CN114620718A

CN114620718A - Preparation method of graphene dispersion liquid

Info

Publication number: CN114620718A
Application number: CN202210062969.6A
Authority: CN
Inventors: 徐政和; 杨帆; 姜峰; 卫晓婷
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2022-01-19
Filing date: 2022-01-19
Publication date: 2022-06-14

Abstract

The invention discloses a preparation method of a graphene dispersion liquid. The method comprises the following steps: providing carboxylated graphene, wherein the carboxylated graphene means that the edge of the graphene has carboxyl; performing amino modification treatment on the carboxylated graphene to enable amino to replace partial carboxyl on the edge of the graphene, so as to obtain the aminated graphene; and dissolving the aminated graphene in water, mixing with a graphene oxide solution, and adjusting the pH value to obtain a graphene dispersion liquid. The invention provides a preparation method of a graphene dispersion liquid with good stability, low cost and no pollution. Dissolving amination graphite alkene in aqueous, through adding oxidation graphite alkene solution and adjusting solution pH value, can control the dispersion degree of consistency of graphite alkene dispersion, can adjust the concentration of graphite alkene dispersion simultaneously.

Description

Preparation method of graphene dispersion liquid

Technical Field

The invention relates to the technical field of graphene, and particularly relates to a preparation method of a graphene dispersion liquid.

Background

Fullerenes and carbon nanotubes have excellent electrical, mechanical and solution dispersibility, and the allotropes of these carbons have attracted a lot of attention in the last 30 years. Kroto et al discovered 0D fullerenes in 1985, which has led to great interest in nanocarbon materials. The emergence of 1D carbon nanotubes has further stimulated the enthusiasm of people in studying carbon-based nanomaterials. Graphene is considered as a basic structural unit of fullerene and carbon nanotube, but is not found by Geim et al until 2004, and has attracted much attention.

The graphene is of a two-dimensional planar structure, and carbon atoms are orderly arranged according to a hexagonal lattice rule and are in a honeycomb shape. The distance between two carbon atoms on the graphene is 1.42A, and the bonding mode of the carbon atoms is sp²Hybridization, sp between adjacent carbon atoms²The orbitals are combined to form s-bonds, and the rest p orbitals are mutually superposed to finally form a large pi conjugated system.

Part of the reason that graphene is discovered this late is that graphene is only one atom thick, which was previously thought to be thermodynamically unstable. However, graphene can exist stably, and has excellent electrical and mechanical properties. The carrier migration rate of the graphene at room temperature is up to 250000cm²/(v.s), much higher than silicon semiconductors and gallium arsenide. Since graphene has a specific energy band structure, the quantum hall effect of graphene can be observed at room temperature. The graphene has high room temperature thermal conductivity of about 5000W/m^-K. Graphene has a young's modulus of about 1TPa and is known as the most robust material in the world.

Many optimistic predictions are made about the applications of graphene in the fields of electronics, medicine and the like. Due to the lack of efficient mass production processes, graphene production faces a dilemma, and compromises must be made between scalability and graphene quality. Liquid phase stripping is an effective way to realize large-scale production of high-quality graphene or graphene oxide. The liquid phase exfoliation method is to add a graphite raw material into an organic solvent or water containing a dispersant, and to subject the graphite to ultrasonic treatment, thereby obtaining single-layer or multi-layer graphene with few defects. The preparation process is simple, the cost is low, and the prepared graphene is high in quality. However, due to the limited dispersion stability of graphene, in these processes, purification and dispersion always require a large amount of solvent. Only very small amounts of graphene (typically <1g/ml) can be dispersed in common solvents, which is only slightly improved by means of dispersants or by prolonged ultrasound. Reducing the amount of solvent used destroys the dispersibility of the graphene and leads to the re-stacking of the graphene through van der waals interactions. This means that at least 1 tonne of solvent is required to produce 1kg of graphene with this dispersion method, which is environmentally unfriendly and economically unfeasible.

