Method for preparing graphene from metal and molten salt composite system

Abstract

The invention provides a method for preparing graphene from a metal and molten salt composite system, which comprises the following steps: (1) heating a catalyst raw material, and reacting under protective gas to obtain a molten medium catalyst; the molten medium catalyst is a composite catalyst composed of a metal cluster and a metal salt; (2) introducing a first type of reaction gas for reaction; (3) introducing protective gas, and cooling to obtain coarse graphene; and (4) washing the coarse graphene to obtain the graphene. The metal cluster and molten salt composite catalyst is adopted, high catalytic activity of metal and good dispersity and stability of molten salt are both achieved, carbon source cracking and graphene nucleation growth are effectively promoted, the obtained graphene has the high graphitization degree and the low metal impurity content, efficient separation can be achieved by washing the product, and the method is suitable for industrial production. And complicated post-treatment is not needed.

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, and particularly relates to a method for preparing graphene using a metal-molten salt composite system. Background Technology

[0002] Graphene, with its unique two-dimensional structure and excellent electrical, thermal, and mechanical properties, has shown great potential for applications in energy, materials, and electronics. Achieving efficient, low-cost, and large-scale preparation of graphene is key to its practical application. Among various preparation methods, chemical vapor deposition (CVD) can produce high-quality graphene films, but it generally suffers from problems such as difficult substrate transfer and high cost. Carbon source pyrolysis for graphene preparation has become a highly attractive technical route due to its co-production of hydrogen, simple process route, and abundant and clean carbon source. In particular, catalytic pyrolysis in a molten medium, the liquid phase characteristics are conducive to the dissolution, diffusion, and self-assembly of carbon atoms into graphene, and the density difference makes the products easy to separate from the reaction medium, theoretically possessing the potential for continuous production.

[0003] However, the reaction temperature of molten metal systems is typically extremely high, resulting in high energy consumption and a high content of metallic impurities in the generated carbon products. Molten salt systems themselves have low catalytic activity, leading to poor carbon source gas conversion efficiency and low graphitization of carbon products, making it difficult to obtain high-quality graphene with controllable layer numbers. Therefore, there is an urgent need in this field to develop a novel pyrolysis process that can achieve efficient catalytic pyrolysis of carbon sources at relatively mild temperatures and directly generate high-quality, easily separable graphene with low impurity content. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing graphene using a metal-molten salt composite system, wherein the graphene prepared by this method has a high degree of graphitization and a low content of metal impurities.

[0005] This invention provides a method for preparing graphene using a metal-molten salt composite system, comprising the following steps:

[0006] (1) The catalyst raw material is heated under a protective gas and reacted to obtain a molten medium catalyst; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts;

[0007] (2) The reaction is carried out by introducing a first-type reactive gas;

[0008] (3) Introduce protective gas again, cool down, and obtain crude graphene;

[0009] (4) Wash the crude graphene to obtain graphene.

[0010] Preferably, the molten medium catalyst is prepared by the following method:

[0011] Metal oxide nanoparticles and metal salts are mixed and ground, then heated to a first temperature, protected by a protective gas, and then heated to a second temperature. A second type of reaction gas is introduced and kept at that temperature to obtain a molten medium catalyst.

[0012] Preferably, the reaction temperature in step (1) is 750~1000℃.

[0013] Preferably, the first type of reactant gas is a carbon source gas, or a mixture of a carbon source gas and a protective gas;

[0014] The carbon source gas is selected from one or more of methane, ethane, propane, butane, ethylene, natural gas, and liquefied petroleum gas;

[0015] The protective gas is selected from one or more of nitrogen, argon, and hydrogen.

[0016] Preferably, the metal oxide nanoparticles are selected from one or more of iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, and tungsten oxide;

[0017] The metal oxide nanoparticles account for 0.1~20wt% of the metal salt.

[0018] Preferably, the metal salt is selected from one or more of potassium chloride, sodium chloride, magnesium chloride, calcium chloride, zinc chloride, copper chloride, lithium chloride, manganese chloride, rubidium chloride, cesium chloride, strontium chloride, barium chloride, ferrous chloride, cobalt chloride, and nickel chloride.

[0019] Preferably, the second type of reactant gas is hydrogen.

