Эксфолиированный графит - полное руководство

With the rapid development of materials science, exfoliated graphite, as a new carbon material, has become a research hotspot. Due to its excellent performance and wide application. Its unique structure confers many characteristics and has great potential in many fields.

What is exfoliated graphite?

Exfoliated graphite (EG) is a kind of graphite material made from natural flake graphite by chemical or electrochemical intercalation treatment, and then by rapid expansion at high temperature. Natural flake graphite has a typical layered crystal structure with weak van der Waals forces binding between layers. Under the action of intercalating agent, some small molecules or ions can be inserted between graphite layers to form graphite intercalating compounds. When the intercalated compound is treated at high temperature, the intercalated material is decomposed and vaporized rapidly. And the resulting expansion force causes the graphite layer to expand violently along the direction perpendicular to the layer. Thus forming loose, porous and worm-like exfoliated graphite.

Main characteristics of exfoliated graphite

High specific surface area:

The unique wormlike porous structure makes it have a large specific surface area, generally up to 100-1000 m2/g. This property provides a broad space for its application in adsorption, catalysis and other fields. A large number of surface active sites can promote the chemical reaction and the adsorption of substances.

Good adsorption performance:

With high specific surface area and rich pore structure, it has excellent adsorption capacity for a variety of substances. ( Including organic pollutants, heavy metal ions and gas molecules.) The adsorption is mainly based on physical adsorption, and the adsorbed material is fixed to the pore surface. At the same time, some functional groups on its surface may also chemically adsorb some substances to further enhance the adsorption effect.

Excellent flexibility and compressibility:

When compressed by external force, the structure can be deformed to a certain extent, and can be partially restored after removing external force. This characteristic makes it have important application value in sealing materials and other fields.

Good thermal stability and chemical stability:

It is obtained by special treatment of graphite, inheriting some excellent properties of graphite. Such as stable chemical properties at high temperatures, and does not react with most chemical reagents. At the same time, it has a high thermal conductivity, can quickly conduct heat within a certain temperature range. You can use it in heat exchange, heat dissipation and other fields.

Хорошая электропроводность:

The graphite layer inside still retains good electrical conductivity, and the electrons can move more smoothly between the layers. This property makes it a potential application prospect in the field of electronics, such as battery electrode materials, electromagnetic shielding materials and so on.

Preparation process of exfoliated graphite

Selection of raw materials

Natural flake graphite:

Природный чешуйчатый графит with high crystallinity and large scale size is usually selected as the raw material for the preparation of exfoliated graphite. The worm-like structure of it obtained after intercalation and expansion treatment is more complete and the properties are relatively better with larger scale size. At the same time, the purity of graphite also has an important effect on the performance of exfoliated graphite. And high purity graphite can reduce the adverse effect of impurities on the performance of it.

Intercalation agent:

The selection of intercalation agent is one of the key links in the preparation process. Commonly used intercalators include concentrated sulfuric acid, concentrated nitric acid, perchloric acid and other strong oxidizing acids. As well as some metal salts, such as iron nitrate, ferrous sulfate and so on. These intercalators can react with graphite under certain conditions to insert small molecules or ions between graphite layers. Different intercalation agents have different effects on the intercalation effect of graphite and the final properties.

Preparation steps and key technologies

Intercalation treatment:

Mix natural flake graphite and intercalation agent in a specific proportion, and stir the reaction at the appropriate temperature. Taking concentrated sulfuric acid as an intercalation agent, slowly adding graphite to concentrated sulfuric acid at low temperature (0-20 °C). And stir for a period of time to promote the sulfuric acid molecules to fully intercalate. Strict control of temperature and reaction time is crucial, otherwise the graphite is prone to excessive oxidation, affecting subsequent expansion. This step is the key to achieving graphite exfoliation, laying the foundation for high-temperature expansion.

Washing and drying:

After the intercalation reaction, wash the product, remove the residual intercalation agent and by-products. Wash until neutral, and then dry to obtain graphite intercalation compounds. It is necessary to control the temperature and time during drying to prevent the early decomposition of intercalation compounds.

High temperature expansion:

Quickly put the dried graphite intercalation compound into a high temperature furnace at 800-1000 °C. The intercalators decompose and vaporize rapidly at high temperature, generating a strong expansion force. Pushing the vertical layer of the graphite layer to expand violently, forming expanded graphite. Rapid heating is the key, allowing the intercalation to fully decompose in a short time. Under the special process, the exfoliated expanded graphite with unique structure and properties can also be obtained.

Application of exfoliated graphite

Environmental protection

Wastewater treatment

It has good adsorption of organic pollutants such as oil and phenols and heavy metal ions. You can use the adsorbent to purify water effectively.

Waste gas treatment

It is made into adsorption materials and filled in the equipment. It can absorb harmful gases such as sulfur dioxide and nitrogen oxides in industrial waste gas and reduce environmental pollution.

Field of energy

Battery electrode material

It has good conductivity, large specific surface area, you can use it as a negative electrode material in lithium-ion batteries. To improve battery charging and discharging performance and cycle stability. And its porous structure is conducive to lithium ion storage and transmission.

Hydrogen storage material

Due to the porous structure, after proper treatment, it has a high hydrogen storage capacity under certain conditions. And it is expected to become a new type of hydrogen storage material to solve the problem of hydrogen energy storage.

Industrial Field

Sealing material

With flexibility and compressibility, it has become an ideal sealing material, in the form of exfoliated graphite gasket. You can make it into various shapes for pipes, valves, pressure vessels and other equipment seal, effectively prevent leakage under harsh conditions.

Heat exchange material

Because of its good thermal stability and thermal conductivity, you can use it to manufacture heat exchangers to speed up heat conduction. And improve heat exchange efficiency in chemical, energy and other industries.

Electronic field

Electromagnetic shielding material

Because of good conductivity, you can make it of electromagnetic shielding materials for equipment shells, circuit boards and other parts because of good conductivity. It can reflect and absorb electromagnetic waves and reduce electromagnetic radiation.

Sensor material

Its high specific surface area and surface activity, so that it has adsorption and response characteristics to specific gases. You can make it into a gas sensor to detect harmful gas concentration. In pressure, humidity sensors and other fields, it also have application potential. When preparing sensor-sensitive materials, the unique structure and chemical properties of exfoliated graphite oxide may enhance sensor performance.

Заключение

Exfoliated graphite has unique structure, excellent performance, high specific surface area, good adsorption, flexible, stable and conductive. It has great potential in many fields such as environmental protection and energy. With the improvement of the preparation process, its performance will be improved, the cost will be reduced. And future research will also expand the application.