Preparation method and application of large-size ultra-thin c2n nanosheet

Abstract

This invention discloses a method for preparing large-size ultrathin C2N nanosheets and their applications. The preparation method includes the following steps: (1) dissolving nitrogen-containing precursor molecules and adding them to a soluble metal salt, then mixing; (2) drying the system obtained in step (1) and annealing it under a protective atmosphere; (3) cooling the annealed product to room temperature, adding deionized water to dissolve the soluble metal salt; letting the system obtained in step (3) stand overnight, vacuum filtering, washing, and freeze-drying the product to obtain large-size ultrathin C2N nanosheets. The C2N nanosheets prepared by this invention have good application prospects in the field of energy storage and conversion. The prepared C2N nanosheet material can be used as a negative electrode material for sodium-ion batteries. The initial reversible capacity was tested to reach 700mAh / g to 1000mAh / g, and the capacity retention rate was about 90% after more than 100 cycles.

Description

Technical Field

[0001] This invention relates to a method for preparing two-dimensional nanosheet materials and their applications, and more particularly to a method for preparing large-size ultrathin C2N nanosheets and their applications. Background Technology

[0002] In recent years, the widespread use of lithium-ion batteries has led to a large consumption of lithium resources, and the manufacturing cost of batteries has been rising year by year. Since sodium resources are abundant and environmentally friendly, and have similar chemical properties to lithium metal, they can show the same excellent application prospects as lithium. Therefore, it is particularly important to develop a sodium-ion battery material with high energy density.

[0003] Graphene, a two-dimensional nanomaterial composed of a single atom-thick layer of carbon atoms, possesses extremely high specific surface area and electrical conductivity, showing promising application prospects in energy storage. However, graphene's non-porous structure and limited effective active sites restrict its application in sodium-ion battery energy storage. Nitrogen carbide materials with graphene-like characteristics, obtained through elemental doping, have the potential to overcome the shortcomings of graphene materials in sodium-ion battery energy storage due to their uniform porous structure and abundant nitrogen active sites. C2N materials, as one type of nitrogen carbide, have abundant benzene and pyrazine rings, possess multiple active sites for alkali metal ion storage, and their porous surface structure is conducive to ion conduction and storage, making them suitable as electrode materials for sodium-ion batteries. Ralf Walczak et al. synthesized bulk C2N materials via chemical vapor deposition [Ralf Walczak, et al. "Template-and Metal-Free Synthesis of Nitrogen-Rich Nanoporous 'Noble' Carbon Materials by Direct Pyrolysis of a Preorganized Hexaazatriphenylene Precursor." Angewandte Chemie International Edition 57(2018):10765-10770.]. However, the specific surface area of ​​bulk materials is relatively small, and the number of effective active sites is relatively small. To solve the problem of bulk material stacking, patent 201910709399.3 prepared C2N nanosheets using a bottom-up method, proposing to use silica spheres as templates and then etch them with HF to obtain ultrathin C2N nanosheets. Although this method avoids C2N bulk stacking, increases the specific surface area of ​​C2N, and increases the number of effective active sites, the use of HF etching raises safety concerns and poses significant risks to the environment and human health.

[0004] Therefore, a green and efficient method is needed to prepare suitable C2N nanosheets for energy storage in sodium-ion batteries. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a green and efficient method for preparing large-size ultrathin C2N nanosheets;

[0006] A second objective of this invention is to provide the application of large-size ultrathin C2N nanosheets prepared by the above method in sodium-ion battery anode materials.

[0007] Technical solution: The preparation method of large-size ultrathin C2N nanosheets according to the present invention includes the following steps:

[0008] (1) Dissolve the nitrogen-containing precursor molecules and add them to the soluble metal salt, then mix.

[0009] (2) Dry the system obtained in step (1) and anneal it under a protective atmosphere;

[0010] (3) Cool the product obtained after annealing to room temperature and add deionized water to dissolve the soluble metal salt.

[0011] (4) The system obtained in step (3) was left to stand overnight, vacuum filtered, washed, and the product was freeze-dried to obtain large-size ultrathin C2N nanosheets.

[0012] In step (1), the precursor molecule is 1,4,5,8,9,11-hexaazabenzonitrile.

[0013] The mass ratio of precursor molecules to metal salt is 1 / 500 to 1 / 50000; the size of the soluble metal salt particles is approximately 50 to 550 μm. Since the mass ratio of precursor molecules to metal salt can control the thickness of C2N nanosheets, and the size of the soluble metal salt particles can control the lateral dimensions of the C2N nanosheets, and based on calculations of the density of the metal salt and precursor molecules, particle size, etc., to prepare nanosheets with different monolayer thicknesses and lateral dimensions, it is necessary to select soluble metal salt particles of different sizes, and different mass ratios of precursor molecules to metal salt can be chosen.

[0014] In step (1), the melting point of the soluble metal salt is higher than the boiling point of the nitrogen-containing precursor molecule.

[0015] In step (1), the soluble metal salt is at least one of chloride, carbonate or sulfate; specifically, the soluble metal salt is at least one of sodium chloride, potassium chloride, magnesium chloride, lithium chloride, sodium carbonate, potassium carbonate, lithium carbonate or sodium sulfate.

[0016] In step (2), the annealing temperature is 550℃~800℃ and the time is 90-120min.

[0017] The resulting large-size ultrathin C2N nanosheets have a sheet thickness of 1 nm to 100 nm and a lateral dimension of approximately 10 to 500 μm. The mass ratio of the precursor molecules to the metal salt can control the thickness of the C2N nanosheets. The size of the soluble metal salt particles can control the lateral dimension of the C2N nanosheets.

[0018] The large-size ultrathin C2N nanosheets prepared by the above method are used as anode materials for sodium-ion batteries.

[0019] Invention Principle: A precursor is uniformly mixed with a large amount of metal salt crystals, promoting the sublimation of the precursor during heating. The mixture is heated from room temperature and held at that temperature for a period of time. During this process, the sublimation of the precursor first coats all surfaces of the metal salt crystals, then the coating vaporizes, followed by CC coupling and C2N2 removal, depositing and polymerizing onto the metal salt to form nanosheets. The mixture is thoroughly washed with deionized water to remove the metal salt template. The hydrophobic nanosheets floating on the water surface are collected and freeze-dried. The thickness of the two-dimensional C2N nanosheets can be easily controlled by adjusting the ratio of precursor molecules to metal salt. The lateral size of the C2N nanosheets can be controlled by adjusting the size of the soluble metal salt particles.

[0020] Beneficial Effects: Compared with existing technologies, this invention achieves the following significant effects: 1. A porous ultrathin C2N nanosheet material with a large lateral dimension is prepared by chemical vapor deposition using a bottom-up method. The sheet thickness is approximately 1 nm to 100 nm, and the lateral dimension is approximately 10 to 500 μm. This C2N nanosheet material has a large specific surface area and numerous surface adsorption sites. 2. The C2N nanosheet material prepared by this invention has uniform and regular pores. These uniform and regular pores can induce uniform conduction and deposition of sodium ions, improving the safety and cycle stability of sodium-ion batteries. 3. The preparation method of this invention is simple and feasible, with straightforward steps. The thickness of the prepared nanosheets can be controlled by the mass ratio of the precursor to sodium chloride. The reaction time is short, which is beneficial for large-scale preparation. 4. The C2N nanosheets of this invention have advantages such as good cycle performance and high capacity in sodium-ion battery applications. Attached Figure Description

[0021] Figure 1 This is an optical image of the ultrathin C2N nanosheets prepared in Example 1;

[0022] Figure 2 This is a SEM image of the ultrathin C2N nanosheets prepared in Example 1;

[0023] Figure 3The image shows the XRD pattern of the ultrathin C2N nanosheets prepared in Example 1.

[0024] Figure 4 This is the AFM image of the ultrathin C2N nanosheets prepared in Example 1;

[0025] Figure 5 This is a pore size distribution diagram of the ultrathin C2N nanosheets prepared in Example 1;

[0026] Figure 6 This is a graph showing the electrochemical performance of the ultrathin C2N nanosheets prepared in Example 1. Detailed Implementation

[0027] The present invention will now be described in further detail.

[0028] Example 1

[0029] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0030] The second step involves adding the system obtained in the first step to 600g of sodium chloride with a particle size of approximately 550μm and mixing it evenly.

[0031] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0032] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0033] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0034] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0035] Step 7: Freeze-dry the product obtained in step 6 to obtain ultrathin C2N nanosheets.

[0036] Figure 1 Optical image of the obtained ultrathin C2N nanosheets, whose lateral dimensions can reach tens of micrometers; Figure 2 SEM image of the obtained ultrathin C2N nanosheets; Figure 3 The XRD pattern of the prepared ultrathin C2N nanosheets; Figure 4 The image shows the AFM pattern of the prepared ultrathin C2N nanosheets, which are approximately 4 nm thick. Figure 5 The pore size distribution of the prepared ultrathin C2N nanosheets is shown in the diagram. Figure 6The image shows the electrochemical performance of the obtained ultrathin C2N nanosheets. The C2N nanosheets exhibit excellent redox reactions in sodium-ion batteries, demonstrating rapid electron transfer and good energy storage performance, specifically at 0.3 A g. -1 Discharged at a current density of 757.50 mAh g, the discharge capacity was 757.50 mAh g. -1 After more than 100 cycles, the capacity remained at 680.83 mAh g. -1 The capacity retention rate is around 90%.