The high-concentration stably-dispersed graphene dispersion liquid has a huge application prospect, and can be applied to the preparation of composite materials, and the fields of transparent conductive films, conductive ink and the like. However, graphene nanoplatelets are neither hydrophilic nor lipophilic, and are also prone to agglomeration due to van der waals forces, making stable dispersion in solution for long periods difficult. Therefore, how to prepare a graphene dispersion liquid with high concentration and stable performance becomes a difficult problem to be solved urgently. The graphene dispersion liquid can be obtained by stripping graphite powder by a long-time high-power ultrasonic technology, but the concentration of the obtained dispersion liquid is very low, and the highest value reported in the literature is only 0.3mg/ml, so that the application of the technology is greatly limited. Common Graphene includes various types such as Graphene Oxide (GO), Graphene oxide (Reduced Graphene oxide (rGO)), and the like, and the preparation of Graphene dispersion liquid is diversified due to the various types. At present, the main method for solving the problem of graphene dispersion is to perform modification treatment on the surface of graphene, for example, loading nanoparticles on the surface, adding surfactant molecules, introducing macromolecules, doping aromatic macromolecules and the like, and stably dispersing the graphene in a solvent; in addition, the electrostatic repulsion action of oxygen-containing functional groups in the planes or edges of the graphene oxide is utilized to weaken the van der Waals force between the sheet layers, so that the aim of stable dispersion can be fulfilled.

At present, there are three main systems for dispersing graphene: (1) an aqueous surfactant solution; (2) an organic solvent; (3) super acid. However, the concentration of the graphene dispersion obtained by using the surfactant in the aqueous solution is low, and the highest value reported in the literature at present is only 0.3 mg/ml; the organic solvent can obtain a graphene dispersion liquid with higher concentration, and the highest concentration can reach 1.2mg/ml, but the organic solvent has high cost and high boiling point, is not easy to remove, and influences the subsequent application of graphene; the graphene dispersion liquid (2mg/ml) with the highest concentration at present can be obtained in a superacid system, but the system has strong acidity, high requirements on equipment and difficult control of the operation process, and is difficult to expand to other applications. If a dispersion of high-concentration graphene can be obtained in an aqueous solution system, the wide application of graphene in various fields can be certainly promoted, which is an important subject in the field of graphene research.

Accordingly, the prior art is yet to be improved and developed.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a preparation method of a graphene dispersion liquid, and aims to solve the problem that the existing method has the limitation of being too complicated and expensive in large-scale production.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a preparation method of a graphene dispersion liquid comprises the following steps:

providing carboxylated graphene, wherein the carboxylated graphene means that the edge of the graphene has carboxyl;

performing amino modification treatment on the carboxylated graphene to enable amino to replace partial carboxyl at the edge of the graphene, so as to obtain aminated graphene;

and dissolving the aminated graphene in water, mixing with a graphene oxide solution, and adjusting the pH value to obtain a graphene dispersion liquid.

Optionally, the preparation method of the carboxylated graphene comprises the following steps:

and putting graphite, dry ice and grinding balls into a ball milling tank, and carrying out ball milling to obtain the carboxylated graphene.

Optionally, in the step of placing graphite, dry ice and grinding balls into a ball milling tank, the mass ratio of the graphite to the dry ice is 5:100 to 5: 1000.

Optionally, the process parameters of the ball milling are as follows: the rotation speed of the ball milling tank is set to be 200-.

Optionally, after obtaining the carboxylated graphene, the method further includes the steps of: and adding the carboxylated graphene into acid for acid washing.

Optionally, the method for performing amino modification treatment on the carboxylated graphene to replace a part of carboxyl groups on the edge of the graphene with amino groups includes the steps of: mixing the carboxylated graphene, ethylene glycol and ammonia water, and carrying out hydrothermal reaction for 1-18h at the temperature of 100-180 ℃.

Optionally, by weight, 1-99 parts of carboxylated graphene, 10-70 parts of ethylene glycol and 5-50 parts of ammonia water.

Optionally, the mass ratio of the aminated graphene to graphene oxide is 1:1 to 100: 1.

Optionally, the pH is adjusted to 4-13.

Optionally, the mass concentration of the graphene dispersion liquid is 1-50%.

Has the advantages that: the invention provides a preparation method of a graphene dispersion liquid with good stability, low cost and no pollution. The aminated graphene (NG) to be produced is dissolved in water, and the dispersion uniformity of the graphene dispersion liquid can be controlled and the concentration of the graphene dispersion liquid can be adjusted by adding a Graphene Oxide (GO) solution and adjusting the pH value of the solution. The graphene dispersion liquid prepared by the method has ultrahigh stability and keeps higher conductivity.

