CN115869983A - Manganese-nitrogen co-doped carbon nanosheet, preparation method and application - Google Patents

Abstract

In the field of wastewater treatment of environmental materials, the present invention provides a manganese-nitrogen co-doped carbon nanosheet, a preparation method and an application thereof. The method successfully anchors the transition metal manganese on the doped carbon nanosheet through a two-step synthesis process of freeze-drying and carbonization. N-doped porous carbon. The material uses melamine as a nitrogen source, glucose as a carbon source, and manganese chloride as a metal precursor, and is formed by one-step carbonization. The primary carbon intermediate of glucose generation combines with the layered g-C ₃ N ₄ formed during the pyrolysis of melamine through donor-acceptor interactions, and g-C ₃ N ₄ acts as a template to guide the carbon layer along the plane to form carbon nanostructures sheet structure; melamine provides a rich nitrogen atom environment, captures transition metal manganese, forms highly dispersed Mn-Nx coordination bonds, fixes nitrogen species on carbon nanosheets, and provides a variety of active nitrogen components. The material can increase the catalyst degradation rate of organic pollutant phenol and has good circulation, reduces the metal leaching concentration, and will not cause secondary pollution to the environment.

Description

A kind of manganese nitrogen co-doped carbon nano sheet, preparation method and application

technical field

The invention relates to the field of waste water treatment of environmental materials, and specifically relates to a manganese-nitrogen co-doped carbon nanosheet, a preparation method and an application.

Background technique

Today, phenolic and antibiotic contaminants are widely detected in wastewater and water environments. Their widespread presence has serious impacts on nature and human health, and even at low concentrations, they have attracted worldwide attention. Therefore, the removal of these organic pollutants in water has given rise to an increasing demand for efficient treatment technologies. In recent years, the activation of peroxymonosulfate (PMS) based on advanced oxidation processes (AOPs) has been proven to be one of the most effective methods for the removal of organic pollutants.

Carbon-based materials, as a kind of metal-resistant, acid-base resistant, large specific surface area, and more active sites, have attracted extensive attention as a new type of heterogeneous catalyst for activating PMS. However, pristine carbon-based materials (such as carbon nanotubes, graphene, diamond, and biochar) still have limited active functional groups, structural defects, and a low degree of graphitization. Although a variety of modification methods have been used to improve the catalytic performance of carbon-based materials, there are few studies on manganese-nitrogen co-doped carbon-based materials.

The information disclosed in this Background section is only for enhancing the understanding of the general background of the present invention and should not be taken as an acknowledgment or any form of suggestion that the information constitutes the prior art that is already known to those skilled in the art.

Contents of the invention

The present invention is carried out in order to solve the above problems, and the purpose is to provide a manganese nitrogen co-doped carbon nanosheet, a preparation method and an application. The material has high-efficiency degradation performance and can activate persulfate to degrade phenol.

The invention provides a method for preparing manganese nitrogen co-doped carbon nanosheets, which has such characteristics and includes the following steps: step 1, dissolving a certain amount of manganese chloride and zinc chloride in water, and mixing them uniformly to obtain liquid A ; Step 2, dissolve a certain amount of melamine and glucose in water, mix evenly to obtain liquid B; step 3, slowly drop liquid A into liquid B to obtain a milky white precipitate; step 4, slowly drop the milky white precipitate into liquid nitrogen Rapid freezing to obtain a frozen product; step 5, put the frozen product in a freeze dryer at -45°C to -55°C to freeze-dry, grind and vacuum dry to obtain a white powder; step 6, put the white powder at high temperature under an inert atmosphere Calcining to obtain a calcined product, grinding, acid leaching, and drying to obtain manganese-nitrogen co-doped carbon nanosheets.

In the preparation method of manganese nitrogen co-doped carbon nanosheets provided by the present invention, it may also have the following characteristics: wherein, in step 1, the manganese chloride is manganese chloride tetrahydrate with a mass of 0.197g to 0.394g, The mass of zinc chloride is 0.136g and the volume of water is 5ml.

