A two-dimensional nitrogen-doped carbon nanosheet and a preparation method and application thereof

Abstract

This invention provides a two-dimensional nitrogen-doped carbon nanosheet, its preparation method, and its application. The preparation method includes the following steps: (1) mixing nitrogen-containing organic solid waste and composite molten salt, and then pyrolyzing the mixture to obtain pyrolysis products; (2) post-processing the pyrolysis products to obtain the nitrogen-doped carbon nanosheets. This invention uses nitrogen-containing organic solid waste as the carbon and nitrogen source, and composite molten salt as the reaction aid, to prepare in-situ two-dimensional nitrogen-doped carbon nanosheets using a high-temperature pyrolysis method. These nanosheets can be used to activate persulfate oxidation to degrade phthalate pollutants or azo dyes in water, to adsorb polystyrene microplastic particles in water, and to enhance the anaerobic fermentation process of organic solid waste. This method is simple, efficient, economical, and environmentally friendly. The composite molten salt is recyclable, achieving the harmless treatment and resource utilization of potentially hazardous solid waste. It offers high economic and environmental benefits and belongs to the comprehensive technology of "treating waste with waste."

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, specifically relating to a two-dimensional nitrogen-doped carbon nanosheet, its preparation method, and its application. Background Technology

[0002] Solid wastes such as livestock and poultry manure, kitchen waste, and industrial organic waste are produced in large quantities, with high water and organic matter content, and are easily digested and decomposed. Anaerobic digestion technology is an effective method for treating organic solid waste, enabling the resource utilization of nutrients and the clean production of energy such as methane. However, current anaerobic fermentation technologies suffer from low methane yields and the accumulation of acidic inhibitors such as organic acids, cyanides, and hydrogen sulfide in the system. Studies have shown that adding carbon materials to anaerobic fermentation systems can increase methane yields and degrade or adsorb inhibitors, thereby enhancing the biogas production potential of anaerobic fermentation. In particular, two-dimensional carbon materials have good electrical conductivity, and nitrogen doping can further enhance their conductivity, promoting electron transfer during anaerobic fermentation and thus strengthening the anaerobic fermentation process.

[0003] The aforementioned organic solid waste has a high nitrogen content and is an intrinsically nitrogen-rich raw material. In addition to anaerobic fermentation, it can also be used as a raw material for preparing nitrogen-doped carbon materials. This eliminates the need to add nitrogen-containing reagents such as urea and melamine during the pyrolysis process, thereby simplifying the pyrolysis steps and saving costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a two-dimensional nitrogen-doped carbon nanosheet, its preparation method, and its applications. This invention uses nitrogen-containing organic solid waste as both carbon and nitrogen sources, and a composite molten salt as a reaction aid, employing a high-temperature pyrolysis method to prepare in-situ two-dimensional nitrogen-doped carbon nanosheets. These nanosheets can be used to activate persulfate oxidation to degrade phthalate pollutants or azo dyes in water, to adsorb polystyrene microplastic particles in water, and to enhance the anaerobic fermentation process of organic solid waste. This method is simple, efficient, economical, and environmentally friendly. The composite molten salt is recyclable, achieving the co-treatment of organic solid waste and wastewater, resulting in high economic and environmental benefits; it belongs to the comprehensive "waste-to-waste" technology.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing two-dimensional nitrogen-doped carbon nanosheets, the method comprising the following steps:

[0007] (1) Mix nitrogen-containing organic solid waste and composite molten salt, and pyrolyze them to obtain pyrolysis products;

[0008] (2) The pyrolysis product is post-processed to obtain the nitrogen-doped carbon nanosheets.

[0009] This invention uses nitrogen-containing organic solid waste as a carbon and nitrogen source and composite molten salt as a reaction aid to prepare in-situ two-dimensional nitrogen-doped carbon nanosheets by high-temperature pyrolysis. These nanosheets can be used to activate persulfate oxidation to degrade phthalate pollutants or azo dyes in water, to adsorb polystyrene microplastic particles in water, and to enhance the anaerobic fermentation process of organic solid waste, thus realizing the resource utilization of organic solid waste.

[0010] This method is simple, efficient, economical, and environmentally friendly. The composite molten salt is recyclable, enabling the joint treatment of organic solid waste and wastewater. It offers high economic and environmental benefits and is a comprehensive technology for "treating waste with waste".

[0011] As a preferred technical solution of the present invention, the nitrogen-containing organic solid waste in step (1) includes any one or a combination of at least two of antibiotic bacterial residue, livestock and poultry manure, kitchen waste, municipal sludge or industrial sludge.

[0012] The present invention does not limit the specific type of antibiotic bacterial residue; for example, it may be oxytetracycline bacterial residue, etc. The present invention does not limit the specific type of livestock and poultry manure; for example, it may be chicken manure, etc.

[0013] Preferably, the nitrogen content in the nitrogen-containing organic solid waste in step (1) is 5-20 wt%, for example, it can be 5 wt%, 7 wt%, 9 wt%, 10 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, or 20 wt%.

[0014] As a preferred technical solution of the present invention, the composite molten salt in step (1) is a composite chloride salt.

[0015] In this invention, a composite chloride salt is used as a reaction aid. Its characteristics are that it promotes the directional synthesis of two-dimensional carbon nanosheets and etches carbon materials. While forming a controllable porous structure, the composite chloride salt can maintain structural stability. After the reaction, the composite chloride salt will be deposited in the pyrolysis products, which can be removed by washing with water and then recycled to achieve the purpose of recycling.

[0016] Preferably, the composite chloride salt is a binary chloride salt.

