Bio-Surfactant Assisted Aqueous Exfoliation of High-Quality Few-Layered Graphene

Abstract

Realizing the efficacy of the liquid-phase exfoliation technique to obtain a greater quantity of graphene, this study demonstrates a cost-effective technique of bio-surfactant-assisted liquid-phase exfoliation of few-layer graphene (FLG) with a low defect ratio. An ultrasonic bath without any toxic chemicals or chemical modification was employed to exfoliate the graphene at room temperature. Several state-of-the-art characterization techniques such as TEM, AFM, XRD UV-Vis, and Raman spectroscopy were used to confirm the presence of the graphene. The dispersion exhibits a typical Tyndall scattering to the red laser beam. After a 7-h sonication of the dispersion, followed by a centrifugation frequency of 500 rpm for half an hour, the graphene concentration was found to be 1.2 mg/mL. The concentration decreases monotonically with an increase in the frequency, as a higher frequency causes sedimentation of the larger flakes or removes the adsorbed surfactant molecules from the graphene structures that collapse the graphene sheets into the graphite. The presence of an amino acid head-group in the surfactant facilitated exfoliation in an aqueous solution at well below the critical micelle concentration (CMC) of the surfactant. The product demonstrates all characteristic features of an FLG system. The TEM and AFM image reveals large-area graphene with a wrinkle-free surface; these morphological properties are confirmed by XRD and Raman spectroscopy. This study suggests that a sonication-induced process with a biocompatible surfactant can produce a cheap, large-surface-area graphene system for a wide range of applications. Moreover, the use of a probe sonicator as an alternative to the bath-type sonicator, together with the demonstrated technique, may reduce the time needed, and leads to a manifold increase in the yield.