Drawings

Fig. 1 is a mechanism diagram of formation of aminated graphene by amino modification of carboxylated graphene;

FIG. 2 is a morphological characterization of graphene dispersion under acidic conditions;

fig. 3 is a morphological characterization of graphene dispersion under alkaline conditions.

Detailed Description

In order to make the objects, technical solutions and effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The existing research methods for producing high-concentration graphene dispersion liquid by scholars at home and abroad have the limitations of difficult technology, complicated and expensive large-scale production, and the development of a novel, efficient and low-cost dispersion method is an important problem to be urgently solved for realizing the large-scale application of graphene.

Accordingly, the embodiment of the invention provides a preparation method of a graphene dispersion liquid, which comprises the following steps:

s1, providing carboxylated graphene, wherein the carboxylated graphene means that the edge of the graphene has a carboxyl group;

s2, performing amino modification treatment on the carboxylated graphene to enable amino to replace partial carboxyl on the edge of the graphene, and obtaining the aminated graphene;

s3, dissolving the aminated graphene in water, mixing with a graphene oxide solution, and adjusting the pH value to obtain the graphene dispersion liquid.

The embodiment provides a preparation method of a graphene dispersion liquid with good stability, low cost and no pollution, which includes the steps of firstly carrying carboxyl on edges of graphene to obtain carboxylated graphene, and then carrying out amino modification treatment on the carboxylated graphene to enable the amino to replace part of the carboxyl on the edges of the graphene to form the aminated graphene. The aminated graphene (NG) to be produced is dissolved in water, and the dispersion uniformity of the graphene dispersion liquid can be controlled and the concentration of the graphene dispersion liquid can be adjusted by adding a Graphene Oxide (GO) solution and adjusting the pH value of the solution. Under an acidic condition, carboxyl and amino at the edge of graphene are active, positive charges and negative charges at the edge of graphene are crossed with each other, and charged edges are stacked together to form small aggregates to be anchored on the surface of graphene oxide. Under the alkaline condition, the graphene oxide is negatively charged, only carboxyl groups at the edge of the graphene are active, hydrogen bonds at the edge of the graphene are combined with the graphene oxide, and the negatively charged end of the aminated graphene is repelled, so that a structure similar to a flaky structure is finally formed. The graphene dispersion liquid prepared by the embodiment has ultrahigh stability and keeps higher conductivity. The method of the embodiment is suitable for large-scale quantitative production, and has low production cost and no pollution.

In step S1, in one embodiment, the preparation method of carboxylated graphene includes the steps of:

and putting the graphite, the dry ice and the grinding balls (such as steel balls) into a ball milling tank (such as a planetary ball mill) for ball milling to obtain the carboxylated graphene.

The graphene is sp²The hybridized and connected carbon atoms are tightly stacked to form a new material with a single-layer two-dimensional honeycomb lattice structure, the graphene is graphite after being stacked, and the graphite with the thickness of 1 mm approximately comprises 300 ten thousand layers of graphene. During the high-speed ball milling process, carbon-carbon bonds between graphite sheets are opened, so that graphene is formed. During ball milling, dry ice serves as a carboxylation agent, and carboxyl functional groups can be added to the edges of graphene flakes.

Further, in the step of placing graphite, dry ice and grinding balls into a ball milling tank, the mass ratio of the graphite to the dry ice is 5: 100-5: 1000.

further, the technological parameters of the ball milling are as follows: the rotation speed of the ball milling tank is set to be 200-.

Further, after obtaining the carboxylated graphene, the method further includes the steps of: and adding the carboxylated graphene into acid (such as hydrochloric acid and the like) for acid washing for later use. The concentration of the carboxylated graphene is 1mol/L based on a system formed by the carboxylated graphene and acid, so that the graphene is not excessively influenced. In this embodiment, the acidity is used to remove oxides on the surface of the graphene, and at the same time, it is ensured that the graphene is not excessively affected.

