CN102659099A - Preparation method of anisotropic graphene foam - Google Patents

Abstract

The present invention relates to a kind of preparation method of anisotropic graphene foam, and the method comprises the following steps: (1) prepare graphite oxide; (2) prepare graphene oxide dispersion liquid: disperse the graphite oxide prepared in step (1) in In the solution, prepare a graphene oxide dispersion; (3) prepare a graphene dispersion: add a surfactant or a reducing agent that itself has a certain surface activity to the dispersion in step 2) as a protective agent, through chemical liquid phase reduction Prepare graphene dispersion; (4) prepare anisotropic graphene foam: destroy the original graphene stabilization system, and make graphene self-assemble into anisotropic foam. The graphene foam prepared by the method is composed of at least one layer of graphene structural units, has structure and characteristic anisotropy along the graphene growth direction and perpendicular to the growth direction, and has a specific surface area of 200-2000m ² /g. The thermal conductivity in the growth direction and perpendicular to the production direction differs by two orders of magnitude.

Description

A kind of preparation method of anisotropic graphene foam

technical field

The invention relates to a preparation method of anisotropic graphene foam, which belongs to the technical field of new materials.

Background technique

The new material industry has become one of the fastest-growing high-tech industries since the 21st century, and it is also a technological highland that countries are competing to occupy. A series of major breakthroughs have been made in the research of new carbon materials represented by graphene. On October 5, 2010, Professor Andre Geim, a physicist at the University of Manchester, and Konstantin Novosho Professor Konstantin Novoselov won the 2010 Nobel Prize in Physics for his research on graphene and revealing its properties.

Graphene is a simple carbon substance composed of carbon atoms arranged in a hexagonal lattice, and its structure is very stable. Studies have shown that graphene has high electron mobility, which can make electrodes thinner and more transparent. Its good electrical conductivity and high transparency to light make it unique in the fields of liquid crystal display and solar cells. Graphene film has field emission characteristics comparable to carbon nanotube films, and has very broad application prospects in semiconductor devices and flat panel displays; due to its unique two-dimensional structure and excellent crystallographic quality, it is a quantum electrodynamic phenomenon The research provides an ideal platform and has important theoretical research value. In addition, graphene, when combined with plastic, can make it a conductor and improve its mechanical properties and heat resistance. The new material made of graphene and plastic composite is light and strong, and can be applied to the new generation of artificial satellites, aircraft and automobiles and other vehicles. Therefore, graphene is expected to be widely used in high-performance nanoelectronic devices, composite materials, gas sensors, and energy storage.

Due to their excellent electrical, thermal and mechanical properties, graphene and its related materials have attracted extensive attention in the fields of physics and materials science. The preparation methods of graphene include: micro-mechanical separation method, orientation epitaxy-crystal film growth, heating SiC method, chemical vapor deposition method, chemical reduction method, etc. Graphene is a monomolecular planar material and a two-dimensional structure. There are few literatures and patents on the construction of three-dimensional materials using this two-dimensional structure material. In 2011, a research team led by Cheng Huiming and Ren Wencai of Shenyang National (Joint) Laboratory of Materials Science, Institute of Metal Research, Chinese Academy of Sciences prepared graphene three-dimensional materials (Chen ZP, Ren WC, GaoLB, Liu BL, Pei SF, Cheng HM , Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition. Nature Material, 2011, 10, 424–428). The method they used is chemical vapor deposition: using metal foam such as copper or nickel as the base material, a single layer of carbon atoms is attached to the surface of the metal foam, so that the graphene body material completely replicates the structure of the metal foam; After the matrix metal material is etched away, the three-dimensional graphene material is obtained. This method uses a method similar to a hard template (using metal foam as a template) to prepare a three-dimensional graphene foam, but the method of chemical vapor deposition, the process conditions are difficult to control, and it requires very professional personnel to precisely adjust and control. Foam metals such as copper or nickel are used as hard templates. The preparation process of the hard template is relatively complicated and expensive, and some defects that affect the performance of graphene may be formed during the process of etching and removing the hard template. At present, few self-assembly methods are used to prepare graphene foams. Compared with the hard template method, the self-assembly method has a simpler preparation process and no environmental pollution pressure, and this method can obtain anisotropic The characteristic graphene foam is of great significance for exerting the characteristics of graphene.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the existing graphene preparation method, and provide a kind of preparation method of anisotropic graphene foam, this method does not adopt matrix materials such as foam metal, does not need to remove metal foam template, has low cost , Simple and easy to implement, and can be produced on a large scale.

