CN115072712A

CN115072712A - Graphene with large sheet diameter and high conductivity and preparation method thereof

Info

Publication number: CN115072712A
Application number: CN202210705268.XA
Authority: CN
Inventors: 孙红娟; 王娅; 彭同江; 刘波
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2022-06-21
Filing date: 2022-06-21
Publication date: 2022-09-20

Abstract

The invention provides graphene with large sheet diameter and high conductivity and a preparation method thereof, wherein the preparation method comprises the following steps: mixing graphite, concentrated sulfuric acid and an expanding agent according to the proportion of 1: 3-12: adding 10-30 g/ml/g of the mixture into a reaction container, and uniformly stirring and mixing to obtain a fluffy graphite mixture containing concentrated sulfuric acid and an expanding agent; statically expanding and reacting the fluffy graphite mixture at a preset temperature for a preset time to obtain crude high-expansion-rate expanded graphite; adding a stripping aid into the rough high-expansion-rate expanded graphite, and carrying out stripping treatment to obtain a rough large-sheet-diameter graphene suspension; settling and separating the rough large-sheet-diameter graphene suspension to obtain a refined large-sheet-diameter graphene dispersion liquid; and filtering, washing and drying the large-sheet-diameter refined graphene dispersion liquid to obtain the large-sheet-diameter high-conductivity graphene. The preparation method has the advantages of simple and convenient preparation process flow, mild reaction, low energy consumption, environmental protection, large sheet diameter of the prepared graphene, excellent conductivity and the like.

Description

Graphene with large sheet diameter and high conductivity and preparation method thereof

Technical Field

The invention relates to the technical field of graphene material preparation, in particular to graphene with large sheet diameter and high conductivity and a preparation method thereof.

Background

Graphene is a material with sp between carbon atoms ² The two-dimensional atomic crystal has a honeycomb-shaped hexagonal honeycomb lattice structure and is in hybrid connection with the hexagonal honeycomb lattice structure. Currently, the most widely used method for preparing graphene is a redox method, or an expanded graphite exfoliation method, which is also a redox method that is substantially oxidized, then exfoliated through an expansion and reduction process. In the redox method, oxygen-containing functional groups are formed in the structure of graphite in the oxidation process, and carbon atoms are lost while the graphite is removed in the reduction process, so that the structure of the prepared graphene is damaged, and the performance, particularly the conductivity, is influenced. Compared with a redox method, the graphene prepared by the graphite expansion and stripping method has a more complete structure and inevitably has more excellent electric conduction, heat conduction, mechanical properties and the like, and the excellent properties enable the graphene material to have wider application and application prospect.

Graphite is a typical layered structure mineral, and atoms all adopt sp ² The hybrid orbit and three adjacent carbon atoms form sigma bonds to form a structural layer in hexagonal network annular arrangement, and the structural layers are combined by Van der Waals force. P in graphite layer _z The interaction of orbital electrons forms delocalized big pi bonds, and pi bond electrons are very active and can freely move in the layer, so that the graphite has good electrical conductivity and thermal conductivity. Meanwhile, the graphite has good chemical stability at normal temperature and is not corroded by any strong acid, strong base and organic solvent, so that the graphite product has chemical stability and anti-corrosion capability. Due to weak interlayer force and chemical activity of pi electrons, chemical substances can enter the graphite interlayer under certain conditions, and graphene can be prepared through an expansion-stripping process.

At present, although scholars at home and abroad carry out a great deal of research work on the preparation of graphene and propose various preparation methods, the following problems still exist: introducing a large amount of oxygen-containing functional groups in the process of producing graphene by a redox method to destroy the structure of the graphene; the expanded graphite produced in an industrialized way mostly adopts high-temperature expansion or microwave expansion, the process is complex, the energy consumption is high, the environmental hazard is large, the water consumption in the cleaning process of the expandable graphite is large, the expansion is not uniform, the stripping process damages the graphene structure, and the like.

Disclosure of Invention

The present invention aims to address at least one of the above-mentioned deficiencies of the prior art. For example, one of the purposes of the present invention is to provide a preparation method of graphene with large sheet size and high conductivity, which has the advantages of simple preparation process, mild reaction, low energy consumption and environmental protection. Another object of the present invention is to provide graphene having a low structural failure, few defects, a larger sheet diameter, and excellent electrical properties.

In order to achieve the above object, an aspect of the present invention provides a method for preparing graphene having a large sheet size and high conductivity, the method comprising the steps of:

mixing graphite, concentrated sulfuric acid and an expanding agent according to the proportion of 1: 3-12: adding 10-30 g/ml/g of the mixture into a reaction container, and uniformly stirring and mixing to obtain a fluffy graphite mixture containing concentrated sulfuric acid and an expanding agent;

statically expanding and reacting the fluffy graphite mixture at a preset temperature for a preset time to obtain crude high-expansion-rate expanded graphite;

adding a stripping aid into the rough high-expansion-rate expanded graphite, and carrying out stripping treatment to obtain a rough large-sheet-diameter graphene suspension;

settling and separating the rough large-sheet-diameter graphene suspension to obtain a refined large-sheet-diameter graphene dispersion liquid;

and filtering, washing and drying the large-sheet-diameter refined graphene dispersion liquid to obtain the large-sheet-diameter high-conductivity graphene.

In an exemplary embodiment of an aspect of the present invention, the feeding of the graphite, the concentrated sulfuric acid, and the swelling agent into the reaction vessel may include: firstly adding graphite or concentrated sulfuric acid, and then adding an expanding agent while stirring; the stirring speed can be 300-1000 r/min, and the stirring time can be 2-20 min.

In an exemplary embodiment of an aspect of the present invention, the predetermined temperature may be 20 to 90 ℃, and the predetermined time may be 1 to 24 hours;

the obtained high-expansion-rate expanded graphite can be vermiform, and the expansion volume can be 100-550 mL/g.

In one exemplary embodiment of an aspect of the present invention, the stripping aid may be one or more of sodium percarbonate, ammonium bicarbonate and concentrated sulfuric acid;

the equipment used for the stripping treatment can comprise a high-speed mechanical stirrer, an ultrasonic disperser or a high-speed dispersing homogenizer;

the time of the stripping treatment can be 1-12 h.

In an exemplary embodiment of an aspect of the present invention, the settling separation may be performed in a centrifuge, the centrifuge rotation speed may be 3000 to 8000rpm, the centrifuge time may be 3 to 10min, and the solid content of the refined large-sheet-diameter graphene dispersion may be 55 to 85%.

In an exemplary embodiment of an aspect of the present invention, the graphene may have a sheet diameter of 5 to 25 μm and a content of graphene having a sheet diameter greater than 10 μm in the total graphene may be 70% or more, and the conductivity of the graphene may be 3.42 × 10 ² ～1.25×10 ⁵ S/m, the graphene yield can be 50-90%.

In an exemplary embodiment of an aspect of the present invention, the number of graphene layers may be 1 to 10, wherein the content of the few-layer graphene may be more than 75%.

In an exemplary embodiment of an aspect of the present invention, the graphite raw material may be 50-100 mesh flake powder, and the carbon content in the graphite may be up to 85% or more;

the expanding agent can be one or more of sodium percarbonate and ammonium bicarbonate.

In another aspect, the present invention provides graphene having a large sheet diameter and high conductivity, which is prepared by the preparation method as described in any one of the above.

In an exemplary embodiment of another aspect of the present invention, the graphene may have a sheet diameter of 5 to 25 μm and a content of graphene having a sheet diameter greater than 10 μm in the total graphene may be 70% or more, and the graphene may have an electrical conductivity of 3.42 × 10 ² ～1.25×10 ⁵ S/m。

Compared with the prior art, the beneficial effects of the invention can comprise at least one of the following:

(1) the preparation process, the high-temperature expansion process and the corresponding process links of the non-oxidized intercalated expandable graphite directly realize the primary expansion to obtain the expandable graphite, and the expandable graphite has good expansion effect and is easy to strip;

(2) the preparation process of the graphene is simple in flow, low in production energy consumption, mild in reaction process, free of harmful gas and easy in control of process conditions;

(3) the sodium percarbonate serving as an expansion stripping auxiliary agent can generate a large amount of gas to enable graphite to be expanded and stripped, cannot oxidize the graphite, reduces the structural damage degree of the graphite, and improves the expansion stripping effect;

(4) the obtained graphene material has the advantages of lower structural damage degree, fewer defects, more perfect structure, larger sheet diameter, more excellent electrical property and easier popularization and application;

(5) the conductivity of the graphene prepared by the conventional oxidation-reduction method is usually 5.2 × 10 ^-2 12.6S/m, which is obviously smaller than the conductivity of the graphene prepared by the invention.

