Environment friendly dual-frequency ultrasonic exfoliation of few-layer graphene

Anastasia V Tyurnina,Justin A Morton,Tungky Subroto,Mohammad Khavari,Barbara Maciejewska,Jiawei Mi,Nicole Grobert,Kyriakos Porfyrakis,Iakovos Tzanakis,Dmitry G Eskin

doi:10.1016/j.carbon.2021.09.036

Abstract

Ultrasound-aided liquid phase exfoliation (ULPE) of graphene in pure water is environment-friendly. Two limiting factors of ULPE are the non-uniform thickness of few-layer graphene (FLG) and a relatively low graphene yield. Here we describe ULPE in water that enables us to produce FLG flakes with a thickness of 3 layers and the flake sizes exceeding 1 μm2 in just 2 h. This process is based on using a combination of two ultrasound sources of high and low frequencies: 1174 kHz and 20 kHz. Two different frequencies generate a wider population and size distribution of cavitation bubbles that act through a number of mechanisms towards the exfoliation of graphene. For the first time ULPE was characterized by acoustic measurements. Results show that a high graphene yield (10%) can be achieved. This study demonstrates that the use of a dual frequency ultrasonic source and control of acoustic pressure is critical in optimizing the quality and yield of the cavitation assisted LPE of graphene in pure water. It is suggested that the width of the acoustic pressure peak reflecting shock-wave emissions can be used as an indicator of ULPE completeness, opening for the first time a way of in-situ monitoring of the process.

Highlights

Since its discovery [1], graphene has established itself as a material with various advanced properties: excellent electrical and thermal conductivity, optical and mechanical characteristics [2e4]
We demonstrate a novel method for ultrasonic LPE (ULPE) of graphite to produce high quality and relatively large in size graphene of up to 3-layers thickness in a benign environment in just 2-h
A systematic study of dual ultrasonic frequency (24 kHz þ1174 kHz) ULPE process configurations was performed with the assessment of the FLG flakes quality, ULPE yield and acoustic characteristics

Summary

Introduction

Since its discovery [1], graphene has established itself as a material with various advanced properties: excellent electrical and thermal conductivity, optical and mechanical characteristics [2e4]. Among different methods of graphene fabrication, liquid phase exfoliation (LPE) is the most promising for some graphene industrial applications due to the feasibility to obtain monolayer or few-layer defect-free graphene in the form of liquid suspensions, inks, or dispersions, stable and scalable for mass eco-friendly medium for graphene LPE [14,23]. Most of these studies combined water with various organic surfactants [21,24] or used weak aqueous alkaline solution [25]. These recent advances suggested that the interaction between water and the graphitic surface had been underestimated

Methods

Results

Conclusion