Study of the exfoliation and functionalization of graphene from graphite flakes with plasma discharge in solution

TL;DR

This study demonstrates a plasma-based method to produce and functionalize graphene flakes from graphite in water, preserving their structure without contamination, and highlights the influence of plasma conditions on exfoliation.

Contribution

It introduces a plasma discharge technique at atmospheric pressure for exfoliating and functionalizing graphene in solution, with detailed analysis of process parameters and effects.

Findings

Graphene flakes are monocrystalline and contamination-free.

Plasma ionizes water, functionalizing graphite flakes.

Exfoliation depends on plasma gas type, with argon being ineffective.

Abstract

Graphene flakes were produced by nanosecond plasma discharge at atmospheric pressure between an electrode and the surface of distilled water, in which were placed graphite flakes. The discharge ionizes the gas and forms free radicals on the surface of the water, functionalizing the graphite flakes in solution. The plasma also gives enough energy to break the Van der Waals bonds between the graphene layers but not enough to break the covalent C-C bonds within the layers. Transmission electron microscopy confirmed the hexagonal structure of graphene sheets, and showed that they were monocrystalline. No contamination was found in the obtained nanomaterial. An unknown phenomenon has been found in the activated distilled water, making its electrical conductivity decrease with an increasing temperature. An acidification of the water is observed. The gas in which the discharge takes place plays a major role on the process, no exfoliation is observed if plasmogen argon gas is used.