CN110203913B - Method for preparing graphene - Google Patents
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- CN110203913B CN110203913B CN201910460949.2A CN201910460949A CN110203913B CN 110203913 B CN110203913 B CN 110203913B CN 201910460949 A CN201910460949 A CN 201910460949A CN 110203913 B CN110203913 B CN 110203913B
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- C01B32/00—Carbon; Compounds thereof
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- C01B32/182—Graphene
- C01B32/184—Preparation
- C01B32/19—Preparation by exfoliation
Abstract
The invention discloses a method for preparing graphene. The graphene is prepared by the following preparation method: 1) carrying out expansion treatment on expandable graphite, and then crushing to obtain expanded graphite powder; 2) mixing and stirring the expanded graphite powder and hydrogen peroxide, degassing, carrying out ultrasonic stripping, heating to decompose the hydrogen peroxide, and drying to obtain the graphene. The invention provides a method suitable for large-scale production and preparation of graphene, which is green, pollution-free, safe and environment-friendly. The graphene prepared by the method has the advantages of uniform size, few defects and the like.
Description
Technical Field
The invention belongs to the technical field of graphene, and particularly relates to a method for preparing graphene.
Background
Graphene is a hexagonal honeycomb lattice monolayer of carbon atoms composed of sp2 hybridized orbitals. Graphene is an essential unit for constructing carbon materials of other dimensions, and when its existence mode is changed, fullerene, carbon nanotube, graphite, and the like can be formed, respectively. Graphene has excellent electrical, optical, mechanical and other properties, excellent thermal conductivity and extremely high charge carrier mobility, and due to the excellent properties, the graphene becomes a hot point for research in various fields such as composite materials, energy sources, big health, seawater desalination and the like. The varying needs for graphene in many areas have also led to numerous methods and processes for preparing graphene.
The common methods for preparing graphene mainly comprise a mechanical stripping method, a vapor deposition method, an epitaxial growth method and a redox method, wherein the mechanical stripping method is only suitable for preparing a graphene sample in a laboratory, the vapor deposition method and the epitaxial growth method have high requirements on equipment requirements and technology and high production difficulty, and although the redox method can be used for mass production, the prepared product has many defects and is seriously polluted in the production process. In the following, a wet grinding process has also been developed to prepare graphene, i.e., crystalline flake graphite is used as a raw material, the crystalline flake graphite is dispersed in a solvent, and the graphene is exfoliated from graphite by using mechanical force. Although the whole preparation process is environment-friendly, the quality of the obtained graphene product is relatively high, the Van der Waals force between graphite layers is large, and the time for preparing the graphene to be peeled is long, so that the price of the graphene prepared by wet peeling is high.
The expandable graphite is a crystal compound which utilizes a physical or chemical method to enable non-carbonaceous reactants to be inserted between graphite layers and combined with the hexagonal network planes of carbon, and simultaneously maintains the layered structure of the graphite. When the expandable graphite meets high temperature, the interlaminar compound is decomposed to generate thrust along the direction of the C axis between the graphite layers, and the thrust is far greater than the interlaminar bonding force of graphite ions, so that the graphite layers can be pushed away to form the vermicular expanded graphite. Compared with the scale graphite, the expanded graphite has larger interlayer spacing and smaller Van der Waals force between layers, and is easier to peel to prepare the graphene.
In the existing published documents, CN107500279A uses expandable graphite as a raw material, graphene quantum dots as an exfoliation solution, and a mechanical exfoliation method and a secondary ultrasonic treatment process are used, so as to realize mass production of graphene. However, the price of the graphene quantum dots is far higher than that of graphene, and although part of the graphene quantum dots can be recycled, the peeled graphene is in the micro-nano level. The graphene quantum dots are well dispersed in the stripped graphene system, and the recycling rate is extremely low. Although the graphene product can be obtained simply and rapidly by the method, the preparation cost is high, and large-scale production cannot be realized.
CN103950927A mixes the expanded graphite and sodium bicarbonate solution, heats up to 190 ℃ and stirs for 1.5h, and then uses sodium bicarbonate to decompose and generate carbon dioxide to generate stripping force between the expandable graphite sheets, and after the carbon dioxide is dissolved in water, the formed alkaline condition makes the graphene sheets form electrostatic repulsion between the layers, thus forming graphene. But the preparation process needs high temperature and high pressure, the energy consumption is high, and the introduced sodium bicarbonate is difficult to be removed completely.