In the preparation method of manganese-nitrogen co-doped carbon nanosheets provided by the present invention, it may also have such features: wherein, in step 2, the mass of melamine is 5g, the mass of glucose is 2g, and the volume of water is 25ml.

In the preparation method of manganese-nitrogen co-doped carbon nanosheets provided by the present invention, it may also have such a feature: wherein, in step 3, liquid A is slowly added dropwise to liquid B, stirring continuously during the dropping process, and adding Continue to stir for 4h after completion, and a milky white precipitate is obtained.

In the preparation method of the manganese-nitrogen co-doped carbon nanosheets provided by the present invention, it may also have such a feature: wherein, in step 4, the white precipitate after standing is dropped into liquid nitrogen at a rate of one drop per second. Blast freeze.

In the preparation method of manganese-nitrogen co-doped carbon nanosheets provided by the present invention, it may also have such a feature: wherein, in step 6, the dried product is heated to 800 °C at a heating rate of 4 ° C to 6 ° C under a nitrogen atmosphere. ℃～900℃ high temperature calcination.

In the preparation method of manganese-nitrogen co-doped carbon nanosheets provided by the present invention, it may also have such a feature: wherein, in step 6, the calcined product is washed in 0.5M sulfuric acid for 10 h, and dried to obtain manganese-nitrogen co-doped carbon Nanosheets.

The present invention also provides a manganese nitrogen co-doped carbon nano sheet, which has such a feature and is prepared by the preparation method of the manganese nitrogen co-doped carbon nano sheet.

The invention also provides an application of manganese nitrogen co-doped carbon nano sheet in activating persulfate to degrade phenol.

In the application of the manganese nitrogen co-doped carbon nanosheets provided by the present invention in the activation of persulfate to degrade phenol, it can also have such characteristics: wherein, in the degradation solution, the content of phenol is 0.2g/L, and the persulfate The content of 0.2g/L, the addition of manganese nitrogen co-doped carbon nanosheets is 0.2g/L.

Function and Effect of Invention

According to a manganese nitrogen co-doped carbon nanosheet, preparation method and application thereof provided by the present invention, the method successfully anchors the transition metal manganese in the N-doped porous through the two-step synthesis process of freeze-drying and carbonization process. on carbon. The material uses melamine as a nitrogen source, glucose as a carbon source, and manganese chloride as a metal precursor, and is formed by one-step carbonization. Melamine forms _gC3N4 during pyrolysis, and the primary carbon intermediate produced by glucose _binds to layered _gC3N4 through donor-acceptor interactions, and _gC3N4 acts as _a template to guide the carbon _layer along the plane to form carbon nanoparticles Secondly, melamine provides a rich nitrogen atom environment, captures the transition metal manganese, forms highly dispersed Mn-Nx coordination bonds, fixes nitrogen species on carbon nanosheets, and provides a variety of active nitrogen components.

The invention uses glucose as a carbon substrate to fix nitrogen atoms to prevent excessive loss of nitrogen atoms during high-temperature heating, and contributes to the formation of high density and uniform distribution of Mn-Nx coordination bonds in carbon-based materials. As the temperature increases, gC ₃ N ₄ is further pyrolyzed to produce a large amount of nitrogen-containing gas, which leads to the curling of carbon nanosheets and the mesoporous carbon skeleton structure, which not only effectively avoids the overlapping of carbon layers, but also increases the number of nitrogen sites fixed on the carbon skeleton. on possibility. Carbon-based materials co-doped with transition metals and nitrogen can effectively adjust the electronic structure of the original carbon materials and improve the catalytic activity; in addition, the doped transition metals exist in the interior of the material in the form of M-Nx coordination bonds, and the outer layer of carbon The protection of the shell reduces the concentration of metal leaching, effectively improving the durability of carbon-based materials in catalytic reactions.

