Evolutionary Chlorination of Graphene: From Charge-Transfer Complex to Covalent Bonding and Nonbonding

Density functional theory (DFT) studies were performed to investigate the chlorination of graphene. Unlike hydrogenation and fluorination, where the adsorption of H and F is always by covalent C–H/C–F bonding, Cl atoms generate various states when single-sided graphene exposed. In the initial reaction stage, it forms Cl–graphene charge-transfer complex, where the C orbitals keep sp 2 hybridization and the graphene is p-type doped. Further chlorination may form two adsorption configurations: one is covalent bonding Cl pairs, where the structure of the C atom is close to sp 3 hybridization. With the Cl coverage increases, this configuration may further cluster into hexagonal rings, and the resulting coverage is less than 25%. The other configuration is nonbonding. This configuration is energy preferable, while Cl atoms will form Cl2 molecules and escaped. When both sides of the graphene are exposed, the most stable adsorption configuration is a homogeneous ordered pattern with a Cl coverage of 25% (C4Cl) rather than collective clusters. The electronic properties of various chlorinated forms were also obtained; these showed that it is possible to tune the graphene bandgap by chlorination in a range of 0–1.3 eV.