In addition, there are many reports on the research on the preparation of graphene from expanded graphite, but the following problems are more or less present: the separation of the unexpanded raw material after the expandable graphite is expanded; the stripping mode problem in the stripping stage of the expanded graphite; the auxiliary stripping auxiliary agent selected during stripping has the problems of stripping efficiency, cost, difficulty in later-stage removal of the auxiliary stripping auxiliary agent and the like.
Disclosure of Invention
In order to overcome the problems in the prior art, the invention aims to provide a green and environment-friendly method for preparing graphene.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention provides a method for preparing graphene, which comprises the following steps:
1) carrying out expansion treatment on expandable graphite, and then crushing to obtain expanded graphite powder;
2) mixing and stirring the expanded graphite powder and hydrogen peroxide, degassing, carrying out ultrasonic stripping, heating to decompose the hydrogen peroxide, and drying to obtain the graphene.
Preferably, in step 1) of the method for preparing graphene, the particle size of the expandable graphite is 50-100 meshes.
Preferably, in the method for preparing graphene, in the step 1), the expansion ratio of the expandable graphite is 200-400 times; more preferably, the expandable graphite has an expansion ratio of 250 to 350.
Preferably, in step 1) of the method for preparing graphene, the carbon content of the expandable graphite is more than or equal to 98 wt%.
Preferably, in step 1) of the method for preparing graphene, the expansion treatment is one or both of a thermal expansion treatment and a microwave expansion treatment.
Preferably, in the expansion treatment in step 1), the thermal expansion treatment is carried out by placing expandable graphite in nitrogen or inert gas atmosphere, heating at 600-800 ℃ for 30-90 s; more preferably, the thermal expansion treatment is carried out by placing expandable graphite in a nitrogen atmosphere and heating to 650-750 ℃ for 50-70 s.
Preferably, in step 1) of the method for preparing graphene, the graphene is pulverized into one or more of ball milling, grinding and jet milling.
Preferably, in step 1) of the method for preparing graphene, crushing until the particle size D50 of the material is not more than 20 μm; it is further preferred that the particle size D50 of the crushed material is not more than 10 μm.
Preferably, in step 2) of the method for preparing graphene, the mass ratio of the expanded graphite powder to hydrogen peroxide is 1: (10-100).
Preferably, in step 2) of the method for preparing graphene, H in hydrogen peroxide solution2O2The mass percentage is 5% -50%; further preferably, H of hydrogen peroxide2O2The mass percentage is 10-40%.
Preferably, in the step 2) of the method for preparing graphene, the mixing and stirring time is 3min to 10 min; more preferably, the mixing and stirring time is 4 to 6 min.
Preferably, in step 2) of the method for preparing graphene, the degassing manner is vacuum degassing.
Preferably, in the step 2) of the method for preparing graphene, degassing is specifically vacuum degassing under 1-10 kPa for 3-10 min.
Preferably, in the step 2) of the method for preparing graphene, the temperature of ultrasonic stripping is 50-100 ℃; further preferably, the temperature of ultrasonic stripping is 50-80 ℃; still more preferably, the temperature of the ultrasonic peeling is 50 ℃ to 60 ℃.
Preferably, in the step 2) of the method for preparing graphene, the ultrasonic stripping time is 0.5-2 h; further preferably, the time for ultrasonic peeling is 1 to 2 hours.
Preferably, in step 2) of the method for preparing graphene, the power of ultrasound is 0.5kW to 3kW, and the frequency of ultrasound is 20kHz to 60 kHz.
Preferably, in step 2) of the method for preparing graphene, the temperature for thermal decomposition is 100 ℃ to 160 ℃.
Preferably, in step 2) of the method for preparing graphene, the time for heating and decomposing is 0.5 h-2 h; more preferably, the time for thermal decomposition is 1 to 2 hours.
In the method for preparing graphene, in step 2), after ultrasonic stripping, hydrogen peroxide is decomposed into water and oxygen by heating and raising the temperature; in the process of heating up, whether hydrogen peroxide is completely decomposed can be detected by carrying out titration test by using a potassium permanganate solution.
