Effects of green solvents and surfactants on the characteristics of few-layer graphene produced by dual-frequency ultrasonic liquid phase exfoliation technique

Abstract

Appendix A. Supplementary data: available online at https://www.sciencedirect.com/science/article/pii/S0008622323000696?via%3Dihub#appsec1 .Copyright © 2023 The Authors. . Nowadays, one of the promising methods for scalable graphene production is ultrasound-aided liquid phase exfoliation (ULPE) of graphite. Two current limiting factors of ULPE are the use of harmful solutions (such as N-Methyl-2-pyrrolidone or Dimethylformamide) and a relatively low graphene yield. In this study, we demonstrate a new dual frequency (20 kHz and 1174 kHz) ULPE approach in various eco-friendly media, which enabled us to produce various few-layer graphene (FLG) solutions of high quality. By implementing sophisticated characterisation techniques consisting of Raman spectroscopy, UV–vis spectroscopy and high-resolution electron microscopy, the final graphene flakes structure was confirmed to correlate the properties of each individual solution. The thinner (∼3 layers) and larger (∼1.5 μm2) flakes were observed while using just water, with the highest yield (11%) of smaller FLG flakes to be achieved in the mixture of water and a surfactant. In order to understand the cavitation mechanism in different solutions, the ULPE process was investigated by acoustic measurements. This study demonstrates the crucial role of ethanol (as a solvent) and surfactants as it regulates the cavitation power and intensity of the ultrasonic field and, thereby, the cavitation effectiveness. It is suggested that the mixture of water, ethanol and a surfactant is the best medium for ULPE process where a high yield of low-defective FLG flakes can be obtained in a solution stable at least for 3 months (around 80%).This study is a part of the project “Sustainable and industrially scalable ultrasonic liquid phase exfoliation technologies for manufacturing 2D advanced functional materials” (EcoUltra2D) funded by the UK Engineering and Physical Sciences Research Council (EPSRC) under the grant nos. EP/R031665/1; EP/R031401/1; EP/R031819/1; EP/R031975/1