Ultrasonic Graphene Dispersion
Introduce:
Ultrasonic graphene dispersion, also known as ultrasonic graphene exfoliation, uses the method of reducing graphene oxide, combined with ultrasonic vibration, to effectively increase the interlayer spacing of graphene oxide. Graphene oxide with larger interlayer spacing not only facilitates the insertion of other molecules, atoms, etc. into the interlayer to form graphene oxide intercalated composite materials, but is also easy to be exfoliated into single-layer graphene oxide, laying a foundation for further preparation of single-layer graphene.
Principle:
Ultrasonic graphene dispersion equipment utilizes the cavitation effect of ultrasound to disperse agglomerated particles. It involves placing the required particle suspension (liquid) into an ultra strong sound field and processing it with appropriate ultrasonic amplitude. Under additional effects such as cavitation, high temperature, high pressure, micro jet, 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 is particularly effective for 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, they can be peeled off layer by layer through external forces, resulting in a single-layer graphene with only one carbon atom thickness.
Common dispersion methods and their drawbacks:
1. Micro mechanical peeling method
Peel off graphene sheets directly from larger crystals using tape and repeat this process continuously.
Friction between a material and expanded or defective pyrolytic graphite results in the formation of flocculent crystals on the surface of bulk graphite, which contain a single layer of graphene.
Disadvantages: Graphene has low yield, small area, difficulty in accurately controlling 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, decomposing and carbonizing the carbon containing gas (usually low-carbon organic gas) through high temperature, and growing 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 the microcomputer exfoliation method. The high cost and strict equipment requirements limit its large-scale preparation of graphene, and the addition of catalysts also reduces the purity of graphene.
3. Crystal epitaxial oriented growth method
One method is to remove Si by heating single crystal 6H SiC, thereby epitaxial growth of graphene on the surface of SiC crystals. Graphene and Si layer come into contact, and the conductivity of this graphene is affected by the substrate; Another approach is to utilize trace amounts of carbon 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, difficult to control, and the generated graphene is tightly adhered to the substrate, making it difficult to peel off, which can affect the characteristics of graphene. At the same time, it needs to grow under extremely harsh conditions of ultra vacuum and high temperature, with high equipment requirements, making it impossible to achieve large-scale and controllable preparation of graphene.
4. Oxidized graphite reduction method
Oxidized graphene is generally obtained by strong acid oxidation of graphite. 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 ultrasonic assistance for graphene dispersion.
Features: 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 method.
The advantages of ultrasonic graphene dispersion:
The ultrasonic graphene dispersion system uses ultrasonic assisted Hummers method to prepare graphene oxide, which uses liquid as the 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 molecular vibration during propagation. Under the cavitation effect, which includes additional effects such as high temperature, high pressure, micro jet, and strong vibration, the 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 obtained interlayer spacing of oxidized graphite shows an expanding trend.
The instantaneous pressure released by ultrasound breaks the van der Waals forces between graphene layers, making it less likely for graphene to aggregate. Large interlayer spacing of graphene oxide not only facilitates the insertion of other molecules, atoms, etc. into the interlayer to form graphene oxide intercalated composite materials, but also makes it easy to be peeled off into single-layer graphene oxide, laying a foundation for further preparation of single-layer graphene.
