CN101830458B - Preparation method of high purity and high concentration graphene suspension - Google Patents

Abstract

A method for preparing a high-purity, high-concentration graphene suspension, reacting natural flake graphite with a strong oxidant to obtain graphite oxide; then dispersing it in a dispersant, and ultrasonically dispersing to obtain a graphene oxide suspension; under nitrogen protection A stable graphene suspension can be prepared by mixing the graphene oxide suspension with hydrazine hydrate and reacting under constant temperature and ultrasonic radiation. Compared with the traditional method of preparing graphene suspension, this method introduces ultrasonic waves in the reduction process of graphene oxide, which has the following advantages: the prepared graphene suspension has high concentration (>1 mg·mL ^-1 ), high purity ( No impact of impurities such as surfactants), high dispersion stability (stable dispersion time is greater than 60 days) and other advantages; the graphene prepared by this method has high electrical conductivity (>700S·m ^-1 ), less The number of layers and higher purity; greatly speed up the reduction reaction speed, improve production efficiency. In addition, this method does not require high temperature, the process is simple and easy, and it is very suitable for large-scale industrial production.

Description

A kind of preparation method of high-purity, high-concentration graphene suspension

technical field

The invention belongs to the field of material preparation, in particular to a method for preparing a high-purity, high-concentration graphene suspension.

Background technique

In recent years, ultrasonic waves have been widely used in the preparation of nanomaterials, which can produce strong cavitation and vibration effects when passing through liquid media, thereby providing unique reaction sites for chemical reactions, and have developed into a universal nanomaterial Preparation. The high temperature generated by ultrasonic cavitation and a large number of tiny bubbles generated on the solid surface reduce the specific surface free energy of tiny grains and inhibit the aggregation and growth of crystal nuclei; the strong shock waves and micro jets generated by ultrasonic cavitation The shearing and crushing of particles effectively reduces the van der Waals force between tiny particles, thereby effectively preventing the agglomeration of tiny particles; ultrasonic waves can form fluid turbulence in liquids, which is conducive to the dispersion of tiny particles and the stability of suspensions .

Since Graphene was discovered by Professor Geim of the University of Manchester in 2004, it has attracted widespread attention in the scientific community with its unique structure and excellent performance, and it is predicted that it will cause revolutionary changes in many fields (Novoselov KSet al. Science, 2004, 306(5296), 666-669). As a new allotrope in carbon, graphene has a special honeycomb two-dimensional structure composed of a single layer of carbon atoms, so it has excellent electrical, mechanical and thermal properties. Graphene has a high electron mobility (2×10 ⁵ cm ² (V·s) ^-1 ), which is 100 times higher than that of silicon semiconductors and 20 times higher than that of gallium arsenide, and can be widely used in electronic devices and nanocircuits. Graphene is a real surface solid, and the theoretical specific surface area of single-layer graphene is as high as 2600m ² ·g ^-1 , making it an ideal energy storage material. Graphene has excellent mechanical properties, and its ideal strength is as high as 110-130GPa; it also has ultra-high thermal conductivity. The thermal conductivity obtained by non-contact measurement technology is 3080-5150W·(m·K) ^-1 , which can be widely Used in composite materials to improve the performance of composite materials (Rao CNR et al Angewandte Chemie-International Edition, 2009, 48, 7752-7778).

Due to the strong π-π interaction between layers, graphene is very easy to agglomerate, which limits its processing and application. The excellent performance of graphene is closely related to its single-layer structure, and the agglomeration leads to the stacking of graphene sheets, which makes it difficult to show the excellent performance of graphene. There are many methods for preparing graphene, such as chemical vapor deposition, solvent exfoliation, and micromechanical exfoliation, etc., and the graphene prepared by these methods has the disadvantage of poor processability. Graphene is composed of a large number of pure carbon atoms, which is not easy to be hydrophilic and lipophilic; graphene has a high specific surface area, and the van der Waals force between layers makes it very easy to undergo irreversible agglomeration; graphene's difficult wettability makes it difficult to disperse in water Or prepare a stable graphene suspension in an organic solvent. These limit the application of graphene in the fields of spin coating, drop coating, spray coating, liquid-liquid self-assembly and composite materials. Therefore, the preparation of stable and dispersed high-concentration graphene suspension is an effective way to expand the application field of graphene. .

Oxidation-reduction method is one of the important methods to prepare graphene. However, in the process of converting graphene oxide to graphene by reducing agent, it is often accompanied by the agglomeration of graphene, and it is difficult to obtain a stable and dispersed high-concentration graphene suspension. . In the early days, adding surfactants, polymers or other modifiers during the reduction process could obtain a stable graphene suspension, but the impurities introduced by these methods reduced the purity of graphene, resulting in lower electrical conductivity and poor thermal conductivity of graphene. , limiting the application of graphene. Later, scholars used ammonia water to adjust the pH in the chemical reduction process, and a stable graphene suspension could also be obtained by means of electrostatic interaction, but it was only suitable for a low concentration (0.5mg·mL ^-1 ), and agglomeration would occur if the concentration was too high ( Li, D.et al.Nature Nanotechnology, 2008, 3(2), 101-105); The graphene suspension prepared in N, N-dimethylacetamide also has Disadvantages of low concentration (0.56mg·mL ^-1 ) and low conductivity (200S·m ^-1 ). Currently existing methods are difficult to prepare graphene with high conductivity and its high concentration and stable suspension. Therefore, in order to expand the application field of graphene, it is particularly urgent to find a simple and stable preparation method of high-concentration graphene suspension.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of high-purity, high-concentration graphene suspension aiming at the limitations still existing in the preparation of graphene suspension at present. The invention prepares high-conductivity graphene and its stably dispersed high-concentration graphene suspension by means of ultrasonic waves, and reduces the reaction temperature and shortens the reaction time, making the production process easy to industrialize.

In order to achieve the above object, the technical scheme adopted in the present invention is:

1) Preparation of graphite oxide:

Mix 2-50g of natural flake graphite with 25-600mL of strong acid solution, then add 3-75g of oxidant and react in a water bath from -2°C to 4°C for 0.5-4h, then react at 20-40°C for 0.5-24h, Then add 50-1150mL of distilled water and react at 60-100°C for 0.5-12h, then dilute with 0.1-3L of distilled water to terminate the oxidation reaction, filter and wash with distilled water until neutral, and vacuum dry to obtain solid graphite oxide;

2) Preparation of graphene oxide suspension:

Add graphite oxide solids into the dispersant to form a graphite oxide suspension of 1.0-2.0 mg·mL ^-1 , and disperse the graphite oxide suspension under ultrasonic waves for 0.5-12 hours to obtain a uniform and stable graphene oxide suspension;

3) preparation of graphene suspension:

The graphene oxide suspension is under the protection of nitrogen, the reaction temperature is controlled at 40-80°C, adding a reducing agent, and reacted under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain a uniform and stable high-concentration graphene suspension, wherein The mass ratio of the graphene oxide suspension to the reducing agent is 10:5-9.

Strong acid solution of the present invention adopts the mixed acid that concentration is 90-98% sulfuric acid, concentration is 60-67% nitric acid or both;

The oxidizing agent is one or more of sodium nitrate, potassium permanganate, potassium perchlorate, potassium chlorate, and phosphorus pentoxide. If potassium permanganate is used, it is necessary to add hydrogen peroxide to reduce the residual potassium permanganate;

The dispersant is one or more of water, ethanol, nitrogen-methylpyrrolidone, N,N-dimethylformamide, and cyclopentanone;

The reducing agent is one or more of hydrazine, dimethylhydrazine, ethylenediamine, p-phenylenediamine, sodium borohydride, and hydroquinone.

The present invention adopts ultrasonic radiation, which not only peels unexfoliated graphite oxide into single-layer or few-layer graphene oxide, but also significantly inhibits the self-assembly and stacking between graphene sheets, which can be attributed to the ultrasonic radiation effect. cavitation in . The strong shock waves and micro jets generated by cavitation weaken the van der Waals force between graphene layers and inhibit the agglomeration of graphene sheets, which provides conditions for the preparation of high-concentration and stable graphene suspensions. The instantaneous high pressure and local high temperature generated by the collapse of cavitation bubbles accelerate the reduction reaction of graphene oxide and improve the production efficiency.