[0037] Example 2

[0038] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0039] The second step involves adding the system obtained in the first step to 50g of sodium chloride with a particle size of approximately 550μm and mixing it evenly.

[0040] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0041] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0042] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0043] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0044] Step 7: Freeze-dry the product obtained in step 6 to obtain ultrathin C2N nanosheets.

[0045] Example 3

[0046] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0047] The second step involves adding the system obtained in the first step to 5000g of sodium chloride with a particle size of approximately 550μm and mixing them evenly.

[0048] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0049] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0050] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0051] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0052] Step 7: Freeze-dry the product obtained in step 6 to obtain ultrathin C2N nanosheets.

[0053] Example 4

[0054] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0055] The second step involves adding the system obtained in the first step to 50g of sodium chloride with a particle size of approximately 50μm and mixing it evenly.

[0056] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0057] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0058] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0059] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0060] Step 7: Freeze-dry the product obtained in step 6 to obtain ultrathin C2N nanosheets.

[0061] Example 5

[0062] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0063] The second step involves adding the system obtained in the first step to 50g of sodium chloride with a particle size of approximately 550μm and mixing it evenly.

[0064] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0065] Fourth, the system obtained in the third step is annealed at 800°C for 120 minutes under argon protection.

[0066] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0067] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0068] Step 7: Freeze-dry the product obtained in step 6 to obtain ultrathin C2N nanosheets.

[0069] Comparative Example 1

[0070] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0071] The second step involves adding the system obtained in the first step to 50g of calcium carbonate with a particle size of approximately 100μm and mixing it evenly.

[0072] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0073] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0074] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0075] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0076] Step 7: Freeze-dry the product obtained in step 6 to obtain C2N nanosheets.

[0077] Comparative Example 2

[0078] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0079] The second step involves adding the system obtained in the first step to 100 mg of sodium chloride with a particle size of approximately 550 μm and mixing them thoroughly.

[0080] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0081] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0082] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0083] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0084] Step 7: Freeze-dry the product obtained in step 6 to obtain C2N nanosheets.

[0085] Comparative Example 3

[0086] The first step was to ultrasonically disperse 100 mg of 1,4,5,8,9,11-hexaazabenzonitrile in 10 mL of dichloromethane for 30 minutes.

[0087] The second step involves adding the system obtained in the first step to 50g of sodium chloride with a particle size of approximately 500nm and mixing them evenly.

[0088] The third step is to bake the system obtained in the second step at 100°C for 360 minutes.

[0089] The fourth step is to anneal the system obtained in the third step at 550°C for 120 minutes under argon protection.

[0090] Fifth step: Cool the product obtained in the fourth step to room temperature, transfer it to a beaker, add a large amount of deionized water, and stir to dissolve the sodium chloride;

[0091] Step 6: Let the system obtained in step 5 stand overnight, filter under vacuum, and wash repeatedly with deionized water and ethanol several times.

[0092] Step 7: Freeze-dry the product obtained in step 6 to obtain C2N nanosheets.

Claims

1. A method for preparing large-size ultrathin C2N nanosheets, characterized in that, Includes the following steps: (1) The nitrogen-containing precursor molecule is dissolved and added to a soluble metal salt and mixed; the precursor molecule is 1,4,5,8,9,11-hexaazabenzonitrile; the mass ratio of the precursor molecule to the metal salt is 1 / 500 to 1 / 50000; the size of the soluble metal salt particles is 50 to 550 μm; the soluble metal salt is at least one of sodium chloride, potassium chloride, magnesium chloride, lithium chloride, sodium carbonate, potassium carbonate, lithium carbonate or sodium sulfate; (2) Dry the system obtained in step (1) and anneal it under a protective atmosphere; the annealing temperature is 550℃~800℃; the time is 90-120min; (3) Cool the product obtained after annealing to room temperature, add deionized water to dissolve the soluble metal salt; (4) The system obtained in step (3) was left to stand overnight, vacuum filtered, washed, and the product was freeze-dried to obtain large-size ultrathin C2N nanosheets.

2. The method of claim 1, wherein the method is characterized by, In step (1), the melting point of the soluble metal salt is higher than the boiling point of the nitrogen-containing precursor molecule. 3.The method of claim 1, wherein the method is characterized by, In step (1), the soluble metal salt is at least one of chloride, carbonate or sulfate. 4.The method of claim 1, wherein the method is characterized by, The resulting large-size ultrathin C2N nanosheets have a sheet thickness of 1 nm to 100 nm and a lateral dimension of 10 to 500 μm.

5. The application of large-size ultrathin C2N nanosheets prepared by the method of claim 1 in sodium-ion battery anode materials.

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