The role of ultrasonic dispersion in the preparation of graphene
Ultrasonic dispersion is a reliable method to produce graphene layers from graphite flakes or particles. Other common dispersion techniques (such as ball mills, roller mills or high shear mixers) are susceptible to the use of aggressive reagents and solvents. The ultrasonic dispersion technology can well overcome this problem and efficiently prepare graphene materials.
Ultrasonic graphene dispersion
Ultrasonic dispersion will transform the graphene in the liquid into a dispersed state, that is, fine or ultra-fine ultrasonic grinding of solids or fluids due to the effect of ultrasonic vibration. Due to the particularity of the ultrasonic field generated in the liquid medium, ultrasonic dispersion provides a highly dispersed uniform, chemically pure suspension (particle size less than 1μm).
The principle of ultrasonic preparation of graphene
Ultrasonic preparation of graphene is based on the cavitation effect, so the quantum structure inside the graphene will not be destroyed. Ultrasonic cavitation can generate high-frequency amplitude through high-power ultrasound. High-power ultrasound can be used for liquid processing, such as mixing, emulsifying, dispersing and de-agglomerating or grinding. When the liquid is sonicated at high intensity, the sound waves propagating into the liquid medium cause alternating high-pressure (compression) and low-pressure (reflection) cycles, the rate being dependent on the frequency. In the low-pressure cycle, high-intensity ultrasound will create small vacuum bubbles or voids in the liquid. When the bubbles reach a volume that cannot absorb energy, they collapse violently during the high-pressure cycle. This phenomenon is called cavitation.
Cavitation
Ultrasonic dispersion equipment will transmit high-frequency vibrations into the liquid, and the application of this mechanical stress can separate the agglomeration of graphene particles. When the liquid is ultrasonically processed, the sound waves propagating into the liquid medium cause high pressure (compression) and low pressure (reflection) to cycle alternately. Ultrasonic cavitation in the liquid can cause high-speed liquid jets up to 1000 km/h (approximately 600 mph). This jet squeezes the liquid at high pressure between the particles and separates the graphene from each other. Smaller particles will accelerate with the liquid jet and collide at high speed. The high-strength shock wave generated by the high-speed collision continuously acts on the surface of the graphite body, and the graphite will reflect and generate tensile stress. When a large number of microbubbles burst, the tensile stress between the graphite flakes will continue to increase, and the graphene flakes will gradually be peeled off.
Exfoliation and dispersion of graphene
If graphene is to be used as a material, graphene must first be evenly dispersed into the formulation. Since graphene is hydrophobic, it is difficult to obtain high-concentration graphene dispersions without surfactants or dispersants.
Graphene nanosheets (GNP) can be made by exfoliating graphite in a solvent by high-power ultrasonic treatment. Ultrasonic exfoliated graphene can be functionalized with biopolymers to obtain water-dispersible graphene. Through ultrasonic cavitation, the synthesized graphene can be further processed into a stable water-based dispersion. It is easy to agglomerate when graphene nanometers are mixed into liquid. Ultrasonic dispersion can break the graphene agglomerated in water and non-aqueous suspensions, and can exert the full potential of nano materials.
Graphene oxide is water-soluble and can be easily dispersed into a stable colloid. Ultrasonic exfoliation and dispersion is a very effective, fast and cost-effective method that can synthesize, disperse and functionalize graphene oxide on an industrial scale. In order to control the size of graphene oxide (GO) nanosheets, the exfoliation method plays a key role. Due to its precise and controllable process parameters, ultrasonic peeling is the most widely used layering technique in the production of high-quality graphene and graphene oxide.
Graphene
Ultrasonic assisted liquid exfoliation
Liquid exfoliation (LPE) is an effective method for exfoliating graphene flakes. The main principle is to add graphite or graphite oxide as a raw material in a specific solvent or surfactant to stir the hot intercalation layer to form a graphene pretreatment solution, and then use the ultrasonic waves emitted by a high-power ultrasonic device to peel the graphene from the graphite surface. come out.
Liquid phase peeling method
The main influencing factors of ultrasonic-assisted graphene exfoliation are the cavitation of ultrasonic waves and high shear force. The cavitation during the ultrasonic treatment causes the graphite dispersed in the solvent to be crushed. The shearing force of ultrasonic waves can make the solvent form micro jets to impact the graphite surface and promote the separation between graphite layers.
Sum up
The high-power ultrasound system can be used for the peeling, dispersion and preparation of graphene and graphene oxide. Reliable ultrasonic processors and advanced reactors can provide the power required for graphene processing and precisely control the processing conditions, so that the ultrasonic processing results can be accurately adjusted to the required processing targets.
