Effects of probe and bath ultrasonic treatments on graphene oxide structure

During the synthesis of graphene oxide (GO) sheets, the exfoliation of graphite oxide (GpO) has become a key step to obtain fully exfoliated sheets, and ultrasound is typically applied. We compared the effect of using water bath or probe sonication on the morphological and chemical characteristics of the obtained GO sheets. The properties of these GO sheets were also characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, elemental analysis, z-potential analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy. When probe sonication was used directly on the GpO samples, it induced deformities between the layers, causing the GO sheets to acquire a greater rugosity and degree of stacking and degrading their morphological properties. Additionally, probe-sonicated samples showed a noticeable reduction in the number of functional groups available for further chemical transformation. Thus, the use of bath ultrasonication to obtain GO sheets is preferable to probe ultrasonication because it is less invasive, enables easy control of the sample temperature, and causes fewer wrinkles and less damage to the sheet structure and morphology. (C) 2019 Elsevier Ltd. All rights reserved.