a mixed solution consisting of 0.15 mL water, 0.35 mL anhydrous ethanol and 0.015 mL 5 wt% Nafion, and sonicate for 30 min.

[0020] Step 3: Soak the raw carbon cloth in water, anhydrous ethanol, and 1 mol / L nitric acid for 30 minutes respectively, then dry and cut it into 2×2 cm pieces. Evenly drop the mixed solution from step 2 onto both sides of the carbon cloth, dry it, and set it aside for later use.

[0021] Step 4: Add the solution prepared in step 1 to the circular electrolytic cell. Connect the carbon cloth prepared in step 3 to the platinum electrode clamp to form the working electrode. Use the platinum mesh or graphite rod as the counter electrode and the calomel electrode as the reference electrode. Immerse one end of the aeration tube in the solution and connect the other end to oxygen. Turn on the oxygen and pre-introduce oxygen into the solution for at least 5 minutes to make the solution reach oxygen saturation.

[0022] Step 5: Connect the electrochemical workstation to the electrode and apply a voltage of -0.6V vs. SCE for 1 hour. Start timing at the moment of power-on and take 0.5 mL of solution from the reaction system at 2, 5, 10, 20, 30, 40, 50, and 60 minutes respectively. Then immediately inject the taken solution into a screw-top bottle containing 0.5 mL of methanol to quench the reaction.

[0023] Step 6: Use a mixed solution containing 70% methanol and 30% deionized water as the mobile phase, control the flow rate at 1 mL / min, and determine the degradation amount of carbamazepine using a high performance liquid chromatograph with a Supersil ODS-B column.

[0024] Step 7: The iron and manganese leaching rate of the catalyst in the reaction solution is determined by inductively coupled plasma atomic emission spectrometry. The carbon cloth supporting the catalyst is recovered and labeled as FeMn@NHGC-2nd, and used as a catalyst again for the catalytic oxidation process in steps 1-6.

[0025] The advantages and positive effects of this invention are:

[0026] 1. This invention discloses a method for preparing a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. Without the aid of a template agent, carbon spheres formed by hydrothermal processing of green raw material glucose are used as the support. The support itself has abundant oxygen-containing functional groups, providing sufficient anchoring sites for the metal, and the oxygen-containing functional groups themselves provide some oxygen reduction performance. Urea is used as the nitrogen source, which not only promotes the dispersion of metal particles but also provides a variety of nitrogen configurations. At the same time, it improves the conductivity and oxygen reduction performance of the material. Furthermore, urea forms a carbon shell during pyrolysis, which coats the metal surface and reduces metal leaching.

[0027] 2. The present invention relates to the application of a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst, with Fe as the main degradation active site and Mn as the auxiliary degradation active site. The synergistic effect between Fe and Mn greatly improves the catalytic activity. Compared with the existing single-metal Fe electro-Fenton catalyst, the performance is significantly improved and the catalytic lifetime is greatly extended.

[0028] 3. This invention discloses a method for preparing and applying a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst. The raw materials are inexpensive and readily available, the preparation method is simple, the catalyst yield is high, it has broad applicability, and a long service life. The catalyst avoids the need for additional oxidants during use, thus avoiding the risks associated with the storage and transportation of hydrogen peroxide, and has industrial potential. Attached Figure Description

[0029] Figure 1 X-ray diffraction (XRD) patterns of NHGC, Fe@NHGC, Mn@NHGC, and FeMn@NHGC;

[0030] Figure 2 (a) is a scanning electron microscope (SEM) image of NHGC;

[0031] Figure 2 (b) is a scanning electron microscope (SEM) image of Fe@NHGC;

[0032] Figure 2 (c) is a scanning electron microscope (SEM) image of Mn@NHGC;

[0033] Figure 2 (d) is a scanning electron microscope (SEM) image of FeMn@NHGC;

[0034] Figure 3 (a) is a transmission electron microscope (TEM) image of FeMn@NHGC;

[0035] Figure 3 (b) is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of FeMn@NHGC;

[0036] Figure 4(a) is the isothermal adsorption-desorption curve of NHGC;

[0037] Figure 4 (b) is a pore size distribution diagram of NHGC;

[0038] Figure 4 (c) is the isothermal adsorption-desorption curve of FeMn@HGC;

