crystals Article Bio-Surfactant Assisted Aqueous Exfoliation of High-Quality Few-Layered Graphene Nasima Akter 1,2,3, *, Muhammad Taqiyuddin Mawardi Ayob 1 , Shahidan Radiman 1 , Mayeen Uddin Khandaker 4, * , Hamid Osman 5 and Sultan Alamri 5   Citation: Akter, N.; Mawardi Ayob, M.T.; Radiman, S.; Khandaker, M.U.; Osman, H.; Alamri, S. Bio-Surfactant Assisted Aqueous Exfoliation of High-Quality Few-Layered Graphene. Crystals 2021, 11, 944. https:// doi.org/10.3390/cryst11080944 Academic Editor: Raghvendra Singh Yadav Received: 10 July 2021 Accepted: 11 August 2021 Published: 13 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia; taqi_wardi@yahoo.com (M.T.M.A.); shahidan.ukm@gmail.com (S.R.) 2 Centre for Environment & Sustainability, Presidency Education, 51 Panchlaish, Chittagong 4203, Bangladesh 3 Directorate of Secondary and Higher Education (DSHE), 16 Abdul Gani Road, Dhaka 1000, Bangladesh 4 Centre for Applied Physics and Radiation Technologies, School of Engineering and Technology, Sunway University, Bandar Sunway 47500, Malaysia 5 Department of Radiological Sciences, College of Applied Medical Sciences, Taif University, Taif 21944, Saudi Arabia; ha.osman@tu.edu.sa (H.O.); s.alamri@tu.edu.sa (S.A.) * Correspondence: nasima.ces@presidency.ac.bd (N.A.); mayeenk@sunway.edu.my (M.U.K.) 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. Keywords: graphene; liquid-phase exfoliation; exfoliation media; few-layer; low defect ratio 1. Introduction Graphene is the two-dimensional form of the carbon monolayer of graphite; it was proven to be stable under average room conditions. The unique properties of graphene in terms of its thermal, electrical, and mechanical conditions are utilized in many areas of technology. It has proven to be efficient for each of these uses [1]. Its applications include electrodes for capacitive deionization, sensors, photodetectors, in the environmental barrier as a coating material, and in the biological systems [2–7]. Since its discovery, from a simple micromechanical cleavage of graphite crystal, graphene has been a prominent research focus due to its versatile properties. Although micromechanical cleavage is the most efficient method in terms of quality, as it gives monolayer graphene a very large size without any defects, this method has significant Crystals 2021, 11, 944. https://doi.org/10.3390/cryst11080944 https://www.mdpi.com/journal/crystals