In an embodiment, in step S2, the method for performing amino modification treatment on the carboxylated graphene to replace a part of the carboxyl groups on the edge of the graphene includes: mixing the carboxylated graphene, ethylene glycol and ammonia water, and carrying out hydrothermal reaction for 1-18h at the temperature of 100-180 ℃. Specifically, the carboxylated graphene, ethylene glycol and ammonia water can be mixed in an autoclave, heated to 180 ℃ through a muffle furnace, and kept for 18 hours.

In this embodiment, the carboxylated graphene is aminated through a hydrothermal reaction, which is characterized in that amino groups are nucleophilic substituted for hydroxyl groups and epoxy groups. Namely, ammonia is used as a ring-opening agent of an epoxy compound, primary amine and alcohol are formed by nucleophilic substitution, and the mechanism is shown in FIG. 1.

Further, by weight, 1-99 parts of carboxylated graphene, 10-70 parts of ethylene glycol and 5-50 parts of ammonia water.

In step S3, the aminated graphene (NG) is dissolved in water, and a graphene dispersion liquid with a desired concentration is prepared by adding an appropriate amount of Graphene Oxide (GO) solution and adjusting the pH value of the solution. Under an acidic condition, carboxyl and amino at the edge of graphene are active, positive charges and negative charges at the edge of graphene are crossed with each other, and charged edges are stacked together to form small aggregates to be anchored on the surface of graphene oxide. Under an alkaline condition, graphene oxide is negatively charged, only carboxyl groups on the edge of the graphene are active, hydrogen bonds on the edge of the graphene are combined with the graphene oxide, and the end, with the negative charge, of the aminated graphene is repelled, so that a structure similar to a flake structure is finally formed.

Experiments show that compared with the existing graphene aqueous solution, the graphene dispersion liquid in the embodiment has uniform particles, high viscosity and slow settling speed, and the graphene aqueous solution particles are agglomerated and have high settling speed. The mass concentration of the graphene dispersion liquid in this embodiment may be 2% to 50%.

Through a comparison test, the ratio of the NG to the GO required by the graphene dispersion liquid to be uniformly dispersed and the pH value are finally determined by changing the ratio of the GO solution and adjusting the pH value. Further, the mass ratio of the aminated graphene to the graphene oxide is 1:1 to 100: 1. Further, the pH is adjusted to 4-13.

The invention is further illustrated by the following specific examples.

Example 1

The preparation method of the graphene dispersion liquid of the embodiment includes the following steps:

putting 10g of graphite, 100g of dry ice and 2000g of 3mm steel ball into a planetary ball mill for ball milling; the ball milling speed is 400rmp, and the ball milling time is 20 hours, so that the carboxylated graphene is obtained.

And adding 10g of carboxylated graphene into 100mL of hydrochloric acid for acid washing for later use.

And mixing 1g of carboxylated graphene after acid washing, 10g of ethylene glycol and 50ml of concentrated ammonia water, and carrying out hydrothermal reaction at 180 ℃ for 18h to obtain aminated graphene.

1g of aminated graphene is dissolved in water, 5ml of graphene oxide solution (concentration of 1mg/ml) is added, and the pH value of the solution is adjusted to 4, so that graphene dispersion liquid is obtained.

Fig. 2 is a morphology characterization of the graphene dispersion under an acidic condition, the graphene dispersion has a relatively high viscosity, and an obvious 3D composite structure can be observed under an electron microscope, and the graphene dispersion under the acidic condition is in a gel state due to the structure.

Example 2

1g of aminated graphene is dissolved in water, 5ml of graphene oxide solution (concentration of 1mg/ml) is added, and the pH value of the solution is adjusted to 10, so as to obtain a graphene dispersion liquid.

Fig. 3 is a morphological characterization of a graphene dispersion liquid under an alkaline condition, the dispersion liquid has a low viscosity, graphene oxide can be observed to be in a lamellar shape under an electron microscope, and aminated graphene is attached to a lamellar structure of the graphene oxide to form a structure like a snake-scale shape.

Example 3

The graphene dispersion liquid prepared in the example 2 is used as a conductive agent to be matched with nano silicon powder and a binder according to a certain proportion to prepare the silicon-carbon negative electrode material of the lithium ion battery.

1. Preparing nano silicon powder: conductive agent: the adhesive is prepared according to the following steps of 6: 2: 2, mixing in a subpackage bottle, adding magnetons, and stirring for 24 hours. The stirred mixture was poured into a mortar and heated to be stirred until viscous.