Description of drawings

Fig. 1 is the photo of the high-concentration graphene suspension prepared by the present invention placed after 60 days.

Fig. 2 is a transmission electron microscope (TEM) photo of graphene oxide (a) and graphene (b) prepared by the present invention.

Fig. 3 is graphite (a) and graphite oxide (b) and graphene (c) Raman spectrograms prepared by the present invention.

Fig. 4 is graphite (a), graphite oxide (b) and graphene (c) Fourier transform infrared (FTIR) spectrogram prepared by the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Example 1:

1) Preparation of graphite oxide:

Take 2g of natural flake graphite and 25mL of sulfuric acid with a concentration of 98% and mix evenly, then add 1g of sodium nitrate and 2g of potassium permanganate and react in a water bath at -2°C for 4h, then react at 40°C for 0.5h, and then add 50mL of React with distilled water at 60°C for 12 hours, then dilute with 0.1L distilled water to terminate the oxidation reaction, then add hydrogen peroxide to reduce the residual potassium permanganate, filter and wash with distilled water until neutral, and vacuum dry to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

The graphite oxide solid was added to water to form a graphite oxide suspension of 1.0 mg mL ^-1 , and the graphite oxide suspension was dispersed for 2 hours under the action of ultrasonic waves to obtain a uniform and stable graphene oxide (see Figure 2a) suspension;

3) preparation of graphene suspension:

Put the graphene oxide suspension under nitrogen protection, control the reaction temperature at 60°C, add hydrazine, and react under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain a uniform and stable high-concentration graphene (see Figure 2b) suspension , wherein the mass ratio of graphene oxide suspension to hydrazine is 10:5.

Example 2:

1) Preparation of graphite oxide:

Mix 50g of natural flake graphite with 400mL of 90% sulfuric acid and 200ml of 67% nitric acid, then add 10g of sodium nitrate, 30g of potassium perchlorate and 35g of potassium chlorate and react in a water bath at -1°C for 3 hours, then incubate at 20°C React for 24 hours, then add 1150 mL of distilled water and react at 80°C for 5 hours, then dilute with 3L of distilled water to terminate the oxidation reaction, filter and wash with distilled water until neutral, and dry in vacuum to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

The graphite oxide solid was added to ethanol to form a graphite oxide suspension of 1.1 mg mL ^-1 , and the graphite oxide suspension was dispersed under ultrasonic waves for 3 hours to obtain a uniform and stable graphene oxide suspension;

3) preparation of graphene suspension:

Put the graphene oxide suspension under the protection of nitrogen, control the reaction temperature at 40°C, add dimethylhydrazine, and react under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain a uniform and stable high-concentration graphene suspension (see Figure 2b) liquid, wherein the mass ratio of graphene oxide suspension to reducing agent is 10:9.

Example 3:

1) Preparation of graphite oxide:

Take 15g of natural flake graphite and 100mL of sulfuric acid with a concentration of 93% and mix evenly, then add 20g of potassium perchlorate, react in a water bath at 2°C for 1h, then react at 30°C for 12h, then add 200mL of distilled water and react at 100°C for 0.5 h, then dilute with 0.5L distilled water to terminate the oxidation reaction, filter and wash with distilled water to neutrality, and dry in vacuo to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

The graphite oxide solid was added to nitrogen methyl pyrrolidone to form a graphite oxide suspension of 2.0 mg mL ^-1 , and the graphite oxide suspension was dispersed under ultrasonic waves for 5 hours to obtain a uniform and stable graphene oxide suspension;

3) preparation of graphene suspension:

Put the graphene oxide suspension under nitrogen protection, control the reaction temperature at 70°C, add ethylenediamine, and react under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain a uniform and stable high-concentration graphene suspension, in which the oxidation The mass ratio of graphene suspension to reducing agent is 10:8.