[0039] Figure 4 (d) shows the pore size distribution of FeMn@HGC;

[0040] Figure 4 (e) is the isothermal adsorption-desorption curve of FeMn@NHGC;

[0041] Figure 4 (f) shows the pore size distribution of FeMn@NHGC;

[0042] Figure 5 X-ray photoelectron spectroscopy (XPS) spectra of Fe@NHGC and FeMn@NHGC;

[0043] Figure 6 Selectivity diagrams for H2O2 formation by NHGC, Fe@NHGC, Mn@NHGC, FeMn@HGC, and FeMn@NHGC under applied voltage;

[0044] Figure 7 The graph shows the changes in the current-response curves of NHGC, Fe@NHGC, Mn@NHGC, and FeMn@NHGC in a 5 mmol H2O2 solution saturated with N2. Detailed Implementation

[0045] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0046] Example 1

[0047] A method for preparing a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst includes the following steps:

[0048] Step 1: Preparation of catalyst precursor:

[0049] Dissolve 3g of glucose in 60mL of deionized water and stir to form a solution. Place the solution in a 100mL hydrothermal reactor for high-temperature hydrothermal treatment at 160℃ for 8h. Wash the hydrothermally treated substance three times with a mixture of water and ethanol, and then freeze-dry it at -45℃ and 10Pa for 12h to remove moisture and dry it to obtain the catalyst precursor.

[0050] Step 2: The catalyst precursor obtained in Step 1 is heated and evaporated.

[0051] Weigh 0.1g of the catalyst precursor obtained in step 1 and place it in a 100mL beaker. Add 0.033g of urea, 0.02g of ferric acetate, and 0.02g of manganese acetate to the beaker in sequence, and add 50mL of deionized water. Stir in a heating mantle at 80℃ for 12h until the solvent is completely evaporated.

[0052] Step 3: Calcine the substance obtained in Step 2 to obtain the catalyst.

[0053] The material obtained in step 2 was transferred to the ark and carbonized in a tube furnace under nitrogen atmosphere. The temperature was raised from room temperature to 800℃ and maintained for 2 hours before being naturally cooled to room temperature. The heating rate was 2℃ / min. The black sample obtained from the calcination was collected as the catalyst, denoted as FeMn@NHGC.

[0054] The catalyst is prepared by calcining carbon spheres generated from glucose hydrothermally as a precursor, after modification with nitrogen source and metal salt. The carbon spheres generated from glucose hydrothermally possess abundant oxygen functional groups, which anchor the metal and prevent the formation of metal-carbon sphere complexes. Furthermore, the oxygen-containing functional groups themselves provide some oxygen reduction performance. The addition of nitrogen source provides a metal-nitrogen coordination structure for the metal, promoting metal dispersion. It also serves as an active site for the oxygen reduction reaction, promoting its occurrence. During pyrolysis, a carbon shell can be formed in situ on the metal surface, reducing metal leaching. In the bimetallic catalyst, iron acts as the primary degradation active site, decomposing H2O2 generated from oxygen reduction into hydroxyl radicals to degrade pollutants. Manganese, as an auxiliary degradation active site, synergistically enhances the degradation activity with iron.

[0055] The hydrothermal temperature is 160-180℃, and the hydrothermal time can be 8-12 hours, preferably 10 hours. The nitrogen source can be at least one of melamine, urea, and dicyandiamide, preferably urea. The metal salt can be iron or manganese nitrates, acetates, or chlorides, preferably acetates. An 8-hour hydrothermal time results in a lower catalyst precursor yield, while 10-hour and 12-hour times are similar; therefore, 10 hours is chosen from the perspective of energy consumption and yield. Urea is selected as the target nitrogen source due to its high nitrogen content, wide availability, and low cost. Among the metal salts, nitrates are controlled substances, and chlorides are doped with heteroatom chlorine; therefore, the corresponding acetates are selected as the target metal sources.

[0056] The mass ratio of iron to manganese metal is 1:2 to 1:0.5, preferably 1:1; the mass ratio of metal salt to carbon precursor is 1:10 to 1:3, preferably 1:5; and the mass ratio of nitrogen source to carbon precursor is 1:4 to 1:2, preferably 1:3.

