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Graphene Oxide – Ultrasonic Exfoliation and Dispersion

Ultrasonic exfoliation is a widely used technique to produce graphene oxide by breaking down graphite oxide into thin, single- or few-layer graphene sheets. Hielscher sonicators create intense acoustic cavitation, where energy-dense ultrasonic waves generate high-energy microbubbles in a liquid medium. These collapsing bubbles create shear forces that separate graphite oxide layers, effectively exfoliating them into graphene oxide nanosheets. Take advantage of high-performance ultrasonics to bring your graphene oxide-based application to the next level!

Ultrasonic Exfoliation of Graphene Oxide

Graphene oxide is water-soluble, amphiphilic, non-toxic, biodegradable and can be easily dispersed into stable colloids. Ultrasonic exfoliation and dispersion is an very efficient, rapid and cost-effective method to synthesize, disperse and functionalize graphene oxide on industrial scale. In downstream processing, ultrasonic dispersers produce high-performance graphene oxide-polymer composites.

Advantages of Ultrasonic Exfoliation

Ultrasonic exfoliation offers several advantages, including simplicity, scalability, and environmental friendliness, as it typically does not require harsh chemicals or complex processing. Additionally, it enables precise control over the size and thickness of graphene oxide nanosheets, crucial for tuning their properties in various applications.

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Industrial sonicator setup for graphene exfoliation and dispersion: High-intensity ultrasonic waves create cavitation forces that break down graphite into graphene oxide nanosheets, ideal for scalable production in energy storage, electronics, and advanced materials applications.

Industrial sonicator UIP16000hdT for graphene oxide exfoliation at high-throughput

The video shows the ultrasonic mixing and dispersing of Graphite in 250mL of Epoxy Resin (Toolcraft L), using an ultrasonic homogenizer (UP400St, Hielscher Ultrasonics). Hielscher Ultrasonics makes equipment to disperse graphite, graphene, carbon-nanotubes, nanowires or fillers in the lab or in high volume production processes. Typical applications are the dispersing nano materials and micro materials during the functionalization process or for dispersing into resins or polymers.

Mix Epoxy Resin with Graphite Filler using Ultrasonic Homogenizer UP400St (400 Watts)

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Protocol: Ultrasonic Exfoliation of Graphene Oxide

Digital touchscreen of the Hielscher probe-type sonicator UP200HTIn order to control the size of graphene oxide (GO) nanosheets, the exfoliation method plays a key factor. Due to its precisely controllable process parameters, ultrasonic exfoliation is the most widely used delamination technique for the production of high quality graphene and graphene oxide.
For the ultrasonic exfoliation of graphene oxide from graphite oxide various protocols are available. Find an exemplary protocol for ultrasonic graphene oxide exfoliation below:
Graphite oxide powder is mixed in aqueous KOH with the pH value 10. For the exfoliation and subsequent dispersion, the probe-type ultrasonicator UP200St (200W) is used. Afterwards, K+ ions are attached onto the graphene basal plane to induce an ageing process. The aging is achieved under rotary evaporation (2 h). In order to remove excessive K+ ions, the powder is washed and centrifuged various times.
The obtained mixture is centrifuged and freeze-dried, so that a dispersible graphene oxide powder precipitates.
Preparation of a conductive graphene oxide paste: The graphene oxide powder can be dispersed in dimethylformamide (DMF) under sonication in order to produce a conductive paste. (Han et al.2014)

Ultrasonic exfoliation is widely used to produce graphene nanosheets and graphene oxide. Hielscher's ultrasonic systems convince as a very efficient, cost-effective and rapid synthesis technique of graphene, which are used for large slurry streams and are used for graphene mass production.
Picture source:  Potts J. R., Dreyer D. R., Bielawski Ch. W., Ruoff R.S  (2011): Graphene-based polymer nanocomposites. Polymer Vol. 52, Issue 1, 2011. 5–25.

The mechanism of ultrasonic graphene oxide exfoliation
(Pic.: Potts et al. 2011)

Ultrasonic Functionalization of Graphene Oxide

Sonication is successfully used to incorporate graphene oxide (GO) into polymers and composites.
Examples:

  • graphene oxide-TiO2 microsphere composite
  • polystyrene-magnetite-graphene oxide composite (core–shell structured)
  • polystyrene reduced graphene oxide composites
  • polyaniline nanofiber-coated polystyrene/graphene oxide (PANI-PS/GO) core shell composite
  • polystyrene-intercalated graphene oxide
  • p-phenylenediamine-4vinylbenzen-polystyrene modified graphene oxide
Probe-type ultrasonicator UP400St for nanoparticle dispersion such as graphene nanoplatelets in a stable aqueous suspension.