[0017] In this invention, the use of binary chloride salts can reduce the melting operation temperature, enabling the synthesis of carbon nanosheets over a wider pyrolysis temperature range and reducing energy consumption. By adjusting the composition and mass ratio of different metal chlorides, carbon nanosheets with different morphological and structural characteristics can be prepared.

[0018] Preferably, the binary chloride salt includes any one or a combination of at least two of sodium chloride-potassium chloride, calcium chloride-potassium chloride, calcium chloride-sodium chloride, magnesium chloride-potassium chloride, magnesium chloride-sodium chloride, lithium chloride-potassium chloride, lithium chloride-sodium chloride, zinc chloride-potassium chloride, or zinc chloride-sodium chloride, with sodium chloride-potassium chloride being the most preferred.

[0019] Preferably, in the sodium chloride-potassium chloride mixture, the mass ratio of sodium chloride to potassium chloride is 1:(0.5-3), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc.

[0020] In this invention, if the mass ratio of sodium chloride to potassium chloride is too small, the melting temperature of the binary chloride salt will be too high, approaching the melting point of potassium chloride, resulting in an indistinct layered structure, poor pore structure, and low surface nitrogen content in the synthesized carbon material. If the mass ratio of sodium chloride to potassium chloride is too large, the melting temperature of the binary chloride salt will be too high, approaching the melting point of sodium chloride, resulting in an indistinct layered structure, poor pore structure, and low surface nitrogen content in the synthesized carbon material.

[0021] As a preferred technical solution of the present invention, the mass ratio of nitrogen-containing organic solid waste and composite molten salt in step (1) is 1:(0.5-50), for example, it can be 1:0.5, 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45 or 1:50, etc., preferably 1:(1-20).

[0022] In this invention, if the mass ratio of nitrogen-containing organic solid waste to composite molten salt is too small, that is, if the amount of composite molten salt is too large, the pore structure of the synthesized carbon nanosheets will partially collapse, the surface nitrogen loss will increase, and there will be problems of large molten salt addition and high energy consumption. If the mass ratio of nitrogen-containing organic solid waste to composite molten salt is too large, that is, if the amount of composite molten salt is too small, the synthesized carbon material will not have a layered structure, poor pore structure, and low surface nitrogen content.

[0023] As a preferred technical solution of the present invention, the specific steps of mixing in step (1) include:

[0024] (a) The composite molten salt and solvent are mixed to obtain a composite molten salt solution;

[0025] (b) Nitrogen-containing organic solid waste is added to the composite molten salt solution for blending, and then dried and ground in sequence.

[0026] Preferably, the solvent in step (a) includes water.

[0027] Preferably, the mass concentration of the composite molten salt solution in step (a) is 15-25%, for example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, etc.

[0028] Preferably, the blending process described in step (b) is accompanied by stirring.

[0029] Preferably, the blending time in step (b) is 0.2-8h, for example, it can be 0.2h, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0030] Preferably, the drying in step (b) includes vacuum drying.

[0031] Preferably, the drying temperature in step (b) is 50-100°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0032] Preferably, the drying time in step (b) is 6-24 hours, for example, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours.

[0033] Preferably, the particle size of the mixture obtained after grinding in step (b) is <1 mm, for example, it can be 0.85 mm, 0.5 mm, 0.35 mm or 0.3 mm, etc.

[0034] As a preferred technical solution of the present invention, the pyrolysis in step (1) is carried out in an inert atmosphere.

[0035] Preferably, the gas in the inert atmosphere includes nitrogen.

[0036] Preferably, the pyrolysis temperature in step (1) is 500-1000℃, for example, it can be 500℃, 600℃, 700℃, 800℃, 900℃ or 1000℃.

[0037] Preferably, the pyrolysis time in step (1) is 1-5 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.

[0038] Preferably, the pyrolysis in step (1) is followed by cooling.

[0039] Preferably, the temperature after cooling is room temperature.

[0040] The present invention does not specifically limit the room temperature. For example, it can be 25±5℃, including 20℃, 25℃ or 30℃, etc.

[0041] As a preferred technical solution of the present invention, the post-processing step (2) includes:

[0042] The pyrolysis products are then washed, filtered, and dried.

[0043] Preferably, the drying temperature is 50-120℃, for example, it can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃.

[0044] Preferably, the drying time is 6-24 hours, for example, 6 hours, 8 hours, 10 hours, 15 hours, 20 hours or 24 hours.

[0045] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0046] (I) Dissolve the complex chloride salt in water to obtain a complex chloride salt aqueous solution with a mass concentration of 15-25%;

[0047] (II) Mix nitrogen-containing organic solid waste with nitrogen content of 5-20wt% and composite chloride salt aqueous solution for 0.2-8h, then vacuum dry and grind at 50-100℃, and then pyrolyze at 500-1000℃ in an inert atmosphere for 1-5h. After cooling to room temperature, the pyrolysis product is obtained.

[0048] The mass ratio of nitrogen-containing organic solid waste to compound chloride salt is 1:(0.5-50);

[0049] (III) The pyrolysis product is washed with water, filtered and dried to obtain the two-dimensional nitrogen-doped carbon nanosheets;

[0050] The drying temperature is 50-120℃, and the time is 6-24 hours.

[0051] In a second aspect, the present invention provides a two-dimensional nitrogen-doped carbon nanosheet, which is prepared by the preparation method described in the first aspect.

[0052] Preferably, the specific surface area of ​​the two-dimensional nitrogen-doped carbon nanosheets is >300 m². 2 / g, for example, could be 350m 2 / g、400m 2 / g、450m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g or 800m 2 / g etc.