[0057] The calcination temperature is 700-900℃, the heating rate is 1-3℃ / min, and the calcination time is 1-3h, preferably 800℃, 2℃ / min, and 2h. Under these conditions, the carbon skeleton of the catalyst can be stabilized, and the Kirkendall effect of the metal can be induced, resulting in a large number of wrinkles and bulges on the catalyst surface, which increases the contact with the solution and promotes the reaction.

[0058] An application of a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst for the catalytic oxidation of organic pollutants in wastewater involves taking 2.5 mg of catalyst, adding 0.15 mL of water, 0.35 mL of anhydrous ethanol, and 0.015 mL of 5 wt% Nafion solution, mixing the solution, sonicating for 15 min, and then uniformly dropping it onto a 2×2 cm pretreated carbon cloth. The carbon cloth is then dried for later use. The carbon cloth is prepared by soaking raw carbon cloth in water, anhydrous ethanol, and 1 mol / L nitric acid for 30 min each.

[0059] The prepared carbon cloth is connected via a platinum electrode clamp as the working electrode, a carbon rod as the counter electrode, and a calomel electrode as the reference electrode. The solution is an oxygen-saturated electrolyte solution containing organic pollutants. Specifically, the organic pollutants include, but are not limited to, at least one of bisphenol A, carbamazepine, rhodamine B, methylene blue, and phenol; the electrolyte is any one of 0.05 mol / L sodium sulfate, sodium chloride, and sodium nitrate, preferably sodium sulfate; the pH of the electrolyte is 2-7, preferably 3; the amount of catalyst added can be 1-5 mg, preferably 2.5 mg; the applied voltage can be -0.2 to -0.8 V vs. SCE, preferably -0.6 V vs. SCE; the oxygen-saturated solution can be obtained by purging the original solution with oxygen for 5 min.

[0060] Includes the following steps:

[0061] Step 1: Prepare 100 mL of carbamazepine solution with 10 ppm and pH=3 in 0.05 mol / L sodium sulfate solution, and sonicate for 30 minutes to simulate organic pollutant wastewater;

[0062] Step 2: Weigh 2.5 mg of catalyst and disperse it in a mixed solution consisting of 0.15 mL water, 0.35 mL anhydrous ethanol and 0.015 mL 5 wt% Nafion, and sonicate for 30 min.

[0063] Step 3: Soak the raw carbon cloth in water, anhydrous ethanol, and 1 mol / L nitric acid for 30 minutes respectively, then dry and cut it into 2×2 cm pieces. Evenly drop the mixture from step 2 onto both sides of the carbon cloth, dry it, and set it aside.

[0064] Step 4: Add the solution prepared in Step 1 to the circular electrolytic cell. Connect the carbon cloth prepared in Step 3 to the platinum electrode clamp to form the working electrode. Use a platinum mesh or graphite rod as the counter electrode and a calomel electrode as the reference electrode, immersing them in the solution. Additionally, immerse one end of the aeration tube in the solution and connect the other end to oxygen. Turn on the oxygen supply and pre-introduce oxygen into the solution for at least 5 minutes to achieve oxygen saturation.

[0065] Step 5: Connect the electrochemical workstation to the electrode and apply a voltage of -0.6V vs. SCE for 1 hour. Start timing at the moment of power-on and take 0.5 mL of solution from the reaction system at 2, 5, 10, 20, 30, 40, 50, and 60 minutes respectively. Then immediately inject the taken solution into a screw-top bottle containing 0.5 mL of methanol to quench the reaction.

[0066] Step 6: Using a mixed solution containing 70% methanol and 30% deionized water as the mobile phase, with a flow rate controlled at 1 mL / min, the degradation amount of carbamazepine was determined by high performance liquid chromatography (HPLC, Hitachi) with a Supersil ODS-B column. The test results are shown in Table 1.

[0067] Step 7: The iron and manganese leaching rate of the catalyst in the reaction solution was determined by inductively coupled plasma atomic emission spectrometry. The carbon cloth supporting the catalyst was recovered and labeled as FeMn@NHGC-2nd, and used as a catalyst again for the catalytic oxidation process in steps 1-6. The test results are shown in Table 2.

