Ultrasonic Graphene Dispersion Exfoliation

Introduce: 

Ultrasonic graphene dispersion, also known as ultrasonic graphene exfoliation, uses the method of reducing oxidized graphite and combines it with ultrasonic vibration to effectively increase the interlayer spacing of oxidized graphite. Oxidized graphite with larger interlayer spacing is not only beneficial for other molecules, atoms, etc. to insert into the interlayer to form oxidized graphite intercalation composite materials, but also easy to be exfoliated into single-layer oxidized graphite, laying the foundation for further preparation of single-layer graphene.

Principle:

Ultrasonic graphene dispersion equipment utilizes the cavitation effect of ultrasound to disperse and aggregate particles. It is to place the particle suspension (liquid) that needs to be processed into a super strong sound field and treat it with appropriate ultrasonic amplitude. Under additional effects such as cavitation, high temperature, high pressure, microjet, and strong vibration, the distance between molecules will continue to increase, ultimately leading to molecular fragmentation and the formation of single-molecule structures. This product has a particularly good effect on dispersing nanomaterials such as carbon nanotubes, graphene, silica, etc.

Objective:

There are a large number of graphite materials in nature, and graphite with a thickness of 1 millimeter contains approximately 3 million layers of graphene. Single layer graphite is called graphene, which does not exist in its free state and exists in the form of layered graphene sheets. Due to the weak interlayer forces of graphite sheets, layer by layer exfoliation can be achieved through external forces, resulting in single-layer graphene with a thickness of only one carbon atom.

Common dispersion methods and their drawbacks:

1. Micro mechanical peeling method

Use tape to directly peel off graphene flakes from larger crystals, and repeat this process continuously.

Friction between a material and expanded or defect introduced pyrolytic graphite results in the formation of flake like crystals on the surface of bulk graphite, which contain a single layer of graphene.

Disadvantages: Graphene has low production yield, small area, difficult to accurately control size, low efficiency, and cannot be prepared on a large scale.

2. Chemical vapor deposition method

The process of introducing one or more gaseous substances containing carbon (usually low-carbon organic gas) into a vacuum reactor, and decomposing and carbonizing the carbon containing gas (usually low-carbon organic gas) at high temperature to grow a carbon element on the substrate surface.

Disadvantages: The hexagonal honeycomb crystal structure of graphene cannot be fully graphitized, and its quality is not as good as that of microcomputer exfoliation method. The high cost and strict equipment requirements limit its large-scale preparation of graphene, and catalysts need to be added to reduce the purity of graphene.

3. Crystal epitaxial orientation growth method

One method is to remove Si by heating single crystal 6H SiC, thereby epitaxially growing graphene on the surface of SiC crystal. Graphene is in contact with the Si layer, and the conductivity of this graphene is influenced by the substrate; Another method is to utilize the trace carbon component in metal single crystals, and through high-temperature annealing under ultra-high vacuum, the carbon element inside the metal precipitates graphene on the surface of the metal single crystal.

Disadvantages: The thickness of graphene film is uneven and difficult to control, and the generated graphene is tightly adhered to the substrate and difficult to peel off, which will affect the characteristics of graphene. Simultaneously, it needs to grow under ultra vacuum and high temperature conditions, which are extremely demanding and require high equipment, making it impossible to achieve large-scale and controllable preparation of graphene.

4. Graphite oxide reduction method

Graphene oxide is generally obtained by oxidizing graphite with strong acid. There are three main methods for preparing oxidized graphite: Brodie method, Staudenmaier method, and Hummers method. Among them, the Hummers method requires the addition of ultrasound assistance for graphene dispersion.

Characteristics: Hummers method for graphene dispersion: The method is simple, time-consuming, has a large processing capacity, is safe and pollution-free, and is currently the most commonly used.

Advantages of Ultrasonic Graphene Dispersion:

The ultrasonic graphene dispersion system uses ultrasonic assisted Hummers method to prepare oxidized graphene, which uses liquid as a medium and adds high-frequency ultrasonic vibration to the liquid. Due to ultrasound being a mechanical wave that is not absorbed by molecules, it causes vibrational motion of molecules during propagation. Under the cavitation effect, which refers to additional effects such as high temperature, high pressure, microjet, and strong vibration, the average distance between molecules increases due to vibration, ultimately leading to molecular fragmentation. It can effectively increase the interlayer spacing of oxidized graphite, and with the increase of ultrasonic power, the interlayer spacing of the obtained oxidized graphite tends to expand.

The pressure instantly released by ultrasound breaks the van der Waals forces between graphene layers, making it less likely for graphene to aggregate together. Graphene oxide with larger interlayer spacing is not only beneficial for other molecules, atoms, etc. to insert into the interlayer to form graphene oxide intercalation composite materials, but also easy to be peeled off into single-layer graphene oxide, laying the foundation for further preparation of single-layer graphene.