Therefore, the present invention modifies the carbon-based material through manganese-nitrogen co-doping engineering, improves the rate of catalyst degradation of organic pollutant phenol and has good circulation, reduces metal leaching concentration, and does not cause secondary pollution to the environment.

Description of drawings

Fig. 1 is the scanning electron microscope schematic diagram of the manganese nitrogen co-doped carbon nanosheet of embodiment 1 in the present invention;

Fig. 2 is the transmission electron microscope schematic diagram of the manganese nitrogen co-doped carbon nanosheet of embodiment 1 in the present invention;

Fig. 3 is the impact of different types of catalysts on the phenol removal effect among the present invention;

Fig. 4 is the impact of different catalyst dosages on the phenol removal effect among the present invention;

Fig. 5 is an effect diagram of the repeated utilization of manganese and nitrogen co-doped carbon nanosheets in the present invention.

Detailed ways

In order to make the technical means, creative features, goals and effects of the present invention easy to understand, a manganese-nitrogen co-doped carbon nanosheet, preparation method and application of the present invention will be described in detail below in conjunction with the examples and accompanying drawings.

Unless otherwise specified, all raw materials used in the following examples are commercially available products, and all equipment used are commercially available conventional equipment.

The persulfate is potassium hydrogen persulfate.

The preparation method of the manganese nitrogen co-doped carbon nanosheet provided by the present invention specifically comprises the following steps:

Step 1, dissolving a certain amount of manganese chloride tetrahydrate and zinc chloride in an ultrapure aqueous solution, and mixing uniformly to obtain liquid A;

Step 2, dissolving a certain amount of melamine and glucose in an ultrapure aqueous solution, and mixing evenly to obtain liquid B;

Step 3: Slowly add liquid A to liquid B dropwise, continuously stir during the dropwise addition, and continue to stir for 4 hours after the dropwise addition is completed, to obtain a milky white precipitate;

Step 4, slowly dropping the milky white precipitate into liquid nitrogen for rapid freezing to obtain a frozen product;

Step 5, putting the frozen product into a freeze dryer to freeze-dry at -45°C to -55°C, grinding and vacuum-drying to obtain a white powder;

Step 6, calcining the white powder at high temperature under a nitrogen atmosphere to obtain a calcined product, grinding, acid leaching, and drying to obtain manganese-nitrogen co-doped carbon nanosheets.

In the above step 1, the mass of manganese chloride tetrahydrate is 0.197g-0.394g, the mass of zinc chloride is 0.136g, and the volume of ultrapure water is 5ml. In step 2, the mass of melamine is 5g, the mass of glucose is 2g, and the volume of ultrapure water is 25ml. In step 4, the white precipitate after standing was dropped into liquid nitrogen at a rate of one drop per second for rapid freezing.

In step 6, the white powder is calcined at a high temperature of 800°C to 900°C under a nitrogen atmosphere at a heating rate of 4°C to 6°C to obtain a black calcined product, which is ground and washed in 0.5M sulfuric acid for 10 hours , and further washed with deionized water for 2 to 4 times, washed and dried to obtain manganese nitrogen co-doped carbon nanosheets.

Manganese nitrogen co-doped carbon nanosheets prepared according to the above preparation method are used as catalysts to activate persulfate to degrade phenol. The specific process of degrading phenol is as follows:

Step S1, configuring a degradation solution containing phenol, manganese nitrogen co-doped carbon nanosheets and persulfate, and then performing degradation under constant temperature conditions;

Step S2, within a given time, take 0.9mL sample, filter it through a 0.22μm membrane filter, then quench it with 0.1ml methanol solution in a glass bottle, analyze it by high performance liquid chromatography after filtration, and obtain the corresponding time Concentration of pollutants, the degradation ends after 5 minutes.

In the above degradation experiment, the concentration of phenol in the degradation solution was 0.2g/L, the concentration of persulfate was 0.2g/L, the amount of catalyst added was 0.2g/L, the pH value was 7.0, and it was carried out at room temperature. Sodium hydrogen phosphate buffer solution was added to the degradation solution, and the pH value of the stable solution was 7.

<Example 1>

In this example, a manganese nitrogen co-doped carbon nanosheet is prepared. The masses of manganese chloride tetrahydrate, zinc chloride, melamine, and glucose are respectively 0.197g, 0.136g, 5g, and 2g. The specific operations are as follows:

Step 1, dissolve 0.197g of manganese chloride tetrahydrate and 0.136g of zinc chloride in 5ml of ultrapure aqueous solution, and mix evenly to obtain liquid A;

Step 2, dissolve 5g of melamine and 2g of glucose in 25ml of ultrapure aqueous solution, and mix evenly to obtain liquid B;

Step 3, slowly add liquid A dropwise to liquid B, and continue to stir during the dropwise addition, and continue to stir for a period of time after the dropwise addition is completed, the stirring time is 4 hours, and a milky white precipitate is obtained;

Step 4, slowly drop the milky white precipitate into liquid nitrogen for rapid freezing, drop it into liquid nitrogen at a rate of one drop per second for rapid freezing, and obtain a frozen product;

Step 5, putting the frozen product into a freeze dryer to freeze-dry at -45°C to -55°C, grinding and vacuum-drying to obtain a white powder;

Step 6: Calcining the white powder in a nitrogen atmosphere at a heating rate of 4°C to 6°C to 800°C to 900°C to obtain a black calcined product, which is ground and washed in 0.5M sulfuric acid for 10 hours, and then further washed with deionized water Washing 2 to 4 times, washing and drying to obtain manganese nitrogen co-doped carbon nanosheets, marked as Mn-N@C-1.

<Example 2>

In this example, a manganese-nitrogen co-doped carbon nanosheet is prepared. The masses of manganese chloride tetrahydrate, zinc chloride, melamine, and glucose are 0.394g, 0.136g, 5g, and 2g respectively. The specific operations are as follows:

Step 1, dissolve 0.394g of manganese chloride tetrahydrate and 0.136g of zinc chloride in 5ml of ultrapure aqueous solution, and mix well to obtain liquid A;

Step 2, dissolve 5g of melamine and 2g of glucose in 25ml of ultrapure aqueous solution, and mix evenly to obtain liquid B;

Step 3, slowly add liquid A dropwise to liquid B, and continue to stir during the dropwise addition, and continue to stir for a period of time after the dropwise addition is completed, the stirring time is 4 hours, and a milky white precipitate is obtained;

Step 4, slowly drop the milky white precipitate into liquid nitrogen for rapid freezing, drop it into liquid nitrogen at a rate of one drop per second for rapid freezing, and obtain a frozen product;

Step 5, putting the frozen product into a freeze dryer to freeze-dry at -45°C to -55°C, grinding and vacuum-drying to obtain a white powder;

Step 6: Calcining the white powder in a nitrogen atmosphere at a heating rate of 4°C to 6°C to 800°C to 900°C to obtain a black calcined product, which is ground and washed in 0.5M sulfuric acid for 10 hours, and then further washed with deionized water Washing 2 to 4 times, washing and drying to obtain manganese nitrogen co-doped carbon nanosheets, marked as Mn-N@C-2.

<Comparative example 1>

In this comparative example, a manganese-nitrogen co-doped carbon nanosheet is prepared. The masses of manganese chloride tetrahydrate, zinc chloride, melamine, and glucose are respectively 0g, 0.136, 5g, and 2g. The rest of the operations are the same as in Example 2, and the obtained The comparison sample nitrogen-doped carbon nanosheets, marked as N@C.

<Comparative example 2>

In this comparative example, a manganese-nitrogen co-doped carbon nanosheet was prepared, and the masses of manganese chloride tetrahydrate, zinc chloride, melamine, and glucose were respectively 0.197g, 0.136, 0g, and 2g, and the rest of the operations were the same as in Example 2. A comparison sample of nitrogen-doped carbon nanosheets was obtained, labeled as Mn@C.

<test case>

Scanning electron microscopy and transmission electron microscopy were performed on the manganese nitrogen co-doped carbon nanosheets prepared in Example 1, and the detection results are shown in FIGS. 1 and 2 .

FIG. 1 is a schematic diagram of a scanning electron microscope of manganese nitrogen co-doped carbon nanosheets in Example 1 of the present invention, and FIG. 2 is a schematic diagram of a transmission electron microscope of manganese nitrogen co-doped carbon nanosheets in Example 1 of the present invention.

As shown in Figures 1 and 2, it can be clearly seen that the SEM and TEM images of Mn-N@C-1 are mainly layered and sheet-like structures, and there are abundant wrinkles on the surface, indicating that the metal manganese Successful doping, in addition, the layered structure provides a larger specific surface area (98.94m ² /g) and more active sites, which improves the catalytic effect of the material.

<Application example 1>

The manganese nitrogen co-doped carbon nanosheets prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were used as catalysts to activate persulfate (PMS) to degrade phenol. The concrete experimental process of this phenol degradation experiment is as follows:

Carried out in a 250 mL beaker containing 100 mL of ultrapure water with magnetic stirring at room temperature. In a typical experiment, 20 mg catalyst and 20 mg oxidant PMS were added to 100 mL phenol solution (20 mgL ⁻¹ ). The pH was stabilized with phosphate buffered saline (PBS, 20 mM).

Every 1 min for a given time, 0.9 mL samples were taken, filtered through a 0.22 μm membrane filter, and then quenched with 0.1 ml of methanol solution in a glass vial for high-performance liquid chromatography (HPLC). Get the corresponding pollutant concentration, stop the degradation after 5 minutes, end the experiment, and process and analyze the measurement data within 5 minutes. The experimental results are shown in Figure 3.

Fig. 3 is the influence of different types of catalysts on the removal effect of phenol in the present invention. Wherein, the abscissas all represent the degradation reaction time in min, and the ordinates all represent the degradation ratio, (that is, the concentration of phenol present in the solution/the initial concentration of phenol) in %.

It can be seen from Figure 3 that after adding Mn-N@C-1, the catalytic performance is remarkable, and the degradation proceeds very quickly. The degradation rate of phenol is about 100% within 5 minutes, and the degradation effect is the best. It is followed by Mn-N@C-2 with a degradation rate of 70.1%. The degradation of N@C and Mn@C was the slowest, and when the degradation stopped after 5 min, the degradation effects were 46.7% and 23.6%, respectively. The enhanced phenol degradation in Mn-N@C-1 further indicates the important role of introducing Mn/N co-doping. The formation of Mn–Nx bonds in carbon-based materials has been shown to tune the electronic structure of carbon-based materials, further enhancing the performance of catalysts for activating PMS.

<Application example 2>

The Mn-N@C-1 prepared in Example 1 was used as a catalyst to compare the effects of different catalyst dosages on the phenol degradation experiment. The catalyst dosages of the four parallel experiments were 5 mg, 10 mg, 20 mg, and 30 mg, respectively. Except that the dosage of the catalyst is different, other steps of the degradation experiment process are the same as those in Application Example 1. The degradation comparison results of catalysts with different dosages are shown in Fig. 4.

Fig. 4 is the effect of different dosages of catalysts in the present invention on the removal effect of phenol. Wherein, the abscissas all represent the degradation reaction time in min, and the ordinates all represent the degradation ratio, (that is, the concentration of phenol present in the solution/the initial concentration of phenol) in %.