[0020] Preferably, the first temperature is 200~600℃, and the temperature is maintained for 5~10 hours;

[0021] The second temperature is 750~1000℃, and the holding time is 3~8h.

[0022] Preferably, the temperature is increased to the first temperature at a rate of 8~12℃ / min;

[0023] Increase the temperature to the second temperature at a rate of 5~10℃ / min.

[0024] Preferably, the washing method is water washing; or water washing plus acid washing;

[0025] The washing method can be one or more of centrifugation, vacuum filtration, and pressure filtration;

[0026] The acid solution used for pickling is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

[0027] This invention provides a method for preparing graphene using a metal-molten salt composite system, comprising the following steps: (1) raising the catalyst raw material to the reaction temperature under a protective gas; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts; (2) introducing a first type of reaction gas for reaction; (3) introducing a protective gas again and cooling down to obtain crude graphene; (4) washing the crude graphene to obtain graphene. This invention uses a metal cluster-molten salt composite catalyst, which combines the high catalytic activity of metals with the good dispersibility and stability of molten salts, effectively promoting carbon source cracking and graphene nucleation and growth. The resulting graphene has a high degree of graphitization and a low content of metal impurities. The product can be efficiently separated by washing, without the need for complex post-processing. Attached Figure Description

[0028] Figure 1 The Raman spectrum of the graphene prepared in Example 2 of this invention;

[0029] Figure 2 The image shows the Raman spectrum of the graphene prepared in Example 3 of this invention. Detailed Implementation

[0030] This invention provides a method for preparing graphene using a metal-molten salt composite system, comprising the following steps:

[0031] (1) The catalyst raw material is heated under a protective gas and reacted to obtain a molten medium catalyst; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts;

[0032] (2) The reaction is carried out by introducing a first-type reactive gas;

[0033] (3) Introduce protective gas again, cool down, and obtain crude graphene;

[0034] (4) Wash the crude graphene to obtain graphene.

[0035] The present invention raises the molten medium catalyst to the reaction temperature under a protective gas; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts.

[0036] The molten medium catalyst described in this invention is prepared by the following method:

[0037] After mixing and grinding metal oxide nanoparticles and metal salts, the mixture is heated to a first temperature, a protective gas is introduced, and the temperature is maintained. The temperature is then raised to a second temperature, a second type of reaction gas is introduced, and the temperature is maintained again to obtain a molten medium catalyst.

[0038] This invention pre-reduces metal oxide nanoparticles to form highly dispersed structures, which are then combined with molten metal salts to form a composite catalyst. Compared to using a single molten metal or molten metal salt, this method achieves highly efficient carbon source pyrolysis at lower temperatures, significantly reducing energy consumption and improving process economy. The composite catalyst, combining metal clusters and molten metal salts, possesses both the high catalytic activity of metals and the good dispersibility and stability of molten salts, effectively promoting carbon source pyrolysis and graphene nucleation and growth. The resulting graphene exhibits a high degree of graphitization and low metal impurity content, and the product can be efficiently separated through washing, eliminating the need for complex post-processing.

[0039] The catalyst raw materials in this invention include metal oxide nanoparticles and metal salts. In this invention, the metal oxide nanoparticles are selected from one or more of iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, and tungsten oxide; the metal oxide nanoparticles are precursors for the preparation of metal clusters.

[0040] The metal oxide nanoparticles account for 0.1~20wt% of the metal salt, specifically 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0041] The metal salt is selected from one or more of potassium chloride, sodium chloride, magnesium chloride, calcium chloride, zinc chloride, copper chloride, lithium chloride, manganese chloride, rubidium chloride, cesium chloride, strontium chloride, barium chloride, ferrous chloride, cobalt chloride, and nickel chloride.

[0042] The protective gas described in this invention is a mixture of argon and hydrogen in a volume ratio of (1:10) to (10:1); the specific ratio can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 2:3, 3:2, 4:6, 6:8, or 5:2; in a specific embodiment, the second type of reactive gas used is hydrogen.

[0043] In this invention, metal oxide nanoparticles and metal salts are mixed, ground, and then filled into a suitable reactor. Preferably, the temperature is increased to a first temperature of 200-600°C at a rate of 8-12°C / min and kept at this temperature for 5-10 hours under a protective gas. Then, the temperature is increased to a second temperature of 750-1000°C at a rate of 5-10°C / min, a second type of reaction gas is introduced, and the temperature is kept at this temperature for 3-8 hours.

[0044] Specifically, the first temperature is 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, or 600℃; the heating rate to the first temperature is 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, 10℃ / min, 10.5℃ / min, 11℃ / min, 11.5℃ / min, or 12℃ / min; after heating to the first temperature, it is preferably held in a mixture of argon and hydrogen gas; the holding time is specifically 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, or 10h.

[0045] Specifically, the second temperature is 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃; the heating rate to the second temperature is 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, or 10℃ / min; the second type of reaction gas is introduced and held at the second temperature for a duration of 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, or 8h.

[0046] In this invention, a molten catalyst is placed in a reactor, a protective gas is introduced, and the temperature is raised to the reaction temperature; the reaction temperature is 750~1000℃, specifically 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃. The protective gas is selected from one or more of nitrogen, argon, and hydrogen.

[0047] In this invention, after the reaction temperature is reached, a first type of reaction gas is introduced to carry out the reaction; the first type of reaction gas is a carbon source gas, or a mixture of a carbon source gas and a protective gas; the carbon source gas is selected from one or more of methane, ethane, propane, butane, ethylene, natural gas and liquefied petroleum gas; the protective gas is selected from one or more of nitrogen, argon and hydrogen.

[0048] If the first type of reactant gas is a mixture of carbon source gas and protective gas, the volume ratio of carbon source gas to protective gas is (1:10):(10:1); specifically 1:10, 2:10, 3:10, 4:10, 5:10, 6:10, 7:10, 8:10, 9:10, 2:3, ...

[0049] The temperature at which the first type of reactive gas is introduced for the reaction in this invention is 750~1000℃.

[0050] In this invention, a protective gas is introduced, and the mixture is cooled to obtain crude graphene. The protective gas used in this invention is selected from one or more of nitrogen, argon, and hydrogen. Preferably, the protective gas is purged before introducing the first type of reactant gas.

[0051] After obtaining the crude graphene, the present invention washes the crude graphene to obtain graphene.

[0052] In this invention, the washing method is water washing; or water washing plus acid washing; the water washing method is one or more of centrifugation, vacuum filtration, and pressure filtration; the acid solution used for acid washing is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid. In this invention, if the metal content in the crude graphene is high, water washing plus acid washing is preferred.

[0053] This invention uses inductively coupled plasma atomic emission spectroscopy (ICP) to perform component analysis on graphene products:

[0054] Before testing, weigh a certain amount of sample into a glass bottle and add aqua regia (V). HCl :V HNO3 = 3:1) Stir for 24 h, take 1 mL of solution into a centrifuge tube, centrifuge at 9000 r / min for 10 min, take the supernatant and dilute to the linear range of the standard curve (1~100 mg / L), and send the diluted solution for testing.

[0055] To further illustrate the present invention, the following detailed description of a method for preparing graphene using a metal-molten salt composite system provided by the present invention is provided in conjunction with embodiments, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] The graphene preparation method provided in this embodiment includes the following steps:

[0058] 5.90 g NiO and 30 g CaCl2 were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen (Ar:H2 = 3:2) was introduced and kept at this temperature for 5 h. Subsequently, the temperature was increased to 900 °C at a heating rate of 7 °C / min, and hydrogen was introduced and kept at this temperature for 3 h to reduce the target catalyst.

[0059] After purging the hydrogen gas with argon, ethane is introduced to initiate the reaction. After the reaction is complete, argon is introduced again as a protective gas. Once the melt has cooled, the mixture in the reactor is washed with deionized water. The product is separated from the metal and salt solution by filtration, and the mixture is repeatedly washed with deionized water. After drying at 60 °C, powdered graphene is obtained.

[0060] Example 2

[0061] The graphene preparation method provided in this embodiment includes the following steps:

[0062] 1.42 g NiO, 0.56 g MoO3 and 30 g KCl were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen (Ar:H2 = 3:2) was introduced and kept at this temperature for 10 h. Then the temperature was increased to 950 °C at a heating rate of 7 °C / min, and hydrogen was introduced and kept at this temperature for 3 h to reduce the target catalyst.

