Preparation method of graphene confinement transition metal sulfide nanosheet

Abstract

The invention relates to the technical field of preparation of nano composite materials, and discloses a preparation method of a graphene confinement transition metal sulfide nanosheet, which comprises the following steps: preparing a three-dimensional graphene framework with a hierarchical porous structure by combining an ice template method and a freeze drying technology with a pore forming agent; introducing a transition metal source precursor and a sulfur source precursor into the nanoscale pore channels of the frame through vacuum impregnation; and carrying out temperature-programmed confinement gas-phase vulcanization reaction in a protective atmosphere, so that sulfur vapor diffuses in the pore channels and reacts with the precursor, thereby growing the ultrathin and small-size transition metal sulfide nanosheet in situ in the nano confinement space of the graphene network. Through the space confinement effect, accurate regulation and control of the number of layers and the size of the nanosheets are achieved, the prepared composite material has the advantages of sufficient exposure of active sites, fast interface electron transmission and high structural stability, and the application performance of the composite material in the fields of energy storage and conversion of lithium ion batteries, electro-catalysis hydrogen evolution and the like is improved.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite material preparation technology, and more specifically to a method for preparing graphene-confined transition metal sulfide nanosheets. Background Technology

[0002] Transition metal sulfides (TMDs) have shown great potential in energy storage and conversion, catalysis, and other fields due to their unique electronic structure and catalytic properties. However, TMD nanosheets prepared by conventional methods are prone to stacking and agglomeration, leading to problems such as reduced active sites, poor conductivity, and insufficient structural stability.

[0003] In existing technologies, combining TMDs with graphene is an effective way to improve their performance. However, conventional physical mixing or simple loading methods (such as CN102320552A) are difficult to achieve uniform distribution and tight coupling of TMDs on graphene. Although vapor deposition (such as CN105271275A) can prepare high-quality composite materials, the process is complex, costly, and it is difficult to precisely control the interface structure. Although the hydrothermal method is simple and easy to implement, it usually yields loosely loaded TMD particles on the graphene surface, which lack effective spatial confinement and are prone to detachment during cycling.

[0004] In particular, the number of layers, size, and orientation of TMDs are difficult to precisely control in existing technologies, resulting in limited interfacial charge transport efficiency between graphene and TMDs. More importantly, the lack of precise confinement of the growth space of TMDs leads to large volume changes and structural collapse during electrochemical cycling or catalysis.

[0005] Based on this, the present invention proposes a method for preparing graphene-confined transition metal sulfide nanosheets to solve the above problems. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing graphene-confined transition metal sulfide nanosheets to solve the problems existing in the background art.

[0007] This invention provides the following technical solution: a method for preparing graphene-confined transition metal sulfide nanosheets, comprising the following steps: Step (1): Using graphene oxide dispersion, pore-forming agent and structure-directing agent as raw materials, a three-dimensional graphene framework with hierarchical porous structure is prepared by ice template directional freezing combined with freeze-drying technology. Step (2): The graphene framework is vacuum impregnated in a mixed solution of transition metal source and sulfur source; Step (3) involves performing a programmed temperature-increasing sulfurization reaction on the graphene framework loaded with the precursor under a protective atmosphere. The sulfur vapor generated by the gasification of the sulfur source diffuses within the graphene channels and reacts with transition metal ions. Step (4): After the reaction is complete, cool, wash and dry to obtain the final product.

[0008] As a further aspect of the present invention: the pore-forming agent in step (1) is polystyrene microspheres or silica nanospheres, and the structure guiding agent is chitosan or polyvinyl alcohol.

[0009] As a further aspect of the present invention: the freezing temperature in step (1) is -30°C to -50°C, and the freeze-drying time is 24-72h.

[0010] As a further aspect of the present invention: the transition metal source in step (2) is one of ammonium molybdate, sodium tungstate, and nickel chloride, and the sulfur source is thiourea, L-cysteine, or thioacetamide.

[0011] As a further aspect of the present invention: the immersion time of the mixed solution in step (2) is 2-12 hours, and vacuum degassing is performed during the immersion process.

[0012] As a further aspect of the present invention: in step (3), the sulfidation reaction temperature is 400-800℃ and the holding time is 1-4h; the sulfur source is placed separately upstream of the reaction system and vaporizes at 150-300℃ to generate sulfur vapor.

[0013] As a further aspect of the present invention, the partial pressure of sulfur vapor is controlled by regulating the temperature of the sulfur source and the gasification rate to achieve the layer-by-layer growth of transition metal sulfides.

[0014] As a further aspect of the present invention: the transition metal sulfide nanosheets have 1-5 layers and a lateral dimension of 20-200 nm.

[0015] A graphene-confined transition metal sulfide nanosheet composite material prepared by any of the methods described above, characterized in that: the transition metal sulfide nanosheets are chemically bonded and confined within the pores of a three-dimensional porous graphene framework.

