Top-Down, Scalable Graphene Sheets Production: It Is All about the Precipitate

Graphene production has been widely explored and developed in the past decade. Most research has aimed at developing scalable, environmentally friendly and cheap procedures to produce defect-free graphene that can be used in a variety of applications such as mechanical properties enhancement and energy storage. Top-down graphene production approaches (from graphite) in liquid, which include high-shear mixing and sonication, were recently scaled up. Nevertheless, their production yields have remained low (<5%) due to the need for stabilization of the graphene in dispersion (supernatant), while the precipitate has usually not been considered as graphene product. In this study, we focus on the liquid-based approach of sonication, from lab to industrial scale, in an attempt to improve the graphene yield. Unlike previous studies, we explore and characterize the product both in the supernatant and in the precipitate. We found that above a certain critical energy all graphite flakes were exfoliated into graphene sheets in an exfoliation-fragmentation mechanism described by a thermogravimetric signature. Remarkably, we discovered that other top-down approaches, namely, shear mixing and ball milling, have similar thermogravimetric signatures, indicating not only that they proceed by the same mechanism but also that they are capable of the same high yield, findings that fundamentally challenge existing knowledge about liquid-based methods of graphene production.