Ultrasonic Preparation of Graphene Materials

By AZoNano

Table of Contents

Introduction
Graphene: A Wonder Material
Ultrasound
Ultrasonic Preparation of Graphene
     Direct Exfoliation of Graphene
     Preparation of Graphene Sheets
     Preparation of Carbon Nanoscrolls
     Preparation of Nanoribbons
     Preparation of Graphene Oxide by Ultrasonic Treatment
Conclusion
About Hielscher

Introduction

Graphite is an allotrope of carbon that contains 2D sheets of hexagonally arranged carbon atoms called graphene, which are stacked in regular fashion. The atom-thin sheets of the graphene form graphite by means of non-bonding interactions. These sheets exhibit a large surface area.

Graphene is exceptionally strong and firm and its basal levels reach up to 1020 GPa, which is about the strength value of diamond. It is the basic structural element of certain allotropes that include carbon nanotubes and fullerenes, in addition to graphite.

Graphene is utilized as an additive and can considerably improve the barrier, mechanical, physical and electrical characteristics of polymer composites at low loadings.

Graphene: A Wonder Material

Graphene is a supermaterial and offers potential applications for industries that manufacture microelectronics, coatings and composite. According to Geim, graphene is the strongest and thinnest material in the universe.

The charge carriers of the graphene have the smallest effective mass, exhibit enormous intrinsic mobility, and are capable of travelling micrometer-long distances without dispersing at room temperature.

Graphene demonstrates high stiffness and thermal conductivity, can maintain present densities 6 orders higher than copper, is impermeable to gases and eliminates issues like ductility and brittleness. Owing to these superior properties, graphene is now one of the most promising materials in nanomaterial research.

Ultrasound

When liquids are sonicated at high intensities, the sound waves travelling into the liquid media result in low-pressure and high-pressure cycles with rates depending on the frequency. Through the low-pressure cycle, ultrasonic waves of high intensity generate tiny vacuum bubbles or voids in the liquid. During a high-pressure cycle, if the bubbles achieve a volume at which they cannot take more energy, they disintegrate belligerently.

This phenomenon is dubbed as cavitation. During the implosion, elevated pressures and temperatures are reached locally. The bubble’s implosion also causes liquid jets of approximately 280 m/s velocity. The cavitation, which was created ultrasonically, causes physical and chemical effects that can be applied to processes.

Ultrasonic Preparation of Graphene

A number of processes are involved to produce graphenes from graphene oxide and need strong reducing and oxidizing agents. However, graphenes fabricated under these chemical conditions tend to have a number of defects, when compared to graphenes produced from other techniques. To overcome such issues, ultrasound offers a suitable option to create high-quality graphene in huge quantities.

Graphene production is a one-step process in which graphite is added to a mixture of water, alcohol, and dilute organic acid. This mixture is then exposed to ultrasonic irradiation. The acid functions as a molecular wedge, which isolates graphene sheets from the main graphite. Through this simple technique, a huge quantity of high-quality graphene can be fabricated.

Direct Exfoliation of Graphene

Ultrasound aids in preparing graphenes in surfactants, water solutions, organic solvents, and ionic liquids. Back in 2007, graphene was synthesized by exfoliation under ultrasonication. The AFM images of graphene oxide, which was exfoliated by the ultrasonic treatment at 1 mg/mL concentrations in water, exposed the presence of sheets with even thickness. This led to the conclusion that exfoliation of graphene oxide down to individual graphene oxide sheets was obtained under these conditions.

Figure 1. AFM image of exfoliated GO sheets with three height profiles acquired in different locations

Preparation of Graphene Sheets

Utilizing a high intensity cavitation field, pure graphene nanosheets were synthesized from natural graphite. This cavitation field was created by Hielscher's ultrasonic processor UIP1000hd in a high-pressure ultrasonic reactor at 5 bar. It is claimed that when graphene is prepared ultrasonically, its quality is significantly higher than graphene obtained through Hummer's technique, wherein graphite is exfoliated and then oxidized.

Preparation of Carbon Nanoscrolls

Figure 2. Synthesis of Carbon Nanoscrolls

Similar to multi-walled carbon nanotubes, carbon nanoscrolls can be produced by intercalating graphite with potassium, followed by exfoliation in water and sonication of the colloidal suspension. The ultrasonication helps in the rolling up of graphene monolayers into carbon nanoscrolls.

Preparation of Nanoribbons

Graphene ribbons are merely thin strips of graphene that exhibit potential properties than graphene sheets. Their behavior is analogous to a semiconductor as electrons are forced to shift in lengthwise directions. This feature makes it a promising material for use in electronics.

Preparation of Graphene Oxide by Ultrasonic Treatment

Ultrasonic irradiation can be used to synthesize graphene oxide layers. In this method 25 mg of graphene oxide powder was suspended in 200 ml of de- ionized water. Upon stirring, an inhomogeneous brown suspension was obtained. The ensuing suspensions were sonicated, and after drying at 373 K the graphene oxide was developed.

Figure 3. SEM image of graphene nanosheets obtained by ultrasonication

Conclusion

Graphene is the strongest and most electrically conductive material. It is also one of the lightest and most flexible materials. The ultrasonically prepared graphene can be used in a variety of applications such as in electronics, sensors, transparent and emissive displays, solar cells, catalysis, transistors, micromechanical resonators and conductive coatings amongst others.

About Hielscher

Hielscher Ultrasonics is a family business, located in Teltow near Berlin (Germany). The main emphasis of its activities is the conception, development and production of ultrasonic devices for the use in laboratory and industrial applications. Technological innovations together with the realization of new ultrasound based processes substantiated the company growth and its market acceptance.

Today, ultrasonic devices made by Hielscher Ultrasonics are being used in laboratories and production plants on all continents across the world. More than 70% of the total sales is based on export. Almost every second device is supplied to customers outside Europe. Hielscher Ultrasonics integrates the ultrasonic devices into complex ultrasonic systems, such as wire cleaning systems, too. The systems are produced to meet the customers requirements in terms of power, extended range of accessories and steady state proof equipment.

Hielscher USA, Inc. is the representative for Hielscher ultrasonic equipment in the North American market. It is located in Ringwood, NJ.

This information has been sourced, reviewed and adapted from materials provided by Hielscher.

For more information on this source, please visit Hielscher.

Date Added: Mar 5, 2013 | Updated: Jun 11, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit