CN111377438B

CN111377438B - Graphene and preparation method thereof

Info

Publication number: CN111377438B
Application number: CN202010126860.5A
Authority: CN
Inventors: 周明; 杨青峰
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2020-02-28
Filing date: 2020-02-28
Publication date: 2021-07-27
Anticipated expiration: 2040-02-28
Also published as: CN111377438A

Abstract

The invention relates to the technical field of carbon nano materials, in particular to graphene and a preparation method thereof. The preparation method comprises the following steps: the method comprises the steps of dry-grinding graphite for a period of time in a grinding machine comprising a grinding body and an auxiliary grinding medium, and then adding obtained powder and an acid solution into a high-pressure reactor for reaction to obtain the graphene, wherein the auxiliary grinding medium is metal or metal oxide particles with the particle size of 5-500 nm. The preparation method provided by the invention has the characteristics of high stripping efficiency (up to 92%), high yield (up to 85.26%) and the like, and the prepared graphene has the advantages of uniform transverse dimension, few thickness layers and the like, and is a technology suitable for being popularized and applied to large-scale preparation of few-layer graphene.

Description

Graphene and preparation method thereof

Technical Field

The invention relates to the technical field of carbon nano materials, in particular to graphene and a preparation method thereof.

Background

Graphene (Graphene) is an sp2 hybridized two-dimensional honeycomb-shaped novel carbon nano material, and the successful preparation of Graphene by Anderson and Constantine, university of Manchester, UK in 2004 and the like through a micromechanical stripping method is one of the research hotspots at home and abroad till now; researches have found that graphene has many excellent properties such as excellent electrical conductivity, good optical properties, higher thermal conductivity, excellent mechanical properties and the like, and has wide application prospects in the fields of electronics, optics, magnetism, biology, materials and the like.

Since the discovery of graphene materials, the preparation method of graphene has been one of the hot points of interest, and the preparation method can be divided into two categories: one is a method for synthesizing graphene by using carbon-containing small molecular materials (gas, liquid and solid) as raw materials, which is called a bottom-up method such as a chemical vapor deposition method; the other is a method for preparing single-layer or few-layer graphene by using graphite as a raw material through a physical or chemical method or a mixed method of the two, which is called a top-down method such as mechanical exfoliation, electrochemistry, a redox method, an intercalation exfoliation method and the like. The top-down method is considered as a method which is more likely to realize large-scale production than the bottom-up method, besides quality factors, the stripping efficiency of graphene is another important factor limiting the preparation of graphene and the application of graphene by the top-down method, the mechanical stripping method is one of applicable methods for preparing graphene in consideration of high quality and high yield, the mechanical stripping mechanism is disclosed, the graphite delamination can be promoted to be changed into graphene by utilizing auxiliary grinding aids, and therefore, scientific researchers develop various auxiliary grinding aids such as dry ice, melamine, cellulose and the like. Although some progress has been made in the field, the conventional mechanical peeling method still has problems of low peeling efficiency, long peeling time, and the like.

The hydrothermal method is a technology capable of effectively hydrolyzing and pyrolyzing substances at high temperature and high pressure, and in the hydrothermal treatment process, the two-dimensional lamellar structure block material can be stripped into few layers of two-dimensional lamellar material through thermochemical molecular intercalation. Although some reports have been made on successful preparation of graphene by a hydrothermal method, large-scale production of graphene is difficult to achieve by a hydrothermal method alone. Therefore, the improved method for preparing the graphene by the efficient mechanical stripping method is developed, and has great technical improvement significance and wide prospects.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for preparing few-layer graphene by stripping with simple operation, easily obtained raw materials and high efficiency. Specifically, the invention provides a method for preparing few-layer graphene in large scale by using composite hydrothermal auxiliary mechanical vibration

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of graphene comprises the following steps: and (2) dry-grinding the graphite for a period of time in a grinding machine comprising a grinding body and an auxiliary grinding medium, and then adding the obtained powder and an acid solution into a high-pressure reactor for reaction to obtain the graphene.

According to the graphene preparation method provided by the invention, metal or metal oxide particles are introduced as auxiliary grinding media under the condition of a traditional main grinding media, and the auxiliary grinding media play a role of particle wedge in the mechanical vibration process of a grinding machine, so that the crushing effect of a graphite sheet layer in the mechanical vibration process can be promoted, and the separation of the graphite sheet layer can be directly promoted; in the hydrothermal treatment process of the high-pressure reactor, under the conditions of high temperature and high pressure, gas molecules, water molecules, solute molecules and the like generated by the reaction of metal and metal oxide with acid can perform molecular intercalation on the graphite sheet layer under the thermal stirring, and meanwhile, the delamination of the graphite sheet layer can be further promoted along with the shearing effect caused by violent molecular Brownian motion. Therefore, efficient preparation of few-layer graphene is achieved, the stripping efficiency can reach 92%, and the yield can reach 85.26%. Compared with the traditional mechanical stripping method or hydrothermal method for independently preparing graphene, the composite method has the characteristics of higher stripping efficiency, higher yield and the like. The method can be popularized and applied to large-scale production of graphene, and plays a great role in promoting numerous applications and industrialization of graphene.

Preferably, in the above preparation method, the graphite is expanded graphite, flake graphite or synthetic graphite, and more preferably, the graphite is scaly or flaky.

Preferably, in the preparation method, the grinding body is a sphere with a diameter of 0.1-15 mm, and more preferably, the grinding body is made of one or more materials selected from ceramics, glass, polymers, ferromagnetism or zirconia.

Preferably, in the preparation method, the mass ratio of the grinding body, the auxiliary grinding aid and the graphite is 1000-2200: 0.5-5: 1-50, and is preferably 1600-2000: 2-2.5: 20-30.

Preferably, in the above preparation method, the mill is a planetary ball mill, a stirred ball mill or a resonance mill.

Preferably, in the preparation method, the auxiliary grinding aid is metal or metal oxide particles, the particle size of the auxiliary grinding aid is 5-500 nm, more preferably, the particle size of the auxiliary grinding aid is 5-100 nm, and/or the auxiliary grinding aid is ferroferric oxide particles, aluminum oxide particles or iron particles.

Preferably, in the preparation method, the dry grinding time is 2-24 h.

Preferably, in the above preparation method, the acid solution is a strong acid solution, the mass-to-volume ratio of the powder to the acid solution is 1:10-40g/mL, and more preferably, the acid solution is concentrated nitric acid or sulfuric acid.

Preferably, in the preparation method, the reaction temperature of the high-pressure reactor is 100-300 ℃, the reaction time is 2-6 h, and more preferably, the reaction pressure of the high-pressure reactor is less than or equal to 3 MPa.

Preferably, in the preparation method, after the reaction in the high-pressure reactor, the method further comprises the steps of centrifugal washing and drying, and more preferably, the centrifugal speed of the centrifugal washing is 5000-12000 rpm, and the centrifugal time is 10-60 min.

The invention also provides graphene prepared by the preparation method.

The invention has the following beneficial effects:

the invention provides a technology which is suitable for being popularized to large-scale preparation of few-layer graphene, and has the characteristics of high stripping efficiency (up to 92%), high yield (up to 85.26%) and the like, and the prepared graphene has the advantages of uniform transverse dimension, few thickness layers and the like.

Drawings

Fig. 1 is SEM and TEM characterization of graphene prepared in example 1, wherein a is an SEM image and b is a TEM image.

Fig. 2 is an SEM image of graphene prepared in example 2.

Fig. 3 is an HRTEM of graphene prepared in example 1.

Fig. 4 is a thickness distribution diagram of graphene prepared in example 1.

Fig. 5 is an NMP dispersion diagram of the graphene powders prepared in example 1 and comparative examples 1 to 3. The sample tube 1 is the NMP dispersion prepared in comparative example 1, the sample tube 2 is the NMP dispersion prepared in comparative example 3, the sample tube F is the NMP dispersion prepared in comparative example 2, and the sample tube H is the NMP dispersion prepared in example 1.

Fig. 6 is an atomic force micrograph AFM of the graphene powder prepared in comparative example 1.

Fig. 7 is an atomic force micrograph AFM of the graphene powder prepared in comparative example 3.

Fig. 8 is an atomic force micrograph AFM of the graphene powder prepared in comparative example 2.

Fig. 9 is an atomic force micrograph AFM of the graphene powder prepared in example 1.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the scope of the present invention is not limited thereto.

The examples, where specific experimental procedures or conditions are not indicated, were carried out according to the procedures or conditions of the conventional experimental procedures described in the literature in the field. The reagents and instruments used are not indicated by manufacturers, and can be purchased in the market.

Example 1

A method for preparing few-layer graphene in a large scale by composite hydrothermal auxiliary mechanical resonance collision comprises the following specific operation steps:

(1) weighing 20g of expanded graphite and 2.5g of 100nm ferroferric oxide auxiliary grinding aid, mixing and putting into a resonance grinding machine, and simultaneously weighing 1.2kg of zirconia balls with the diameter of 4mm and 0.4kg of zirconia balls with the diameter of 6mm, and adding the two zirconia balls into the resonance grinding machine, wherein the mass ratio of the two zirconia balls with the diameters is 3: 1;

(2) the vibration amplitude of the mill is 11mm, the vibration frequency is 16Hz, the vibration excitation mode is vibration of a vibration motor, the vibration mode is vibration of a spiral spring, and the resonance collision time of the mill is 6 h;

(3) the powder prepared by collision is mixed with 30ml of concentrated nitric acid (HNO) per 1g₃65-68 percent) of the graphene powder, placing the mixture in a 50m polytetrafluoroethylene high-pressure reaction kettle at 180 ℃ for 3h, centrifugally washing the obtained substance for many times at 8000rpm of deionized water until the pH value of the solution is about 7.0, and freeze-drying the obtained precipitate for 36h to obtain 17.052g of few-layer graphene powder with the yield of 85.26 percent.

Nitride gas generated in the hydrothermal treatment process can be removed by a commercial yellow smoke remover, and redundant acid solution obtained by centrifugation can be treated after being neutralized by alkali.

Example 2

(1) weighing 30g of expanded graphite and 2g of 50nm alumina grinding aid, mixing and putting into a resonance grinding machine, and simultaneously weighing 1.6kg of zirconia balls with the diameter of 4mm and 0.4kg of zirconia balls with the diameter of 6mm, and adding the zirconia balls with the two diameters in a mass ratio of 4: 1;

(2) the vibration amplitude of the mill is 11mm, the vibration frequency is 16Hz, the vibration excitation mode is vibration of a vibration motor, the vibration mode is vibration of a spiral spring, and the resonance collision time of the mill is 4 h;

(3) the powder prepared by collision is mixed with 20ml sulfuric acid (H) per 1g₂SO₄98 percent of the mass concentration), placing the mixture in a 50mL polytetrafluoroethylene high-pressure reaction kettle, keeping the temperature at 160 ℃ for 4h, centrifugally washing the obtained substance for many times at 8000rpm of deionized water until the pH value of the solution is about 7.0, and freeze-drying the obtained precipitate for 36h to obtain the few-layer graphene powder.

Comparative example 1

(1) Weighing 20g of expanded graphite, putting the expanded graphite into a resonance mill, and simultaneously weighing 1.2kg of zirconia balls with the diameter of 4mm and 0.4kg of zirconia balls with the diameter of 6mm, and adding the two balls into the resonance mill, wherein the mass ratio of the two balls is 3: 1.

