Bromination of Graphene and Graphite

TL;DR

This study uses density functional theory to compare bromination behaviors in graphene and graphite, revealing distinct molecular configurations, electronic effects, and stability differences that could impact material applications.

Contribution

It provides the first detailed theoretical comparison of bromination mechanisms and molecular states in graphene versus graphite, highlighting unique molecular orientations and electronic doping effects.

Findings

Bromination induces a small band gap in graphene.

Distinct bromine molecule orientations are found in graphene and graphite.

Low density bromination in graphite is endothermic and less stable.

Abstract

We present a density functional theory study of low density bromination of graphene and graphite, finding significantly different behaviour in these two materials. On graphene we find a new Br2 form where the molecule sits perpendicular to the graphene sheet with an extremely strong molecular dipole. The resultant Br+-Br- has an empty pz-orbital located in the graphene electronic pi-cloud. Bromination opens a small (86meV) band gap and strongly dopes the graphene. In contrast, in graphite we find Br2 is most stable parallel to the carbon layers with a slightly weaker associated charge transfer and no molecular dipole. We identify a minimum stable Br2 concentration in graphite, finding low density bromination to be endothermic. Graphene may be a useful substrate for stabilising normally unstable transient molecular states.