CN113277503A - Preparation method of reduced graphene oxide and graphene heat-conducting film - Google Patents

Abstract

The invention provides a preparation method of reduced graphene oxide, which comprises the following steps: selecting a GO raw material; pretreating a GO raw material, wherein the pretreatment comprises drying, grinding and screening the GO raw material; and reducing the pretreated GO raw material to prepare rGO. The invention also provides a preparation method of the graphene heat-conducting film, which comprises the following steps: preparing a blended slurry of rGO and GO; coating and drying the blended slurry on a substrate to obtain a GO membrane; and carrying out heat treatment on the GO membrane to obtain the graphene heat conduction membrane. The invention relates to a method for industrially preparing rGO and a preparation method for obtaining a graphene heat-conducting film with high heat-conducting property.

Description

Preparation method of reduced graphene oxide and graphene heat-conducting film

Technical Field

The invention relates to the technical field of preparation of heat conduction materials, in particular to a preparation method of reduced graphene oxide and a preparation method of a graphene heat conduction film.

Background

The reduced graphene oxide is mainly used in the application fields of anticorrosive coatings, plastic-reinforced electric and heat conduction, composite materials, electric conduction ink, sensors and the like. The reduced graphene oxide (rGO) is a graphene material with a small amount of oxygen-containing functional groups, which is obtained by reducing Graphene Oxide (GO) by means of chemical reduction, electrochemical reduction, thermal reduction and the like. The small amount of oxidative energy-containing groups present on the surface of rGO is a major factor in its ability to serve downstream applications.

The rGO is mainly applied to the related field of heat conduction of composite materials in the aspect of graphene heat conduction materials, and is used as a heat conduction additive to be blended with materials such as high polymers and the like to improve a part of heat conduction performance of the composite materials; but the graphene heat-conducting film is still to be excavated.

In 2020, Ruoff professor reduces rGO and GO by using HI acid, and then the rGO and GO are blended and coated to prepare the high-density graphene heat-conducting film, wherein the transverse heat conductivity coefficient of the high-density graphene heat-conducting film reaches 2025 +/-25W/(m.K) @8 μm (Matter2020,2, 1-9). Due to the existence of the graphene, the thermal expansion phenomenon of the GO membrane in the heat treatment process is reduced, so that the compactness of the membrane is improved. The rGO obtained by reducing hydroiodic acid is characterized in that GO surface defects are repaired in situ and part of GO functional groups are removed to obtain a flat and relatively comparatively high rGO sheet, so that a well-assembled GO membrane can be prepared after the rGO is blended with nematic GO colloid, and a compact graphene heat-conducting membrane can be obtained. However, in practical application, the halide reduction of GO is limited by environmental influence and is difficult to realize industrial production.

Disclosure of Invention

In view of one or more of the problems of the prior art, according to an aspect of the present invention, there is provided a method for preparing reduced graphene oxide, including:

selecting a GO raw material;

pretreating a GO raw material, wherein the pretreatment comprises drying, grinding and screening the GO raw material;

reducing the pretreated GO raw material to prepare rGO;

wherein, the step of preparing rGO by reducing the pretreated GO raw material comprises the following steps:

and placing the pretreated GO raw material in a closed heat treatment environment containing air or inert gas at 175-250 ℃ for annealing to obtain the rGO.

Optionally, the step of selecting the GO raw material includes:

selecting a GO raw material with carbon content of 48% -45%, preferably, the size distribution of the GO raw material is 8-30 μm; preferably, the solid content of the GO raw material is 41-46%.

Optionally, the step of pretreating the GO feedstock comprises:

drying the GO raw material at 100 ℃ for 1.5-3 h to remove water to obtain blocky solid, grinding and finely crushing the blocky solid, sieving the solid with a 200-mesh sieve, and removing large particles on the upper layer to obtain GO.

Optionally, in the step of preparing rGO by reducing the pretreated GO raw material, the annealing time is 1-10 min.