Example 4:

1) Preparation of graphite oxide:

Take 30g of natural flake graphite and 400mL of nitric acid with a concentration of 60% and mix evenly, then add 40g of phosphorus pentoxide and react in a water bath at 4°C for 0.5h, then react at 25°C for 20h, then add 60mL of distilled water at 70°C React for 7 hours, then dilute with 1.5L distilled water to terminate the oxidation reaction, filter and wash with distilled water until neutral, and dry in vacuo to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

Add graphite oxide solids to N,N-dimethylformamide to form a 1.2 mg·mL ^-1 graphite oxide suspension, and disperse the graphite oxide suspension under ultrasonic waves for 10 hours to obtain uniform and stable graphene oxide suspension;

3) preparation of graphene suspension:

Put the graphene oxide suspension under nitrogen protection, control the reaction temperature at 70°C, add p-phenylenediamine, and react under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain a uniform and stable high-concentration graphene suspension, in which the oxidation The mass ratio of graphene suspension to reducing agent is 10:7.

Example 5:

1) Preparation of graphite oxide:

Take 40g of natural flake graphite and 500mL of nitric acid with a concentration of 63% and mix evenly, then add 60g of phosphorus pentoxide and react in a water bath at 0°C for 2h, then react at 35°C for 6h, then add 800mL of distilled water at 90°C React for 2 hours, then dilute with 2L distilled water to terminate the oxidation reaction, filter and wash with distilled water until neutral, and dry in vacuo to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

The graphite oxide solid was added to cyclopentanone to form a graphite oxide suspension of 1.5 mg mL ^-1 , and the graphite oxide suspension was dispersed under ultrasonic waves for 12 hours to obtain a uniform and stable graphene oxide suspension;

3) preparation of graphene suspension:

The graphene oxide suspension is under the protection of nitrogen, and the reaction temperature is controlled to be 50° C. Add hydroquinone and hydrazine, and react for 10-180 min under ultrasonic radiation with a frequency of 20-100 kHz to obtain uniform and stable high-concentration graphene (see Figure 2b) Suspension, wherein the mass ratio of graphene oxide suspension to reducing agent is 10:2:4.

Embodiment 6:

1) Preparation of graphite oxide:

Take 20g of natural flake graphite and 300mL of sulfuric acid with a concentration of 95% and mix evenly, then add 50g of sodium nitrate and react in a water bath at 1°C for 1.5h, then react at 32°C for 10h, then add 400mL of distilled water and react at 85°C After 10 hours, dilute with 1L distilled water to terminate the oxidation reaction, filter and wash with distilled water until neutral, and dry in vacuo to obtain graphite oxide solid;

2) Preparation of graphene oxide suspension:

The graphite oxide solid was added to water and N,N-dimethylformamide to form a 1.8 mg·mL ^-1 graphite oxide suspension, and the graphite oxide suspension was dispersed for 0.5 h under the action of ultrasonic waves to obtain a uniform and stable Graphene oxide suspension;

3) preparation of graphene suspension:

Put the graphene oxide suspension under nitrogen protection, control the reaction temperature at 80°C, add p-phenylenediamine and sodium borohydride, and react under ultrasonic radiation with a frequency of 20-100kHz for 10-180min to obtain uniform and stable high-concentration graphene (see Figure 2b) suspension, wherein the mass ratio of graphene oxide suspension to reducing agent is 10:4:4.5.

The salient features of the present invention are:

(1) Provide a method for preparing graphene with high conductivity (>700S·m ^-1 ) and its high concentration (>1mg·mL ^-1 ) suspension;

(2) The prepared high-concentration graphene suspension has good stability and can be placed stably for more than 60 days;

(3) Ultrasonic waves can peel off unstripped graphene and inhibit the agglomeration of graphene, so the number of graphene layers prepared is less and the quality is higher;

(4) Ultrasonic wave is introduced in the reduction process of graphene oxide, which greatly accelerates the speed of reduction reaction and improves production efficiency;

