Graphene Nanoplatelets Synthesized and Dispersed via Probe-Sonication

Graphene nanoplatelets (GNPs) can be synthesized and dispersed with high efficiency and reliability using sonicators. High-intensity ultrasonication is employed to exfoliate graphite and obtain few-layer graphene, often referred to as graphene nanoplatelets. Sonication also excels in achieving excellent graphene nanoplatelet distribution in both low and highly viscous suspensions.

Graphene Nanoplatelet Processing – Superior Results with Sonication

For graphene nanoplatelet processing, probe-type sonicators are most efficient, reliable and easy-to-use tool. Since ultrasonication can be applied for synthesis, dispersion and functionalization of graphene nanoplatelets, sonicators are used for numerous graphene-related applications:

• Exfoliation and Synthesis Probe-type sonicators are used to exfoliate graphite into few-layer graphene or graphene nanoplatelets. The high-intensity ultrasonication disrupts the interlayer forces and breaks down the graphite into smaller, individual sheets of graphene.
• Dispersion: Achieving uniform dispersion of graphene nanoplatelets in a liquid medium is crucial for all graphene-related applications. Probe-type sonicators can disperse the nanoplatelets evenly throughout the liquid, preventing agglomeration and ensuring a stable suspension.
• Functionalization: Sonication facilitates the functionalization of graphene nanoplatelets by promoting the attachment of functional groups or molecules to their surfaces. This functionalization enhances their compatibility with specific polymers or materials.

Graphene Nanoplatelet Synthesis via Sonication

Graphene nanoplatelets can be synthesized by ultrasonically-assisted graphite exfoliation. Therefore, a graphite suspension is sonicated using a probe-type ultrasonic homogenizer. This procedure has been tested with very low (e.g. 4wt% or lower) to high solid (e.g. 10wt% or higher) concentrations.
 
Ghanem and Rehim (2018) report the ultrasonic exfoliation of graphite in water with the aid of sodium dodecyl benzene sulfonate (SDS) in order to prepare dispersed graphene nanoplatelets using a the probe-type sonicator UP 100H allowed for the successful preparation of defect-free few-layer graphene (>5). The following precursor was used: reduced graphene nanosheets were prepared via Hummer method and treated with two additional steps, oxidation of graphite followed by reduction of graphene oxide. Thereby, dispersed graphene nanoplatelets were obtained in water via solvent dispersion method (see scheme below). Graphite layers were exfoliated with sonication using the probe-type sonicator UP100H (100 W). 0.25 g SDS was dissolved in 150 mL deionized water and then 0.5 g of graphite was added. The graphite solution was sonicated for 12h in an ice bath and then the suspension solution was centrifuged at 686× g for 30 min to remove the large particles. The precipitate was discarded and supernatant was re-centrifuged for 90 min at 12,600× g. The obtained dispersed graphene nanoplatelets were washed well several times to get rid of the surfactant. Finally, the product was dried at 60ºC under vacuum.

High resolution transmission electron microscope images of graphene nanosheets obtained
via ultrasonically-assisted aqueous phase dispersion and Hummer method.
(Study and graphic: Ghanem and Rehim, 2018)

What is the Difference between Graphene Sheets and Nanoplatelets?

Graphene sheets and graphene nanoplatelets are both nanomaterials composed of graphene, which is a single layer of carbon atoms arranged in a hexagonal lattice. Sometimes, graphene sheets and graphene nanoplatelets are used as interchangeable terms. But scientifically, there are a few differences between these graphene nanomaterials: The primary difference between graphene sheets and graphene nanoplatelets lies in their structure and thickness. Graphene sheets consist of a single layer of carbon atoms and are exceptionally thin, while graphene nanoplatelets are thicker and composed of multiple stacked graphene layers. These structural differences can impact their properties and suitability for specific applications. The use of probe-type sonicators is a highly effective and efficient technique to synthesize, disperse, and functionalize graphene single-layer graphene sheets as well as few-layer stacked graphene nanoplatelets.