2. The slurry with the viscous stirring was coated on a copper foil current collector using a coater with a coating thickness controlled to 13 μm, and after the coating was completed, it was dried in a vacuum drying oven at 110 ℃ for 12 hours.

3. The large pole pieces obtained in step 2 were cut into small circular pole pieces on a microtome using a 12mm diameter die, and the weight of each pole piece was weighed and recorded, while the mass of the small discs without the slurry applied was recorded.

And (3) placing the weighed polar plate in a small muffle furnace in an Ar atmosphere glove box, heating to 110 ℃, preserving heat for 1h, and cooling for later use.

And (3) assembling the button cell according to the sequence of the positive electrode shell, the positive electrode plate, the diaphragm, the lithium plate, the gasket and the negative electrode shell, dripping 1-3 drops of electrolyte between every two layers, wherein the electrolyte contained in each cell is not more than 1 mu l.

Example 4

The graphene dispersion liquid prepared in example 2 was added to the gel as a conductive agent to prepare a conductive gel.

The conductivity was measured with four probes, and the resistance was measured to be 123 Ω. The gel was found to have some electrical conductivity.

In summary, the invention provides a preparation method of a graphene dispersion liquid. In the preparation process, dry ice ball milling is adopted to ball mill graphite, so that the obtained graphene is provided with carboxyl on the edge to obtain carboxylated graphene, and then amination treatment is carried out on the carboxylated graphene to obtain aminated graphene. The aminated graphene and the graphene oxide are mixed according to a certain proportion, the dispersion uniformity of the graphene dispersion liquid can be controlled by adjusting the pH, and meanwhile, the concentration of the graphene dispersion liquid can be adjusted. The graphene dispersion liquid prepared by the method has ultrahigh stability and keeps higher conductivity. The method is suitable for large-scale quantitative production, and has low production cost and no pollution.

It will be understood that the invention is not limited to the examples described above, but that modifications and variations will occur to those skilled in the art in light of the above teachings, and that all such modifications and variations are considered to be within the scope of the invention as defined by the appended claims.

Claims

1. A preparation method of a graphene dispersion liquid is characterized by comprising the following steps:

performing amino modification treatment on the carboxylated graphene to enable amino to replace partial carboxyl on the edge of the graphene, so as to obtain the aminated graphene;

2. The method for preparing a graphene dispersion according to claim 1, wherein the method for preparing carboxylated graphene comprises the steps of:

and putting the graphite, the dry ice and the grinding balls into a ball milling tank, and carrying out ball milling to obtain the carboxylated graphene.

3. The preparation method of the graphene dispersion liquid according to claim 2, wherein in the step of placing graphite, dry ice and grinding balls into a ball milling tank, the mass ratio of the graphite to the dry ice is 5:100 to 5: 1000.

4. the preparation method of the graphene dispersion liquid according to claim 2, wherein the ball milling process parameters are as follows: the rotation speed of the ball milling tank is set to be 200-.

5. The method for preparing a graphene dispersion according to claim 2, further comprising, after obtaining the carboxylated graphene, the steps of: and adding the carboxylated graphene into acid for acid washing.

6. The method for preparing the graphene dispersion liquid according to claim 1, wherein the method for performing amino modification treatment on the carboxylated graphene to replace a part of carboxyl groups on the edge of the graphene with amino groups comprises the steps of: mixing the carboxylated graphene, ethylene glycol and ammonia water, and carrying out hydrothermal reaction for 1-18h at the temperature of 100-180 ℃.

7. The method for preparing a graphene dispersion liquid according to claim 6, wherein the carboxylated graphene is 1 to 99 parts by weight, the ethylene glycol is 10 to 70 parts by weight, and the ammonia water is 5 to 50 parts by weight.

8. The method for preparing a graphene dispersion liquid according to claim 1, wherein the mass ratio of the aminated graphene to the graphene oxide is 1:1 to 100: 1.

9. The method for producing a graphene dispersion liquid according to claim 1, wherein the pH is adjusted to 4 to 13.

10. The method for preparing the graphene dispersion liquid according to claim 1, wherein the graphene dispersion liquid has a mass concentration of 1% to 50%.