Water-Based Graphene Exfoliation
Ultrasonic exfoliation allows to produce few-layer graphene without the use of harsh solvents using pure water only. High-power sonication delaminates graphene sheets within a short treatment. The avoidance of solvents turns graphene exfoliation in a green, sustainable process.
Graphene Production via Liquid Phase Exfoliation
Graphene is commercially manufactured via so-called liquid phase exfoliation. Liquid phase exfoliation of graphene requires the use of toxic, environmentally harmful, and expensive solvents, which is used as chemical pre-treatment or in combination to/with a mechanical dispersion technique. For mechanical dispersion of the graphene sheets, ultrasonication has been established as highly reliable, efficient and safe technique to produce high-quality graphene sheets in large quantities on fully-industrial level. Since the use of harsh solvents is always accompanied with costs, contamination, complex removal and disposal, safety concerns as well as environmental burden, a non-toxic and safer alternative is significantly advantageous. Graphene exfoliation using water as solvent and power ultrasound for mechanical delamination of few layer graphene sheets is therefore a highly promising technique for a green graphene manufacturing.
Common solvents, which are often used as liquid phase to disperse graphene nanosheets, include Dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), Tetramethylurea (TMU), Tetrahydrofuran (THF), propylene carbonateacetone (PC), ethanol, and formamide.
As an already long-term established technique for graphene exfoliation on commercial scale, ultrasonication enables to produce high-quality graphene of high purity at low cost. As ultrasonic graphene exfoliation can be completely linear scaled to any volume, the production yield of high-quality graphene flakes can be easily implemented for mass production of graphene.
Ultrasonic Exfoliation of Graphene in Water
Tyurnina et al. (2020) investigated the effects of amplitude and sonication intensity on pure water-graphite solutions and the resulting graphene exfoliation. In the study, they used a Hielscher UP200S (200W, 24kHz). Ultrasonic exfoliation using water was applied as a single step process for few layer graphene delamination. A short treatment of 2h was sufficient to produce few-layer graphene in an open beaker sonication setup.
Optimization of Ultrasonic Graphene Exfoliation
The ultrasonic setup used by Tyurnina et al. (2020) can be easily optimized for more efficiency and faster exfoliation by using a closed ultrasonic reactor in flow-through mode. Ultrasonic inline treatment allows for a significantly more uniform ultrasonic treatment of all graphite raw material: feeding the graphite / water solution directly into the confined space of ultrasonic cavitation, all graphite becomes uniformly sonicated resulting in a high yield of high-quality graphene flakes.
Hielscher Ultrasonics systems allow for precise control over all important processing parameters such as amplitude, time / retention, energy input (Ws/mL), pressure, and temperature. Setting the optimum ultrasonic parameters results in highest yield, quality and overall efficiency.
How Does Ultrasonication Promote Graphene Exfoliation
When high-power ultrasound waves are coupled into a slurry of graphite powder and water or any solvent, sonomechanical forces such as high-shear, intense turbulences and high pressure and temperature differentials create energy-intense conditions. These energy-intense conditions are the result of the phenomenon of acoustic cavitation. Read more about ultrasonic cavitation here!
The power ultrasound initiates the expanding of the graphite powder, since fluids are pressed between the graphene layers, of which graphite is composed. The ultrasonic shear forces delaminate the single sheets of graphene and disperse them as graphene flakes in the solution. To obtain long-term stability of graphene in water, a surfactant is required.
High-Performance Ultrasonicators for Graphene Exfoliation
The smart features of Hielscher ultrasonicators are designed to guarantee reliable operation, reproducible outcomes and user-friendliness. Operational settings can be easily accessed and dialled via intuitive menu, which can be accessed via digital colour touch-display and browser remote control. Therefore, all processing conditions such as net energy, total energy, amplitude, time, pressure and temperature are automatically recorded on a built-in SD-card. This allows you to revise and compare previous sonication runs and to optimize the graphene exfoliation process to highest efficiency.
Hielscher Ultrasonics systems are used worldwide for the manufacturing of high-quality graphene sheets and graphene oxides. Hielscher industrial ultrasonicators can easily run high amplitudes in continuous operation (24/7/365). Amplitudes of up to 200µm can be easily continuously generated with standard sonotrodes (ultrasonic probes / horns and CascatrodesTM). For even higher amplitudes, customized ultrasonic sonotrodes are available. Due to their robustness and low maintenance, our ultrasonic exfoliation systems are commonly installed for heavy duty applications and in demanding environments.
Hielscher ultrasonic processors for graphene exfoliation are already installed worldwide on commercial scale. Contact us now to discuss your graphene manufacturing process! Our well-experienced staff will be glad to share more information on the exfoliation process, ultrasonic systems and pricing!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices|
|1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Anastasia V. Tyurnina, Iakovos Tzanakis, Justin Morton, Jiawei Mi, Kyriakos Porfyrakis, Barbara M. Maciejewska, Nicole Grobert, Dmitry G. Eskin (2020): Ultrasonic exfoliation of graphene in water: A key parameter study. Carbon Vol. 168, 2020. 737-747.
(Available under a Creative Commons Attribution 4.0: CC BY-NC-ND 4.0. See full terms here.)
- Štengl V., Henych J., Slušná M., Ecorchard P. (2014): Ultrasound exfoliation of inorganic analogues of graphene. Nanoscale Research Letters 9(1), 2014.
- Unalan I.U., Wan C., Trabattoni S., Piergiovannia L., Farris S. (2015): Polysaccharide-assisted rapid exfoliation of graphite platelets into high quality water-dispersible graphene sheets. RSC Advances 5, 2015. 26482–26490.
- Bang, J. H.; Suslick, K. S. (2010): Applications of Ultrasound to the Synthesis of Nanostructured Materials. Advanced Materials 22/2010. pp. 1039-1059.
- Štengl, V.; Popelková, D.; Vlácil, P. (2011): TiO2-Graphene Nanocomposite as High Performance Photocatalysts. In: Journal of Physical Chemistry C 115/2011. pp. 25209-25218.
Facts Worth Knowing
Graphene is a monolayer of sp2-bonded carbon atoms. Graphene offers unique material characteristics such as an extraordinary large specific surface area (2620 m2 g-1), superior mechanical properties with a Young’s modulus of 1 TPa and an intrinsic strength of 130 GPa, an extremely high electronic conductivity (room-temperature electron mobility of 2.5 × 105 cm2 V-1 s-1), very high thermal conductivity (above 3000 W m K-1), to name the most important properties. Due to its superior material properties, graphene is heavily used in the development and production of high performance batteries, fuel cells, solar cells, supercapacitor, hydrogen storages, electromagnetic shields and electronic devices. Furthermore, graphene is incorporated into many nanocomposites and composite materials as reinforcing additive, e.g. in polymers, ceramics and metal matrices. Due to its high conductivity, graphene is an important component of conductive paints and inks.
The rapid and safe ultrasonic preparation of defect-free graphene at large volumes at low costs allows for widening the applications of graphene to more and more industries.
Graphene is a one-atom-thick layer of carbon, which can be described as a single-layer or 2D structure of graphene (single layer graphene = SLG). Graphene has an extraordinarily large specific surface area and superior mechanical properties (Young’s modulus of 1 TPa and intrinsic strength of 130 GPa), offers great electronic and thermal conductivity, charge carrier mobility, transparency, and is impermeable to gases. Due to these material characteristics, graphene is used as reinforcing additive to give composites its strength, conductivity, etc. In order to combine the characteristics of graphene with other materials, graphene must be dispersed into the compound or is applied as a thin-film coating onto a substrate.