CN111892044A

CN111892044A - Method for large-scale preparation of graphene powder

Info

Publication number: CN111892044A
Application number: CN202010885206.2A
Authority: CN
Inventors: 胡国荣; 杜柯; 彭忠东; 曹雁冰; 王永志
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2020-11-06
Anticipated expiration: 2040-08-28
Also published as: CN111892044B

Abstract

The invention discloses a method for preparing graphene powder on a large scale, which comprises the following steps: 1) adding graphite powder, an oxidant and strong acid into a hydrothermal kettle, stirring and mixing uniformly, and carrying out oxidation stripping reaction at a certain temperature to form graphene oxide; 2) continuously heating the hydrothermal kettle for forming the graphene oxide to a pre-reduction temperature for hydrothermal pre-reduction reaction to form partially reduced graphene oxide; 3) filtering the pre-reduced reaction solution, recovering sulfuric acid from the filtrate, washing and drying the filter residue to obtain partially reduced graphene oxide powder; 4) and carrying out reduction reaction on the partially reduced graphene oxide powder in an inert atmosphere to obtain graphene. The process of the invention has closed reaction and low requirement on temperature control; the sulfuric acid can be recovered after the hydrothermal reaction, so that the method is more environment-friendly; the product after sulfuric acid recovery can be directly and rapidly filtered and washed, so that the problem that graphene oxide is difficult to filter and wash is solved, and the preparation efficiency of graphene is improved.

Description

Method for large-scale preparation of graphene powder

Technical Field

The invention belongs to the technical field of carbon materials, and particularly relates to a method for preparing graphene powder on a large scale.

Background

Graphene is used as a novel carbon nano material, and the unique single-layer two-dimensional honeycomb structure of graphene brings unique performances such as extremely high electron mobility, extremely high thermal conductivity, extremely large specific surface area and extremely high mechanical strength. The excellent performances determine that the graphene has wide application in various fields such as photoelectric devices, energy storage and conversion, composite materials, functional materials and the like.

Since the discovery in 2004, researchers have developed various methods for preparing graphene, such as micro-mechanical lift-off, liquid phase lift-off, redox, epitaxial growth, chemical vapor deposition, and the like. Among them, the redox method is considered as an important method having the most potential for realizing the industrial production of graphene. And the precursor graphene oxide is the key for preparing the graphene. At present, the preparation of graphene oxide is mainly based on a Hummers method. The method takes potassium permanganate and strong acid as oxidant and intercalation agent, and Mn which is easy to explode is generated in the reaction process₂O₇The requirement for temperature control is extremely high. Waste acid containing heavy metal ions is generated in the purification process of the graphene oxide solution, and pressure is brought to environmental protection. Due to the fact that rich oxygen-containing functional groups exist on the surface of the graphene oxide, the graphene oxide can swell when meeting water, and great inconvenience is brought to a washing process. Therefore, the problem of green, safe and rapid production of graphene oxide is a problem to be solved urgently for large-scale preparation of graphene.

Disclosure of Invention

The invention aims to provide a method for preparing graphene powder safely, environmentally and rapidly in a large scale.

The method for preparing the graphene powder on a large scale comprises the following steps:

1) preparing graphene oxide: adding graphite powder, an oxidant and strong acid into a hydrothermal kettle, stirring and mixing uniformly, and carrying out oxidation stripping reaction at a certain temperature to form graphene oxide;

2) pre-reduction of graphene oxide: continuously heating the hydrothermal kettle which forms the graphene oxide in the step 1) to a pre-reduction temperature for hydrothermal pre-reduction reaction to form partially reduced graphene oxide;

3) pre-reducing graphene oxide solution: filtering the reaction solution pre-reduced in the step 2), recovering sulfuric acid from filtrate, and washing and drying filter residues to obtain partially reduced graphene oxide powder;

4) preparing graphene powder: carrying out reduction reaction on the partially reduced graphene oxide powder in the step 3) in an inert atmosphere to obtain graphene.

In the step (1), the graphite is selected from one or more of natural crystalline flake graphite, expanded graphite, highly oriented pyrolytic graphite and artificial graphite; the oxidant is selected from potassium permanganate, potassium ferrate, potassium dichromate and sodium dichromate; the strong acid is selected from concentrated sulfuric acid, concentrated phosphoric acid, concentrated nitric acid or a mixed acid thereof; the mass ratio of the graphite to the oxidant is 1 (1-3), and the mass fraction of the strong acid is 90-98%; the mass-volume ratio of the graphite to the strong acid is 1 (20-40) g/mL; the temperature of the oxidation stripping reaction is 35-100 ℃; the time is 1-5 h.

In the step (2), the hydrothermal pre-reduction temperature is 150-220 ℃; the time is 1-5 h.

In the step (4), the high-temperature thermal reduction temperature is 550-900 ℃; the time is 1-10 h; the inert atmosphere is nitrogen or argon.

The principle of the invention is as follows:

in the process of preparing graphene by adopting hydrothermal reaction, after the oxidation stripping reaction is finished, a large amount of-OH bonds, C-O bonds and double bonds are generated, so that the hydrophilicity of the graphene oxide is very strong, and finally the obtained reaction solution is in a gel state. According to the invention, a pre-reduction reaction step is added on the basis of a hydrothermal reaction method, in the pre-reduction process, part of graphene oxide is reduced, a large number of hydrophilic bonds are reduced, and finally, a solution with obvious solid-liquid separation is obtained, and the rapid separation can be realized by a common filtration method.

The invention has the beneficial effects that:

the process is green, safe, simple, convenient and efficient, saves time and labor, and is easy to realize large-scale production. Compared with the traditional Hummers method, the process has the advantages of closed reaction, low temperature control requirement, safety and high efficiency; the sulfuric acid can be recovered after the hydrothermal reaction, so that the method is more environment-friendly; the product after sulfuric acid recovery can be directly and rapidly filtered and washed, so that the problem that graphene oxide is difficult to filter and wash is solved, and the preparation efficiency of graphene is improved. According to the invention, the traditional graphene oxide purification process such as centrifugation and dialysis does not need complicated steps, water consumption, time consumption and energy consumption, and the prepared pre-reduced graphene oxide has weak hydrophilicity, can be directly dried and cannot agglomerate.

Drawings

FIG. 1 SEM image of graphene prepared in example 1 of the present invention

FIG. 2 TEM image of graphene prepared in example 1 of the present invention

FIG. 3 is a graph comparing pre-reduced graphene oxide prepared in example 1 of the present invention with a graphene oxide solution without pre-reduction

Detailed Description

Example 1:

the method comprises the following steps of taking crystalline flake graphite, potassium permanganate and sulfuric acid as raw materials (wherein the mass ratio of the crystalline flake graphite to the potassium permanganate is 1:3, the mass fraction of the sulfuric acid is 98%, and the mass volume ratio of the crystalline flake graphite to the sulfuric acid is 1:30g/mL), placing the raw materials in a reaction kettle, carrying out hydrothermal reaction for 1h at 100 ℃, and then continuing the hydrothermal prereduction reaction for 3h at 180 ℃. After the reaction is finished, the reaction liquid is filtered to separate sulfuric acid, and filter cakes are diluted by water and then are filtered and washed. And drying the washing product in an oven at 60 ℃ for 12h to obtain the pre-reduced graphene oxide.

And (3) placing the pre-reduced graphene oxide in an argon atmosphere, and preserving heat at 900 ℃ for 5 hours to obtain graphene powder. SEM and TEM detection are carried out on the graphene powder, as shown in the attached drawings 1 and 2 respectively, the obvious fold morphology structure of the graphene can be seen, and the morphology of the graphene is consistent with the microstructure of the graphene prepared by the traditional method.