[0016] As a further aspect of the present invention: the application of the composite material in lithium-ion batteries, sodium-ion batteries, electrocatalytic hydrogen evolution, and carbon dioxide reduction reactions.

[0017] pass.

[0018] The technical effects and advantages of this invention are as follows: Structural advantages: In the prepared composite material, TMD nanosheets are uniformly confined in the graphene channels in the form of a single layer or few layers, which effectively prevents stacking and exposes more active edge sites.

[0019] Interface advantages: Tight chemical bonding interfaces significantly improve electron transport rate and reduce charge transfer impedance.

[0020] Stability advantages: The graphene framework provides mechanical support and buffer space for TMDs, mitigating volume changes during charging, discharging or catalysis, and improving cycle stability.

[0021] Universality advantage: This method is applicable to a variety of TMDs systems, has strong process controllability, and is easy to scale up for production. Attached Figure Description

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] Figure 1 This is a flowchart of a method for preparing graphene-confined transition metal sulfide nanosheets according to the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Please see Figure 1 As shown, a method for preparing graphene-confined transition metal sulfide nanosheets is characterized by comprising the following steps: (1) Preparation of three-dimensional porous graphene framework: Using graphene oxide dispersion, pore-forming agent and structure-directing agent as raw materials, hierarchical porous graphene framework with vertical channels and horizontal micropores is prepared by ice template directional freezing combined with freeze drying technology; the pore-forming agent is polystyrene microspheres or silica nanospheres, and the structure-directing agent is chitosan or polyvinyl alcohol; (2) Introduction of confined growth precursor: The graphene framework obtained in step (1) is vacuum impregnated in a mixed solution of transition metal source and sulfur source. The transition metal source is one of ammonium molybdate, sodium tungstate, and nickel chloride, and the sulfur source is thiourea, L-cysteine, or thioacetamide. The precursor loading is controlled by adjusting the solution concentration and impregnation time. (3) Confined gas phase sulfidation reaction: The graphene framework with the precursor is placed in a tube furnace and the sulfidation reaction is carried out by programmed temperature rise under a protective atmosphere; during the reaction, the sulfur vapor generated by the gasification of the sulfur source diffuses in the graphene channels and reacts with the transition metal ions confined in the micropores to generate TMDs nanosheets in situ. (4) Post-processing: After the reaction is completed, the product is allowed to cool naturally, washed with organic solvent to remove unreacted substances, and dried under vacuum to obtain the final product.

[0026] Preferably, the concentration of the graphene oxide dispersion in step (1) is 2-10 mg / mL; the mass ratio of the pore-forming agent to the graphene oxide is 1:5 to 1:1; the amount of the structure-directing agent added is 10-50% of the mass of the graphene oxide; the freezing temperature is -30℃ to -50℃; and the freeze-drying time is 24-72h.

[0027] Preferably, in step (2), the concentration of transition metal ions in the mixed solution is 0.01-0.1 mol / L, the concentration of sulfur source is 2-4 times the concentration of transition metal ions, the impregnation time is 2-12 h, and vacuum degassing treatment is used during the impregnation process.

[0028] Preferably, the conditions for the sulfidation reaction in step (3) are: heating rate 1-5℃ / min, reaction temperature 400-800℃, holding time 1-4h, and protective atmosphere is argon or nitrogen; the sulfur source is placed separately in the upstream low-temperature zone of the furnace body, and the sulfur vapor partial pressure is controlled by controlling its temperature (150-300℃).

[0029] Preferably, the transition metal sulfide is molybdenum disulfide (Mo). ), tungsten disulfide ( It is one of nickel sulfide (NiS), with 1-5 nanosheet layers, a lateral size of 20-200 nm, and uniformly confined within the pores of the graphene framework.

[0030] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1 (1) 100 mg of graphene oxide was dispersed in 20 mL of deionized water and ultrasonically treated for 2 h to obtain a uniform dispersion. 20 mg of polystyrene microspheres (about 100 nm in diameter) and 20 mg of chitosan were added and stirred to mix evenly. The mixture was poured into a mold and placed in a -40 °C low temperature freezer for 12 h for directional freezing. Then it was dried in a freeze dryer for 48 h to obtain a three-dimensional porous graphene framework.

[0032] (2) Prepare 50 mL of an aqueous solution containing 0.05 mol / L ammonium molybdate and 0.15 mol / L thiourea. Immerse the graphene framework completely in the solution and place it in a vacuum drying oven at -0.1 MPa for 6 h. After removing it, air dry it at room temperature.

[0033] (3) Place the graphene framework with the precursor in the central constant temperature zone of the tube furnace, and place 1g of sulfur powder separately upstream. Introduce argon to remove air, raise the temperature to 200℃ at 2℃ / min and hold for 30min to remove moisture, continue to raise the temperature to 600℃, and at the same time raise the temperature of the sulfur powder zone to 250℃ to generate sulfur vapor. Hold at 600℃ for 2h to carry out the sulfidation reaction.

[0034] (4) After the reaction is complete, allow the mixture to cool naturally to room temperature, wash it three times with ethanol, and dry it under vacuum at 60°C for 12 hours to obtain the desired product. Graphene composite materials grown in confined spaces.

[0035] Comparative Example 1 Using the traditional hydrothermal method: graphene oxide, sodium molybdate, and thiourea were added to a hydrothermal reactor in a specific ratio and reacted at 200°C for 12 hours. The mixture was then washed and dried to obtain the final product. / Graphene composite materials.

[0036] Comparative Example 2 Using a physical mixing method: commercial The powder and graphene powder were ball-milled together at a mass ratio of 1:1 for 2 hours.

[0037] Performance testing Structural characterization: In the product of Example 1 The nanosheets consist of 2-3 layers, with a lateral dimension of approximately 50 nm, and are uniformly distributed within the graphene channels. (Comparative Example 1) It appears as large aggregates (100-500nm), partially stacked on the graphene surface.

[0038] Electrochemical testing (lithium-ion battery anode materials): In Example 1, the material exhibited an initial discharge specific capacity of 1250 mAh / g at a current density of 0.1 A / g, and retained 92% of its capacity after 100 cycles. Comparative Example 1 had an initial discharge capacity of 980 mAh / g, and a retention rate of only 68% after 100 cycles; Comparative Example 2 had an initial discharge capacity of 720 mAh / g and a retention rate of 52% after 100 cycles.

[0039] Catalytic performance testing (electrocatalytic hydrogen evolution reaction): Example 1 material in The overpotential at the current density is 180mV, and the Tafel slope is 65mV / dec. Comparative Example 1 has an overpotential of 240mV and a Tafel slope of 85mV / dec.

[0040] Example 2 By replacing the transition metal source with sodium tungstate, and maintaining the same conditions as in Example 1, WS2-confined graphene composite materials were successfully prepared. The nanosheets consist of 1-2 layers, with a lateral dimension of approximately 30 nm. Electrocatalytic hydrogen evolution tests show that they... The overpotential was 210mV, which is better than that of Comparative Example 1. Material (240mV).

[0041] Example 3 By replacing the pore-forming agent in step (1) with silica nanospheres (approximately 20 nm in diameter) and the structure-directing agent with polyvinyl alcohol, a graphene framework with even smaller pore sizes (average pore size of approximately 25 nm) was prepared. This framework allows for confined growth... The nanosheets are more uniform in size (approximately 30 nm) and are primarily single-layered. This results in a significant improvement in the rate performance of lithium-ion batteries, maintaining a specific capacity of 650 mAh / g even at a high current of 2 A / g.

[0042] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing graphene-confined transition metal sulfide nanosheets, characterized in that, Includes the following steps: Step (1): Using graphene oxide dispersion, pore-forming agent and structure-directing agent as raw materials, a three-dimensional graphene framework with hierarchical porous structure is prepared by ice template directional freezing combined with freeze-drying technology. Step (2): The graphene framework is vacuum impregnated in a mixed solution of transition metal source and sulfur source; Step (3) involves performing a programmed temperature-increasing sulfurization reaction on the graphene framework loaded with the precursor under a protective atmosphere. The sulfur vapor generated by the gasification of the sulfur source diffuses within the graphene channels and reacts with transition metal ions. Step (4): After the reaction is complete, cool, wash and dry to obtain the final product.

2. The method according to claim 1, characterized in that: The pore-forming agent in step (1) is polystyrene microspheres or silica nanospheres, and the structure guiding agent is chitosan or polyvinyl alcohol.

3. The method according to claim 1, characterized in that: In step (1), the freezing temperature is -30℃ to -50℃ and the freeze-drying time is 24-72h.

4. The method according to claim 1, characterized in that: The transition metal source mentioned in step (2) is one of ammonium molybdate, sodium tungstate, and nickel chloride, and the sulfur source is thiourea, L-cysteine, or thioacetamide.

5. The method according to claim 1, characterized in that: In step (2), the soaking time of the mixed solution is 2-12 hours, and vacuum degassing is performed during the soaking process.

6. The method according to claim 1, characterized in that: In step (3), the sulfidation reaction temperature is 400-800℃ and the holding time is 1-4h; the sulfur source is placed separately upstream of the reaction system and vaporizes at 150-300℃ to produce sulfur vapor.

7. The method according to claim 6, characterized in that: By controlling the sulfur source temperature and gasification rate to regulate the partial pressure of sulfur vapor, the layer-by-layer growth of transition metal sulfides can be achieved.

8. The method according to claim 1, characterized in that: The transition metal sulfide nanosheets have 1-5 layers and a lateral dimension of 20-200 nm.

9. A graphene-confined transition metal sulfide nanosheet composite material prepared by the method according to any one of claims 1-8, characterized in that: Transition metal sulfide nanosheets are chemically bonded and confined within the pores of a three-dimensional porous graphene framework.

10. The application of the composite material according to claim 9 in lithium-ion batteries, sodium-ion batteries, electrocatalytic hydrogen evolution, and carbon dioxide reduction reactions.

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