Drawings

FIG. 1 is a Raman spectrum of raw graphite;

FIG. 2 is a scanning electron micrograph of raw graphite;

fig. 3 is a raman spectrum of graphene prepared in example 1;

fig. 4 is a scanning electron micrograph of graphene prepared in example 1;

fig. 5 is a raman spectrum of graphene prepared in example 2;

FIG. 6 is a scanning electron micrograph of the expanded graphite prepared in example 2;

fig. 7 is a scanning electron micrograph of graphene prepared in example 2;

fig. 8 is a raman spectrum of graphene prepared in example 3;

fig. 9 is a scanning electron micrograph of graphene prepared in example 3.

Detailed Description

Hereinafter, the graphene having a large sheet diameter and high conductivity and the method for preparing the same according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

In a first exemplary embodiment of the present invention, a method for preparing graphene having a large sheet diameter and high conductivity, the method comprising the steps of:

the first step is as follows: mixing graphite, concentrated sulfuric acid and an expanding agent according to the proportion of 1: 3-12: and adding 10-30 g/ml/g of the mixture into a reaction container, and uniformly stirring and mixing to obtain a fluffy graphite mixture containing concentrated sulfuric acid and an expanding agent. Here, the reaction vessel may be an acid-resistant reaction vessel with a high-speed mechanical stirring and heating device and an attachment for a high-speed dispersion homogenizer. g/ml/g represents graphite in g, concentrated sulfuric acid in ml, and swelling agent in g.

The second step is that: and (3) carrying out static expansion reaction on the fluffy graphite mixture obtained in the first step at a preset temperature for a preset time to obtain the crude high-expansion-rate expanded graphite. Here, the temperature of the static expansion may be 20 to 90 ℃, for example, 25 ℃, 40 ℃, 50 ℃, 60 ℃, 80 ℃. The static expansion time can be 1-24 h, for example, 2h, 4h, 8h, 12h, 14h, 18h, 20 h. Specifically, a certain amount of expanding agent is taken, a small amount of expanding agent is slowly added into a mixture of flake graphite and concentrated sulfuric acid (namely, a fluffy graphite mixture in the first step) for many times, the mixture is continuously stirred in the adding process, and after the mixture is uniformly mixed, the system is controlled to stand and react for a period of time under a certain temperature condition, so that the rough expanded graphite with high expansion rate is directly obtained. Wherein, the mass ratio of the graphite to the expanding agent can be 1: 3 to 12, for example 1: 5. 1: 8. 1: 10. 1: 11. wherein, the expanding agent can be one or more of sodium percarbonate and ammonium bicarbonate. For example, the expansion agent is sodium percarbonate.

The third step: and (3) adding a stripping aid into the rough high-expansion-rate expanded graphite prepared in the second step, and carrying out stripping treatment to obtain a rough large-sheet-diameter graphene suspension. Here, the temperature at the time of the peeling treatment may be 20 to 90 ℃, for example, 45 ℃. If the reaction temperature is too high, exfoliation may not be complete and damage may be caused to the graphene structure. The stripping time may be 1-12 h, for example 4 h. Here, the stripping aid may be one or more of sodium percarbonate, ammonium bicarbonate and concentrated sulfuric acid. For example, the stripping agent is sodium percarbonate and concentrated sulfuric acid, the adding ratio of the sodium percarbonate to the graphite to the expanding agent is 1: 0.5-1 g/g, and the adding ratio of the concentrated sulfuric acid in the third step to the adding of the concentrated sulfuric acid in the first step is 1: 2-5 ml/ml. The stripping treatment equipment can comprise a high-speed mechanical stirrer, an ultrasonic disperser or a high-speed dispersing homogenizer, and the stripping treatment time can be 1-12 h.