(5) The required reaction temperature of the preparation method of the present invention is low, safe and easy to operate, the process is simple and easy, easy to scale up production, and the operation cost is low;

The high-concentration and stable graphene suspension prepared by the present invention greatly improves the machinability of graphene, so that it can be widely used in fields such as spin coating, drop coating, spray coating, liquid-liquid self-assembly and composite materials, and is beneficial to The deviceization of graphene can be used to construct electronic devices such as nanoscale computer chips, solar cell electrodes, supercapacitor electrodes, sensors, and field effect transistors. The graphene suspension prepared by the invention improves the compatibility and dispersion of the graphene in the composite material, and improves the mechanical properties and barrier properties of the composite material. The invention has extremely important practical application value.

The present invention adopts the method of introducing ultrasonic waves in the reduction process of graphene oxide, and the prepared graphene suspension still shows a uniform and stable phenomenon after standing for 60 days (Fig. 1). The photo (Fig. 2) of transmission electron microscope (TEM) shows that graphene oxide and graphene prepared by the present invention have a flat and thin sheet structure, and obvious agglomeration does not take place in the prepared graphene, and ultrasonic wave plays a very important role . Raman (Raman) spectroscopy proves that the orderly crystal structure is destroyed in the process of graphite to graphite oxide, and after the reduction of hydrazine hydrate under ultrasonic waves, the partially ordered crystal structure of graphene is restored and some defects of graphene are repaired. (image 3). Fourier transform infrared spectroscopy (FT-IR) shows that graphite oxide is completely reduced by hydrazine hydrate under ultrasonic waves, and almost all oxygen-containing groups are removed, which is close to the structure of graphite (Figure 4).

Claims (5)

1. the preparation method of the graphene suspension of a high purity, high density is characterized in that:

1) preparation of graphite oxide:

After getting 2-50g natural flake graphite and 25-600mL strong acid solution and mixing; The oxygenant that adds 3-75g again reacts 0.5-4h in-2 ℃ to 4 ℃ water-baths after; Again in 20-40 ℃ of reaction 0.5-24h, and then the zero(ppm) water that adds 50-1150mL is at 60-100 ℃ of reaction 0.5-12h, again with 0.1-3L distilled water diluting termination oxidizing reaction; Filtration also is washed with distilled water to neutrality, and vacuum-drying obtains oxidation graphite solid;

2) preparation of graphene oxide suspension-s:

Oxidation graphite solid joined be configured to 1.0-2.0mgmL in the dispersion agent ^-1Graphite oxide suspension-s, this graphite oxide suspension-s is disperseed 0.5-12h under the UW effect, obtain uniform and stable graphene oxide suspension-s;

3) preparation of graphene suspension:

With graphene oxide suspension-s under nitrogen protection; Control reaction temperature is 40-80 ℃ and adds reductive agent; In frequency reaction 10-180min under the UW radiation of 20-100kHz; Obtain uniform and stable high concentration graphene suspension, wherein the mass ratio of graphene oxide suspension-s and reductive agent is 10: 5-9.

2. the preparation method of the graphene suspension of high purity according to claim 1, high density is characterized in that: it is that 90-98% sulfuric acid, concentration are 60-67% nitric acid or both mixing acid that described strong acid solution adopts concentration.

3. the preparation method of the graphene suspension of high purity according to claim 1, high density; It is characterized in that: described oxygenant is one or more in SODIUMNITRATE, potassium permanganate, potassium perchlorate, Potcrate, the Vanadium Pentoxide in FLAKES, if adopt potassium permanganate need add the remaining potassium permanganate of ydrogen peroxide 50 reduction.

4. the preparation method of the graphene suspension of high purity according to claim 1, high density is characterized in that: described dispersion agent is water, ethanol, n-formyl sarcolysine base pyrrolidone, N, one or more in dinethylformamide, the ketopentamethylene.

5. the preparation method of the graphene suspension of high purity according to claim 1, high density is characterized in that: described reductive agent is one or more in hydrazine, dimethylhydrazine, quadrol, Ursol D, Peng Qinghuana, the Resorcinol.

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