[0053] Preferably, the nitrogen doping content on the surface of the two-dimensional nitrogen-doped carbon nanosheet is 3-15 at.%, for example, it can be 3 at.%, 5 at.%, 7 at.%, 9 at.%, 11 at.%, 13 at.%, or 15 at.%.

[0054] Preferably, the pore volume of the two-dimensional nitrogen-doped carbon nanosheets is 0.2-0.6 cm³. 3 / g, for example, could be 0.2cm 3 / g, 0.25cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g or 0.6cm 3 / g etc.

[0055] Preferably, the thickness of the two-dimensional nitrogen-doped carbon nanosheet is 5-30 nm, for example, it can be 5-25 nm, 10-30 nm or 5-28 nm.

[0056] Thirdly, the present invention provides an application of two-dimensional nitrogen-doped carbon nanosheets as described in the second aspect, wherein the two-dimensional nitrogen-doped carbon nanosheets are used to activate persulfate oxidation to degrade recalcitrant organic pollutants in wastewater, or to adsorb microplastic particles in water, or to enhance the anaerobic fermentation process of organic solid waste.

[0057] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) This invention provides a method for preparing two-dimensional nitrogen-doped carbon nanosheets. This method uses nitrogen-containing organic solid waste as both a carbon and nitrogen source, and a composite molten salt as a reaction medium to prepare nitrogen-doped carbon nanosheets. Specifically, the nitrogen-containing organic solid waste is used as a pyrolysis raw material, fully utilizing its organic matter. High-temperature pyrolysis converts it into nitrogen-doped carbon materials, achieving resource utilization. The use of a composite molten salt to assist in the pyrolysis of organic solid waste provides a stable and uniform liquid environment for the pyrolysis process. The composite molten salt acts as a hard template at low temperatures, preventing particle agglomeration. Furthermore… High-energy ionic melts at high temperatures exfoliate pyrolytic carbon particles to form a layered structure similar to reduced graphene oxide. Furthermore, the pore structure of carbon materials was activated, thereby controlling the morphology and structure of nitrogen-doped carbon nanosheets.

[0060] (2) The two-dimensional nitrogen-doped carbon nanosheets provided by this invention have thinner sheets and are undulating and curled; the sp of the two-dimensional nitrogen-doped carbon nanosheets is relatively thin. 2The hybrid carbon structure provides abundant free-flowing electrons, the sheet defects provide a large number of unpaired electrons, and the nitrogen element uniformly doped in the carbon nanosheets provides abundant adsorption sites and catalytic active sites, which provides a basis for its application as an advanced persulfate oxidation catalyst, a polystyrene microplastic adsorbent, and an additive for anaerobic fermentation of organic solid waste.

[0061] (3) The present invention provides the application of two-dimensional nitrogen-doped carbon nanosheets to catalyze the oxidation and degradation of persulfate in wastewater, to adsorb microplastic particles in water, and to enhance the anaerobic fermentation process of organic solid waste. The two-dimensional nitrogen-doped carbon nanosheets have high catalytic activity in the process of activating persulfate, have good adsorption capacity in the process of adsorbing microplastic pollutants, and can significantly increase the methane production in the anaerobic fermentation process of organic solid waste. Attached Figure Description

[0062] Figure 1 Scanning electron microscope (SEM) images of carbon materials prepared in Examples 2, 4, Comparative Example 1, and Comparative Example 2 of this invention.

[0063] Figure 2 The curves showing the change in the removal rate of dibutyl phthalate over time when the carbon materials provided in Examples 1-6 and Comparative Examples 1-2 are used as catalysts for potassium persulfate.

[0064] Figure 3 The curves showing the change in the removal rate of Rhodamine B over time when the carbon materials provided in Examples 1-6 and Comparative Examples 1-2 are used as catalysts for potassium persulfate.

[0065] Figure 4 The curves showing the change in the removal rate of Orange G over time when the carbon materials provided in Application Examples 1-6 and Comparative Examples 1-2 are used as catalysts for potassium persulfate.

[0066] Figure 5 The curves showing the change in the removal rate of polystyrene microplastics over time when the carbon materials provided in Examples 7-12 and Comparative Examples 12-13 are used as adsorbents.

[0067] Figure 6 The curves showing the change in daily methane production when the carbon materials provided in Application Examples 13-14 and Comparative Examples 14-16 are added to the anaerobic fermentation system. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] In the following examples, room temperature refers to 25°C.

[0070] Example 1

[0071] This embodiment provides a method for preparing two-dimensional nitrogen-doped carbon nanosheets, the method comprising the following steps:

[0072] (1) Dissolve the dichloride salt in water to obtain a dichloride salt aqueous solution with a mass concentration of 15%;

[0073] The dichloride salt consists of sodium chloride and potassium chloride in a mass ratio of 1:1;

[0074] (2) At room temperature of 25°C, 1g of nitrogen-containing organic solid waste and a dichloride salt aqueous solution were stirred and mixed for 2h. The mixture was then placed in a vacuum drying oven at 80°C and dried for 24h. The dried mixture was then pulverized and ground to a particle size of <1mm. The mixture was then subjected to a pyrolysis reaction at 700°C for 2h under a nitrogen atmosphere. After the pyrolysis was completed, the mixture was naturally cooled to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0075] The nitrogen-containing organic solid waste is oxytetracycline bacterial residue, which consists of 9.85% ash, 71.56% volatile matter, 9.45% moisture, and 18.59% fixed carbon. The elemental composition of the oxytetracycline bacterial residue is: carbon content 45.26%, oxygen content 28.23%, and nitrogen content 9.25%. The mass ratio of nitrogen-containing organic solid waste to dichloride salt is 1:4.