For realizing the purpose of the present invention, technical scheme of the present invention is:

A preparation method of anisotropic graphene foam, the method comprises the following steps:

(1) prepare graphite oxide;

(2) preparing a graphene oxide dispersion: dispersing the graphite oxide prepared in step (1) in the solution to prepare a graphene oxide dispersion;

(3) prepare graphene dispersion: in the dispersion in step 2), add surfactant or the reductant that itself has certain surface activity as protective agent, prepare graphene dispersion by chemical liquid phase reduction;

(4) Preparation of anisotropic graphene foam: Destroy the original graphene stabilization system to make graphene self-assemble into anisotropic foam.

In a preferred embodiment of the present invention, the method for preparing anisotropic graphene foam, in step 1), the method for preparing graphite oxide is Hummers method, improved Hummers method, improved Brodie method, improved Staudenmaier method or Hofmann one of the methods.

In a preferred embodiment of the present invention, in step 2) of the method for preparing anisotropic graphene foam, the solution is water or ethanol.

In a preferred embodiment of the present invention, in the method for preparing anisotropic graphene foam, in step 2), the dispersion of graphite oxide is carried out by ultrasound, mechanical stirring or both.

In a preferred embodiment of the present invention, in the method for preparing anisotropic graphene foam, in step 3), the surfactant is one of polyethylene glycol, polyvinylpyrrolidone or sodium polyacrylate a mixture of two or more.

In a preferred embodiment of the present invention, in the method for preparing anisotropic graphene foam, in step 3), the reducing agent is L-cysteine, citric acid, sodium citrate, ascorbic acid or One or more mixtures of sodium ascorbate.

In a preferred embodiment of the present invention, in the method for preparing anisotropic graphene foam, in step 4), the method of destroying the original graphene stable system adopts one of heating, radiation or flocculation or a common implementation of both.

Compared with the existing preparation method, the present invention has the advantages and positive effects as follows: the method for preparing anisotropic graphene foam disclosed by the present invention uses the graphene oxide dispersion as a precursor, and prepares the anisotropic graphene foam through the reduction of graphene oxide. Graphene dispersion liquid, and then destroy the original graphene stable system by heating, radiation or flocculation, and change graphene from hydrophilic to non-hydrophilic, thereby self-assembling into graphene foam, which has Large specific surface area (200-2000m ² /g); during the assembly process of graphene, due to migration resistance and other reasons, it has anisotropic characteristics, and its thermal conductivity along the graphene growth direction and perpendicular to the production direction The difference is two orders of magnitude, which cannot be achieved by chemical vapor deposition. The thermal conductivity along the graphene growth direction can reach 200W/mk, while the thermal conductivity perpendicular to the production direction is only 0.5W/mk.

Description of drawings

Fig. 1(a) is a photo of the sample prepared in Example 1 in the synthesis solution, and Fig. 1(b) is a photo of the sample prepared in Example 1 after it is taken out. The graphene foam is cylindrical, with a diameter of about 3cm and a height of 3.5cm. Its specific surface area is 2012m ² /g, the thermal conductivity along the graphene growth direction is 211W/mk, and the thermal conductivity perpendicular to the production direction is 0.5 W/mk.

Figure 2(a) is a photo of the sample prepared in Example 2. The graphene foam is cylindrical, with a depression in the middle, a diameter of about 2.8 cm, and a height of about 4 cm. Figure 2(b) is the scanning electron microscope image of the sample. It can be seen that the graphene foam is obviously anisotropic, its specific surface area is 536m ² /g, and the thermal conductivity along the graphene growth direction is 120W/mk. The thermal conductivity perpendicular to the production direction is 0.3W/mk.