Preferably, in step 2) of the method for preparing graphene, the drying mode is spray drying.
The invention also provides graphene prepared by the method.
The invention has the beneficial effects that:
the invention provides a method suitable for large-scale production and preparation of graphene, which is green, pollution-free, safe and environment-friendly. The graphene prepared by the method has the advantages of uniform size, few defects and the like.
Compared with the prior art, the invention has the following advantages:
1. the invention takes the expandable graphite as the raw material, after the expansion treatment, the interlamellar spacing of the product is larger than that of the crystalline flake graphite, the Van der Waals force is smaller, and the energy required for stripping is less. Compared with the traditional method of stripping by utilizing crystalline flake graphite or highly oriented pyrolytic graphite, the method has the advantages of shorter time and higher stripping efficiency. The graphite oxide is used as a raw material, and the preparation process is complex and high in cost, and is at least 5 times of that of expandable graphite.
2. When the sample before ultrasonic stripping is subjected to crushing treatment, the smaller the sample is, the more obvious the 'cavitation effect' acting on the sample during ultrasonic stripping is, so that the sample is easier to strip.
3. The hydrogen peroxide is used as the stripping solution, so that the surface tension of the hydrogen peroxide is smaller compared with that of deionized water, and the expanded graphite is easier to wet. And degassing treatment is also carried out, so that hydrogen peroxide can more easily permeate into gaps of the expanded graphite to replace the original air, and the hydrogen peroxide can fully wet the expanded graphite. In the ultrasonic stripping stage, hydrogen peroxide is slowly decomposed when the temperature is raised, the generated bubbles completely strip the expanded graphite, and the 'cavity effect' generated by the ultrasound is utilized to be cooperated with the bubbles generated by the hydrogen peroxide to completely strip the expanded graphite into graphene when the temperature is raised. After stripping is finished, heating to completely decompose hydrogen peroxide, and drying graphene to obtain the graphene. The whole stripping efficiency is efficient and convenient, no three wastes are discharged in the production process, and the stripping efficiency is far better than that of stripping by using water or an organic solvent. And the stripping time is short, and the obtained product has small defects, more uniform particle size and better quality.
4. In the whole production process, the energy consumption is low, the safety is realized, the efficiency is high, the production process is green and environment-friendly, and the amplification and the popularization are easy.
Drawings
FIG. 1 is a scanning electron micrograph of a sample prepared in example 1;
FIG. 2 is a scanning electron micrograph of a sample prepared in comparative example 1.
Detailed Description
The present invention will be described in further detail with reference to specific examples. The starting materials used in the examples are, unless otherwise specified, commercially available from conventional sources.
Example 1
The graphene preparation method of the present example is as follows:
100g of expanded graphite having a carbon content of 99 wt%, 80 mesh and an expansion ratio of 300 times was placed in a high-temperature expansion furnace, expanded at 700 ℃ for 60 seconds in a nitrogen atmosphere, and the expanded sample was ground with a jet mill to a particle size of D50 of 10 μm. 10g of the ground sample was placed in a flask and 500mLH was added2O2And (3) continuously stirring 30% hydrogen peroxide by mass for 5min, degassing for 5min in vacuum, heating to 60 ℃, continuously stripping for 1h by using 3kW and 30kHz ultrasound, heating to 150 ℃, stirring for 1h until no bubbles are formed (judging that hydrogen peroxide is completely decomposed by titration with a potassium permanganate solution), and spray-drying to obtain the graphene sample.
Example 2
The graphene preparation method of the present example is as follows:
100g of expanded graphite having a carbon content of 99 wt%, a particle size of 100 mesh and an expansion ratio of 300 times was placed in a high-temperature expansion furnace, expanded at 700 ℃ for 60 seconds in a nitrogen atmosphere, and the expanded sample was ground with a jet mill to a particle size of D50 of 8 μm. 10g of the ground sample was placed in a flask and 800mLH was added2O2Mass percentContinuously stirring for 5min after 20% hydrogen peroxide, vacuum degassing for 5min, heating to 70 ℃, continuously stripping for 1h by utilizing 2kW and 30kHz ultrasound, heating to 150 ℃, stirring for 1h until no bubbles are formed (judging that hydrogen peroxide is completely decomposed by titration with potassium permanganate solution), and spray drying to obtain the graphene sample.
