Štengl V., Preparation of graphene by using an intense cavitation field in a pressurized ultrasonic reactor, Chemistry - A European Journal, DOI: 10.1002/chem.201201411

Abstract: We demonstrate a new and efficient method to produce a large quantity of high-quality and non-oxidized graphene flakes from powdered natural graphite using a high intensity cavitation field in a pressurized ultrasonic reactor. Transmission electron microscopy and selected area electron diffraction confirmed the ordered graphite crystal structure of graphene. Atomic force microscopy was used to examine the thickness of graphene sheets. The delamination (exfoliation) of natural graphite in a liquid phase depends on physical effects of ultrasound, which break down the three-dimensional (3D) graphite structure to a two-dimensional (2D) graphene structure. The prepared graphene is of high purity without defects since no strong oxidizing chemicals are used and no toxic products result. Transmission electron microscopy (TEM) shows that graphene nanosheets were produced with sizes in the range of tens to hundreds square nanometers, smooth and without any ripples and corrugations. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis confirmed the products are graphene nanosheets.