Optionally, in the step of preparing rGO by reducing the pretreated GO raw material, the temperature of the closed heat treatment environment is 175-200 ℃.

Optionally, the carbon content of the rGO is 70-80%; preferably, the carbon content of rGO is 21-28%.

According to another aspect of the present invention, there is provided a method for preparing a graphene thermal conductive film, including:

preparing the blend slurry of the rGO and the GO;

coating and drying the blended slurry on a substrate to obtain a GO membrane;

and carrying out heat treatment on the GO membrane to obtain the graphene heat conduction membrane.

Optionally, the preparation method of the blend slurry comprises the following steps:

preparing GO slurry;

adding rGO powder accounting for 0.5-5% of GO into the GO slurry while stirring the GO slurry, and continuously stirring to obtain uniform colloidal slurry;

homogenizing the colloidal slurry by a high-pressure homogenizer to obtain uniform blended slurry with the viscosity of 20 Pa.s-50 Pa.s.

Optionally, the step of preparing the GO slurry comprises:

the GO material is stirred and dispersed in deionized water to prepare GO slurry with the solid content of 3.0-5.0%.

Optionally, in the step of homogenizing the colloidal slurry by using a high-pressure homogenizer, the pressure is 800-1300 Mpa, and preferably, the homogenization is performed for multiple times.

Optionally, the step of coating and drying the blended slurry on a substrate to obtain the GO film comprises:

and coating the uniform blended slurry on a PET substrate by using a blade coater, and drying in a forced air drying oven at 80 ℃ for 3-5 h to obtain a dried GO membrane.

Optionally, the step of performing heat treatment on the GO film to obtain the graphene thermal conductive film includes:

the temperature of the GO membrane is raised to 2900 ℃, the GO membrane is kept at 2900 ℃ for 1-3 hours, and the GO membrane is pressed for 4-15 hours to the graphene heat-conducting membrane under the pressure of 10-70 MPa, preferably, the heat conductivity coefficient of the graphene heat-conducting membrane reaches 1500-1800W/(m.K).

The preparation method of the reduced graphene oxide provided by the invention is used for preparing the rGO with a specific oxygen content by using a low-temperature thermal reduction method, and is a method capable of industrially preparing the rGO.

According to the graphene heat conduction film, rGO and GO which improve the performance of the graphene heat conduction film are uniformly blended in a water phase to obtain a colloidal dispersion liquid of GO, and a coating-drying-heat treatment process is performed to obtain the graphene heat conduction film with high heat conduction performance.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is an SEM image of a GO feedstock of the present invention;

FIG. 2 is a Raman spectrum of the GO feedstock of the present invention;

FIG. 3 is an SEM image of rGO of the present invention;

FIG. 4 is a Raman spectrum of rGO of the present invention;

fig. 5 is an SEM image of a GO membrane of the invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

In one embodiment, a method of preparing reduced graphene oxide (rGO) comprises:

GO raw materials are selected for use and are pretreated, including:

the method comprises the following steps of taking a GO raw material prepared by a Hummers method, wherein the carbon content is 48% -45%, the size condition is shown in figure 1, the GO is in a single-layer peeling condition, when the GO peeling condition is not good, the GO is in a dispersed state in water (amplified by 200 times and under a reflection mode test condition) through an optical microscope test, the GO is represented as a clear and obvious boundary and large sheet, and the size is distributed in 8-30 mu m, for example, a Heizhou sixth element SE2430W-N product with the solid content of 41-46%;

drying the GO raw material at 100 ℃ for 1.5-3 h to remove water to obtain blocky solid, then grinding and finely crushing the blocky solid, sieving the solid with a 200-mesh sieve, and removing large particulates on the upper layer to obtain GO powder. The resulting GO powder was tested for raman spectra, as shown in fig. 2.

