Ultrasound-Assisted Preparation of Large-Area Few-Layer Graphene

Abstract

We use a simple liquid-phase exfoliation process to prepare a large-area 2-D material, few-layer graphene (FLG) sheets, with the assistance of short-time sonication. Big-sized and layered raw materials, natural graphite flakes (NGFs), were used in this research. No surfactant was added, and only low boiling point solvents and ionic chemicals were used. NGFs was added as the raw material and ethanol and ammonia were used as solvents, then ultrasound was applied to help direct exfoliation in a bath. The size of the as-prepared directly exfoliated graphene sheets (DEGS) was greater than 20 μm on the longer side. The number of layers is less than five, and the presence of a Moiré fringe is due to the folding occurring in the as-prepared DEGS. The direct exfoliation mechanism for preparing large-area graphene sheets is proposed. The X-ray diffraction patterns provide the evidence of the increasing of the layer spacing. The layer spacing of graphite is increased after the sonication treatment with the addition of the ethanol, ammonia and NaCl. The concentration of large-area DEGS suspension is up to 18 ∼ 20 μg/mL in a simple and short time process.