As shown in Figure 4, when the amount of material added is 0.2 g/L, the removal rate of phenol is about 100% within 5 minutes, and then with the increase of the amount of catalyst Mn-N@C-1, the removal rate of phenol The removal rate showed an upward trend. When the dosage was 0.3g/L, the removal rate of phenol almost reached the maximum value. It shows that the degradation rate of phenol is directly proportional to the content of catalyst. As the catalyst content increased, more active sites were provided for PMS activation, resulting in abundant active oxygen for phenol removal.

<Application example 3>

This application example is the cycle performance experiment of the manganese-nitrogen co-doped carbon nanosheets in Example 1, using the manganese-nitrogen co-doped carbon nanosheets Mn-N@C-1 as the catalyst in Example 1, and carried out 5 times Loop experiment. The devices and testing instruments used in the experiment are the same as those in Application Example 1, and the time course is the same as Application Example 1 except for the amount of substances added and the sampling time.

The experimental process is as follows:

At 25°C, use 50 mg of the material made in Example 1, 20 mg of persulfate, and add it to 100 ml of phenol solution with a concentration of 20 mg/l to form a degradation solution. Take 0.9 mL of sample every 1 minute within 5 minutes, and pass Filter through a 0.22 μm membrane filter, then quench with 0.1 ml of methanol solution in a glass vial, and perform high-performance liquid chromatography (HPLC). After 5 minutes, the catalyst was filtered through a suction filtration device, washed, and dried in a vacuum oven at 60° C. for 12 hours to recover the catalyst. In the second cycle, the completely dried samples were re-run under the experimental conditions of the first cycle, and the cycle was repeated until the fifth cycle ended. The results are shown in Figure 5.

Fig. 5 is a cycle degradation effect diagram in application example 3 of the present invention.

It can be seen from Figure 5 that after 5 cycles of experiments, the manganese-nitrogen co-doped carbon nanosheets prepared in Example 1 still have good catalytic degradation performance, and the degradation effects within five minutes are 100%, 99.5%, 99.0%, and 95.4%, respectively. , 89.5%, indicating that Mn-N@C-1 has a good cycle.

Function and effect of embodiment

A manganese-nitrogen co-doped carbon nanosheet, preparation method and application provided according to the embodiments of the present invention, the method successfully anchors the transition metal manganese in the doped N on porous carbon. The material uses melamine as a nitrogen source, glucose as a carbon source, and manganese chloride as a metal precursor, and is formed by one-step carbonization. Melamine forms _gC3N4 during pyrolysis, and the primary carbon intermediate produced by glucose _binds to layered _gC3N4 through donor-acceptor interactions, and _gC3N4 acts as _a template to guide the carbon layer along the _plane to form carbon Nanosheet structure; secondly, melamine provides a rich nitrogen atom environment, captures transition metal manganese, forms highly dispersed Mn-Nx coordination bonds, immobilizes nitrogen species on carbon nanosheets, and provides a variety of active nitrogen components.

This method uses glucose as a carbon substrate to fix nitrogen atoms to prevent the loss rate of nitrogen atoms from being too high during high-temperature heating, which contributes to the formation of high density and uniform distribution of Mn-Nx coordination bonds in carbon-based materials. As the temperature increases, gC ₃ N ₄ is further pyrolyzed to produce a large amount of nitrogen-containing gas, which leads to the curling of carbon nanosheets and the mesoporous carbon skeleton structure, which not only effectively avoids the overlapping of carbon layers, but also increases the number of nitrogen sites fixed on the carbon skeleton. on possibility.

Carbon-based materials co-doped with transition metals and nitrogen can effectively adjust the electronic structure of the original carbon materials and improve the catalytic activity; in addition, the doped transition metals exist in the material in the form of M-Nx coordination bonds, and the outer layer of carbon The protection of the shell reduces the concentration of metal leaching, effectively improving the durability of carbon-based materials in catalytic reactions.