GO powder reduction preparation rGO includes:

and placing the dried GO powder in a closed heat treatment environment containing air or inert gas (N2) at 175-250 ℃, annealing for 1-10 min, and taking out to obtain a fluffy black powder material rGO. And (4) characterizing the obtained rGO, and testing to obtain the black powder with the carbon content of 70-80%. The gas pressure adopted here is 1 atmosphere, and the temperature is designed to be 175-200 ℃ so that GO is decomposed into CO through functional groups at the temperature₂、H₂Gas escape such as O takes place the phenomenon of exploding in the twinkling of an eye under the effect of external atmospheric pressure, appears GO functional group and deviate from when exploding in the twinkling of an eye the GO piece of stacking together in the twinkling of an eye and is strutted, obtains peeling off the good rGO piece of degree in the microcosmic, combines the oxygen-containing functional group of a small amount on the rGO piece, is favorable to rGO to appear the phenomenon of homogeneous blending at next step and GO. Typical SEM pictures of the obtained black powder rGO are shown in fig. 3, the rGO powder shows a sheet in a swollen state, the raman spectrum of the rGO powder is shown in fig. 4, and the rGO after low temperature reduction still shows a tendency that the D peak increases due to the presence of oxygen-containing functional groups and insufficient edge defect repair.

In one embodiment, a method for preparing a graphene thermal conductive film includes:

preparation of rGO and GO blend slurries and GO membranes, comprising:

weighing a proper amount of GO material, stirring and dispersing in deionized water to prepare slurry with solid content of 3.0-5.0%, adding rGO powder accounting for 0.5-5% of GO while stirring, and continuously stirring to obtain uniform colloidal slurry. Homogenizing the slurry obtained by stirring by using a high-pressure homogenizer under the pressure condition of 800-1300 MPa, and obtaining uniform slurry with the viscosity of 20-50 Pa.s and suitable blade coating viscosity after two times of homogenization;

coating the uniform slurry on a PET substrate by using a blade coater, and then drying in an air drying oven at 80 ℃ for 3-5 h to obtain a dried GO film, wherein as shown in FIG. 5, the GO film obtained by the method is in a layer-by-layer compact stacking state, and no visible small pieces or agglomerated particles of the rGO are sandwiched between layers, which indicates that the rGO can be uniformly dispersed in the uniform slurry at the ratio;

the GO membrane is heated to 2900 ℃ by a program, is kept warm for 1-3 h at the temperature, is pressed for 4-15 h under the pressure of 10-70 MPa to form the graphene heat-conducting membrane, and the heat-conducting coefficient of the graphene heat-conducting membrane is measured to be 1500-1800W/(m.K).

The preparation method of reduced graphene oxide (rGO) is a method for preparing rGO under a low temperature condition, and is a method capable of industrially preparing rGO, and the rGO can be used for improving the performance of a graphene heat-conducting film. The surface of the rGO is required to have a certain oxygen element retention amount in the preparation process of the rGO, the rGO can be well dispersed in an aqueous medium by utilizing the surface functional group of the rGO and can be uniformly adsorbed on the surface of the GO, and poor agglomeration and the like are avoided, so that the obtained uniform aqueous slurry of the rGO and the GO is subjected to film coating, drying and thermal reduction to obtain the graphene heat-conducting film with high heat dissipation performance.

In the following specific examples, in the preparation of dry GO powder: taking a certain amount of GO filter cake with model SE2430W-N, and crushing to about 1cm³The small blocks are placed in a forced air drying oven at 100 ℃ and dried for 2 hours to obtain dried black small blocks. Grinding the black small blocks, finely crushing, and removing the screened GO powder by using a 200-mesh screen to serve as a raw material for later use.

