Ultrasound-Assisted Synthesis, Exfoliation and Functionalisation of Graphene Derivatives

For the last two decades, application of ultrasound in materials synthesis has been a very promising topic especially for the fabrication or modification of various nanomaterials. Simplicity, high efficacy, short reaction tenure along with power saving features are responsible for the popularization of sonochemistry. The physical phenomenon essential for sonochemical process is largely accepted owing to acoustic cavitation, involving formation, growth, and implosive collapse of the micro-bubbles inside liquid. The resulting hot spots/microjets generate very high temperatures ~5000 K and high pressure ~150 MPa due to collapsing bubbles within a nanosecond, with high cooling rates exceeding 1011 Ks−1 at the local reaction centre, providing necessary activation for faster kinetics. These extreme reaction conditions are not typically attainable through conventional synthesis techniques, generating smarter systems with unique properties. Subsequently, ultrasound techniques have been massively employed in graphene preparation along with its dispersion in various solvents which otherwise requires several days with poor yield using conventional techniques. Graphene has been the material of the millennium owing to its unique large surface area, high charge transport features and mechanical properties and widely employed in nearly every aspects of modern technology. Ultrasonic irradiation offers tuning of graphene layer thickness also. Even oxidation to graphene oxide and subsequent reduction to reduced-graphene oxide at faster kinetics are possible without the use of any external redox agents. Besides, thin-layered functionalized graphenes has been achieved by sonochemistry. Ultrasonic treatment provides scope for direct exfoliation of graphite to graphene layers in presence of suitable intercalating/stabilizing agents with substantial dispersion stability. In addition, various geometries such as scrolled graphene, ribbon or foam graphenes can be purposefully designed. Even smooth and rough edged graphenes have displayed unique implications in energy storage, catalysis, biomedical and other technological fields. Ultrasonic-assisted synthesis of various graphene based composites lead to more homogeneous with diversified nanostructures formation like core-shell, nano-discs, nano-platelets, etc. along with specific deposition at the graphene edges have become feasible. This chapter provides comprehensive fundamental concepts of sonochemistry with first hand outline on the sonochemical/ultrasound assisted synthesis of graphene and its various derivatives. Moreover, the ultrasound assisted-dispersion, exfoliation of graphenes and formation of various graphene-based nanocomposites has been emphasized. Important tuneable sonochemical parameters including ultrasound frequency, input power, sonication time, type of sonication probes, etc. have been highlighted to provide an overview of the topic.