The reaction solution after the pre-reduction in example 1 was bottled in a clear glass bottle, and after standing for 10 minutes, as shown in the left bottle in FIG. 3, hydrothermal reaction occurred without pre-reduction, and the reaction solution obtained was bottled in a clear glass bottle and after standing for 10 minutes, as shown in the right bottle in FIG. 3. From the comparison of the two, the solution is obviously layered after the pre-reduction reaction is carried out, while the solution is gelatinous and is not layered when the pre-reduction reaction is not carried out, so that the filterability of the reaction solution can be obviously improved by the pre-reduction reaction.

Example 2:

the method comprises the following steps of taking crystalline flake graphite, potassium permanganate and sulfuric acid as raw materials (wherein the mass ratio of the crystalline flake graphite to the potassium permanganate is 1:2, the mass fraction of the sulfuric acid is 93%, and the mass volume ratio of the crystalline flake graphite to the sulfuric acid is 1:40g/mL), placing the raw materials in a reaction kettle, carrying out hydrothermal reaction for 1h at 80 ℃, and then heating to 150 ℃ to continue the hydrothermal prereduction reaction for 3 h. After the reaction is finished, the reaction liquid is filtered to separate sulfuric acid, and filter cakes are diluted by water and then are filtered and washed. And drying the washing product in an oven at 60 ℃ for 12h to obtain the pre-reduced graphene oxide.

And (3) placing the pre-reduced graphene oxide in an argon atmosphere, and preserving heat for 2h at 700 ℃ to obtain graphene powder.

Example 3:

the method comprises the steps of taking crystalline flake graphite, potassium permanganate, sulfuric acid and phosphoric acid as raw materials (wherein the mass ratio of the crystalline flake graphite to the potassium permanganate is 1:3, the mass fraction of the sulfuric acid is 98%, the concentration of the phosphoric acid is 85%, the volume ratio of the sulfuric acid to the phosphoric acid is 9:1, and the mass volume ratio of the crystalline flake graphite to mixed acid is 1:40g/mL), placing the raw materials in a reaction kettle, carrying out hydrothermal reaction for 1.5h at 60 ℃, and then heating to 200 ℃ to continue the hydrothermal prereduction reaction for 3 h. After the reaction is finished, filtering and separating the reaction liquid to obtain mixed acid, and filtering and washing after the filter cake is diluted by adding water. And drying the washing product in an oven at 60 ℃ for 12h to obtain the pre-reduced graphene oxide.

And (3) placing the pre-reduced graphene oxide in an argon atmosphere, and preserving heat for 4 hours at 600 ℃ to obtain graphene powder.

Claims

1. A method for preparing graphene powder on a large scale comprises the following steps:

2. The method for preparing graphene powder on a large scale according to claim 1, wherein in the step (1), the graphite is selected from one or more of natural crystalline flake graphite, expanded graphite, highly oriented pyrolytic graphite and artificial graphite; the oxidant is selected from potassium permanganate, potassium ferrate, potassium dichromate and sodium dichromate; the strong acid is selected from concentrated sulfuric acid, concentrated phosphoric acid, concentrated nitric acid or a mixed acid thereof.

3. The method for preparing the graphene powder on a large scale according to claim 1, wherein in the step (1), the mass ratio of the graphite to the oxidant is 1 (1-3), and the concentration of the strong acid is 90-98%; the mass-to-volume ratio of the graphite to the strong acid is 1 (20-40) g/mL.

4. The method for preparing graphene powder on a large scale according to claim 1, wherein in the step (1), the temperature of the oxidation stripping reaction is 35-100 ℃; the time is 1-5 h.

5. The method for preparing graphene powder on a large scale according to claim 1, wherein in the step (2), the hydrothermal pre-reduction temperature is 150-220 ℃; the time is 1-5 h.

6. The method for preparing graphene powder on a large scale according to claim 1, wherein in the step (4), the high-temperature thermal reduction temperature is 550-900 ℃; the time is 1-10 h; the inert atmosphere is nitrogen or argon.