The fourth step: and settling and separating the rough large-sheet-diameter graphene suspension to obtain a refined large-sheet-diameter graphene dispersion liquid. And placing the obtained crude large-sheet-diameter graphene suspension in a centrifuge for sedimentation separation. Wherein the centrifugal speed is 3000-8000 rpm, such as 5000rmp, the centrifugal time is 3-10 min, such as 5min, and the solid content of the obtained refined large-sheet-diameter graphene dispersion liquid is 55-85%, such as 70%.

The fifth step: and filtering, washing and drying the large-sheet-diameter refined graphene dispersion liquid to obtain the large-sheet-diameter high-conductivity graphene. And filtering, washing and drying the obtained refined large-sheet-diameter graphene suspension to obtain large-sheet-diameter high-conductivity graphene. The graphene suspension liquid is washed to be nearly neutral, the generated waste liquid is neutralized by a calcareous raw material and then discharged after reaching the standard, and the precipitate is used as a building material raw material; and freeze drying for 48 hours to obtain the large-sheet-diameter high-conductivity graphene powder.

In the present exemplary embodiment, the adding of the graphite, the concentrated sulfuric acid, and the swelling agent into the reaction vessel may include: firstly adding graphite or concentrated sulfuric acid, and then adding an expanding agent while stirring; the stirring speed can be 300-1000 r/min, such as 500r/min, 700r/min, 900 r/min. The stirring time can be 2-20 min. The purpose of mixing graphite with concentrated sulfuric acid is to provide an acidic environment for the subsequent expansion process, and to react with the expanding agent to promote the expansion process. On the other hand, the graphite is acidified, so that the graphite edge is intercalated, and the graphite interlayer is easier to open.

Further, the obtained high expansion rate expanded graphite can be vermiform, and the expansion volume can be 100-550 mL/g.

In the exemplary embodiment, the settling separation can be performed in a centrifuge, the centrifuge rotation speed can be 3000-8000 rpm, the centrifuge time can be 3-10 min, and the solid content of the refined large-sheet-diameter graphene dispersion can be 55-85%.

In the exemplary embodiment, the graphene with the sheet diameter of 5-25 μm and the sheet diameter of more than 10 μm may be contained in the total graphene by more than 70%, and the conductivity of the graphene may be 3.42 × 10 ² ～1.25×10 ⁵ S/m, the graphene yield can be 50-90%.

In the exemplary embodiment, the number of graphene layers may be 1 to 10, and the content of the few-layer graphene (the number of graphene layers is less than or equal to 5) may be more than 75%. The graphene product has more excellent conductivity when the content of the few-layer graphene in the graphene product is higher, and has better application prospect in the field of subsequent preparation of the functionalized composite coating.

In the exemplary embodiment, the graphite raw material can be 50-100 mesh flake powder, and the carbon content in the graphite can reach more than 85%. Here, the larger the sheet diameter of graphite, the larger the expansion volume thereof; the carbon content of graphite affects its expansion effect, and too much impurities consume reagents during the reaction, thereby reducing the expansion volume.

In the second exemplary embodiment of the present invention, the graphene having a large sheet diameter and high conductivity may be prepared by the preparation method described in the first exemplary embodiment above.

In the exemplary embodiment, the graphene with the sheet diameter of 5-25 μm and the sheet diameter of more than 10 μm may be contained in the total graphene by more than 70%, and the conductivity of the graphene may be 3.42 × 10 ² ～1.25×10 ⁵ S/m。

FIG. 1 is a Raman spectrum of raw graphite; FIG. 2 is a scanning electron micrograph of raw graphite; fig. 3 is a raman spectrum of graphene prepared in example 1; fig. 4 is a scanning electron micrograph of graphene prepared in example 1; fig. 5 is a raman spectrum of graphene prepared in example 2; FIG. 6 is a scanning electron micrograph of the expanded graphite prepared in example 2; fig. 7 is a scanning electron micrograph of graphene prepared in example 2; fig. 8 is a raman spectrum of graphene prepared in example 3; fig. 9 is a scanning electron micrograph of graphene prepared in example 3. The abscissa in the raman spectrum represents the raman shift, i.e., the difference in the number of waves of the scattered light relative to the incident light, and the ordinate represents the photon count, i.e., the intensity of the scattered light.