[0076] (3) The pyrolysis product is washed and filtered with deionized water, and then dried in an oven at 80°C for 12 hours to obtain two-dimensional nitrogen-doped carbon nanosheets with a surface nitrogen doping amount of 8.65 at.% and a thickness of 5-25 nm, denoted as T-CNS700.

[0077] Example 2

[0078] This embodiment provides a method for preparing two-dimensional nitrogen-doped carbon nanosheets, the method comprising the following steps:

[0079] (1) Dissolve the dichloride salt in water to obtain a dichloride salt aqueous solution with a mass concentration of 20%;

[0080] The binary chloride salt comprises sodium chloride and potassium chloride in a mass ratio of 1:1.2;

[0081] (2) At room temperature of 25°C, 1g of nitrogen-containing organic solid waste and a dichloride salt aqueous solution were stirred and mixed for 4h. The mixture was then placed in a vacuum drying oven at 100°C and dried for 18h. The dried mixture was then pulverized and ground to a particle size of <1mm. The mixture was then subjected to a pyrolysis reaction at 800°C for 2.5h under a nitrogen atmosphere. After the pyrolysis was completed, the mixture was naturally cooled to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0082] The nitrogen-containing organic solid waste is oxytetracycline bacterial residue, which consists of 9.85% ash, 71.56% volatile matter, 9.45% moisture, and 18.59% fixed carbon. The elemental composition of the oxytetracycline bacterial residue is: carbon content 45.26%, oxygen content 28.23%, and nitrogen content 9.25%. The mass ratio of nitrogen-containing organic solid waste to dichloride salt is 1:6.

[0083] (3) The pyrolysis product is washed and filtered with deionized water, and then dried in an oven at 100°C for 10 hours to obtain two-dimensional nitrogen-doped carbon nanosheets with a surface nitrogen doping amount of 8.91 at.% and a thickness of 5-25 nm, denoted as T-CNS800.

[0084] Example 3

[0085] This embodiment provides a method for preparing two-dimensional nitrogen-doped carbon nanosheets, the method comprising the following steps:

[0086] (1) Dissolve the dichloride salt in water to obtain a dichloride salt aqueous solution with a mass concentration of 25%;

[0087] The binary chloride salt comprises sodium chloride and potassium chloride in a mass ratio of 1:1.5;

[0088] (2) At room temperature of 25°C, 1g of nitrogen-containing organic solid waste and a dichloride salt aqueous solution were stirred and mixed for 6h. The mixture was then placed in a vacuum drying oven at 100°C and dried for 18h. The dried mixture was then pulverized and ground to a particle size of <1mm. The mixture was then subjected to a pyrolysis reaction at 900°C for 3h under a nitrogen atmosphere. After the pyrolysis was completed, the mixture was naturally cooled to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0089] The nitrogen-containing organic solid waste is oxytetracycline bacterial residue, which consists of 9.85% ash, 71.56% volatile matter, 9.45% moisture, and 18.59% fixed carbon. The elemental composition of the oxytetracycline bacterial residue is: carbon content 45.26%, oxygen content 28.23%, and nitrogen content 9.25%. The mass ratio of nitrogen-containing organic solid waste to dichloride salt is 1:8.

[0090] (3) The pyrolysis product is washed and filtered with deionized water, and then dried in an oven at 100°C for 10 hours to obtain two-dimensional nitrogen-doped carbon nanosheets with a surface nitrogen doping amount of 8.53 at.% and a thickness of 5-25 nm, denoted as T-CNS900.

[0091] Example 4

[0092] The difference between this embodiment and embodiment 1 is that the nitrogen-containing organic solid waste in step (2) is chicken manure, which has the following composition: ash content 24.26%, volatile matter 62.32%, moisture 6.14%, and fixed carbon 13.42%; the elemental composition of the chicken manure is: carbon content 32.56%, oxygen content 25.34%, and nitrogen content 6.42%.

[0093] The prepared two-dimensional nitrogen-doped carbon nanosheets have a surface nitrogen doping amount of 5.96 at.% and a thickness of 10-30 nm, and are denoted as C-CNS700.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 2 is that the nitrogen-containing organic solid waste in step (2) is chicken manure, and the composition of the chicken manure is the same as that in embodiment 4;

[0097] The prepared two-dimensional nitrogen-doped carbon nanosheets have a surface nitrogen doping amount of 6.35 at.% and a thickness of 10-30 nm, and are denoted as C-CNS800.

[0098] The remaining preparation methods and parameters are consistent with those in Example 2.

[0099] Example 6

[0100] The difference between this embodiment and embodiment 3 is that the nitrogen-containing organic solid waste in step (2) is chicken manure, and the composition of the chicken manure is the same as that in embodiment 4;

[0101] The prepared two-dimensional nitrogen-doped carbon nanosheets have a surface nitrogen doping amount of 5.84 at.% and a thickness of 10-30 nm, and are denoted as C-CNS900.

[0102] The remaining preparation methods and parameters are consistent with those in Example 3.

[0103] Example 7

[0104] The difference between this embodiment and Example 1 is that the mass ratio of sodium chloride to potassium chloride in step (1) is 1:0.1. The rest of the preparation methods and parameters are the same as in Example 1.

[0105] Example 8

[0106] The difference between this embodiment and Example 1 is that the mass ratio of sodium chloride to potassium chloride in step (1) is 1:4. The remaining preparation methods and parameters are the same as in Example 1.

