Ultrasonic cavitation effects on the structure of graphene oxide in aqueous suspension

Ultrasonic treatments are a common procedure to exfoliate graphite oxide for the preparation of graphene oxide flakes in aqueous suspension. High-power ultrasonic instrumentation is capable to produce cavitation on the solution that may cause undesirable side effects on the structure and properties of graphene oxide flakes. In this work, we investigate the effects of cavitation on graphite oxide pH neutral aqueous suspensions by monitoring its structural and optical properties as a function of exposure time to ultrasonic cavitation (UC). From analysis of the evolution of these properties, we identify three stages in which both flake exfoliation and fragmentation evolve, including partial reduction caused by removal of oxygen moieties due to the harsh mechanical vibrations and thermal effects produced by UC. Photoluminescence emission red-shifts due to the appearance of low lying excited defect energy levels caused by long exposure to UC.