[0068] Table 1

[0069]

[0070]

[0071] Table 2

[0072]

[0073] As can be seen from Tables 1 and 2, when the catalyst is used to oxidize pollutants in wastewater, it exhibits high catalytic oxidation activity and strong regeneration capacity. Furthermore, after the first reaction, the leaching of iron and manganese are 0.95 ppm and 1.26 ppm, respectively, which meet the emission standards of GB 13456-2012 and GB 8978-1996.

[0074] Example 2

[0075] The difference between Example 2 and Example 1 is that the hydrothermal time was changed to 8 hours during the preparation of the catalyst, resulting in catalyst 2#, denoted as FeMn@NHGC (hydrothermal 8h).

[0076] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst 2#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 3.

[0077] Table 3

[0078]

[0079] Example 3

[0080] The difference between Example 3 and Example 1 is that in the preparation of the catalyst, urea was replaced with an equal mass of melamine, and the other conditions were the same, resulting in catalyst 3#, denoted as FeMn@NHGC (melamine);

[0081] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst #3. The degradation amount of carbamazepine was determined, and the test results are shown in Table 4.

[0082] Table 4

[0083]

[0084] Example 4

[0085] The difference between Example 4 and Example 1 is that in the preparation of the catalyst, ferric acetate was replaced with an equimolar amount of ferrous chloride, and manganese acetate was replaced with an equimolar amount of manganese chloride. The other conditions were the same, and catalyst 4# was obtained, denoted as FeMn@NHGC (chloride salt).

[0086] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst 4#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 5.

[0087] Table 5

[0088]

[0089] Example 5

[0090] The difference between Example 5 and Example 1 is that, during the catalyst preparation process, with a constant total mass, the mass ratio of ferric acetate to manganese acetate was changed to 1:2 and 1:0.5, respectively, while all other conditions remained the same. Catalysts 5# and 6# were obtained, denoted as Fe1Mn2@NHGC and Fe2Mn1@NHGC, respectively.

[0091] The catalysts added during the catalytic oxidation of organic pollutants in wastewater were catalysts 5# and 6#, respectively. The degradation of carbamazepine was determined, and the test results are shown in Tables 6 and 7.

[0092] Table 6

[0093]

[0094] Table 7

[0095]

[0096] Example 6

[0097] The difference between Example 6 and Example 1 is that the amount of urea added was changed to 0.05g during the preparation of the catalyst, while the other conditions remained the same, resulting in catalyst 7#, denoted as FeMn@NHGC (nitrogen increase);

[0098] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst #7. The degradation amount of carbamazepine was determined, and the test results are shown in Table 8.

[0099] Table 8

[0100]

[0101] Example 7

[0102] The difference between Example 7 and Example 1 is that the calcination temperature was changed to 700℃ and 900℃ during the catalyst preparation process, while the other conditions remained the same, resulting in catalysts 8# and 9#, denoted as FeMn@NHGC-700 and FeMn@NHGC-900 respectively.

[0103] The catalysts added during the catalytic oxidation of organic pollutants in wastewater were catalysts 8# and 9#, respectively. The degradation of carbamazepine was determined, and the test results are shown in Tables 9 and 10.

[0104] Table 9

[0105]

[0106] Table 10

[0107]

[0108]

[0109] Example 8

[0110] The difference between Example 8 and Example 1 is that the pH of the pollutant solution in the catalytic oxidation process of organic pollutants in wastewater was changed to 4, while the other conditions remained the same. The degradation amount of carbamazepine was measured, and the test results are shown in Table 11.

[0111] Table 11

[0112]

[0113] Example 9

[0114] The difference between Example 9 and Example 1 is that the amount of carbon cloth-loaded catalyst in the catalytic oxidation process of organic pollutants in wastewater was changed to 5 mg, while the other conditions remained the same. The degradation of carbamazepine was measured, and the test results are shown in Table 12.

[0115] Table 12

[0116]

[0117]

[0118] Example 10

[0119] The difference between Example 10 and Example 1 is that the voltage in the catalytic oxidation process of organic pollutants in wastewater was changed to -0.8V vs. SCE, while the other conditions remained the same. The degradation of carbamazepine was measured, and the test results are shown in Table 13.