[0107] Example 9

[0108] The difference between this embodiment and Example 1 is that the mass ratio of nitrogen-containing organic solid waste to binary chloride salt in step (2) is 1:0.1. The remaining preparation methods and parameters are consistent with those in Example 1.

[0109] Example 10

[0110] The difference between this embodiment and Embodiment 1 is that the mass ratio of nitrogen-containing organic solid waste to binary chloride salt in step (2) is 1:55. The remaining preparation methods and parameters are consistent with those in Embodiment 1.

[0111] Comparative Example 1

[0112] This comparative example provides a method for preparing pyrolytic carbon. The difference between this method and Example 2 is that step (1) is not performed, that is, a dichloride salt aqueous solution is not added in step (2).

[0113] The pyrolytic carbon obtained is designated as T-C800.

[0114] The remaining preparation methods and parameters are consistent with those in Example 2.

[0115] Comparative Example 2

[0116] This comparative example provides a method for preparing pyrolytic carbon. The difference between this method and Example 4 is that step (1) is not performed, that is, a dichloride salt aqueous solution is not added in step (2).

[0117] The pyrolytic carbon obtained is denoted as C-C800.

[0118] The remaining preparation methods and parameters are consistent with those in Example 4.

[0119] Comparative Example 3

[0120] The difference between this comparative example and Example 1 is that the binary chloride salt in step (1) is replaced with a monochloride salt, namely sodium chloride. The rest of the preparation methods and parameters are the same as in Example 1.

[0121] Comparative Example 4

[0122] The difference between this comparative example and Example 1 is that the binary chloride salt in step (1) is replaced with sodium sulfate. The remaining preparation methods and parameters are the same as in Example 1.

[0123] Figure 1 Scanning electron microscope (SEM) images of the carbon materials prepared in Examples 2, 4, Comparative Example 1, and Comparative Example 2 of the present invention are shown. As can be seen from the figures, Figure 1 (a), (b), (c), and (d) are SEM images of T-CNS800, C-CNS800, T-C800, and C-C800 provided in Examples 2, 4, Comparative Example 1, and Comparative Example 2, respectively. Figure 1 As can be seen from (a) and (b), the carbon material exhibits a distinct layered structure with thicknesses ranging from a few nanometers to tens of nanometers, indicating that the composite molten salt-assisted pyrolysis of nitrogen-containing organic solid waste is highly effective in preparing carbon nanosheets.

[0124] from Figure 1 As can be seen from (c) and (d), the carbon material is an irregularly shaped block of carbon with an uneven surface and few pores, indicating that the carbon material obtained by direct pyrolysis has a poor pore structure.

[0125] Application Examples 1-6

[0126] This application example provides an application of two-dimensional nitrogen-doped carbon nanosheets for catalytic persulfate oxidation to degrade recalcitrant organic pollutants in wastewater. The two-dimensional nitrogen-doped carbon nanosheets are T-CNS700, T-CNS800, T-CNS900, C-CNS700, C-CNS800, and C-CNS900 provided in Examples 1-6. The recalcitrant organic pollutants include phthalates and azo dyes. The application process includes the following steps:

[0127] Two-dimensional nitrogen-doped carbon nanosheet catalysts T-CNS700, T-CNS800, T-CNS900, C-CNS700, C-CNS800, and C-CNS900 were placed with 1 mM potassium persulfate (PMS) in a 20 mg / L aqueous solution of dibutyl phthalate (pH 5.0), or a 50 mg / L aqueous solution of rhodamine B, or a 50 mg / L aqueous solution of Orange G. Catalytic degradation experiments of dibutyl phthalate, rhodamine B, or Orange G were carried out under normal pressure, temperature of 25 °C, and shaking speed of 200 r / min. The treatment time was 30 min.

[0128] Application Example 7-12

[0129] This application example provides an application of two-dimensional nitrogen-doped carbon nanosheets for adsorbing microplastic pollutants in water. The two-dimensional nitrogen-doped carbon nanosheets are T-CNS700, T-CNS800, T-CNS900, C-CNS700, C-CNS800, and C-CNS900 provided in Examples 1-6. The microplastic pollutant is polystyrene microplastic. The application process includes the following steps:

[0130] A 50 mg / L solution of polystyrene microplastics with a diameter of 1-3 µm was prepared. Two-dimensional nitrogen-doped carbon nanosheet adsorbents T-CNS700, T-CNS800, T-CNS900, C-CNS700, C-CNS800, and C-CNS900 were placed in the 50 mg / L polystyrene microplastic solution. The polystyrene adsorption experiment was carried out under the conditions of normal pressure, temperature of 25 °C, and shaking speed of 120 r / min for 6 h.

[0131] Application Examples 13-14

[0132] This application example provides an application of two-dimensional nitrogen-doped carbon nanosheets to enhance the anaerobic fermentation process of organic solid waste. The two-dimensional nitrogen-doped carbon nanosheets are T-CNS800 and C-CNS800 provided in Examples 2 and 4. The application process includes the following steps:

[0133] Two-dimensional nitrogen-doped carbon nanosheets T-CNS800 and C-CNS800 were applied to the anaerobic fermentation of food waste. The dosage in the fermentation bottle was 3 g / L. Anaerobic activated sludge was used as the inoculum. The ratio of food waste to inoculum was 1:1 (based on the total solids content (TS) of the fermentation substrate). The concentration of the digestate was 10%TS. The fermentation temperature was 35℃, the fermentation volume was 400 mL, and the total fermentation cycle was 40 days. The anaerobic fermentation was carried out on a fully automated methane potential testing system.

