A new method for determining energetically favorable landing sites of carboxyl groups during the functionalization of graphene nanomesh

In this paper, we propose a new method for the stepwise functionalization of graphene nanomesh (GNM) with carboxyl (COOH) groups. The key point of this method is the determination of landing sites for COOH groups. As a criterion for determining the most favorable arrangement of COOH groups, it is proposed to use the charge distribution over the GNM atoms. According to our idea, atoms with the largest negative charge will more easily form strong covalent bonds with functional groups. Testing of the proposed method is carried out on the example of GNM supercell with a circular hole 1.2 nm in diameter and 2.46 nm in the direction of zigzag edge and 2.55 nm in the direction of armchair edge. The self-consistent charge density functional tight-binding (SCC-DFTB) method is used to simulate the stepwise functionalization of GNM with a sequential increase in the number of COOH groups from 1 to 9. During landing, COOH groups are located at the GNM hole edges. The orbital charge distribution is analyzed according to the Mulliken. According to the binding energy calculations, the addition of COOH groups by selected GNM atoms is energetically favorable at each step of functionalization. In the course of functionalization, the energy gap of GNM practically does not change, and the Fermi level shifts downward by several tenths of electron volts. At the maximum saturation of the hole edge atoms with COOH groups, the Fermi level and the energy gap of the functionalized GNM take values close to the values of the non-functionalized GNM.