[0120] Table 13

[0121]

[0122] Comparative Example 1

[0123] The difference between Comparative Example 1 and Example 1 is that, in the preparation of the catalyst, ferric acetate was replaced with an equal amount of manganese acetate, and the other conditions were the same, resulting in catalyst D1#, denoted as Mn@NHGC;

[0124] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst D1#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 14.

[0125] Table 14

[0126]

[0127]

[0128] Comparative Example 2

[0129] The difference between Comparative Example 2 and Example 1 is that in the preparation of the catalyst, manganese acetate was replaced with an equal amount of ferric acetate, while the other conditions were the same, and catalyst D2# was obtained, denoted as Fe@NHGC;

[0130] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst D2#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 15.

[0131] Table 15

[0132]

[0133] Comparative Example 3

[0134] The difference between Comparative Example 3 and Example 1 is that manganese acetate and ferric acetate were not added during the preparation of the catalyst, while the other conditions were the same, resulting in catalyst D3#, denoted as NHGC;

[0135] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst D3#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 16.

[0136] Table 16

[0137]

[0138]

[0139] Comparative Example 4

[0140] The difference between Comparative Example 4 and Example 1 is that urea was not added during the preparation of the catalyst, while the other conditions were the same, resulting in catalyst D4#, denoted as FeMn@HGC;

[0141] The catalyst added during the catalytic oxidation of organic pollutants in wastewater was catalyst D4#. The degradation amount of carbamazepine was determined, and the test results are shown in Table 17.

[0142] Table 17

[0143]

[0144] like Figure 1 As shown, NHGC is composed of both amorphous and non-amorphous carbon. In Fe@NHGC, Fe is Fe3C, and in Mn@NHGC, Mn is MnO. In FeMn@NHGC, ZVI is also present in addition to Fe3C and MnO, demonstrating the synergistic effect between Fe and Mn. Furthermore, the C peak is significantly enhanced in Fe@NHGC, Mn@NHGC, and FeMn@NHGC, indicating the formation of a well-crystallized carbon shell on the surface of the metal particles under the induction of the metal.

[0145] like Figure 2 As shown in (a), NHGC is composed of carbon nanospheres with a smooth, wrinkle-free surface; Figure 2 As shown in (b), the surface of the carbon spheres is covered with metal nanoparticles and a small number of wrinkles and bulges formed by the Kirkendall effect; as Figure 2 As shown in (c), the material is a mixture of carbon spheres and octahedral MnO; as Figure 2 As shown in (d), the morphology of FeMn@NHGC is similar to that of Fe@NHGC, but the interaction between Fe and Mn increases the wrinkles and bulges on the material surface, which increases the contact between the catalyst and the pollutant solution and is beneficial to increasing the reaction rate.

[0146] like Figure 3 As shown in (a), the metal particles are uniformly distributed on each carbon sphere; as Figure 3 As shown in (b), N and O are uniformly distributed on the surface of the carbon spheres, and the distribution of Fe and Mn shows a high degree of consistency, proving the existence of their interaction.

[0147] like Figure 4 As shown in (a), 4(c), and 4(e), the numerous wrinkles and bulges in metals caused by the Kirkendall effect under high-temperature conditions can significantly increase the BET specific surface area of ​​the material, and melamine can further increase the specific surface area of ​​the material during carbonization; such as Figure 4 As shown in (b), 4(d), and 4(f), the material is mainly mesoporous, which helps to confine pollutants to the material surface and promotes the degradation of pollutants.

[0148] like Figure 5 As shown, compared to Fe@NHGC, FeMn@NHGC generates ZVI under the influence of Mn, further demonstrating the interaction between the bimetals.

[0149] like Figure 6 As shown, the addition of N greatly improves the material's selectivity for H2O2.

[0150] like Figure 7 As shown, Fe@NHGC and FeMn@NHGC exhibit the largest current response to H2O2, confirming that the materials have the ability to activate H2O2 into hydroxyl radicals.

[0151] In summary, the nitrogen-doped carbon-supported iron-manganese bimetallic catalyst provided by this invention has a suitable pore structure, a high specific surface area, and a large number of active sites for oxygen reduction and degradation, thus exhibiting good degradation performance for organic pollutants.