Example 1

And (3) placing the GO powder in a closed oven at 200 ℃, carrying out heat treatment for 5min, and taking out to obtain the rGO material. Elemental analysis test EA results are given in table 1 below:

TABLE 1

C％	H％	O％	S％
				78.2	1.1	20.6	0.1

Taking a proper amount of SE2430W-N cake material, preparing slurry with solid content of 3.5%, adding rGO material accounting for 1% of the dry weight of GO under the condition of stirring, continuously stirring at the rotating speed of 500rpm for 2h to obtain uniform GO aqueous slurry, and homogenizing the GO aqueous slurry for 2 times by a high-pressure homogenizer under the pressure of 800MPa to obtain black GO slurry with the viscosity of 20 Pa.s. Scraping and coating the homogenized GO slurry on a PET (polyethylene terephthalate) film, placing the PET film in a blast oven at 80 ℃ for drying for 3h to obtain a dried GO film, taking the GO film off the PET film, carrying out temperature programming heat treatment to 2900 ℃, then carrying out heat preservation for 2h, and then pressing the GO film for 12h under the condition of 15MPa at normal temperature to obtain a graphene heat conduction film, wherein the measured density of the graphene heat conduction film is 1.95g/cm³The thickness was 30 μm, and the thermal conductivity was 1503W/(mK).

Example 2

Placing the GO powder in a 175 ℃ closed oven, carrying out heat treatment for 8min, and then taking out to obtain a rGO material, wherein the elemental analysis test EA result is shown in the following table 2:

TABLE 2

C％	H％	O％	N％
				75.3	1.0	23.5	0.2

Taking a proper amount of SE2430W-N cake material, preparing slurry with solid content of 4.0%, adding rGO material accounting for 1.5% of the dry weight of GO under the condition of stirring, continuously stirring at the rotating speed of 500rpm for 2h to obtain uniform GO aqueous slurry, and homogenizing the GO aqueous slurry for 2 times by a high-pressure homogenizer under the pressure of 800MPa to obtain black GO slurry with the viscosity of 27.5 Pa.s. Scraping and coating the homogenized GO slurry on a PET (polyethylene terephthalate) film, placing the PET film in a blast oven for drying at 80 ℃ for 3 hours to obtain a dried GO film, taking the GO film off the PET film, carrying out temperature programming heat treatment to 2900 ℃, then carrying out heat preservation for 2 hours, and then pressing the GO film for 8 hours under the condition of normal temperature of 30MPa to obtain a graphene heat conduction film, wherein the measured density of the graphene heat conduction film is 2.15g/cm³The thickness is 20 μm, and the thermal conductivity 1728W/(m.K).

Example 3

Placing the GO powder in a sealed oven at 230 ℃, carrying out heat treatment for 2min, and then taking out to obtain a rGO material, wherein the elemental analysis test EA result is shown in the following table 3:

TABLE 3

C％	H％	O％	N％
				74.2	1.2	24.5	0.1

Taking a proper amount of SE2430W-N cake material, preparing slurry with solid content of 4.5%, adding rGO material accounting for 2% of the dry weight of GO under the condition of stirring, continuously stirring at the rotating speed of 500rpm for 2h to obtain uniform GO aqueous slurry, and homogenizing the GO aqueous slurry for 2 times by a high-pressure homogenizer under the pressure of 800MPa to obtain black GO slurry with the viscosity of 35.6 Pa.s. Scraping and coating the homogenized GO slurry on a PET (polyethylene terephthalate) film, drying the PET film in a blast oven at 80 ℃ for 3 hours to obtain a dried GO film, taking the GO film off the PET film, carrying out temperature programming heat treatment to 2900 ℃, then carrying out heat preservation for 2 hours, then pressing the GO film for 10 hours at normal temperature under 20MPa to obtain a graphene heat conduction film, and measuring the density of the graphene heat conduction film to be 2.14g/cm³The thickness was 26 μm, and the thermal conductivity was 1601W/(mK).

