Ultrasonic graphene dispersion equipment is a reliable method to produce graphene layers from graphite flakes or particles

Product Description

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. Ultrasonic dispersion technology can overcome this problem well and efficiently prepare graphene materials

Product Details

ultrasonic graphene dispersion equipment
Due to the well-known special properties of graphite, several methods for preparing graphite have been developed. Graphene is prepared from graphene oxide through complex chemical processes, involving the addition of very strong oxidizing and reducing agents. The graphene produced under these harsh chemical conditions often contains a large number of defects.
Ultrasonic waves are a validated alternative method for producing large quantities of high-quality graphene. Graphite is added to a mixture of dilute organic acid, alcohol, and water, which is then exposed to ultrasonic radiation. The acid acts as a 'molecular wedge' to separate graphene sheets from the parent graphite. Through this simple process, large amounts of undispersed, high-quality graphene dispersed in water are produced.

Introduction to Graphene

Graphene molecular structure diagram

Graphene is a two-dimensional carbon nanomaterial composed of carbon atoms arranged in a hexagonal lattice resembling a honeycomb structure through sp² hybridized orbitals. Graphene's thin layers of carbon atoms form graphite through non-bonding interactions and possess an enormous surface area.
It is the thinnest material in the universe and also the strongest material ever recorded. It exhibits an enormous intrinsic carrier mobility with minimal effective mass (zero) and can propagate over micrometer distances at room temperature without scattering. Graphene can sustain current densities six orders of magnitude higher than copper, showing record-breaking thermal conductivity and hardness, being impermeable, and reconciling conflicting properties such as brittleness and ductility. Electron transport in graphene is described by Dirac-like equations, which allow for the study of relativistic quantum phenomena in tabletop experiments.

The principle of ultrasonic graphene dispersion
Ultrasonic graphene dispersion equipment uses the cavitation effect of ultrasound to disperse agglomerated particles. It involves placing the required particle suspension (liquid) into a strong ultrasonic field and treating it with appropriate ultrasonic amplitude. Under additional effects such as cavitation, high temperature, high pressure, micro-streaming, and strong vibration, the distance between molecules continuously increases, ultimately leading to molecular breakage and the formation of single-molecule structures. This product is particularly effective for dispersing nanomaterials (such as carbon nanotubes, graphene, silica, etc.).

The purpose of graphene dispersion
In nature, there are abundant graphite materials. A graphite sheet that is 1 millimeter thick contains approximately 3 million layers of graphene. A single layer of graphite is called graphene, which does not exist independently in its free state but always exists as graphite flakes composed of multiple layers of graphene stacked together. Due to the weak interlayer forces between graphite sheets, they can be peeled apart layer by layer under external force, thus obtaining single-layer graphene with a thickness of only one carbon atom.

Common dispersion methods
--Micromechanical exfoliation method: Directly peel off graphene flakes from larger crystals using adhesive tape, repeating this process continuously. By rubbing a material against thermally expanded or defect-introduced pyrolytic graphite, flaky crystals containing monolayer graphene form on the surface of bulk graphite. 
Disadvantages: Low yield of graphene, small area, difficult to precisely control size, low efficiency, unsuitable for large-scale production.

--Chemical vapor deposition: involves introducing one or more carbon-containing gaseous substances (usually low-carbon organic gases) into a vacuum reactor, where high temperatures cause the carbon-containing gas to decompose and carbonize (typically low-carbon organic gases). This process leads to the growth of a carbon allotrope on the substrate surface. 
Disadvantages: The hexagonal honeycomb crystal structure of graphene prevents it from being fully graphitized, resulting in lower quality compared to micromechanical exfoliation methods. High costs and stringent equipment requirements limit its large-scale production of graphene. Additionally, the need for catalysts reduces the purity of graphene.

--Epitaxial growth method for graphene on crystals: One approach involves heating a single crystal of 6H-SiC to remove silicon, allowing graphene to grow epitaxially on the surface of the SiC crystal. The graphene layer contacts the silicon layer, and its conductivity is influenced by the substrate. Another approach uses trace carbon components in metal single crystals, where high-temperature annealing under ultra-high vacuum causes carbon elements within the metal single crystal to precipitate as graphene on its surface.

Disadvantages: The thickness of the graphene film is uneven and difficult to control. The resulting graphene adheres tightly to the substrate, making it hard to peel off, which can affect the properties of the graphene. Additionally, the growth requires ultra-high vacuum and high temperatures, creating extremely stringent conditions that demand sophisticated equipment, making large-scale, controllable production of graphene unfeasible.

--Oxidation-reduction method for graphite：Oxidation of graphite to produce graphene oxide typically involves treating graphite with strong acids. There are mainly three methods for preparing graphene oxide: the Brodie method, the Staudenmaier method, and the Hummers method. In the Hummers method, ultrasonic assistance is required to disperse the graphene.

Ultrasonic preparation of graphene
When high-intensity ultrasound is applied to a liquid, sound waves transmitted into the liquid medium cause alternating cycles of high pressure (compression) and low pressure (rarefaction), the rate of which depends on the ultrasonic frequency. During the low-pressure cycle, high-intensity ultrasound generates small vacuum bubbles or voids within the liquid. When these bubbles reach a size where they can no longer absorb energy, they collapse violently during the high-pressure cycle. This phenomenon is known as cavitation. During the implosion, extremely high local temperatures (about 5,000K) and pressures (about 2,000 atm) are reached. The implosion of cavitation bubbles also results in liquid jet speeds up to 280 m/s. The physical and chemical changes induced by ultrasonic cavitation can be applied to graphene preparation.

Ultrasonic dispersion and disaggregation

Cavitation-induced sonochemistry provides unique interactions between energy and matter. The hot spots inside bubbles reach temperatures of approximately 5000K and pressures of around 1000bar, with heating and cooling rates exceeding 10^10 K/s. These special conditions allow access to a range of chemical reaction spaces that are typically inaccessible, enabling the synthesis of various unusual nanostructured materials.

Graphene direct exfoliation
The quality of graphene prepared by direct ultrasonic exfoliation is significantly higher than that obtained using the Hummer method. Ultrasonication can be used to prepare graphene in organic solvents, surfactant/water solutions, or ionic liquids. This means that strong oxidizers or reducers are not required; graphene can be produced through exfoliation under ultrasonic conditions. AFM images of a solution with a concentration of 1 mg/ml of graphene oxide show uniformly thin sheets (1 nm) always present. There are no graphene flakes thicker than 1 nm or thinner than 1 nm in these well-exfoliated samples of oxidized graphene. Therefore, it can be concluded that, under these conditions, complete exfoliation of graphene oxide into individual graphene oxide sheets has been achieved.

Non-contact mode AFM image

Ultrasonic dispersion equipment can be used for dispersing and homogenizing materials such as graphene, ink coatings; emulsifying petroleum; extracting active ingredients from traditional Chinese medicine; breaking down cells and ballast water, disinfection treatment; accelerating chemical reactions of raw materials, etc.

Product specifications are as follows: