Dual frequency ultrasonic liquid phase exfoliation method for the production of few layer graphene in green solvents

• Published in: Ultrasonics sonochemistry 2024-08, Vol.108, p.106954, Article 106954
• Main Authors: Kaur, Amanpreet, Morton, Justin A., Tyurnina, Anastasia V., Priyadarshi, Abhinav, Ghorbani, Morteza, Mi, Jiawei, Porfyrakis, Kyriakos, Eskin, Dmitry G., Tzanakis, Iakovos
• Format: Article
• Language: English
• Subjects: Acoustic pressure; Eco-friendly solution; Few-layer graphene; Shock wave emission; Ultrasonic exfoliation
• ISSN: 1350-4177; 1873-2828; 1873-2828
• DOI: 10.1016/j.ultsonch.2024.106954

[Display omitted] •Equal volume ratio mixtures of Water-Ethanol and Water-isopropyl alcohol eco-friendly solvents are found to be processing efficient for the production of stable few layer graphene.•Water-Ethanol and Water-isopropyl alcohol mixed solvents have low cavitation pressure threshold.•Sonotrode surface area is an important factor in affecting the cavitation zone and exfoliation processing times.•High quality graphene of good yield (6 %), with tailored thicknesses (4–10 layers), stable for 6 + months in less than 1-hour of treatment is produced. In this work, we implement a dual frequency (24 kHz and 1174 kHz) ultrasonic assisted liquid phase exfoliation (ULPE) technique in deionized water (DIW) and other eco-friendly solvents, to produce a variety of high-quality few-layer graphene (FLG) solutions under controlled ultrasonication conditions. The resulting FLG dispersions of variable sizes (∼0.2–1.5 μm2) confirmed by characterisation techniques comprising UV–Vis spectroscopy, Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM). For the first time we demonstrate that high yield of FLG flakes with minimal defects, stable for 6 + months in a solution (stability ∼ 70 %), can be obtained in less than 1-hour of treatment in either water/ethanol (DIW:EtOH) or water/isopropyl alcohol (DIW:IPA) eco-friendly mixtures. We also scrutinized the underlying mechanisms of cavitation using high-speed imaging synchronized with acoustic pressure measurements. The addition of ethanol or IPA to deionized water is proposed to play a central role in exfoliation as it regulates the extend of the cavitation zone, the intensity of the ultrasonic field and, thus, the cavitation effectiveness. Our study revealed that lateral sizes of the obtained FLG depend on the choice of exfoliating media and the diameter of a sonotrode used. This variability offers flexibility in producing FLG of different sizes, applicable in a wide spectrum of size-specific applications.