(2) The vibration amplitude of the mill is 11mm, the vibration frequency is 16Hz, the vibration excitation mode is vibration of a vibration motor, the vibration mode is vibration of a spiral spring, and the resonance collision time of the mill is 6h, so that the graphene-containing powder is obtained.

Comparative example 2

(2) the vibration amplitude of the mill is 11mm, the vibration frequency is 16Hz, the vibration excitation mode is vibration of a vibration motor, and the vibration mode is vibration of a spiral spring. The resonance collision time of the mill is 6h, and the powder containing graphene can be obtained.

Comparative example 3

(1) Weighing 20g of expanded graphite, putting the expanded graphite into a resonance mill, and simultaneously weighing 1.2kg of zirconia balls with the diameter of 4mm and 0.4kg of zirconia balls with the diameter of 6mm, wherein the mass ratio of the two kinds of zirconia balls is 3: 1;

(2) the vibration amplitude of the mill is 11mm, the vibration frequency is 16Hz, the vibration excitation mode is vibration of a vibration motor, and the vibration mode is vibration of a spiral spring. The resonance collision time of the mill is 6 h;

(3) collision to prepare powderMixing the powder with 30ml concentrated nitric acid (HNO) per 1g₃65-68 percent) of the graphene powder, placing the mixture in a 50m polytetrafluoroethylene high-pressure reaction kettle at 180 ℃ for 3h, centrifugally washing the obtained substance for many times at 8000rpm of deionized water until the pH value of the solution is about 7.0, and freeze-drying the obtained precipitate for 36h to obtain the graphene powder.

Comparative example 4

Weighing 1g of expanded graphite and 30ml of concentrated nitric acid (HNO)₃65-68 percent) of the precipitate, placing the mixture in a 50m polytetrafluoroethylene high-pressure reaction kettle at 180 ℃ for 3h, centrifugally washing the obtained substance for many times at 8000rpm of deionized water until the pH value of the solution is about 7.0, and freeze-drying the obtained precipitate for 36h to obtain the product. The graphite in the obtained product is not effectively stripped through detection.

The following tests were carried out on the graphene powders prepared in the above examples and comparative examples:

1. SEM and TEM

The graphene powder prepared in example 1 is prepared into NMP dispersion liquid of 0.1mg/ml for SEM and TEM characterization, and the result is shown in FIG. 1, wherein a is SEM picture and b is TEM picture. As can be seen from fig. 1, the graphene prepared in example 1 has a good uniform sheet shape and less wrinkles, and has a uniform transverse dimension.

The graphene powder prepared in example 2 is prepared into NMP dispersion liquid of 0.1mg/ml for SEM characterization, and the result is shown in FIG. 2, and the prepared graphene has better transverse dimension and thickness. However, compared with the SEM image of example 1, the result shows that the graphene prepared in example 1 has a more uniform lateral size distribution and a thinner thickness, i.e., example 1 has a better exfoliation effect.

2、HRTEM

The few-layer graphene powder prepared in example 1 is configured into 0.1mg/ml NMP dispersion liquid for HRTEM characterization, and the result is shown in fig. 3, it can be seen from fig. 3 that the number of edge layers of most nanosheets is less than 10, single-layer graphene and two-layer graphene can be observed, statistical analysis is performed on 100 edge thicknesses in the HRTEM diagram, and the result is shown in fig. 4, and it can be seen from fig. 4 that the percentage of graphene in ten layers can be as high as 92%.

3. The graphene powders prepared in example 1 and comparative examples 1 to 3 were prepared into NMP dispersions of 0.1mg/ml and placed in sample tubes, respectively, and the results were shown in fig. 5, where sample tube No. 1 was the NMP dispersion prepared in comparative example 1, sample tube No. 2 was the NMP dispersion prepared in comparative example 3, sample tube No. F was the NMP dispersion prepared in comparative example 2, and sample tube No. H was the NMP dispersion prepared in example 1. As can be seen from fig. 5, the graphene powder in the NMP dispersions of sample tubes No. 1 and No. 2 is easy to aggregate and precipitate, the graphene powder in the NMP dispersion of sample tube No. F is seriously aggregated after 7 days, and the graphene powder in the NMP dispersion of sample tube No. H is stably dispersed.