[0152] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. An application of a nitrogen-doped carbon-supported iron-manganese bimetallic catalyst, characterized in that: Nitrogen-doped carbon-supported iron-manganese bimetallic catalysts were prepared by the following method: Step 1: Preparation of catalyst precursor: Dissolve 3g of glucose in 60mL of deionized water and stir to form a solution. Place the solution in a 100mL hydrothermal reactor for high-temperature hydrothermal treatment at a temperature of 160-180℃ for 8-12 hours. Wash the hydrothermally treated substance three times with a mixture of water and ethanol, and then freeze-dry it at -45-60℃ and 10-50Pa for 10-12 hours to remove moisture and dry it to obtain the catalyst precursor. Step 2: The catalyst precursor obtained in Step 1 is heated and evaporated. Weigh 0.1 g of the catalyst precursor obtained in step 1 and place it in a 100 mL beaker. Add the metal salt and nitrogen source to the beaker in sequence, and add 50 mL of deionized water. Stir in a heating mantle at 80-90 °C for 10-12 h until the solvent is completely evaporated. The metal salt is an iron salt and a manganese salt. Step 3: Calcine the substance obtained in Step 2 to obtain the catalyst. The material obtained in step 2 was transferred to a corundum boat and calcined and carbonized in a tube furnace under N2 atmosphere. The temperature was raised from room temperature to 700-900℃ and maintained for 1-3 hours. Then it was naturally cooled to room temperature. The heating rate was 1-3℃ / min. The black sample obtained by calcination was collected as the catalyst and denoted as FeMn@NHGC. The application of nitrogen-doped carbon-supported iron-manganese bimetallic catalysts in the catalytic oxidation of organic pollutants in wastewater includes the following steps: Step (1): Prepare 100 mL of carbamazepine solution with 10 ppm and pH=3 in 0.05 mol / L sodium sulfate solution, and sonicate for 30 minutes to simulate organic pollutant wastewater; Step (2): Weigh 2.5 mg of catalyst and disperse it in a mixed solution consisting of 0.15 mL water, 0.35 mL anhydrous ethanol and 0.015 mL 5 wt% Nafion, and sonicate for 30 min. Step (3): Soak the raw carbon cloth in water, anhydrous ethanol, and 1 mol / L nitric acid for 30 min respectively, then dry and cut it into 2×2 cm pieces. Add the mixed solution from step (2) evenly to both sides of the carbon cloth, dry and set aside. Step (4): Add the solution obtained in step (1) to the circular electrolytic cell, connect the carbon cloth obtained in step (3) with the platinum electrode clamp to form the working electrode, use the platinum mesh or graphite rod as the counter electrode, and immerse the calomel electrode as the reference electrode in the solution. Immerse one end of the aeration tube in the solution and connect the other end to oxygen. Turn on the oxygen and pre-introduce oxygen into the solution for at least 5 minutes to make the solution reach the oxygen saturation state. Step (5): Connect the electrochemical workstation to the electrode and apply a voltage of -0.6V vs. SCE for 1 hour. Start timing at the moment of power-on and take out 0.5 mL of solution from the reaction system at 2, 5, 10, 20, 30, 40, 50, and 60 min respectively. Then immediately inject the taken-out solution into a screw-top bottle containing 0.5 mL of methanol to quench the reaction. Step (6): Use a mixed solution containing 70% methanol and 30% deionized water as the mobile phase, control the flow rate at 1 mL / min, and determine the degradation amount of carbamazepine by using a high performance liquid chromatograph with a Supersil ODS-B column. Step (7): The iron and manganese leaching rate of the catalyst was determined by inductively coupled plasma atomic emission spectrometry after the reaction. The carbon cloth supporting the catalyst was recovered and recorded as FeMn@NHGC-2nd, and used as a catalyst again for the catalytic oxidation process in steps (1)-(6).

2. The application of the nitrogen-doped carbon-supported iron-manganese bimetallic catalyst according to claim 1, characterized in that: In step 2, the nitrogen source is at least one of melamine, urea, or dicyandiamide.

3. The application of the nitrogen-doped carbon-supported iron-manganese bimetallic catalyst according to claim 1, characterized in that: In step 2, the metal salt is an iron or manganese nitrate, acetate, or chloride salt, and the mass ratio between iron and manganese is 1:2 to 1:0.5.

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