[0063] After purging hydrogen with argon gas, methane was introduced to initiate the reaction. After the reaction was complete, argon gas was introduced again as a protective gas. Once the melt cooled, the mixture in the reactor was washed with deionized water. The product was separated from the metal and salt solution by filtration, and the mixture was repeatedly washed with deionized water. 1 mol / L dilute H₂SO₄ was added, and the mixture was stirred at 70 °C for 4 h. The product was then washed three times with deionized water by filtration and dried at 60 °C to obtain powdered graphene with a purity of 91.29%.

[0064] Figure 1 The Raman spectrum of the graphene prepared in Example 2 of this invention; by Figure 1 It can be seen that I D / I G =0.58, I 2D / I G =0.61.

[0065] Example 3

[0066] The graphene preparation method provided in this embodiment includes the following steps:

[0067] 2.91 g Fe2O3, 1.30 g MoO3 and 70 g KCl were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen (Ar:H2 = 3:2) was introduced and kept at this temperature for 10 h. Then the temperature was increased to 750 °C at a heating rate of 7 °C / min, and hydrogen was introduced and kept at this temperature for 8 h to reduce the target catalyst.

[0068] After purging hydrogen with argon gas, methane was introduced to initiate the reaction. After the reaction was complete, argon gas was introduced again as a protective gas. Once the melt cooled, the mixture in the reactor was washed with deionized water. The product was separated from the metal and salt solution by filtration, and the mixture was repeatedly washed with deionized water. 1 mol / L dilute H₂SO₄ was added, and the mixture was stirred at 80 °C for 8 h. The product was then washed three times with deionized water by filtration and dried at 60 °C to obtain powdered graphene with a purity of 91.85%.

[0069] Figure 2 The Raman spectrum of the graphene prepared in Example 3 of this invention; by Figure 1 It can be seen that I D / I G =0.11, I 2D / I G =0.98.

[0070] Example 4

[0071] The graphene preparation method provided in this embodiment includes the following steps:

[0072] 2.49 g Fe2O3, 1.81 g WO3, and 60 g CuCl2 and KCl mixture (CuCl2 and KCl mass ratio of 2:1) were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen gas (Ar:H2 = 3:2) was introduced and kept at this temperature for 7 h. Subsequently, the temperature was increased to 1000 °C at a heating rate of 10 °C / min, and hydrogen gas was introduced and kept at this temperature for 8 h, and the target catalyst was obtained by reduction.

[0073] After purging hydrogen with argon gas, propane was introduced to initiate the reaction. After the reaction was complete, argon gas was introduced again as a protective gas. Once the melt had cooled, the mixture in the reactor was washed with deionized water. The product was separated from the metal and salt solution by filtration and repeatedly washed with deionized water. 1 mol / L dilute H2SO4 was added and the mixture was stirred at 80 °C for 8 h. Subsequently, the product was washed three times with deionized water by filtration and dried at 60 °C to obtain powdered graphene.

[0074] Example 5

[0075] The graphene preparation method provided in this embodiment includes the following steps:

[0076] 3.89 g CoO, 1.87 g MoO3 and 30 g KCl were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen (Ar:H2 = 3:2) was introduced and kept at this temperature for 10 h. Then, the temperature was increased to 950 °C at a heating rate of 7 °C / min, and hydrogen was introduced and kept at this temperature for 3 h to reduce the target catalyst.

[0077] After purging the hydrogen gas with argon, methane is introduced to initiate the reaction. After the reaction is complete, argon is introduced again as a protective gas. Once the melt has cooled, the mixture in the reactor is washed with deionized water. The product is separated from the metal and salt solution by filtration, and the mixture is repeatedly washed with deionized water. After drying at 60 °C, powdered graphene is obtained.

[0078] Example 6

[0079] The graphene preparation method provided in this embodiment includes the following steps:

[0080] 1.17 g CoO, 0.91 g WO3 and 30 g MgCl2 were ground and mixed, and then packed into a quartz reactor. The temperature was increased to 400 °C at a heating rate of 10 °C / min, and a mixture of argon and hydrogen (Ar:H2 = 3:2) was introduced and kept at this temperature for 8 h. Then the temperature was increased to 950 °C at a heating rate of 7 °C / min, and hydrogen was introduced and kept at this temperature for 5 h to reduce the target catalyst.

[0081] After purging the hydrogen gas with argon, natural gas was introduced to initiate the reaction. After the reaction was complete, argon was introduced again as a protective gas. Once the melt had cooled, the mixture in the reactor was washed with deionized water. The product was separated from the metal and salt solution by filtration and repeatedly washed with deionized water. 1 mol / L dilute H2SO4 was added and the mixture was stirred at 80 °C for 8 h. Subsequently, the product was washed three times with deionized water by filtration and dried at 60 °C to obtain powdered graphene.

[0082] This invention uses Raman spectroscopy to characterize the graphitization degree and number of layers of graphene. Three spectra were acquired at each location, with an integration time of 6 s and a laser power of 10%. The final data were baseline corrected and peak fitted using Labspec software.

[0083] As can be seen from the above embodiments, the present invention provides a method for preparing graphene using a metal-molten salt composite system, comprising the following steps: (1) heating the catalyst raw material under a protective gas and reacting it to obtain a molten medium catalyst; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts; (2) introducing a first type of reaction gas to carry out the reaction; (3) introducing a protective gas again and cooling it to obtain crude graphene; (4) washing the crude graphene to obtain graphene. The present invention uses a metal cluster-molten salt composite catalyst, which combines the high catalytic activity of metals with the good dispersibility and stability of molten salts, effectively promoting carbon source cracking and graphene nucleation and growth. The obtained graphene has a high degree of graphitization and a low content of metal impurities. The product can be efficiently separated by washing without complex post-processing.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing graphene using a metal-molten salt composite system, comprising the following steps: (1) The catalyst raw material is heated and reacted to obtain a molten medium catalyst; the molten medium catalyst is a composite catalyst composed of metal clusters and metal salts; (2) The reaction is carried out by introducing a first-type reactive gas; (3) Introduce protective gas again, cool down, and obtain crude graphene; (4) Wash the crude graphene to obtain graphene.

2. The method according to claim 1, characterized in that, The molten medium catalyst is prepared by the following method: After mixing and grinding metal oxide nanoparticles and metal salts, the mixture is heated to a first temperature, a protective gas is introduced to maintain the temperature, the temperature is raised to a second temperature, a second type of reaction gas is introduced to maintain the temperature again, and a molten medium catalyst is obtained.

3. The method according to claim 1, characterized in that, The reaction temperature in step (1) is 750~1000℃.

4. The method according to claim 1, characterized in that, The first type of reactant gas is a carbon source gas, or a mixture of a carbon source gas and a protective gas; The carbon source gas is selected from one or more of methane, ethane, propane, butane, ethylene, natural gas, and liquefied petroleum gas; The protective gas is selected from one or more of nitrogen, argon, and hydrogen.

5. The method according to claim 2, characterized in that, The metal oxide nanoparticles are selected from one or more of iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, and tungsten oxide; The metal oxide nanoparticles account for 0.1~20wt% of the metal salt.

6. The method according to claim 2, characterized in that, The metal salt is selected from one or more of potassium chloride, sodium chloride, magnesium chloride, calcium chloride, zinc chloride, copper chloride, lithium chloride, manganese chloride, rubidium chloride, cesium chloride, strontium chloride, barium chloride, ferrous chloride, cobalt chloride, and nickel chloride.

7. The method according to claim 2, characterized in that, The second type of reaction gas is a mixture of argon and hydrogen in a volume ratio of (1:10) to (10:1).

8. The method according to claim 2, characterized in that, The first temperature is 200~600℃, and the temperature is maintained for 5~10 hours; The second temperature is 750~1000℃, and the holding time is 3~8h.

9. The method according to claim 8, characterized in that, Increase the temperature to the first temperature at a rate of 8~12℃ / min; Increase the temperature to the second temperature at a rate of 5~10℃ / min.

10. The method according to claim 1, characterized in that, The washing method is water washing; or water washing plus acid washing; The washing method can be one or more of centrifugation, vacuum filtration, and pressure filtration; The acid solution used for pickling is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

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