[0134] Application Comparative Example 1-2

[0135] Comparative Examples 1-2 provide an application of pyrolytic carbon for catalytic persulfate oxidation to degrade recalcitrant organic pollutants in wastewater, wherein the pyrolytic carbon is T-C800 and C-C800 provided in Comparative Examples 1 and 2, respectively.

[0136] The remaining application methods and parameters are consistent with those in Application Example 1.

[0137] Application Comparative Example 3

[0138] The difference between this comparative example and Comparative Example 1 is that this comparative example does not add carbon materials, but only adds PMS to oxidize and degrade recalcitrant organic pollutants in water.

[0139] The remaining application methods and parameters are consistent with those in Application Comparison 1.

[0140] Application of Comparative Example 4-11

[0141] The difference between this comparative example and Comparative Example 1 is that this comparative example does not add PMS, but only adds carbon materials to adsorb recalcitrant organic pollutants in water. The carbon materials are T-CNS700, T-CNS800, T-CNS900, C-CNS700, C-CNS800, C-CNS900 provided in Examples 1-6 and T-C800 and C-C800 provided in Comparative Examples 1-2.

[0142] The remaining application methods and parameters are consistent with those in Application Example 1.

[0143] Application Comparative Examples 12-13

[0144] Comparative Examples 12-13 provide an application of pyrolytic carbon for adsorbing microplastic pollutants in water, wherein the pyrolytic carbon is T-C800 and C-C800 provided in Comparative Examples 1 and 2, respectively.

[0145] The remaining application methods and parameters are consistent with those in application example 7.

[0146] Application of Comparative Examples 14-15

[0147] Comparative Examples 14-15 provide an application of pyrolytic carbon to enhance the anaerobic fermentation process of organic solid waste, wherein the pyrolytic carbon is T-C800 and C-C800 provided in Comparative Examples 1 and 2, respectively.

[0148] The remaining application methods and parameters are consistent with those in application example 13.

[0149] Application Comparative Example 16

[0150] The difference between Comparative Example 16 and Application Example 13 is that no carbon material is added to the fermentation bottle.

[0151] The remaining application methods and parameters are consistent with those in application example 13.

[0152] Performance testing

[0153] (a) N2 adsorption-desorption experiments were conducted on the carbon materials provided in Examples 1-10 and Comparative Examples 1-4 to verify the activation effect of adding composite molten salt on the pore structure of two-dimensional nitrogen-doped carbon nanosheets during the pyrolysis of nitrogen-containing organic solid waste.

[0154] The experimental results are shown in Table 1.

[0155] Table 1

[0156]

[0157] The data from Examples 1-6 and Comparative Examples 1-2 show that the T-C800 and C-C800 prepared without composite molten salt have poor pore structure. As the ratio of composite molten salt and the pyrolysis temperature increase, the etching effect of composite molten salt on carbon materials increases, and the specific surface area and pore volume of carbon materials both increase.

[0158] The data from Examples 1 and 7-8 show that if the mass ratio of sodium chloride to potassium chloride is too small, the melting temperature of the binary chloride salt is too high, approaching the melting point of potassium chloride, resulting in a weak etching effect on the synthesized carbon material and an underdeveloped pore structure. Conversely, if the mass ratio of sodium chloride to potassium chloride is too large, the melting temperature of the binary chloride salt is too high, approaching the melting point of sodium chloride, resulting in a weak etching effect on the synthesized carbon material and an underdeveloped pore structure.

[0159] The data from Examples 1 and 9-10 show that if the mass ratio of nitrogen-containing organic solid waste to binary chloride salt is too small, i.e., the amount of composite molten salt is too large, the etching effect will be too strong, causing the pore structure of the two-dimensional carbon nanosheets to collapse, resulting in a reduction in specific surface area and pore volume. If the mass ratio of nitrogen-containing organic solid waste to binary chloride salt is too large, the etching effect of the molten salt on the carbon material will be weak, and the pore structure of the carbon material will be underdeveloped.

[0160] The data from Example 1 and Comparative Example 3 show that when the binary chloride salt is replaced with a monochloride salt, i.e., sodium chloride, the pore structure of the carbon material is underdeveloped, and the activation effect on the pore structure of the two-dimensional nitrogen-doped carbon nanosheets is weak.

[0161] The data from Example 1 and Comparative Example 4 show that when the binary chloride salt is replaced with sodium sulfate, the high melting point of sodium sulfate has little effect on promoting the development of the pore structure of carbon materials.

[0162] (ii) X-ray photoelectron spectroscopy (XPS) was performed on the carbon materials provided in Examples 1-10 and Comparative Examples 1-4 to verify the beneficial effect of adding composite molten salt to the pyrolysis of nitrogen-containing organic solid waste on the surface nitrogen content of two-dimensional nitrogen-doped carbon nanosheets.

[0163] The results of the XPS analysis are shown in Table 2.

[0164] Table 2

[0165]

[0166] The data from Examples 1-6 and Comparative Examples 1-2 show that the direct pyrolysis of organic solid waste provided in Comparative Examples 1 and 2 resulted in pyrolyzed carbon with low surface nitrogen content. In contrast, the surface nitrogen content of the two-dimensional nitrogen-doped carbon nanosheets provided in Examples 1-6 was much higher than that in Comparative Examples 1 and 2. This indicates that composite molten salt-assisted pyrolysis can promote the retention of nitrogen-containing functional groups on the surface of two-dimensional nitrogen-doped carbon nanosheets.