Graphic visualizing the ultrasonic synthesis of graphene nanoplatelets using the sonicator UP100H
(Study and graphic: Ghanem and Rehim, 2018)

Dispersion of Graphene Nanoplatelets using Sonication

The uniform dispersion of graphene nanoplatelets (GNPs) is crucial in various applications because it directly impacts the properties and performance of the resulting materials or products. Therefore, sonicators are installed for graphene nanoplatelet dispersions in various industries. The following industries are prominent examples for the use of power-ultrasound:
 

• Nano-composites: Graphene nanoplatelets can be incorporated into various nanocomposite materials, such as polymers, to enhance their mechanical, electrical, and thermal properties. Probe-type sonicators aid in uniformly dispersing the nanoplatelets within the polymer matrix, resulting in improved material performance.
• Electrodes and Batteries: Graphene nanoplatelets are used in the development of high-performance electrodes for batteries and supercapacitors. Sonication helps create well-dispersed graphene-based electrode materials with increased surface area, which improves energy storage capabilities.
• Catalysis: Sonication can be used to prepare catalytic materials based on graphene nanoplatelets. The uniform dispersion of catalytic nanoparticles on the graphene surface can enhance catalytic activity in various reactions.
• Sensors: Graphene nanoplatelets can be employed in the fabrication of sensors for various applications, including gas sensing, biosensing, and environmental monitoring. Sonication ensures homogeneous distribution of the nanoplatelets in sensor materials, leading to improved sensitivity and performance.
• Coatings and Films: Probe-type sonicators are used to prepare graphene nanoplatelet-based coatings and films for applications in electronics, aerospace, and protective coatings. Uniform dispersion and proper adhesion to substrates are crucial for these applications.
• Biomedical Applications: In biomedical applications, graphene nanoplatelets can be used for drug delivery, imaging, and tissue engineering. Sonication helps in the preparation of graphene-based nanoparticles and composites used in these applications.

SEM images of graphene nanoplatelets at (b) X3000 and (c) X8000
(Study and images: ©Alizadeh et al., 2018)

Science-Proven Results for Ultrasonic Graphene Nanoplatelet Dispersions

Scientists have used Hielscher sonicators for the synthesis and dispersion of graphene nanoplatelets in numerous studies and tested the effects of ultrasonication vigorously. Below, you can find a few examples for the successful mixing of graphene nanoplatelets into different mixtures such as aqueous slurries, expoy resins or mortar.
 
A common procedure for the reliable, quick an uniform dispersion of graphene nanoplatelets is the following procedure:
For dispersion, the graphene nanoplatelets were sonicated within pure acetone using the Hielscher ultrasonic mixer UP400S for almost one hour in order to prevent an agglomeration of graphene sheets. Acetone was completely removed by evaporation. Then, the graphene nanoplatelets were added at 1 wt % of the epoxy system and were sonicated in the epoxy resin at 90W for 15 minutes.
(cf. Cakir et al., 2016)
 
Another study investigates the reinforcement of ionic liquid-based nanofluids (ionanofluids) by adding graphene nanoplatelets. For superior dispersion, the mixture of graphene nanoplatelets, ionic liquid and sodium dodecyl benzene sulfonate was homogenized using the Hielscher probe-type sonicator UP200S for around 90 min.
(cf. Alizadeh et al., 2018)

 
Tragazikis et al. (2019) report the effective incorporation of graphene nanoplatelets into mortar. Therefore, aqueous graphene suspensions were produced by addition of nanoplatelets – at weights inscribed by the desirable target contents in the resultant materials – in mixtures of regular tap water and plasticizer and subsequent magnetic stirring for 2 min. The suspensions were homogenized by ultrasonication for 90 min at room temperature, using a Hielscher UP400S device (Hielscher Ultrasonics GmbH) equipped with a 22mm-sonotrode delivering a power throughput of 4500 J/min at a frequency of 24 kHz. The specific combination of energy rate and sonication duration was established as optimum following a meticulous investigation of the effect of ultrasonication parameters of suspension quality.
(cf. Tragazikis et al., 2019)
 
Zainal et al. (2018) state in their research that a proper dispersion technique such as sonication ensures that nanomaterials such as graphene nanoplatetelets can enhance the properties of infill materials. This is due to the fact that dispersion is one of the most important factors for the production of high-quality nanocomposites such as epoxy grout.

High-Performance Sonicators for Graphene Nanoplatelet Processing

Hielscher Ultrasonics is the market leader when it comes to high-performance ultrasonicators for nanomaterial processing. Hielscher probe-type sonicators are used worldwide in laboratories and industrial settings for various applications, including the processing of graphene nanoplatelets.
State-of-the-art technology, German craftsmanship and engineering as well as long-time technical experience make Hielscher Ultrasonics your preferred partner for succesful ultrasonic application.

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: