Delamination and defects in graphene nanosheets exfoliated from 3D precursors

Abstract

Delaminating Van der Waals-based three-dimensional (3D) solid precursors into ultra-thin sheets of layered materials using liquid-phase exfoliation gained global interest due to the process' simplicity and industrial applicability. The characteristics of exfoliated graphene depend on the processing technique and starting precursor materials' properties. In this work, graphene is stabilized after exfoliation in a water/surfactant medium where 3D graphite of various sizes, including large flakes (∼700 μm) to fine powders (∼8 μm) are used as initial precursors in ultrasonication (bath and probe). The graphene concentration exhibited a peak-like and flat trend in these processes. After exfoliating from different-sized graphite, the nanosheet's morphology is assessed extensively by electron microscopy, and defects are probed by Raman spectroscopy. Large graphite flakes (∼700 μm and <N > 17000) produced nanosheets with high aspect ratios (∼700) with average lateral size of ∼1 μm and <N > 4 ± 1. Surprisingly, graphite with the size of 8 μm and <N > 1235 also produced graphene with lateral size of ∼1 μm and <N > 8 ± 5. Graphite with a large particle size undergoes significant fragmentation and then exfoliation. In contrast, fragmentation is less when the small-sized graphite undergo exfoliation. This study provides insights into the role of initial 3D precursors in creating 2D materials.