Example 3
The graphene preparation method of the present example is as follows:
80g of expanded graphite having a carbon content of 99 wt%, a mesh size of 50 and an expansion ratio of 300 times was placed in a high-temperature expansion furnace, expanded at 700 ℃ for 60 seconds in a nitrogen atmosphere, and the expanded sample was ground with a jet mill to a particle size of D50 of 10 μm. 10g of the ground sample was placed in a flask and 1000mLH was added2O2Continuously stirring 30% hydrogen peroxide by mass for 5min, vacuum degassing for 5min, heating to 60 ℃, continuously stripping by using 1kW and 30kHz ultrasound for 0.5h, heating to 155 ℃, stirring for 2h until no bubbles are formed (judging complete decomposition of hydrogen peroxide by titration of potassium permanganate solution), and spray drying to obtain the graphene sample.
Comparative example 1
The preparation method of the sample of this example is as follows:
100g of expanded graphite having a carbon content of 99 wt%, 80 mesh and an expansion ratio of 300 times was placed in a high-temperature expansion furnace, expanded at 700 ℃ for 60 seconds in a nitrogen atmosphere, and the expanded sample was ground with a jet mill to a particle size of D50 of 10 μm. And (3) placing 10g of ground sample in a flask, adding 500mL of deionized water, continuously stirring for 5min, vacuum degassing for 5min, heating to 60 ℃, continuously stripping for 1h by utilizing 3kW and 30kHz ultrasound, heating to 150 ℃, stirring for 1h, and spray drying to obtain the mixed sample of graphene and expanded graphite.
The scanning electron microscope image of the sample prepared in the example 1 is shown in the attached figure 1, and the scanning electron microscope image of the sample prepared in the comparative example 1 is shown in the attached figure 2. As can be seen from the comparison of the SEM images of fig. 1 and 2, the sample obtained in example 1 has a more uniform particle size, fewer defects, and a better peeling effect is demonstrated. In contrast, the sample size of the sample prepared in comparative example 1 further expanded with the ultrasonic exfoliation, but the exfoliated expanded graphite had a structure that was not exfoliated, and the exfoliation effect was poor.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (6)
1. A method of preparing graphene, characterized by: the method comprises the following steps:
1) carrying out expansion treatment on expandable graphite, and then crushing to obtain expanded graphite powder;
2) mixing and stirring the expanded graphite powder and hydrogen peroxide, degassing, performing ultrasonic stripping, heating to decompose the hydrogen peroxide, and drying to obtain graphene;
in the step 1), crushing until the particle size D50 of the material is not more than 20 μm;
in the step 2), the mass ratio of the expanded graphite powder to the hydrogen peroxide is 1: (10-100); the temperature of ultrasonic stripping is 50-100 ℃, and the time of ultrasonic stripping is 0.5-2 h; the temperature of the heating decomposition is 100-160 ℃, and the time of the heating decomposition is 0.5-2 h.
2. The method for preparing graphene according to claim 1, wherein: in step 1), the expansion treatment is a thermal expansion treatment.
3. The method for preparing graphene according to claim 1, wherein: in the step 1), the crushing is one or more of ball milling, grinding and jet milling.
4. The method for preparing graphene according to claim 1, wherein: h of hydrogen peroxide in step 2)2O2The mass percentage is 5% -50%.
5. The method for preparing graphene according to claim 1, wherein: in step 2), the degassing mode is vacuum degassing.
6. A graphene characterized by: is prepared by the method of any one of claims 1 to 5.
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| CN111285361B (en) * | 2020-04-14 | 2022-12-27 | 中北大学 | High-performance liquid-phase mechanical preparation method of low-defect and high-dispersion graphene |
| WO2023087135A1 (en) * | 2021-11-16 | 2023-05-25 | 广东聚石化学股份有限公司 | Method for preparing graphene |
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| US10381646B2 (en) * | 2015-12-24 | 2019-08-13 | Semiconductor Energy Laboratory Co., Ltd. | Secondary battery, graphene oxide, and manufacturing method thereof |
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