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

Abstract

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.

Liquid-Phase Exfoliation of Graphene: An Overview on Exfoliation Media, Techniques, and Challenges

“…However, these substrate-based techniques are limited by restricted dimensions and high cost, so that it cannot meet the requirement for commercial application of high-quality graphene [ 14 ]. Top-down methods [ 15 ], such as reduction of graphene oxide [ 16 ] generally involve three steps: the preparation of graphite oxide (GO) via chemical oxidation [ 17 ], the exfoliation of GO using sonication to prepare the dispersions of GO, and the reduction of dispersions of GO [ 13 ]. However, doughty chemical oxidation destroys the electronic structure of graphene, which limits the application in the microelectronics, etc.…”

Photocatalytic activity of 2D nanosheets of ferroelectric Dion–Jacobson compounds

“…Therefore, our samples inevitably contained some large bulk material. As demonstrated by M. Buzaglo et al 28 in their graphene scale-up work, for liquidphase-sonicated and then centrifuged samples, most of the graphene products were from the precipitates and had larger size than those in the supernatant, and Raman conrmed that neither were damaged by the sonication process in terms of inplane defects (however, there were edge defects).…”

Mechanochemical Routes to Functionalized Graphene Nanofillers Tuned for Lightweight Carbon/Hydrocarbon Composites

“…In this scalable process, the remaining non‐exfoliated graphite particles were separated in a subsequent centrifugation step (200 g for 100 min) to produce a mixture of mono‐ and multilayer graphene with a sheet width of 300–800 nm . Moreover, a microfluidizer with much higher shear rates of 10 8 s −1 afforded aqueous graphene dispersions . According to Ferrari et al., 100 microfluidization cycles in the presence of a surfactant gave 100% exfoliation and enabled the fabrications of printing inks without requiring the second centrifugation step when fairly large amounts of carboxymethyl cellulose were added as dispersing agent .…”