For a better understanding of the invention, the following further illustrates the invention in connection with specific examples 1, 2, 3, but the invention is not limited to the following examples only.

Example 1

(1) 4mL of 98% concentrated sulfuric acid is poured into an acid-resistant reaction kettle with a stirring and heating device, 0.2g of 50-mesh graphite is weighed and added into the reaction kettle to be uniformly stirred.

(2) 0.8g of sodium percarbonate is weighed, slowly added into a reaction kettle and uniformly stirred, and the mixture is kept stand and reacts for 12 hours at normal temperature to obtain the crude high-expansion-rate expanded graphite.

(3) And after the expansion is finished, continuously adding 20mL of concentrated sulfuric acid and 2g of sodium percarbonate into the reaction kettle, uniformly mixing, and mechanically stirring at normal temperature for stripping reaction for 4 hours to obtain a rough large-sheet-diameter graphene suspension.

(4) And placing the obtained rough large-sheet-diameter graphene suspension in a centrifuge for sedimentation separation to obtain a refined large-sheet-diameter graphene dispersion liquid.

(5) And after the reaction is finished, taking ultrapure water to wash the reaction product to be neutral, filtering, and freeze-drying the product for 48 hours to obtain the large-sheet-diameter high-conductivity graphene powder.

FIG. 1 is a Raman spectrum of raw graphite; FIG. 2 is a scanning electron micrograph (200X) of the starting graphite. As can be seen from fig. 1 and 2, the raw material graphite has a dense layered structure and a smooth surface. Fig. 3 is a raman spectrum of the large-sheet-diameter highly conductive graphene prepared in example 1, and as can be seen from a comparison of fig. 1 and fig. 3, the raman spectrum of the graphene prepared in example 1 has a slightly enhanced D-peak intensity compared to that of the raw material graphite. FIG. 4 is a scanning electron micrograph (1.0KX) of graphene prepared in example 1, and it is found that, as compared with the raw graphite in FIG. 2, the graphite sheets were exfoliated to obtain graphene having a smaller number of layers, the number of graphene sheets having a diameter of 10 to 25 μm was about 76%, and the electrical conductivity was 5.27X 10 ⁴ S/m。

Example 2

(1) Same as in example 1.

(2) Weighing 1.6g of sodium percarbonate, slowly adding the sodium percarbonate into a reaction kettle, uniformly stirring, and standing in a constant-temperature water bath at 85 ℃ for reaction for 2 hours to obtain the expanded graphite.

(3) And after the expansion is finished, continuously adding 20mL of concentrated sulfuric acid and 2g of sodium percarbonate into the reaction kettle, uniformly mixing, and stirring in a constant-temperature water bath at 85 ℃ for stripping reaction for 4 hours to obtain a rough large-sheet-diameter graphene suspension.

Fig. 5 is a raman spectrum of the large-sheet-diameter high-conductivity graphene prepared in example 2, and compared with fig. 1, the prepared graphene has a complete structure and a low destruction degree. Fig. 6 is a scanning electron micrograph (100X) of an intermediate expanded graphite prepared in example 2. As can be seen from FIG. 6, the expanded graphite is in the form of loose worms, and the graphite sheets are bent to form irregular holes at the edges and increase the surface wrinkles of the sheets. This is because the decomposition of sodium percarbonate releases gas into the graphite layers, and the increased pressure of the gas generates thrust, overcoming the van der waals forces between the layers, causing the graphite to expand rapidly in the c-axis direction. Fig. 7 is a scanning electron micrograph (2.0KX) of the large-sheet-diameter highly conductive graphene prepared in example 2. As can be seen from fig. 7, the prepared graphene sample has reduced wrinkles, a smooth and flat surface, and is in the form of a transparent gauze. And part of samples are stacked, and the obtained sample is light and thin in sheet layer and few in layer number. The method proves that the expanded graphite is completely stripped into graphene, and the sodium percarbonate can effectively strip the expanded graphite in a strong acid environment. The graphene has the sheet diameter of 10-25 mu m accounting for about 80%, and the conductivity of 1.18 multiplied by 10 ⁵ S/m。

Example 3

(1) Same as in example 1.