[0167] The data from Examples 1 and 7-8 show that if the mass ratio of sodium chloride to potassium chloride is too small, the effect on the retention of nitrogen-containing functional groups on the surface of carbon materials is relatively small; if the mass ratio of sodium chloride to potassium chloride is too large, the effect on the retention of nitrogen-containing functional groups on the surface of carbon materials is relatively small.

[0168] The data from Examples 1 and 9-10 show that if the mass ratio of nitrogen-containing organic solid waste to binary chloride salt is too small, i.e., the amount of composite molten salt is too large, the etching effect will be too strong, resulting in an increase in the loss of nitrogen-containing functional groups on the surface of carbon materials. If the mass ratio of nitrogen-containing organic solid waste to binary chloride salt is too large, the auxiliary effect of molten salt on pyrolysis will be small, which is not conducive to the retention of nitrogen-containing functional groups on the surface of carbon materials.

[0169] The data from Example 1 and Comparative Example 3 show that replacing the binary chloride salt with a monochloride salt, i.e., sodium chloride, results in a lower nitrogen content on the surface of the carbon material.

[0170] The data from Example 1 and Comparative Example 4 show that when the binary chloride salt is replaced with sodium sulfate, the sodium sulfate has a high melting point and only acts as a pyrolysis template for the carbon material, with little effect on the surface nitrogen content.

[0171] (iii) Take timed samples of the aqueous solutions corresponding to Case 1-6 and Comparative Examples 1-11 to determine the concentrations of dibutyl phthalate, rhodamine B or orange G, and calculate the removal rates of the corresponding pollutants respectively.

[0172] The removal rates of dibutyl phthalate, rhodamine B, and orange G in Application Examples 1-6 and Comparative Examples 1-2 over time are shown in the following figures: Figure 2 , Figure 3 and Figure 4 As shown in the figure, when potassium persulfate (PMS) and T-C800 or C-C800 were added together in Comparative Examples 1-2, the removal rates of dibutyl phthalate, rhodamine B, and orange G were all improved after 30 minutes. In Examples 1-6, the two-dimensional nitrogen-doped carbon nanosheets provided in Examples 1-6 were added, and more than 97% of dibutyl phthalate, 99% of rhodamine B, and 99% of orange G were degraded and removed after 30 minutes, which were significantly higher than those in Comparative Examples 1-2. This indicates that the two-dimensional nitrogen-doped carbon nanosheets prepared by composite molten salt-assisted pyrolysis have more catalytic active sites, which is beneficial to the catalytic oxidation and degradation process of persulfate.

[0173] The removal rates of dibutyl phthalate, rhodamine B, and orange G in Comparative Examples 3-11 at 30 min are shown in Table 3.

[0174] Table 3

[0175]

[0176] As shown in Table 3, the removal rate of pollutants by adding only potassium persulfate (PMS) is very low, indicating that the oxidation capacity of potassium persulfate (PMS) is very weak in the absence of a catalyst; the removal rate of pollutants by adding only carbon materials is also low, indicating that the adsorption capacity of carbon materials for phthalate pollutants and azo dye pollutants is weak.

[0177] (iv) In Application Examples 7-12 and Comparative Examples 12-13, after 6 hours of adsorption experiments, the water was allowed to stand for 15 minutes. The upper water sample was then filtered using a 0.45µm needle filter. The mass change before and after filtration was recorded to determine the concentration of polystyrene microplastics in the aqueous solution after adsorption. By comparing the concentration with that before adsorption, the polystyrene microplastic removal rate was obtained. Figure 5 As shown in the figure, T-C800 and C-C800 in Comparative Examples 12-13 adsorbed and removed 16.3% and 20.1% of polystyrene microplastics, respectively, within 6 hours. The two-dimensional nitrogen-doped carbon nanosheets from Examples 1-6 added to Examples 7-12 showed significantly higher removal rates of polystyrene microplastics within 6 hours than those in Comparative Examples 12-13. Among them, C-CNS900 adsorbed and removed 95.7% of polystyrene microplastics. This indicates that the two-dimensional nitrogen-doped carbon nanosheets prepared by composite molten salt-assisted pyrolysis have significantly increased specific surface area and pore volume, providing more adsorption sites, and therefore can remove microplastic pollutants from water more efficiently.

[0178] (v) Monitor and convert the methane production in corresponding use cases 13-14 and application comparison examples 14-16 to standard conditions (based on the organic dry matter content (VS) of the fermentation substrate), such as Figure 6As shown in the figure, the peak daily methane production of Comparative Example 16 without added carbon material occurred on day 18 (146 mL / g). With Comparative Examples 14 and 15, after adding pyrolytic carbon T-C800 or C-C800, the peak daily methane production occurred earlier, on day 16, increasing to 163 mL / g and 155 mL / g, respectively. With Examples 13-14, after adding T-CNS800 and C-CNS800 provided in Examples 2 and 4, the peak daily methane production occurred earlier, on day 14, increasing to 192 mL / g and 178 mL / g, respectively. Furthermore, the addition of T-CNS800 increased the total methane production over 40 days by 56.7% compared to Comparative Example 16 without added carbon material, and by 14.7% compared to Comparative Example 14 with added pyrolytic carbon T-C800. The addition of C-CNS800 increased the total methane production over 40 days by 48.5% compared to Comparative Example 16 without added carbon material, and by 19.5% compared to Comparative Example 15 with added pyrolytic carbon C-C800. This indicates that the two-dimensional nitrogen-doped carbon nanosheets prepared by composite molten salt-assisted pyrolysis help increase the electron transfer rate during anaerobic fermentation, thereby improving the methane production of the anaerobic fermentation system.