Fig. 3 (a) is the scanning electron micrograph of the sample prepared by adopting example 3, as can be seen therefrom, this graphene foam is obvious lamellar structure, and this graphene foam has formed crack in the drying process, Fig. 3 (b ) is an enlarged photo of the sample. It can be clearly seen that the graphene is tiled in one direction and also presents obvious anisotropy. Its specific surface area is 365m ² /g, and the thermal conductivity along the graphene growth direction is 63W/ mk, the thermal conductivity perpendicular to the production direction is 0.8W/mk.

Fig. 4(a) is a scanning electron micrograph of the sample prepared in Example 4, from which it can be seen that the sample is in the shape of a strip. Since the precursor concentration of the graphene foam is relatively low, the prepared graphene foam is relatively small. Figure 4(b) is the scanning electron microscope image of the end face of the sample. It can be seen that the anisotropy of the graphene foam is very significant, its specific surface area is 536m ² /g, and the thermal conductivity along the graphene growth direction is 870W/mk, and the vertical The thermal conductivity in the production direction is 0.7W/mk.

Fig. 5 (a), (b) is the scanning electron micrograph of the different angles of the graphene foam that adopts example 5 to prepare, can find out therefrom, (a) is graphene tiling direction, and (b) is the side of tiling direction It can be seen that the graphene foam has an obvious layered structure and anisotropic characteristics. Its specific surface area is 1036m ² /g, and its thermal conductivity along the graphene growth direction is 96W/mk. The thermal conductivity is 0.5W/mk.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention.

Example 1

Adopt Hummers method to prepare graphite oxide: in ice bath, 10g graphite powder and 5g sodium nitrate are mixed with 230mL concentrated sulfuric acid, slowly add _30g KMnO in stirring; Add 460mL of deionized water, and continue to react for 40 minutes when the temperature rises to 98°C, the mixture turns from brown to bright yellow, further dilute with water, and treat with 30% H ₂ O ₂ solution to neutralize unreacted Permanganic acid, centrifugal filtration and repeated washing of the filter cake, and finally vacuum drying to obtain graphite oxide; grind graphite oxide, prepare 100 mL of 2 mg/mL suspension in water, and ultrasonically treat for 30 minutes to obtain homogeneous and stable graphene oxide Colloidal suspension; add 0.2g of surfactant polyvinylpyrrolidone (PVP-K30), ultrasonically dissolve, add 1g of L-cysteine to obtain a stable graphene dispersion; heat the dispersion to 95°C to continue the reaction 2 hours, after cooling, the graphene foam can be obtained.

Example 2

Adopt the Staudenmaier method to prepare graphite oxide: first prepare the mixed solution of fuming nitric acid (27ml) and the vitriol oil (87.5ml) in the three-necked flask, then place the three-necked flask to cool in an ice bath, then 5g graphite powder is stirred (note: the three-neck flask needs to be placed in an ice bath all the time to slow down the reaction speed and avoid explosion), add 55g of sodium chlorate to the above reaction system, and continue stirring for 96 hours. After the reaction is over, the reaction The mixture was filtered and washed to obtain graphite oxide; grind the graphite oxide, prepare 100 mL of a 2 mg/mL suspension in water, and ultrasonicate for 30 minutes to obtain a homogeneous and stable graphene oxide colloidal suspension; add 0.2 g of surfactant sodium polyacrylate , ultrasonically dissolved, and 2 g of sodium citrate was added; the dispersion was heated to 95° C. for 4 hours, and then rapidly cooled to obtain a graphene foam.

Example 3

Graphite oxide was prepared by the modified Brodie method: 10 g of graphite powder and 85 g of sodium chlorate were mixed with 200 mL of fuming nitric acid in an ice bath, and stirred at room temperature for 24 hours. After the reaction is finished, centrifugally filter and repeatedly wash the filter cake, purify, and finally vacuum-dry it to obtain graphite oxide. Grind graphite oxide, prepare 100 mL of a 2 mg/mL suspension in water, and ultrasonically treat it for 30 min to obtain a homogeneous and stable graphene oxide colloidal suspension. Add 2 g of ascorbic acid, ultrasonically dissolve to obtain a stable graphene dispersion. The graphene dispersion was irradiated with microwaves for 15 minutes, and the graphene foam could be obtained in 12 hours after cooling.