4. AFM characterization

The graphene powders prepared in example 1 and comparative examples 1 to 3 were prepared into NMP dispersions of 0.1mg/ml, respectively. 10uL of the NMP dispersion liquid of example 1, comparative example 1 and comparative example 3 was dropped on a mica plate to perform a topography scan by an atomic force microscope, the NMP dispersion liquid prepared in comparative example 2 was allowed to stand 24 on a magnet stand, the upper 80% solution was centrifuged at 3000rpm for 30min, and then 10uL of the supernatant liquid was dropped on the mica plate to perform a topography scan by an atomic force microscope, and the results are shown in FIGS. 6 to 9. Fig. 6 is a characteristic diagram of the AFM of comparative example 1, fig. 7 is a characteristic diagram of the AFM of comparative example 3, fig. 8 is a characteristic diagram of the AFM of comparative example 2, and fig. 9 is a characteristic diagram of the AFM of example 1. As can be seen from fig. 6 to 9, the particle thickness of the graphene powder prepared in comparative example 1 is 32.69 to 263.00nm, the particle thickness of the graphene powder prepared in comparative example 3 is 15.74 to 82.60nm, the particle thickness of the graphene powder prepared in comparative example 2 is 1.97 to 5.02nm, and the particle thickness of the graphene powder prepared in example 1 is 1.30 to 1.99 nm.

Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. A preparation method of graphene is characterized by comprising the following steps: dry-grinding graphite for a period of time in a grinding machine comprising a grinding body and an auxiliary grinding medium, and then adding the obtained powder and an acid solution into a high-pressure reactor for hydrothermal reaction to obtain graphene;

the auxiliary grinding aid is metal or metal oxide particles, the particle size of the auxiliary grinding aid is 5-500 nm, and the auxiliary grinding aid is ferroferric oxide particles, aluminum oxide particles or iron particles;

the acid solution is a strong acid solution, the mass-to-volume ratio of the powder to the acid solution is 1:10-40g/mL, and the acid solution is a concentrated nitric acid or sulfuric acid aqueous solution;

the reaction temperature of the high-pressure reactor is 100-300 ℃.

2. The production method according to claim 1, wherein the graphite is flake graphite or synthetic graphite.

3. The production method according to claim 2, wherein the graphite is scaly or flaky.

4. The production method according to any one of claims 1 to 3, wherein the milling body is a sphere having a diameter of 0.1 to 15 mm.

5. The method according to claim 4, wherein the material of the grinding body is selected from one or more of ceramics, glass, polymer, ferromagnetism or zirconia.

6. The production method according to any one of claims 1 to 3, wherein the mass ratio of the abrasive body, the auxiliary grinding aid and the graphite is 1000 to 2200:0.5 to 5:1 to 50.

7. The preparation method according to claim 6, wherein the mass ratio of the grinding body, the auxiliary grinding aid and the graphite is 1600-2000: 2-2.5: 20-30.

8. The preparation method according to claim 1, wherein the auxiliary grinding aid has a particle size of 5 to 100 nm.

9. The method according to any one of claims 1 to 3, wherein the dry-milling time is 2 to 24 hours.

10. The production method according to any one of claims 1 to 3, wherein the reaction time of the high-pressure reactor is 2 to 6 hours.

11. The production method according to claim 10, wherein the reaction pressure of the high-pressure reactor is 3MPa or less.

12. The method according to any one of claims 1 to 3, wherein the high-pressure reactor further comprises a step of centrifugal washing and drying after the reaction.

13. The method according to claim 12, wherein the centrifugation speed of the centrifugal washing is 5000 to 12000rpm, and the centrifugation time is 10 to 60 min.