Therefore, the embodiment of the present invention uses manganese-nitrogen co-doped modified carbon-based materials to increase the rate of catalyst degradation of organic pollutant phenol and has good circulation, reduces metal leaching concentration, and will not cause secondary pollution to the environment. For example, in application example 1, when the degradation is performed for 5 minutes, the degradation ratio reaches about 100%; in application example 2, the degradation effect of manganese-nitrogen co-doped carbon nanosheets with different dosages is still excellent; in application example 3, It can still achieve a good catalytic effect after being recycled 5 times.

The above embodiments are preferred examples of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent structure or equivalent process conversion made by using the description of the present invention, or direct or indirect application in other related technical fields are also included in the scope of patent protection of the present invention.

Claims (10)

1. The preparation method of the manganese and nitrogen co-doped carbon nanosheet is characterized by comprising the following steps of:

step 1, dissolving a certain amount of manganese chloride and zinc chloride in water, and uniformly mixing to obtain a solution A;

step 2, dissolving a certain amount of melamine and glucose in water, and uniformly mixing to obtain a solution B;

step 3, slowly dripping the solution A into the solution B to obtain milky white precipitate;

step 4, slowly dropping the milky white precipitate into liquid nitrogen for quick freezing to obtain a frozen product;

step 5, putting the frozen product into a freeze dryer for freeze drying at the temperature of between 45 ℃ below zero and 55 ℃ below zero, and grinding and vacuum drying to obtain white powder;

and 6, calcining the white powder at high temperature in an inert atmosphere to obtain a calcined product, grinding and acid leaching, and drying to obtain the manganese-nitrogen co-doped carbon nanosheet.

2. The preparation method of manganese-nitrogen co-doped carbon nanosheet according to claim 1, wherein:

in the step 1, the manganese chloride is manganese chloride tetrahydrate, the mass of the manganese chloride is 0.197 g-0.394 g, the mass of the zinc chloride is 0.136g, and the volume of the water is 5ml.

3. The preparation method of manganese and nitrogen co-doped carbon nanosheet according to claim 1, wherein:

in step 2, the mass of the melamine is 5g, the mass of the glucose is 2g, and the volume of the water is 25ml.

4. The preparation method of manganese-nitrogen co-doped carbon nanosheet according to claim 1, wherein:

and 3, slowly dropwise adding the solution A into the solution B, continuously stirring in the dropwise adding process, and continuously stirring for 4 hours after dropwise adding is finished to obtain the milky white precipitate.

5. The preparation method of manganese-nitrogen co-doped carbon nanosheet according to claim 1, wherein:

in step 4, the white precipitate after standing is dropped into liquid nitrogen at a speed of one drop per second for quick freezing.

6. The preparation method of manganese-nitrogen co-doped carbon nanosheet according to claim 1, wherein:

in step 6, the dried product is heated to 800-900 ℃ at a heating rate of 4-6 ℃ in a nitrogen atmosphere and is calcined at high temperature.

7. The preparation method of manganese-nitrogen co-doped carbon nanosheet according to claim 1, wherein:

in step 6, washing the calcined product in 0.5M sulfuric acid for 10 hours, and drying to obtain the manganese-nitrogen co-doped carbon nanosheet.

8. Manganese-nitrogen-codoped carbon nanosheet, characterized by being prepared by the preparation method of manganese-nitrogen-codoped carbon nanosheets according to any one of claims 1-7.

9. The application of the manganese and nitrogen co-doped carbon nanosheet in activating persulfate to degrade phenol is characterized in that the manganese and nitrogen co-doped carbon nanosheet is the manganese and nitrogen co-doped carbon nanosheet as defined in claim 8.

10. The application of the manganese-nitrogen co-doped carbon nanosheet in activating persulfate to degrade phenol according to claim 9, wherein:

wherein, in the degradation liquid, the content of phenol is 0.2g/L, the content of persulfate is 0.2g/L, and the addition amount of the manganese-nitrogen co-doped carbon nanosheet is 0.2g/L.

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