Ultrasonicator UP400St for the preparation of graphene nanoplatelet dispersions

Applications of Graphene Oxide Produced by Ultrasonic Exfoliation

Graphene oxide produced via ultrasonic exfoliation has broad applications across diverse fields. In electronics, it is used in flexible conductive films and sensors; in energy storage, it enhances the performance of batteries and supercapacitors. Graphene oxide’s antibacterial properties make it valuable in biomedical applications, while its high surface area and functional groups are advantageous in catalysis and environmental remediation. Overall, ultrasonic exfoliation facilitates the efficient production of high-quality graphene oxide for use in cutting-edge technologies.

Sonicators for Graphene and Graphene Oxide Processing

Hielscher Ultrasonics offers high-power ultrasonic systems for exfoliating, dispersing, and processing graphene and graphene oxide. Reliable ultrasonic processors and sophisticated reactors deliver precise control, enabling the tuning of ultrasonic processes to desired goals.
One crucial parameter is the ultrasonic amplitude, which determines the vibrational expansion and contraction of the ultrasonic probe. Hielscher industrial ultrasonicators deliver high amplitudes, up to 200µm, continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic probes are available. All processors can be precisely adjusted to process conditions and monitored via built-in software, ensuring reliability, consistent quality, and reproducible results.
Hielscher sonicators are robust and can operate continuously in heavy-duty environments, making sonication the preferred production technology for large-scale graphene, graphene oxide, and graphitic material preparation.
A wide product range of ultrasonicators and accessories, including sonotrodes and reactors with various sizes and geometries, allows the selection of optimal reaction conditions and factors, such as reagents, ultrasonic energy input, pressure, temperature, and flow rate, to achieve the highest quality. Hielscher’s ultrasonic reactors can even pressurize up to several hundred barg, enabling the sonication of highly viscous pastes with viscosities exceeding 250,000 centipoise.
Ultrasonic delamination and exfoliation excel conventional techniques due to these factors.

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Hielscher Ultrasonics

  • high power
  • high shear forces
  • high pressures applicable
  • precise control
  • seamless scalability (linear)
  • batch and continuous
  • reproducible results
  • reliability
  • robustness
  • high energy efficiency
7kW ultrasonic dispersing system for inline graphene production (Click to enlarge!)

Ultrasonic system for graphene oxide exfoliation

 
To learn more about ultrasonic graphene synthesis, dispersion and functionalization, please click here:

 

Facts Worth Knowing

Ultrasound and Cavitation: How is Graphite Exfoliated to Graphene Oxide using Sonication?

Ultrasonic exfoliation of graphite oxide (GrO) is based on the high shear force induced by acoustic cavitation. Acoustic cavitation arises due to the alternating high pressure / low pressure cycles, which are generated by the coupling of powerful ultrasound waves in a liquid. During the low pressure cycles occure very small voids or vacuum bubbles, which grow over the alternating low pressure cycles. When the vacuum bubbles achieve a size where they cannot absorb more energy, they collapse violently during a high pressure cycle. The bubble implosion results in cavitational shear forces and stress waves, extreme temperature of up to 6000K, extreme cooling rates above 1010K/s, very high pressures of up to 2000atm, extreme pressure differentials as well as liquid jets with up 1000km/h (∼280m/s).
Those intense forces affect the graphite stacks, which are delaminated into single- or few-layer graphene oxide and pristine graphene nanosheets.

What is Graphene Oxide?

How to produce graphene oxide? Hielscher Ultrasonics supplies powerful ultrasonic processors for the exfoliation of graphite oxide bulk material into graphene oxide. www.hielscher.comGraphene oxide (GO) is synthesized by exfoliating graphite oxide (GrO). While graphite oxide is a 3D material consisting in millions of layers of graphene layers with intercalated oxygens, graphene oxide is a mono- or few-layer graphene that is oxygenated on both sides.
Graphene oxide and graphene differ from each other in the following characteristics: graphene oxide is polar, whilst graphene is nonpolar. Graphene oxide is hydrophilic, whilst graphene is hydrophobic.
This means, graphene oxide is water-soluble, amphiphilic, non-toxic, biodegradable and forms stable colloidal suspensions. The surface of graphene oxide contains epoxy, hydroxyl, and carboxyl groups, which are available to interact with cations and anions. Due to their unique organic–inorganic hybrid structure and exceptional properties, GO–polymer composites offer high potential for manifold industrial applications. (Tolasz et al. 2014)

What is Reduced Graphene Oxide?

Reduced graphene oxide (rGO) is produced by ultrasonic, chemical or thermal reduction of graphene oxide. During the reduction step, most oxygen functionalities of graphene oxide are removed so that the resulting reduced graphene oxide (rGO) has very similar characteristics to pristine graphene. However, reduced graphene oxide (rGO) is not defect-free and pristine as pure graphene.

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