[0179] In summary, the method provided by this invention utilizes a pyrolysis process, using nitrogen-containing organic solid waste as both carbon and nitrogen sources. This raw material is mixed with a composite molten salt to obtain pyrolysis feedstock. After high-temperature pyrolysis and carbonization, the pyrolysis product is obtained. This product is then cooled, dissolved, washed, filtered, and dried to yield two-dimensional nitrogen-doped carbon nanosheets with high nitrogen content and abundant pore structure. This invention achieves the resource utilization of organic solid waste and the harmless treatment of antibiotic bacterial residue, featuring a simple and environmentally friendly approach. The obtained nitrogen-doped carbon nanosheets exhibit excellent quality in applications such as catalytic persulfate oxidation to degrade recalcitrant organic pollutants in wastewater, adsorbing microplastic pollutants in water, and enhancing anaerobic fermentation processes based on organic solid waste. This method achieves the joint treatment of organic solid waste and wastewater, representing a comprehensive "waste-to-waste" technology with high economic and environmental value.

[0180] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing two-dimensional nitrogen-doped carbon nanosheets, characterized in that, The preparation method includes the following steps: (1) Mix nitrogen-containing organic solid waste and composite molten salt, and pyrolyze them to obtain pyrolysis products; The nitrogen-containing organic solid waste includes any one or a combination of at least two of the following: antibiotic bacterial residue, livestock and poultry manure, kitchen waste, municipal sludge, or industrial sludge. The composite molten salt is sodium chloride-potassium chloride; in the sodium chloride-potassium chloride mixture, the mass ratio of sodium chloride to potassium chloride is 1:(0.5-3); The mass ratio of the nitrogen-containing organic solid waste to the composite molten salt is 1:(0.5-50); The specific steps of the mixing process include: (a) The composite molten salt and solvent are mixed to obtain a composite molten salt solution; (b) Nitrogen-containing organic solid waste is added to the composite molten salt solution for blending, and then dried and ground in sequence; The solvent in step (a) includes water; The mass concentration of the composite molten salt solution in step (a) is 15-25%; The pyrolysis temperature in step (1) is 500-1000℃; the pyrolysis time is 1-5h. (2) The pyrolysis products are post-processed to obtain the nitrogen-doped carbon nanosheets; The preparation method described above yields two-dimensional nitrogen-doped carbon nanosheets with a specific surface area >300 m². 2 / g; the pore volume of the two-dimensional nitrogen-doped carbon nanosheets is 0.2-0.6 cm³. 3 / g; the thickness of the two-dimensional nitrogen-doped carbon nanosheets is 5-30nm; The two-dimensional nitrogen-doped carbon nanosheets are used to adsorb microplastic particles in water or to enhance the anaerobic fermentation process of organic solid waste.

2. The preparation method according to claim 1, characterized in that, The nitrogen content in the nitrogen-containing organic solid waste in step (1) is 5-20 wt%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of nitrogen-containing organic solid waste and composite molten salt in step (1) is 1:(1-20).

4. The preparation method according to claim 1, characterized in that, The blending process described in step (b) is accompanied by stirring.

5. The preparation method according to claim 1, characterized in that, The blending time in step (b) is 0.2-8 hours.

6. The preparation method according to claim 1, characterized in that, The drying process described in step (b) includes vacuum drying.

7. The preparation method according to claim 1, characterized in that, The drying temperature in step (b) is 50-100℃.

8. The preparation method according to claim 1, characterized in that, The drying time in step (b) is 6-24 hours.

9. The preparation method according to claim 1, characterized in that, The pyrolysis in step (1) is carried out in an inert atmosphere.

10. The preparation method according to claim 9, characterized in that, The gas in the inert atmosphere includes nitrogen.

11. The preparation method according to claim 1, characterized in that, After pyrolysis in step (1), the mixture is cooled.

12. The preparation method according to claim 1, characterized in that, The post-processing steps in step (2) include: The pyrolysis products are then washed, filtered, and dried.

13. The preparation method according to claim 12, characterized in that, The drying temperature in the post-processing step is 50-120℃.

14. The preparation method according to claim 12, characterized in that, The drying time in the post-processing step is 6-24 hours.

15. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (I) Dissolve the composite molten salt in water to obtain a composite molten salt aqueous solution with a mass concentration of 15-25%; (II) Mix nitrogen-containing organic solid waste with nitrogen content of 5-20wt% and composite molten salt aqueous solution for 0.2-8h, then vacuum dry and grind at 50-100℃, and then carry out pyrolysis reaction at 500-1000℃ in an inert atmosphere for 1-5h. After cooling to room temperature, the pyrolysis product is obtained. The mass ratio of nitrogen-containing organic solid waste to composite molten salt is 1:(0.5-50); (III) The pyrolysis product is washed with water, filtered and dried to obtain the two-dimensional nitrogen-doped carbon nanosheets; In step (III), the drying temperature is 50-120℃ and the time is 6-24h.

16. A two-dimensional nitrogen-doped carbon nanosheet, characterized in that, The two-dimensional nitrogen-doped carbon nanosheets were prepared using the preparation method described in any one of claims 1-15.

17. The two-dimensional nitrogen-doped carbon nanosheet according to claim 16, characterized in that, The nitrogen doping content of the two-dimensional nitrogen-doped carbon nanosheets is 3-15 at.%.

18. An application of the two-dimensional nitrogen-doped carbon nanosheets as described in claim 16 or 17, characterized in that, The two-dimensional nitrogen-doped carbon nanosheets are used to adsorb microplastic particles in water or to enhance the anaerobic fermentation process of organic solid waste.

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