(2) Weighing 2.4g of sodium percarbonate, slowly adding the sodium percarbonate into the reaction kettle, uniformly stirring, and standing at normal temperature for reaction for 12 hours to obtain the expanded graphite.

(3) And after the expansion is finished, continuously adding 20mL of concentrated sulfuric acid and 2g of sodium percarbonate into the reaction kettle, uniformly mixing, stirring at normal temperature, and carrying out stripping reaction for 4 hours to obtain a rough large-sheet-diameter graphene suspension.

Fig. 8 is a raman spectrum of large-sheet-diameter highly conductive graphene prepared in example 3. As can be seen from fig. 8, the destruction degree of the graphene structure is low. Fig. 9 is a scanning electron micrograph (2.0KX) of the large-sheet-diameter high-conductivity graphene prepared in example 3, and compared with fig. 7, the obtained graphene has a difference in the thickness of the sheet layer and the size of the sheet diameter, because the difference in the degree of expansion at the previous stage causes the difference in the peeling effect. It can be seen that the larger the expansion volume of the precursor expanded graphite, the thinner the graphene sheet layer obtained by exfoliation and the larger the sheet diameter. The obtained graphene has the number of the sheet diameter of 10-25 mu m accounting for 83 percent and the conductivity of 6.59 multiplied by 10 ⁴ S/m。

In summary, the beneficial effects of the present invention can include at least one of the following:

While the present invention has been described above in connection with the accompanying drawings and exemplary embodiments, it will be apparent to those of ordinary skill in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A preparation method of graphene with large sheet diameter and high conductivity is characterized by comprising the following steps:

2. The method for preparing graphene with large sheet diameter and high conductivity according to claim 1, wherein the adding of graphite, concentrated sulfuric acid and a swelling agent into a reaction vessel comprises: firstly adding graphite or concentrated sulfuric acid, and then adding an expanding agent while stirring; the stirring speed is 300-1000 r/min, and the stirring time is 2-20 min.

3. The method for preparing graphene with large sheet diameter and high conductivity according to claim 1, wherein the predetermined temperature is 20-90 ℃, and the predetermined time is 1-24 hours;

the obtained high-expansion-rate expanded graphite is vermiform, and the expansion volume is 100-550 mL/g.

4. The method for preparing graphene with large sheet diameter and high conductivity according to claim 1, wherein the peeling auxiliary agent is one or more of sodium percarbonate, ammonium bicarbonate and concentrated sulfuric acid;

the equipment used for stripping treatment comprises a high-speed mechanical stirrer, an ultrasonic wave dispersing instrument or a high-speed dispersing homogenizer;

the stripping treatment time is 1-12 h.

5. The method for preparing graphene with large sheet diameter and high conductivity according to claim 1, wherein the sedimentation separation is performed in a centrifuge, the centrifuge speed is 3000-8000 rpm, the centrifuge time is 3-10 min, and the solid content of the refined large-sheet-diameter graphene dispersion liquid is 55-85%.

6. The method for preparing graphene having a large sheet diameter and high conductivity according to claim 1, wherein the graphene having a sheet diameter of 5 to 25 μm and a sheet diameter greater than 10 μm is contained in an amount of 70% or more of the total graphene, and the graphene has an electrical conductivity of 3.42 x 10 ² ～1.25×10 ⁵ S/m, and the graphene yield is 50-90%.

7. The method for preparing graphene with large sheet diameter and high conductivity according to claim 1 or 6, wherein the number of graphene layers is 1-10, and the content of few-layer graphene is more than 75%.

8. The preparation method of graphene with large sheet diameter and high conductivity according to claim 1, wherein the graphite raw material is 50-100 mesh flaky powder, and the carbon content in the graphite is up to 85% or more;

the expanding agent is one or more of sodium percarbonate and ammonium bicarbonate.

9. Graphene with a large sheet diameter and high conductivity, wherein the graphene is prepared by the preparation method according to any one of claims 1 to 8.

10. The graphene with large sheet diameter and high conductivity according to claim 9, wherein the graphene has a sheet diameter of 5 to 25 μm, a content of graphene with a sheet diameter of more than 10 μm in the total graphene is 70% or more, and a conductivity of the graphene is 3.42 x 10 ² ～1.25×10 ⁵ S/m。