According to the invention, the weight loss temperature of the GO functional group is utilized, so that the GO is instantaneously removed from the functional group to obtain good peel and dispersed rGO, and thus a densely stacked GO membrane is prepared. And because rGO has certain thermal conductivity, when the rGO is doped in GO, the good thermal conductor effect of the rGO is exerted during thermal treatment, so that the surrounding GO can be reduced better, and the graphene thermal conductive film with higher thermal conductivity can be prepared.

As described above, according to the embodiments of the present invention, various changes and modifications can be made by those skilled in the art without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims (10)

1. A preparation method of reduced graphene oxide is characterized by comprising the following steps:

selecting a GO raw material;

pretreating a GO raw material, wherein the pretreatment comprises drying, grinding and screening the GO raw material;

reducing the pretreated GO raw material to prepare rGO;

wherein, the step of preparing rGO by reducing the pretreated GO raw material comprises the following steps:

and placing the pretreated GO raw material in a closed heat treatment environment containing air or inert gas at 175-250 ℃ for annealing to obtain the rGO.

2. The method of claim 1, wherein the step of selecting the GO material comprises:

selecting a GO raw material with carbon content of 48% -45%, preferably, the size distribution of the GO raw material is 8-30 μm; preferably, the solid content of the GO raw material is 41-46%.

3. The method of claim 1, wherein the step of pretreating the GO feedstock comprises:

drying the GO raw material at 100 ℃ for 1.5-3 h to remove water to obtain blocky solid, grinding and finely crushing the blocky solid, sieving the solid with a 200-mesh sieve, and removing large particles on the upper layer to obtain GO.

4. The preparation method of reduced graphene oxide according to claim 1, wherein in the step of preparing rGO by reducing the pretreated GO raw material, the temperature of the closed heat treatment environment is 175-200 ℃, preferably, the annealing time is 1-10 min, and preferably, the carbon content of the rGO is 70-80%.

5. A preparation method of a graphene heat conduction film is characterized by comprising the following steps:

preparing a blended slurry of rGO and GO according to any one of claims 1 to 4;

coating and drying the blended slurry on a substrate to obtain a GO membrane;

and carrying out heat treatment on the GO membrane to obtain the graphene heat conduction membrane.

6. The method for preparing the graphene thermal conductive film according to claim 5, wherein the method for preparing the blend slurry comprises:

preparing GO slurry;

adding rGO powder accounting for 0.5-5% of GO into the GO slurry while stirring the GO slurry, and continuously stirring to obtain uniform colloidal slurry;

homogenizing the colloidal slurry by a high-pressure homogenizer to obtain uniform blended slurry with the viscosity of 20 Pa.s-50 Pa.s.

7. The method of preparing a graphene thermal conductive film according to claim 6, wherein the step of preparing the GO slurry comprises:

the GO material is stirred and dispersed in deionized water to prepare GO slurry with the solid content of 3.0-5.0%.

8. The method for preparing the graphene thermal conductive film according to claim 6, wherein in the step of homogenizing the colloidal slurry with a high-pressure homogenizer, the pressure is 800-1300 MPa, and preferably, the homogenization is performed for a plurality of times.

9. The method for preparing the graphene thermal conductive film according to claim 5, wherein the step of coating and drying the blended slurry on the substrate to obtain the GO film comprises:

and coating the uniform blended slurry on a PET substrate by using a blade coater, and drying in a forced air drying oven at 80 ℃ for 3-5 h to obtain a dried GO membrane.

10. The method for preparing the graphene thermal conductive film according to claim 5, wherein the step of performing thermal treatment on the GO film to obtain the graphene thermal conductive film comprises the following steps:

the temperature of the GO membrane is raised to 2900 ℃, the GO membrane is kept at 2900 ℃ for 1-3 hours, and the GO membrane is pressed for 4-15 hours to the graphene heat-conducting membrane under the pressure of 10-70 MPa, preferably, the heat conductivity coefficient of the graphene heat-conducting membrane reaches 1500-1800W/(m.K).

Images