Example 4

Graphite oxide was prepared by the Hummers method: In an ice bath, mix 10g of graphite powder and 5g of sodium nitrate with 230mL of concentrated sulfuric acid, slowly add 30g of KMnO ₄ while stirring, transfer it to a 35°C water bath for 30 minutes, and then gradually Add 460mL of deionized water, and continue to react for 40 minutes when the temperature rises to 98°C, the mixture turns from brown to bright yellow, further dilute with water, and treat with 30% H ₂ O ₂ solution to neutralize unreacted Permanganic acid, centrifugal filtration and repeated washing of the filter cake, and finally vacuum drying to obtain graphite oxide; grind graphite oxide, prepare 100 mL of 0.5 mg/mL suspension in ethanol, and ultrasonicate for 30 minutes to obtain homogeneous and stable oxide Graphene colloidal suspension; add surfactant polyvinylpyrrolidone (PVP-K30) 0.2g, ultrasonically dissolve, add 1g L-cysteine to obtain a stable graphene dispersion; add flocculant chlorine to the dispersion Aluminum chloride 0.1g, graphene foam can be obtained after 12 hours.

Example 5

Adopt the Staudenmaier method to prepare graphite oxide: first prepare the mixed solution of fuming nitric acid (27ml) and the vitriol oil (87.5ml) in the three-necked flask, then place the three-necked flask to cool in an ice bath, then 5g graphite powder is stirred (note: the three-neck flask needs to be placed in an ice bath all the time to slow down the reaction speed and avoid explosion), add 55g of sodium chlorate to the above reaction system, and continue stirring for 96 hours. After the reaction is over, the reaction The mixed solution was filtered and washed to obtain graphite oxide; the graphite oxide was ground, and 100 mL of a 2 mg/mL suspension was prepared in water, and ultrasonic and stirred for 60 minutes to obtain a homogeneous and stable graphene oxide colloidal suspension; the surfactant polyethylene glycol was added Alcohol 0.2g, ultrasonically dissolved, adding 2g L-cysteine, to obtain a stable graphene dispersion; react the dispersion with microwave radiation for 30min, after slow cooling, the graphene foam can be obtained.

Claims (7)

1. the preparation method of an anisotropy grapheme foam is characterized in that, this method may further comprise the steps:

(1) preparation graphite oxide;

(2) preparation graphene oxide dispersion liquid: the graphite oxide of preparation in the step (1) is dispersed in the solution preparation graphene oxide dispersion liquid;

(3) add tensio-active agent or itself have the active reductive agent of certain surface in the dispersion liquid preparation Graphene dispersion liquid: to step 2), through chemical liquid phase reduction preparation Graphene dispersion liquid as protective material;

(4) preparation anisotropy grapheme foam: destroy original Graphene stabilising system, make Graphene be self-assembled into anisotropic foam.

2. preparation according to claim 1 has the method for anisotropy grapheme foam; It is characterized in that; In the step 1), the method for preparing graphite oxide is a kind of in Staudenmaier method or the Hofmann method of Brodie method, improvement of Hummers method, improvement Hummers method, improvement.

3. the method for preparing the anisotropy grapheme foam according to claim 1 is characterized in that step 2) in, said solution is water or ethanol.

4. the method for preparing the anisotropy grapheme foam according to claim 1 is characterized in that step 2) in, what said graphite oxide disperseed employing is ultrasonic, or mechanical stirring or both common implementings.

5. the method for preparing the anisotropy grapheme foam according to claim 1 is characterized in that, in the step 3), described tensio-active agent is one or more the mixture in polyoxyethylene glycol, Vinylpyrrolidone polymer or the ZX-I.

6. the method for preparing the anisotropy grapheme foam according to claim 1; It is characterized in that; In the step 3), described reductive agent is one or more the mixture in L-halfcystine, Hydrocerol A, Trisodium Citrate, xitix or the sodium ascorbate.

7. the method for preparing the anisotropy grapheme foam according to claim 1 is characterized in that, in the step 4), what destroy that the method for original Graphene stabilising system adopts is one in heating, radiation or the flocculation or both above common implementings.

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